Methane Emissions from Livestock Slurry: Effects of Storage Temperature and Changes in Chemical Composition

Abstract

Livestock production contributes to releasing methane into the atmosphere. Liquid manure management offers significant opportunities to reduce these emissions. A better understanding of the factors controlling methane emissions from manure is necessary to select effective mitigation strategies. Our study aimed to identify the influence of storage temperature and the associated change in chemical composition on methane emissions from dairy and fattening pig manure. Storage temperature affects microbial activity and induces changes in chemical composition that are key influences in methane emissions. Dairy and fattening pig manure samples were stored at five different temperatures (5–25 °C) for 90 days in a laboratory-scale experiment to measure the methane production. The chemical composition of the slurry samples was analyzed, and the biochemical methane potential (BMP) tests were performed before and after storage. For pig manure stored at 25 °C and 20 °C, methane emissions accounted for 69.3% and 50.3% of the BMP, respectively. Maximum methane emissions for dairy slurry were observed at 25 °C but remained at a low level. Analyses of the accumulation of volatile fatty acids (VFAs) during storage are presented in few studies, this work revealed a potential inhibition of methane production, where the accumulation of VFAs was most elevated in samples stored at 20 °C and 25 °C. This partly counteracted the increase in methane emissions expected from the higher temperatures. The degree of VFA and dissociated fatty acids accumulation in dairy cattle slurry should be assessed for more accurate estimations of methane emissions from slurry stores.

Pig slurry organic matter transformation and methanogenesis at ambient storage temperatures

“…Hilgert et al. (2022) measured ∼9, ∼30, ∼119, and ∼166 L CH4 kg VS −1 from pig slurries incubated for 90 days at 10°C, 15°C, 20°C, and 25°C. These figures are equivalent to ∼4.5, 16.5, 65.5, and 91.4 g CH4 kg VS −1 , which is close to our measurements.…”

“…Hilgert et al. (2022) found 19% and 60% VS loss at 5°C and 25°C in pig manure stored for 90 days, but CH 4 loss at 25°C was 130 times higher than at 5°C. This suggests that both composition of VS and methanogenic community development are important to understand at varying temperatures.…”

Simple Management Changes Drastically Reduce Pig House Methane Emission in Combined Experimental and Modeling Study

“…Emission Calculations. Gas emission was estimated according to eq 1, where E is the emission rate (g h −1 ), M is the molar mass (g mol −1 ), C out is the concentration (atm) measured in the air outlet from the sections, C in is the concentration (atm) measured in the air inlet for the sections, Q is the ventilation rate (m 3 h −1 ), R is the gas constant (m 3 • atm•K −1 •mol −1 ), and T is the temperature (K).…”

“…These default settings were initially chosen based on fitting to methane productivity at varying temperatures as reported by Elsgaard et al 25 Here, the numbers of methanogen groups were reduced to three (m0, m1, and m2) to decrease computation time and complexity during parameter estimation. In light of recent studies on methanogen activity at low temperatures, 3,26 VFA substrate conversion rates (q max,opt ) at low temperatures were reduced taking into consideration measured methane potential curves 3 and implementing of a new methanogen group (m0) (Supporting Information, Table S2 and Figure S1). Enrichment of VSd in the residual slurry remaining after slurry removal (from pig houses as well as from outside storages) was implemented in a similar fashion as for methanogens, which has previously been described.…”

“…In many regions with intensive livestock production, manure from pigs and cattle is managed as the liquid slurry in pits and channels underneath the barn floor. In such systems, the slurry environment is anaerobic, and anaerobic microbes transform organic matter to methane and carbon dioxide. , The biological processes driving organic matter transformation depend strongly on temperature. − Therefore, strategic removal of slurry from pig houses with a temperature around 20 °C to cold outside storages or anaerobic digesters can reduce net methane emission from the whole management chain. In Danish finisher pig houses, slurry pits underneath the floor are typically 40–60 cm deep, and the slurry is removed with a vacuum flushing system when the pit is nearly full (after 5–6 weeks).…”