Process intensification in methane generation during anaerobic digestion of Napier grass using supercritical carbon dioxide combined with acid hydrolysis pre‐treatment

Napier grass was subjected to pre‐treatment techniques such as thermal acid hydrolysis and supercritical carbon dioxide (scCO2) and combination of both. Anaerobic batch digestion was conducted using activated sludge mixed microbial consortia for 15 days. Parameters influencing scCO2 hydrolysis were optimized. scCO2‐acid and acid pre‐treatment gave maximum production of biogas, which was 2.5 times higher than that without pre‐treatment. The optimum condition were 100 °C and 99 atm pressure, supercritical carbon dioxide, 0.6 % w/v sulphuric acid, time 1 h. The highest methane yield of the pre‐treated samples were 118 ml CH 4 /g total solids added. The production of hydrolysate and volatile fatty acids during pre‐treatment ensures increase in chemical oxygen demand levels which promotes methane productivity. These results indicated that scCO2 with acid hydrolysis pre‐treatment could be an effective method for increasing biodegradability and improving methane yield of Napier grass.