Early diagenesis of garbage : landfills as engineered anoxic basins

• Early diagenesis of buried organic carbon in anoxic basins is dominated by microbial decomposition processes at temperatures and pressure slightly above ambient. Such conditions also describe decomposition of refuse in sanitary landfills and provide a reasonable model for systematic studies of their long-term geochemistry. For shorter time frame (decades), controlled high-solids anaerobic digestion systems provide a second model for investigation of optimized landfill systems. In this paper, we introduce both models through a series of preliminary mass-balances to develop a realistic overview of landfill processes, especially emphasizing carbon cycling in field settings over various time-frames. The terminal product of short-term anaerobic decomposition is methane--produced by methanogenic bacteria from some fraction of organic carbon landfilled. Laboratory studies of optimized landfill systems (ours and from the literature) indicate that, at best, 25-45% of organic carbon is converted to biogas carbon (methane and carbon dioxide); such percentages are rarely attained in field settings. Most of the methane is produced from cellulosic substrates while lignin substrates are recalcitrant, with lignin carbon entering sedimentary storage for time frames longer than the four decades of widespread landfilling experience in the U.S. and western Europe. Over time frames in excess of centuries, further transformations via kerogen pathways are possible but highly speculative. Certainly, exhumation of old refuse at archeologic sites indicates that organic carbon preservation can be documented for at least one or two millenia. From controlled incubation of unamended field samples and from field studies of net methane emissions, it is clear that rates of methane production and consumption both vary of several orders of magnitude in field settings; their dynamic are rapid and complex spatially and temporally. Unraveling these dynamics is necessary to suggest the overall relevance of these engineered anoxic basins to issues of atmospheric methane increases and terrestrial carbon storage.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Naturresursteknik -- Annan naturresursteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Environmental Engineering -- Other Environmental Engineering (hsv//eng)

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Avfallsteknik

Waste Science and Technology

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