Continuous removal and recovery of metals from wastewater using inverse fluidized bed sulfidogenic bioreactor

Abstract

Acid mine drainage (AMD) is a serious environmental hazard in many countries with historic or ongoing mining industries. Biological sulfide precipitation is an emerging technique for both removal and recovery of heavy metals from such wastewater. This study demonstrated heavy metal removal and recovery from synthetic wastewater containing Cd2+, Cu2+, Fe3+, Ni2+, Pb2+ and Zn2+ using two continuously operated sulfidogenic anaerobic inverse fluidized bed reactors (referred as R1 and R2) supplied with an influent of pH 7.0 and 3.0, respectively. In case of R1, more than 95% metal removal efficiency was achieved for all the metals except for Fe3+ (90%) and Ni2+ (85%), and in case of R2 the removal was more than 90% for all the metals except with Fe3+ (88%) and Ni2+ (82%). The metals were subsequently recovered in the form of metal nanopowder from the reactor bottom and equalizer, and the metal recovery was in the order: Cu > Pb > Cd > Zn > Ni > Fe. However R1 yielded a good recovery percentage (50–65%) of the metals in comparison with the reactor supplied with influent of pH 3.0 (46–55%). The presence of immobilized sulfate reducing bacteria onto the support material in the bioreactors were identified using field emission scanning electron microscopy. The size and shape of the biometal nanoparticles were confirmed using field emission transmission electron microscopy, which revealed their excellent potential for industrial application. This study demonstrates successful recovery of metal sulfides in the form of nanoparticles using IFBR.