Methane inhibition from a slurry storage by addition of chemical and natural additives

B. Mohd Saufi, J. Davey and C. Dave

Abstract
Mitigating methane (CH₄) emission from beef and dairy slurry manure by biogas processing is well adopted. However, the main constrains for small-medium farmers are start-up infrastructure, maintenance costs and efficiency and these issues need to be attended. A study was carried out to assess an alternative strategy in reducing CH₄ emission during beef slurry storage by means of using additives. In doing so, cattle slurry from commercial beef farm was collected and stored with various additives at small scale (500 mL). The slurry CH₄ emission, pH and oxidation redox potential (ORP) value were observed during the storage period. A closed respiratory meter (Micro-Oxymax) was employed to monitor the methane emissions during storage. Notably, a reduction in slurry
pH (pH 4.0) through the addition of hydrochloric acid (HCl) has significantly reduced (p ≤0.05) CH₄ emission. Furthermore, the addition of glucose (10%w/v)
has reduced slurry pH to <4.0. In contrast, CH₄ emission was not significantly reduced through the slurry amendments as measured by respiratory meter using various concentrations of effective microorganisms (EMs). It was found that slurry induced acidification through induced carbohydrate fermentation in
both fresh and aged slurry reduced the CH₄ emission during storage period as indicated by lower methane headspace concentration (<0.05% CH₄) compared to the untreated slurry (>0.10% CH₄). Apart from that, glucose addition revealed inconsistent effect on volatile fatty acids production and hence, the mechanism for ‘self-acidification’ is unclear. The addition of fermentable carbohydrates into slurry during storage period induced acidification by anaerobic fermentation, which subsequently has inhibited CH₄ emission.

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