Biosorption of Dye and Heavy Metal Pollutants by Fungal Biomass: A Sustainable Approach

Abstract

Dye and heavy metal pollutants present in the aquatic and terrestrial ecosystem are hazardous to the environment as well as the human health due to their toxicity even at the lower concentration. A significant volume of dye and heavy metals released in industrial effluents, i.e., textile, tannery, electroplating, mines, and dyes, are polluting the environment in an inorganic or organic form. Several strategies have been applied for the removal of dyes and to detoxify heavy metals using the techniques, viz., landfill, incineration, solvent extraction, recycling, filtration, evaporation, and chemical precipitation. However the average yield, high-cost, toxic by-product and the production of secondary environment pollutants limit their application. Biosorption is an alternative approach for the bioremediation of the dyes and heavy metals from the environment using microbial biomass either live or dead. Biosorption of dyes and heavy metals by using potential fungal biomass is more feasible compared to the bacteria and yeast due to efficient capability of dye and heavy metal absorption, intracellular metal immobilization, bioaccumulation, and presence of the enzymes that helps in conversion of metals into their oxides. Fungal spp., i.e., Aspergillus, Trichoderma, Verticillium, Fusarium, and Penicillium, are well known for their accessibility as biosorbent. Biosorption mechanism involved two different modes for the uptake of dyes and heavy metals from the environment which are fungal cell wall structure and cell metabolism. Various physiochemical parameters play important role in the biosorption process, i.e., pH, temperature, biosorption rate, initial concentration of dye/heavy metal, metal speciation, dye/heavy metal solubility and form, binding site of the metal, and contact time. Fungal biomass concentration, cell wall composition, extracellular product formation, biomass dosage, and dissolved oxygen are some of the environmental factors that influence dye and heavy metal sorption efficiency of the fungal biomass during the process. Chemisorption, adsorption-coupled reduction process, ion exchange resins, metal precipitation, and electrostatic interaction between pollutants and fungal biomass are the key components for the biosorption process through fungal biomass. Equilibrium isotherm equations are used to describe the relationship between dyes or metal ions and biosorbent using different models to obtain experimental adsorption data. Two-parameter models Langmuir, Freundlich, Temkin, Dubinin- Radushkevich, and Flory- Huggins and three-parameter models Sips, Khan, Toth, Redlich- Peterson, and Radke-Prausnitz provide details about adsorbent’s surface properties, affinities, and adsorption dynamics. Metal recovered from the fungal biomass reduces the need of mining and extraction/purification cost. Regeneration of the fungal biomass enhances the biosorption capacity after a number of cycles. Biosorption can be emerged as cost-effective and nontoxic and as green approach for the removal and recovery of dyes and heavy metals from industrial effluents.