Effect of pH modification on ammonia emissions, greenhouse gas emissions, and sanitisation of pig slurry during short-term storage

Storage is an important part of the manure management chain where considerable losses of ammonia (NH₃) and greenhouse gases (GHG) can occur. Modification of the pH value is a promising approach to achieve slurry sanitisation and provide a safe organic fertiliser to farmers. Furthermore, such treatment should ideally induce a decrease of NH₃ or GHG emissions during storage. Therefore, the aim of the present work was to assess the effect of pH modification on NH₃ and GHG emissions during short-term storage of pig slurry. Three treatment strategies were considered: mineral acidification (pH 5), biological acidification (bio-acidification; pH 5) and alkalinisation (9.5). By-products from the paper-industry or carbon-rich substrates were used as alternative additives to mineral acidification. Results showed that all treatment strategies reduced E. coli numbers. However, complete slurry sanitisation (<1000 colony forming units (CFU) g⁻¹ slurry) was evident only with mineral acidification. A reduction of >85 % NH₃ emissions compared to raw slurry was obtained with slurry (bio)-acidification whereas alkalinisation led to NH₃ volatilisation similar to raw slurry. Sugar addition stimulated methane (CH₄) emissions during storage while alkalinisation led to minimal CH₄ emissions. The acid by-product used for slurry acidification significantly reduced carbon dioxide (CO₂) emissions. Slurry alkalinisation presented the lowest total GHG emissions, even when indirect nitrous oxide emissions were considered from volatilised NH₃. Results suggest that strategies used to sanitise pig slurry through pH modification can also be beneficial to mitigate NH₃ and/or GHG emissions during storage.