Summary of the reasons for the sudden rise of the effluent COD detector

- Jul 14, 2020-

Summary of the reasons for the sudden rise of the effluent COD detector


1.The reason for the increase in the COD value of the effluent from the activated sludge method is as follows: The reason for the low visibility is that when large flocs appear behind the diving wall or in the outlet channel, or when the visibility in the secondary settling tank is small or reduced, Caused by suspended matter. When the effluent visibility is less than 1.5m, it is caused by the content of dissolved sewage. When the surface load of the secondary sedimentation tank is too high and the solid content in the activated sludge is too high, it must be noted that the sludge content in the activated sludge must not be reduced by more than 25% within 24 hours, and cannot be increased due to the extraction of residual sludge. The content of NH4+N in water.


2. Reasons for the increase of COD effluent value in the activated sludge treatment process:   

The sludge index is too high. When the reflux ratio is sufficient, when the water depth of 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 reflux ratio is too small, and the reflux ratio is at least 50-70% of the inflow. RV <0.5 (=50%) → increase the return flow of activated sludge → change the height of the mud surface of the secondary sedimentation tank. If the mud surface is not reduced, check the sludge volume load q.   


3. Reasons for increased COD effluent value in activated sludge treatment process 

The flocculation is broken, which can lead to high concentration of filterable substances in the effluent, (>30mg/L or 12TE/F), insufficient deaeration, gas formation, and sludge residence time in the secondary sedimentation tank is too long. The removal rate of the diving wall and floating objects is not effective. The temperature difference between the inlet and outlet of the second settling tank is too small. The pipeline is blocked. Water quality analyzer inlet COD load is too high.

 

COD detector

COD detector


4. Reasons for the increase of COD effluent value in the activated sludge treatment process: 

The ammonium nitrogen value of the effluent is too low; the turbidity is increased; the water intake is too high; the operation of the return sludge pump is faulty; the PH value is too low or too high; the sludge is crushed mechanically; the nitrite content is increased. 


Recognition feature 1: High pH value of influent>8.5; Alkaline sewage discharge, damage or inhibit microorganisms; Emergency measures: Introduce sewage into other empty ponds (rainwater overflow pond, primary settling pond, accident pond), 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 reduce PH value.  


Recognition feature 2: When the PH value of influent is lower than 6,There is acidic sewage discharge, which damages or inhibits microorganisms; there is a risk of eroding structures. The discharge of organic acids will also increase the load of organic pollutants, which in turn increases oxygen consumption.

Emergency measures: Introduce sewage into other empty ponds (rainwater overflow ponds, primary settling ponds), and continuously measure the PH value of the nitrification zone. The only feasible measure is to add alkaline substances to neutralize. In emergency, dry hydrated lime can be used.  

 

Recognition feature 3: The temperature of the inlet water rises significantly; Hot production wastewater is discharged, and usually other substances are discharged. Foam and floating sludge are formed; if foam and floating sludge suddenly appear in the range of activated sludge tank or secondary settling tank, it may come from the impact load of surfactants, from the impact load of detergents and other easily degradable substrates, usually From the food industry.  

COD detector

Recognition feature 4: There is oil film in the inlet water: There are mineral oil products discharged, no treatment measures when there is danger of explosion, the sewage is introduced into other empty ponds (rainwater overflow ponds, primary settling ponds, accident ponds), and the transportation of return sludge and circulating sludge is stopped. Stop the stirring device in the non-aerated zone, and set oil baffle at the outlet of the denitrification zone (or anaerobic zone). If oil appears in the aerated zone, stop the aeration and sprinkle the binding agent. Recognition feature 5; gas smells like alcohol;  


Sometimes it is related to sewage covering; it contains flammable and explosive gas and liquid. 

Emergency measures, use the alarm equipment to measure the explosion risk, introduce the sewage into other empty pools (rainwater overflow pool, primary sink pool), stop all engines and electrical equipment in all explosion hazard areas; turn off all heating equipment and extinguish open flames . Close the doors and windows without sewage structures, and stop the operation of the ventilation equipment in the blower room, but some blowers operate as usual to extract harmful substances. As far as possible, remove the sealing cover of the pool and drain. Stop the extraction of suspended sludge and excess sludge.