Observations of production and emission of greenhouse gases and ammonia during storage of solids separated from pig slurry: Effects of covering

Separation of slurry produces a solid fraction that is stored in manure heaps before being used as a fertiliser in crop production. Considerable amounts of ammonia (NH3) and greenhouse gases may be emitted during storage, which has deleterious environmental effects. The emission levels can be expected to depend on oxygenation level inside the bulk of the stored manure and therefore on storage conditions. An experiment was thus set up to study gaseous emissions during storage of the solid fraction, and the effects of the oxygenation of manure heaps on emissions of NH3 and various greenhouse gases. Emissions of NH3 and the greenhouse gases methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) from an uncovered and covered heap of solids separated from pig slurry were compared, and related to the oxygenation level inside the manure heap. Approximately 15% of the initial nitrogen content was lost when separated solids were stored uncovered. Of the initial nitrogen content, 4.8% was lost as N2O, 0.3% was lost as NH3, while the 9.6% unaccounted for was assumed lost as dinitrogen (N2). Of the initial carbon content, 28% was lost during uncovered storage; the majority of this was emitted as CO2 (25%), while 1.3% was emitted as CH4. Oxygenation level inside the heap was found to influence the production and emission of greenhouse gases. Covering the heap with an airtight material delayed aeration of the bulk of the stored manure, which reduced the internal heat production, degradation of organic matter, and emission of NH3 and greenhouse gases. Emissions of NH3, N2O, and CH4 were reduced by 12%, 99%, and 88%, respectively, when the manure heap was covered with an airtight material.