Three Questions and Answers on Activated Sludge Process Operation Failures

Activated sludge is a wastewater biological treatment technology, and it is the main method of wastewater biological treatment using activated sludge as the main body. This technology mixes and aerates wastewater with activated sludge (microorganisms), decomposing organic pollutants in the wastewater. The biological solids are then separated from the treated wastewater and can be partially returned to the aeration tank as needed.

A sludge-like flocculent formed after a certain period of time due to the reproduction of aerobic microorganisms. Microorganism groups, mainly microbial flocs, inhabit it, possessing strong adsorption and oxidation capabilities for organic matter.

Activated sludge is a method of wastewater biological treatment. This method involves continuous mixed cultivation of wastewater and various microbial populations under artificial oxygenation conditions to form activated sludge. The bio-coagulation, adsorption, and oxidation of activated sludge are utilized to decompose and remove organic pollutants from wastewater. Then, the sludge is separated from the water, most of the sludge is returned to the aeration tank, and the excess is discharged from the activated sludge system.

The main factors affecting the working efficiency (treatment efficiency and economic benefits) of the activated sludge process are the choice of treatment method and the design and operation of the aeration tank and sedimentation tank.

I. There is little sludge in the oxidation ditch, and it is difficult to cultivate microorganisms due to the cold weather. What should I do?

Answer:

1. If it is during the initial cultivation of the system, a small amount of sludge is normal. As the cultivation progresses, the amount of sludge will increase. Excessive aeration during cultivation is very unfavorable to sludge cultivation.

2. Of course, the amount of microorganisms is related to the hydrocarbon content in your source water. If there is insufficient hydrocarbon, the number of microorganisms will naturally not increase. Please check.

3. If your system has been started for a long time and you want to increase the number of microorganisms, I don't think it is necessary. Reaching equilibrium is enough; what matters is the treated effluent.

4. Deliberately increasing the number of microorganisms will cause sludge aging, which is detrimental to the effluent water quality.

5. Regarding temperature, I think if the effluent water temperature is not lower than 10 degrees, there is no major problem with microbial activity.

6. Based on the size of the F/M value, you can tell whether the number of your microorganisms is too low. If this value is not greater than 0.25, it means that the number of your microorganisms is not too low.

II. During the treatment of chemical wastewater, there are problems with the sludge cultivation in the hydrolysis acidification tank and the contact oxidation tank. No activated sludge has been attached to the filler in the hydrolysis acidification tank, affecting the treatment effect. The influent concentration COD was around 1200 mg/l for about a month. During this period, I reduced the influent concentration to around 400 mg/l COD, and found that the sludge on the filler in the contact oxidation tank showed signs of reduction. How can I cultivate the sludge in the hydrolysis acidification tank and the contact oxidation tank as soon as possible, and what are the ideal influent and effluent indicators?

Answer:

1. The hydrolysis acidification stage can convert macromolecular substances into small molecular substances, which facilitates the degradation of organic matter by the subsequent biological process. In other words, pollutants in the hydrolysis stage are not easily degraded by microorganisms.

2. In view of this, adding fillers to the hydrolysis acidification tank and growing a biofilm requires sufficient organic matter content in the source water and hydraulic retention time.

3. With a source water COD of 1200 ppm, I think that if the retention time is insufficient, a biofilm will naturally not be produced. Not to mention 400 ppm. Therefore, the biomass in the contact oxidation tank will also decrease.

4. Biomass and influent organic matter are balanced. I think your influent concentration is not enough to produce a biofilm. But the effluent water quality should still be acceptable!

III. What are the reasons for sludge bulking sometimes occurring in the secondary sedimentation tank?

Answer:

1. When the biological system treatment load (water volume and concentration) increases, sludge bulking can occur. This is often because after the water volume increases, the retention time of the secondary sedimentation tank is shortened, and the activated sludge does not have enough time to settle before flowing out of the secondary sedimentation tank, thus causing sludge bulking. At the same time, an increase in influent concentration will lead to increased activated sludge activity, which is unfavorable for sedimentation. The effluent is turbid and contains sludge bulking.

2. Operation under excessively low loads, sludge aging, and self-oxidation of microorganisms, and deflocculation can also cause sludge bulking.

3. Filamentous bacteria expansion, and sludge not having enough time to settle can also cause sludge bulking.

4. In addition, low temperatures, excessive aeration, excessive changes in PH, and the entry of toxic and inert substances into the biological system can also cause sludge bulking.

5. To understand these reasons, you must repeatedly experience them in practice to make flexible and accurate judgments. Of course, relevant detection methods are also essential; they are the basis of your judgment.