Summary of the reasons for the sudden increase in effluent COD!

The reason for the sudden increase in COD and BOD of the effluent from the secondary sedimentation tank reflects the failure of sewage treatment. There are external reasons and internal reasons that lead to functional failures. It is necessary to classify harmful substances. To identify its characteristics, we must first determine the COD of the effluent; analyze the phenomenon of increased COD and BOD5 values of the effluent in sewage treatment, most of which are caused by particulate matter or soluble compounds. There are many ways to determine the cause.

1. Reasons for the increase of COD effluent value in the activated sludge treatment process 1:

The reason for the low visibility is 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, it is caused by suspended solids. When the visibility of the outlet water is less than 1.5 meters When it is caused by the contents of soluble sewage. The surface load of the secondary settling 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 exceed 25% within 24 hours, and the remaining sludge must be avoided. The extraction results in an increase in the NH4 +N content in the effluent.

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

The sludge index is too high. In the case of sufficient reflux ratio, 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 reflux ratio is too small, the reflux 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 settling tank. If the mud level is not lowered, check the sludge volume load q.

3. Reasons for the increase of COD effluent value in the activated sludge treatment process 3:

Fragmentation of flocs can lead to high concentration of filterable substances in the effluent, (>30mg/L or 12TE/F), insufficient degassing, gas formation, and long residence time of sludge in the secondary settling tank. The removal rate of diving walls and floating objects cannot reach the effect. The temperature difference between the inlet and outlet water of the secondary sedimentation tank is too small. The pipeline is blocked. The influent COD load is too high.

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

The ammonium nitrogen value of the effluent is too low; the turbidity is increased; the inflow is too high; the return sludge pump is malfunctioning; the PH value is too low or too high; the sludge is crushed by machinery; the nitrite content is increased.

Identification feature 1: Influent pH value is high> 8.5; alkaline sewage is discharged to damage or inhibit microorganisms;

Emergency measures: Lead the sewage into other empty tanks (rainwater overflow tank, primary sedimentation tank, accident tank), 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.

Identification feature 2: When the pH value of the inlet water is lower than 6;

The discharge of acidic sewage can damage or inhibit microorganisms; there is a risk of erosion of structures, and the discharge of organic acids will increase the load of organic pollutants, thereby increasing oxygen consumption.

Emergency measures: Lead the sewage into other empty ponds (rainwater overflow pond, primary sedimentation pond), and continuously measure the pH value of the nitrification zone. The only feasible measure is to add alkaline substances to neutralize it. In an emergency, dry slaked lime can be used.

Recognition feature 3: The inlet water temperature is significantly increased;

Hot production wastewater is discharged, and other substances are usually discharged. Formation of foam and floating sludge; if foam and floating sludge suddenly appear in the range of the activated sludge tank or the secondary settling tank, it may come from the impact load of the surfactant, the impact load of the detergent and other easily degradable substrates, usually From the food industry.

Recognition feature 4: There is oil film in the inlet water:

When mineral oil products are discharged and there is no danger of explosion, the sewage is introduced into other empty tanks (rainwater overflow tank, primary sedimentation tank, accident tank), and the transportation of return sludge and circulating sludge is stopped. Stop the stirring device in the non-aeration zone, and install an oil baffle at the exit of the denitrification zone (or anaerobic zone). If oil appears in the aeration zone, stop the aeration and sprinkle the binder.

Recognition feature 5; the gas has the smell of alcohol, etc.;

Sometimes related to sewage covering; contains flammable and explosive gases and liquids.

Emergency measures: use alarm equipment to measure the explosion hazard, lead sewage into other empty pools (rainwater overflow pool, primary sedimentation pool), stop all engines and electrical equipment in all explosion danger zones; turn off all heating equipment and extinguish open flames . Close the doors and windows of sewage-free 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 coverings of pools and drains. Stop the suction of suspended sludge and excess sludge.