Life cycle assessment of the mechanical biological pretreatment of residual wastes
In Germany the handling of wastes is regulated by the 'Kreislaufwirtschaftsgesetz (i.e. Closed Cycle Economy and Waste Act) which gives priority to waste avoidance. Waste that cannot be avoided has to be recycled or reused as long as it is environmentally favourable. The residual wastes have to be pre-treated before landfill to reduce the negative effects of the landfill as production of landfill gases, leachates, and landfill setting. The pre-treatment of residual wastes is regulated by the 'Technische Anleitung Siedlungsabfall' which defines the standards for the landfill site and includes an appendix with standards for the pre-treated wastes. Of special importance is the stipulation that only waste with a volatile solid content of less than 5% can be deposited. The de facto result of this is that only thermal pre-treatment is legally possible. Biological-mechanical processes, which are far less expensive and which are especially effective in substantially copying with the problem when easily degradable substances are involved. Otherwise, they may reduce the total content of volatile solids to between 15-30%. However, the real reactivity of a landfill is not fully represented by the loss on ignition as it describes the whole organic content, instead of the portion which is available for biological degradation. That means it includes substances which cannot be degraded biologically in the landfill, such as plastics, for example. As many municipalities would prefer, at least for economic reasons, the MBP of residual waste, there is political pressure to re-examine the standards of the TASi. While there is consensus, that the landfill parameters of the TASi are a useful and sufficient standard for thermal pre-treated wastes to comply with the requirements of a sustainable waste disposal, the discussion is going on, whether they are appropriate and necessary for the mechanically and biologically pre-treated wastes.