Sewage Sludge Disposal: Current and Future Options

Abstract

Sewage sludge is an inevitable product of all conventional sewage treatment processes. Disposal of sludge in an economic and environmentally-acceptable manner is becoming generally more difficult. Sludge quantities are rising and disposal options decreasing. Disposal will increasingly require positive and careful management. There are four basic destinations for sludge - agriculture, other types of land, the sea or minor outlets. Treatment methods are available for the production of nine basic types of end-product to suit particular disposal requirements. The new EC Directive will regulate sludge to agriculture and will require that all sludge to farmland is treated unless it is immediately buried under the soil. Sludge to agriculture (grassland or arable) is subject to soil metal limits and to the need to minimise the risk of disease transmission. Sludge to landfill is subject to increasing constraints, particularly on physical stability. Sludge to sea is still practised by the UK but is closely controlled by Government licence and a requirement for monitoring. Minor outlets such as oil production, protein extraction etc are only at the experimental level. A computer program (WISDOM) provides a means of evaluating the short/long-term viability of alternative treatment and disposal options to identify the most economic and environmentally-acceptable strategy on an objective basis.