Recent Developments in the Biological Filtration of Sewage to Produce High‐Quality Nitrified Effluents

Abstract

AbstractThe biological filtration of sewage remains the process which is most commonly used for small works in rural areas throughout the UK. In many cases, the need to produce an effluent of high quality with full nitrification is essential in order to comply with the standards set by the Environment Agency. Traditionally, design loading rates of biological filters have been based on historical experience of performance, and on relatively short‐term statistical evaluation of the performance of a large number of treatment works, using average and maximum values for flow and loading rates. Many works which were designed on such information have failed to nitrify consistently, particularly during the winter and spring months.This paper describes the detailed evaluation of six full‐scale, biological‐filtration sewage‐treatment works over a period of two years, in which there were significant changes in sewage flow rate, composition and temperature, from summer to winter. The key parameters which influence the production of high‐quality nitrified effluents were determined. The conclusions are used to provide a detailed guide on the design of conventional‐media biological filters to produce, consistently, fully‐nitrified effluents.