FAQ on Activated Sludge Treatment of Wastewater
Thread Content
This post was last edited by cdpulin on 2010-1-13 at 10:23. All the information in this post comes from the Internet. There is little sludge in the oxidation ditch, and it’s difficult to cultivate microorganisms due to the cold weather – what should be done? 1. If the cultivation is carried out right after the system is started, it is normal for there to be a small amount of sludge; as the cultivation progresses, the amount of sludge will increase. During cultivation, excessive aeration is very detrimental to sludge growth. 2. Of course, the amount of microorganisms is related to the hydrocarbon content in your source water; a lack of hydrocarbons naturally prevents an increase in the number of microorganisms. Please check as well. 3. If your system is already running and you want to increase the number of microorganisms. I don’t think it’s really necessary. Reaching equilibrium is sufficient; what’s important is dealing with the effluent. 4. Intentionally increasing the microbial population will age the sludge, which is detrimental to the quality of the effluent. 5. Regarding temperature, I think as long as the water temperature exiting the system is at least 10 degrees, there should be no major issues with microbial activity. 6. Based on the F/M value, it is possible to determine whether the amount of microorganisms present is too low; if this value is not greater than 0.25, it means that the level of microorganisms is not too low. I calculated the sludge age in our plant last week today – isn’t its calculation formula (effective volume of the aeration tank × sludge concentration) / (sludge discharge rate × return sludge concentration × 24)? There must be a difference from the formula you provided! ), it is around 4 days, while our designed sludge age is 9 days. Even if the BOD of our designed influent differs by half from the actual value, it shouldn’t differ that much, right! Also, the F/M value is around 0.17, which should meet the requirements; so what exactly is the problem? I also want to ask, what is the reason why the water coming out of the sedimentation tank is slightly green? 1. I’m really sorry; it was my negligence. Your formula is correct. 2. Your food-to-sludge ratio is normal, but the sludge age is on the low side. As a result, biological activity increases, which is not conducive to the separation of sludge and water in the secondary sedimentation tank. 3. I don’t know if your plant is an urban sewage treatment plant. If so, it’s normal for the water to have a slight green tint. This should be the result of anaerobic decomposition occurring in the sewage pipeline network. 4. Please check the SV30 value; this value should be helpful to you. A value greater than 50% may indicate a problem with filaments. Less than 25%; the supernatant is turbid and contains fine particles, and microscopic examination reveals a large number of non-activated sludge flagellates (such as peritrichs and protozoa). It may be due to a low sludge age. We deal with domestic wastewater; other wastewater treatment plants don’t seem to experience this phenomenon of the effluent turning green. Our influent BOD is very low, around 50. I would like to ask how we can control the microbial population at a certain stage After anaerobic treatment, it enters the oxidation ditch – is there any specification for dissolved oxygen? Also, we add urea and potassium dihydrogen phosphate in an effort to improve microbial activity; then what indicators should we pay attention to when monitoring? If the activity of microorganisms is high, could it cause other negative effects? Problems such as poor sedimentation properties and an excessive degradation rate leading to a shortage of nutrients and subsequent depletion, etc. 1. I’m not very familiar with the specific details of your water treatment plant. Because, with BOD=50, COD is around 130 as well. 2. Since it is domestic wastewater, N and P should not be lacking. It seems unnecessary to add urea and potassium dihydrogen phosphate. 3. With such a low inlet concentration, it’s unknown what the outlet concentration will be, and what the removal rate will be as well 4. The aeration method in the oxidation ditch is relatively suitable for microbial degradation of organic matter, that is, the dissolved oxygen concentration is high at the front and low at the back. 5. Treating low-concentration wastewater can easily lead to sludge aging, with the effluent containing a large number of small active sludge particles. This aspect leads to an increase in the COD of the effluent; in cases where the activated sludge is not severely affected, it is carried away with the effluent, resulting in a COD increase of between 10 and 20 ppm. 6. I recommend reducing the aeration volume; ensuring an outlet dissolved oxygen level of 1.5 is sufficient. This can prevent the activated sludge from undergoing excessive auto-oxidation. 7. I think, relative to the volume of your oxidation ditch, your treatment capacity should be quite high, that is, the surface load is high. So, with BOD=50, your MLSS can still be maintained at 1000 ppm. With a higher load, the overcurrent speed also increases. As a result, microbial sedimentation is insufficient, and active sludge may also flow out with the discharged water. How to reduce the energy consumption of wastewater treatment plants? **The allocated funds are meager; I hope you can share your experience in operational management. The largest cost in operating a wastewater treatment plant is likely electricity, and if sludge is outsourced for treatment, the costs associated with that are also high. To address the above issues: 1. Reduce aeration volume to lower electricity costs. From my experience, maintaining an oxygen concentration of 3 ppm in the aeration tank theoretically is not conducive to saving energy and reducing consumption. Generally, I believe that when the biological system is operating at a low load (with F/M less than 0.15), an oxygen concentration of 1.5 ppm is sufficient. This can result in power savings. 2. If the system is equipped with a regulating tank and intermediate lift pump stations, its water storage capacity can be utilized to operate intermittently, thereby reducing operating costs. 3. If sludge costs arise, they can be used for composting plants and trees on site, as appropriate. Thus, only the overtime cost needs to be added. However, with dissolved oxygen controlled at 1.5 ppm, could this affect the reproduction of certain highly efficient microorganisms during winters in the north (in the oxidation ditch process), thereby reducing the quality of the treated water? 1. The growth rate of microorganisms is most closely related to the hydrocarbon content in the source water. 2. The dissolved oxygen concentration in the effluent from the aeration tank (oxidation ditch) that I use on a regular basis remains at 1.0 ppm, with little change even in winter. You can try adjusting the parameters to find those that work well for your own water treatment plant. 3. Controlling the effluent with low dissolved oxygen allows microorganisms to enhance their endogenous respiration during the sedimentation phase, which is highly beneficial for them to exert a better adsorption and oxidation effect once they return to the beginning of the biological tank. I would like to consult regarding the sludge cultivation in the hydrolysis-acidification tank and the contact oxidation tank during chemical wastewater treatment. No active sludge has formed on the fillers in the hydrolysis-acidification tank, which affects the treatment efficiency. Some time ago, the COD concentration of the incoming water was around 1200 mg/l, and this has persisted for a month now. During this period, I reduced the influent concentration to around 400 mg/L of COD, and observed signs of a decrease in the sludge on the fillers in the contact oxidation tank. How can I promote the proper development of sludge in both the hydrolysis-acidification tank and the contact oxidation tank? What are the most ideal parameters for the influent and effluent water? Hello! The operating contact time for the hydrolytic acidification and contact oxidation processes is not very long for me. The following personal opinions are provided for your reference only: 1. The hydrolysis-acidification stage can convert large-molecule substances into smaller ones, which facilitates the degradation of organic matter by microorganisms in subsequent stages. In other words, the pollutants in the hydrolysis stage are not easily degraded by microorganisms. 2. In light of this, to install packing in the hydrolysis-acidification tank and allow a biofilm to form, the source water must have an adequate amount of organic matter as well as an appropriate hydraulic retention time. 3. With a source water COD of 200 ppm, I think no biofilm will form when the residence time is insufficient. Not to mention 400ppm. Therefore, the biomass in the contact oxidation tank will also decrease. 4. The biomass is in balance with the organic matter content of the influent water; I think the concentration of the influent water is not sufficient to allow biofilm formation. But the water quality after treatment should be okay, right? ? 5. At this stage, as long as the water can be discharged, what does it matter whether a biofilm forms or not! I have some experience in carrying out hydrolytic acidification and contact oxidation treatments on industrial wastewater; would like to share some of my thoughts? 1. First of all, since you are dealing with chemical wastewater, you need to consider whether the water contains large amounts of substances that are difficult to biodegrade. It naturally takes a long time to cultivate microorganisms capable of degrading these hard-to-degrade organic compounds; however, if sludge from wastewater treatment plants that are used to treat such wastewater is used as a seed culture, the process may start more quickly. 2. Although the COD of the incoming water is 1200 mg/L, very little of it is likely to be readily usable by microorganisms (as chemical wastewater may contain a large amount of high-molecular-weight substances that are difficult to degrade). Therefore, as Sanpei-kun said, there is no need to consider the concentration of the effluent during the startup phase ； And when you reduce the COD of the incoming water to 400 mg/L, the amount of microorganisms is naturally lower, as the proportion of readily degradable organic matter is already small. By reducing it from 1200 to 400, there’s less food available for the microorganisms, so their growth slows down. 3. If the water you are treating is not easily biodegradable, some domestic wastewater or other degradable carbon sources can be added during the initial stage to increase the number of microorganisms, and then the sludge can be trained. 4. I wonder if you have heard of the co-substrate metabolism method; theoretical research on it has reached a certain level, but I’m not sure if it is applied in practice. "It is because the effluent quality does not meet the standards that I reduced the concentration of the feed water; when the feed water concentration is around 400 mg/L, the effluent concentration is still around 200 mg/L! I want to first reduce the influent concentration to ensure that the effluent meets the standards, and only then increase it. I was wondering if this approach is feasible? " 1. As sludge cultivation at system startup, it is incorrect for the influent concentration to be high first and then low. 2. Since this is the startup phase of the trial operation, you don’t need to worry too much about whether the output concentration exceeds the limits; you can increase it gradually at a faster pace. 3. Especially in biological systems with large bioreactors and a large amount of packing material, reducing the influent concentration will result in a microorganism-to-feed ratio that is lower than the normal value, making it difficult for a biofilm to form in the natural hydrolysis tank. "Recently, the water quality has deteriorated, with SS levels increasing significantly. What factors should be considered to determine the cause? 1. The SS has increased significantly, and there are many reasons for this; short-term changes may be related to excessive load. Long-term, periodic changes may be related to the swelling of filaments or the aging of sludge. 2. Please also check the control parameters and changes in the composition of the incoming water. Make judgments and determine the handling methods. 3. Sludge age, feed-to-microorganism ratio, influent water quality, the effectiveness of previous physical and chemical treatment processes, and filamentous microorganism testing are important methods for evaluation. For domestic wastewater treatment, what should be done if a large amount of oil suddenly appears (the composition of the oil is unknown; it could be diesel, gasoline, or something else)? What impact will this oil have on us? I don’t know if your factory has equipment for degreasing. If not, the level of petroleum compounds in the discharged water may exceed the limits. As a hydrocarbon substance, it should also be able to be degraded by microorganisms, although it will take longer. If possible, I suggest installing an outlet baffle at the exit of the aeration tank. As a result, the floating oil on the surface can remain in the aeration tank and be degraded through prolonged biological oxidation. However, if a large amount of oily wastewater keeps flowing in over a long period of time, you may need to install oil removal equipment. When oil phenomena are noticeable, the level is around 20 mg/l or so. Not all oils can be degraded by microorganisms, right? Is there no impact at all? There is aeration at the outlet of our aeration tank, so installing baffles should not be feasible. 1. The degradation of oils takes a relatively long time. Of course, in terms of our treatment process, after the oils are initially degraded, they are absorbed by microorganisms and removed along with the sludge, thereby eliminating the oil substances as well. 2. There is aeration at the outlet of the aeration tank; it is sufficient to reduce or turn off the aeration at that outlet, as excessive aeration in the later stages also hinders the sedimentation of microorganisms. In this way, the baffle can be installed. “I would like to ask how the sludge age is determined?” And how is it used for control? Should it be determined by the sludge discharge volume, or should the sludge discharge volume be determined by it? Filamentous fungi probably aren’t the key issue; could it be that the sludge concentration is too high? Around 1000, or lower, with an inlet BOD of around 50 – is this sludge concentration appropriate? I would appreciate your advice! Thank you! " 1. Sludge age: It refers to the residence time of activated sludge in the aeration tank. It is a key parameter for controlling whether the sludge ages, and it is a very important control parameter; without proper control of this parameter, it is difficult to ensure the proper operation of the biological system. 2. Calculation formula: (MLSS * effective volume of the aeration tank) / (24 hours * sludge discharge rate per hour * MLSS return rate). 3. This parameter is used to control the amount of sludge discharged. 4. First, by running the system, determine the appropriate sludge age control value for one’s own water treatment plant; this value can then be used to guide sludge discharge. From my experience, after 30 days, the sludge may become aged; of course, the specific operating conditions vary from plant to plant. One needs to summarize and figure it out on their own. Any available parameters are merely for reference only. 5. Is the sludge concentration high? Check the feed-to-sludge ratio; it should not be less than 0.1! Just looking at the values, with MLSS=1000 and BOD5=50, your sludge concentration is high. What are the reasons for sludge leakage in secondary sedimentation tanks? I think there are many reasons for sludge escaping from the secondary sedimentation tank. 1. When the processing load on biological systems (in terms of water volume and concentration) increases, sludge loss can occur. This usually happens when the water volume rises, resulting in a shorter retention time in the secondary sedimentation tank; as a result, the activated sludge does not have enough time to settle before flowing out of the tank, thereby causing sludge loss. At the same time, an increase in the influent concentration leads to enhanced activity of the activated sludge, which is unfavorable for sedimentation. The effluent is turbid and shows sludge carryover. 2. Operating at too low a load causes the sludge to age, leading to self-oxidation of microorganisms and flocculation breakdown. Sludge running will also occur. 3. When filaments swell, sludge leakage can occur if there is not enough time for the sludge to settle. 4. Additionally, low temperatures, excessive aeration, large pH fluctuations, and the entry of toxic and inert substances into the biological system can also cause sludge loss. 5. I think that to understand these reasons, one must experience them repeatedly in practice in order to be able to make flexible and accurate judgments. 6. Of course. Relevant testing methods are also essential. It is the basis for your judgment. 1. Which process, activated sludge or contact oxidation, is more effective for treating printing and dyeing wastewater in the north? 2. Is it better to perform decolorization before biochemistry or after it? 1. Textile printing and dyeing wastewater is likely to be a type of wastewater that is difficult to treat. The decomposition of its pollutants requires longer periods of biological oxidation and contact time. 2. Chromogenic molecules pose a challenge for treatment in activated sludge; generally, microorganisms remove such chromogenic substances by adsorbing them and then discharging them along with the sludge. 3. I think decolorization should be done before the biochemical treatment stage. The remaining parts that are difficult to remove can then be removed through biological adsorption, which should work better. 4. The contact oxidation method should be better than the traditional activated sludge method, as it provides a longer biological retention time, which facilitates the breakdown of hard-to-degrade organic substances. Additionally, local anaerobic conditions in the biofilm also help to remove such substances. Question: How is the sludge return ratio determined in the oxidation ditch process? 1. According to the definition, the return ratio is the ratio of the amount of sludge returned to the amount of water flowing into the biochemical system. Textbooks and reference books often provide reference values, but the specific control values can be determined through observation during actual operation. 2. The biological activity and treatment efficiency can be improved by controlling the reflux ratio. There is a lot of foam on the surface of the oxidation ditch, as well as plenty of sludge, which affects the quality of the effluent. Several attempts were made to remove the sludge, but there was no improvement. How can this problem be solved? Regardless of the process used in biochemical systems, the reasons for foam or sludge formation are more or less the same. 1. Observation of the foam focuses on summarizing aspects such as the generation cycle, color, viscosity, and fragility. Of course, changes in the quality of the incoming water, as well as any alterations in other operational parameters, also need to be monitored and understood. 2. When sludge floats to the surface, it is also necessary to observe its color, viscosity, and whether it contains bubbles. If needed, microscopic examination of both normal sludge and the floating sludge should be carried out for comparison in order to understand the properties of the sludge. 3. By using the above main observation methods and key points to identify the causes of foam or sludge formation and taking targeted actions to address them, I believe the system will be able to return to normal operation! I have a question: A few days ago, the ammonia nitrogen level in the effluent suddenly rose from 5 mg/L to 22 mg/L within one day, and it has remained high ever since! What could be the main reasons for this? Below are some of the water quality parameters at my plant:Inlet parameters: COD: 300 mg/L, BOD: 100 mg/L, NH3-N: 35 mg/L, SS: 350 mg/L, TP: 9 mg/L, Alkalinity: 280 mg/L, pH: 7.5
Effluent parameters: COD: 40 mg/L, BOD: 6 mg/L, NH3-N: 22 mg/L, SS: 20 mg/L, TP: 1.2 mg/L, Alkalinity: 120 mg/L, pH: 7.8
There have been no changes to the operating procedures at my plant; the dissolved oxygen levels in the three channels of the oxidation ditch are 1-2-3. We tried increasing the dissolved oxygen level, but it had no effect on nitrogen removal. What additional information is needed?
1. I would like to check first whether the ammonia nitrogen level in your inlet water has increased. This can also be used to confirm whether the experimental data is incorrect. 2. Please also check whether there have been any changes in the substrate concentration and flow rate of the incoming water. 3. I don’t think it’s necessary to increase the aeration volume. I have been working with the contact oxidation method for a few years. In my opinion, a COD level of 1200 isn’t that high; you can stop feeding water in, add bacteria, and continue aeration until the water meets the required standards, after which you can gradually start feeding water in again to see if it works As far as I know, it indeed should be done as the guy upstairs suggested: stop the water inflow and introduce activated sludge for aeration. However, I don’t think water inflow should start once the water quality meets the standards; rather, it should begin after biological microscopy confirms that the biofilm on the fillers has formed and matured. In the fluidized bed biofilm process, to what extent of static cultivation is generally required during the cultivation phase before continuous feedwater feeding can begin? The principle of biofilm formation on the packing is based on the microorganisms adhering to the packing reproducing and thus forming a biofilm, rather than being the result of large amounts of activated sludge adhering to it. Therefore, after adding the inoculated activated sludge to the reactor and allowing it to undergo aeration for 24 hours, the remaining activated sludge is removed (to prevent free-floating microorganisms from competing with those on the packing for organic nutrients), followed by continuous water feeding to facilitate biofilm formation. During cultivation, the aeration volume should not be too high, as this facilitates biofilm formation. I’m not sure whether by ‘fluidized bed’ you mean a fluidized bed or a moving bed, but the principle behind the formation of biofilms should be the same. As for monitoring SV, I think it is not an important control parameter in membrane treatment. I use the fluidized bed biofilm process; generally, at what stage of static cultivation during the growth process can continuous water feeding be initiated? ? How are indicators such as DO and SV controlled during this process? If the COD concentration of the incoming water is around 50 mg/L (low-concentration domestic wastewater), the BOD is around 15 mg/L, and the water temperature is 12 degrees, what considerations are necessary when starting the cultivation process? I think that by comparing the inlet and outlet water (removal rate) and observing the condition of the biofilm, it is possible to determine whether continuous water feeding is feasible. With such a low concentration of organic matter in the inlet water (which requires oligotrophic microorganisms) and a low temperature of 12 degrees, I think it will be difficult to form a biofilm; if the performance of the packing material itself is not very good, it will only be even more difficult. Can a carbon source be added during film-forming culture to make film formation easier after the membrane base is formed?
15. Question about the OOC process? How is the operation of this process? What are the investment and operating costs per ton of water? How are domestic sewage treatment plants being used? The OOC process, similar to the OCO process, is an improved version of the aeration tank. In this process, the aeration tank is divided into an inner zone and an outer zone; the inner zone serves as the aeration area, while the outer zone is a zone where aeration and non-aeration phases alternate. It is less commonly used in China, but it is suitable for treating wastewater with low pollution loads. Its advantages include energy savings, reduced operating costs, good water quality, simplified management, and stable operation. 16. Question: How is the sludge return ratio determined in the oxidation ditch process? 1. According to the definition, the return ratio is the ratio of the amount of sludge returned to the amount of water flowing into the biochemical system. Textbooks and reference books often provide reference values, but the specific control values can be determined through observation during actual operation. 2. The biological activity and treatment efficiency can be improved by controlling the reflux ratio. 17. There is a lot of foam on the surface of the oxidation ditch, as well as excessive sludge, which affects the quality of the effluent. Several attempts were made to remove the sludge, but there was no improvement. How can this problem be solved? Regardless of the process used in biochemical systems, the reasons for foam or sludge formation are more or less the same. 1. Observation of the foam focuses on summarizing aspects such as the generation cycle, color, viscosity, and fragility. Of course, changes in the quality of the incoming water, as well as any alterations in other operational parameters, also need to be monitored and understood. 2. When sludge floats to the surface, it is also necessary to observe its color, viscosity, and whether it contains bubbles. If needed, microscopic examination of both normal sludge and the floating sludge should be carried out for comparison in order to understand the properties of the sludge. 3. By using the above main observation methods and key points to identify the causes of foam or sludge formation and taking targeted actions to address them, I believe the system will be able to return to normal operation! 18. We are dealing with domestic wastewater; other wastewater treatment plants don’t seem to have this phenomenon of the effluent turning green. Our influent BOD is very low, around 50. I would like to ask how we can control the microbial population at a certain stage After anaerobic treatment, it enters the oxidation ditch – is there any specification for dissolved oxygen? Also, we add urea and potassium dihydrogen phosphate in an effort to improve microbial activity; then what indicators should we pay attention to when monitoring? If the activity of microorganisms is high, could it cause other negative effects? Problems such as poor sedimentation properties and an excessive degradation rate leading to a shortage of nutrients and subsequent depletion, etc. 1. I’m not very familiar with the specific details of your water treatment plant. Because, with BOD=50, COD is around 130 as well. 2. Since it is domestic wastewater, N and P should not be lacking. It seems unnecessary to add urea and potassium dihydrogen phosphate. 3. With such a low inlet concentration, it’s unknown what the outlet concentration will be, and what the removal rate will be as well 4. The aeration method in the oxidation ditch is relatively suitable for microbial degradation of organic matter, that is, the dissolved oxygen concentration is high at the front and low at the back. 5. Treating low-concentration wastewater can easily lead to sludge aging, with the effluent containing a large number of small active sludge particles. This aspect leads to an increase in the COD of the effluent; in cases where the activated sludge is not severely affected, it is carried away with the effluent, resulting in a COD increase of between 10 and 20 ppm. 6. I recommend reducing the aeration volume; ensuring an outlet dissolved oxygen level of 1.5 is sufficient. This can prevent the activated sludge from undergoing excessive auto-oxidation. 7. I think, relative to the volume of your oxidation ditch, your treatment capacity should be quite high, that is, the surface load is high. So, with BOD=50, your MLSS can still be maintained at 1000 ppm. With a higher load, the overcurrent speed also increases. As a result, microbial sedimentation is insufficient, and active sludge may also flow out with the discharged water. 19. I have a question: A few days ago, the ammonia nitrogen level in the effluent suddenly rose from 5 mg/L to 22 mg/L within one day, and it has remained high ever since! What could be the main reasons for this? Here are some of the water quality parameters at my plant:
Inlet parameters: COD: 300 mg/L, BOD: 100 mg/L, NH3-N: 35 mg/L, SS: 350 mg/L, TP: 9 mg/L, Alkalinity: 280 mg/L, pH: 7.5
Effluent parameters: COD: 40 mg/L, BOD: 6 mg/L, NH3-N: 22 mg/L, SS: 20 mg/L, TP: 1.2 mg/L, Alkalinity: 120 mg/L, pH: 7.8
There have been no changes to the operating procedures at my plant; the dissolved oxygen levels in the three channels of the oxidation ditch are 1-2-3. We tried increasing the dissolved oxygen level, but it had no effect on removing nitrogen. What additional information do you need?
1. I would like to first check whether the ammonia nitrogen level in your inlet water has increased. This can also be used to confirm whether the experimental data is incorrect. 2. Please also check whether there have been any changes in the substrate concentration and flow rate of the incoming water. 3. I don’t think it’s necessary to increase the aeration volume. 20. I have been working with the contact oxidation method for a few years; in my opinion, a COD level of 1200 isn’t that high. You can stop feeding water in, add bacteria, and continue aeration until the water meets the required standards, after which you can gradually start feeding water in again to see if it works As far as I know, it indeed should be done as the guy upstairs suggested: stop the water inflow and introduce activated sludge for aeration. However, I don’t think water inflow should start once the water quality meets the standards; rather, it should begin after biological microscopy confirms that the biofilm on the fillers has formed and matured. 21. With the fluidized bed biofilm process, to what extent of static cultivation is generally required during the cultivation phase before continuous feeding of water can begin? The principle of biofilm formation on the packing is based on the microorganisms adhering to the packing reproducing and thus forming a biofilm, rather than being the result of large amounts of activated sludge adhering to it. Therefore, after adding the inoculated activated sludge to the reactor and allowing it to undergo aeration for 24 hours, the remaining activated sludge is removed (to prevent free-floating microorganisms from competing with those on the packing for organic nutrients), followed by continuous water feeding to facilitate biofilm formation. During cultivation, the aeration volume should not be too high, as this facilitates biofilm formation. I’m not sure whether by ‘fluidized bed’ you mean a fluidized bed or a moving bed, but the principle behind the formation of biofilms should be the same. As for monitoring SV, I think it is not an important control parameter in membrane treatment. 22. I use a moving-bed biofilm process; generally, to what extent of static cultivation is required during the growth phase before continuous feeding of water can begin? ? How are indicators such as DO and SV controlled during this process? If the COD concentration of the incoming water is around 50 mg/L (low-concentration domestic wastewater), the BOD is around 15 mg/L, and the water temperature is 12 degrees, what considerations are necessary when starting the cultivation process? I think that by comparing the inlet and outlet water (removal rate) and observing the condition of the biofilm, it is possible to determine whether continuous water feeding is feasible. With such a low concentration of organic matter in the inlet water (which requires oligotrophic microorganisms) and a low temperature of 12 degrees, I think it will be difficult to form a biofilm; if the performance of the packing material itself is not very good, it will only be even more difficult. Can a carbon source be added during film-forming culture to make film formation easier after the membrane base is formed? 23. The activated sludge grows rapidly, resulting in fluctuating levels of TP in the effluent. How can the amount of sludge be controlled? 1. Sludge removal is an important method for removing total phosphorus. 2. The sludge grows too quickly; I think sludge discharge will also increase. This facilitates the removal of total phosphorus. 3. Anaerobic control facilitates the effective removal of phosphorus by phosphorus-oxidizing bacteria. 4. The concentration of organic matter in the influent also affects the effective removal of phosphorus; compared to operation at higher loads, the total phosphorus removal rate is lower under low-load operation. 5. As for the fluctuating levels of TP in the effluent, I think it is related to changes in the phosphorus concentration in the water, adjustments in the amount of nutrients added, control of dissolved oxygen, as well as sludge discharge as mentioned earlier. You might want to check those aspects. As long as it’s not a major issue in the design, I think total phosphorus control is manageable. 24. Due to a malfunction, the AAO process experimental unit, which was previously operating normally (with a volume of 4 m3, influent COD of 260, effluent COD of 25, MLSS of 2000, HRT of 12 hours, a ratio of 1:3:6, DO of 2, and a water temperature of 30°C – levels typical for domestic wastewater), lost approximately 30% of its water due to leaks. Under normal operating conditions, how long will it take for it to return to its previous operational level? It may take 1~2 weeks! 25. If there is no sludge recirculation and all of the discharged sludge is dewatered, how can the sludge age be determined? Furthermore, what’s your view on high-load and low-load operation during runtime? 1. Without backflow, it is still possible to perform calculations using the formula mentioned in previous discussions on this site. 2. Under high-load operation, the effluent parameters will naturally increase, and the impact resistance will relatively decline. 3. Operation at low load is the opposite, but sludge aging can also lead to an increase in effluent parameters. 4. It is best to control the natural conditions reasonably; excessive or too low loads over a long period are not conducive to maintaining stable water quality parameters, and they can also have adverse effects on microorganisms, such as the formation of scum, foam, growth of filamentous bacteria, and breakdown of sludge. 26. What should be considered during the design of the CASS process, and how should the effluent weir be designed (what load value is appropriate)? Also, in this process, what equipment is used? It’s my first time dealing with this process, and I’m not very familiar with the equipment involved. Please give me some guidance! At the same time, how should activated sludge be cultivated and acclimated, and what aspects should be considered during the commissioning and operation of the entire system? How to achieve a high level of self-control skills. During the aeration process, which type of aeration device is better? 1. The CASS process – I have visited sites and learned about it, but I am not familiar with the specific operations involved, so my assistance to you may be limited; please forgive me! ! 2. The CASS process is somewhat similar to the SBR process, which is well-known to us, and it falls under the category of batch processing. To improve the efficiency of nitrogen and phosphorus removal and suppress the growth of filaments. An anaerobic and anoxic section have been added in front of the aeration tank. 3. In the design, the size and proportions of each tank should be determined based on the water volume and load. 4. The outlet weir is mostly replaced by a weep hole to ensure a uniform drop in the liquid level during drainage. The displacement can be determined and selected based on the set drainage time. 5. The equipment used is similar to that in the SBR process; a water separator and submersible mixers for the anoxic and anaerobic zones are required. Of course, a set of automatic control devices is also needed. 6. There is nothing particularly special about sludge cultivation either. First, inoculate the sludge and carry out aeration without oxygen exchange for 24 hours, after which normal aeration should be applied (but not excessively). Start by draining and adding water in small amounts, then gradually increase the amount of water added. 7. During debugging and operation, one must independently determine appropriate operating parameters, such as the time for water intake, reaction, sedimentation, and water discharge ； Amount of return sludge, etc. 8. Selection of the aeration device: When choosing the aeration head, it should ensure that blockages do not occur during sedimentation; jet aerators can also be used, as they are effective for both stirring and oxygenation, and blockages rarely happen with them. 27. How to initiate biological cultivation under low-temperature conditions, and what precautions should be taken? The wastewater is municipal sewage, with most of it being industrial waste water; the COD level is around 500 mg/L. The local temperature is about minus 8 degrees, while the water temperature is around 10 degrees. It is required that the COD level of the treated water be below 60 mg/L. Please advise on how to start the treatment process and what precautions should be taken. Thank you! 1. It is necessary to use sludge from a water treatment plant whose water quality is similar to that of the water to be treated as an inoculum. 2. There should be no major issues with culturing at a water temperature of 10 degrees. 3. The requirement that the effluent concentration be below 60 mg/L is quite stringent. I’m not sure about your processing technology; if it operates at full capacity, the sedimentation tank isn’t designed with an enlarged volume, and I think it will be difficult to maintain this effluent standard over a long period of time. 4. Method of culturing bacteria. It’s available in some textbooks and reference books, so I won’t go into further detail. 5. It should be noted that continuous aeration is necessary during startup, but excessive aeration over a long period is not conducive to the rapid reproduction of microorganisms. Especially when the concentration of organic matter in your inlet water is low. 6. Depending on the water quality, it is also essential to add nutrients. 7. The control of the water inflow rate should be increased gradually. 28. The IC reactor does not have any particle emission facilities during operation! We know that wastewater contains some suspended substances or substances that are difficult to degrade! If there is too much granular sludge, does it need to flow out with the effluent? So, is there any subsequent processing? I’m probably an amateur when it comes to anaerobic treatment processes. So, my help for you might be limited. 1. IC reactors, including other types of reactors. Both in selection and use, there are applicable scenarios and requirements. 2. For wastewater with low COD concentration and high levels of inorganic impurities, I think such reactors are not very suitable. 3. The microorganisms in the anaerobic stage possess extremely strong self-oxidation capabilities. Decomposing organic matter does not require oxygen, but it does not need the free oxygen in the air. It merely makes use of the chemically bonded oxygen in organic molecule molecules. Therefore, anaerobic microorganisms can also achieve a good removal rate for recalcitrant organic substances. 4. Since the sludge is not discharged, some of it inevitably ages; after being utilized through endogenous respiration and by other organisms, the amount of sludge produced becomes minimal. 5. The sludge that is discharged along with the water flow is, naturally, a form of sludge removal, and I think it is necessary. It’s just the outflow of large amounts of sludge. It is related to a fault that has occurred in the system. 6. For subsequent processes, in the case of the sludge that flows out, the focus is naturally on improving the operation of the reactor itself. I don’t think it’s necessary to have sedimentation tanks or filtration tanks! This post was last edited by johncom on 2009-2-20 14:59.]
Inlet parameters: COD: 300 mg/L, BOD: 100 mg/L, NH3-N: 35 mg/L, SS: 350 mg/L, TP: 9 mg/L, Alkalinity: 280 mg/L, pH: 7.5
Effluent parameters: COD: 40 mg/L, BOD: 6 mg/L, NH3-N: 22 mg/L, SS: 20 mg/L, TP: 1.2 mg/L, Alkalinity: 120 mg/L, pH: 7.8
There have been no changes to the operating procedures at my plant; the dissolved oxygen levels in the three channels of the oxidation ditch are 1-2-3. We tried increasing the dissolved oxygen level, but it had no effect on removing nitrogen. What additional information do you need?
1. I would like to first check whether the ammonia nitrogen level in your inlet water has increased. This can also be used to confirm whether the experimental data is incorrect. 2. Please also check whether there have been any changes in the substrate concentration and flow rate of the incoming water. 3. I don’t think it’s necessary to increase the aeration volume. 20. I have been working with the contact oxidation method for a few years; in my opinion, a COD level of 1200 isn’t that high. You can stop feeding water in, add bacteria, and continue aeration until the water meets the required standards, after which you can gradually start feeding water in again to see if it works As far as I know, it indeed should be done as the guy upstairs suggested: stop the water inflow and introduce activated sludge for aeration. However, I don’t think water inflow should start once the water quality meets the standards; rather, it should begin after biological microscopy confirms that the biofilm on the fillers has formed and matured. 21. With the fluidized bed biofilm process, to what extent of static cultivation is generally required during the cultivation phase before continuous feeding of water can begin? The principle of biofilm formation on the packing is based on the microorganisms adhering to the packing reproducing and thus forming a biofilm, rather than being the result of large amounts of activated sludge adhering to it. Therefore, after adding the inoculated activated sludge to the reactor and allowing it to undergo aeration for 24 hours, the remaining activated sludge is removed (to prevent free-floating microorganisms from competing with those on the packing for organic nutrients), followed by continuous water feeding to facilitate biofilm formation. During cultivation, the aeration volume should not be too high, as this facilitates biofilm formation. I’m not sure whether by ‘fluidized bed’ you mean a fluidized bed or a moving bed, but the principle behind the formation of biofilms should be the same. As for monitoring SV, I think it is not an important control parameter in membrane treatment. 22. I use a moving-bed biofilm process; generally, to what extent of static cultivation is required during the growth phase before continuous feeding of water can begin? ? How are indicators such as DO and SV controlled during this process? If the COD concentration of the incoming water is around 50 mg/L (low-concentration domestic wastewater), the BOD is around 15 mg/L, and the water temperature is 12 degrees, what considerations are necessary when starting the cultivation process? I think that by comparing the inlet and outlet water (removal rate) and observing the condition of the biofilm, it is possible to determine whether continuous water feeding is feasible. With such a low concentration of organic matter in the inlet water (which requires oligotrophic microorganisms) and a low temperature of 12 degrees, I think it will be difficult to form a biofilm; if the performance of the packing material itself is not very good, it will only be even more difficult. Can a carbon source be added during film-forming culture to make film formation easier after the membrane base is formed? 23. The activated sludge grows rapidly, resulting in fluctuating levels of TP in the effluent. How can the amount of sludge be controlled? 1. Sludge removal is an important method for removing total phosphorus. 2. The sludge grows too quickly; I think sludge discharge will also increase. This facilitates the removal of total phosphorus. 3. Anaerobic control facilitates the effective removal of phosphorus by phosphorus-oxidizing bacteria. 4. The concentration of organic matter in the influent also affects the effective removal of phosphorus; compared to operation at higher loads, the total phosphorus removal rate is lower under low-load operation. 5. As for the fluctuating levels of TP in the effluent, I think it is related to changes in the phosphorus concentration in the water, adjustments in the amount of nutrients added, control of dissolved oxygen, as well as sludge discharge as mentioned earlier. You might want to check those aspects. As long as it’s not a major issue in the design, I think total phosphorus control is manageable. 24. Due to a malfunction, the AAO process experimental unit, which was previously operating normally (with a volume of 4 m3, influent COD of 260, effluent COD of 25, MLSS of 2000, HRT of 12 hours, a ratio of 1:3:6, DO of 2, and a water temperature of 30°C – levels typical for domestic wastewater), lost approximately 30% of its water due to leaks. Under normal operating conditions, how long will it take for it to return to its previous operational level? It may take 1~2 weeks! 25. If there is no sludge recirculation and all of the discharged sludge is dewatered, how can the sludge age be determined? Furthermore, what’s your view on high-load and low-load operation during runtime? 1. Without backflow, it is still possible to perform calculations using the formula mentioned in previous discussions on this site. 2. Under high-load operation, the effluent parameters will naturally increase, and the impact resistance will relatively decline. 3. Operation at low load is the opposite, but sludge aging can also lead to an increase in effluent parameters. 4. It is best to control the natural conditions reasonably; excessive or too low loads over a long period are not conducive to maintaining stable water quality parameters, and they can also have adverse effects on microorganisms, such as the formation of scum, foam, growth of filamentous bacteria, and breakdown of sludge. 26. What should be considered during the design of the CASS process, and how should the effluent weir be designed (what load value is appropriate)? Also, in this process, what equipment is used? It’s my first time dealing with this process, and I’m not very familiar with the equipment involved. Please give me some guidance! At the same time, how should activated sludge be cultivated and acclimated, and what aspects should be considered during the commissioning and operation of the entire system? How to achieve a high level of self-control skills. During the aeration process, which type of aeration device is better? 1. The CASS process – I have visited sites and learned about it, but I am not familiar with the specific operations involved, so my assistance to you may be limited; please forgive me! ! 2. The CASS process is somewhat similar to the SBR process, which is well-known to us, and it falls under the category of batch processing. To improve the efficiency of nitrogen and phosphorus removal and suppress the growth of filaments. An anaerobic and anoxic section have been added in front of the aeration tank. 3. In the design, the size and proportions of each tank should be determined based on the water volume and load. 4. The outlet weir is mostly replaced by a weep hole to ensure a uniform drop in the liquid level during drainage. The displacement can be determined and selected based on the set drainage time. 5. The equipment used is similar to that in the SBR process; a water separator and submersible mixers for the anoxic and anaerobic zones are required. Of course, a set of automatic control devices is also needed. 6. There is nothing particularly special about sludge cultivation either. First, inoculate the sludge and carry out aeration without oxygen exchange for 24 hours, after which normal aeration should be applied (but not excessively). Start by draining and adding water in small amounts, then gradually increase the amount of water added. 7. During debugging and operation, one must independently determine appropriate operating parameters, such as the time for water intake, reaction, sedimentation, and water discharge ； Amount of return sludge, etc. 8. Selection of the aeration device: When choosing the aeration head, it should ensure that blockages do not occur during sedimentation; jet aerators can also be used, as they are effective for both stirring and oxygenation, and blockages rarely happen with them. 27. How to initiate biological cultivation under low-temperature conditions, and what precautions should be taken? The wastewater is municipal sewage, with most of it being industrial waste water; the COD level is around 500 mg/L. The local temperature is about minus 8 degrees, while the water temperature is around 10 degrees. It is required that the COD level of the treated water be below 60 mg/L. Please advise on how to start the treatment process and what precautions should be taken. Thank you! 1. It is necessary to use sludge from a water treatment plant whose water quality is similar to that of the water to be treated as an inoculum. 2. There should be no major issues with culturing at a water temperature of 10 degrees. 3. The requirement that the effluent concentration be below 60 mg/L is quite stringent. I’m not sure about your processing technology; if it operates at full capacity, the sedimentation tank isn’t designed with an enlarged volume, and I think it will be difficult to maintain this effluent standard over a long period of time. 4. Method of culturing bacteria. It’s available in some textbooks and reference books, so I won’t go into further detail. 5. It should be noted that continuous aeration is necessary during startup, but excessive aeration over a long period is not conducive to the rapid reproduction of microorganisms. Especially when the concentration of organic matter in your inlet water is low. 6. Depending on the water quality, it is also essential to add nutrients. 7. The control of the water inflow rate should be increased gradually. 28. The IC reactor does not have any particle emission facilities during operation! We know that wastewater contains some suspended substances or substances that are difficult to degrade! If there is too much granular sludge, does it need to flow out with the effluent? So, is there any subsequent processing? I’m probably an amateur when it comes to anaerobic treatment processes. So, my help for you might be limited. 1. IC reactors, including other types of reactors. Both in selection and use, there are applicable scenarios and requirements. 2. For wastewater with low COD concentration and high levels of inorganic impurities, I think such reactors are not very suitable. 3. The microorganisms in the anaerobic stage possess extremely strong self-oxidation capabilities. Decomposing organic matter does not require oxygen, but it does not need the free oxygen in the air. It merely makes use of the chemically bonded oxygen in organic molecule molecules. Therefore, anaerobic microorganisms can also achieve a good removal rate for recalcitrant organic substances. 4. Since the sludge is not discharged, some of it inevitably ages; after being utilized through endogenous respiration and by other organisms, the amount of sludge produced becomes minimal. 5. The sludge that is discharged along with the water flow is, naturally, a form of sludge removal, and I think it is necessary. It’s just the outflow of large amounts of sludge. It is related to a fault that has occurred in the system. 6. For subsequent processes, in the case of the sludge that flows out, the focus is naturally on improving the operation of the reactor itself. I don’t think it’s necessary to have sedimentation tanks or filtration tanks! This post was last edited by johncom on 2009-2-20 14:59.]
29. A municipal wastewater treatment plant with a capacity of 30,000 tons per day, using the oxidation ditch process; it features a pre-denitrification zone and is capable of nitrogen and phosphorus removal. Influent TN: 30-35 mg/l; the effluent level should be kept below 12 mg/l. The requirement for nitrogen removal rate is very high, and it is difficult to meet it through conventional nitrification-denitrification control. Are there any good solutions? What other data do you need from me? Please give me some advice. 1. Inlet TN: 30-35 mg/l; the outlet concentration is required to be below 12 mg/l. I think the removal rate isn’t very high. It’s just that the lower the concentration, the harder it is to increase the removal rate. 2. How is anaerobic control in the anti-digestion section? The backflow should not be too large, otherwise it is difficult to achieve an anaerobic condition, and as a result the efficiency of natural retrodigestion is low. 3. Of course, a high reflux ratio and a small volume in the pre-anoxic section are both factors that reduce the residence time of retrograde-fermenting bacteria in the anaerobic zone. It can also lead to incomplete digestion. 4. It is also possible to examine whether the substrate level is too low. 30. The designed hydraulic retention time for the oxygen-deficient area in our plant is 1 hour, but due to the amount of returned sludge, the actual retention time is less than 1 hour. The reflux ratio is around 100%. The dissolved oxygen in the hypoxic zone is below 0.7. The current COD level of the influent water is 200–300 mg/L; the COD/TN ratio is 6.5–8.5, and the MLSS level is around 4.5 g/L. Will reducing the reflux rate lower the denitrification efficiency? I would like to reduce the DO level in the aerobic zone, thereby enabling a shift from synchronous nitrification-denitrification and nitrogen removal processes to nitrite-based nitrogen removal, in order to improve the efficiency of nitrogen removal. Do you have any suggestions? I think there’s no issue with the carbon source; please reduce the amount of recirculated sludge by 40%~50% to minimize the dissolved oxygen level in the anaerobic zone. A dissolved oxygen level of 0.07 ppm is still too high. The efficiency of simultaneous digestion and anti-digestion is low; you can learn by giving it a try – of course, that’s perfectly fine. 31. 1. Our factory is currently facing difficulties; the incoming water contains a large amount of printing and dyeing wastewater. Will this have an impact on the bacterial culture we are maintaining in our factory? ? The incoming water appears as a relatively transparent light red liquid. cod=290, bod=20, ph=5.6. We use the oxidation ditch process. The strain has not yet been cultured. It is still in the exploratory stage. The pH value of the incoming water is too unstable! ! Sometimes 3, sometimes 9. Moreover, the Bod/cod of the incoming water is extremely low! ! ! We have not yet managed to cultivate our strain. The raw water is quite complex, containing a lot of sediment, having low nutrient levels, and experiencing significant pH fluctuations. The activated sludge concentration fails to increase; we have been using intermittent inoculation for almost two months with little success. 1. It’s really difficult to help you with this matter. 2. I think the current task is to cultivate the bacteria; whether the effluent parameters exceed the limits is no longer that important. 3. It is necessary to increase the hydrocarbon content of the raw water. Textile printing and dyeing wastewater is inherently difficult to degrade. As an oxidation ditch process, it has a lower operational load compared to the conventional activated sludge method; however, it still faces challenges when dealing with wastewater having low BOD/COD values and containing substances that are hard to degrade. Culturing bacteria is indeed difficult. 4. Reduce the aeration volume to meet the minimum dissolved oxygen requirement. Otherwise, under low-load conditions, the activated sludge will oxidize on its own or be carried away with the effluent. 5. Increase the switching frequency of water inflow and outflow for each pool. It’s not the case that microorganisms settle for too long under conditions of nutrient deficiency; an excessive length of time in such conditions will also lead to the oxidation of the microorganisms themselves. and it is not easy to cultivate bacteria. 6. For other aspects such as pH adjustment, detection methods, and improving sediment removal, please decide on them accordingly. 32. Second, after careful tuning, the sludge in the two oxidation ditches has gradually stabilized (there are a total of four oxidation ditches). SVI (30) has only left and right. There is still sludge floating in the effluent from the secondary sedimentation tank (there was not much sludge to begin with). Our procedure is as follows: qualified raw water (with appropriate pH, color, etc.) is fed in; two aeration tanks are equipped with two aeration units each (with a DO level of 8–9), and the aeration units are of the surface type with a power rating of 30 KW. Four secondary sedimentation tanks feed back into these two oxidation ditches, with two for each. The COD of the influent water is 350, BOD is 80, and SS is 60; the quality of the influent water is not very stable! ! ! I hope experts can give me some guidance on the work in the second half of the culture process! ! ! 1. The culture growth has improved; congratulations! 2. After reading your description, I feel that your process doesn’t seem to be much like the oxidation ditch process. 3. Regardless of the process used, I think your dissolved oxygen level is too high; please measure it – check the dissolved oxygen at the outlet of the aeration tank! If it’s greater than 1.5, turn off a few aeration units; if oxygenation becomes uneven after that, switch them on and off frequently. 4. Pay attention to the proper application of nutrients. 5. You already have control over the raw water, so I think culturing the bacteria will go smoothly. 6. The outflow of activated sludge is related to factors such as a relatively high load and a small amount of activated sludge; it will naturally disappear once it has developed to a certain extent. Moreover, most of the sludge that flows out is likely to be the lower-quality part. 33. The wastewater I handle contains *** and aniline compounds; the treatment process consists of a regulating tank, air flotation, an acid addition tank, an iron-carbon tank, an alkali addition tank, a sedimentation tank, a hydrolysis-acidification tank, a contact oxidation tank, a secondary sedimentation tank, and finally the effluent discharge. During the cultivation process, I added sludge from a nearby chemical wastewater plant as an inoculum. The BOD in the oxidation tank is over 400. (The error may be large due to the high dilution factor.) ) When the inlet flow was 1200, the outlet flow was over 800. That is why the influent concentration is reduced. Now, the water quality does not meet the standards, so the Environmental Protection Agency has raised objections! I’m not sure if there is a better way to ensure that the water quality meets the standard of 100 mg/l or comes close to it (as this is the most clear goal at present), while also serving to cultivate sludge. To prevent repeated issues with the water output in the future! Additionally, I would like to ask again: what kind of flocculant is better to use in the primary sedimentation tank, secondary sedimentation tank, and sludge dewatering room? (Of course, there is no urgency regarding the flocculant for the sludge dewatering room at the moment.) What are the typical concentrations and amounts used? At present, the flocculation effect in the primary sedimentation tank and the secondary sedimentation tank is not very good (I am using polyaluminum PAC). I. 1. *** and aniline are pollutants that are difficult to degrade; therefore, proper control is necessary at all stages of treatment to remove such wastewater. Otherwise, there will be pressure when treating the water. 2. You need to measure the removal rate of organic matter before and after adding the flocculant PAC. I recommend adding coagulants (PAM) simultaneously, as I believe this will increase the removal rate of organic matter at that physical stage. This will reduce the impact of such hard-to-degrade substances on subsequent biological systems. 3. Within the factory, water-saving measures should be adopted to reduce water production volume and lower the amount of water returned to the secondary sedimentation tank; the return ratio can be set at less than 50%. By using the above methods to increase the retention time of wastewater in the biological system, it contributes to improving the removal efficiency. 4. If possible, please provide information on parameters such as the current water treatment volume, the volume of the contact oxidation tank, the target dissolved oxygen level, and the biological concentration in the contact oxidation tank. 5. PAC + anionic PAM is a good combination of flocculants. Secondary sedimentation tanks usually do not require flocculants. Positive PAM is usually sufficient for dehumidification rooms. Of course, anionic and non-ionic PAMs can also be used in some cases. 6. The dosing concentration varies depending on the water quality of each water treatment plant; please determine it through small-scale tests using cups and bottles. II. 1. Based on the data you provided: the influent concentration is 1200 mg/L, while the effluent concentration is over 800 mg/L; furthermore, with a BOD value of 400 mg/L in the oxidation tank, it can be seen that the recalcitrant organic compounds such as anilines in the influent have hardly been degraded at all. This indicates that the favorable microbial community within the entire biological treatment system – microorganisms capable of breaking down aniline compounds – has not yet been established; as a result, the wastewater treated by this biological system does not meet the required standards. 2. In fact, getting the anoxic-aerobic system up and running takes time. If you use sludge from wastewater treatment processes that contain aniline compounds, it is important to control parameters such as the hydraulic retention time in the hydrolysis tank and the sludge return rate during startup. You can monitor changes in pH value and volatile fatty acids (VFA) in the hydrolysis tank to determine whether it is functioning properly. 3. If granular sludge from relevant wastewater treatment can be inoculated, the process may start more quickly. 4. The key now is to get the biological system up and running properly; without this prerequisite, it’s impossible to meet the standards. 5. You might want to take a look at a book on anaerobics written by He Yanling; it provides some theoretical foundations, and by combining those with practical applications, you won’t feel anxious. III. “It is possible to monitor the changes in pH value and volatile fatty acids (VFA) in the hydrolysis tank to determine whether the tank is functioning properly.” 1. I fully agree with using the above methods for such testing. It also serves as a basis for evaluating the efficacy of the hydrolysis tank. But it seems that neither the pH value nor the volatile fatty acids (VFA) will change significantly. 2. During the system debugging and trial operation phase, the environmental protection agency should not place too much emphasis on the wastewater meeting the required standards, right? 34. Our current sludge age is very short, at most four days; this is calculated based on the sludge concentration and the amount of sludge removed, rather than through control measures! I observed that the biological sedimentation capacity of the aeration tank was very poor, and there was a lot of material on the surface of the secondary sedimentation tank – likely sludge – in any case, it was in a suspended state; as a result, our effluent was quite turbid! At first, I suspected that excessive aeration was ruining the flocculation properties, but our dissolved oxygen level isn’t that bad – it’s set at 1.5. What could be the reason? Could you help me analyze this? 1. In the conventional activated sludge process, with a sludge age of 4 days, this control method works well when the influent concentration is high and the volume of water is large (i.e., the sludge load is high). However, it is not appropriate to use such sludge age control when the sludge load is low. 2. If you have a good understanding of how to manipulate various parameters, then it can be calculated either based on sludge concentration and sludge discharge volume, or through control methods! It doesn’t matter. However, it must be considered together with other parameters to determine the optimal control points for each scenario. 3. The sedimentation performance of the aeration tank is poor; the parameter used to assess this is the SV30 value. A value below 30% is considered normal; otherwise, a microscope examination should be conducted to check for the growth of filamentous bacteria. 4. The turbidity of the supernatant is mostly due to a high sludge load, which leads to increased biological activity and makes it difficult for the particles to settle. Under a microscope, a large number of non-active sludge protozoa can be observed, such as parameciums and flagellates with rapid movement that are commonly found, like trichomonads. Such organisms can directly use free bacteria and organic matter as food sources. At high loads, the amount of free, non-flocculating bacteria increases, providing an abundant food source for such organisms, which leads to their massive proliferation. Bacteria that do not flocculate easily, along with such protozoa, lead to poor sedimentation of activated sludge. The mechanism lies here; please understand it on your own. 5. There are also many reasons for the formation of floating silt. It is necessary to examine its source in space: does it rise after sinking to the bottom of the pool, or does it rise before even reaching the bottom? Color, viscosity, and microscopic examination of floating particles are all things that need to be checked. A small amount of production poses no major problem, but large-scale production will raise the effluent parameters and reduce the sludge volume in the aeration tank. 6. Normal microorganisms are not easily broken apart by aeration; nevertheless, even in the secondary sedimentation tank, they can aggregate rapidly when the water shear force is low. 7. Controlling the dissolved oxygen at 1.5 is based on cost considerations, and it refers to the dissolved oxygen level in the water exiting the aeration tank. The aeration process at the beginning of the aeration tank needs to be monitored regularly to ensure that this level is maintained; this is because the main site of adsorption and oxidation takes place in the first 2/3 of the tank, while the latter 1/3 should be prepared for flocculation. Imagine if there is excessive aeration at the outlet – this would increase biological activity, which would not facilitate biological flocculation and sedimentation in the secondary sedimentation tank Especially as the sludge ages, its viscosity increases, making it easy for it to adhere to the small bubbles from aeration and form scum that does not settle easily. 35. Question: The COD value of the wastewater from our company’s cafeteria, after passing through the oil separator, is around 1200 mg/l. The volume of wastewater generated is 20,000 tons per month. We require that the COD level of the wastewater be below 300 mg/l. How can this be achieved? ? Based on the water volume, costs, and treatment requirements, I would like to add a biological treatment system. Relying solely on materialization may not meet the requirements, and the costs will also be high. 36. 1. During the cultivation of activated sludge, the C:N:P ratio is 100:5:1; but how should the amounts of flour, urea, and diammonium hydrogen phosphate to be added be calculated? 2. Sludge bulking may occur during the cultivation process in my plant – how should this be monitored using microscopic examination? 3. Please tell me the detailed procedures for cultivating and acclimating activated sludge! 1. In fact, not only is culture cultivation involved; during operation, the addition of nutrients can also be determined according to the ratio of C:N:P=100:5:1. However, it should be noted that the nitrogen and phosphorus levels in the raw water must be measured before testing the incoming water of the biological system, and these values should be deducted. 2. Adding flour to promote bacterial growth is a bit of a waste, isn’t it? Simply dissolve the flour in water, measure the BOD5, and then make the conversion based on the amount added and the water volume. 3. The nitrogen content of urea seems to be 46%; don’t forget to take this into account when calculating the dosage. 4. For diammonium hydrogen phosphate, calculate the phosphorus content by yourself using its molecular formula! 5. For example! Based on the actual daily water treatment volume (e.g., 15,000 tons), with an inlet BOD5 of 200 ppm and the inflow water containing almost no nitrogen or phosphorus (any such contents are deducted), the amount of urea to be added is = (15,000*200*5) / (100*1000*0.46) = 326 kg; the same calculation applies to phosphate, with the 5 in the numerator replaced by 1 and 0.46 in the denominator replaced by the phosphorus content in diammonium hydrogen phosphate. 6. Filamentous fungi are easy to detect, but difficult to control. 7. Generally, the filamentous or filament-like organisms I have seen possess the following characteristics: they are transparent to semi-transparent and as thin as hair strands. They have a uniform thickness; some contain sulfur particles that give them a blackish appearance. Some of them are mobile, and in extreme cases, the bacterial cells develop fine branches to enhance their ability to absorb nutrients. The internal structure can be seen under 1000x magnification, while the optical lens can be seen under 600x magnification. 8. Some algae also have a filamentous shape, but they are generally green and can be distinguished! 9. There are specialized textbooks and reference books on culture and acclimatization; you can take a look at them. It’s impossible for me to list them all here, so please forgive me! This post was last edited by johncom on 2009-2-20 15:02.]
37. What measures should be taken if the BOD is too low? Also, you mentioned last time that the MLSS levels in different channels of the oxidation ditch vary; I understand now that it’s because the amount of organic matter gradually decreases, right? But I used an MLSS meter to measure each corridor, and found that their values were pretty similar. What’s going on here? 1. I’ll say the same thing again: as much organic matter as there is, that’s how many microorganisms can be produced. Therefore, when the BOD is low, it’s necessary to reduce the concentration of activated sludge to accommodate this situation. Intentionally increasing the sludge concentration will lead to an extended sludge age. thus aging the sludge. 2. For wastewater with a low B/C ratio, it is advisable to increase this ratio as much as possible through physical-chemical treatment or hydrolysis-acidification, thereby making it easier for microorganisms to function. 3. At the same time, increasing the return flow of biological sludge to reduce the residence time of microorganisms in the biological tank can decrease their degree of aging. 4. In the oxidation ditch process, influenced by the sedimentation function of the side tanks, its concentration should be higher than that in the intermediate tank. 5. There is no real need to use an MLSS meter for comparison, as in some channels during operation sedimentation occurs – how can you then measure MLSS? Moreover, the measurement values taken at different times probably don’t have any comparative value either! 6. The concentrations of microorganisms in each corridor change dynamically; due to different treatment stages and the influence of influent water, the concentrations vary across different time periods as well. Regarding the decrease in the sludge concentration distribution due to the reduction in organic matter concentration, I think there won’t be any significant reaction within the volume of the oxidation ditch. 38.1) The influent water contains a large amount of dyeing and printing wastewater; after just twenty minutes of aeration, white foam about half a meter high appears on the surface of the oxidation ditch. An oxidation ditch is equipped with six aerators (30kw), whose main functions are oxygenation and flow promotion. DO is basically 8 to 9. So I usually turn on the aerator alternately. What other hazards do printing and dyeing wastewater pose besides white foam? How should we put an end to it? 2) How many aeration machines should we turn on when water is introduced? What should be done if no water enters? 3) How many return pumps should be used in the secondary sedimentation tank? One or three recirculation pumps (37kw)? How is it possible that the water outlet isn’t muddy? 4) The MLSS in the oxidation ditch has increased. The SVI(30) reaches 5%, but the sludge is relatively fine, so the slurry phase is still in good condition. Strains can be identified! ! ! How should we proceed with the next steps? 5) Can excess sludge be treated? 1. I want to tell you that the formation of white foam has little to do with printing and dyeing wastewater; it’s likely due to a low number of microorganisms in your system. With a relatively high concentration of substances in the incoming water, the load is high, and as a result, when aeration occurs in conditions with high substrate levels, white, tough, and sticky foam is naturally produced. That’s probably why the pools where biological cultivation is better do not produce foam. As long as the population of organisms increases, the foam will disappear. 2. If, when measuring dissolved oxygen, the value at each measurement point is 8–9 ppm, then it is necessary to reduce the aeration volume. You might think that I have already set the aeration units to a low level, yet the dissolved oxygen level remains high; I believe this is because there are few microorganisms, resulting in less oxygen being utilized. 3. I think you can operate 2 aerators, switching them on alternately, but make sure that one of them is always running to supply oxygen. 4. The concentration of printing and dyeing wastewater is not very high, so the hazards are not significant; however, when the concentration is too high, substances that are difficult to degrade can interfere with the normal metabolism of organisms, which is why the growth of microorganisms in such wastewater is slow. At the same time, if the physical and chemical control in the early stages is not proper and it has an impact on the organisms, this will lead to an increase in the color intensity of the effluent, resulting in values that exceed the specified limits. 5. The sludge return rate can be set at a value slightly higher than the normal return ratio. 100% reflux is also feasible. 6. I do not recommend sludge discharge when the relative load has not decreased. 7. The formation of floating sludge is closely related to excessive aeration. 8. Surface aeration machines have one drawback: it is difficult to adjust the oxygen supply level. Turning off the equipment to reduce oxygen supply results in insufficient mixing. 39. Our plant uses the A-A-O process; there are two agitators in the anoxic section, separated from each other by a concrete wall. After operating for some time, sludge was found on both sides of the corridor, and this sludge became solid and dry within a few days. After cleaning, it returns to its original state in a few days, which affects the appearance. Help analyze the reasons. 1. It may be that your mixing equipment is not mixing thoroughly, resulting in dead zones! 2. Or the hydraulic load is insufficient. 3. The formation of sludge will not affect the efficiency of your treatment process. Some of the material that flows out of the anaerobic zone is also broken down in the aerobic zone. 4. It doesn’t look very appealing from a sensory perspective, but there’s no need to make special adjustments for it. 5. I think this phenomenon is also common in other wastewater treatment plants using this process that perform well. 40. Our AO tank produced a lot of foam today, and that foam contained many sludge particles. Why is this? Last night we didn’t add water to the AO tank, but we did add flour. And a lot of sludge also floated to the surface in the secondary sedimentation tank. Is there any way to solve this? 1. It seems to be related to the flour you added. 2. Flour contains a large amount of starch, specifically amylose, which does not break down easily; this has an impact on microorganisms. 3. The foam that forms is mostly caused by repeated aeration when no water has been added, as well as an excessive amount of undegraded organic matter. 4. Generally, excessive foam and scum in your AO tank will affect the secondary sedimentation tank. 5. After water is introduced, things should improve in a few days. 6. To increase the substrate concentration, adding flour is not the only option; its effectiveness and cost are also unsuitable. When the volume of water to be treated is not large, purchasing industrial methanol might be more cost-effective! 41. What are the processes for treating oily wastewater? Is there a process with low investment and good treatment results? Oil separation, coagulation, and air flotation seem to be quite commonly used! 42. Our current treatment process is hydrolysis acidification + CASS. The designed maximum load for the influent COD is 1000, but currently the influent COD is often around 1500; meanwhile, the ammonia nitrogen level is around 150, and the pH value is 9.5. Currently, the effluent concentration is around 250; the treatment effect is very poor, the sludge is fragmented, the microorganisms are small in size, and the SV value is at 99%, indicating severe sludge bulking. How should I adjust the operating parameters? Our parameters are divided into aeration, sedimentation, decanting, and interval, which are carried out in sequence within one tank. 1. The pH of the incoming water at 9.5 definitely needs to be adjusted, otherwise it is harmful to microorganisms. 2. The concentration of the incoming substrate exceeds the design standards, but it is unknown whether the treatment capacity is also overloaded ! If the water volume to be treated is only 70% of the designed amount, it should still not exceed the designed load. 3. Operation under high load is generally not considered to cause filamentous bacterial proliferation; if sludge is returned to the hydrolysis-acidification tank and the return flow rate is sufficient, filamentous bacterial proliferation will even be less likely to occur. 4. Please also check whether the aeration is evenly distributed and there are no dead zones, as this can also be a cause of filamentous bacteria growth. 5. If you are dealing with industrial wastewater that has a simple composition, it may be difficult to avoid the growth of filamental bacteria. 6. I think by making full use of the function of the hydrolysis tank and creating staged oxygen deficiency, it should be beneficial to suppress filamentous bacteria. 7. I’m not sure about the B/C ratio; this could be one of the reasons for the excessive discharge levels. Please try to increase this value as much as possible. 8. For the removal of ammonia nitrogen, please also take into account the effect of hypoxia and whether the substrate is used as a treatment medium; since I am not aware of your specific procedures, I am unable to provide a more detailed assessment. 43. Our water treatment plant receives water in intermittent batches, and at present only primary treatment is carried out. I would like to ask you: when taking water samples from the primary sedimentation tank for testing, does it still necessary to consider the retention time in that tank? If not, then how should the best location and timing for sampling be determined? 1. The results of periodic tests serve as a basis for making decisions regarding periodic operations. 2. There is no need to consider the dwell time. 3. Data collection should involve good statistical analysis and summarization, so as to guide production activities in the end. 4. The sampling location is usually at the outlet where the water from the primary sedimentation tank converges. 44. Can molds be seen when observing the biological community in activated sludge under a microscope? What magnification level of microscope is needed to see mold? Of course, it can be done under an ordinary low-power microscope; you can refer to the Handbook of Microbial Testing in Environmental Engineering compiled by Yu Yuxin and others. 45. In the activated sludge process, the amount of sludge is decreasing. The COD level of the water entering the aeration tank is around 100–200 mg/l; it is difficult for the sludge to grow, and there is a large amount of dead sludge in the tanks that are not in use. What should be done? 1. Adopt intermittent aeration and intermittent, small-scale sludge discharge. Leave pools that are not in use idle. Do not let water in. II. 1. With water intake in this manner, it seems that the sludge concentration cannot be ensured either. 2. Please also minimize the aeration time and operate at low dissolved oxygen levels. 3. If the water volume to be treated is small, an appropriate amount of external carbon source can be added. Or introduce nearby domestic wastewater. 46. There is a machine in Germany that is very good at separating water, oil, and mud – what’s its name again? The centrifugal dewatering machines from German company Foluwei work very well for oily sludge. 47. Can molds be seen when observing the biological community in activated sludge under a microscope? What magnification level of microscope is needed to see mold? Molds can be seen, but they are not easy to identify, and there are relatively few species (those visible under an optical microscope). 48. There is 5,000 cubic meters per day of cotton spinning and dyeing wastewater, and a treatment plant is currently under construction. The treatment process involves coagulation and primary sedimentation – hydrolysis and acidification – contact oxidation – coagulation and sedimentation – decolorization using sodium hypochlorite. The hydrolysis and acidification tank uses a baffle design with internal sludge recirculation, while no sludge recirculation occurs in the contact oxidation tank. I wonder if this approach is feasible; are there any examples of such systems? It seems feasible that there be no sludge discharge from the hydrolysis and acidification tank, but the contact oxidation tank appears to require a sludge discharge system. Otherwise, if there is no sludge discharge from any of the biological treatment tanks, it could lead to issues with the quality of the treated water when there are significant changes in conditions. 49. What are your insights on the management of holidays in biological tanks? Please share your advice! 1. The characteristics of different processes and environmental protection facilities. Management seems different. 2. Low-load maintenance is necessary. 50. My wastewater treatment plant uses the A/O/O process. Recently, it has been affected by sulfur-containing wastewater, resulting in extremely high levels of H2S in the incoming water; as a consequence, the effluent from the secondary sedimentation tank is dark red in color. Additionally, the ammonia nitrogen levels in the incoming water are also high. Which factor is responsible for this discoloration: H2S or ammonia nitrogen? 1. Sewage treatment plants in municipal or industrial areas often encounter such situations. 2. Such situations have a significant impact on wastewater treatment plants, usually due to the wastewater discharged by newly established enterprises or accidental discharges from other enterprises. 3. Implement strict control at the source; it is important to establish discharge standards for enterprises (inflow standards for sewage treatment plants). Regular inspections can also help reduce the occurrence of such issues. 51. Does intermittent sludge discharge affect the treatment efficiency? Does sludge discharge influence changes in the sludge age, and could this impact the process? 1. Try to carry out sludge discharge continuously. 2. When discharging sludge intermittently, please also keep the intervals from being too large and ensure regularity. Thus, the impact on sludge age and the process is relatively small. 52. In the treatment of printing and dyeing wastewater, why do large amounts of algae grow in the aerobic tank and final sedimentation tank, yet is the effluent very clear? Is it possible for the ammonia nitrogen level to be too high? How to solve it? 1. Algae and activated sludge live in symbiosis; if the nutritional needs of the activated sludge are met, then the needs of the algae are essentially also satisfied. 2. The large presence is mostly due to an excessive amount of nutrients in the released water. 3. Similarly, algae cannot survive easily if the water outlet is turbid. 53. The pretreatment stage of the wastewater reuse system I am working on uses biological contact oxidation; the COD of the incoming wastewater is 50, and its BOD is 8. Will the contact oxidation method be effective? Such a concentration doesn’t seem very good! 54. Activated sludge process, with a low SVI and MLSS around 2 g/l. The ammonia nitrogen level in the incoming water is around 2 mg/l, while it is around 5 mg/l in the outgoing water; all other parameters are within normal ranges. May I ask everyone, what methods can be used to increase SVI and reduce ammonia nitrogen in the effluent? Increasing the food-to-microorganism ratio can reduce the activated sludge concentration. 55. Our secondary sedimentation tank has recently experienced back-digestion; large amounts of black sludge have risen to the surface. At the tank’s outlet, the H2S level is above 100PPM. When it was designed, equipment for removing this floating sludge (AIR TO SKIMER) was installed, but now, whenever I turn that equipment on, the water in the tank becomes extremely turbulent! In a short while, the sludge floated to the surface. What is the working principle of this equipment? How should we manage the secondary sedimentation tank? ? ? 1. I think the denitrified sludge that floats to the surface in the secondary sedimentation tank should be brownish-yellow. Please also determine whether oxygen deficiency is causing the sludge to float. 2. I’m not very familiar with your sludge scraping device. 3. For issues related to secondary sedimentation tanks, the key is to control the operating conditions of the aeration tank. This post was last edited by johncom on 2009-2-20 15:04]
56. How can I increase the sludge in a surface aeration tank ( ours is of the completely mixed type)? I would like to know if there are any direct, effective, and quick methods for doing this The usual approach is to reduce sludge discharge and increase the substrate concentration in the influent water. It can be decided by oneself which specific substrate to add. 57. Design for beer wastewater treatment: After anaerobic treatment, the COD level of the effluent is 550 mg/L, while the standard requires an emission level of 400 mg/L. It was decided to install an anaerobic selector at the inlet of the aeration tank. Due to limited experience in this area, I would like to understand what potential disadvantages might arise if the size of the selector is increased. Currently, we set the volume of the anaerobic selector tank to 25% of the total biochemical tank volume, with the contact time between the recycled sludge and wastewater being approximately 1 hour. 1. Filamentous swelling in municipal wastewater is not very common, as municipal wastewater has a balanced composition; unlike industrial wastewater, which has a simpler composition and is therefore more prone to swelling. 2. Adding an upstream anaerobic tank is indeed a good method for controlling filaments. 3. From a technical standpoint alone, it’s better to make it larger naturally! Based on the information you provided, the residence time in the biochemical tank is 4 hours, which seems a bit short. If the sludge load is high, it is recommended to increase the size of this anaerobic selector. 65. In wastewater treatment, why is the water leaving the sedimentation tank green? The water in ponds is also green; the reason is probably the same! I think in most cases, the green color of pond water is caused by algae. In the case of wastewater, even when the treated water meets the discharge standards, planktonic algae such as Chlorella can still grow, causing the effluent to take on a colored appearance. Of course, it is also common for the effluent to become colored due to the coloring in the raw water, as is the case with wastewater from dyeing and printing factories, as well as paper mill coating processes that produce colored wastewater. 66. At present, our wastewater meets the standards for now, but this is because our sewer network is still under construction. Most of the water that enters the system comes from groundwater used for building the network, with only a small portion being domestic wastewater originating from one university; as a result, the BOD level of the incoming water is very low. Our designed capacity for incoming water is 25,000 tons per day, but the actual amount of water entering the system is not sufficient to meet the requirements of a continuous inflow and outflow process. The current daily water intake is around 8,000 cubic meters. If we ignore the SV30 value, the water does meet the standards, but it seems there is no sludge in the aeration tank. Given that the sewer network will be completed by March or April, and most of the city’s wastewater will start flowing into the system, I’m concerned that the standards won’t be met. If the standards aren’t met, we won’t receive payment, and that will cause dissatisfaction among the employees. If the SV30 value could be at least 10%, I wouldn’t be so worried. But two months have passed now, and it’s still only 2%. Moreover, tests using a magnetic furnace showed that organic components account for only about 20% of the sludge used to calculate the SV30 value; the rest is made up of inorganic or inert substances. It’s doubtful whether such sludge will be effective in dealing with the wastewater that will flow in during March or April. 1. Some form of investigation is still necessary. For example, once the external sewer network is completed, we need first-hand data on the volume and quality of the water entering the system, so that we can properly manage our biological treatment system to handle this incoming water. 2. I think it’s not necessary for you to raise the MLSS at this time; in fact, it’s quite difficult to do so. If possible, half a month before the completion of the pipeline network and the start of water inflow, add a large amount of additional organic matter to the wastewater (the specific amount to be determined based on the planned water volume and concentration) in order to increase the MLSS. Industrial methanol is relatively inexpensive and could be considered as an option. 3. In that case, there should be no problems. If the cost is not worthwhile, there’s no need to add additional organic substances; one can simply wait for water to arrive and then proceed with the cultivation gradually. I think that with proper handling, the levels won’t exceed the limits for even a few days! 67. We are currently carrying out the commissioning of the wastewater treatment plant. Things were going well, but yesterday the pH of the incoming water changed (hydrochloric acid entered the wastewater pipeline; the plant operated for about 20 hours), which caused sludge to escape from the secondary sedimentation tank and resulted in turbid effluent. Currently, the pH of the incoming water is normal; the pH in the aeration tank is around 6.5, while it is about 4.8 in the secondary sedimentation tank. I have now stopped the water inflow and backflow. Can the system be restored? What should I do next? Please advise. At the current testing stage, the wastewater flow rate is 100 M3/h, the COD level is 50 mg/l, and the water temperature is around 15 degrees. 1. Indeed, since it has been running for 20 hours, sludge accumulation will occur. 2. The pH is low; it’s incorrect not to add water! Consider that water can enter. 3. The reflux can be reduced a bit. 4. Under normal circumstances, water quality may deteriorate for a short period of time, but it can recover. Once normal water supply is restored, normal conditions are generally achieved within 2 to 3 days. 5. To understand the degree of stress on biochemical systems, it is best to observe the activity of protozoa and metazoans under a microscope. As long as that part of the organism remains intact, it is usually no problem to recover in a short time. 68. Our factory uses the oxidation ditch process. Recently, the COD level of the effluent has not met the standard (which is 100); the SV value has decreased, but the effluent remains clear. The DO level is similar to normal levels (around 0.4), while the ammonia nitrogen level is a bit high (it has always been somewhat high). Could you help analyze what might be causing this? The secondary aeration tank shows sludge floating phenomenon (AB process); the aeration volume is low and the DO level is not high – could it be due to sludge aging? 1. Based on the data you provided, the dissolved oxygen level seems to be too low, which may in turn inhibit the normal proliferation of normal coccolithophores. Raising it to 1.5 appropriately seems pretty good to me! 2. Sludge scumming occurs in the secondary aeration tank (AB process); the aeration volume is low and the DO level is not high. It may also be due to sludge aging, but sludge aging isn’t closely related to the low aeration volume and low DO level. For the reasons behind sludge aging and sludge floating in the effluent, you can take a look at some of the previous discussions on this site! I believe some answers will be found! This post was last edited by johncom on 2009-2-20 15:06.]
69. I’m facing a problem: in our secondary sedimentation tank, sludge has been floating to the surface in clumps these past few days; it’s quite loose, and it might be sludge bulking, but not to a severe extent. What surprises me, though, is that the MLVSS in the biochemical tank is around 2000 mg/L; the sludge age is relatively short, and the sludge has not aged, which is also within acceptable limits. The dissolved oxygen level at the end of the biochemical tank is between 2 and 4, which is excellent. (We use siphonic sludge return; from my observations, the return system in the secondary sedimentation tank is working properly, and almost all of the sludge in the tank is being returned.) The COD of the incoming water is not very high either; the COD of the secondary effluent is below 60 mg/L (which is quite good), and the entire biochemical system is functioning perfectly. Under such circumstances, why does sludge bulking occur? Also, with the three secondary sedimentation tanks we are using, why does only one of them experience sludge floating and becoming loose, while the other two remain normal? 1. First, it is necessary to determine whether filamentous bacterial bulking has occurred in the activated sludge. To what extent will it expand? 2. It can usually be determined by the following methods: a. SV30 testing. b. SVI testing. c. Microscopic examination. But it seems that the information you gave me does not include these three parameters. 3. My experience is that filamentous fungus expansion is related to a simple composition of wastewater, insufficient dissolved oxygen, and a too low food-to-microbe ratio. Other cases caused by factors such as pH and temperature basically do not occur; at most, they play only a supplementary role. 4. The composition of wastewater is simple, which makes it easy to inhibit the growth of normal microbial flocs; whereas some components in wastewater facilitate the proliferation of filamental fungi. 5. Insufficient dissolved oxygen and dead zones in aeration also facilitate the growth of filamental bacteria, as this results in a large surface area for these bacteria; a low-oxygen environment is more conducive to their proliferation. 6. The reasons for excessive low food-to-oxygen ratio leading to filamentous fungus proliferation are basically the same as those for insufficient dissolved oxygen. 7. The environment in which normal bacterial aggregates and filaments are found determines whether filamentous swelling will occur. 8. Please think carefully about and integrate the above explanations. 9. Determine whether filamentous swelling has occurred through diagnostic methods. 10. If it is filamentous bacteria expansion, all three secondary sedimentation tanks will experience expansion simultaneously; it is impossible for only one of them to expand. Therefore, please confirm whether filamentous bacteria expansion has occurred. 70. What issues should be considered during the commissioning of a new sewage treatment plant? ? What are the main steps? ? Where should I look for relevant information? ? By the way, the method used is (anaerobic UASB + high-load biological filter method/solid contact method). 1. For issues related to debugging, I think it would be better for you to consult the design and construction company responsible for your facility’s environmental protection systems! Generally, the construction company is responsible for commissioning and employee training. 2. Sludge inoculation and load adjustment are I think the most important tasks. 71. I wonder how the compliance rate of wastewater treatment plant effluent is calculated? Is there a calculation for the weekly average? How is it done? I wonder if there is a fixed requirement regarding what the standard rate of water quality should be? I hope colleagues and experts who visit this site can offer me some help. As far as I know, there seems to be no strict requirement; it can be used in internal corporate management. You can decide how many cycles there will be! 72. Why does a large amount of foam occur when treating beer wastewater using contact oxidation, and why is the COD level in the treated water unstable? 1. The processing equipment produces foam for various reasons; you can find out more in the discussions available on this site, which will help you determine how to adjust your operations in order to address the foam problem. 2. Beer wastewater is a type of wastewater with a relatively high B/C ratio, making it easy to be degraded by biological systems. Thus, it has higher biological activity. A large amount of foam (white) tends to form especially under high shock loads and an excessively high food-to-sludge ratio; increasing the activated sludge concentration can generally help reduce foam formation. 3. Due to the influence of the production process on beer wastewater, the volume and concentration of this water vary significantly throughout the day. When the regulating tank does not have sufficient capacity for adjustment, shock loads are likely to occur, which in turn can lead to foam formation and unstable outlet water parameters. 4. Of course, the pH of beer wastewater can vary significantly, and it needs to be adjusted properly to ensure that the pH of the wastewater entering the biological treatment tank is at the appropriate level; otherwise, foam may form, but this usually occurs only during improper operation. 5. Since the information you provided regarding the process and parameters is limited, I can only offer suggestions based on common possibilities. There are also many other reasons that lead to the above phenomena, so they will not be detailed here! 73. I want to know something about SBR – how to control it based on various factors? Which method is better: ORP or others? If there are any articles on this topic, please mention them as well as how to achieve these controls using measuring instruments. Are there any other factors that we need to take into consideration? 1. The SBR method is a type of batch treatment process, with microorganisms being the key agents involved in the treatment. Therefore, the control parameters remain consistent with those of the conventional activated sludge process. 2. The key to control lies in the time allocation for each control segment. That is, the water inlet time, aeration time, sedimentation time, and water discharge time. 3. Index control: Neither Do nor ORP is a parameter that can handle everything on its own; it is incorrect to rely on a single parameter to control the entire system. 4. Generally, emphasis is placed on controlling the food-to-microbe ratio (0.15~0.25) and the biochemical reaction time (determined based on laboratory tests). A dissolved oxygen level of 3 ppm is sufficient for control. 5. At the same time, it is equally important to adjust the quality of the water entering the biochemical treatment process; that is, physical and chemical treatment steps are used to remove factors that affect biochemical reactions, such as pH, SS, heavy metal ions, and an overly uniform water quality. 6. Additionally, adjust the reaction time appropriately according to the influent concentration. It is important to note that better treatment results have been achieved. One cannot stick to an unchanging allocation of processing time. 74. The wastewater from multiple printing and dyeing enterprises is treated centrally, with the main treatment processes being physicochemical treatment, anaerobic treatment, and aerobic treatment. The aerobic treatment process makes use of the activated sludge method. Currently, the COD level in the wastewater entering the aerobic tank is around 600 mg/L, while the sulfur content is about 100 mg/L. The COD level in the wastewater exiting the aerobic tank after sedimentation is approximately 100 mg/L; the sludge concentration (MLSS) is 800 mg/L, and the F/M ratio is around 0.35. The dissolved oxygen level at the end of the aerobic tank is about 2 mg/L. The tricky problem is that the sludge has poor settling properties in the secondary sedimentation tank; it remains mostly in a suspended state and is lost along with the effluent. The sludge concentration at the bottom of the secondary sedimentation tank is very low, not much higher than that in the aeration tank. This loss of sludge leads to effluent quality that exceeds the specified standards. Microscopic examination of the sludge revealed a small amount of filamental bacteria. I suspect that the suspension of the sludge is caused by combined water-soluble sludge bulking, but since I am not very clear about the characteristics of this condition, I cannot be certain whether it indeed is combined water-soluble sludge bulking. I would like to hear your opinion – what are some effective countermeasures? Also, could excessive S2- in the influent cause sludge poisoning? And what consequences will it have on the sludge? 1. The COD removal rate is 83%, which is fairly good, considering the difficulty of treating the source water you are working with. 2. The control of various indicators is also good. 3. Regarding the issue of sediment in the effluent, I believe it is related to the quality of the raw water you are using for treatment. I am not aware of the SV30 settlement values, so it’s difficult to make a judgment. However, I think there are two ways in which activated sludge can remain suspended: a) the activated sludge remains suspended after flocculation. b The activated sludge remains in a non-flocculated suspended state. The former is formed by activated sludge enclosing bubbles, while the latter is caused by sludge bulking. 4. Usually, the source water contains large amounts of sulfides, which facilitates the growth of filamentous bacteria containing sulfur particles, leading to sludge flocculation. 5. At the same time, excessive sulfide content can easily reduce the activity of the sludge, leading to sludge flocculation. 6. Therefore, it can be concluded that excessive sulfide content is the cause of sludge formation. 7. I think increasing the sludge concentration appropriately can help alleviate the problem of sludge floating. Meanwhile, as the system operates, the activated sludge should be able to be acclimated to such water quality. 75. What indicators can the food-to-energy ratio monitor? And how can it be detected? The food-to-sludge ratio is the ratio of the organic matter content in the water before it enters the biochemical system to the concentration of active sludge within that system. By using this ratio, it is possible to determine the level of load, thereby adjusting operations to prevent sludge aging and excessive load that could lead to abnormal water quality. The calculation formula is an empirical one; for details, please refer to the relevant discussions earlier. 76. In your previous post on how to reduce the operating costs of wastewater treatment plants, you said that \"if sludge costs arise, they can be used for composting plants’ plants and trees, depending on the circumstances.\" Therefore, it only requires an increase in the overtime cost,” I completely agree. We have a small-scale municipal wastewater treatment plant in a town here, and the sludge generated is intended to be used for composting plants and flowers. Is it necessary to treat this sludge before using it? What method is the most reliable and cost-effective for handling? I think you can dig a trench 0.5 meters wide and 0.3 meters deep next to the plants; fill it with the sludge and then cover it with the original soil. I don’t think any treatment is necessary, after all, your wastewater is just municipal sewage! 77. I’m worried that harmful microorganisms and pathogens in sludge could have an impact on the environment and humans. Is my concern justified? The microorganisms used in wastewater treatment are part of the natural microbial flora; they are not infectious, so there is no need to worry. Otherwise, wouldn’t the microorganisms present in the wastewater contaminate the water bodies? ! As for the sludge from industrial wastewater, it is regulated by laws and regulations. 78. How long does it take for general sludge bulking to subside? After my sludge bulking occurred (over about two to three weeks), the quality of the effluent remained good; however, the removal rate of NH3-N was not high, and there weren’t many filamental bacteria observed under a microscope. Initially, I concluded that the pH of the influent water was too low. Later, I added lime for one or two weeks, and the nitrification rate improved, but the sedimentation properties of the sludge remained poor. Eventually, the sludge escaped. May I ask what caused this? 1. As you mentioned, filamental bacterial bulking is periodic, with the duration depending on water quality and treatment conditions. 2. Sludge running is a consequence of the swelling of filamentous fungi; identifying the cause is necessary to reduce the degree of swelling. 79. What are the reasons for the rapid increase in sludge concentration in oxidation ditches, and how can it be addressed? The increase in my substrate concentration is the main reason for the growth of sludge; of course, rising temperatures also need to be taken into account! 80. Treatment of printing and dyeing wastewater is currently in progress, using a hydrolysis-acidification + aerobic treatment + membrane reactor. I would like to ask the following: 1. What is the reason for the increase in COD levels in the effluent after hydrolysis-acidification? The increase is quite significant; when the COD level in the influent is around 900 mg/L, it rises to around 1100 mg/L in the effluent. 2. The color of the influent often changes, being red, black, or blue, yet the colors of the supernatant from the hydrolysis-acidification stage, the aerobic treatment stage, and the effluent are all yellow. Why is that? 1. There are two possible reasons for this prolonged increase in COD levels in the effluent. First, there might be issues with your sampling procedures; secondly, sludge might be escaping from the hydrolysis tank, which would result in higher values in the laboratory tests. 2. When red, yellow, and black are mixed together, it is likely to turn black; it is also possible for it to turn yellow after being diluted and mixed with activated sludge. I think the long-term decolorization effect of conventional biochemical systems is limited; it is necessary to enhance the effects of the physicochemical stage as well! 81. The sludge density in the hydrolysis-acidification tank is 1.002–1.006 (as stated in textbooks); therefore, sludge loss is inevitable. It is thus necessary to return the sludge to the hydrolysis tank after the aerobic stage. Is this correct? Some manuals state that in a contact oxidation tank, part of the sludge remains suspended while another part adheres to the fillers. As Brother Sanfeng mentioned earlier, during tuning, it is first necessary to carry out an aeration step before removing the remaining active sludge (to prevent free-floating microorganisms from competing with those on the fillers for organic nutrients). This seems to contradict what was said earlier??? If the mixture after the aerobic stage is returned to the hydrolysis-acidification tank, what should be the appropriate range for the DO level in that tank? I would appreciate your guidance. 1. In the case of slight sludge loss, I don’t think it’s necessary to implement sludge return; the microorganisms in the hydrolysis tank should be able to replenish what is lost through their own reproduction. 2. At the same time, in this process, the key point of treatment and the final control stage are no longer the hydrolysis tank; therefore, appropriate fluctuations in the concentration within the hydrolysis tank do not have a significant impact on the subsequent processes. 3. Regarding the issue of anaerobic aeration, I think this approach is not contradictory to sludge removal, as it is only during the bacteria cultivation phase and not part of normal production operations. 82. There is a type of industrial wastewater generated during the production of refined cotton; it has a high content of organic substances and is acidic in nature. I would like to add acid here to adjust the pH of the wastewater, and at the same time acidify the organic matter in it; do you think this is possible? This water quality is somewhat similar to that of papermaking wastewater, but its water quality parameters are much lower than those of papermaking wastewater. Artificial acidification, I think, cannot effectively degrade organic matter; it is hydrolytic acidifying bacteria that can degrade organic matter. I don’t think it’s necessary to adjust the acidity with special additives! 83. I have just finished treating 7,000 tons of food wastewater, and I would like to ask some questions regarding microbial cultivation: I plan to use direct seeding for cultivation – is it possible to use the sludge cakes resulting from the dewatering process in urban sewage treatment plants? PAM was added to this sludge during the dewatering process; does it have an impact on the microorganisms? Was the incubation time increased? I think there should be no problem; it won’t increase the incubation time, and the activity will remain the same. This post was last edited by johncom on 2009-2-20 15:07.]
84. I once worked at a sewage treatment plant that used the Carrousel oxidation ditch process to treat municipal domestic wastewater. Once, the people in the laboratory told me that the ammonia nitrogen level in the effluent was higher than that in the influent, but the TP level in the effluent was very low; the TP level in the influent was around 2.5 mg/L, while it was only about 0.2 mg/L in the effluent. I can’t figure out what the cause is at all; it’s extremely frustrating. What’s going on? Run 3 aeration units at full capacity; use Carrousel blower aerators to reduce the dissolved oxygen level a bit! 85. I found my formula in the book \"Chemical Wastewater Treatment Technology\" published by Chemical Industry Press ； I don’t have any specific examples on hand, so I was wondering if Teacher Sanfeng could use my formula to do the calculations and see if the results are the same as those obtained using your formula. It would be best if they are the same; if they’re different~~~~~~ which formula should I use? I think the data and trends should be quite similar! 86. I need to inoculate the UASB! Since I was doing adjustments in a small town, I didn’t bring any books with me. I’m not sure how to control Stage A of the AB process right now. May I ask: 1\ Is it necessary to continuously recycle sludge from the primary sedimentation tank to Stage A at an equal flow rate? 2\ What should the SV30 value be? Is it 5%-10%? 3\ Should the sludge from the primary sedimentation tank be discarded? 1. I’m not quite sure what you mean by the primary sedimentation tank; I understand the concept better when it comes to the secondary sedimentation tank. 2. In my understanding, the AB process is a two-stage biochemical treatment method, and it is advantageous for treating relatively hard-to-degrade organic substances using this method, as the residence time can be better ensured. 87. Regarding the formula for calculating sludge age, why is the formula in my book different from yours? The formula in my book is: Sludge age = (MLSS * aeration tank volume) / (wastewater flow rate * influent BOD concentration). Which one should I use for the calculation? ? 1. I calculated the sludge age based on the residence time of microorganisms in the aeration tank. 2. It is indeed different from the formula you provided; your formula seems to be the reciprocal of the food-to-micro ratio. 88. I would like to ask a question: Our plant handles oil-contaminated wastewater. The water quality entering the regulation tank is good, but the treatment capacity of the aeration tank is poor, and there is a lot of oil floating on the surface. Is this due to aged sludge? Oil is inherently difficult to biodegrade, so it isn’t closely related to aged sludge. 89. Our company has currently taken on a project to treat ammonia-containing wastewater from a coking plant. This plant previously used the activated sludge method as well, but due to the extremely high concentrations of ammonia and phenol, all bacterial strains died. Its water quality is as follows: COD=8000-11000 ； Volatile phenols = 1700-2300 ； Volatile ammonia = 300 ； Thiocyanate = 635. The pretreatment process we use is as follows: ammonia-vaporized wastewater (with alkali added) → oil separation and adjustment tank (for oil removal) → sealed stripping tank → double-machine air flotation → intermediate water tank. The sand filtration still does not yield good results; is there any better method? What further improvements are needed in the preprocessing process? 1. For such wastewater, an increase in treatment costs is inevitable. 2. To ensure that the effluent meets the standards, I think adding A/B treatment in the later stage of filtration could yield good results. 3. By adding biochemical systems and requiring the design and installation units to provide design plans and justifications, a reasonable selection of biochemical processes should not present any problems. 90. I would like to ask what the specifications and precautions are regarding the installation of aeration heads under the aeration tank? Volume 5, Second Edition of the Water Supply and Drainage Design Manual – Specifications for Blowing and Aeration Design – might be useful to you. 91. What type of flocculant is suitable for use in the primary sedimentation tank, secondary sedimentation tank, and sewage sludge dewatering facilities? (Of course, there is no urgent need for a flocculant right now for the sludge dewatering facilities.) What are the typical concentrations and amounts used? At present, the flocculation effect in the primary sedimentation tank and the secondary sedimentation tank is not very good (I am using polyaluminum PAC). It is recommended to use ferric aluminum sulfate as a flocculant; polyaluminum PAC should not be used, as this may yield better results. The concentration and dosage can be determined through pilot tests based on the specific conditions of the wastewater. I think it’s unreasonable to add flocculants in the secondary sedimentation tank. Even if the sludge deteriorates, a careful decision should be made! 92. I’ve read some materials stating that the food-to-microorganism ratio in the activated sludge process ranges from 0.1 to 0.6. However, processes such as CAST, A/A/O, and Bölkow seem to be used quite often for treating urban wastewater at low load levels. What are the differences between these operating modes and those with normal load levels? 1. The inherent process characteristics and water inlet conditions determine the type of load under which it will operate. 2. Generally, operating at low load can better ensure that the effluent meets the standards (compared to other conditions) ； High-load operation is the opposite. 3. Extreme conditions, namely too low or too high loads, should be avoided during operation. 93. Our plant uses primary treatment, with intermittent water intake; the quality of the incoming water exceeds certain standards, and the treatment efficiency does not meet the required levels. I would like to ask you: what are the factors that affect primary treatment? 1. There are many factors that influence primary treatment, including the original design, operating procedures, choice of chemicals, and methods of operation. 2. The main aspects that can be changed are the selection of drugs and the method of administration. 3. I think you can carefully select the flocculant to achieve the desired treatment results. 94. I have just completed a preliminary design plan for industrial wastewater treatment, and I would like to ask you to help me check whether this process flow is feasible and reasonable. This wastewater is generated during the production of refined cotton; its COD level is 5,000 mg/L, and its color intensity is 50,000. The daily volume of wastewater treated is 6,000 tons. Additionally, the COD value of this wastewater varies considerably, ranging from several hundred to 10,000. The process I use is as follows: wastewater → adjustment tank → acid addition → neutralization tank → flocculant addition → sedimentation tank → decolorizing agent addition → reaction tank → flocculant addition → sedimentation tank → anaerobic reaction tank → CASS reaction tank → decolorizing agent addition → reaction tank → flocculant addition → sedimentation tank → discharge up to standard specifications. My goal is to reduce the chromaticity in the water to below 200 through a second decolorization process; at the same time, I aim to ensure that the suspended solids in the wastewater meet the required standards by adding flocculants. I also use anaerobic digestion in the anaerobic reactor along with the aerobic treatment process of the CASS system to control the COD levels in the wastewater. For wastewater like this, is it appropriate to calculate my investment budget at 2,500 yuan per ton as the one-time cost for treating one ton of wastewater? Your proposed solution is too conservative; while the effluent will meet the standards, it involves high investment costs and substantial operating expenses. You could use the following process: wastewater → adjustment tank → acid addition → neutralization tank → coagulation tank → sedimentation tank → anaerobic reactor → aerobic reactor → sedimentation tank → decolorizing agent → decolorized effluent tank → discharge after meeting the standards. The investment is within 1,200 yuan, and the operating cost is less than 0.8 yuan per ton; however, the efficacy of the dyeing and decolorizing agents used is not high, which makes it rather wasteful! 95. Low-concentration domestic wastewater from the southern area is treated using conventional activated sludge processes. The effluent typically has a COD level of less than 20 mg/l and a BOD5 level around 10 mg/l. However, it is difficult to keep the total suspended solids level below 20 mg/l. The secondary sedimentation tank is circular in design, with water entering from the center and exiting around the perimeter; fine particles rise from the bottom of the tank within a 1-m radius around the outlet weir, giving it an unsightly appearance. Even if SS meets the standards, it still won’t pass the scrutiny of leaders, journalists, and laypeople with absolute influence. Low-load operation is the main cause of this situation; it is also an inevitable phenomenon. It can be attempted to reduce the sludge concentration appropriately based on the food-to-sludge ratio. 96. Our plant uses an oxidation ditch treatment process. The water inflow rate is 3,700 cubic meters per hour, with a BOD5 level of around 80 mg/l, which meets the secondary discharge standards. The sludge discharge rate is 50 cubic meters per hour. Currently, the sludge concentration MLSS has reached 13,000 mg/l; we are not sure what to do This condition should not occur or should not persist for long – is it a gauge failure or sludge accumulation? If that is indeed the case, I would kindly ask Brother Sanfeng to clarify it for me. I think it’s impossible to achieve such a high MLSS value! With such a large number of microorganisms, simple aeration devices can no longer meet their oxygen demand! 97. Inlet COD = 150, BOD = 35; outlet COD = 90, BOD = 28. Moreover, the water inflow is not continuous. The pump runs for 30 minutes before needing to be stopped (as there is no water to pump). Generally, it’s 30 minutes of working followed by 40 minutes of rest. Microscopic examination revealed only flagellates, in small numbers. SVI(30) is only 3%. In the oxidation ditch, a large amount of small particulate sludge can be seen moving around. The compression sedimentation effect in the secondary sedimentation tank is fairly good. Please advise: how to increase MLVSS and what points to pay attention to in the next stage! 1. I believe an increase in water volume and a rise in the concentration of pollutants in the incoming water are the fundamental prerequisites for the proper operation of your system! 2. The improvement of MLVSS still depends on the aforementioned prerequisites. 3. Since there isn’t enough water, it’s better to shut down a few lines temporarily for operation; alternatively, the water volume can be increased to carry out cultivation on a centralized basis. Once the water volume is increased enough, turn them all on! 98. How should the grates of sewage treatment plants with low flow rates be designed? The grid width calculated using the formulas in the textbook or design manual is too small to be installed. For projects with low water volumes, the calculated grid width turns out to be too small; it is possible to keep the gap between the grid bars unchanged and simply increase the width to match that of the canal, without having to adhere strictly to the manual guidelines. 99. The secondary sedimentation tank is circular with water entering and exiting around the perimeter (not from the center). Within a 1-m range of the outlet weir plate, fine floating particles are rising from the bottom of the tank, giving it an unsightly appearance. It’s just that our water output has not yet met the standards. COD is about 89 mg/L, BOD is about 28 mg/L, and SS is about 23 mg/L. At present, our culture cultivation work is progressing smoothly. About 10% of SVI(30). Microscopic examination reveals a small number of rotifers. It’s probably related to the heavy rainfall these past couple of days, which has led to an increase in water inflow. However, the BOD/COD level of our water is too low, which slows down the bacterial culture process. Sludge discharge has not yet taken place. Given our current situation, I have a few questions: 1. Can we supply water continuously, and is our sludge already resistant to normal shock loads? 2. The DO level in the oxidation ditch is around 8; is it sufficient to use just one aeration machine for mixing? Still, operate the aerator occasionally; there is water inflow to push the flow in the front of the oxidation ditch, and returned sludge helps to push the flow at the back. 3. When is it estimated that the excess sludge pump will be started? How to control the reflux ratio? 1. The settlement ratio is 10%, and f/m should not be greater than 0.25 ； Continuous water inflow is no problem. 2. Check whether the dissolved oxygen level of the mixture from the oxidation ditch flowing into the secondary sedimentation tank meets the requirements; 1.5 mg/L of dissolved oxygen is sufficient. It is advisable to monitor the dissolved oxygen levels throughout the entire oxidation ditch. Then decide on the aeration method. 3. If the dissolved oxygen level of the oxidization ditch mixture flowing into the secondary sedimentation tank is greater than 3.0, I believe this leads to two problems: first, energy waste, and second, the effluent contains small particles of active sludge that have not settled. 4. Intermittent short-term sludge discharge is necessary. Otherwise, a 10% settlement ratio will result in a significant discount. 5. The control of the reflux ratio can be adjusted based on the water inflow volume; as in traditional sludge treatment methods, if nitrogen and phosphorus removal is not required, a range of 50~100% is suitable. 6. The production and quantity of rotifers are not closely related to rainfall or high water inflow; rather, they are associated with low load levels and long sludge age. This also suggests that continuous water inflow is possible in order to increase the load. Of course, proper sludge discharge is also required. 100. Recently we emptied the sedimentation tank; for some reason, about a day after water was introduced, a large amount of black sludge appeared, and this situation has persisted for over a week – it’s still there today. Why exactly does this happen? Are there any ways to remedy it or prevent it? 1. I don’t know whether your sedimentation tank is used for wastewater treatment or for treating tap water. If it is a sedimentation tank for wastewater treatment, I think you should check whether there are any changes in the conditions of the water flowing into the sedimentation tank before and after cleaning! Such as water inflow volume, dissolved oxygen content in the inlet water, water retention time, etc.! 2. As an aerobic biological treatment process, when the sludge in the secondary sedimentation tank turns black and floats to the surface, the dissolved oxygen level in the tank should be considered first, in order to avoid hypoxia or anaerobic conditions. 3. It is also necessary to check whether the sludge return in the sedimentation tank is smooth, whether the return flow rate is too low, and whether there are any hidden faults in the sludge scraping equipment. 4. If the sludge from the primary sedimentation tank floats to the surface, it may be necessary to consider whether the concentration of organic particles in the wastewater has increased, whether sludge removal is being carried out properly, whether the retention time is too long, and whether there are any hidden faults with the sludge scraping equipment. 101. I am currently studying the denitrification efficiency of the CASS process in treating wastewater with high ammonia nitrogen levels. Since this is being conducted in a laboratory, the water parameters are as follows: COD (glucose) – 400, ammonia nitrogen – 100, phosphorus – 8. Sodium bicarbonate is used to maintain a pH of around 7.5. The sludge concentration is approximately 4500. The process duration consists of 2 hours of aeration, 1.5 hours of sedimentation, and 0.5 hours for water discharge. The dissolved oxygen level at the end of the aeration phase is 2, with a hydraulic retention time of 12 hours. The water discharge ratio is 1/3, and the recirculation ratio is 150%. However, the current denitrification rate is only around 50%. Is it possible to improve this rate? If so, how? I want to remove nitrogen and phosphorus; regardless of the process used, the principles are more or less the same. Your MLSS is high; I’m not sure if your carbon source is being used properly, as otherwise it will affect the denitrification process. By checking the food-to-microbe ratio, it is possible to determine whether the carbon source is functioning properly. It has been determined whether you should add a carbon source to improve denitrification efficiency. This post was last edited by johncom on 2009-2-20 15:09]
102. One of the parameters for online monitoring during the operation of an oxidation ditch is the redox potential. It was found in a book that \"the redox potential is a comprehensive representation of the total redox couples in wastewater, and it characterizes the electrochemical properties of the wastewater.\" May I ask: what are the specific applications and functions of this? Literally speaking, I believe that: 1. The redox potential is a comprehensive representation of the total redox couples in wastewater; it can be understood as the potential value resulting from the combined effect of various substances with redox capabilities present in the water. 2. It characterizes the electrochemical properties of wastewater: in other words, the redox potential value can be used to understand the electrochemical properties of the redox substances present in wastewater. 103. My residential complex generates 50 m3 of wastewater per day (including water from bathing, laundry, toilets, and kitchen waste, among other domestic wastewater). I now want to design a wastewater treatment system that meets Class B standard for discharge, with a focus on the removal of nitrogen and phosphorus. I would like to adopt a treatment process of: pretreatment -- anaerobic fermentation tank (for biogas recovery) -- aerobic stage (for phosphorus removal and nitrification) -- anaerobic stage (for denitrification). Please advise on the feasibility of this system? Note: Firstly, the purpose of treatment is to ensure that domestic wastewater meets regulatory standards; reuse is not required. This is because new residential areas do not have centralized wastewater treatment facilities, and the domestic wastewater discharged there is hardly treated at all. Secondly, fecal water is discharged into wastewater, and I hope it can be decomposed through anaerobic fermentation to produce methane; therefore, biogas is not the goal but a by-product, and the amount doesn’t really matter ； Finally, how to remove the settled sludge is a problem, but it is estimated that the amount of sludge should not be large, as there are two stages of anaerobic decomposition. 1. For your process, the safety factor is already quite high, so there should be no problems. As for the design parameters, further consideration needs to be given based on the water volume and concentration. 2. For nitrogen and phosphorus removal, it seems that the anoxic-anaerobic stage (denitrification) is placed before the aerobic stage. 3. Sludge production can indeed be controlled, as the volume of water to be treated is not large; the aerobic sludge can also be returned to the anaerobic fermentation tank, which helps to reduce sludge generation. 104. We are using the DE oxidation ditch process, and we are currently in the stage of sludge cultivation. A large number of water fleas have appeared in both the oxidation ditch and the secondary sedimentation tank. What could be the cause of this, and how should it be dealt with? 1. Water fleas usually appear in the water that is discharged. This indication occurs in water with low pollution and low turbidity. 2. In addition to the above conditions, free sludge particles suspended in the effluent water are required for them to multiply in large numbers. 3. In summary, when the effluent quality meets the standards and the sludge is slightly aged, such arthropods are likely to appear. 105. I would like to ask a question: if a conventional activated sludge process is required to handle some industrial wastewater (mainly printing and dyeing wastewater), how can the existing process be modified to meet the requirements? 1. I think a small amount of inflow should not have a significant impact on the biochemical system, especially when the quality of your effluent water is **below the discharge standards. 2. For this type of printing and dyeing wastewater, flocculation and sedimentation in the physical-chemical treatment stage must be carried out properly; otherwise, it may be uncertain whether the effluent will meet the required standards. Pilot tests can be used to determine the physicochemical treatment capacity of mixed wastewater, thereby assessing whether a biochemical system can handle it. 106. Can the decomposition resulting from excessive sludge aeration be considered sludge aging? Theoretically, it cannot be understood in this way, but in practice, it can be understood this way! Aeration by blowing air generally does not cause sludge disintegration. Surface aeration has a slight impact! For decomposition to occur due to aeration, there must be underlying causes such as sludge aging; the effect of aeration merely accelerates this decomposition and does not alone constitute the main cause of it. As long as factors such as the age of the activated sludge are normal, aeration will not cause sludge decomposition (at least not to the extent of significant decomposition that results in a thick layer of scum). 107. The BOD of the water entering our factory is very low. But right now, the excessive amount of water fleas is causing the effluent SS to not meet the standards, and I don’t know how to solve this problem. 1. I think I should adjust the manufacturing process to solve this issue? ! 2. When the load is too low, the quality of the effluent water can be quite good; however, the removal rate of pollutants is not high. This leads to sludge aging, which can serve as food for organisms such as water fleas, resulting in their rapid proliferation. 3. Proper sludge discharge to increase the feed-to-microbe ratio – worth giving it a try! ! 108. The wastewater passes through coarse and fine screens as well as a sedimentation tank before entering the A/O tank and the final sedimentation tank. Part of the sludge is then returned to the A/O tank via a sludge lift pump, while another part goes into the earthworm bioreactor; from there it proceeds to a radial dryer. Finally, the sludge, along with screen residues and sand, is transported to a solid waste landfill. The water from the final sedimentation tank enters the contact tank, and after chlorination it is discharged. Biological deodorization is added at the pretreatment stage and in the earthworm bed. I’m sorry for writing like this; please forgive a newbie for only being able to do this much. This is my graduation project; I don’t want it to be something put together haphazardly like previous ones, and I’m hoping to get some guidance. 1. I have no objections to your arrangements regarding the design and manufacturing process. I lack experience with worm biofilters, and their effectiveness as well as operating costs are unknown to me. 2. Chlorination in contact tanks is a method commonly used in many municipal wastewater treatment plants; however, few actually employ it, as most opt not to use it. 3. I want to work with chlorination for disinfection; it’s not related to hospital wastewater. Can I be exempted from this? This is a practical consideration regarding operation! 109. 1. I would like to ask you where the filtrate resulting from sludge dewatering should be discharged? The filtrate from our plant is very turbid (probably due to the amount of flocculant used), and it is discharged directly into the feed water pump room, which results in high levels of COD and BOD in the feed water. Could you tell me what the consequences of this would be? And the methods for improvement. 2. Isn’t the internal circulation in the A2O process also the return of the supernatant? Why can’t the CAST process be used? 1. It is common practice to let the filtrate flow into a pumping well; such a high concentration of substrates in the incoming water indicates that your dewatering efficiency must be very poor. Normal dehydration filtrates do not cause a significant increase in the substrate concentration of the feed water. It’s generally around 10%. The improvement method is to increase the dehydration efficiency. 2. The internal circulation in the A2O process is not the return supernatant, but the mixed liquid. 110. In the A/A/O process, the MISS level is 3200 mg/l and the F/M ratio is around 0.1. The various parameters in the influent water have not changed much compared to before; however, during recent operations it has been observed that the settling ratio is particularly high, at around 80%-90%. The sludge is in a relatively fragmented state, and microscopic examination revealed that the bioflocs are not compact, although rotifers could be seen. The effluent remains clear, and all quality parameters meet the standards; however, when the water volume is high (in horizontal flow sedimentation tanks with sufficient retention time), floculent sludge may flow out with the water, affecting its appearance. And there is some brown foam on the aeration tank now; I hope it’s not biological foam. I would like to ask how to resolve the current situation, reduce settlement, decrease the brown foam, and ensure long-term stability of the effluent. 1. Your process and the design of the sedimentation tank are similar to those of the Suzhou Industrial Park Wastewater Treatment Plant (100,000 tons per day). 2. A low food-to-microbe ratio may lead to the growth of filamental fungi (although this does not occur frequently in this process); please have the laboratory conduct a microscopic examination to confirm. 3. Given the clear quality of the water discharged, it can be inferred that sludge aging is not severe. 4. If your daily water treatment volume is far from reaching the designed capacity, I think it will be difficult to operate. What you mentioned could indeed happen. There are usually two extremes: one is a situation like yours, and the other is sludge aging, which leads to reduced shock resistance of the effluent. 5. The usual approach is to make use of lift stations at various levels (on the premise of treating municipal wastewater), transforming decentralized treatment into centralized treatment, which can generally improve the conditions associated with these two extremes. 111. Our treatment process consists of acid hydrolysis + UBF + CASS, with a capacity to treat 4,000 tons of antibiotic wastewater per day. However, there is no recirculation in the CASS system; I’m not sure if this affects the normal operation of the process. As for your entire treatment process, there should be no problems! 112. Our water treatment plant receives water in intermittent batches, and at present only primary treatment is carried out. I would like to ask you: when taking water samples from the primary sedimentation tank for testing, does it still necessary to consider the retention time in that tank? If not, then how should the best location and timing for sampling be determined? 1. The results of periodic tests serve as a basis for making decisions regarding periodic operations. 2. There is no need to consider the dwell time. 3. Data collection should involve good statistical analysis and summarization, so as to guide production activities in the end. 4. The sampling location is usually at the outlet where the water from the primary sedimentation tank converges. 113. The company’s commissioning department has reported issues with the SBR process for treating food wastewater; please help analyze the situation: 1. The system fails to operate properly, and parameters such as color intensity and COD do not meet the required standards (COD is above 1500) ； 2. The pH in the anaerobic tank is between 4 and 5 ； 3. The SBR tank produces a large amount of foam (jet aeration); there was no foam during aeration before the addition of bacteria, so it is likely a problem with the bacteria. The process consists of: anaerobic tank – equalization tank – SBR tank – sand filter. Additionally, the flow rate is 22 cubic meters, the volume of the anaerobic tank is 18 cubic meters, that of the equalization tank is 18 cubic meters, and that of the SBR tank is 18 cubic meters (13 cubic meters per cycle, with aeration lasting 6 hours). 1. Please check whether the microorganisms in the SBR tank have been properly cultivated. 2. Excessive aeration is not conducive to microbial cultivation and foam reduction. 3. Please also gradually increase the load to cultivate microorganisms; otherwise, the effort will yield half the results! 114. Based on the quality of the incoming water, can it be determined how much sludge can be present per 10,000 tons of water? For the sludge handling facility, how can the amount of sludge produced each day be quantified? Theoretical calculations often differ from reality; if design is not possible, insights can be gained through practical experience! 115. During this season, the moss on the secondary sedimentation tank grows too rapidly; it not only spoils the aesthetic appearance but also forms clumps that cause blockages, and removing it is ineffective due to its fast growth rate. What should be done? How do people usually handle it? Moreover, the flange bottom valve often gets clogged at the water outlet – what should be done? 1. Such situations are indeed troublesome. As for trying to retrieve it, I don’t think it will work; could it possibly grow faster than what can be retrieved! 2. I want to control the nitrogen and phosphorus in the effluent. On one hand, I want to reduce the amount of nutrients added, or improve the efficiency of nitrogen and phosphorus removal through process adjustments! 116. Regarding the issue of moss growth on the secondary sedimentation tanks that I asked you about last time, my current approach is to stop the water supply to a single secondary sedimentation tank, lower the water level so that the entire triangular weir plate is exposed, then expose it to the sun for three to five days; afterwards, it can be easily removed using a brush. After going through this process, no more algae growth was observed when water was added again. You’re right; it is indeed troublesome. However, our ammonia and phosphorus levels are not above the limit – it’s just eutrophication that creates conditions for algae to grow and multiply. We simply eliminate the basic conditions for moss growth, namely the eutrophic water source; as a result, the moss can disappear quite completely. In particular, our processes for nitrogen and phosphorus removal are already very effective, so there is no need to improve these processes any further – this method is the only one that works. It’s also important to eliminate the problem completely; the moss needs to be exposed to the scorching sun for several days to ensure that it won’t grow again. I imagine that in our region in the south, many wastewater treatment plants suffer from algae problems during this season. Although algae don’t affect the quality of the water discharged, they do detract from the appearance and the overall environment. I hope this method will be useful to everyone! 117. We are a petrochemical plant that mainly processes heavy oil wastewater; currently, the water obtained from heavy oil treatment poses a significant strain on our wastewater treatment facility. What aspects should we pay attention to? 1. I don’t have any practical experience in this area. In terms of controlling shocks, I think it is necessary to focus on adjusting the key elements of the biochemical system – namely the concentration and activity of microorganisms – in order to enhance their resilience to shocks. 2. At the same time, the processing time (residence time) can also be extended to ensure that the processing meets the required standards. 3. It is advisable to provide a storage area for the sludge-free effluent to ensure uniformity when it enters the system. Avoid the impact caused by concentrated entry. 118. The “three types of sludge” generated by my plant have a high oil content, and we are unable to separate them effectively during centrifugation. Could you please give me some advice? 1. Equipment improvements and adjustments to the characteristics of the sludge fed into the system – these are things you can consider on your own. 2. The proper selection of sludge flocculation chemicals and the control of their concentration require multiple experiments to determine; Nantian Flocculant from Jiangsu could be tried. 119. What is the most cost-effective method for treating wastewater with high concentration but low flow rate? Q=200M3/d, COD=5000, BOD=3000; it’s landfill leachate! I want to use the UASB-SBR process for treatment, but I’m not very clear about the calculations for those two processes! Is an oxidation ditch economical for low-flow applications? 1. I can’t help you with the issue of design parameters. 2. The treatment efficiency using an oxidation ditch for low flow rates may not be guaranteed. 120. I am engaged in promoting the use of artificial wetland technologies for wastewater treatment; hydrolysis-acidification and biological contact aeration processes are commonly used for pre-treatment, but the biofilm formation is not effective. I would appreciate your advice. I have not studied your specific research topic. I’ll just share my simple opinion. The formation of biofilms is essentially the same as that in the conventional activated sludge process for culturing microorganisms. Forming biofilms does not require stringent conditions, but to create ideal, intact biofilms, it is still necessary to focus on improving dissolved oxygen levels, the food-to-microorganism ratio, and the composition of the wastewater. It seems quite important to make multiple adjustments to the process in order to find parameters suitable for one’s own process. This post was last edited by johncom on 2009-2-20 15:10]
121. When treating nitric acid wastewater, the final step is the aerobic activated sludge process. The COD level of the incoming water is around 500, but it drops to 200–300 in the treated water; the color of the water is dark red, the DO level is kept around 3, numerous bubbles are formed due to aeration, and green algae appear in the water. I would appreciate some advice from those with more experience on how to improve the quality of the treated water. 1. First of all, I’m not quite sure what nitric acid wastewater is. 2. In the case of the aerobic activated sludge process, the formation of foam and the effluent parameters seem to indicate that your load is relatively high; please increase the concentration of activated sludge and ensure that nutrients are added in the correct amounts. 3. The presence of green algae here doesn’t mean anything. 4. Observations under a microscope can help us better understand the situation of microorganisms, thereby identifying the reasons for the deterioration in treatment effectiveness. 122. In filtration and backwashing experiments, what does the variation in head pressure at different depths within the filter layer indicate? What is its significance? 1. Changes do indeed exist. 2. It indicates the resistance of the filter media. 123. Our plant’s wastewater treatment process employs the Sequential Batch Reactor activated sludge method, namely SBR; the aeration is provided by micro-pore aerators through forced air supply. The designed treatment capacity is 3000 m3/d. Two aeration tanks, 1800 m3 each. It was originally designed to treat wastewater from beer production, but the adoption of clean production methods and separate treatment for clean and polluted water during production has resulted in changes in the quality of the incoming water; the COD load of this water is low, at around 600 mg/l. The pH value can sometimes be above 14. By adding hydrochloric acid for neutralization, the effluent remains relatively stable as well. However, a strange phenomenon has occurred recently: the color of the treated water has become significantly darker, turning dark brown. Even after the raw water in the SBR tank is drained and aeration is applied to the incoming water, the color still changes. The sludge settling ratio also remains within the range of 30–60%. The COD level of the effluent is acceptable, being around 100 mg/l; the pH value is around 7, and the supernatant in the measuring cylinder is light brown in color. We are currently in the peak production period at our company, and such handling results are causing us great concern. I wonder if sludge bulking or algae in the water is causing the discoloration? Is it related to the aeration volume? Furthermore, when the temperature exceeds 35 degrees Celsius, the water level in the SBR tank cannot reach the designed level; otherwise, the fan cannot operate properly. What is the reason for this? 1. The sludge discharge volume has been increased; meanwhile, I am also taking other measures. 2. By using less water input and less water removal, the treatment cycle is shortened – the original aeration time of 2.5 hours has been reduced to 2 hours. Reducing aeration helps to lower the degree of self-oxidation among the microorganisms. 3. Add waste beer yeast 4. It can shorten the treatment cycle. 5. There is no need to reduce the water inflow. Yeast substrates can be added. 6. All measures are taken to reduce the degree of sludge aging. 124. For some time now, the B/C value of our influent water has been between 0.3 and 0.4; the SS level in the influent is around 500 (as it is urban wastewater), the COD level is about 180, and the BOD level is around 70. The performance was good some time ago, but it has now deteriorated. Microscopic examination shows that the sludge particles are small; after sedimentation, small particles remain, and there are few microorganisms of various types. Rotifers make up a large proportion, while the number of ciliates has decreased rapidly. The DO level was high some time ago; we use the CAST process. I suspect that insufficient nutrients are causing the sludge to age, but I don’t want to add nutrients. Is there any way to get through the rainy season and resolve this issue? Also, it seems that too high an SS level poses limitations for the SBR process; what is the specific reason? 1. If both the B/C values are between 0.3 and 0.4, there should be no problem, but please verify that the calculations are correct; otherwise, it will be impossible to guide production. 2. High dissolved oxygen levels are unfavorable for sludge flocculation, as small bacterial aggregates can lead to the formation of rotifers. 3. If there are many inorganic particles in the incoming water, it will naturally affect the treatment capacity of microorganisms. 125. Our plant is an urban sewage treatment plant that uses the Oberl oxidation ditch, with an anaerobic selection tank in the upstream section. The main problems currently existing are sludge floating in the secondary sedimentation tank and a low ammonia nitrogen removal rate, along with an abundance of viscous bubbles in the oxidation ditch. Our operating parameters: COD at the inlet of the oxidation ditch = 300, BOD = 90, NH3-N = 28, MLSS = 2600, DO = 1.0~2.2 (at the outlet of the oxidation ditch); NH3-N = 18 (the target value in our plant is 10). Question: How to adjust the process parameters? At the same time, we are arranging for a comprehensive measurement of process operation data. 1. Main manifestations: sticky bubbles. I think this situation can occur at two extremes, namely excessive and insufficient load. It is quite common for sludge to age, resulting in the formation of floating sludge as well as sticky foam and scum on the surface of the liquid. 2. Sludge aging indicates a low load; I think insufficient substrate concentration is the reason, which results in suboptimal nitrogen removal performance. 3. Please also reduce the sludge concentration and observe for a period of time to see if it is effective. 126. The process is a delayed aeration oxidation ditch, using inverted umbrella-type aerators. The capacity is 100,000 tons per day; currently, the inflow is around 50,000 to 60,000 tons. Currently, an oxidation ditch is in use, with a capacity of 33,000 cubic meters, along with two sedimentation tanks, each with a capacity of around 7,000 cubic meters. The influent BOD is 50 to 80, and COD is 80 to 150; the effluent undergoes secondary treatment. The dissolved oxygen in the ditch is 4 to 5. The MLSS is below 700, and the SV30 is very low; however, the water quality meets the standards (with SS being slightly high, at around 40). How should this be dealt with? Is it necessary to take measures to increase MLSS? If so, how? 1. I’d like to keep things as they are; otherwise, it will increase operating costs. 2. Once the concentration of the incoming water increases, the sludge concentration can be increased gradually. 127. I’m about to start the MBR tests; as per the design, an A/O system is placed before the MBR (it should be noted that since this equipment is intended for pilot-scale use with a treatment capacity of 0.5 tons per hour, the A/O system involved is only a small one). Before starting the tests, can the microbial film be established by directly transferring sludge from the wastewater treatment tank and then carrying out an aeration process? Is this method effective and feasible? The microbes seem to be common; I think it should work fine if operated properly. 128. There is no microbial culture method for printing and dyeing wastewater – what should be done? It’s better to carry out inoculation and cultivation in the vicinity! 129. Sludge acclimatization has been going on for a month now; recently, nematodes were detected under microscopic examination in the aerobic tank, and the water quality has deteriorated. I believe this is due to the aging of the sludge, so I applied sludge removal as a solution. Are there any other methods available? A small amount is part of the normal biological phase; aging can be determined based on factors such as the sludge color, sludge age, and load conditions! 130. I would like to ask: I use sand filtration (with ordinary quartz sand) to remove turbidity and color from water. By selecting the appropriate particle size and determining the filtration rate, the turbidity is removed effectively, but the color is not removed as well. Is there any way to address this issue? I think the main purpose of sand filtration is to remove turbidity; as for color, it can only eliminate certain types of false colors, while it’s unable to remove true colors. In such cases, it’s possible to enhance the oxidation capacity in the earlier stages of the treatment process. 131. We know that the BOD load rate is directly related to sludge bulking; in other words, there is a relationship curve between the BOD load rate and the SVI value. What I would like to ask is whether there is also a relationship curve between the COD load rate and the SVI value, or whether it makes sense to use the COD load rate to describe the SVI value! 1. I think it is relevant, but I don’t use the SVI value very often. Usually, the variation in MLSS isn’t significant; therefore, I usually rely on SV30 for assessment. When observing the degree of expansion, it’s also possible to check issues such as the settling effect and whether there are bubbles present in the activated sludge. 2. Generally, there is a linear relationship between the two, but this is not absolute, as there are many factors that affect expansion, and expansion also experiences peaks and troughs. It’s fine to use it as a reference, but there’s no need to rely on it entirely. 132. What are the characteristics of a stable operating processing process, according to you? For example, sludge, the biological community... I’ll still use the traditional activated sludge process as an example! 1. The removal rate can be used as a reference for the treatment effect. 2. Microbial examination parameters such as microbial sedimentation capacity are also applicable. 3. The fresh color and fishy odor of the activated sludge, etc. 4. The dominant position of attached protozoa in the biotic phase, etc. 133. Activated sludge process: inlet COD 150, outlet COD 301. The measured SV30 value is 80%2. A layer of earthy-yellow sludge floated on the surface of the secondary sedimentation tank.3 Microscopic examination (at 500x magnification) revealed small rotifers, but in small numbers ； No rotifers, nematodes, etc. were found. 4. There are filaments on the myxocyst. Question: Are these filaments filamentous fungi? Is there sludge bulking? How to solve it? Can filamentous fungus expansion be determined by the number of mycorrhizal filaments on a colony of gelatinous mass? Judging from the photos you provided, it is filamentous fungal swelling. Reduce aeration to lower the MLSS value. 134. In the third edition of \"Drainage Engineering\", within the chapter on activated sludge processes, there is a curve showing the relationship between the BOD load rate and the SVI value for urban sewage activated sludge systems. As can be seen from this curve, there is a high-load area and a low-load area for sludge load; in both areas, the SVI value is below 150, so sludge bulking does not occur. However, between these two areas, the SVI value is very high, indicating an area where sludge bulking takes place. What I’m thinking is, when treating chemical industrial wastewater using the activated sludge method, what about using the COD load rate (given the limitations in conducting BOD tests, it’s difficult to measure them, so the COD load rate is used instead; I’m not sure if this is feasible?) ) whether it is related to the SVI value, and whether there are also high-load and low-load zones, sludge bulking zones, and so on. 1. I have not read the third edition of \"Drainage Engineering\". I think that simply drawing a relationship curve between the BOD load rate and SVI value makes it difficult to address the problem of filamentous bacterial overgrowth in actual production. Because there are many reasons that cause filamentous fungi to swell; some of these can be adjusted, but others are difficult to adjust in production. 2. It is relatively easy to understand theoretically why low loads cause filamentous fungi to expand, but I’m not quite sure why high loads do the same. 3. Regarding mycelial swelling, I personally believe that there is a process leading to the onset of this condition. Sometimes, the operating environment can easily cause mycelial swelling, but in reality no swelling occurs. On the contrary, since such episodes have happened before, even slight changes in operations or water levels can lead to swelling, either regularly or irregularly. It’s mainly a matter of getting sick. Normal bacterial aggregates and filaments have similar biochemical and physical properties, making them very difficult to treat naturally. 4. If analysis is required, it’s of course no problem to use the COD load rate instead. It’s possible to conduct some research, but guiding production practices can probably only serve as a reference! 135. The contact oxidation tank is covered in moss; how to get rid of it? (I) 1. Reduce the N and P levels in the raw water ； 2. Light blocking ； 3. Chlorination, continuous or intermittent. (II) Do you think these mosses will affect the water quality of the effluent? I think it only grows on the upper layer of the filler, so its proportion isn’t very large. As for whether it affects water quality, you might want to compare the data Abundant sunlight and high levels of nitrogen and phosphorus in the water are the main reasons. If possible, there’s no need to worry too much! 136. Recently, sludge has been floating in the aerobic tank, which results in inaccurate measurements of COD for both the inlet and outlet water. (My experiment is on a small scale, so it’s not possible to use a sludge scraper.) I wonder if this is related to sludge bulking. What should I do? (1) Filter with a 0.45 μm membrane to measure SCOD (soluble COD). (2) Filamentous bacteria are an important cause of the floating of activated sludge. The huge expanded surface area of filaments makes it easy to trap small bubbles, causing the activated sludge to float to the surface. 137. I worked on a project that used fully mixed activated sludge to treat wastewater from fish processing; the initial operation results were good, with the COD level dropping from 1200 to around 35. However, recently many swimming organisms have appeared in the sedimentation tank, seemingly water fleas. Could this be a problem? What is the cause? How to solve it? Congratulations! The performance is so good. The presence of water fleas indicates good water quality; there’s no need to worry about them! 138. Can pectin wastewater be treated using the conventional activated sludge process? 1. Determine it based on the biodegradability of the raw water! 2. Not less than 0.25 – basically no problem at all! 139. I think in wastewater treatment, the number or variety of microorganisms decreases due to water temperature issues, or in other words, the sludge concentration doesn’t increase. If that’s the case, it’s possible to increase the amount of hydrocarbon-containing substances in the water, as well as raise the aeration level—but not to an excessive extent. This can help raise the water temperature or prevent it from dropping. Additionally, the duration of cultivation should be increased. Will this cause sludge to float? 1 The view is correct, but it may be difficult to apply in practice! 2. When carrying out wastewater treatment operations, we strive to follow the correct procedures, and that is also the purpose of this facility – to analyze problems based on the issues raised and the current situation, in order to correct the methods of operation! The proposed improvement solutions are designed to be simple and easy to implement, with efforts made to avoid suggesting methods that require additional equipment or changes to existing processes! It mainly depends on the pH level of the water entering the system. If the alkalinity isn’t too high, then you can add some laundry detergent to address this issue. There is one condition though: since laundry detergent is alkaline, it should be added in a way that does not affect the activity of microorganisms. Of course, if the pretreatment stage of the wastewater treatment process you use includes a skimming and grit removal tank, that would be better, as it can remove some of the oils and fats that surround the sand particles. This post was last edited by johncom on 2009-2-20 15:12]
140. Treatment of leather wastewater: the average parameters are as follows: 1. Food-to-microorganism ratio of 0.05 kgBOD/kgMLSS.d ； 2. Nitrogen concentration in the effluent: 100 mg/l ； 3. Aeration method: Puncture tube aeration ； 4. The dissolved oxygen distribution is uniform throughout the biochemical tank. Long-term operation at low load levels may be the cause of filamentous microbial growth in your biochemical system. The food-to-micro ratio can be increased to above 0.2. At the same time, test the total phosphorus content in the effluent; if it is low, it is not conducive to the growth of normal flocculent bacteria. 141. Our factory is facing some issues with its operation, and we would like to seek your advice! We hope you can give us some guidance if you have time. Our factory uses the SAST process, and after more than a year of operation, the nitrogen removal efficiency has not been very good; we haven’t been able to find any ways to improve it. Below are the inlet and outlet water parameters of our factory as of March 20, 2004: Inlet Outlet COD 951 mg/L 58.2 mg/L BOD5 480 mg/L 16 mg/L TP 6.07 mg/L 0.4 mg/L TN 34.71 mg/L 24.99 mg/L SS 798 mg/L 33 mg/L NH3-N 22.05 mg/L 19.86 mg/L. Given that the ammonia nitrogen concentration in your wastewater is not high and there is an adequate supply of substrates, we suggest extending the sedimentation time (i.e., the anaerobic period), which will help facilitate thorough denitrification for nitrogen removal. During precipitation, avoid operations that could affect the anaerobic condition, such as water ingress and aeration. 142. The key issue isn’t denitrification itself, but rather the fact that the nitrification of ammonia nitrogen in the first stage of denitrification is extremely unsatisfactory; efforts should be focused on the aerobic phase, right? Your view is correct. As the two aspects of nitrogen removal, nitrification and denitrification are closely linked; poor performance in one aspect will affect the other. 2. Inadequate denitrification leads to the accumulation of nitrite, which inhibits the progress of the nitrification process. 3. Given the fairly good results you achieved in previous runs, please also check whether there have been any changes in the process and operations that need to be taken into consideration. And find the reason. At the same time, laboratory data is usually quite important to consider. 143. The high COD and BOD levels in our plant are due to the filtrate from the excess sludge being directly discharged into the feed water pump room; it is not because of an adequate supply of substrates. (Before the dehydrating plant was started, COD was 300 mg/L and BOD was 120 mg/L). Also, our denitrification takes place in a selection tank. Although denitrification occurred during the final 1 hour of sedimentation in the biological tank, I think it was only a small portion. Regarding the low ammonia nitrogen removal efficiency in our plant, I wonder if there might be a problem with the recirculation tank; our return sludge pump is turned on only during the aeration phase, and the return sludge contains high levels of DO, which directly affects the efficiency of denitrifying bacteria in removing nitrogen. I want to measure the dissolved oxygen level in the selection pool to see if it’s below 0.5 mg/L, before making a decision. Additionally, I would like to ask about what you mentioned in your reply: that extending the settling time can facilitate thorough denitrification. But our biological tank doesn’t have a stirrer; without complete mixing, how can denitrification take place properly? As you said, that’s indeed the case; I agree with your view. 1. The denitrification dissolved oxygen in the selection pool must be controlled. 2. The backflow volume does not need to be too large; the time control for each stage is relatively flexible. One should not be too rigidly adhered to the theoretical timing requirements – it’s important to draw one’s own conclusions through experience. 3. It’s indeed not good to have no mixing; if possible, it’s better to address the ammonia nitrogen removal issue by adjusting the process. After all, installing mixing equipment requires investment. 4. Please also focus on controlling the dissolved oxygen and hydraulic retention time in the selection pool; such control is closely related to sludge return, and it is necessary to determine the return flow rate appropriately. 144. I have read some information stating that the food-to-microorganism ratio in the activated sludge process ranges from 0.1 to 0.6. However, processes such as CAST, A/A/O, and BACT seem to be used quite often for treating municipal wastewater at low load levels. What are the differences between these operating modes and those at normal load levels? Our water treatment plant uses the Pauleck process, which is characterized by suspended aeration chains and a low F/M ratio; the required value for this parameter is between 0.05 and 0.08. The advantage of this process is its strong resistance to changes in load levels, as well as reduced amounts of excess sludge. Compared to high-F/M systems, the volume of the aeration tank is larger; if you’re interested, you can do the calculations – the formula can be found in Gao Tingyao’s book on water pollution engineering, so I won’t go into details here. 1. Operation at low load levels results in low efficiency. 2. It is indeed possible to reduce sludge production. 3. It has strong impact resistance, but I don’t think that’s the case; compared to operation under heavy load, its impact resistance is weaker. 4. The main criterion is to determine the appropriate size based on the quality of the water to be treated. 145. How to reduce ammonia nitrogen in the effluent? Our factory has a small domestic wastewater treatment plant that uses the A/O contact oxidation process. The sludge in the tanks was re-cultivated about a month ago, and as a result, the COD level in the treated water is quite low, around 50. However, there is currently a problem: the ammonia nitrogen level is always above the acceptable limit. I maintain a DO level of 0.3–0.7 in tank A and 2.6–4 in tank O. Since the COD concentration of the incoming water is relatively low, at only a little over 100, I add glucose to the adjustment tank six times a day to keep the COD level in the incoming water around 300. The NH3-N level in the influent water is at most a little over 20; sometimes it’s around 10. The ammonia nitrogen level in the effluent water is always higher than that in the influent water. Based on the curves generated from my daily measurements, the ammonia nitrogen level in the effluent water is generally above that in the influent water, so it ranges between 15 and 25. Our entire process consists of screening, adjustment, anoxic treatment, aerobic treatment (with partial recirculation to the anoxic stage), sedimentation, sand filtration, disinfection, and effluent discharge. The exact location for adding glucose is between the grids, with the aim of ensuring thorough mixing of glucose with the wastewater in the equalization tank to achieve a uniform water quality. Theoretically, the anoxic tank should maintain a certain concentration of organic matter; it cannot be too low. The controlled range of dissolved oxygen in the anoxic tank is set at 0.3~0.7, taking into account that the fan should not be turned on and off frequently. However, in this case, the ammonia nitrogen level in the effluent is always above the limit, yet the treatment efficiency for COD is very good. Judging from the biofilm formation in the aerobic tank on site, the sludge is growing well. If it is said that the water level rises more than the inlet water level, it seems illogical by common sense. I think the reasons are as follows: 1. The influence of the sludge returning to section A. If it is permissible from a production perspective, the sludge returned to section A could be replaced with effluent from the secondary sedimentation tank, which should solve the problem. If the phosphorus requirements in the effluent water are not high, the return of sludge to section A can be stopped, and aeration to the anoxic section can also be ceased to reduce its oxygen content. It is also advisable to return the sludge directly to the aeration section; it is not clear whether this can be achieved in terms of process design. 2. Have you measured the ammonia nitrogen in the water discharged during the hypoxic period? If the results are normal after completion, then consider the issues related to the aeration stage. If it’s not working properly, try the method in 1. 3. You use a membrane method in the aeration section; what about the anoxic section? Is that so? If it’s the method from 1, it should be able to solve it. 4. Finally, it is possible to check whether the sludge index of the sludge in the aeration tank is normal; a value that is too low may be due to the influence of sludge fragments formed as a result of the decomposition of old sludge during testing. I believe that since the ammonia nitrogen level in the incoming water is not high, the problem should be ultimately resolved. 146. The process utilizes a two-stage conventional activated sludge method, with tubular micro-porous aerators. The designed processing capacity is 1500 m3/h. There are 12 primary aeration tanks and 6 secondary ones. The COD load of the influent water is low, around 200 mg/l. (All types of water are introduced for treatment.) During treatment, the DO level is high (around 6–8 mg/l) (oxygen is supplied via blower), and the MLSS level is low. Question: (1) How can the DO level be reduced and the MLSS level increased? To what extent should the air supply volume be controlled, as can be seen from the appearance? Does minor aeration have an impact on the low sludge level in the tank? (2) What are the appropriate control levels for the sludge return flow in the two-stage aeration tanks? (3) How many chambers are appropriate for each of the two-stage aeration tanks? How long after running should the pool be switched? (4) How often should sludge be removed from the tank during operation? When the operation time is long and there is little sludge in the pool, is it better to discharge the sludge continuously or intermittently? To what extent is it appropriate to discharge sludge? (5) In this case, is a BOD:N:P ratio of 100:5:1 good, or is another ratio better? What should that ratio be? 1. Lower the dissolved oxygen level by reducing the aeration volume; this can be achieved by adjusting the valves on the air ducts or by reducing the number of blowers in operation. The control of the air supply volume can be determined based on the measured dissolved oxygen level (1–3 represent the theoretical control values). 2. An increase in MLSS depends on an increase in the substrate concentration in the influent; by reducing dissolved oxygen levels and shortening the retention time, it seems possible to appropriately prevent a decrease in MLSS. 3. Recirculation is necessary, and usually the recirculation rate for the first stage can be greater than that of the second stage. Fluctuations of 50~100% can be checked by oneself; of course, it’s even better to draw conclusions on one’s own during production. 4. Determine the appropriate number of units to operate based on the water inflow rate and substrate concentration; for example, if the food-to-waste ratio is low, fewer units should be used. 5. It is better to discharge sludge continuously; just reduce the size of the outlet valve a bit! 6. Be reasonable – determine the amount of nutrient to add based on whether the nitrogen and phosphorus levels in the effluent exceed the allowed limits! 147. Our factory has a small domestic wastewater treatment plant that uses the A/O contact oxidation process. The sludge in the tanks was re-cultivated about a month ago, and as a result, the COD level in the treated water is quite low, around 50. However, there is currently an issue: the ammonia nitrogen level is always above the allowed limit. I keep the DO level at 0.3–0.7 in tank A and at 2.6–4 in tank O. Since the COD concentration of the incoming water is relatively low, at only a little over 100, I add glucose to the adjustment tank six times a day to keep the COD level in the incoming water around 300. The NH3-N level in the influent water is at most a little over 20; sometimes it’s around 10. The ammonia nitrogen level in the effluent water is always higher than that in the influent water. Based on the curves generated from my daily measurements, the ammonia nitrogen level in the effluent water is generally above that in the influent water, so it ranges between 15 and 25. What is the problem, and how can it be solved? 1. Please also verify the experimental data. 2. Consider the introduction of dissolved oxygen during the return flow in the aerobic tank. I think a DO level of 1.5 in the aerobic tank is sufficient. 3. Pool A should be kept in an anaerobic state as much as possible. 4. Observe the anaerobic conditions in Tank A closely to confirm whether gas is being released from the surface. 5. In terms of process control, the residence time in Tank A should not be too short, otherwise denitrification will not occur sufficiently. This post was last edited by johncom on 2009-2-20 15:13]
Chaos – that’s the only word for it. I’ll say it again, haha