CH₄ and N₂O from waste composting

Hobson, Andrew Michael Bogan (2007). CH₄ and N₂O from waste composting. PhD thesis The Open University.



This research programme aimed to investigate methane (CH4) and nitrous oxide (N20) emissions from large-scale composting facilities, with particular emphasis on advanced and newly emerging composting technologies. The atmospheric concentrations of CH4 and N20 are increasing, and they are respectively the second and third largest contributors to the global greenhouse effect after carbon dioxide. During field trials at large-scale composting facilities and in laboratory studies, the generation of CH4 and N20 was detected from a range of composting processes. Gaseous emissions from composting result from the interaction of a complex combination of controlling factors influencing the microbial production of CH4 and N20. Waste biodegradability in particular was shown to have significant influence on emission of CH4 and N20. Compliance with the EU landfill directive will result in the composting of wastes of varying biodegradability, the effect of this compliance on emission of CH4 and N20 from composting requires further investigation. Emissions of CH4 and N20 during composting have not been adequately quantified in the UK. A future projection of the contribution of composting to the UK greenhouse gas inventory was an estimated 24.6 Kt CH4 year-1 and 2.5 Kt N20 year-1 from open windrows, which currently account for 80% of the composting systems employed. There is urgent need for further study into the emission of CH4 and N20 from the UK composting sector as the Kyoto protocol requires emissions from all sources to be accounted for. While significant emission of CH4 and N20 was recorded for open air mechanically turned windrow systems, the level of emissions from in-vessel composting facilities was more difficult to determine. The combination of in-vessel composting and open air windrow composting would appear to greatly mitigate emissions compared to windrow systems alone, but more research into the environmental benefits of combining composting systems is required.

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