Greenhouse gas emissions during composting of dairy manure: Delaying pile mixing does not reduce overall emissions

Authors: Mulbry, Walter; ANH, HEEKWON - Chungnam National University

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2014
Publication Date: 10/2/2014
Publication URL: http://handle.nal.usda.gov/10113/59641
Citation: Mulbry III, W.W., Anh, H. 2014. Greenhouse gas emissions during composting of dairy manure: Delaying pile mixing does not reduce overall emissions. Bioresource Technology. 126:117-122.

Interpretive Summary: Composting is an environmentally friendly technology for treating and recycling a variety of organic wastes. However, gaseous emissions of methane and nitrous oxide are negative consequences of composting because they contribute toward total greenhouse gas (GHG) emissions. Although there are general recommendations for minimizing methane and nitrous oxide emissions (such as 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 specific purpose of this study was to test the prediction that delaying initial compost pile mixing would decrease GHG emissions during dairy manure composting. Results showed that GHG emissions from piles that were mixed once or twice during a six week trial were about 20% higher than emissions from unmixed piles. Increased GHG emissions were primarily due to increased emissions of carbon dioxide within the first 21 days of composting. Delaying initial mixing of piles from two weeks to five weeks did not reduce total GHG emissions in mixed piles. Although GHG emissions can be reduced by storage of manure in unmixed (static) piles, dairies will have to balance this benefit against the need to mix piles for pathogen and weed seed reduction.

Technical Abstract: The effect of the timing of pile mixing on greenhouse gas (GHG) emissions during dairy manure composting was determined using large flux chambers designed to completely cover replicate pilot-scale compost piles. GHG emissions from compost piles that were mixed at 2, 3, 4, or 5 weeks after initial construction were approximately 20% higher than emissions from unmixed (static) piles during a six week trial period. Delaying initial pile mixing (2, 3, 4, or 5 weeks) did not affect total GHG emissions. Carbon dioxide, methane, and nitrous oxide accounted for 75%, 14-19%, and 6-12%, respectively, of total GHG emissions from static and mixed piles during the trial. These results suggest that in order to minimize GHG emissions, farmers should store dairy manure in static piles.