Report No FR0265

March 1992

I OBJECTIVES

To provide members of the Foundation for Water Research with information concerning the strategic planning of sludge treatment and disposal facilities based on the experiences reported for major urban areas in Europe, the USA and Japan.

II REASONS

There have been significant new developments in the legislation affecting sewage sludge disposal (notably the decision to phase out disposal to sea and adoption of the EC Directive on urban waste water treatment) and more are known to be under consideration. Public concern about the conventional land-based methods of disposal is important and known to be voiced in other countries. The published plans for major urban areas can provide useful background information in the development of management strategies for the UK.

III CONCLUSIONS

1. Sludge production has increased significantly in recent years in most of the countries reviewed as a result of (a) increases in the population served by municipal sewerage systems and (b) the provision of more extensive treatment. Further increases are predicted in EC countries following implementation of the Directive on Urban Waste Water Treatment and, in some countries, the requirement to precipitate phosphorus during sewage treatment.
2. The main outlet routes (landfill, agriculture and incineration) are used to varying degrees in most countries, with significant regional differences in individual countries. No sludge is incinerated in Sweden or Norway, and sludge is not landfilled in Switzerland.
3. Although costs of sludge treatment and disposal are subject to site-specific factors, a comparative study of five operations involving sludge quantities between 50 t(ds)/y and 10000 t(ds)/y concluded that total costs (capital and operating) increased in the order agricultural use < landfill < incineration.
4. Disposal of sludge to landfill in EC countries is subject to existing Directives; new proposals concerned with the classification of wastes have been published which could restrict the types of landfill allowed to accept sludge. Existing guidelines apply in most countries on the physical condition of landfilled sludge, with chemical quality also specified in Belgium. Limited landfill capacity is the main constraint reported on the continued use of this route, although pressure exists particularly in the USA and Sweden for the beneficial utilisation of sludge.
5. A number of countries (Belgium, Denmark, Netherlands and Japan) apply more stringent quality requirements on sludge used in agriculture than those required by the 1986 EC Directive (86/278/EEC), and there is a wide-ranging debate about proposed new legislation in the USA. The annual addition of metals is also more severely limited in Denmark, France, Germany, Netherlands and Switzerland. Further pressure must therefore be expected for the existing limits to be reduced, and for the inclusion of limits on levels of dioxins. Competition from other organic wastes (manure and composts) is a significant factor in several countries, notably the Netherlands.
6. There is a potential for increasing the use of sludge in the reclamation of derelict land, including areas of colliery waste, shale tips, mine waste, china clay waste and other soil-deficient substrates. Guidelines have been adopted in Pennsylvania where substantial areas of strip-mined land have been reclaimed.
7. While present EC Directives on waste incineration specifically exclude the incineration of sewage sludge, it must be expected that similar regulatory restrictions will be applied to sludge incineration. At present the emission limits applied in Germany (TA Luft), which were revised in December 1990, are widely recognised. While public concern about the siting of incinerators is a common problem, the main constraints relate to the control of emissions to the atmosphere. Improved incineration technology is reported to be adequate to meet existing emission limits. The ash from sludge incineration typically represents 30% of the original dry solids content and is usually landfilled, although methods of utilising the material in bricks, paving slabs and other building products are being studied, notably in Japan.
8. Strategic studies of future sludge disposal in a number of urban areas have illustrated how the environmental and economic factors are assessed. Issues concern the status of the technology and the outlet route, environmental impact and working conditions, route security, costs and energy efficiency, potential for resource recovery and implications for sewage treatment.
9. Treatment and disposal options selected were as follows:

Gothenburg, Sweden: anaerobic digestion prior to pumping 7 km to underground caverns (existing) initially: affording up to 10 years' storage capacity.

Los Angeles, USA: extend existing anaerobic digestion capacity for up to twice 1988 sludge volumes, increase centrifuge capacity for dewatering and provide additional drying using rotary steam dryers; maintain diversity of disposal outlets (energy recovery, landfill, utilisation on land and composting) including existing Carver-Greenfield energy recovery facilities; future decisions needed on use of coagulants, additional generating capacity and energy recovery from digester gas.

Philadelphia, USA: emphasis on composting (following ending of disposal to sea in 1980) and utilisation of various product mixtures for targeted outlets, including strip-mine reclamation and use on farmland; landfill of surplus quantities; future consideration of heat treatment processes to recover energy value of sludge, and chemical fixation.

New York, USA: requirement to process all sludge into usable products by 1998; composting of dewatered sludge, with future plans for chemical stabilisation and thermal drying.

Amsterdam, Netherlands: centralisation of sludge processing (from existing five works); dewatering of polymer-conditioned sludge; further decisions to be taken regarding alternatives of incineration and composting/landfill of digested sludge.

The Hague, Netherlands: anaerobic digestion of thickened sludge (15 day retention); interim disposal to consolidation reservoir (Rotterdam Harbour); decisions to be taken in 1993 regarding alternatives of incineration or combustion/energy recovery.

Toronto, Canada: incineration in use since 1949 with expansion programmes in 1978, 1980 and 1987; thermal conditioning (wet-air oxidation) introduced in 1980 together with modified incinerators; recent changes reverted to anaerobic digestion, polymer conditioning, dewatering (centrifuge) prior to incineration.

Munich, Germany: incineration introduced in 1985 following the abandonment of agricultural utilisation in 1980 because of concern about the mobilisation of metal contaminants and their subsequent effects; sludge production expected to increase 50% by 2000; recent review confirmed choice of incineration with ash disposal to landfill. Sludge will be incinerated together with municipal waste (already operational), together with coal for electricity and heat generation (currently under construction, completion 1992) and in a dedicated incinerator (to be completed in 1994). Some capacity in a landfill will be reserved for emergencies. 10.A number of novel sludge utilisation techniques have been reported to have commercial potential, although most are still at the experimental stage. Various construction materials have been manufactured using a proportion of sewage sludge or in some cases incinerator ash, including bricks, vitrified clay pipes, pavement blocks, hardcore substitute and lightweight aggregates. The melting of sludge, and utilisation of the resulting slag, is being extended in Japan. Costs of sludge disposal by conventional routes have been predicted to increase (notably in Germany), so that alternative novel uses could become economically viable.

10. Finally there is a conflict of interest or of aspiration. On one hand sludge is regarded as contaminated and potentially dangerous, so that it should be concentrated and contained. On the other hand it is seen as a valuable resource which should be recycled. How far, therefore, will controls on the use of potentially dangerous substances, together with the regulation of point discharges, reduce contaminant levels and make sludge more acceptable for recycling?

IV RECOMMENDATIONS

The information on sludge treatment and disposal in urban areas of other countries should be noted when developing strategies for the future management of sewage sludge in the UK. Where it has been indicated that additional legislation is under consideration, or decisions about future strategy postponed, the situation should continue to be monitored.

V RESUME OF CONTENTS

Information is summarised on the trends in sludge production and the existing and predicted future use of conventional outlet routes in Europe, USA and Japan. The regulations applicable to sludge disposal to landfill, agriculture, land reclamation and incineration are discussed, together with reported constraints on the continued use of individual routes. Novel uses for sewage sludge are briefly reviewed.

Case studies of specific major urban areas are reported based on published literature, drawing attention to the factors which influenced future management plans and the options selected.

Copies of the report are available from FWR, price £25.00, less 20% to FWR Members.