title: Responses of anammox to long-term p-nitrophenol stress: from apparent and microscopic phenomena to mechanism simulation+S1
design: P-nitrophenol is usually present in ammonia-rich wastewaters produced by some chemical plants, so the response of anammox to long-term p-nitrophenol stress was investigated. The changes in the efficiency, sludge characteristics, and microorganisms of the anammox system under different levels p-nitrophenol stress were examined, and the potential stress mechanisms of p-nitrophenol on anammox were further speculated. The results showed that 10-50 mg/L p-nitrophenol had no obvious impacts on nitrogen removal efficiency, but stimulated secretion of more extracellular polymeric substances. 60 mg/L p-nitrophenol caused the reactor to lose the 64.47% nitrogen removal efficiency in 5 days. Long-term exposure to p-nitrophenol led to 8.6% reduction in Candidatus_Kuenenia abundance and 18.4%-35.9% decrease in the expression level of anammox bacterial functional genes. Molecular simulation indicated that p-nitrophenol could bind to key enzymes of anammox. This study provides new insights into the treatment of ammonia-rich wastewater containing PNP or phenols by anaerobic ammonia oxidation.