Mercury and antimony in wastewater: fate and treatment.

Andrew J Hargreaves,Gabriela Dotro,Carlos Constantino,Jonathan Whelan,Elise Cartmell,Peter Vale

doi:10.1007/s11270-016-2756-8

Abstract

It is important to understand the fate of Hg and Sb within the wastewater treatment process so as to examine potential treatment options and to ensure compliance with regulatory standards. The fate of Hg and Sb was investigated for an activated sludge process treatment works in the UK. Relatively high crude values (Hg 0.092 μg/L, Sb 1.73 μg/L) were observed at the works, whilst low removal rates within the primary (Hg 52.2 %, Sb 16.3 %) and secondary treatment stages (Hg 29.5 %, Sb −28.9 %) resulted in final effluent concentrations of 0.031 μg/L for Hg and 2.04 μg/L for Sb. Removal of Hg was positively correlated with suspended solids (SS) and chemical oxygen demand (COD) removal, whilst Sb was negatively correlated. Elevated final effluent Sb concentrations compared with crude values were postulated and were suggested to result from Sb present in returned sludge liquors. Kepner Tregoe (KT) analysis was applied to identify suitable treatment technologies. For Hg, chemical techniques (specifically precipitation) were found to be the most suitable whilst for Sb, adsorption (using granulated ferric hydroxide) was deemed most appropriate. Operational solutions, such as lengthening hydraulic retention time, and treatment technologies deployed on sludge liquors were also reviewed but were not feasible for implementation at the works.

Highlights

Wastewater treatment works (WWTWs) receive metal inputs from both domestic and industrial sources; discharges from WWTWs have the capacity to elevate metal concentrations in rivers such that harm may occur (Stumm and Morgan 2012)
Ribeirao Preto WWTWs (Brazil) serves over 1000 diverse industrial activities and the majority of these are defined as small businesses, many contribute to the 0.1 μg/L Hg concentration observed in crude samples (Oliveria et al 2007)
A mean crude Hg concentration of 0.1 μg/L was recorded at Henriksdal WWTWs (Sweden) with dental inputs recognised as having a prominent contribution (Sorme and Lagerkvist 2002)

Summary

Introduction

Wastewater treatment works (WWTWs) receive metal inputs from both domestic and industrial sources; discharges from WWTWs have the capacity to elevate metal concentrations in rivers such that harm may occur (Stumm and Morgan 2012) Whereas metals such as copper and zinc have been the subject of numerous studies (Chipasa 2003; Beck and Birch 2012; El Khatib et al 2012), trace metals such as mercury (Hg) and antimony (Sb) are not monitored on a regular basis (Choubert et al 2011). The WFD currently requires that Hg concentrations do not exceed 0.05 μg/L as an annual average (AA) and 0.07 μg/L as a maximum allowable concentration (MAC) in inland surface waters. For Hg, the criterion continuous concentration (CCC) is 0.77 μg/L and the criteria maximum concentration (CMC) is 1.4 μg/L, whilst Sb concentrations may not exceed 5.6 μg/L

Methods

Results

Conclusion