Biological removal of selenite from wastewater and recovery as selenium nanoparticles using inverse fluidized bed bioreactor

Abstract

This study evaluated the performance of an inverse fluidized bed (IFB) bioreactor with anerobic biomass immobilized onto Kaldness-K1 media as the biosupport material for selenite removal and recovery as selenium nanoparticle from waste stream. The effect of different process parameter and nutrient supplement on selenium removal was first studied in a batch system using serum bottles. The results revealed that among the different nitrogen substrates, ammonium bicarbonate was most suitable, whereas, lactate was found to be the preferred carbon substrate with 98% selenite removal efficiency and 90% COD removal. Later studies with the continuously operated IFB bioreactor operated at different hydraulic retention time (HRT) and different influent selenite concentrations revealed an efficient removal of selenite at 24 h HRT and 1.0 mM of influent Se (IV). Furthermore, selenium nanoparticles formed at the bottom of the bioreactor were successfully recovered with a recovery efficiency in the range 35–58% with a maximum recovery obtained at 1.0 mM selenite concentration and 24 h HRT. The extracellular produced selenium nanoparticles were found to be spherical in shape with 90–150 nm in size. Fourier transform infrared (FTIR) spectroscopy confirmed the presence of extracellular polymeric substances (EPS) as capping agent on the outer surface of Se nanoparticles.