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Title: Pile mixing increases greenhouse gas emissions during composting of dairy manure

Author
item Ahn, Hee Kwon
item Mulbry, Walter
item White, Kathryn
item Kondrad Ingram, Shannon

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2010
Publication Date: 11/4/2010
Citation: Ahn, H., Mulbry III, W.W., White, J.W., Ingram, S.K. 2010. Pile mixing increases greenhouse gas emissions during composting of dairy manure. Bioresource Technology. 102:2904-2909.

Interpretive Summary: Composting is an environmentally friendly technology for treating and recycling a variety of organic wastes. However, gaseous emissions of nitrogen-based, sulfur-based, and volatile organic compounds are negative consequences of composting and present practical problems for large-scale facilities and farms. Emissions of methane and nitrous oxide have attracted renewed attention more recently because of their contributions to total greenhouse gas (GHG) emissions. Although there are general recommendations for minimizing methane and nitrous oxide emissions (such as the use of feedstocks with high carbon/nitrogen and low moisture content values), there is a need to develop and evaluate management measures for minimizing these emissions at the farm-scale. The purpose of this study was to compare the GHG emissions from mixed and unmixed pilot-scale dairy manure compost piles. Results showed that GHG emissions from piles that were mixed four times during an 80 day trial were about 20% higher than emissions from unmixed piles. Increased GHG emissions were primarily due to increased emissions of methane within the first 23 days of composting. Although additional experiments are needed to confirm these results using larger piles of stockpiled manure, these results suggest that farmers should store manure in undisturbed piles or, at the very least, delay the first turning of manure piles for approximately four weeks.

Technical Abstract: The effect of pile mixing on greenhouse gas (GHG) emissions from stored dairy manure was determined using large flux chambers designed to completely cover pilot-scale manure piles. GHG emissions from piles that were mixed four times during the 80 day trial were about 20% higher than unmixed piles. For both treatments, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) accounted for 75-80%, 18-21%, and 2-4% of GHG emissions, respectively. Approximately 70% of CO2 and CH4 emissions from all piles occurred within first 23 days. In contrast, 60-75% of N2O emissions occurred during the later stages of composting. Mixed and static piles released 2 kilograms (kg) and 1.6 kg GHG (CO2-eq.) for each kg of volatile solids degraded, respectively. Our results suggest that with respect to minimizing GHG emissions, farmers should store manure in undisturbed piles or, at the very least, delay the first turning of manure piles for at least four weeks.