The heavy metals are reduced by using immobilization process. The Cr(VI) is reduced to Cr(III) by using both anaerobic and aerobic microorganisms. The presence of oxygen in aerobic condition and the reduction of Cr(VI) by microbes are generally catalyzed though soluble enzyme and lessening of Cr(VI) to Cr(III) by microbes as an eco-friendly method [77]. The bacterial strain such as E. coli, Pseudomonas putida, Desulfovibrio sp., Bacillus sp., Shewanella sp., Arthobacter sp., Microbacterium sp., and Cellulomonas sp., which reduce Cr(VI) isolated from contaminated area [78]. Arsenic compound used as an electron donor or accepter by microorganisms and possess the detoxification of arsenic, with pushes up to the membrane level of cells to eradicate As(III) from cells and metabolites of cell, finally As(V) removal arise [69]. Anaerobic bacteria are capable to reduce contaminated As(V) to As(III) and sulfate to elemental sulfur and precipitates in the form of arsenite sulfide [79]. Therefore sulfide precipitation is a useful mechanism for reduction of arsenic. The EPS of Chryseomonas luteola immobilized the metal ions such as cadmium, cobalt, nickel, and copper through adsorption [64].
Figure 3.5 Schematic diagram of bioimmobilization.
3.6 Conclusion
Biodetoxification is mainly treated by biosorption, bioleaching, biovolatilization, bioimmobilization, and bioaccumulation mechanism of bacterial cell. These processes are economically significant. EPSs present in bacterial cell are involved in bacteria and metal ion interaction and established the process of biosorption. The metals transform toxic to less toxic or less available or removed from environment by using these mechanisms. Among all mechanisms, biosorption mechanism is more effective and beneficial, and it includes ion-exchange and precipitation mechanisms. These detoxification mechanisms are eco-friendly and cost effective.
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