What are the effects of abnormally high dissolved oxygen in sewage treatment

At present, there are many studies on industrial wastewater treatment, but few studies on sudden abnormal inflow of municipal sewage plants. Taking common leachate, oil, and heavy metal inflow as examples, this paper summarizes the experience of the impact characteristics of sudden abnormal water inflow on DO in a municipal sewage plant in Shandong Province, and provides reference for timely detection and screening of abnormal water inflow. in order to take countermeasures. 1. The impact characteristics of abnormal water inflow 1. Oily water inflow. The factory adopts the plug-flow A/A/O process, the residence time in the aerobic zone is 8h, and 8 points are evenly taken along the process to detect the DO content. In the case of oily influent water (170mg/L), DO was lower than the normal value, and it was more obvious in the front part of the aerobic zone, and this difference gradually weakened in the latter part of the aerobic zone. According to the online detection results of the effluent, the concentration of COD and NH3-N increased slightly, which indicates that the degradation rate of COD and NH3-N of the activated sludge is affected by the oil, and the oxygen consumption is reduced at this time, which should show the increase of DO. Phenomenon, which is contrary to the detection results of DO. The possible reason is that, on the one hand, the oil film affects the transfer of DO to the sludge floc, reducing the degradation rate of COD and NH3-N; on the other hand, an oil film is also formed on the surface of the DO detection probe, which affects the transfer of DO. , resulting in inaccurate DO test results. With the continuation of the reaction, the oily substance gradually migrates and transforms to eliminate this effect. 2. Heavy metal influent In the case of influent containing heavy metals (take Cu as an example, 45mg/L), the DO in the front part of the aerobic zone is higher than the normal value, while in the latter part of the aerobic zone, it is lower than the normal value, such as Figure 1 shows. Heavy metals (Cu) can inhibit sludge activity and reduce microbial activity. Therefore, the oxygen consumption in the front part of the aerobic zone is reduced, and the DO is higher than the normal value. Due to the decrease of microbial degradation rate, there are still high contents of COD and NH3-N in the latter part of the aerobic zone, resulting in higher oxygen demand and DO lower than the normal value in the latter part of the aerobic zone. 3. The COD of the high-concentration influent water is designed to be 500mg/L. During the operation, the influent water is often overloaded, 700-800mg/L, and even exceeds 1000mg/L instantaneously. In the case of high-concentration influent, the overall DO in the aerobic zone was lower than normal, as shown in Figure 1. The impact of high-concentration influent water on DO is mainly because the increase in pollutant concentration increases oxygen consumption, and DO is lower than the normal value. At this time, the oxygen supply should be increased. 2. Identification of influent types and countermeasures According to the change characteristics of DO and combined with the online COD detection data of influent, a preliminary judgment can be made on the type of abnormal influent, and countermeasures can be taken in time. In the process of operation, there are often complex water inflows, such as high-concentration water inflow accompanied by heavy metals, which is difficult to deal with and needs to be analyzed in detail according to specific conditions. 3. Conclusion Sudden abnormal water inflow is a common problem in the operation of municipal sewage treatment plants, which will have a great impact on process operation. By summarizing the impact characteristics of different types of abnormal water inflow on DO, combined with the online COD detection results of inflow water, the type of inflow water can be quickly and preliminarily judged, so that corresponding emergency measures can be taken to minimize the risk.
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