Biosorption of Heavy Metals and Dyes from Industrial Effluents by Microalgae

Abstract

Discharge of industrial effluents containing heavy metals and dyes is of concern as the pollutants may adversely affect the environment by contaminating surface- and groundwater resources. Heavy metals and dyes are very persistent and may pose a threat to various organisms and human health. Physicochemical methods such as chemical precipitation and adsorption are commonly used to remove heavy metals, while flocculation, flotation, membrane filtration and activated carbon are used to treat dye wastewater. However, these conventional technologies are costly and may not be fully effective in removing heavy metals and dyes. Biosorption refers to the ability of living or dead biomass to sequestrate pollutants such as heavy metals and dyes through passive binding. The biosorption capacity of microalgae is due to their high surface-to-volume ratio and high binding affinity. The mechanisms involved in biosorption include ion exchange, complexation, precipitation and physical adsorption. Functional sites on the cell wall of microalgae involved in biosorption include carboxyl, imidazole, sulfhydryl, amino, phosphate and sulphate moieties. Despite the extensive research in this area, there has been limited success in commercializing the technologies using algal biosorbents. Detailed economic and market analyses are required to assess the feasibility of the technologies. Integration of wastewater treatment and biofuel production with heavy metal and dye removal using biosorption process would be an attractive approach. Apart from treating the wastewater, the microalgae can be harvested for biofuel production, and the residual biomass can be used for biosorption of heavy metals and dyes.