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TECHNICAL REPORTS

Waste Management

Effect of Cattle Slurry Separation on Greenhouse Gas and Ammonia Emissions during Storage

^a Instituto Superior de Agronomia, UIQA, TU Lisbon, Tapada da Ajuda, 1349-017– Lisboa, Portugal
^b Chemistry Centre, Dep. of Soil Science, Universidade de Trás-os-Montes e Alto Douro, Apartado 1013, 5001-801 Vila Real, Portugal
^c North Wyke Research, Okehampton EX20 2SB, UK
^d Centre for the Research and Technology of Agro-Environment and Biological Sciences, Dep. of Plant Science and Agricultural Engineering, Universidade de Trás-os-Montes e Alto Douro, Apartado 1013, 5001-801 Vila Real, Portugal

^* Corresponding author (dfangueiro{at}isa.utl.pt).

Received for publication June 21, 2007. Storage of cattle slurry leads to emissions of methane (CH₄), nitrous oxide (N₂O), ammonia (NH₃), and carbon dioxide (CO₂). On dairy farms, winter is the most critical period in terms of slurry storage due to cattle housing and slurry field application prohibition. Slurry treatment by separation results in reduced slurry dry matter content and has considerable potential to reduce gaseous emissions. Therefore, the efficiency of slurry separation in reducing gaseous emissions during winter storage was investigated in a laboratory study. Four slurry fractions were obtained: a solid and a liquid fraction by screw press separation (SPS) and a supernatant and a sediment fraction by chemically enhanced settling of the liquid fraction. Untreated slurry and the separated fractions were stored in plastic barrels for 48 d under winter conditions, and gaseous emissions were measured. Screw press separation resulted in an increase of CO₂ (650%) and N₂O (1240%) emissions due to high releases observed from the solid fraction, but this increase was tempered by using the combined separation process (CSP). The CSP resulted in a reduction of CH₄ emissions ( 50%), even though high emissions of CH₄ (46% of soluble C) were observed from the solid fraction during the first 6 d of storage. Screw press separation increased NH₃ emissions by 35%, but this was reduced to 15% using the CSP. During winter storage greenhouse gas emissions from all treatments were mainly in the form of CH₄ and were reduced by 30 and 40% using SPS and CSP, respectively.

Abbreviations: DM, dry matter • GHG, greenhouse gases • PAM, polyacrylamide • PAM-sup, PAM-supernatant fraction • PAM-sed, PAM-sediment fraction • TGA, trace gas analyzer