Environmental evaluation of systems for the recovery of biogenic wastes

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The recovery of waste materials is promoted by the German Waste Act 'Kreislaufwirtschafts- und Abfallgesetz'. It requires that among the recovery routes available for a specific waste category the priority has to be on those which are more environmentally compatible. As a restriction given by the law, only those recovery routes which are technically feasible and economically reasonable must be taken into account.

In order to comply with the requirements of the law an environmental ranking of the available recovery routes is necessary. As a consequence, a method for a comparative environmental assessment has to be applied. However, such a method should not be restricted to the comparison of individual waste treatment technologies. On the contrary, the environmental impacts of the whole recovery system including all process steps starting from waste collection until the production of a defined product from waste, should be analysed. In addition, it should be regarded, that recovery will take place if the products obtained are competitive at the market. Therefore, existing products with the same function will be substituted and the related environmental loads will be saved. This benefit should be credited within the ranking procedure.

Growing efforts in the management of organic wastes during the last years have lead to an increased availability of products from organic wastes such as e.g. compost and secondary fertilisers. Nevertheless, there is still a considerable potential for the recovery of organic materials in wastes from private households as well as for the recovery of biowastes from public gardens and individual industrial branches.

Comparative assessments of individual treatment technologies for biowaste have already been performed in the past (Krogmann 1994, Kern. 1993, Müsken et al. 1994, Franke et al. 1994). In our project supported by the Deutsche Bundesstiftung Umwelt for the first time a method for the comparison of recovery systems developed by Giegrich et al. (1999) is applied in order to compare selected recovery routes for several organic waste categories.

The method is based on the life cycle assessment approach as fixed in the international standard ISO 14040. The process steps involved in the conversion of biowaste into a secondary product are analysed and for each of this process steps data on the resources consumed, the solid waste generated as well as on the emissions to water and to air, the so-called inventory data, are balanced. This is exemplarity shown in figure 1 where the same biowaste is fed into the two recovery routes A and B which again result in the different products A and B. Each of these products is assumed to substitute a specific product on the market, product Aeq and product Beq respectively. For the processing of these products inventory data are set up too.

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