Report No FR0265
CURRENT DISPOSAL PRACTICE AND
FUTURE DEVELOPMENTS IN SELECTED COUNTRIES
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.
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.
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.
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.