Aerobic biodegradation of the sulfonamide antibiotic sulfamethoxazole by activated sludge applied as co-substrate and sole carbon and nitrogen source

- Elimination of sulfamethoxazole (SMX) turned out to be based on biodegradation.
- Activated sludge communities utilize SMX as carbon and/or nitrogen source for growth.
- SMX biodegradation is enhanced in the presence of a C source and N deficiency.
- With SMX as co-substrate 3-amino-5-methyl-isoxazole represents the main stable metabolite.
- SMX as sole C and N source maybe yields hydroxyl-N-(5-methyl-1,2-oxazole-3-yl)benzene-1-sulfonamide as further metabolite.

Potential aerobic biodegradation mechanisms of the widely used polar, low-adsorptive sulfonamide antibiotic sulfamethoxazole (SMX) were investigated in activated sludge at bench scale. The study focused on (i) SMX co-metabolism with acetate and ammonium nitrate and (ii) SMX utilization when present as the sole carbon and nitrogen source. With SMX adsorption being negligible, elimination was primarily based on biodegradation. Activated sludge was able to utilize SMX both as a carbon and/or nitrogen source. SMX biodegradation was enhanced when a readily degradable energy supply (acetate) was provided which fostered metabolic activity. Moreover, it was raised under nitrogen deficiency conditions. The mass balance for dissolved organic carbon showed an incomplete SMX mineralization with two scenarios: (i) with SMX as a co-substrate, 3-amino-5-methyl-isoxazole represented the main stable metabolite and (ii) SMX as sole carbon and nitrogen source possibly yielded hydroxyl-N-(5-methyl-1,2-oxazole-3-yl)benzene-1-sulfonamide as a further metabolite.