Deciphering the migration of naproxen and its impact on nitrogen removal in CANON system

Naproxen (NPX) has been frequently detected in various nitrogenous wastewaters and been proved have significant impact on nitrogen removal systems. Completely autotrophic nitrogen removal over nitrite (CANON) process was one of the most economical nitrogen removal technologies and has good application prospect. However, whether it was suitable for treating NPX containing wastewater was still unclear. This study investigated the migration of NPX in CANON process by adopting a membrane bioreactor (MBR), and analyzed its impact on the nitrogen removal and microbial characteristics by suppling incremental NPX. The results showed the NPX supplied in 0.001 to 1000 μg L −1 was mainly bio-adsorbed by the sludge, which then led to continuous suppression on anaerobic ammonium-oxidizing bacteria (AAOB) and decreased the TN removal from 79.1 % to 50.6 %. Additionally, the activity of hydroxylamine oxidoreductase and nitrite oxidoreductase enzymes both decreased. However, the abundance of AAOB and the functional gene hzsB initially increased as a stress response. Ammonia-oxidizing bacteria (AOB) were slightly impacted and then adapted, with the amoA gene amplifying 2.3 times and the abundance of Nitrosomonas increasing from 2.4 % to 4.0 %. Nitrite-oxidizing bacteria (NOB) were significantly enhanced, leading to an increase in effluent nitrate concentration from 34.7 to 101.6 mg L −1 , and in the abundance of Nitrospira from 2.2 % to 13.5 %. The enhancement in NOB significantly limited the AAOB activity in return via competing nitrite, and further limited the TN removal. Denitrifying bacteria experienced only slight impact, with the expression of narG , nirK , and nirS genes slightly fluctuated. It is essential to thoroughly washout NOB and introduce additional strategy for enhancing NPX biodegradation for stable operation of the CANON process when treating NPX containing wastewater.