RESUMO
The knowledge gaps regarding the degradation of sulfamethoxazole (SMX) in biofilters include the effect of aeration, constant feeding with readily biodegradable organic carbon and the presence of reactive media such as manganese oxides (MnOx). Thus, the goal of this study was to assess the removal of SMX in lab-scale biofilters with various operation variables: aeration, presence of MnOx as an amendment of filtering medium and the presence of readily biodegradable organic carbon (acetate). The sand used in the experiment as a filtering medium was previously exposed to the presence of SMX and acetate, which provided acclimation of the biomass. The removal of SMX was complete (>99%) with the exception of the unaerated columns fed with the influent containing acetate, due to apparent slower rate of SMX degradation. The obtained results suggest that bacteria were able to degrade SMX as a primary substrate and the degradation of this compound was subsequent to the depletion of acetate. The LC-MS/MS analysis of the effluents indicated several biotransformation reactions for SMX: (di)hydroxylation, acetylation, nitrosation, deamonification, S-N bond cleavage and isoxazole-ring cleavage. The relative abundance of transformation products was decreased in the presence of MnOx or acetate. Based on the Microtox assay, only the effluents from the unaerated columns filled with MnOx were classified as non-toxic. The results offer important implications for the design of biofilters for the elimination of SMX, namely that biofilters offer the greatest performance when fed with secondary wastewater and operated as non-aerated systems with a filtering medium containing MnOx.