Abstract: Rural leisure tourism sewage has the characteristics of discontinuous discharge and large fluctuation with time, which poses a great challenge to the management and operation of decentralized sewage treatment equipment. In this study, a two-stage AO-MBR setup is designed, which uses simulated sewage as the inlet water. Through the operation mode of shutdown/restart in different time periods, the impact of shutdown on the biochemical performance and recovery of the treatment process was explored. The results show that the shutdown operation had a significant impact on the biochemical treatment efficiency of the experimental setup, and the decline degree of biochemical treatment efficiency and the recovery time had a significant correlation with the shutdown time of the setup. As the shutdown time was extended from 1 d to 8 d, the COD removal efficiency could be decreased from 90% to 80%, and the longest recovery time was up to 5 d; the removal efficiency of ammonia nitrogen could be decreased from 90% to around 70%, and the longest recovery time was up to 5 d; the total nitrogen removal efficiency could be decreased from 48% to 34%, and the longest recovery time of the system required 5 d too. From the perspective of sludge activity, with the extension of shutdown time, the sludge activity indexes such as SOUR, dehydrogenase activity and SATP decreased accordingly. Through the method of microbial sequencing, it was also found that the microbial population changed greatly before and after the shutdown. From the perspective of phylum level, the proportion of heterotrophic bacteria of Proteobacteria decreased significantly after the shutdown, and the proportion of anaerobic bacteria such as Bacteroidea increased. From the perspective of genus classification, the number of traditional nitrifying bacteria decreased, but the number of bacteria with synchronous nitrification and denitrification showed an upward trend. For the wastewater treatment facilities that have to be shut down, an aeration operation with less oxygen is a feasible alternative way to maintain the activity of the sludge.

Key words: decentralized sewage treatment, shutdown/restart, two stage AO device, sludge activity, microbial flora