Q&A on Abnormalities in Wastewater Treatment Operations

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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 matters is the condition of the treated water. 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 not below 10 degrees, there should be no major issues with microbial activity. 6. Based on the F/M value, it is possible to determine whether your microbial count is too low; if this value is 0.25 or less, it indicates that your microbial count is not too low. I calculated today the sludge age in our plant from last week. 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! 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 truly 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 unfavorable for sludge-water separation 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 degradation 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-type flagellates (such as paramecia and trichomonads). It may be due to a low sludge age. How to reduce the energy consumption of wastewater treatment plants? **The allocated funds are pitiful; I hope you can share your experience in operational management. 　　The largest cost in operating a sewage treatment plant is likely electricity costs; if sludge is sent out for treatment, the associated costs are also high. To address these issues: 1. Reduce the aeration volume to lower electricity expenses. From my experience, maintaining an oxygen concentration of 3 ppm in the aeration tank theoretically is not conducive to energy savings and cost reduction. 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 energy savings. 2. If the system has a regulating tank and intermediate lift 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, keeping the dissolved oxygen at 1.5 ppm – will this affect the reproduction of certain highly efficient microorganisms during winters in the north (in the oxidation ditch process)? 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 inquire about the sludge cultivation issues 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 content 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 quality of the water discharged should be okay, right? ? 5. At this stage, as long as the water can be discharged, what does it matter whether a film forms or not! I have some experience in treating industrial wastewater through hydrolytic acidification and contact oxidation, so I’d like to share some of my thoughts. 1. Since you are dealing with chemical wastewater, you need to consider whether it contains large amounts of substances that are difficult to biodegrade. It naturally takes a long time to develop microorganisms capable of breaking down such organic compounds; however, using sludge from wastewater treatment plants that have been treated with similar waste might speed up the process. 2. Although the COD level of the incoming water is 1200 mg/L, very little of it can be immediately utilized by microorganisms (as chemical wastewater often contains many high-molecular-weight, hard-to-degrade substances). Therefore, as Sanpei said, there’s no need to worry about the concentration of the effluent during the initial stage ； 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, followed by the acclimatization of the sludge. 　　4. I’m not sure if you’ve heard of the co-substrate metabolism method; theoretical research on it has reached a certain level, but I’m not aware of any practical applications of it. 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 feeding of water 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 supply is feasible. With such a low concentration of organic matter in the influent 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? The activated sludge grows rapidly, causing the TP level in the effluent to fluctuate. How can the amount of sludge be controlled? 1. Sludge removal is an important method for removing total phosphorus. 　　2. The sludge grows too rapidly; 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 when operating at lower loads. 5. Regarding the fluctuations in TP levels 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 may want to check these aspects. As long as it’s not a major issue in the design, I think total phosphorus control is manageable. Due to a malfunction, the AAO process experimental unit, which was previously operating normally (with a volume of 4 m3, an inlet COD level of 260, an outlet COD level of 25, MLSS levels of 2000, an HRT of 12 hours, a ratio of 1:3:6, a DO level of 2, and a water temperature of 30°C – values corresponding to normal domestic wastewater conditions), 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 levels? 　　It may take 1 to 2 weeks! If there is no sludge return and all 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. What should be considered when designing 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 considerations should be taken 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 help 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 in a sealed environment for 24 hours, after which normal aeration should be applied (without overdoing it). 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.