Evaluating the use of municipal solid waste as a feedstock for in-vessel composting

For centuries, the dominant form of waste disposal has been landfill, however, \nthis is now deemed to be non-viable from a social, legislative, environmental \nand economic perspective. Therefore, more sustainable methods of waste \ndisposal are needed globally to reduce the amount of waste going to landfill \n(e. g. composting). This thesis considered two different forms of in-vessel \ncomposting and their effectiveness in treating the biodegradable fraction of \nMunicipal Solid Waste (MSW) that had been mechanically separated prior to \ncomposting in two areas of Wales. Further to this, the potential for using MSWbased \ncomposts as growth media was investigated alongside the physical \ncomposition of MSW-based composts. \nThis thesis found that primary-screened MSW contained a high amount \n(>50%) of biodegradable matter with varying amounts of glass (ca. 23%), \nplastic (ca. 10%) and other components present. Both in-vessel composting \nmethods were successful at treating MSW and produced composting profiles \nsimilar to those for green waste (e. g. increased pH, reduced EC and increased \nN03" content). Alongside this, both methods also reached temperatures high \nenough to cause destruction of human enteric pathogens making them \ncompliant with the 2005 Animal By-Products Regulations. Inert matter (i. e. \nglass and plastic) remained unchanged during composting, but beneficially \nenhanced composting by improving aeration. In contrast, small bench-scale \ncomposting units failed to realistically mimic the performance of the larger \nscale MSW composting systems; the results obtained with them suggested that \ncommercial composting additives did not enhance the rate of composting. The \nuse of the MSW-based growth media showed that as the materials matured, \nyields of two common pasture land species increased significantly, and in some \ncases exceeded those of commercially available growth media used widely in \nhorticulture. Combining agricultural soils with these MSW-based materials \ngave increased plant yields in comparison to soil alone, however, the benefits \nwere dependent on the amount and type of MSW compost added. Further \nresearch is needed into the removal of physical and chemical contaminants from \nthe parent materials for composting of MSW based materials along with clearer \nlegislative definitions as to the possible end uses for such materials. The \npresence of clear markets has the potential to drive improvements in the \ntechnology used for MSW composting. In conclusion, composting provides a \nviable method for the treatment of MSW-derived biodegradable waste and has \nthe potential to form an important component of sustainable waste management \nin the UK.