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Conference paper, 2010

Greenhouse gas emission from covered windrow composting with controlled ventilation

Ermolaev, Evgheni; Pell, Mikael; Smårs, Sven; Sundberg, Cecilia; Jönsson, Håkan

Abstract

There are only a few studies on green house gas (GHG) emissions from full scale composting of municipal solid waste investigating the effect of different process temperature and aeration combinations. It has been shown that oxygen availability affects the composition of gases emitted during composting (Amon et al. 2001; Brown et al. 2008; de Guardia et al. 2008). Methane emissions can be expected when anaerobic conditions are present within parts of the compost (He et al. 2000) and there is a rapid decrease in CH4 when oxygen supply is increased (Smårs, 2002). Based on the literature 0.2 to 2.5% of the initial C can be lost as CH4 (Brown et al. 2008), even though Szanto et al. (2007) measured 12.6% of volatile solids (VS) for a static system. Amlinger et al. (2008) found a clear relationship between temperature and GHG emission. CH4 and NH3 concentrations were highest at 40-50°C, while N2O appeared when temperature was below 45°C. In the present study, the combined effects of different aeration and temperature settings on the GHG emission during windrow composting with forced aeration following three different control schemes were measured. For one windrow, the control mechanism was set to keep the temperature below 40°C until the pH increase, another windrow had minimal aeration at the beginning of the process, which could provoke GHG emissions, and the third one had constant aeration. Since the windrows were not turned there was a possibility for material density to increase and for anaerobic zones to form. The measurements were performed on three covered windrows in Uppsala, Sweden. The air was evacuated from the top part of the windrows using ventilation pipes located under plastic liners covering each windrow down to about 30 cm from the bottom. The ventilation pipes were connected to a separate fan for each windrow. The compost substrate was a mixture of source separated compostable municipal solid waste (MSW) and structural amendment (woodchips, garden waste and reused compost mixture) in the volume proportion 1:2. Gas samples were taken daily from the exhaust of the fan of each windrow. The samples were analyzed for concentrations of CO2, N2O and CH4 by gas chromatography. Two 20-day experiments were performed in the period from the mid May until the end of June. In the first trial, CH4 concentrations increased with time, measured as CH4-C as % of CO2-C, from around 0.1% to between 1 and 2% of CO2-C in different windrows. In the second trial, the initial values for methane were similar to the first trial and showed similar patterns of increase in all three windrows until day 12 of the experiment when concentration peaked in two of the windrows. After this the concentrations decreased to the same range as in the first trial. The emissions of CH4 and N2O were similar between windrows and low regardless of the amount of ventilation while the minimum level of ventilation was maintained. Data also indicated the need to measure methane frequently, if possible continuously, to be sure not to miss significant emission peaks

Published in

Title: Proceedings of the 7th International Conference ORBIT 2010
ISBN: 978-960-6865-28-2
Publisher: ORBIT

Conference

7th International Conference ORBIT 2010. Organic Resources In The Carbon Economy