Biological conversion of sulfisoxazole in an autotrophic hydrogen-based membrane biofilm reactor

Sulfisoxazole (SIZ), a common antimicrobial prescribed for treating infections in livestock, is frequently detected in surface water and groundwater along with nitrate. The interactions of SIZ biotransformation and nitrate removal were investigated in a H2-based membrane biofilm reactor (H2-MBfR) through long-term reactor operation augmented by short-term batch experiments in serum bottles. Denitrification in the H2-MBfR was not influenced by SIZ when its input concentration was <= 5 mg L-1, although SIZ removal was inhibited by nitrate. Transformation products identified by mass spectrometry were formed via hydrogenation (reduction) reactions. The addition of SIZ shaped the microbial community structure, leading to the relative abundance of denitrifiers decreasing with the highest SIZ loading. Sulfate-reducing bacteria (SRB) were present in all stages, as the bio-films had relatively high abundances of the dsrA gene and its transcription products, while sulfide was generated in the final stage. SRB also appeared to be important in SIZ biotransformation, perhaps using SIZ as an electron donor, electron acceptor, or both. Concurrent SIZ removal and stable denitrification make the H2-MBfR a pro-spective technology for the treatment of wastewaters polluted with nitrate and SIZ.