Bioaugmentation for the removal of the antiobiotic sulfamethoxazole in wastewater

Antibiotics are intensively used in medical therapy, veterinary medicine, and the farming indus-try, resulting in continuous releases of the compounds into WWTPs and fresh water resources. Since conventional WWTPs are not effective to completely remove antibiotics, there are growing concerns related to the influence of its mode of action to microbial communities, as well as the risk to human health, by promoting and spreading antibiotic resistance. The aim of this research is to develop an ef-fective and practical bio-augmentation strategy for the removal of the antibiotic sulfamethoxazole SMX - one of the most frequently detected synthetic sulfonamide antibiotics in wastewater. A strain identified as Achromobacter denitrificans PR1, previously isolated from activated sludge (AS), was found as a potential organism for bio-augmentation for SMX removal in polluted waters. The SMX degradation kinetics of this organism are stimulated in the presence of biogenic substrates, e.g. ace-tate/succinate, and are two to three orders of magnitude higher than the degradation kinetics of activat-ed sludge at environmentally relevant concentrations. Bioaugmentation of AS with the strain PR1 (batch experiments) led to superior biotransformation rates of SMX (by sixty times) compared to AS, within a complex carbon environment in WWTPs. Biological degradation models were calibrated to describe accurately the fates of sulfamethoxazole and the two human metabolites, e.g. N4-acetyl-SMX and SMX-N1-Glucuronide, in the systems, under various redox conditions. The strain was subsequently bioaugmented into membrane bioreactors operated under aerobic conditions, which led to the enhancement and stabilization of the SMX removal, especially when SMX shock loads occurred. Changing hydraulic retention times, and thus the availability of primary substrates, was found to affect the cometabolism of SMX by the bioaugmented strain in activated sludge. After the bioaugmentation, the loss of viability of the introduced strains was observed and re-inoculation of the degrading strain seems to be a logical solution to maintain removal efficiency of the target compound.