Microalgae in removing heavy metals from wastewater – An advanced green technology for urban wastewater treatment

The wastewater bioremediation is an emerging research area to meet the existing/increasing water crisis challenges. The Heavy metals persist in water bodies, which can bioaccumulate in the food chain and cause serious health and environmental problems. The deteriorating effects of heavy metals both on human health and the environment have drawn great attention and have become a major area of study. Phycoremediation is one of the most promising areas being explored currently. The conventional methods such as chemical precipitation, ion exchange, membrane filtration, floatation, coagulation-flocculation and electrochemical methods inherit limitations in bringing down the cost of treatment, increasing efficiency and formation of toxic sludge as secondary pollution. The phycoremediation of wastewater serves to be green technology. This review highlights current advances in using different species of microalgae to treat various industrial effluents and mechanism of removal of heavy metals from them. A comprehensive look into microalgae-based systems (MBSs) has been covered to assess the efficiency of different species through extracellular and intracellular mechanisms in biosorption, bioaccumulation and detoxification of various heavy metals. It brings into focus all the emerging technologies in current times that have utilised microalgae in the bioremediation of urban wastewater systems. In addition, challenges, bottlenecks and future prospects of phycoremediation are also discussed with a focus on achieving a circular bioeconomy in water management.