Microbial biosorbents: Meeting challenges of heavy metal pollution in aqueous solutions

Heavy metal pollution in the aquatic system has become a serious threat today. The chemical processes that exist are not economical for treating a large volume of water bodies of dilute metal concentration. In this endeavour, microbial biomass has emerged as an option for developing economic and ecofriendly wastewater treatment processes. Nonliving and dead microbial biomass may passively sequester metal(s) by the process of biosorption from dilute solutions. This biosorption technology has advantages of low operating cost, is effective in dilute solutions and generates minimum effluent. Here the dead microbial biomass functions as an ion exchanger by virtue of various reactive groups available on the cell surface such as carboxyl, amine, imidazole, phosphate, sulfhydryl, sulfate and hydroxyl. The process can be made economical by procuring natural bulk biomass or spent biomass from various fermentation industries. The performance of a biosorbent can further be improved by various physical and chemical treatments. The pretreatments modify the cell surface either by removing or masking the groups or exposing more metal binding sites. Immobilized biomass of these microbes offers the continuous sorption–desorption system in a fixed bed reactor. Various commercial microbial biosorbents available are AlgaSorb, AMT-Bioclaim and Bio-fix. The economics of these sorbents merit their commercialization, over chemical ion exchangers.