Composting: Past and Present

Municipal Solid Waste (MSW) poses a difficult and complex problem for society

Municipal Solid Waste (MSW) poses a difficult and complex   problem for society.  Some of the difficulties arise because the MSW stream is quantitatively large and qualitatively   heterogeneous, reflecting the myriad consumer products manufactured in modern industrial society.  Inconveniently,   MSW is largely generated in densely populated areas where its   management is most constrained.  Thus the problem cuts across   a very wide range of human activities and interests.  At the same time, MSW represents a uniquely familiar environmental   problem, in that everyone contributes to it palpably in the course of daily living. (Finstein 1992)

The application of composting to municipal solid wastes in mechanised treatment plants has been recorded in the technical literature going back 50 years of more.  The recorded use of "refuse derived fuel" (RDF) is even older (Alter 1984).  The earliest recorded use of municipal solid waste in its  discarded form as a fuel to generate steam during the last quarter of the nineteenth century, apparently in England. The technology  was quickly adopted in the United States, Germany and Japan.   In New York City, in the 1890's solid waste was handpicked to remove useful materials and the residue became  another form of RDF which was burned to generate electricity.  Jeris and Regan (1973) describe composting plants of the 1920s and 1930s.  In 1961 Brunt described the Engineering and Economics of Composting Plant, reviewing plants in Scotland against "old fashioned" processes in the USA, Italy and Denmark.  Interestingly this paper has one of the first mentions of 60 degrees C as a minimum composting temperature.   Gothard (1959) describes a composting plant in Jersey and suggests process temperatures should be greater than 65oC to ensure sanitisation of materials.  Harrison (1965) describes the composting plant in Leatherhead.  Hoortenstein and Rothwell (1973) review the use of composted municipal refuse as a "soil amendment" going back to 1944.  de Haan 1981 and Obeng et al. 1987 briefly review the use of composting by the Netherlands, another country with a long history of applying composting to waste.  The composting plant at Wijster was opened in 1929, and by the end of 1960 fifteen composting plants were operating in the Netherlands, some at very large scales (Teensma 1961) and a number of composting plants operated in the USA through the 1960s (US EPA 1971).  Indeed the first issues of the journal "Compost Science" date back to 1961.  The year the authors of this critical review were born.

By 1971 composting in the UK had declined to 0.3% of the annual MSW arising. Composting plants existed at Worthing and Chesterfield. A Working Party on Refuse Disposal report to the Department of the Environment (1971) described the state of the art in composting in some detail, and much of what it says about composts (then produced from mechanically segregated and ground refuse) might seem very familiar to today’s experts.  The compost was seen as a soil conditioner rather than a fertiliser, given its contamination with "undesirable" inorganic materials.  The Working Party concluded that it is evident that to date municipal compost has had little or no attraction in agriculture or horticulture in Britain, nor do we think its attraction to be much greater as a humus or soil conditioner in private gardens. In these circumstances there seemed to be no justification for installing composting plants on the basis of an expected sale of compost unless governmental subsidies were made available for the agricultural use of compost. Composting a fill material for landfill was seen as having few advantages over using pulverised refuse.  Net composting production costs, allowing for sale of compost, were estimated at £3 per tonne, which is probably higher in real terms than net processing costs today (typical gate fees £15 to £25 per tonne, depending on throughput). 

The research into composting by Biddlestone et al. at the University of Birmingham stimulated renewed interest in composting (e.g. Gray et al. 1973).   Their work investigated and documented the key composting process control parameters: aeration and temperature and to a lesser extent pH, referring back as far as the work of Waksman in the 1930s (e.g. Waksman and Cordon 1939).  Gray et al. 1973 listed  composting plants around the world.  Three composting process approaches were identified in the UK: DANO, NUSOIL, and RENOVA., all based on mechanically segregated fractions of MSW.  Operating plants in the UK were located at: Blyth (2 tonnes per day throughput), Chesterfield (40-50 tpd), Cowdenbeath (DANO 10-13 tpd), Locherbie  (DANO 30 tpd), Dum. Kirkconnel (10 tpd), Jersey (vertical compost reactor - up to 80 tpd),  Leatherhead (DANO 45 tpd), Leicester (DANO 70 tpd), Newark, Paisley (80 tpd), Radcliff (DANO 20-25 tpd), Wetherby (up to 66 tpd), Worthing (up to 45 tpd).  However, Gray et al. also listed a number of composting plants which were closed down between 1971 and 1973, located at: Bristol, Cheadle and Gatley, Edinburgh, Kilmarnock, Manchester,  Middlesbrough, Twickenham.  A plant at Caister was the only facility built after 1971 (Gray and Biddlestone 1980).  Biddlestone and Gray reported retrospectively on their work in 1980.  While there was clearly concern about the content of trace elements in the composts made from MSW, acute toxicity in crop plants was rarely observed and boron appeared to be the chief culprit.  Stead and Irwin (1980) described a composting facility near Chichester.

The most well known of the composting plants in the UK was the DANO plant at Leicester (Wanlip) which produced a composted product called "Lescost".  This even merited an item on the children’s TV show  Blue Peter, which mentioned that the compost could be used in parks, but was not suitable for growing food.  Ultimately the Lescost plant shut down (Hughes 1977).  The Wanslip plant was originally built in 1966, damaged by fire in 1968 and recommissioned in 1969. The plant operated till the mid-1970s and shut down because it could not find markets for its composts.  Hughes (1977) reports that the compost stockpile was sold on quite easily, although Clark (1973) reports that the compost quality was poor and could not easily be sold while the plant was operating.  The plant (and others) is listed in the case studies section of this review.  Wanlip was the last major composting plant processing mechanically segregated MSW for some time in the UK.

In the late 1970s through to the late 1980s a large programme of work was carried out by the Department of the Environment, and subsequently ETSU,  to investigate recent advances in refuse processing technology for producing refuse derived fuel (e.g. Barton and Poll 1983).  This centred on two new plants, one built at Byker based on what was seen as a more established approach based on the processing of shredded refuse, and one built at Doncaster based on a more technically risky approach of trommel screening refuse before processing to RDF.  The trommel screening approach was found to be more reliable and produce a better quality fuel.  The Doncaster and Byker plants implemented much of what is regarded today as "MBT" technology, but even they were based on earlier technologies improved over time.

Research at Warren Spring Laboratory considered both composting (Ege and New 1988)  and anaerobic digestion (Le Roux 1979) as possible recycling routes for the organic rich rejects from the RDF process.  These were seen as a potential opportunity for organic matter recycling (Bardos et al. 1991, Poll 1994).  It became clear that trommel screening rather than shredding as the "front end" for MSW processing also resulted in better quality composts.  However by the early 1990s the work at Warren Spring had concluded that even with advanced separation and refining techniques the quality of compost produced from mechanically segregated composts was fundamentally limited by the nature of the feedstock, with particular concerns over inerts and heavy metal contamination levels, matching similar findings across Europe (Favioni 2002).  Quality of composts from source segregated materials was found to be much better (Newport et al. 1993) in line with findings from many other investigations, (e.g. Richard 1991).  However, review work indicated that the heavy metal contamination levels in some composts produced from source segregated materials was no better than that of the better composts from mechanically segregated feedstocks (Wheeler and Bardos 1992).

In the early 1990s research work was proposed to the Department of Trade and Industry and the then Department of the Environment to develop a programme for developing composting approaches for source segregated wastes, particularly from civic amenity sites, which in preliminary studies had shown great promise for producing a step change in compost quality.  However, this work was not carried out as funding was ended.

Since then interest in composts derived from source segregated materials has been unstoppable (Border 1999, DETR 2000, Gale and Walker 1997, The Composting Association 2003), although some interest in composting from mechanically separated wastes continued. 

A composting plant. based on mechanically segregated MSW was built at Castle Bromwich and then shut down in the early 1990s.  Composting plant. based on mechanically segregated MSW was proposed at Reading in Berkshire, but could not be financed.  Very recently composts produced from mechanically segregated wastes have been applied to land in Greater Manchester and in Norfolk.  In both cases the poor quality of the compost has lead to major controversy.  Composting plants based on mechanically segregated MSW have recently been commissioned in Neath, Wales and in Aberdeenshire (Pringle and MacDonald 1999, Pringle and Svoboda 2002).  The Neath Plant also produces "green waste composts" from separately collected materials.  It is still developing ideas for end-uses for the mechanically segregated waste compost, but anticipates no revenue from them.  The Aberdeen compost is intended for landfill restoration. (Note: - the feasibility of converting mixed-MSW composting plants to source segregated feedstocks is discussed by Kranert and Horst 1990.)

The Neath plant is perhaps in the vanguard of the so-called "mechanical biological treatment" plants which seek to apply mechanical segregation and biological processing to mixed refuse, ideally residual waste left after source segregated materials have been removed (Crowe et al. 2002), an approach known in the Warren Spring days as "Integrated waste management".  A large number of MBT plants have been proposed in the UK, and they are seen by many, including Greenpeace, as an alternative to thermal conversion of residual wastes left after source segregation of materials including compostables (Greenpeace 2001).  The actual scale of MBT processing in the UK appears, as yet to be relatively small, with 85,000 tonnes reportedly processed in 2001 (The Composting Association 2003).  However, major uncertainties remain about how the compost (or digestate) products of MBT will be used.  Currently envisaged applications are:

·                       Applications perceived as less sensitive by producers, such as restoration (Godley et al. 2002)

·                       Simply as a landfill pre-treatment (Bockreis and Steonberg 2004)

·                       As a feedstock for energy from waste conversion (Efstathios. and Stentiford 2004)

So the circle of composting continues to turn in the UK and elsewhere (each country seems to be making similar voyages of discovery and rediscovery, e.g. Ernst 1989, European Commission 1997).

The purpose of this review is that the "cycles" of the past can be recycled to inform the present cycle of interest in composting and mechanical segregation, which is most commonly expressed as "MBT".  The aim is for decision-makers and developers to have the opportunity to benefit from lessons learned in the past.

In 2003 the House of Commons Environment, Food and Rural Affairs Committee found that "Biodegradable (organic) waste is important because it represents a high proportion of household waste and because when disposed of in landfill it produces the greenhouse gas methane. Conversely, when managed well, biodegradable waste can be used to make valuable high quality compost, which in turn can reduce our reliance on peat-based composts and can be used as a soil improver."