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

Causes and Countermeasures of Sludge Turning Black in Aeration Tank

by:BOQU     2023-03-19
Dissolved Oxygen Analyzer | Can DO dissolved oxygen really make the sludge turn black? There are many reasons for the blackening of sludge in the operation of sewage treatment, such as the blackening of sludge caused by the lack of dissolved oxygen in the aeration tank, the influent contains more pigment substances, etc. The blackening of the sludge in the aeration tank is often caused by the lack of dissolved oxygen in the sludge. Therefore, once the sludge is blackened, the dissolved oxygen content in the aeration tank should be checked first, and then the influent water quality should be checked. The result, specifically judge what caused it. Common causes and countermeasures for sludge blackening are as follows: Oxygen Analyzer | Can DO dissolved oxygen really make sludge black? There are many reasons for the blackening of sludge in the operation of sewage treatment, such as the blackening of sludge caused by the lack of dissolved oxygen in the aeration tank, the influent contains more pigment substances, etc. The blackening of the sludge in the aeration tank is often caused by the lack of dissolved oxygen in the sludge. Therefore, once the sludge is blackened, the dissolved oxygen content in the aeration tank should be checked first, and then the influent water quality should be checked. The result, specifically judge what caused it. Common causes and countermeasures for sludge blackening are as follows: The corresponding solution to sludge blackening caused by low DO is: increase the oxygen supply of the aeration tank, so that the mass concentration of dissolved oxygen is greater than 2mg/L in a short time. To reach 4-5mg/L, as long as the dissolved oxygen content of the mixed solution in the aeration tank is increased, the sludge will gradually return to normal within a few hours. Blackening of aeration tank sludge caused by influent water quality For example, when the influent water contains a large amount of Fe2+, and at the same time, when the dissolved oxygen in the aeration tank is insufficient, the anaerobic decomposition of organic matter will release H2S, and H2S will react with Fe2+ to form FeS , and the color of FeS is dark brown, which will make the whole aeration tank sludge black. The corresponding solution is: determine the cause of sludge blackening through water quality testing, and then prescribe the right medicine; at the same time, the situation of sludge blackening in the aeration tank can be improved by increasing the aeration volume and increasing the reflux ratio. When the influent water contains substances that are toxic to microorganisms, the microorganisms will die and the sludge in the aeration tank will turn black. The corresponding solution is: first check the influent water quality, if the influent water contains substances that are highly toxic to microorganisms The toxic substances that act must be controlled from the front end. Secondly, the load resistance capacity of the aeration tank can be improved by increasing the aeration volume and increasing the return flow, thereby improving the condition of sludge blackening. For a large amount of toxic substances If the waste liquid enters the system and causes the system to collapse, the sludge in the system should be replaced. If the sludge stays in the aeration tank for too long, the sludge in the aeration tank will turn black due to the aging of the sludge. The residence time is long, and the mud is discharged in time. In addition, a sudden increase in the influent load will also cause the sludge in the aeration tank to turn black. The countermeasures for this situation are relatively easy. As long as the water inflow is reduced, the blackening of the sludge in the aeration tank can be significantly improved. In short, there are many reasons for the blackening of the sludge in the aeration tank, and the corresponding countermeasures are also different. However, under normal circumstances, the corresponding measures for the blackening of the sludge are: first check the water quality of the influent, if there is no problem with the water quality, then Investigate whether the process parameters are set properly; if there is a problem with the quality of the influent water, the influent water and process parameters should be adjusted at the same time. The cause of sludge blackening and the solution The sludge blackening in the aeration tank of the sewage station is different from that in the conventional aeration tank. The difference is that the sludge in the primary aeration tank of the sewage station is normal in color, only The secondary aeration tank is black. The results of the dissolved oxygen content measurement show that the mass concentration of dissolved oxygen on the surface of the aeration tank reaches about 5mg/L, so it is not the sludge blackening caused by the lack of oxygen in the aeration tank; if the sludge poisoning is caused by the sudden change of the influent water quality, In order to make the sludge in the aeration tank black, then the primary aeration tank should also be black, not just the sludge in the secondary aeration tank; in addition, usually it will cause the possibility of blackening the sludge in the aeration tank The cause was also ruled out due to the normal color of the sludge in the primary aeration tank in the 2-stage A/O system. According to daily experience, there are many reasons for the blackening of the sludge in the aeration tank, and the countermeasures for the blackening of the sludge in the aeration tank caused by different reasons are different, but in general, when encountering the blackening of the sludge in the aeration tank , can be solved by conventional solutions, such as increasing the dissolved oxygen content and increasing the reflux ratio. For the blackening of sludge in the secondary aeration tank in the 2-level A/O system, conventional countermeasures are ineffective. It is necessary to increase the dissolved oxygen content in the aeration tank and close the return valve from the secondary sedimentation tank to the secondary aeration 1. Cleaning the rotted sludge in the secondary settling tank and adding nutrients to the aeration tank can change the blackening of the sludge in the secondary aeration tank in the secondary A/O system.
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