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

[Display omitted] • First report of biochemical methane potential (B 0) for grazing dairy effluent. • B 0 of grazing dairy effluent is 161 L CH4 ·kg VS -1. • B 0 of intensive dairy (barn) effluent is 202 L CH4 ·kg VS -1. • Manure solids content is affected by cleaning method; and amount by capture extent. • Mechanical manure separation can reduce fugitive methane losses from effluent ponds. This study investigated biochemical methane potential (B 0) 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 B 0 was measured. A first B 0 value for grazing dairy effluent is reported, at 161 L CH4 ·kg VS -1. The B 0 of manure residues from intensive dairies with total mixed ration feeding was not significantly different, at 202 L CH4 ·kg VS -1. Passive solid–liquid separation decreased B 0 with potential fugitive methane losses. Mechanical separation preserved B 0 , 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, B 0 for Australian dairy residues was estimated at 76.2 million m3 N methane per annum, with a total energy content of 2.8 petajoules·annum−1. [ABSTRACT FROM AUTHOR]