Effects of Storage Conditions, Total Solids Content and Silage Additives on Fermentation Profiles and Methane Preservation of Cattle Manure Before Anaerobic Digestion

The impacts of storage conditions, total solids content and silage additives were investigated at laboratory scale for cattle manure during up to 120 days. Wheat straw was used as co-substrate in the study of the effects of total solids content. Glucose and starch were used as model molecules of sugar-rich co-substrates. Single-handedly cattle manure lost 37% of its original methane potential after 120 days of anaerobic storage. This was essentially caused by the low total solids content and by the absence of water soluble carbohydrates in the feedstock. Wheat straw addition decreased moisture content and enabled cattle manure stabilization for a pH of 6.0. In contrast, extensive heterofermentative lactic acid bacteria fermentation occurred during co-ensiling with glucose and the pH quickly dropped to values below 4.0. Starch was used as substrate for fermentation but its hydrolysis limited bacterial activity and acidification. Finally, all the three co-substrates led to minimal methane potential losses after 120 days of storage. Co-ensiling will improve the energy efficiency of agricultural biogas plants that use stored cattle manure as feedstock.