E-mail: michael@shboqu.com   |   Expert in Water Quality Measurement and Water Treatment Project

Key Points of AAO Process Control in Sewage Plant

by:BOQU     2023-03-24
The AAO method in sewage treatment is suitable for large and medium-sized urban sewage and industrial wastewater treatment projects. The AAO method has a good denitrification function and is suitable for treating sewage containing nitrogen, phosphorus, COD and other pollutants. Its core is the biochemical system, mainly including anaerobic pool, anoxic pool, aerobic pool and so on. The AAO method is greatly affected by the fluctuation of the source sewage quality. If the concentration of pollutants such as COD and ammonia nitrogen changes, the water quality after treatment will fluctuate accordingly, which will easily cause the concentration of pollutants to exceed the standard. Therefore, the flexibility of AAO sewage treatment is limited, and the activated sludge The impact resistance is not good, and the requirements for the source water quality are strict. The AAO biochemical treatment process constitutes a system, which shows that its structure is huge and there are many structures. The sewage station is actually composed of multiple large sewage pools, which covers a large area, high infrastructure costs, and a large one-time investment. Under the premise of the same design scale, the occupied area of ​​the AAO method biochemical system is basically 2 to 5 times that of the SBR method biochemical pool. The AAO method itself has the function of inhibiting sludge bulking. Under anaerobic, anoxic and aerobic alternating operating conditions, filamentous bacteria cannot proliferate in large quantities, and sludge filamentous bulking is not easy to occur. The sludge volume index is generally less than 100. At the same time, the AAO method is easy to operate, reliable in equipment operation, mature in biochemical treatment technology, less difficult in production management, good in sewage treatment, can realize continuous operation, and has low requirements for instrument automation. In production practice, the main points of AAO process control are as follows: 1. Strengthen the management of the source of sewage, decompose the sewage discharge and pollutant indicators to each process and workshop, and leave a certain margin to ensure that the sewage plant enters the water The flow rate is within the design capacity. 2. Strictly control the influent index of the sewage plant, especially the concentration of COD and ammonia nitrogen in the sewage of the anaerobic tank should not be higher than 250mg/L, and the maximum fluctuation per shift should not exceed 10%. 3. When the concentration of COD or ammonia nitrogen in any channel of the sewage plant is not less than 500mg/L, the water from this channel should be immediately cut into the accident sewage pool or fire-fighting wastewater pool to prevent the impact of activated sludge, causing the sewage plant to exceed the standard. 4. Control C:N:P=100:5:1 in the sewage in the anaerobic tank. When the carbon source is low, methanol or glucose should be added; when the nitrogen source is insufficient, urea or ammonia water should be added; when the phosphorus source is missing, trisodium phosphate and ammonium hydrogen phosphate should be added. 5. If the main pollutants in the sewage are COD and ammonia nitrogen, and the concentration of the two cannot meet the nutritional requirement of C:N=2:1, waste methanol from the low-temperature methanol washing process can be added to supplement the carbon source. 6. The pH value of the sewage in the aerobic pool should be controlled at 6~9. When the pH value is not higher than 6, the amount of alkali should be greatly increased to facilitate the degradation of ammonia nitrogen; generally the pH value should not be higher than 9, otherwise it should be neutralized with acid, preferably citric acid. 7. Sludge settlement test should be carried out in each shift, and the activated sludge settlement ratio should be strictly controlled at 30% to 40%. When the SV30 is not higher than 30%, the sludge discharge should be reduced, and when the SV30 is not lower than 40%, the sludge discharge and desludge should be increased. 8. When the SV30 is greater than 90% for a long time, great attention should be paid to strengthen process adjustment, reduce sludge return, desludge at full capacity, and ensure that the sludge volume index is not higher than 100 to prevent sludge bulking. 9. Test the aerobic reaction tank SV30 once every shift, and test the sludge concentration and organic sludge concentration in the aerobic reaction tank once a week. Combined with the test results, the secondary sedimentation tank and the high-efficiency sedimentation tank should be continuously discharged. 10. Strictly control the wind pressure and air volume of the aeration fan, keep the dissolved oxygen concentration in the sewage in the aerobic pool at 2~4 mg/L, and the dissolved oxygen concentration in the anoxic pool at 0.2~0.5 mg/L, to ensure the process of nitrification and denitrification went smoothly. However, it should be noted that the sedimentation performance of AAO activated sludge is better, and the water quality after treatment is basically stable. The concentration of ammonia nitrogen in the effluent of the sewage plant is low, usually not exceeding 1.0 mg/L, but the COD is easy to exceed the standard, and the effluent is easy to carry Sludge flocs will affect the quality of effluent in severe cases. However, the disadvantages of the AAO method also include the large return flow of sludge and high energy consumption; the agitator, reflux device, and pusher installed in the biochemical tank are underwater equipment, which has a high failure rate after long-term operation and is difficult to repair; it is used for small In sewage treatment plants, the treatment cost is high.
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