Enhanced removal of veterinary antibiotic from wastewater by photoelectroactive biofilm of purple anoxygenic phototroph through photosynthetic electron uptake

Abstract Purple anoxygenic phototrophs have been recently attracted substantial attention for their growing potential in wastewater treatment and their diverse metabolic patterns can be regulated for process control and optimization. In this study, the photoheterotrophic metabolism of Rhodopseudomonas palustris (R. palustris) was modified by photosynthetic electron uptake using a poised electrode which was explored to enhance removal of veterinary antibiotic from aqueous medium. The results showed that R. palustris grown as biofilm on electrode surface had excellent photoelectroactive activity and the photosynthetic electron uptake from the photoelectroactive biofilm significantly enhanced antibiotic florfenicol (FLO) degradation. The specific degradation rate of FLO at the set electrode potential of 0 V was 2.59-fold higher than that without applied potential. Enhanced co-metabolic reductive dehalogenation by use of the photosynthetic electrons extracted from co-substrate was mainly responsible for FLO degradation which eliminated the antibacterial activity of FLO. The electrode potential controlled the processes of photosynthetic electron uptake and its resultant FLO degradation. The fastest degradation of FLO was achieved at 0 V because the electrode poised at this potential stroke a proper balance between the enhancing photosynthetic electron uptake by serving as electron acceptor and minimizing competition with FLO for the photosynthetic electron from co-substrate. The activity of photoelectroactive biofilm was not negatively affected by FLO at environmental relevant concentration, suggesting its great potential for removal of antibiotic contaminants in wastewater. R. palustris could serve as a reservoir for floR resistance gene but its abundance can be diminished by choosing appropriate electrode potential.