The composition of municipal waste arisings in the UK is known at best poorly. The data used by DETR in Waste Strategy 2000 are shown in Table 1, and though no source was quoted, they appear to have been based upon old data from the National Household Waste Analysis Programme (NWHAP) carried out at the start of the 1990s. This data may be of limited use. Quite apart from the fact that the data refers to bin waste arisings only as opposed to municipal waste as a whole (i.e., less than two-thirds of the total stream - see above), the actual methodology used in the NHWAP has been the subject of some criticism. For example, the lack of significance accorded to sampling dates may have biased results from samples, and the fact that materials may have been mixed together, so transferring mass from 'wet' to 'dry' fractions, will have influenced the weight ascribed to a specific fraction.

Table 1: Waste Composition Data used by DETR/NAW and in Environment Agency Demonstration Disk for Wisard

Quite apart from the fact, therefore, that one would expect street litter, bulky collections, CA waste arisings and other contributing wastes to have a composition different to bin waste, the limitations of the approach undertaken imply that this data is unlikely to constitute an adequate basis upon which to base waste planning decisions. Furthermore, the fact that the base data is now so dated forces one to ask questions concerning the evolution of composition over time. This is something we know relatively little about.

Compositional data are important in understanding which materials are available in which quantities for diversion through recycling and composting. Indeed, ideally one requires a more detailed breakdown (than that given by DETR/NAW, itself supplied by the Environment Agency) if one is to assess accurately the suitability of materials for recycling, composting, energy from waste incineration and other waste treatment options. An even finer resolution in the characterisation of waste is required if one is to seek to understand the merits of pursuing materials reduction (in industry) as a strategy for minimising waste at the household level. This would be required to improve understanding of how to minimise wastes associated with specific products.[332]

The discussions around composition are by no means trivial ones. They can skew strategies in one direction or another since they suggest what is and is not feasible in terms of different waste treatment methods. Under the Landfill Directive, the biodegradable components of the municipal waste stream are most important. These are, principally:

* Paper and card;
* Putrescibles;
* Nappies; and
* Textiles.

DETR estimated that these constitute 62% of all wastes. Note once again, however, that these data referred only to household waste as opposed to all municipal wastes.

Whether this figure is 'correct' is difficult to know. It may be that it is a good estimate for the total fraction (though as mentioned above, some feel it is too low), but the breakdown of that fraction is as important as the total figure. In the DETR/NAW work, the breakdown of this biodegradable fraction is such that the proportion that is paper is larger than the proportion that is putrescible. Other work suggests that the opposite may be the case. Furthermore, European data on composition seems to confirm this. Alongside other countries, the UK data appears rather off with the putrescibles fraction very low. The different breakdowns suggest different strategies.

For these reasons, waste composition data is a matter of considerable debate. In particular, in the wake of the publication of A Way With Waste (the consultation draft of the England and Wales Strategy), many disputed the compositional data being used, especially in respect of what were believed to be low figures for the putrescible fraction. Network Recycling comments that all of their most recent domestic waste audits (bin waste) have found a putrescible content of at least 30 % (putrescible meaning kitchen and garden waste, and not including other types of biodegradable waste as defined in the Landfill Directive). Recent waste analysis work conducted in six areas in South Gloucestershire found that the average putrescible content of the waste stream was 39 % (range: 34 % ­ 56 %).[333] Sampling in Brixworth (for Waste Watch) gave a putrescibles figure of 49%. Ecologika report on seventeen waste analyses carried out in London. The average figure for compostables (again excluding paper) quoted is 38%.[334] Other individuals we have spoken to suggest that evidence increasingly points to a percentage figure in the high 30's. This raises the question as to whether the data used in Waste Strategy 2000 is sufficiently robust to base a strategy upon.

All of these comments refer to bin waste only. It is true, of course, that if one seeks to separately collect (as, for example, in Brixworth) compostables in Brown Bins, one may draw out more putrescible material into bins that might otherwise have gone elsewhere (i.e. CA sites, or home composting). However, this may make the collection more representative of total wastes (as opposed to just bin wastes).

As regards CA site wastes, two similar sets of data are shown in Table 2. Relatively few studies have been carried out on CA waste composition (and even fewer on street litter etc.). Yet materials delivered at CA sites may be very easily separated, and much of the material, including inert construction materials (presumably, a major part of the DIY non­combustible fraction), and wood (which is frequently lumped into the 'miscellaneous combustibles' category, even though wood packaging is now covered by the Packaging Regulations), may be suitable for re­use, recycling and composting. Again, the putrescibles fraction is of the order 40%.

Table 2: Results of Two Studies Concerning CA Site Waste Composition

Much better data is needed on composition than we have at present. The Environment Agency is due to commence shortly the next stage of the National Household Waste Analysis Programme.

Dr Dominic Hogg, March 2001

333   Personal communication Rachel Jarrett, Network Recycling. Back

334   Ecologika (1998) Re­Inventing Waste: Towards a London Waste Strategy, London: Ecologika for LPAC and the Environment Agency. Back