Mutual influence mechanism of nitrate and sulfamethoxazole on their biotransformation in poly (3-hydroxybutyrate-3-hydroxyvalerate) supported denitrification biofilter for a long-term operation

Nitrate and SMX both play a critical role in their biotransformation in biodegradable polymer-supported denitrification biofilters. However, the mutual influences of nitrate and SMX on their biotransformation for long-term operation remained obscure. Results showed SMX and nitrate had divergent effects on SMX removal. SMX removal rates was positively related with its loading rates, whereas they were negatively related to NLRs. The most abundant metabolite C₁₀H₁₄O₃N₃S (the reduced form of SMX moiety) from the N-O bond cleavage pathway by UHPLC-LTQ-Orbitrap-MS/MS and effluent TOC variations confirmed the presence of electron donor competition between nitrate and SMX. SMX less than 1000 μg/L had a negligible influence on denitrification performance. Denitrifiers such as Azospira and Denitratisoma were still enriched after chronic exposure, and nosZ/narG positively correlated with sul1/sul2 resistance genes, which were both responsible for the negligible influence of SMX. This work could guide the operational management of denitrification biofilters for simultaneous nitrate and antibiotics removal.