The majority of waste water drainage in the U.K. is provided by municipal sewage treatment works. However, in some rural locations it is not uncommon to find that mains drainage in inaccessible and it’s the responsibility of the land owner to find an alternative method of waste water disposal.
Certain commercial applications such as pubs, hotels, theme parks, visitors centres and industrial units will require the installation of a ‘packaged sewage treatment plant’ to receive and treat the waste water. These sewage treatment plants are typically designed to treat the sewage to such degree that the resulting ‘treated effluent’ is suitable for discharge to a natural watercourse or underground drainage field / soakaway.
Commercial sewage treatment plants typically contain primary settlement, biological treatment and final settlement zones. They provide treatment for Biological Oxygen Demand (BOD), Suspended Solids (SS) and ammonia (NH4). Some systems have an option of ‘add-on’ sand filters to provide further treatment before discharge. The Environment Agency in England and Wales are responsible for setting the quality of effluent the treatment plant would need to meet, and this standard can vary on each application.
Applications where commercial catering takes place will generate significant volumes of grease and fat which should not be allowed to enter the sewage treatment plant. In these applications a suitably sized grease trap should be installed upstream of the sewage treatment plant.