Aerobic biodegradation of micropollutants by nitrifiers and heterotrophs: Changes in biodegradation rate constant depending on levels of growth substrates and microbial activities

Abstract

This study investigated how the biodegradation rate constant (kbio) of 11 micropollutants (MPs) responded to changes in the concentrations of growth substrates and microbial activities while considering the predominant microbial degraders of MPs. Metformin, losartan, valsartan, and cimetidine (group A) were biodegraded predominantly by nitrifiers. MPs of group A showed a positive correlation with kbio and nitrifying activity, while a negative correlation was observed with the initial concentration of ammonium, possibly due to competitive inhibition. Atenolol, caffeine, and naproxen (group B) were biodegraded predominantly by heterotrophs, with kbio remaining stable despite changes in organic matter concentration or heterotrophic activity. Olmesartan, candesartan, diclofenac, and sulfamethoxazole (group C) showed low kbio regardless of growth substrate concentration and microbial activity, which could be attributed to their chemical structures. These findings suggest that the kbio of MPs in WWTPs could respond differently to growth substrate concentration and microbial activity depending on their predominant degraders.