Environmental assessment of supercritical water oxidation and other sewage sludge handling options.

Sustainable development relies on the eco-efficient use of all flows in society; more value created out of each resource unit. Supercritical water oxidation (SCWO) can be used for treatment of wet organic waste. The technology has been under development for over 20 years but has not yet been fully commercialized. SCWO allows for complete oxidation of all organics in sewage sludge and almost complete recovery of the inherent energy, essentially without harmful emissions. In this paper, a life-cycle assessment (LCA) of sewage sludge SCWO (Aqua-Critox) is presented and the results are compared with LCA results for other sludge handling options: agricultural use, co-incineration with municipal solid waste, incineration with subsequent phosphorus extraction (Bio-Con) and sludge fractionation with phosphorus recovery (Cambi-KREPRO). For SCWO, beneficial utilization of the heat of reaction is of crucial importance for the outcome. The electricity consumed by pumping and the nitrous oxide produced are other important parameters. The best sludge handling option from an environmental point of view depends on what aspect is considered more important in the impact assessment. Regarding global warming, the energy recovery methods perform better than agricultural use.

Driving forces for import of waste for energy recovery in Sweden.

Between 1996 and 2002, the Swedish import of so-called yellow waste for energy recovery increased. The import mainly consisted of separated wood waste and mixes of used wood and paper and/or plastics that was combusted in district heat production plants (DHPPs). Some mixed waste was imported to waste incineration plants for energy recovery (10% of the import of yellow waste for energy recovery in 2002). The import came primarily from Germany, the Netherlands, Norway, Denmark and Finland. We identified six underlying driving forces for this recent increase of imported waste which are outlined and their interactive issues discussed. --The energy system infrastructure, which enables high energy recovery in Sweden. --The energy taxation, where high Swedish taxes on fossil fuels make relatively expensive solid biofuels the main alternative for base load production of district heat. --The quality of the waste-derived fuels, which has been higher in the exporting countries than in Sweden. --The bans on landfilling within Europe and the shortage of waste treatment capacity. --Taxes on waste management in Europe. --Gate fee differences between exporting countries and Sweden. In the future, the overall strength of these driving forces will probably be weakened. A Swedish tax on waste incineration is being investigated. In other European countries, the ambition to reach the Kyoto targets and increase the renewable electricity production could improve the competitiveness of waste-derived fuels in comparison with fossil fuels. Swedish DHPPs using waste-derived fuels will experience higher costs after the Waste Incineration Directive is fully implemented. The uncertainty about European waste generation and treatment capacity, however, might have a large influence on the future gate fees and thus also on the yellow waste import into Sweden.

How model-based systems analysis can be improved for waste management planning.

Waste management models have been developed worldwide since the late 1960s. The overall aim of the models is to assist decision makers who are facing a complex task in order to handle waste in a cost-efficient and environmentally sound way. International research publications regarding waste management models point out the major benefits to be their capacity to deal with complexity and uncertainty and of finding benefits of co-operation and handling different goals. Such models have been developed and used successfully in Swedish research projects since the beginning of the 1990s, but the current situation is that such models are rarely requested for waste management planning in the country. Based on case studies (with the waste management models MIMES/Waste and ORWARE) in the Swedish municipality of Jönköping and a follow-up study, the paper discusses and draws conclusions on how to improve and increase the use of models to better correspond to the needs of decision makers involved in waste management planning.