Assessing the Relative Contribution of Wastewater Treatment Plants to Levels of Metals in Receiving Waters for Catchment Management

摘要

The selection of control measures for reducing metal contamination in rivers has targeted point sources such as wastewater treatment plants (WWTPs) and industrial discharges without a proper evaluation of their relative contribution to metal loads at the catchment level. The necessity of controlling pollutant inputs in a sound and cost-effective way to prevent the deterioration of chemical and ecological quality of receiving waters has highlighted the need for appropriate source assessment. As metals in rivers emanate from a wide range of sources, it is necessary to understand their relative contribution in order to reduce effectively the concentrations in receiving waters. This study presents a simple method for calculating the relative contribution of WWTPs to levels of metals in receiving waters as applied to the Aire-Calder catchment in the UK. In this catchment, the apportionments to WWTP effluents of metal levels in rivers were 37, 31, 36 and 60 % of total cadmium (Cd), lead (Pb), mercury (Hg) and nickel (Ni), respectively. Spatial metal distribution in rivers with maximum concentrations of 0.47 μg L~(-1) for Cd, 8.54 μg L~(-1) for Pb, 0.05 |ig L"1 forHg and 10.17 μg L~(-1) forNi caused by the discharge of WWTP effluents was estimated. The findings demonstrate that the proposed approach using quantification of metal loads and estimation of concentrations in receiving waters could adequately calculate the relative contribution of WWTP effluents to metal levels in receiving waters. Applications to various river catchments using site-specific data would further validate the effectiveness of the approach proposed.