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Hall T.,WRc
Chemical Engineer

Tom Hall examines the disinfectants that are responsible for keeping drinking water clean. Water treatment processes designed to remove natural particulate or colloidal material provide a degree of disinfection through the removal of micro-organisms, particularly the protozoan pathogens. However, in the UK it is standard practice to include a purpose-designed disinfection stage within the treatment stream, usually as the final treatment process and usually chemically based. The process is managed by controlling the chlorine dose to achieve a target residual concentration in the water, leaving the contact tank to provide the minimum design Ct. Using chlorine has led to some concerns over organo-chlorine by-products, which arise from reaction with natural organic material in water. Maximum concentrations are regulated worldwide. Chlorine dioxide is used as a primary disinfectant and in distribution in some European countries, but not in the UK because of limitations on the by-products, chlorate and chlorite, under UK regulations. Source

Barnes B.,UK Environment Agency | Glennie E.,WRc | Davey A.,WRc | Thomas J.,University of Sussex
Land Contamination and Reclamation

This paper discusses the 2008 Chartered Institute of Environmental Health (CIEH) and CLAIRE 'Guidance note on comparing soil contamination data with a critical concentration'. It discusses the different statistical tests and the underlying assumptions within the document with reference to worked examples. We conclude that in contrast to CIEH/CL:AIRE 2008, the t-est can be used for the Environmental Protection Act 1990 Part 2A scenario whatever the distribution of the underlying data set, as long as the dataset is not negatively skewed. The implications of sample size and statistical power are also considered. Collecting a very limited number of samples will mean that the assessor has little chance of rejecting the null hypothesis. In this situation a non-significant result is difficult to interpret and the compliance monitoring is largely a pointless exercise. © 2010 EPP Publications Ltd. Source

Jonsson J.,WRc | Camm R.,WRc | Hall T.,WRc
Journal of Water Supply: Research and Technology - AQUA

Glyphosate is a broad spectrum, non-selective herbicide, widely used for the post-emergence control of annual and perennial weeds in a variety of applications. Although of low toxicity, its presence in drinking water is undesirable and can cause drinking water compliance failure in the EU if found at concentrations >0.1 μgL-1. Treatment methods such as ozonation and activated carbon are currently used for pesticide degradation and removal. This article provides a review of the reported efficiency in removal and degradation of glyphosate and aminomethylphosphonic acid (AMPA) by some commonly employed treatment options. Additional experiments have been carried out where knowledge gaps have been identified. Oxidants used in water treatment, particularly Cl2 and O3, are highly effective in degrading glyphosate and AMPA. Removal by coagulation and activated carbon is ineffective as a barrier against contamination in drinking water. UV treatment is also ineffective for glyphosate and AMPA degradation but the combination of UV/H2O2 provided significant degradation of glyphosate, but not AMPA, under the conditions investigated. UV/TiO2 treatment can degrade significant amounts of glyphosate but the irradiation time needed is long. Removal or degradation by bank filtration, slow sand filtration, ClO2 and membranes is variable but can provide significant removal under the right conditions. © IWA Publishing 2013. Source

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