Biochemical methane potential of dairy manure residues and separated fractions: An Australia-wide study of the impact of production and cleaning systems

This study investigated biochemical methane potential (B0) of manure residues and solid-liquid separation fractions from Australian dairies. This is important for country-specific sector emissions and biogas potential estimates. A range of samples were collected from 12 farms across 4 Australian states, and B0 was measured. A first B0 value for grazing dairy effluent is reported, at 161 LCH4·kgVS-1. The B0 of manure residues from intensive dairies with total mixed ration feeding was not significantly different, at 202 LCH4·kgVS-1. Passive solid-liquid separation decreased B0 with potential fugitive methane losses. Mechanical separation preserved B0, allowing organic matter diversion to reduce fugitive methane emissions. Cleaning method at a dairy significantly influenced residue total solids content, important for solid-liquid separation and selection of anaerobic digestion technology. Overall, B0 for Australian dairy residues was estimated at 76.2 million m3N methane per annum, with a total energy content of 2.8 petajoules·annum-1.