Fate and removal of metals in municipal wastewater treatment: a review

ABSTRACT Municipal effluents contain heavy metals in particular copper, lead, nickel, zinc and mercury. The concern regarding the impact of these contaminants in the aquatic environment is reflected in the latest criteria revisions to water-related legislation, such as the Clean Water Act in the US and the Water Framework Directive in Europe. These revisions may lower metal concentrations considered acceptable in final effluents. The study of metal behaviour within the wastewater treatment process is crucial to develop and optimise systems to achieve acceptable metal concentrations in effluent discharges. To comply with more stringent environmental quality standards, utilities may require the implementation of additional treatment technologies. This review evaluates the performance of conventional municipal wastewater treatment processes, that is, primary sedimentation and biological treatment via the activated sludge and trickling filter processes. The mechanisms and parameters influencing metal removal are discussed to evaluate how an understanding of metal behaviour within wastewater treatment processes may allow optimisation and enhancement of conventional treatment processes, or inform the selection of new technologies to enhance trace metal removal. The performance of advanced treatment technologies capable of removing metals from municipal wastewater under real-world conditions has also been evaluated.