Open access publications in the SLU publication database

Abstract

A simulation model, ORWARE, for the handling system for organic waste has been constructed. The purpose of the model is to accomplish a comprehensive view of the environmental effects, plant nutrient utilisation and energy turnover for this large and complex system. The ORWARE model consists of several sub-models; sewage system, incineration, landfill, compost, anaerobic digestion, truck transport, transport by sewers, residue transport and finally spreading of residues on arable land. This thesis is mainly focused on the compost, truck transport and residue transport sub-models, but the entire model is also discussed. Throughout the ORWARE model, all physical flows are described by the same variable vector, consisting of 43 substances, e.g. carbohydrates, carbon dioxide, dioxins, phosphorus, SOX, NOX and heavy metals. This extensive vector facilitates a thorough analysis of the results from an environmental point of view, but involves some difficulties in acquiring relevant data. However, the benefit is that it gives large possibilities for evaluating the outcome thoroughly. The main conclusions from simulations with the model are; l) There are no alternatives for handling the organic waste that are best in all respects. To find the best alternative, comparisons between different environmentally hazardous emissions, energy use and re-circulation of plant nutrients have to be made. 2) To evaluate a large-scale transition towards a more sustainable use of organic waste, i.e. increasing the recirculation of plant nutrients, it is necessary to include both solid and liquid organic waste in the same model. 3) The choice of system boundaries is crucial for the results. This implies that the choice of system boundaries in this type of studies have to be clearly defined before the results are evaluated. The impact of chosen system boundaries also has to be discussed after the evaluation.