Greenhouse gas emissions from home composting in practice

• Home composting is a wide-spread treatment option for biological household waste in Sweden. According to theSwedish Waste Management association (Avfall Sverige, 2011), 60 000 tonnes of compostable waste were homecomposted in 2010. This represents a rather large portion (10 %) of all the household waste treated biologically.Nevertheless, research on process efficiency and environmental effects of home composting is scarce. The objective ofthis study was to investigate the influence of different process parameters on greenhouse gas (GHG) emissions(methane, CH4, nitrous oxide, N2O and carbon dioxide, CO2) from home composting under real householdmanagement.Eighteen home composts in use by single households were randomly selected within the city of Uppsala, Sweden. Thecomposts were studied for 13 months from June 2010 until June 2011. The households were requested to keep theirnormal composting practices. Among the 18 composts there were eight different bin types. Headspace gas, ambient gasand compost material samples were collected 13 times during the study period. At the sampling times, ambient andcompost temperatures were measured. The gas samples were analysed by gas chromatography for CO2, CH4 and N2O,and the material samples were analysed for pH, moisture and ash content. Information about compost management andfeeding was continuously provided by the households via protocols. The material fed to the composters was mainlykitchen food waste. In some cases garden waste and other biological materials were added. The average amounts ofmaterial added to all composts varied from 0.21 to 0.51 kg/day with an extreme of 1.35 kg/day in one of the composts.The temperature in most composts followed the ambient levels. The overall average pH in the composts was 7.2. Themoisture was generally high with an overall average of 73 % wet weight.Average concentrations of CO2, CH4 and N2O were 6430, 28 and 5 ppm above ambient levels, respectively. Both CH4and N2O were represented as ratios to CO2 in order to estimate and be able to compare emission rates. High moisturecontent was expected to give higher methane emissions, but such a relationship could not be discerned. Composts withhigher temperatures had high ratios of CH4:CO2 at some sampling occasions. It was not possible to establish any singlevariable affecting the N2O emissions. The average emission rates, given as ratios CH4:CO2 and N2O:CO2 were 0.38 and0.15 %, respectively and were relatively low but within the same order of magnitude or lower than those reported inother studies on home composts (Andersen et al., 2010a, Amlinger et al., 2008, Chan et al., 2011). When compared withlarge-scale composting (Ermolaev et al., 2012, Amlinger et al., 2008, Hermann et al., 2011), home composting seemedto emit less CH4.In conclusion, in this study the emissions of CH4 and N2O were relatively low. Methane emissions from homecomposting seemed to be smaller than from large composts. Notably, composts with extremely large amounts ofmaterial added, with more frequent mixing or bad aeration, displayed the highest GHG emission rates. This suggeststhat home compost units should not be too large to avoid intensified process when mixing the compost.Keywords: composting, greenhouse gas, kitchen waste, methane, nitrous oxide.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Naturresursteknik -- Miljöledning (hsv//swe)

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

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Klimatforskning (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Climate Research (hsv//eng)

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

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

LANTBRUKSVETENSKAPER  -- Annan lantbruksvetenskap -- Miljö- och naturvårdsvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Other Agricultural Sciences -- Environmental Sciences related to Agriculture and Land-use (hsv//eng)

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