Efficient biogas production from the liquid fraction of dairy manure

A farm integrated process for small scale biogas production from manure is designed. The anaerobic digestion (AD) process is tested on diary manure and consists of a manure storage tank, a separation unit to remove coarse solids, and an AD reactor for biogas production using the resulting manure liquid fraction as substrate. The performance of the 220 L pilot AD reactor, run at 8.8 days hydraulic retention time depended on the raw manure storage time. The biogas production was 0.7-1.5 g COD L-1 reactor d-1, and the maximum biogas methane yield was 0.19 g COD g-1 feed COD. The overall AD process gained 29 % of the total methane potential of the raw dairy manure. High manure alkalinity (8-9 g CaCO3 L-1) ensures stable pH (7.8-8.0) at high load. The results imply that diary manure can be treated more sustainable by AD at even higher loadings.