Effects of pH and substrate:inoculum ratio on batch methane fermentation

Batch digestion experiments were conducted to determine the effects of inoculum:substrate ratio and initial medium pH on methane production from glucose. A ratio between the chemical oxygen demands (COD) of the substrate and inoculum solids (SISR) was used to quantify the food to microorganisms (F/M) ratio. Two periods of active methane production, separated by a period of inactivity, characterized the fermentation. The duration of inactivity was affected by both SISR and the initial medium pH. It decreased as SISR was decreased or when a higher initial pH was used. With a SISR of 4.8 and a pH of 7.2 or 7.0, the inactive period was eliminated, indicating satisfactory coupling of the acid- and methane-forming phases. Ultimate methane yield at a SISR of 4.8 was higher than at a SISR of 38.5.