Mechanisms of Heavy Metal Separation in Bioelectrochemical Systems and Relative Significance of Precipitation

Heavy metal pollution is a severe environmental issue. Most heavy metals are toxic and can threaten human health. Conventional methods such as precipitation and adsorption have been used to separate heavy metals from aqueous solution. Due to the high energy and chemical cost of conventional methods, there is a need for new cost-effective and sustainable technologies to separate heavy metals. Bioelectrochemical systems (BES) have been reported as an efficient method. To provide a clear understanding of heavy metal separation in BES, this review summarizes previous research work on BES applications for separating heavy metals and discusses various removal mechanisms, including electrochemical reduction, precipitation and adsorption. The separation of various heavy metals such as cobalt, cadmium, copper, mercury, gold, silver, vanadium, chromium, nickel, zinc and selenium are also discussed. Comparing with the previous reviews which focused on the mechanism of the electrochemical reduction of heavy metal separation in BES, we emphasize important roles of precipitation in metal separation.