Environmental efficiency of composting versus anaerobic digestion of separately collected, organic waste

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Courtesy of ORBIT e.V.

Environmental policy in the Netherlands among others aims at closing material cycles and minimising the amount of waste requiring final disposal. In this policy the highest priority is given to the prevention of waste production followed by (in descending order of preference) reuse, incineration with energy recovery and sanitary landfilling. In the implementation of this solid waste policy also targets for the reduction of the emission of CO2 are taken into account. Waste treatment should contribute to this national CO2 emission reduction with 3.5 to 4.5 million tons in the year 2000.

Since the beginning of 1994 municipalities in the Netherlands are obliged to collect the organic fraction of the household waste separately from the other waste fractions. In the Netherlands this biowaste fraction is called VFGwaste (Vegetable, Fruit and Garden waste), which must be processed into VFG-compost. Two technologies can be used: composting and anaerobic digestion. Both produce VFG-compost, which can result in reuse of stable organic matter. If certain quality standards are met, VFG-compost can even be used as a substitute for peat as a soil improver, thus giving a positive contribution to the reduction of CO2 emission. In this manner both composting and anaerobic digestion of separately collected VFG-waste contribute substantially to reaching the goals set in the policy concerning waste treatment in the Netherlands. However, because of the production of biogas, anaerobic digestion also produces energy from waste. If this presents a better overall energy balance for an anaerobic digestion plant than for a composting plant a further positive contribution to these policy goals is given.

When the decision was taken to start separate collection of VFG-waste and the production of high quality compost out of this material only limited experience was available with regard to large scale anaerobic digestion of this specific material in the Netherlands. The Dutch government, through Novem (the Netherlands agency for energy and the environment) and the European commission have subsidised two anaerobic digestion initiatives. In 1994 a plant (Valorga technology) went into operation in the city of Tilburg and at the end of 1996 a second plant (Biocel technology) followed in the city of Lelystad.

To be able to develop a sound basis for future policy in this field the knowledge of the environmental, technical and economic aspects of anaerobic digestion had to be increased. For this purpose the Ministry of Housing, Spatial planning and the Environment and Novem have initiated an extensive monitoring programme, which has been executed by DHV Environment and Infrastructure, at the two anaerobic digestion plants mentioned before and at one composting plant in order to collect reference data. As result of this project the environmental efficiency and cost effectiveness of anaerobic digestion has been determined in relation to that of composting. On basis of the results of the project the Dutch government now considers anaerobic digestion as technically equal to composting. From an environmental point of view the Dutch government prefers anaerobic digestion to composting. This point of view is now being incorporated in the waste treatment structure in the Netherlands.

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