System analysis of energy utilization from waste - evaluation of energy, environment and economy. Case study - Stockholm

Energy, environmental, and economic consequences of different management systems for municipal solid waste have been studied in a systems analysis. In the systems analysis, different combinations of incineration, materials recycling of separated plastic and cardboard containers, and biological treatment (anaerobic digestion) of easily degradable organic waste, were studied and also compared to landfilling. In the study a computer model (ORWARE) based on LCA methodology was used. The following parameters were used for evaluating the different waste management options: consumption of energy resources, global warming potential, acidification, eutrophication, photo oxidant formation, heavy metal flows, financial economy and welfare economy, where welfare economy is the sum of financial economy and environmental economy. The study shows that reduced landfilling to the benefit of an increased use of energy and material from the waste is positive, from an environmental and energy as well as economic aspect. This is mainly due to the fact that the choice of waste management method affects processes outside the waste management system, such as production of district heating, electricity, vehicle fuel, plastic, cardboard, and fertiliser. This means that landfilling of energy-rich waste should be avoided as far as possible, both because of the the environmental impact, and because of the low recovery of resources. Incineration should constitute a basis in the waste management system of Stockholm. Once the waste is collected, longer regional transports are of little significance, as long as the transports are carried out in an efficient manner. Comparing materials recycling and incineration, and biological treatment and incineration, no unambiguous conclusions can be drawn. There are benefits and drawbacks associated with all these waste management options. Materials recycling of plastic containers is comparable to incineration from a welfare economic aspect, but gives less environmental impact and lower energy use - on condition that the recycled plastic replaces virgin plastic. Materials recycling of cardboard containers is comparable to incineration concerning welfare economy and energy, but has both environmental advantages and disadvantages. Anaerobic digestion of easily degradable waste gives a higher welfare economic cost than incineration, and has both environmental advantages and disadvantages. Conclusions regarding energy use depends upon how the biogas is used