A UNITED KINGDOM PERSPECTIVE ON RESEARCH ON SLUDGE DISPOSAL TO SEA AND RECYCLING TO LAND

This paper gives an account of how the UK has made use of its own domestic research together with research carried out elsewhere, especially in Europe and North America, to develop a scientific basis for controls on sludge disposal to sea and biosolids recycling to land.Sea disposal of sludge ceased in the UK at the end of 1998 as part of the requirements of the Urban Wastewater Treatment Directive 91/271/EEC. The reasons for closing this outlet were largely to do with harmonisation and equality of options as some Member States did not have access to dispersive coastal waters suitable to take sludge with minimal environmental impact. Sea disposal as practised in the UK involved dispersal of sludge from ships at licensed sites remote from beaches and where environmental impact would be minimal. Sea disposal has accounted for about 30% of sludge production, and more on a regional basis as in Scotland. The disposal sites had been licensed by government since 1974. The sites have been subject to environmental monitoring, including water and sediment quality and surveys of benthic organisms. At some sites more detailed studies were undertaken including, for instance, of fish quality and health.Landspreading of biosolids has usually been the preferred route on the basis of best practicable environmental option (BPEO) analysis, at least in those areas where suitable land (agriculture, forestry, reclamation or other) is accessible. It has not always enjoyed positive media coverage especially when expansion of the outlet was predicted as a result of Directive 91/271/EEC. It remains the principal outlet for UK biosolids, accounting for about 50% of biosolids production, although only about 1% of the available land is needed each year for this amount of landspreading.Active promotion of landspreading of biosolids began in the UK to the west of London in the 1950s as the sewage undertakers had to find outlets for increasing amounts of sludge. The preferred product at that time was liquid digested sludge which was favoured by farmers for application to grass which responded very positively to the liquid ammonia in this type of biosolids. Field trials were undertaken to quantify the fertiliser replacement value of liquid digested sludge and the research has continued ever since to underpin agricultural practice and ensure environmental protection where biosolids are recycled to land. The research has investigated all aspects of heavy metals and other potentially toxic elements, pathogen occurrence and die-off, and organic contaminants. As this research was going on all over Europe, The European Commission ran a‘Concerted Action’(COST 681) on the topic from 1972–1990 which gave researchers the opportunity to meet periodically to exchange and discuss research findings and resulted in many publications. Canada and occasionally the USA were represented at the COST meetings.Guidelines for biosolids recycling were first introduced in the UK in 1971 and included limits for copper, nickel, zinc and boron. Since that time the guidelines have been progressively developed and acquired statutory status in 1989 through implementation of the ‘Sludge to Land’ Directive 86/278/EEC. The paper describes how research over the years has influenced the controls on landspreading of biosolids up to the present time.In the last five years, the relationship between science, expressed as risk assessment, and environmental standards for sewage sludge disposal has become less direct. Environmental standards must now be seen to embody the precautionary principle, which is seen as a cornerstone of sustainability, and to be socially acceptable to an increasingly well-informed public. These developments are leading inevitably to more demanding standards and uncertainty about future requirements. This presents a considerable quandary for both regulators and operators going into the future and threatens to jeopardise the future of biosolids recycling to land in Europe.