A Review of Treatment Process Options to Meet the EC Sludge Directive

New UK regulations from June 1989 will enforce the provisions of an EC Directive on the use of sewage sludge in agriculture. Among the requirements is one that sludge should be treated before surface application to farmland. Treatment is needed to reduce 'significantly' both the fermentability of sludge and the health hazards resulting from its use on farms. In the UK, the health risks associated with sludge are principally beef tapeworm ( Taenia saginata and cysticercosis) and Salmonellosis. Research on the effects of various treatment processes on pathogens has shown the conditions required to produce a 90% reduction of T. saginata and Salmonellae. This information has been used as a basis for describing a list of 'effective' treatment processes and process conditions - as given in a new UK National Code of Practice on the use of sludge in agriculture. The uprating of existing treatment plant, or provision of new plant, to meet the Code of Practice recommendations could involve significant costs. A comparison of the economics of each of the 'effective' treatment processes for different population sizes shows a fairly wide range of net present costs. In general, increased sludge quality means increased costs.