Greenhouse Gas Mitigation through Dairy Manure Acidification

Abstract

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. Core Ideas Acidification reduced total CO2–eq GHGs from liquid dairy manure by 85 to 88%. Total CH4 emissions were reduced by 87 to 89% from acidified manure. NH3 emissions were reduced by 41 to 53% from acidified manure. A range of yearly H2SO4 cost was estimated to be Can$6.55 to $19.6 cow−1.

Acidification of Residual Manure in Liquid Dairy Manure Storages and Its Effect on Greenhouse Gas Emissions

“…where Total CH 4 is the total production over two storage periods, Acidified manure CH 4 is the production from one storage period where all manure was acidified (reported by Sokolov et al, 2019), and PA inoculum CH 4 is the total CH 4 production from the PA inoculum treatment.…”

“…Fresh manure was added to each tank on May 28 and 29, 2018 using a pumping truck to transport manure from the farm to the research site. The NA inoculum treatment received 1.1 L m −3 H 2 SO 4 , which is half as much as a previous meso-scale study (Sokolov et al, 2019) but considerably more than in the laboratory study where rates were only 0.16 L H 2 SO 4 m −3 of total manure (i.e., 0.03 mL of 98% H 2 SO 4 in 180 mL of stored manure; Sokolov et al, 2020).…”

“…The previously acidified (PA) manure was acidified using sulphuric acid (70% H 2 SO 4 ; 2.4 L m −3 manure) to pH 6. Both the PA manure and untreated manure inoculum remained in storage for 1-yr (Sokolov et al, 2019). Additional information about storage conditions of the inoculating manure prior to this study can be found in Sokolov et al (2019).…”

“…Liquid dairy manure is a substantial source of methane (CH 4 ) and moderate source of nitrous oxide (N 2 O), and ammonia (Le Riche et al, 2016;Sokolov et al, 2019). Both CH 4 and N 2 O are greenhouse gases (GHG) contributing to global warming and climate change, while ammonia (NH 3 ) is an indirect source of N 2 O and is a toxic gas hazardous to human health (Jayasundara et al, 2016;Sokolov et al, 2019). Liquid manure is often stored on farms for >100 days prior to spreading onto fields.…”

“…Dairy manure acidification (to pH 6-6.5) with sulfuric acid (H 2 SO 4 ) was found to decrease CH 4 (>87%) and NH 3 (>40%) emissions (Sokolov et al, 2019). Sommer et al (2017) reported 68% reductions of CH 4 and 62% of NH 3 with H 2 SO 4 acidification (to pH 5.2-5.5).…”