Microalgae-Mediated Heavy Metal Removal From Wastewater: A Review on Recent Perspectives and Future Trends

Human activities such as the development of industries, mining, disposal of heavy metal and electronic wastes, use of coal, leaded gasoline, pesticides, and various fertilizers cause contamination of water resources with heavy metals such as Zn, Hg, Cd, Pb, and Cr. Exposure to heavy metals can cause acute poisoning, cancer, damage to the kidneys, liver, and lungs, and even death. Recent innovations introduce modern and environmentally friendly techniques to remediate heavy metal contamination in wastewater. Meanwhile, the biological processes using algal species are gaining importance for sustainability, simplicity, and environmental benefits. Phytoremediation, as this method is known, involves intracellular and extracellular mechanisms, including cell surface biosorption, intracellular accumulation, and interaction with antioxidant enzymes. Such mechanisms change the pollutants by reducing their toxicity and reactivity, ultimately leading to their detoxification or transformation into less harmful compounds. The type of microalgae, the concentration and type of heavy metals, and the physicochemical conditions of the environment are factors that affect the efficiency of this process. In addition, the toxic effects of these elements on the environment and living organisms and their removal/detoxification mechanisms by microalgae and finally the challenges and perspectives of this method were investigated. The commercial application of microalgae still demands attention because of extended retention times compared to other methods, which leads to the need for larger areas. Thus, further improvement of this technique for optimal results is still needed and necessitates detailed analysis.