An Examination of the Pyrolysis Scheme


For some time now Cambridge City Council and East Waste have been working on a plan for the disposal of domestic waste by pyrolysis. A report[1] by the city's Head of Environmental Health and Protection to the city's Environment Committee explains that pyrolysis:

In June 1999 Cambridge City Council's Environment Committee considered this report. It explained the council's thinking on the need to dispose of waste by pyrolysis and recommended that the committee ask council officers to press ahead with this scheme “working in partnership with adjoining authorities and [...] private sector partners to progress the development of a plant for the gasification of our domestic waste". The committee agreed to this recommendation.

Access to this document by the public was only possible after the committee had met and so I was unable to comment on it ahead of that meeting. Cllr Knowles kindly for-warded a copy of the paper after the meeting and I've subsequently had a discussion by email with her. This document is a re-working of that discussion, with more substantive figures based on more recent researches based on other publicly available papers.

What Is To Be Burned?

This is a key question, as the make up of the plume will vary depending on what is burned. The report makes it clear that what is currently being proposed is to burn domestic[2] organic[3] waste. There is no proposal to burn inorganic domestic waste, or to burn industrial or commercial waste.

The definition of organic here is important. The Cambridgeshire and Peterborough Waste Local Plan[4] uses organic as a synonym for compostable[5] but in the pyrolysis scheme documents they appear to be talking about organic in the strict chemists' sense of the word: compounds which are based on carbon. This isn't clear from the report to the city council's Environment Committee but the briefing document for the Environment and Transport Joint Strategic Forum suggests that to be the definition they're using. The only domestic waste being excluded is "metals, glass and minerals ('fines')"[6]. Hence it appears that the fuel will be food products, garden waste, paper and card, and plastics. To avoid any more confusion this document uses compostable to mean waste which could be composted (which the Waste Local Plan calls organic) and uses organic to mean compostable plus paper, card and plastics.

What Effect Will This Have on the Total Waste Burden?

It's hard to be precise on figures because the published data doesn't give sufficient information to be exact, but we can get pretty close. Cambridgeshire County Council's published figures [4] say that domestic waste makes up only 9% of the total of controlled waste[7]. Of that the compostable part of it, excluding paper and card, form about 20%[8]. There seem to be no separate figures for paper and card, or for plastic, but let's be generous, and assume they make up 50% of the total. This means that domestic organic waste, the waste to be burned, makes up around 6.5% of the total waste burden. Burning will reduce its volume by a factor of around twenty and its weight by a factor of ten so the total effect of burning by pyrolysis is about 6% less waste to be disposed of.

70% of waste is land filled[9]. If we assume that all domestic waste is land filled (we know that at least some portion of it is currently re-cycled, as paper, card, glass and through composting) then the best effect this can have on land fill is to reduce the total by 8.5%, probably somewhat less.

Alternative Disposal Methods

There is already a non-landfill means of disposing of domestic organic waste. The compostable element, around 20% of the total of domestic waste, can be composted. As yet only the city has pressed ahead with such a scheme but the Waste Local Plan suggests that composting is a viable method of disposing of organic waste and that "there is considerable potential to produce more compost". Composting not only effectively disposes of the waste without the need to landfill but also contribute to the environment in other ways by reducing the reliance on fossil peat and the need to fell trees. A survey by the Composting Association in May 1997 found that there were 47 local authority composting sites in the UK. One could safely assume that figure will be even higher two years down the line.

Curiously neither of the documents presented to council committees pays much attention to composting, indeed the latest document going to the Joint Strategic Forum doesn't mention it at all, preferring to concentrate on other methods.

Anaerobic digestion is another variation discussed at some length in the Waste Local Plan, but virtually ignored by the documents advocating pyrolysis. Anaerobic digestion has a long history of use in the sewage industry and looks like a favourable option for dealing with household waste as long as contamination of the organic fraction can be minimised or eliminated. Over sixty plants worldwide are now in operation and seventy are planned or under construction. Examples of where anaerobic digestion is working for household waste include; Saltzburg in Austria, Arhus in Denmark, and Tilburg in the Netherlands.

Of the other organic elements paper and card can be recycled as paper and card, and could also be composted. Only plastics are more difficult to dispose of, although some areas (Hampshire for example) do have plastics recycling schemes in place.

What Else Could be Burned?

It should be clear from the above that pyrolysis of domestic organic waste is an odd choice. Of all waste inputs organic waste is one of the easier ones to re-cycle (other than the plastics) and it only makes up a small part of the total land fill burden.

Pyrolysis does however make good sense as a means of disposing of plastics and other inorganic waste such as paints and solvents, which are difficult to dispose of by other means.

In addition, if one is burning domestic waste, then why not also burn at least an element of the industrial and commercial waste? These together make up 66% of the total waste burden[7].


The report to the city council was extremely coy about location, and in my conversations with Cllr Knoyles she said that she wasn't aware that any decision had been made. The briefing paper for the Joint Strategic Forum is more blunt. It states that "development at Milton would be contrary to the policies in the emerging Waste Local Plan, and to the position of [SCDC]". However it goes on to talk in general terms about the need to locate the plant near the city and says it could be either outside the Green Belt or inside its inner boundary, but suggests that perhaps the proposed review of the Green Belt might "take account of the need for a waste facility" ie to relax the constraints to allow it to be built at Milton land fill site.

Looking at the Waste Local Plan it's clear that building the pyrolysis plant at Milton would contradict this plan for a number of reasons, not just its location in the Green Belt (which is directly opposed by key policy WLP11 which says the only reason for putting a site in the Green Belt is if this is the only option for reclaiming a site, ie land filling a mineral working, as was done in Milton). In particular:

WLP8 calls for the disposal of waste as close as possible to the point of generation.

WLP10 calls for the avoidance of waste development in the countryside

WLP12 calls for the avoidance of visual instrusion or risk to human health

WLP17 calls for the avoidance of loss of agricultural land

WLP21 lists the preferred sites for future waste management

Other Issues Relating to the Waste Local Plan

WLP1 calls for a hierarchy of waste management options.

WLP28 and WLP29 looks at means of processing compostable waste

WLP30 says that pyrolysis like schemes should be considered


Reading the city council document again in the light of what we now know it's hard to understand why the scheme is being proposed in the form it is. The only waste to be disposed of through this plant is domestic organic waste, which we've seen comprises only a small proportion of the total being land filled and for which there are other means of disposal.

It does seem however that the plant would start to have a significant effect on the total volume of waste land filled if it were to burn both inorganic waste and commercial and industrial waste, which would result in a considerable saving in land fill tax. Why isn't this being proposed?

Re-reading the Waste Local Plan it's WLP1 which sticks most in the mind. Reduce. Re-use. Before you even consider recovery.

If you must use recovery then WLP28 through 30 suggest that pyrolysis should come low on your list of priorities behind better proven technologies.

The economics of such a scheme depend largely on the expected increase in landfill tax. It's worth noting that there is a distinct possibility that incineration will itself be taxed in the future[11]. One hopes this possibility has been taken into consideration.

Finally, if such a plant were to go ahead then the location most in keeping with the Waste Local Plan appears to be the Blue Circle site in Coldham's Lane, Cambridge, with ash being taken on to an appropriate land fill site.

Paul Oldham
18th July 1999


  1. Report by Head of Environmental Health and Protection, Cambridge City Council to Cambridgeshire City Environment Committee, The Gasification (Pyrolysis) of Domestic Refuse, 7th June 1999
  2. Same document section 3.5
  3. Same document section 3.8
  4. Cambridgeshire and Peterborough Waste Local Plan (Consultation Draft), July 1998
  5. Waste Local Plan section 9.28.2, 9.29.1 and elsewhere
  6. Report by Head of Environmental Health and Protection, Cambridge City Council, Assistant Director Environment, Cambridgeshire County Council, and Chief Environmental Health Officer, South Cambridgeshire District Council to the Cambridge City/South Cambridgeshire Environment and Transport Joint Strategic Forum to be presented on 21st July 1999
  7. Waste Local Plan section 5.1.5
  8. Waste Local Plan section 9.29.3
  9. Waste Local Plan section 5.1.6
  10. Report to Environment and Transport Joint Strategic Forum[6] section 5.2
  11. HM Customs and Excise, Review of the landfill tax report, 1998