Improving pig manure conversion into biogas by thermal and thermo-chemical pretreatments

Thermal (70–190 °C) and thermo-chemical (pH = 10 and 12, 25 °C and 90–190 °C) treatments were investigated in order to maximise the production of methane from pig manure. Methane production from treated and raw manure was assessed from batch mesophilic biochemical methane potential tests. Methane potential of manure soluble fraction increased with the temperature of thermal treatments whereas temperatures higher than 135 °C were necessary to improve the methane potential of the total fraction. The best results were obtained with the highest temperature (190 °C).When thermo-chemical treatments were carried out at pH = 12, both liquid phase and total fraction manure biodegradabilities were significantly decreased. Methane potential of manure total fraction was improved by treatments at pH = 10 and temperatures ranging from 150 to 190 °C but biodegradability of liquid fraction was highly degraded, except for treatment at 190 °C. In both cases of thermal and thermo-chemical treatments at pH = 10, the increase in manure biodegradability seemed to be linked to the reduction of the hemicellulosic like fraction.