Isolation and characterization of heavy metal removing bacterial bioflocculants

Thirteen metal-tolerant bacteria capable of producing metal-removing bioflocculants were isolated from an industrial effluent sample. Pseudomonas sp. was found to be the pre-dominant species among the isolates (8 out of 13), followed by Herbaspirillium spp. (4) and one Paenibacillus sp. The flocculating activity of bioflocculants produced by these microorganisms was assayed using the kaolin clay. The heavy-metal-removal efficiency was determined using atomic absorption spectrometer before and after mixing the bioflocculant with the heavy metal solutions. Bioflocculants exhibit different flocculating abilities of removing kaolin clay in the presence of different heavy metals. Bioflocculants produced by Pseudomonas sp. CH9 possessed the highest flocculating activity (1.8) compared to the remaining bioflocculants. The flocculating activities of CH11 and CH13 increased to 0.95 and 0.87 in the presence of Pb2+ and to 0.89 and 0.98 in the presence of Hg2+ respectively from 0.015 in the presence of Ca2+ in the standard kaolin clay assay. Up to 90% of Pb2+ was removed by Pseudomonas sp. CH8 bioflocculants. Seventy-eight percent of Hg2+ and 66% of Cd2+ was removed by Pseudomonas sp. CH6 and Herbaspirillium sp. CH13 bioflocculants respectively. Most of the bioflocculants demonstrated a higher percentage of heavy-metal removal at low concentrations. This study demonstrates that microbial bioflocculants have potential to be used as an alternative bioremedial tool for industrial effluents and wastewater treatments which are co-contaminated with heavy metals.