Title

Resource recovery and life cycle assessment in co‐treatment of organic waste substrates for biogas versus incineration value chains in Poland and Norway

Conference Dates

June 5-10, 2016

Abstract

Present waste management policies are characterized by some main shifts compared to previous practices; such as increased focus on resources recovery, banning of landfilling of organic waste fractions, waste-to-energy value chains optimization, and environmental life cycle impact optimization. In order to comply with such new policies there is a need for research on methodological and empirical aspects of LCA for value chains for co-treatment and resource recovery from organic waste substrates; including processes from generation, treatment, energy conversion and final use of products and byproducts. This study examines two generic value chains (aiming at what are common solutions) for co-treatment of selected organic waste substrates, converted to energy, in Norway and Poland. The waste substrates that are studied are sewage sludge (46% dry matter), organic fractions of municipal solid waste (27.1%), and fat (26.9), in different combinations of quantity mix.

Chemical properties for these substrates are gathered from a newly executed state-of-the-art analysis in addition to comprehensive laboratory experiments to find methane yield characteristics of different co-treatment substrate mix situations. Technologies examined in this study include pretreatment, anaerobic digestion, biogas upgrading to CHP-generation or to biofuel for use in transport, bioresiduals separation or upgrading to compost for use in agriculture or as soil amendment, all as part of an anaerobic route, compared to waste incineration with energy recovery to CHP-generation as alternative to the anaerobic route. Products and byproducts of both treatment options are substituting mineral fertilizers, fossil fuels and electricity grid mixes common of today, by system expansion, to determine possible avoided impacts when comparing alternative technologies. The LCA model is based on input from a feedstock-driven and mass-balance consistent MFA model that estimates the life cycle inventory. This provides increased flexibility and accuracy regarding system and technology assumptions, on the basis of a given set of transfer coefficients and parameters that can be altered according to what value chain and technologies are to be examined. This study presents LCA results from two defined and alternative value chains, based on what are typical assumptions and input variable values for applications in a Norwegian and in a Polish setting. The study account for the differences in technologies and practices in the typical waste systems, the typical energy systems and the typical transportation systems in each country, where the main differences between the two systems are that bioresidual is used as fertilizer in Norway and not in Poland additional to the different electricity mixes. LCA calculations are performed using different mix ratios of incoming waste substrates (sewage sludge, organic waste, fat), and assessing the corresponding energy recovery efficiency, nutrient recovery efficiency, and the associated impacts affected by applied technologies, transport distances, carbon capture potential, as well as estimating direct emissions for CH4, N2O and NH3, according to chosen end-use practices within the systems. The study shows what are the main important system processes and elements and what turn to be the critical variables and assumptions in the LCA modeling. It also gives recommendations for what factors to focus when trying to improve the resource recovery for energy and nutrients and the life-cycle environmental impacts of organic waste-to-energy value chains.

Additional Files
Simon A. Saxegård - 35.pdf (186 kB)

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