Dawn and I recently completed a review for the Environment Agency on compost-like outputs from MBT plants (follow this link for the full report). The main objectives of this review were to describe current EU practice for the production, regulation and use of compost-like outputs from mechanical-biological treatment (MBT) plants, with specific reference to their application to land. A further objective was to assess national differences in approaches across the EU and to attempt to establish why such differences exist. The relevance to the UK situation of uses of MBT outputs on agricultural land in other European countries is also discussed in the full report.
“Mechanical-biological treatment” (MBT) refers to systems for the treatment of mixed waste and municipal solid waste feedstocks. MBT is a generic term used for a process stream including mechanical sorting and separation of waste into distinct fractions of biodegradable and non-biodegradable materials. MBT is often a key element in national strategies for the diversion of biodegradable municipal waste (BMW) from landfill. Unlike incineration, it provides flexibility in the system, which is important in those Member States where the system will have to undergo widespread changes in the amount and quality of residual waste that is dealt with.
Product (compost)-orientated MBT is practised on a larger scale in France, Spain, Portugal, Poland, parts of Italy and Turkey. Several factors are thought to have influenced this development, not least the lower soil organic content in southern Europe’s and desertification issues. Although Italy has a long tradition in MBT, the emphasis for MBT outputs is on refuse derived fuel (RDF), with some MBT plants producing compost suitable for restricted applications.
After an initial widespread interest in composting municipal solid waste (MSW), there appears to have been a move away from producing a compost end product due to uncertainties about the economic market for this output. However, whilst the general opinion is that composts from source-segregated materials are likely to make higher quality composts, there still remains interest in composting mechanically segregated MSW feedstocks as part of a MBT process.
There is no uniform system for setting compost standards across the EU. However, almost all EU-15 countries have statutory standards, with just a few relying on voluntary standards (i.e. UK and Sweden). Most countries differentiate between two compost classes, but a few such as Austria and the Netherlands apply three standards. Very few standards consider non-source-segregated MSW outputs. The standards can differ quite significantly from one country to another. While the seven most common metals are typically covered by the standards, the limit values vary and some countries apply limit values for additional substances. For example, Denmark, Germany and Sweden have limit values for dioxins, Polychlorinated biphenyls (PCBs), Polycyclic aromatic hydrocarbons (PAHs), nonylphenols and Di(2-ethylhexyl)phthalate (DEHP), yet few have a comprehensive or adequate list. A number of countries have based compost standards on the limit values set out in the EU Sewage Sludge Directive (86/278/EC). Other policies that have influenced these limit values are the Strategy on Soil Protection (COM(2002)179 final) and the Nitrate Directive (91/676/EEC).
Whilst it is evident that compost from non-source-segregated MSW has been applied to agricultural land in a number of countries it has not been possible to obtain data on the amount that has been applied, nor where and for what specific purpose. Concerns about loading soil with metals and the high salt content of MSW compost have led to many field studies taking place, particularly in southern Europe where application of mixed waste outputs has been highest.
Compost-like outputs (CLO) are treated differently across Member States. For example, Germany uses MBT mostly as a pre-treatment prior to landfill, partially to stabilise biodegradable municipal solid waste, and does not use CLO on land. In France there are 70 plants processing 1.9 million tonnes per annum (tpa) of MSW with CLO used on land. Other countries also have substantial MBT capacities and use some of the CLO output on land, including agricultural land, such as Spain which has treatment capacity of 3 million tpa and Italy which has treatment capacity of 11.7 million tpa. In the UK the current regulatory position precludes the use of CLO from mixed waste sources for any agricultural land.
The development of MBT technologies and the potential recycling of CLO to agricultural land provide a challenge to both regulators and operators to ensure sustainable environmental use. In addition, public perception of risk and heightened awareness of health-related issues from agricultural re-use of wastes requires a robust evidence-based approach if public confidence is to be fostered and markets are to develop.