Factors and mechanisms regulating heavy metal phycoremediation in polluted water

Abstract Rapid advances to industrialization and population increases have put aquatic ecosystems at high risk of pollution from various industrial and municipal effluents. The effluents consist of heavy metals (HM), micropollutants, nutrients, microorganisms, solids, particulates and dissolved matter. To this effect, pollutant remediation in such ecosystems is inevitable and of interest in global research. In this study, phycoremediation and its potential to bioremediate HM from polluted aqueous solutions is of focus. The factors influencing the process and the mechanisms involved are explored. The study established that available functional groups in microalgae, cell surfaces characteristics, type of microalgae species used, nutrient availability, size of biosorbent and metal concentration are some environmental factors, which influence phycoremediation success. Uptake of HM from contaminated water is regulated by mechanisms such as volatilization, bio-methylation, enzyme catalyzation, compartmentalization, extracellular polymeric substances-complexation, extracellular biosorption and intracellular bioaccumulation. To ensure high pollutant removal efficacy, improved adaptability of microalgae to HM-polluted systems and high resilience to attack by foreign agents, a number of mechanisms can be adopted. These include microalgal pretreatment with chemicals, bioengineering and biotechnological advances such a gene encoding, synthesis of transgenic proteins, gene overexpression, modification of microalgal cell surfaces with nanoparticles and the use of a consortium of microbes. This study noted that optimizing the discussed factors and mechanisms will promote field-scale application of phycoremediation in water treatment to remove HM.