DEVELOPING ACCEPTABLE SEWAGE SCREENING PRACTICES

Severn Trent Water screens approximately 1.9 million cubic metres of s ewage every day, producing 46000 m(3) of screenings annually. Although the company's sludge incinerators are able to burn small quantities o f screenings most of the material has to be landfilled. Over the last few years the company has investigated the areas relating to the devel opment of an environmentally sound disposal strategy at minimum cost. These areas have included the volume and ''quality'' of screenings pro duced, the costs of collection, treatment and disposal and the variati on of screenings production rates under high flow conditions. Various items of screenings handling equipment have been assessed to identify acceptable options for permanent installations. The required quality o f screenings for economic disposal has been established and a ''Qualit y Factor'', combining biological oxygen demand, density and dryness de veloped to provide a scientific basis to judge the aesthetic and comme rcial acceptability of a screenings product. This factor has been test ed widely and found to coincide with visual assessment. Data on the va riation of screenings production with sewage flow have been collected to assist with the sizing of future installations. The information obt ained has been used to develop an application matrix for screenings ha ndling equipment at large sewage treatment works. Copyright (C) 1996 I AWQ.