Greenhouse gas mitigation through dairy manure acidification


Sokolov, V., VanderZaag, A., Habtewold, J., Dunfield, K., Wagner-Riddle, C., Venkiteswaran, J.J., Gordon, R. (2019). Greenhouse gas mitigation through dairy manure acidification. Journal of Environmental Quality, [online] 48(5), 1435-1443.

Plain language summary

Liquid dairy manure storages are sources of greenhouse gases, including methane, nitrous oxide, and ammonia. Adding acid to the manure causes the pH to decrease, which reduces ammonia loss; however, little is known about the effects on methane and nitrous oxide. This study compared emissions from dairy manure (pH 7.4) with two acidified treatments which had pH of 6.5 and 6.0. Emissions were measured in small outdoor manure tanks for the spring, summer, and fall. The results showed total methane emissions were greatly reduced, by 87 and 89% for the 6.5 and 6.0 pH treatments. Ammonia emissions were also reduced, while nitrous oxide was not affected. These results indicate that acidification is a promising technique, and more research is needed to adapt this strategy to farm-scale manure storages.


Liquid dairy manure storages are sources of methane (CH4), nitrous oxide (N2O), and ammonia (NH3) emissions. Both CH4 and N2O are greenhouse gases (GHGs), whereas NH3 is an indirect source of N2O emissions. Manure acidification is a strategy used to reduce NH3 emissions from swine manure; however, limited research has expanded this strategy to reducing CH4 and N2O emissions by acidifying dairy manure. This study compared control dairy manure (pH 7.4) with two treatments of acidified manure using 70% sulfuric acid (H2SO4). These included a medium pH treatment (pH 6.5, 1.4 mL acid L−1 manure) and a low pH treatment (pH 6, 2.4 mL acid L−1 manure). Emissions were measured using replicated mesoscale manure tanks (6.6 m2) enclosed by large steady state chambers. Both CH4 and N2O were continuously measured (June-December 2017) using tunable diode laser trace gas analyzers. Ammonia emissions were measured three times weekly for 24 h using acid traps. On a CO2 equivalent basis, the medium pH treatment reduced total GHG emissions by 85%, whereas the low pH treatment reduced emissions by 88%, relative to untreated (control) manure. Total CH4 emissions were reduced by 87 and 89% from medium and low pH tanks, respectively. Ammonia emissions were reduced by 41 and 53% from medium and low pH tanks, respectively. Additional research is necessary to make acidification an accessible option for farmers by optimizing acid dosage. More research is need to describe the manure buffering capacity and emission reductions and ultimately find the best approaches for treating farm-scale liquid dairy manure tanks.

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