Recovery and dormancy of nitrogen removal characteristics in the pilot-scale denitrification-partial nitrification-Anammox process for landfill leachate treatment

The pilot-scale partial nitrification-anaerobic ammonia oxidation (PN-Anammox) process for landfill leachate treatment has been running stably for 2 years. The degradation characteristics of nitrogen removal performance of PN-Anammox in this system were discussed during shutdown, and different recovery strategies were analyzed from the perspective of economy and easy implementation. The results showed that during the 166 d dormancy period, the decrease in Anammox bacteria activity occurred earlier than that of Anammox bacteria, and both tended to slow down after 128 d. The recovery strategy of simulated wastewater was the fastest, followed by the pretreated landfill leachate recovery strategy with inoculation of some corresponding functional sludges, while the worst strategy was the direct pretreated landfill leachate recovery strategy. The recovery start-up of the pilotscale PN-Anammox process further showed that microbial activities were difficult to recover simultaneously during operation using raw wastewater directly due to the presence of high NH4+-N levels and the coupling process, which easily led to the accumulation of NH4+-N or NO2-N, thereby inhibiting microbial activity. The addition of some functional bacteria was more conducive to the rapid recovery of microbial activity. This study provides a new strategy for the rapid recovery of microbial activity for the engineering application of the PNAnammox process.