Solar photocatalytic oxidation of recalcitrant natural metabolic by-products of amoxicillin biodegradation.

Abstract The contamination of the aquatic environment by non-metabolized and metabolized antibiotic residues has brought the necessity of alternative treatment steps to current water decontamination technologies. This work assessed the feasibility of using a multistage treatment system for amoxicillin (AMX) spiked solutions combining: i) a biological treatment process using an enriched culture to metabolize AMX, with ii) a solar photocatalytic system to achieve the removal of the metabolized transformation products (TPs) identified via LC-MS, recalcitrant to further biological degradation. Firstly, a mixed culture (MC) was obtained through the enrichment of an activated sludge sample collected in an urban wastewater treatment plant (WWTP). Secondly, different aqueous matrices spiked with AMX were treated with the MC and the metabolic transformation products were identified. Thirdly, the efficiency of two solar assisted photocatalytic processes (TiO 2 /UV or Fe 3+ /Oxalate/H 2 O 2 /UV–Vis) was assessed in the degradation of the obtained TPs using a lab-scale prototype photoreactor equipped with a compound parabolic collector (CPC). Highest AMX specific biodegradation rates were obtained in buffer and urban wastewater (WW) media (0.10 ± 0.01 and 0.13 ± 0.07 g AMX  g biomass −1  h −1 , respectively). The resulting TPs, which no longer presented antibacterial activity, were identified as amoxicilloic acid ( m / z  = 384). The performance of the Fe 3+ /Oxalate/H 2 O 2 /UV–Vis system in the removal of the TPs from WW medium was superior to the TiO 2 /UV process (TPs no longer detected after 40 min ( Q UV  = 2.6 kJ L −1 ), against incomplete TPs removal after 240 min ( Q UV  = 14.9 kJ L −1 ), respectively).