What is the reason for the sudden increase in COD and BOD in the effluent from the secondary sedimentation tank?

The reason for the sudden increase in COD and BOD in the secondary sedimentation tank effluent reflects the failure of sewage treatment. There are external reasons and internal reasons that lead to functional failures. Hazardous substances must be classified properly. To identify its characteristics, we must first measure the effluent COD ； Analyze the phenomenon of increased COD and BOD5 values ​​of effluent in sewage treatment. Most of them are caused by particulate matter or soluble compound substances. There are many methods to determine the cause. 1. Reasons for the increase in COD effluent value in the activated sludge treatment process 1: The reason for low visibility is caused by suspended solids when large flocs appear behind the submersible wall or in the outlet channel, or when the visibility in the secondary sedimentation tank is small or reduced. When the visibility of the outlet water is less than 1.5 meters, it is caused by dissolved sewage inclusions. The surface load of the secondary sedimentation tank is too high and the solid content in the activated sludge is too high. At this time, it must be noted that the sludge content in the activated sludge must not decrease by more than 25% within 24 hours, and it must be avoided that the NH4 + N content in the effluent will increase due to the extraction of the remaining sludge. 2. Reasons for the increase in COD effluent value in the activated sludge treatment process 2: The sludge index is too high. When the return ratio is sufficient, when the water depth in the clear water area is less than 1 meter, and the sludge index exceeds 150ml/g, measures must be taken to improve the sludge index. The return flow ratio is too small, and the return flow ratio is at least 50-70% of the inflow. RV<0.5 (=50%) → increase the return flow of activated sludge → change the mud surface height of the secondary sedimentation tank. If the mud level does not decrease, check the sludge volume load q. 3. Reasons for the increase in COD effluent value in the activated sludge treatment process 3: The broken flocs can lead to high concentrations of filterable substances in the effluent (>30mg/L or 12TE/F), insufficient degassing, formation of gas, and excessive residence time of sludge in the secondary sedimentation tank. Submersible wall and floating debris removal rates are not effective. The temperature difference between the inlet and outlet water of the secondary sedimentation tank is too small. The pipe is clogged. The incoming water COD load is too high. 4. Reasons for the increase in COD effluent value in the activated sludge treatment process 4: The effluent ammonium nitrogen value is too low ； increased turbidity ； Water intake is too high ； Return sludge pump operation failure ； PH value is too low or too high ； The sludge is mechanically crushed ； Elevated nitrite levels. Identifying Features 1: The pH value of the incoming water is high＞8.5 ； Alkaline sewage is discharged into the water, damaging or inhibiting microorganisms ； emergency measures: Introduce the sewage into other empty pools (rainwater overflow pool, primary sedimentation pool, accident pool), and continuously measure the pH value of the nitrification zone. When the pH value is higher than 9, increase the aeration intensity. Add iron salt or aluminum salt to neutralize alkaline sewage and lower the PH value. Identifying features 2: When the pH value of the incoming water is lower than 6 ； Acidic sewage is discharged, damaging or inhibiting microorganisms ； There is a risk of erosion of structures, and the discharge of organic acids will also increase the load of organic pollutants, thereby increasing oxygen consumption. emergency measures: Introduce the sewage into other empty tanks (rainwater overflow tank, primary sedimentation tank), and continuously measure the pH value of the nitrification zone. The only feasible measure is to add alkaline substances for neutralization. Dry hydrated lime can be used in emergencies. Identifying features 3 ； The inlet water temperature rises significantly ； Hot production wastewater is discharged, and usually other substances are discharged. Formation of foam and floating sludge ； If foam and floating sludge suddenly appear within the activated sludge tank or secondary sedimentation tank, it may be from surfactant shock load, shock load from detergents, other easily degradable substrates, usually from the food industry. Identifying features 4 ； There is an oil film in the water: When mineral oil products are discharged and there is no risk of explosion, the treatment measures are to introduce the sewage into other empty pools (rainwater overflow pool, primary sedimentation pool, accident pool), and stop the transportation of return sludge and circulating sludge. Stop the stirring device in the non-aerated zone, and set up an oil baffle at the outlet of the denitrification zone (or anaerobic zone). If oil appears in the aerated zone, stop aeration and sprinkle in the binding agent. Identifying features 5 ； The gas smells like alcohol ； Sometimes associated with sewage coverings ； Contains flammable and explosive gases and liquids. Emergency measures include using alarm equipment to measure the risk of explosion, directing sewage into other empty pools (rainwater overflow pools, primary sedimentation tanks), and stopping all engines and electrical equipment in all explosion risk areas. ； Turn off all heating equipment and extinguish open flames. Close the doors and windows of structures without sewage and stop the operation of ventilation equipment in the blower room, but some blowers will continue to operate to extract harmful substances. Remove sealing coverings from pools and drains where possible. Stop the pumping of suspended sludge and remaining sludge.

The sudden increase in COD and BOD in the secondary sedimentation tank is caused by a variety of factors, which can be considered:: 1. The sedimentation performance of the secondary sedimentation tank is not good, which causes more SS in the effluent, thereby causing COD and BOD to increase. ； 2. The incoming water quality suddenly changes, causing changes in the outlet water quality indicators. ； 3. The incoming water contains toxic substances, which disintegrate or poison the activated sludge, causing its precipitation or treatment effect to be greatly reduced, and the effluent exceeds the standard. ； 4. The sludge discharge from the secondary sedimentation tank is not smooth, causing the sludge to float anaerobically and worsening the effluent quality. ；