The effect of two dairy manure treatments, solid-liquid separation (SLS) and anaerobic digestion (AD), on methane potential and the speed of production was evaluated. Assays were performed in the lab to measure methane (CH4) production over 202 d from dairy manure samples taken before and after each treatment. Compared to raw manure, CH4 emissions on a per-L basis were reduced 81% by SLS and 59% by AD, on average. The mean (SD) ultimate CH4 emission potential (B0) per kg of volatile solids (VS) was 247 (8) L CH4 kg-1 VS for raw manure, 221 (9) L CH4 kg-1 VS for separated liquid, and 160 (4) L CH4 kg-1 VS for anaerobic digestate. Thus, SLS reduced the B0 of the liquid fraction by 11% and AD reduced B0 by up to 35% compared to raw manure. Manure treatment affected the speed of CH4 production: SLS increased the CH4 production rate and thus separated liquid manure was the fastest to produce 90% of the ultimate CH4 production. Therefore, both the speed of degradation and B0 should be considered when assessing these techniques for farm-scale manure storages, because actual emission reductions will depend on storage conditions.
Keywords: Dairy manure treatment; anaerobic digestion; biochemical methane potential test; maximum methane production rate; solid–liquid separation.