Release mechanisms of greenhouse gases, ammonia and hydrogen sulfide from liquid dairy manure
Abstract
Methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) are greenhouse gases (GHG) generated from animal agriculture that can contribute to global climate change. Liquid dairy manure produces large quantities of GHG and other gases, such as ammonia (NH3) and hydrogen sulfide (H2S). Previous work revealed that various mechanisms are associated with releases of NH3, H2S, CO2, and sulfur dioxide (SO2) from liquid swine manure. However, studies of CH4 and N2O release mechanisms from swine manure have not been reported. In addition, release mechanisms of all five gases have not been studied for dairy manure. This thesis presents two laboratory experiments on mechanisms of gas releases from liquid dairy manure stored in eight reactors. Each bioreactor was 61 cm tall and 38.1 cm in diameter and was initially filled with 25.4-cm high dairy manure. The headspaces of the bioreactors were continuously ventilated with 6.5 L/min fresh air to simulate manure storage conditions on dairy farms. Concentrations of CH4, N2O, CO2, H2S and NH3 in the exhaust air from each bioreactor were measured for 10 min every 90 min. Surface and bottom manure pH was continuously monitored during the second experiment. After a test of three months under steady-state conditions in the first experiment, gas releases under transient conditions were studied by one reactor-shaking test and two manure-mixing tests. After almost five months under steady-state conditions in the second experiment, a mixing test using a magnetic stirrer was conducted to study gas release behaviors and pH changes. Results from this research confirmed previous research that "Mass-transfer" governed NH3 release and, "Bubble-release" affected H2S release. Moreover, this research revealed that CH4 and N2O also exhibited the "Bubble-release" behavior. The release mechanism of CO2 was more complicated than previously understood and depended on several factors including manure degradation phases, manure surface pH, and CH4/CO2 release ratio. The manure pH change was also found to have close correlation with CO2 and NH3 releases.
Degree
M.S.A.B.E.
Advisors
Ni, Purdue University.
Subject Area
Agriculture|Agricultural engineering
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