Effects of different treatments of manure on mitigating methane emissions during storage and preserving the methane potential for anaerobic digestion

Current agricultural practices in regards to storage of manure come with a significant GHG contribution, due, to a big extent, to CH₄ emissions. For example, in Denmark, the agricultural sector is responsible for about 11.1 metric tons of CO₂ equivalents; only about 0.2 metric tons come directly from CO₂, while 6.0 tons come from CH₄. The present study aims at evaluating and comparing two methods based on their effect on suppressing CH₄ emissions during storage as well as on preserving and enhancing CH₄ yield in a subsequent anaerobic digestion step: the commonly applied acidification with H₂SO₄ as acidifying agent and thermal treatment at the mild temperatures of 70 and 90 °C (pasteurization). Although both treatments effectively suppressed CH₄ emissions during storage, they exhibited a significant difference in preserving and/or enhancing the CH₄ potential of manure. Specifically, thermal treatment resulted in 16–35% enhancement of CH₄ potential, while acidification resulted in decreasing the CH₄ yield by 6–23% compared to non-treated manure. Further investigation showed that storage itself positively affected the CH₄ potential of treated manure in a subsequent anaerobic digestion step; this was attributed to microbial activity other than biomethanation during storage. In overall and based on the results obtained regarding suppression of CH₄ emissions during storage as well as CH₄ potential enhancement, pasteurization at the temperatures tested is a promising alternative to the broadly applied acidification of manure.