Evolution of chemical composition and gas emissions from aged pig slurry during outdoor storage with and without prior solid separation

Chemical composition and gas emissions from two types of pig slurry were evaluated: the liquid fraction of mechanical solid–liquid separated slurry (SS), and raw slurry (RS). The slurry was obtained at the end of a pig fattening period and was stored in 100 l vessels for 15 weeks simulating outdoor storage conditions. During this period, representative samples were taken and analysed for chemical composition. Methane, carbon dioxide, ammonia, water vapour and nitrous oxide emissions were recorded. The results showed a high biological degradation during the first five weeks of outdoor storage in SS and RS slurries, as a result of an increase in the dissolved chemical oxygen demand, volatile fatty acids and carbon dioxide emission observed in this period. However, methanogenic activity was not evident until week 6 of storage in both slurries, confirmed by the volatile fatty acids accumulation and the negligible methane emissions during the first five weeks of storage. The results showed that differences in the initial slurry organic matter content, influenced by solid separation process affects the evolution pattern of the organic matter degradation. Storage time can considerably affect the biodegradability of organic matter in pig slurry. ► Two types of aged pig slurry: with and without previous solid–liquid separation. ► Results show a high biological degradation during the first 5 weeks of storage. ► Methanogenic activity was not evident until week 6 of storage in both slurries. ► Storage time can considerably affect the biodegradability of OM in pig slurry. ► Solid separation process alters the initial content and degradation of OM.