Methane emissions reduced using gypsum in pilot-scale dairy manure tanks

Animal manure storage facilities are sources of greenhouse gas emissions in Canada, with the majority of emissions in the form of methane and nitrous oxide. This study was conducted to assess how effective adding gypsum powder to cow manure is at reducing the emissions of methane and nitrous oxide. At a pilot-scale research facility in Nova Scotia, Canada, gypsum powder was added to tanks containing ∼10,000 L of local dairy manure in duplicate at three rates: low rate (3.2 g L^-1), high rate (7.1 g L^-1), and the control (0 g L^-1). Each manure tank was enclosed within a steady-state chamber, and gas samples were manually taken using a syringe from the exhaust into pre-evacuated vials at regular intervals between June and November (143 days). Using gas chromatography, methane and nitrous oxide measurements were analyzed from each vial, allowing for calculations of cumulative emissions and CO₂-e. Compared to the control, both the high rate and low rate of gypsum significantly reduced cumulative methane emissions. Though the cumulative nitrous oxide emissions were reduced using both rates of gypsum, the nitrous oxide emissions were minor and not statistically significant. Methane emissions were reduced by 87% using the low rate of gypsum and by 92% using the high rates of gypsum. Gypsum additive to slurry in storage facilities is a safe and effective mitigation strategy to reduce greenhouse gas emissions. Further research is required to support on-farm application rates and feasibility.