Collect! Aeration Tank Operation and Maintenance Manual (Part 1)
Written by: Jasmine
Contact email: Kate@aquasust.com
1. Five major items of routine monitoring of aeration tank water intake
1.1 Temperature
1.2 PH value
1.3 COD and BOD5
1.4 Ammonia nitrogen and phosphate
1.5 Toxic substances
2. Routine monitoring project of mixed liquid in aeration tank
2.1 How to control the MLSS or MLVSS value of the aeration tank?
2.2 What is the sludge settling ratio (SV) of the aeration tank mixture? What is the function?
2.3 What abnormal phenomena are prone to occur when measuring the SV value? Why?
2.4 What is Sludge Volume Index (SVI)?
2.5 What is the reason for the increase in the SVI value of the aeration tank mixture?
3. Operation management of aeration tank - foam problem
3.1 Brown-yellow foam
3.2 gray-black foam
3.3 White foam
3.4 Colored foam
4. Operation management of aeration tank - sludge expansion
4.1 The environmental conditions that cause the expansion of filamentous bacteria in activated sludge are:
4.2 Conditions and causes that lead to the expansion of non-filamentous bacteria
4.3 Measures to control sludge bulking in aeration tank
Written by: Jasmine
Contact email: Kate@aquasust.com
1. Five major items of routine monitoring of aeration tank water intake
1.1 Temperature
The optimum temperature range for the normal physiological activities of aerobic activated sludge microorganisms is 15-30 °C. Generally, when the water temperature is lower than 10°C or higher than 35°C, the function of aerobic activated sludge will be adversely affected. It even stops completely when the temperature is above 40°C or below 5°C.
Within a certain range, with the increase of temperature, although it is not conducive to the transfer of oxygen to water, it can speed up the rate of biochemical reactions and the rate of microbial proliferation. However, when the temperature rises suddenly and exceeds a certain limit, irreversible damage will occur. In contrast, the impact of temperature reduction on microorganisms is smaller, and irreversible damage generally does not occur.
If the water temperature decreases slowly, the microorganisms in the activated sludge can gradually adapt to this change. By taking measures such as reducing the load, increasing the dissolved oxygen concentration, and prolonging the aeration time, a better treatment effect can still be achieved.
Therefore, in the actual production operation, it is necessary to pay attention to the sudden change of the water temperature, especially the sudden increase of the water temperature. In order to prevent the industrial wastewater with high water temperature from adversely affecting aerobic biological treatment, cooling treatment should be carried out.
Written by: Jasmine
Contact email: Kate@aquasust.com
1.2 PH value
The optimum PH for activated sludge microorganisms is between 6.5 and 8.5. When the PH value drops below 4.5, all the protozoa in the activated sludge will disappear, and the activities of most microorganisms will be inhibited.
When the PH value is greater than 9, the metabolic rate of microorganisms will be greatly adversely affected, the bacterial micelles will disintegrate, and sludge bulking will also occur. When the PH value of the sewage is higher than 10 or lower than 5, before entering the aeration tank, acid-base neutralization must be carried out to adjust the PH value, so that the PH value of the sewage entering the aeration tank is at least between 6-9.
The activated sludge mixture itself has a certain buffering effect on the change of PH value, because the metabolic activity of aerobic microorganisms can change the PH value of its active environment. For example, the utilization of nitrogen-containing compounds by aerobic microorganisms produces acids due to denitrification, which reduces the PH value of the environment; and alkaline acids are generated due to decarboxylation, which can increase the PH value. Therefore, after a long period of domestication, the activated sludge method can also treat sewage with a certain acidity or alkalinity. In addition, the alkalinity of sewage itself has a certain inhibitory effect on the decrease of PH value.
However, when the PH value of sewage changes suddenly, for example, when alkaline sewage enters an activated sludge system that has been adapted to an acidic environment, it will have an impact on the microorganisms in it, and may even destroy the normal operation of the entire system.
Therefore, whether acid-base sewage is neutralized depends on the actual situation. If the PH value of the sewage entering the activated sludge system does not change much, especially when there is only one of slightly acidic water or slightly alkaline water, it is often not necessary. Neutralization treatment, and when the PH value changes greatly, the neutralization treatment should be carried out in advance to adjust the PH value to neutral.
Written by: Jasmine
Contact email:Kate@aquasust.com
1.3 COD and BOD5
No matter which activated sludge method is adopted, the organic load that the aeration tank can bear has a certain limit. If the limit is exceeded, the operation effect of the aeration tank will be difficult to guarantee. For the running aeration tank, the highest value of BOD5 in the influent is fixed. Due to the long period of BOD5 analysis, the COD analysis results are actually used to guide production.
Once the organic load of the influent water of the aeration tank exceeds the standard, measures such as reducing the influent water, increasing the sludge return flow, and improving the oxygenation efficiency should be taken immediately to avoid impact on the entire secondary biological treatment system and ensure the effluent quality.
If the COD value of the influent water is low, measures should be taken immediately to increase the influent water, reduce the sludge return flow, reduce the number of fans, reduce the speed of the surface aerator, etc., to reduce the oxygenation efficiency, so as to avoid unnecessary power waste.
Written by: Jasmine
Contact email:Kate@aquasust.com
1.4 Ammonia nitrogen and phosphate
Theoretically, the requirements of microorganisms for nitrogen and phosphorus should be calculated according to BOD5:N:P - 100:5:1, but the ratio of BOD5 to nitrogen and phosphorus in the aeration tank of the actual activated sludge treatment system is often Below this value, the system can operate normally.
The content of nitrogen and phosphorus varies greatly depending on the type of industrial wastewater to be treated. Some sewage contains high nitrogen and phosphorus content. Without dephosphorization and nitrogen removal, the nitrogen and phosphorus content of the effluent from the secondary sedimentation tank will exceed the standard. For sewage with very low nitrogen and phosphorus content, if a certain amount of nitrogen and phosphorus cannot be replenished in time, the function of microorganisms will be limited, and the COD and BOD5 of the effluent from the secondary sedimentation tank will not be guaranteed to meet the standards.
When dealing with industrial wastewater with very low nitrogen and phosphorus content, for the running aeration tank, the content of ammonia nitrogen and phosphate in the influent of the aeration tank is about 10mg/L and 5mg/L respectively, which can satisfy the mixed solution Microorganisms need for nitrogen and phosphorus. If the content of ammonia nitrogen and phosphate in the influent of the aeration tank is lower than the above values for a long time, the dosage of nitrogen and phosphorus should be increased in time.
Written by: Jasmine
Contact email: Kate@aquasust.com
1.5 Toxic substances
For a specific industrial wastewater, the types of toxic substances are generally unchanged, but the content and drainage volume are difficult to be constant. In addition to the need to take primary treatment measures such as homogenization adjustment, the content of toxic substances in the influent of the aeration tank must be monitored and controlled.
After the domestication of activated sludge is completed, the maximum limit of toxic substances in the influent water that affects the biochemical system should be determined according to the degree of adaptation of the mixed solution to the toxic substances in the influent water and combined with operating experience.
If the content of toxic substances in the influent of the aeration tank exceeds the limit for a long time, measures such as reducing the influent water, increasing the sludge return flow, and improving the oxygenation efficiency should be taken to avoid affecting the treatment effect due to the microbial poisoning of the mixed solution.
Written by: Jasmine
Contact email:Kate@aquasust.com