Analysis and solution of abnormal conditions in aerobic wastewater treatment tanks

The function of aerobic tanks in wastewater treatment is to allow activated sludge to undergo aerobic respiration, further decomposing organic matter into inorganic substances and removing pollutants. Running an aerobic tank requires optimal control of oxygen content and other necessary conditions for microorganisms, in order to enable them to carry out aerobic respiration with maximum efficiency.
Today, let's take a look at the abnormal situation analysis and solutions of aerobic tanks in sewage treatment.
1. What abnormal phenomena may occur in aerobic tanks?
① Aerobic sludge turns black or white (low or high dissolved oxygen)
② The clear liquid on the aerobic tank is turbid (sludge adsorption performance deteriorates or high dissolved oxygen leads to sludge disintegration, and low dissolved oxygen prevents organic matter from being oxidized)
③ The sludge foam returning from the secondary sedimentation tank becomes viscous (the sludge stays in the secondary sedimentation tank for too long, resulting in decreased activity after denitrification)
④ Increased foam in aerobic tanks (judged by the color and viscosity of the foam, whether it is caused by changes in the sludge itself or by substances added during production)
⑤ The removal rate of the aerobic tank has decreased (specific analysis reasons: sludge activity, sludge load, dissolved oxygen, sludge concentration, water temperature, etc.)
⑥ Aerobic tank sludge expansion (controlled by increasing sludge discharge and adjusting nutrient feed to stabilize inflow, ensure sufficient dissolved oxygen and suitable water temperature)
⑦ When using aerobic sludge for sedimentation ratio, the supernatant is turbid and has more fine and fragmented sludge (sludge load is too high or sludge disintegration occurs, sludge structure is loose during microscopic inspection, and bacterial clumps are thin and small)
⑧ Fewer aerobic microorganisms, looser structures, and smaller bacterial clusters (low or high load, insufficient dissolved oxygen, sludge bulking, and insufficient nutrients)
⑨ The dissolved oxygen in the aerobic tank is high for a long time, while the effluent is turbid and has high COD (the sludge load is low for a long time, and the sludge disintegrates and bacterial flocs are oxidized, without consuming oxygen)
⑩ Sludge aging (The reasons for sludge aging include long sludge age, low load, etc. The aging of sludge leads to poor effluent, more fine sludge and rotifers, and an increase in oxygen consumption)
2. Why does the phenomenon of clear supernatant with high COD occur when aerobic sludge expands?
① Filamentous bacteria have a strong adsorption effect, and a large number of filamentous bacteria have a net trapping effect, so the supernatant is clear
② A large number of filamentous bacteria extend out of the bacterial gel, blocking the bacterial gel from obtaining sufficient oxygen and failing to oxidize and convert organic matter into inorganic matter
③ Bacterial gel clusters do not receive sufficient oxygen, resulting in reduced reproductive activity and a decrease in their thinness and activity
3. What are the reasons for insufficient dissolved oxygen in aerobic tanks?
① Rapid increase in sludge concentration in aerobic tanks or increase in oxygen consumption due to sludge aging
② There is a lot of suspended solids in the effluent of the anaerobic tank, and a large amount of dissolved oxygen is consumed after entering the aerobic tank
③ The blower malfunctions and stops running or the fan pressure is insufficient (this situation is rare)
④ The sudden increase in COD in the effluent of the anaerobic tank or the sudden increase in influent result in a high impact load, leading to an increase in the load of the aerobic tank
⑤ The aeration head is severely damaged or blocked, and there is a lot of foam in the aerobic tank
4. What are the reasons for sludge expansion in aerobic tanks?
① Long term low or high dissolved oxygen in aerobic tanks (possible)
② Excessive sulfide content in raw water or anaerobic effluent leads to the proliferation of sulfur bacteria
③ The aerobic tank load is consistently low or high
④ The water temperature in the aerobic pool is too high
⑤ Imbalance or lack of nutrients (low N, P)
⑥ PH value issue of incoming water
⑦ The sludge age in the aerobic tank is too long, leading to an increase in oxygen consumption and insufficient dissolved oxygen
5. What are the reasons for the phenomenon of sludge disintegration and excessive crushing of supernatant in aerobic tanks?
① The aerobic tank has a low sludge load, excessive aeration, self oxidation of sludge, deterioration of sludge flocculation, and loose sludge structure (clear, with more fine sludge and low COD)
② The aerobic tank sludge load is too high, the sludge adsorption performance deteriorates, organic matter is not completely decomposed, and the sludge structure is loose (turbid, opaque, high COD) during microscopic inspection
③ Excessive sludge discharge from aerobic tanks leads to short sludge age (SVI value is suitable between 70-120, within which the secondary sedimentation tank has less finely crushed sludge)
④ The influent of the aerobic tank contains toxic substances or aged sludge, with a long sludge age (turbid, fine sludge, high COD, and many rotifers detected by microscopy)
⑤ Insufficient or uneven proportion of nutrients in aerobic tanks (low N and P)
6. Why is there a large amount of foam in aerobic tanks?
① The raw water contains a large amount of surfactant components (caused by substances added during the production process, with white foam, small bubbles, light and non sticky)
② Small bubbles generated after the installation of the new aeration head (short-term impact)
③ A large amount of lipid substances or microorganisms are produced during microbial reproduction (caused by the growth and reproduction activities of microorganisms themselves, with mud colored foam, large bubbles, and sticky properties)
④ Sludge denitrification foam (the foam produced by aerobic sludge after prolonged residence in the secondary sedimentation tank and denitrification is sticky and mud colored)
7. What are the reasons for the low COD removal rate in aerobic tanks?
① Aerobic tank sludge aging, with long sludge age
② The aerobic tank has high sludge load, short sludge age, high reflux rate, and short retention time
③ The aerobic tank has a low sludge load and a long-term high dissolved oxygen, which leads to self oxidation of the sludge (low removal rate, high dissolved oxygen). There are more finely crushed sludge and less active sludge
④ Insufficient dissolved oxygen in aerobic tank
⑤ Insufficient or unbalanced proportion of nutrients (N, P ratio too high)
⑥ The COD removal rate of anaerobic tank is low, the anaerobic hydrolysis effect is poor, and the COD concentration in the effluent is too high
⑦ Raw water contains toxic substances, sludge poisoning
⑧ The cumulative value of inorganic salts exceeds the specified range
⑨ High impact load of aerobic tank or sludge expansion phenomenon in aerobic tank
8. What are the reasons why the clear liquid of the aerobic tank contains a lot of finely crushed sludge, which is difficult to settle due to rolling?
① Insufficient or uneven proportion of nutrients in aerobic sludge
② The sludge load in the aerobic tank is too high (the effluent of the secondary sedimentation tank is turbid, with high COD. After the sedimentation of the sludge water in the aerobic tank, the supernatant is fine and the sludge is crushed, resulting in turbidity)
③ The sludge load in the aerobic tank is too low, the aeration is excessive, and the fine sludge produced by the self oxidation of the sludge (the COD removal rate in the aerobic tank is low, and the effluent COD is high)
④ The sludge load in the aerobic tank is too low, the sludge retention time is long, and excessive aeration leads to poor sludge flocculation (loose sludge structure but high or not low COD removal rate)
9. How to solve the problem of sludge expansion in aerobic tanks?
① Firstly, increase the sludge discharge to solve the problem of poor sedimentation effect, and then improve it before increasing the sludge concentration and reducing the sludge load
② Increase the discharge of sludge from aerobic tanks and reduce sludge age (in severe cases, it should be persisted for about two months)
③ Control the water temperature within an appropriate range, stabilize the inflow, and maintain sufficient dissolved oxygen in the aerobic tank (mandatory)
④ Increase the feeding of nutrients in the aerobic tank
⑤ If the mud layer in the secondary sedimentation tank is high, the reflux rate can be increased, the inflow of each secondary sedimentation tank can be adjusted, or polyaluminum and polypropylene can be added (temporary control measures)