Issues related to sludge cultivation during wastewater treatment

Why isn’t anyone answering? I’m really anxious now: L :L :L

This cultivation scheme is not very good; there is enough sludge. During the initial stage of sludge adjustment, the COD level of the incoming water should be kept between 500 and 800, with a relatively high biochemical activity, but the volume of water used should be much lower. Once the microorganisms have adapted and multiplied, the amount of water introduced can be increased gradually until it reaches the designed level. Currently, you are using methanol to adjust the water volume, which is a bit limited, and using river water is not ideal either; it’s best to use raw water.

Here is some information for your reference: Methods for cultivating activated sludge. The activated sludge process is the primary method of biological wastewater treatment that relies on activated sludge. The activated sludge process involves the continuous introduction of air into wastewater; after a certain period of time, sludge-like flocs are formed due to the growth of aerobic microorganisms. It is inhabited by a microbial community primarily composed of gelatinous masses, which possess a strong ability to adsorb and oxidize organic substances. From a microbial perspective, the sludge in the biochemical tank is a biological community composed of various bioactive microorganisms. If the sludge particles are observed under a microscope, it is possible to see various microorganisms inside—bacteria, molds, protozoa, and metazoans (such as rotifers, insect larvae, and worms). These organisms form a food chain; bacteria and molds can break down complex organic compounds to obtain the energy necessary for their activities and to build themselves. Protozoa feed on bacteria and molds, and they in turn are consumed by metazoans, which can also live off bacteria directly. These microbial-rich, floc-like sediment particles with the ability to degrade organic matter are known as activated sludge. In addition to being composed of microorganisms, activated sludge also contains some inorganic substances and organic matter that is adsorbed on the activated sludge and cannot be biodegraded any further (i.e., metabolic residues of microorganisms). The moisture content of activated sludge is generally 98-99%. Activated sludge, resembling flocs, has a large surface area, which gives it strong adsorption capacity and the ability to oxidize and decompose organic matter. 1. Natural fermentation: Natural fermentation is also known as the direct fermentation method. It is a cultivation process that makes use of the small amount of microorganisms already present in wastewater to allow them to multiply gradually. For urban sewage and some industrial wastewater with a relatively complete range of nutrients and low toxicity, such as that from food factories and meat processing plants, this cultivation method can be considered; however, the cultivation time is relatively long. Natural fermentation can be further divided into batch fermentation and continuous fermentation. (1) Batch fermentation. Fill the aeration tank with wastewater and carry out anoxic aeration (that is, only aeration without adding wastewater). After a few days, stop aeration, let the mixture settle for 1 hour, then remove about 1/5 of the upper layer of wastewater from the tank and add an equal amount of fresh sewage. These processes of aeration, settling, and water addition are repeated in this manner, with the amount of water added each time being greater than before, and the aeration time being shorter than before. During spring and autumn, sludge can be initially cultivated in about two to three weeks. When the sludge concentration in the aeration tank mixture reaches around 1 gram per liter, continuous water feeding and aeration can proceed. Since the sludge concentration is low in the early stages of cultivation, less sludge accumulates in the sedimentation tank, and thus the amount of recycled sludge is also lower. As the amount of sludge increases over time, the amount of recycled sludge increases accordingly. Once the sludge concentration reaches the level required by the process, normal operation can begin, with control carried out in accordance with the process requirements. Environmental Technology Network! (2) Continuous culture. First, fill the aeration tank with wastewater, then stop feeding water; after allowing it to stagnate for half a day to a day, water can be fed continuously. With continuous aeration and the inflow rate being increased gradually from low to high, and after operating continuously for a period of time (similar to the batch method), activated sludge will appear and gradually increase in quantity. When the sludge volume in the aeration tank reaches the concentration required by the process, it is controlled in accordance with the process requirements. Since the natural microbial cultivation method involves directly culturing activated sludge using wastewater, the cultivation process is also one in which microorganisms gradually adapt to the properties of the wastewater and become acclimated. 2. Inoculation cultivation: The cultivation time for this method is short; it is a commonly used technique for culturing activated sludge and is suitable for most industrial wastewater treatment plants. If there is such mud nearby in urban sewage treatment plants, this method can also be used to shorten the cultivation time. The two commonly used methods for inoculation culture are as follows: (1) Inoculation culture using concentrated sludge. Concentrated sludge from a nearby sewage treatment plant is used as a strain (seed sludge) for cultivation. For the cultivation of activated sludge in systems for treating municipal wastewater and industrially wastewater that is rich in nutrients and low in toxicity, seed sludge can be added directly to the wastewater to be treated and aeration can be carried out; once the sludge turns brownish-yellow, the wastewater can be fed in continuously (the flow rate should be increased gradually). At this point, the sedimentation tank is also put into operation to allow the sludge to circulate within the system. To accelerate the cultivation process, unfermented manure water or other nutrients can be added during cultivation. The culture development process is complete once the activated sludge concentration reaches the required value for the process. Economically speaking, the amount of sludge used should be as low as possible; generally, it is kept such that the sludge concentration in the mixture after dilution is above 0.5 g/L. When culturing toxic industrial wastewater, river water can be introduced into the aeration tank first, or tap water can be used (which needs to be aerated for a while to remove any residual chlorine). Then, seed sludge and untreated manure wastewater are added and aerated until the sludge turns brownish-yellow; at that point, aeration is stopped, the sludge is allowed to settle and some of the supernatant liquid is removed. An additional amount of manure wastewater is then added to continue the aeration process. Once the amount of sludge increases significantly, the flow rate of the wastewater is gradually increased. In the later stages of cultivation, the microorganisms in the sludge have been able to adapt well to the quality of industrial wastewater. (2) Inoculation and culture of dry sludge. ““Dried sludge” generally refers to the sludge cake obtained after dehydration using a dehydrator, with a moisture content of around 70–80%. This law applies to remote areas and situations where the distance for transporting the seed sludge is long. The process of inoculating and culturing dry sludge is basically the same as that of culturing concentrated sludge. For sludge inoculation, use fresh sludge cakes that have just been dewatered; a small amount of water should be added before introducing them into the aeration tank, and they need to be mixed into a slurry. The amount of dry sludge added is generally 2 to 5% of the tank volume. Dry sludge may contain a certain concentration of chemical agents (used for sludge conditioning); if the concentration of these agents is too high or their toxicity is significant, it is not suitable to be used as seed sludge for culturing bacteria. To determine whether sludge can be used for inoculation, a small amount of the sludge can be crushed and placed in a small container such as a beaker or plastic bucket; water is added and aeration is provided. If the color of the sludge changes to yellow after some time, it can then be used for inoculation.

In the early stages of sludge cultivation, I usually use raw water. Based on the conditions of the sludge on site, it is carried out as a percentage of the designed flow rate. I have some materials available; if you need them, you can send me an email. I hope they can be helpful to you

1. Prepare it with raw water; use it even if it’s ineffective, and if necessary, add some glucose； 2. There’s no need to rush with the carbon source; wait until the nitrifying bacteria have been cultivated. Once you measure the nitrate level, you’ll know how much to add. Take your time – there’s no need to hurry:lol

1. The so-called activated sludge cultivation involves providing the microorganisms in the activated sludge with certain conditions for growth and reproduction, namely nutrients, dissolved oxygen, an appropriate temperature, and pH levels. (1) Nutrients: That is, the ratio of carbon, nitrogen, and phosphorus in water should be maintained at 100∶5∶1. (2) Dissolved oxygen: For aerobic microorganisms, an environmental dissolved oxygen level of over 0.3 mg/l is sufficient for normal metabolic activities. However, since the sludge exists in the aeration tank in the form of flocs, for activated sludge flocs with a diameter of 500 µm, when the dissolved oxygen concentration around them is 2 mg/l, the concentration at the center of the flocs drops below 0.1 mg/l, which inhibits the growth of aerobic bacteria. Therefore, the dissolved oxygen concentration in the aeration tank usually needs to be higher than 3–5 mg/l, and it is commonly maintained at 5–10 mg/l. It is generally believed in debugging that it is appropriate to maintain a dissolved oxygen level of 2 mg/l at the outlet of the aeration tank. (3) Temperature: Every type of bacterium has an optimal temperature for growth. As the temperature rises, bacterial growth accelerates, but there is a minimum and maximum range for growth, generally between 10–45ºC, with the suitable range being 15–35ºC; temperature changes within this range have little impact on performance. (4) pH value: Generally, the pH is 6–9. Under special circumstances, the pH of the incoming water can reach up to 9–10.5; if it exceeds these values, acid or base should be added for adjustment. 2. Culture method: (1) Domestic wastewater culture method: During the warm seasons, first fill the aeration tank with domestic wastewater and allow it to sit there with aeration but no addition of wastewater for several dozen hours before starting to introduce water. The inflow rate is gradually increased from low to high; after several days of continuous operation, activated sludge will appear and its amount will increase steadily. To accelerate the cultivation process, some concentrated fecal water or rice-water is added in the early stage of culture to increase the nutrient concentration. It should be noted that during the culture period (especially in the early stages), since sludge has not yet been produced in large quantities and the sludge concentration is low, the aeration volume must be controlled to be **lower than that during normal periods. (2) Dry sludge inoculation cultivation method: It is best to use the dry sludge obtained from a sewage system with similar water quality that is operating normally, after dehydration, as the source of microorganisms for inoculation and cultivation. Generally, an amount of dry sludge equal to 1% of the total volume of the aeration tank is used; it is crushed by adding an appropriate amount of water, and then an appropriate amount of industrial wastewater and concentrated manure water is added. By culturing the bacteria using the above method, sludge can be formed quickly and increased to the desired concentration. (3) Stepwise scale-up cultivation method: Taking advantage of the rapid growth and reproduction of microorganisms, this method follows the stepwise scale-up process used in the fermentation industry, namely strain → seed tank → fermentation tank. If a project is designed with three-stage aeration tanks, it is possible to first cultivate bacteria in one tank; under conditions of low inoculation levels, the bacteria can be cultivated in one aeration tank, and once this is successful, the system can be expanded to include the second and third stages. (4) Direct bacterial cultivation using industrial wastewater: Certain types of industrial wastewater, such as that from canned food production, soy product manufacturing, and meat processing, can be used for direct bacterial cultivation ； Another type of industrial wastewater contains all the necessary nutrients, but in insufficient concentrations; therefore, nutrients need to be added to accelerate the growth process. Commonly added nutritional substances include: starch slurry, kitchen rice water, and noodle broth (carbon source) ； Or urea, thiourea, ammonia water (nitrogen source), etc.; the specific choice should depend on the quality of the water. (5) Culturing bacteria using toxic or hard-to-degrade industrial wastewater: For toxic or hard-to-degrade industrial wastewater, it is necessary to first use domestic sewage to cultivate bacteria, and then gradually introduce the industrial wastewater in a step-by-step acclimatization process. (6) Direct introduction of strain cultivation: Some strains suitable for specific water qualities are difficult to cultivate; in such cases, local research capabilities can be utilized, with specialized industrial microbiology institutes being used to cultivate the strains before inoculation for further growth. For example, specific aerobic bacteria are used for the aerobic digestion of PVA (polyvinyl alcohol). This method requires large investment and a long time frame, and is only used in special cases. 3. Acclimatization: In the later stages of culture, the amount of domestic wastewater and external nutrients is gradually reduced, while the proportion of industrial wastewater increases gradually; eventually, it is entirely replaced by industrial wastewater. This process is known as acclimatization. Theoretically, bacteria require enzymes to break down organic matter, and each enzyme must be present in sufficient quantities. During acclimatization, each time the ratio is changed, it is necessary to maintain that ratio for several days; only after operation stabilizes (that is, when the sludge concentration does not decrease and the treatment efficiency remains normal) can the ratio be changed again, until the acclimatization process is complete.