How to deeply treat urban domestic sewage? Experimental research using a single reactor

Tech 2023-10-23 02:59:53 Source: Network

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With the increasing importance of environmental protection and resource reuse, research in the field of wastewater treatment has become increasingly popular. The regeneration and reuse of urban sewage has become an internationally recognized and important field, also known as the "second water source" of cities. In this trend, anaerobic ammonia oxidation (Anammox) technology has become a highly concerned approach for wastewater denitrification. Compared with traditional nitrification/denitrification processes, Anammox technology has significant advantages such as low oxygen consumption, no need for additional carbon sources, and low sludge production.

In order to explore the deep treatment of urban sewage in the same reactor, we conducted an experiment using the SBR activated sludge process. During the experiment, we conducted in-depth research on the parameter changes and operational efficiency of treating urban domestic sewage at room temperature, in order to seek a more concise and efficient wastewater treatment plan.

In the experiment, we used an SBR reactor with a volume of 5 liters, which can not only treat urban domestic sewage at room temperature, but also achieve anaerobic/aerobic biological phosphorus removal during the treatment. The experimental water was taken from the sludge and A-O biological phosphorus removal activated sludge in the living system of the faculty members and their families in the western district of Beijing University of Technology, which helps to quickly start the reactor. The specific water quality parameters of the experiment are as follows: CODCr (Chemical Oxygen Demand) mass concentration is 150

Between 650mg/L, the mass concentration of BOD5 (biological oxygen demand) is 80

Between 360mg/L, the mass concentration of SS (suspended solids) does not exceed 200mg/L, and the mass concentration of NH-N (ammonia nitrogen) is within 50

Between 90mg/L, the mass concentration of NO-N (nitrite nitrogen) is less than 1mg/L, the mass concentration of NO-N (nitrate nitrogen) is less than 1mg/L, and the mass concentration of TP (total phosphorus) is 3.5

Between 16.5mg/L, maintain the water temperature at 13

Between 8.0.

In the experiment, we inoculated Anammox granular sludge and A-O biological phosphorus removal activated sludge, and then precisely controlled the aeration rate. After 30 days of stable operation, we used this system to treat urban domestic sewage at room temperature and observed the changes in the concentrations of various main indicators (NH-N, NO-N, NO-N, TN, COD, and TP). Through data analysis, we divided the experimental process into two stages, with 5.5 hours as the cut-off point.

In stage I, we observed that the degradation rate of COD was significantly higher than that of stage II, while the removal rates of NH-N and TN were relatively low. This indicates that when treating domestic sewage, the nitrogen removal rate will only rapidly increase when the degradation of organic matter reaches a certain level. The experimental results show that there is a significant correlation between the concentration changes of NH-N and TN and the removal rate in the SBR system, with a linear correlation coefficient of up to 0.9998. This phenomenon is mainly due to the metabolic utilization of NO-N in the form of electron acceptors in the Anammox reaction, while producing a portion of NO-N. These NO-N may be subjected to heterotrophic denitrification treatment in the presence of organic matter, resulting in TN mainly existing in the form of NH-N in the SBR reactor. The mass concentration of TN in the experimental effluent was 6.046mg/L, with a removal rate of 92.4%, while the removal rates of COD and TP were only 43.6% and 0.1%, respectively. This is mainly because the dominant bacteria in the SBR system are AOB and Anammox, which have limited removal ability for COD and P.

As the reaction progresses, we also observed changes in parameters such as DO, ORP, and pH. At different stages of the SBR reaction cycle, these parameters exhibit different trends. Throughout the entire experimental process, the DO mass concentration remained at a level of 0.03-0.04mg/L, as the oxygen supply and demand balance in the SBR system was maintained under constant aeration conditions. It is not until NH-N and TN in the reactor decrease below the limiting substrate concentration that a significant inflection point appears in the DO curve, with DO sharply increasing to 1mg/L, and ORP also showing corresponding inflection points. At the same time, there is a "pH valley" at the end of the pH curve, which is caused by the blowing off effect of excessive aeration on CO2.

Next, we conducted another set of experiments, inoculated with A-O biological phosphorus removal activated sludge, and continued to treat urban domestic sewage at room temperature under constant aeration conditions. The experimental results show that the SBR system can not only deeply remove TN, but also COD and TP. The effluent quality meets the Class A discharge standard for urban sewage treatment plants in China (GB18918-2002).

In summary, we explored the feasibility of using the SBR activated sludge process to treat urban wastewater under room temperature conditions through experiments. We have demonstrated that in an SBR reactor, inoculation with Anammox bacteria or A-O biological phosphorus removal activated sludge can achieve advanced treatment of urban wastewater, achieving deep removal of TN and COD/TP, respectively. This provides a new, simple and efficient solution for urban sewage treatment.

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Tag: How to deeply treat urban domestic sewage Experimental research