Production and characterization of heavy-metal removing bacterial bioflocculants

Abstract

Bioflocculants produced by Herbaspirillium sp. CH7, Paenibacillus sp. CH11, Bacillus sp. CH15 and Halomonas sp. are potential flocculanting agents in the treatment of industrial wastewater effluents. Up to 250% increases in bioflocculant production were achieved by manipulation of the media composition. Increases in peptone and glycerol contents, up to 2 and 3%, respectively enhanced the bioflocculants production. With the exception of Herbaspirillium sp. CH7, all isolates preferred higher yeast extract content for bioflocculant production. Physicochemical analysis showed most of bioflocculants produced appeared to contain high protein content, then carbohydrate. All bioflocculants contained similar hexosamine and uronic acid contents in the range of 0.0115 to 0.0150 mM and 0.0054 to 0.0068 mM, respectively. Purified bioflocculants produced under optimized conditions possessed higher flocculating activities (up to 14-fold increases) in comparison to those under the control conditions with the exception of that from Herbaspirillium sp. CH7. A decrease in bioflocculant concentration from 10000 ppm to 1 ppm resulted in a significant increase in the removal percentages of Pb⁺², Zn⁺² and Hg⁺² with the optimal dosage of 1 to10 ppm. Bioflocculants in this study removed Cd⁺² effectively only at 10000 ppm, but not at the lower concentrations. This Cd⁺²-removing capacity of bioflocculant could be further stimulated by an increase in temperature. The pH requirement for maximum flocculating activity seems to be varied for different strains of microorganisms.

Key words: Bioflocculant, heavy metal removal, physiochemical properties, pH, temperature.