Bioelectrochemical Systems for Heavy Metal Removal and Recovery

Abstract

Although metal bearing wastes are toxic, they possess economic value and hence need attention towards remediation/recovery. Various physical and chemical methods are being practiced for treating metal laden wastewaters, but are limited owing to the problems associated with maintenance and operational costs. Biological methods that use microbes as catalyst are cost effective and easy to operate, but only a little progress has been made in terms of recovery than the treatment. Recently, there is a shift in focus from bioremediation of metal wastes towards the recovery of valuable metals which are scanty. In this context, bioelec- trochemical systems (BES) have emerged as a potential technological platform for recovery of metal ions from metallurgical waste (end-of-life products), process streams and wastewaters. In bioelectrochemical systems, microbial oxidation of organic substrate at the anode is coupled to abiotic or biotic reduction of metal ions at the cathode. With this perspective, this chapter gives an insight on the redox mechanisms of bacteria towards metal recovery along with the influence of in situ and ex situ potentials in bioelectrochemical systems. The exo-electron transport mechanism in bacteria for metal reduction and speciation is also discussed. Besides, the chapter also provides an overview on the metal speciation in bioelectrochemical systems along with electrochemical, physical and chemical methods for metal removal and recovery from wastewaters. Emerging metal recovery concepts based on bioelectrochemical systems are also presented in detail.