Anaerobic digestion of dairy cow and goat manure: Comparative assessment of biodegradability and greenhouse gas mitigation

• Anaerobic digestion (AD) of dairy cow and goat manure was studied. • Dairy goat manure exhibited lower biodegradability compared to cow manure. • Higher methane yields were achieved from cow manure compared to goat manure. • 2.21 t CO 2 -eq/cow·year and 0.27 t CO 2 -eq/goat·year GHG reductions were achieved. This study evaluated the anaerobic digestion (AD) of dairy cow and goat manure from dairy farming operations. The physicochemical characteristics, biodegradability and greenhouse gas emissions (GHG) reduction potential were assessed. Dairy goat manure exhibited higher volatile solids (16 % vs. 10 %) and 34 % greater chemical oxygen demand content (COD) compared to cow manure, indicating better suitability for AD. However, biochemical methane potential tests revealed higher methane yields from cow manure (81 % biodegradability) compared to goat manure (26 % biodegradability), attributed to slower hydrolysis rates and recalcitrant composition of goat manure. Both manures displayed suboptimal carbon-to-nitrogen ratios (<20:1) and excessive levels of mineral nutrients such as calcium. The ammonia–nitrogen and volatile fatty acid levels remained below threshold limits throughout the anaerobic digestion process, indicating no significant accumulation or inhibition. Recovering biogas through AD showed potential GHG reductions of 64 % (2.21 t CO 2 -eq/cow·year) and 69 % (0.27 t CO 2 -eq/goat·year) compared to conventional manure management practices. While pretreatment and co-digestion could enhance biogas production, further research is needed to optimise these strategies for efficient resource recovery and environmental sustainability in dairy farming operations. Abbreviations: AD, anaerobic digestion; AWMS, animal waste management systems; BMP, biochemical methane potential; CHNS, carbon, hydrogen, nitrogen, and sulphur; C/N, carbon-to-nitrogen, COD, chemical oxygen demand; GC-FID, gas chromatography-flame ionisation detection; GHG, greenhouse gas; GWPM, global warming potential of methane; He, helium; ICP-MS, inductively coupled plasma mass spectrometry; I/S, inoculum-to-substrate ratio; IPCC, International Panel on Climate Change; NH 3 -N, ammonia–nitrogen; SD, standard deviation; TBMP, theoretical biochemical methane potential; TN, total nitrogen; TS, total solids; VFAs, volatile fatty acids; VS, volatile solids.