Revisit the role of hydroxylamine in sulfur-driven autotrophic denitrification

Through dedicated batch tests using the enriched sludge dominated by sulfur-oxidizing bacteria (SOB), the potential transformation of hydroxylamine (NH2OH) by SOB and the effects of NH2OH on the rate-limiting sequential reduction processes of sulfur-driven autotrophic denitrification (SDAD) were systematically explored in this study. The results indicated that NH2OH might be first converted to NO by SOB and then participate in the SDAD process, thus accelerating the utilization of S2- and contributing to the formation of N2O. Up to 3.5 mg-N/L NH2OH didn't affect the NO3 - or NO2 - reduction of SDAD, during which no significant changes were observed for the NH2OH concentration. Comparatively, even though NH2OH had no direct impact on the N2O reduction of SDAD, it could be consumed and therefore affect the depletion of N2O indirectly by regulating the toxic effect and electron supply of S2-. These findings provide novel implications for applying NH2OH to SDAD-based integrated processes for biological nitrogen removal.