An Evaluation of Metal Removal During Wastewater Treatment: The Potential to Achieve More Stringent Final Effluent Standards

Abstract

Metals are of particular importance in relation to water quality, and concern regarding the impact of these contaminants on biodiversity is being encapsulated within the latest water related legislation such as the Water Framework Directive in Europe and criteria revisions to the Clean Water Act in the USA. This review undertakes an evaluation of the potential of two stage wastewater treatment consisting of primary sedimentation and biological treatment in the form of activated sludge processes, to meet more stringent discharge consents which are likely to be introduced as a consequence. The legislation, sources of metals and mechanisms responsible for their removal are discussed, to elucidate possible pathways by which the performance of conventional processes may be optimized or enhanced. Improvements in effluent quality, achievable, by reducing concentrations of suspended solids or biochemical oxygen demand may also reduce metal concentrations although meeting possible requirements for the removal of copper my be challenging. Running head:The removal of metals in wastewater treatment.

Performance of UK wastewater treatment works with respect to trace contaminants

“…Although AS works have been reported to achieve higher removals (50% for dissolved copper) than TF, the removal values reported for this process also vary widely. However, data are usually reported for total metals with removal ranging from 25% (Roberts et al, 1977) up to 79% (Ziolko et al, 2011). Therefore, the ultimate performance, as observed in this study, is highly variable and depends on both physico-chemical characteristics of the wastewater (Constantino et al, 2011) and operational parameters (Ziolko et al, 2009).…”

“…Therefore, the ultimate performance, as observed in this study, is highly variable and depends on both physico-chemical characteristics of the wastewater (Constantino et al, 2011) and operational parameters (Ziolko et al, 2009). An understanding of metal behaviour and removal processes has led to the conclusion that reducing TSS and BOD will lead to reduced concentrations of dissolved and total metals in effluents (Ziolko et al, 2011). The regulated and emerging organic trace substances such as industrial chemicals TBT, triclosan and DEHP, along with the pharmaceuticals, PAHs and BDEs (47, 99), pose an important compliance risk on account of the relatively low EQS that have been set or proposed (Gardner et al, 2012).…”

Investigation of the inhibitory effects of heavy metals on heterotrophic biomass activity and their mitigation through the use of natural minerals

“…[16,17] Metal toxicity depends on several parameters, such as the intrinsic toxic properties of the specific metal species, their bioavailability, metal forms (dissolved or particulate, free ion or complex, sorbed on sludge), contact time between metals and microorganisms, pH, metal concentration, suspended solids concentration, sludge age, microbial acclimation to the particular heavy metal, concentrations of other cations or other inert substances that are present in the wastewater, type of bacteria in the mixed liquor. [9,18,19] The presence of more than one metal in wastewater and their simultaneous interactions may have synergic, antagonistic or additive effects. [4,20] Microorganisms develop resistance mechanisms in order to acclimate to heavy metals.…”

“…[4,8] The removal of heavy metals by activated sludge in wastewater treatment plants can be effective, provided the metals are in low concentrations. [9] The main removal mechanisms include precipitation, physical entrapment of particulate metals by biomass, sorption of soluble metals on extracellular polymeric substances (EPS), intracellular accumulation and volatilization of metals. [10,11] The toxic action of heavy metals results in the inactivation of enzymatic activity, loss of floc structure, change in the structure of nucleic acids and proteins, change in the cell permeability, loss of sludge viability, damage of lysosomes resulting in the release of hydrolytic enzymes that cause cell damage.…”

Mercury removal from municipal secondary effluent with hydrous ferric oxide reactive filtration

“…Municipal and industrial wastewater treatment facilities can be a significant source of Hg pollution to the environment, causing Hg pollution near discharges (Diez et al., ) and accounting for a meaningful portion of Hg loading to receiving waters (CEPA, ; Fricke, Götz, Schleyer, & Püttmann, ). In addition, toxicity associated with high levels of Hg in some wastewaters may negatively affect biological treatment processes (Ziolko, Martin, Scrimshaw, & Lester, ). But trace levels of Hg in municipal wastewater (ng/L levels), the focus of this study, are strongly associated with suspended solids and organic matter (Balogh & Nollet, ; Hsu & Sedlak, ) in wastewater and pose little threat of direct toxicity to biological treatment processes.…”