Raising the Standard of Operation of Small Sewage Works

Abstract

Thames Water operates about 400 sewage works in the catchment area of the River Thames, over half of these serve populations of less than 2000. These small works are mainly biological filter works but also include oxidation ditches and reed beds. Most of these works discharge to the headwaters of salmonid rivers which are used as drinking water sources and therefore have to meet high standards including in many cases full nitrification and low suspended solids. The paper describes the consent standards set for the works. Currently a number of small works do not meet these standards so Thames Water has committed itself to having all works operating within standards by 1992. There are a number of reasons for failure which include, overloading due to increase in population and water use, trade effluent discharges, and operational problems. Small works may also fail to meet their standards because they are unmanned apart from infrequent maintenance visits, and thus any plant failure may go unnoticed for some days. Thames Water is adopting a two fold strategy to overcome these problems. Firstly, so that operational problems may be identified quickly a simple cost effective system of automation and telemetry is being installed and secondly, to overcome operational and facility deficiencies, a Project Management team has been set up to identify the causes of failure, to prioritise remedial work, to recommend alternative operational strategies, if appropriate, to design and build extensions or new works if appropriate, and, if remedial works cannot be built quickly enough, to install temporary plant to ensure compliance with effluent standards.

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