The effects of storage time and temperature on biogas production from dairy cow slurry

Abstract

The effects of length of storage time and storage temperature on subsequent biogas production from dairy cow slurry by anaerobic digestion were investigated. Slurry was stored under anaerobic conditions at 9 °C and 20 °C for between 1 and 26 weeks prior to digestion. Digestion was carried out in 7 l continuously stirred tank reactors, with an average hydraulic retention time of 25 d. Storage of slurry at 9 °C had no significant effect on subsequent biogas production. However, after 8 weeks of storage at 20 °C there was an increasing negative impact on subsequent biogas production so that after 26 weeks of storage at 20 °C biogas production had decreased from 16.4 m3 t−1 to 5 m3 t−1 of fresh slurry. This reduction was strongly related to the decrease in the concentration of volatile solids in the stored slurry which was approximately 0.4 g kg−1 week−1. Storage time and temperature had no affect on the total nitrogen concentrations in the slurries, though both factors resulted in small increases in ammonia nitrogen concentrations.