There are many reasons for sludge blackening in sewage treatment operation, such as sludge blackening caused by the lack of dissolved oxygen in the aeration tank, and more pigment substances in the influent water.
The blackening of sludge in the aeration tank is often caused by the lack of dissolved oxygen in the sludge, so once the blackening of the sludge occurs, the dissolved oxygen content of the aeration tank should be checked first, and then the inlet water quality should be checked, and according to the results of the water quality inspection, the specific reason should be judged. The common causes of sludge blackening and countermeasures are as follows:
Sludge blackening due to low DO
The corresponding solution is: increase the oxygen supply of the aeration tank, so that the mass concentration of dissolved oxygen is greater than 2mg/L, and it can reach 4~5mg/L in a short time, as long as the dissolved oxygen content of the aeration tank mixture is increased, the sludge will gradually return to normal in a few hours.
Blackening of the aeration tank sludge caused by the quality of the influent water
For example, when the influent contains a large amount of Fe2+, and at the same time, when the dissolved oxygen in the aeration tank is insufficient, the anaerobic interpretation of organic matter will release H2S, and H2S and Fe2+ will react to form FeS, and the color of FeS is black-brown, which will make the entire 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 blackening of the sludge in the aeration tank can be improved by increasing the aeration capacity and increasing the reflux ratio.
When the influent water contains substances that are toxic to microorganisms, the microorganisms will die, and it will also cause the sludge of the aeration tank to turn black
The corresponding solution is: firstly, check the water quality of the influent, if the inlet water contains toxic substances that have a highly toxic effect on microorganisms, it must be controlled from the front end, secondly, the load resistance of the aeration tank can be improved by increasing the aeration volume and increasing the reflux, so as to improve the situation of sludge blackening, and the sludge of the system should be replaced for the situation that a large amount of toxic waste liquid has entered the system and caused the system to collapse.
If the sludge stays in the aeration tank for too long, the sludge will turn black due to the aging of the sludge
The corresponding solution is: appropriately reduce the aeration capacity, and at the same time, pay attention to the residence time of sludge in the aeration tank and discharge the sludge in time. In addition, the sudden increase of the inlet load will also cause the aeration tank sludge blackening, and the countermeasures in this situation are relatively easy, as long as the inlet water volume is reduced, the aeration tank sludge blackening situation 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 not the same, but, under normal circumstances, the corresponding measures for the blackening of the sludge are: first check the inlet water quality, if there is no problem with the water quality, and then check 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 causes of sludge blackening and the response to the blackening of the sludge in the aeration tank of the sewage station is different from the blackening of the sludge in the conventional aeration tank, the difference is that the sludge in the primary aeration tank of the sewage station is normal in color, and only the secondary aeration tank is blackened. The results of dissolved oxygen content measurement showed that the dissolved oxygen concentration on the surface of the aeration tank reached about 5mg/L, which was not caused by the lack of oxygen in the aeration tank. If the sludge poisoning is caused by the sudden change in the influent water quality, and then the sludge in the aeration tank is blackened, then the primary aeration tank should also be blackened, not just the sludge in the secondary aeration tank; In addition, the possible cause of the blackening of the aeration tank sludge, which is normally caused, was ruled out by the normal color of the sludge in the primary aeration tank in the Class 2 A/O system.
According to the summary of 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 under normal circumstances, 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 the sludge in the secondary aeration tank in the 2-stage A/O system, the conventional countermeasures are ineffective, and the blackening of the sludge in the secondary aeration tank in the secondary A/O system can be changed by increasing the dissolved oxygen content of the aeration tank, closing the return valve from the secondary aeration tank to the secondary aeration tank, cleaning the corrupted sludge of the secondary aeration tank, and adding nutrients to the aeration tank.
