Anaerobic digestion of the liquid fraction of dairy manure in pilot plant for biogas production: Residual methane yield of digestate

The performance of the only dairy manure biogas plant in Cantabria (Northern coast of Spain) was evaluated in terms of liquid–solid separation and anaerobic digestion of the liquid fraction. Screened liquid fraction was satisfactorily treated in a CSTR digester at HRTs from 20 to 10 days with organic loading rates ranging from 2.0 to 4.5 kg VS/(m3 d). Stable biogas productions from 0.66 to 1.47 m3/(m3 d) were achieved. Four anaerobic effluents collected from the digester at different HRTs were analyzed to measure their residual methane potentials, which ranged from 12.7 to 102.4 L/g VS. These methane potentials were highly influenced by the feed quality and HRT of the previous CSTR anaerobic digestion process. Biomethanization of the screened liquid fraction of dairy manure from intensive farming has the potential to provide up to 2% of total electrical power in the region of Cantabria.

► High solids concentration in manure enhances efficiency of screw press separators.
► VFA concentration in manure is a good indicator in terms of methane potential.
► Digestate can yield an attractive amount of gas.
► Biogas from dairy manure can supply 2% of electrical power consumption in Cantabria.