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Centre for Earth and Environmental Science Research

Evaluation of the impact of treated wastewater discharges on river water phosphorus and metal concentrations


Executive Summary
ResearchersHelen Millier, CEESR
Dr P.S Hooda, CEESR
Professor Kym Jarvis, CEESR
Funding Body/SourceKingston University
Duration2006 - 2009
Project SummaryThe overall aim of this project is evaluate the extent of phosphorus and metal inputs from STW and their impact on river water quality.
The aim will be achieved through the following STW inputs-specific objectives:
(1) Assess the impact on phosphorus concentrations and daily loads in receiving waters. This will include total, particulate and soluble reactive forms of phosphorus;
(2) Assess the impact on a range of potentially toxic metals, both in terms of concentrations and loads, to include total, particulate and soluble forms of metals.
(3) Investigate the role and significance of particulate and colloidal material in contaminant (metals and phosphorus) transport and mobilisation-immobilisation processes.
(4) Quantify the inventories, bioavailability and distribution coefficients of metal contaminants and phosphorus in riverbed sediments, both upstream and downstream points of STWs.
(5) Evaluate sediment quality with respect to metals, as there are no agreed guidelines for phosphorus. However, using results from #4, the potential of sediments becoming source of metals and phosphorus to overlying water will be assessed.

Background

The Water Framework Directive (European Community 2000) aims to restore all waters to 'good ecological status' by 2015. This necessitates understanding and regulation of the inputs of substances to surface waters, which may impair water quality from chemical and ecological standpoints.

Within the UK, little information is available on inputs from sewage treatment works (STW) in the context of water quality. Water companies are granted licences based upon their wastewater treatment specifications. It is therefore logical to assess the pollution potential of treated wastewater inputs as part of the process for compliance with the WFD (European Community 2000).

Inputs to rivers and streams from STW's have been identified as a substantial source of pollutants (Alcock et al., 1999; Neal, 2005; Hernando et al.,. 2006). STW inputs can include a cocktail of chemicals, such as nutrients, pesticides, metals and other emerging contaminants (e.g. endocrine disrupting chemicals). However, metals (e.g. As, Pb. Cd, Cr, Ni, Cu, Zn) and nutrients (N and P) are particularly relevant because of their persistence and storage in sediments (metals) and implication for eutrophication (nutrients). Nitrogen (nitrate-N) and phosphorus are key water quality issues of relevance to the WFD and to much of the lowland UK (EA, 2000). These two nutrients come primarily from sewage and agricultural sources (Jarvie et al., 2002; Neal et al., 2005).

Pollution sources such as acid-mine drainage (Jeong et al., 1999) urban runoff (Davis et al., 2001), leaching and runoff from municipal or industrial waste amended soils (Unlu 1998; Gove et al., 2001) are renowned for introducing metals to receiving surface- and ground-waters. However, STW inputs as a source of surface water contamination with heavy metals has received little attention.

Progress to date

Sewage Treatment Works (SWT's) at Hogsmill Valley, Berrylands and Lyne Lane, Thorpe, discharge into small rivers where no other potential source of contaminant exists. River water samples up and downstream of their wastewater outflows are being analysed for P species and heavy metals on a regular basis. Flow and depth measurements are taken manually, and flow data obtained from the E.A., to allow calculation of metal and P loads as well as concentrations to be used to determine the potential effect of discharges into the receiving waters.

Sediment samples from a number of locations up and downstream of these STW's have been taken for analysis of P and metals. In addition, one off sampling of other STW's is being undertaken to provide spatial information on the possible progress of contaminants along the river path.

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