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

• Slurry storage for 26 weeks at 9 °C had no significant impact on biogas production.
• Slurry storage at 20 °C had little effect on biogas production for first 8 weeks.
• After 8 weeks storage at 20 °C there was a steep decrease in biogas production.
• After 26 weeks storage at 20 °C biogas production was reduced by 70%.
• Storage time and temperature had no affect on slurry total N concentration.

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.