Effect of spent mushroom substrate and waste paper briquette on methane production from anaerobic digestion

The objective of the study was to assess the methane yield of briquettes prepared from spent mushroom substrate and waste papermixed in equal proportion. Spent mushroom substrate after cultivation of Pleurotus florida on rice straw and waste paper was milled to less than 5 mm size. They were briquetted in equal mass proportion in a screw type machine. Briquette and individual substrates were assessed for their methane potential under anaerobic conditions in 125 ml bottles incubated at 37°C for 60 days. Data was statistically analyzed using analysis of variance. Dunnett's post hoc test was used to assess the significance (P < 0.05). When waste paper was co-digested with spent mushroom substrate as powder, methane yield of 168 ml CH4 g'1 VS was observed. When spent mushroom substrate - waste paper as briquette was used, highest methane yield of 250 ml CH4 g-1 VS was observed. Size reduction in briquetting process made the cellulose and other components of plant cell walls more accessible to the microorganisms. SEM and FT-IR studies confirmed the impact of briquetting as a pretreatment step. Volatile fatty acid (VFA) to alkalinity ratio was observed as 0.26 at the end ofdigestion ofbriquettes, which confirmed the process stability. Methane yield from anaerobic digestion process was found to be enhanced by briquetting of spent mushroom substrate and waste paper.