Novel insights into mechanism of biometal recovery from wastewater by sulfate reduction and its application in pollutant removal

Biological sulfate reduction is an emerging technique for both removal and recovery of heavy metals from wastewater. In this study, anaerobic biomass from three different sources were initially screened based on their metal removal and sulfate reduction efficiencies. The effect of metal loading on the removal of sulfate and chemical oxygen demand (COD) was further investigated to examine its toxic effect on sulfate reducing bacteria (SRB) present in the anaerobic biomass. At low metal loading conditions, biomass obtained from anaerobic rotating biological contactor (An-RBC) reactor treating metallic wastewater showed a maximum metal removal (95 +/- 0.5%), sulfate reduction (90 +/- 1.56%) and COD removal (80 +/- 0.88%); the values decreased at a high metal concentration for all the biomass. Metals were then subsequently recovered from bioprecipitates in the form of nanopowder and the metal recovery efficiency was in the order Cu > Pb > Cd > Zn > Ni > Fe > Mn. Analysis of the bioprecipitates by field emission scanning electron microscopy (FESEM) and energy dispersive X-ray diffractometer spectroscopy (EDX) confirmed that it was mainly composed of metal sulfide. Size, shape and crystallinity of the nanoparticles were determined by field emission transmission electron microscopy (FETEM) and X-ray (XRD) which revealed its excellent potential for industrial reuse and application, particularly for treating toxic dye containing wastewater. (C) 2019 Elsevier B.V. All rights reserved.