Biomethane Potential of Fresh Horse Manure and Straw-Based Litter

Abstract. Manure management is strategic for improving the environmental sustainability of farming. Anaerobic digestion (AD) has been considered one of the most appealing technologies for the production of biogas or biomethane (or renewable natural gas - RNG), playing a significant contribution to the ecological transition. AD has been implemented for years for the treatment of dairy, cattle, pig and poultry manures, but limited interest was encountered by horse farms. A laboratory-scale experiment was conducted with the aim of assessing the Biochemical Methane Potential of fresh horse manure, and straw-based litter from a farm equipped with a scraping removal system. The tests were performed employing the BioReactor Simulator System (BRS, Bioprocesscontrol, Sweden), consisting of 6 reactors with a volume of 2.0 L each. The inoculum was represented by digestate from a 1MWe digester fed with dairy cow manure and silages. The test were performed in mesophilic conditions (38°C) for 40 days. Horse manure presented total solids (TS) of 19.4% and volatile solids (VS) of 90.7%TS, while horse litter presented TS of 49.8% and VS of 90.0%TS. The results showed a methane yield of 48.2 NL/kg, 237.6 NL/kgTS, and 262.1 NL/kgVS for horse fresh manure, and of 82.1 NL/kg, 164.9 NL/kgTS, 183.2 NL/kgVS for litter. These results could be of interest for large horse facilities with litter collection, or for the codigestion of these feedstocks in existing AD plants.