Heavy metal removal from aqueous solution using sodium alginate immobilized sulfate reducing bacteria: Mechanism and process optimization.

Heavy metal removal was evaluated using sodium alginate immobilized sulfate reducing bacteria (SRB) under batch and continuous mode. Under batch conditions, more than 95% metal removal was achieved due to formation of insoluble metal sulfides exterior to the bead surface. Best heavy metal removal results were obtained at 48 h hydraulic retention time (HRT). Metal loading rate values upto 2.20 mg/L∙h for Fe(III), Zn(II), Cd(II), Pb(II) and Ni(II) and upto 4.29 mg/L∙h for Cu(II) were proved to be favorable for their removal using the continuous downflow column reactor packed with the immobilized SRB beads. Continuous metal removal from a mixture of the heavy metals showed that Cu(II) removal was maximum (99%), followed by Zn(II) (95.8%) and other metals at their respective low inlet concentrations. However, the removal values were reduced at a high inlet concentration of these metals, which matched well with low COD and sulfate reduction values.