Abstract
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•Good SMX removal was achieved by AnMBR under variable feed SMX of 10–100000 μg/L.•SMX biotransformation followed pseudo-first order reaction kinetics in AnMBR.•SMX biotransformation pathway was proposed based on 7 TPs identified by GC–MS.•Non-antibiotic Butylbenzenesulfonamide was the dominant TP under low SMX load.•Sulfanilamide with low antibiotic toxicity was the dominant TP under high SMX load.
A lab-scale mesophilic anaerobic membrane bioreactor (AnMBR) was used to treat synthetic municipal wastewater with variable concentrations of antibiotic Sulfamethoxazole (SMX) and bulk organics in this study. The removal and biotransformation pathway of SMX in the AnMBR were systematically investigated during a 170 d of operation under hydraulic retention time of 1 d. Average SMX removal was 97.1% under feed SMX of 10–1000 μg/L, decreasing to 91.6 and 88.0% under feed SMX of 10,000 and 100,000 μg/L due to the inhibition effects of high SMX loading rate on anaerobic microorganisms. SMX biotransformation followed pseudo-first order reaction kinetics based on SMX removal independent of feed SMX of 10–1000 μg/L during continuous operation and also in a batch test under initial SMX of 100,000 μg/L. According to the identified 7 transformation products (TPs) by gas chromatography-mass spectrometry, the biotransformation pathway of SMX from municipal wastewater treatment via AnMBR was first proposed to consist of 2 primary routes: 1) Butylbenzenesulfonamide without antibiotic toxicity dominated under feed SMX of 10–100 μg/L; 2) Sulfanilamide with much lower antibiotic toxicity than SMX dominated under feed SMX of 1000–100000 μg/L, further transforming to secondary TPs (4-Aminothiophenol, Aniline, Acetylsulfanilamide) and tertiary TPs (4-Acetylaminothiophenol, Acetylaniline).