The digestion temperature has an influence on the
ultimate methane yield, as well as the methane content. In the mesophilic temperature range,
25–35 °C, the higher the temperature, the better the methane yield. However, the yield did not
linearly increase with increasing tempera- ture. The yields at 30 and 35 °C were similar, but were
quite high compared to that at 25 °C, by more than 13–17%. However, this result does not
mean the higher temperature the more optimal, due to the larger energy requirement at higher
digesting temperatures. Therefore, careful consider- ation of the net energy balance between the
increased heat- ing energy demands and improved additional methane production at higher operating
temperatures must be simultaneously taken into account when deciding the eco- nomical digesting
temperature. Furthermore, this net energy balance is inevitably dependent upon the VS con- tent
of the feed, as methane comes from the degradation of VS. Temperature shocks led to a reduction
in the biogas production rate compared to that of the control,