Effect of Substrate to Inoculum Ratio on Biogas Yield

Abstract

This paper aims at finding the effect of substrate to inoculum ratio on biogas yield. The batch anaerobic digestion experiment was conducted using the Automatic Biogas Potential Test System (AMPTS II). Substrate to inoculum ratios of 1:1, 2:1 and 3:1 were used for the study on anaerobic digestion of both food waste and cow dung. Tests were carried out starting with the preparation of substrates, substrate characterization to determine the moisture content (MS), ash content (AC), total solids (TS), volatile solids (VS) and ultimately batch anaerobic digestion experiments under thermophilic conditions (37 0 C). The TS and VS contents of food waste ranged between 19.6–22.0% and 90.7 – 92.6% respectively while moisture content, total solids and volatile solids for cow dung were 67.2, 32.8 and 96.0% respectively. The cumulative biogas yields of reactors with cow dung were 12847 Nml, 3598.3 Nml and 4199.4 Nml for the ratios of substrate to inoculum of 2:1, 3:1 and 1:1 respectively. A 67% increase in accumulated volume of biogas was obtained by increased Substrate/Inoculum ratio from 1:1 to 2:1. On the other hand the cumulative biogas yields of reactors with food waste and inoculum were 110.2 Nml, 70.1 Nml and 46.7 Nml for the ratios of substrate to inoculum of 2:1, 3:1 and 1:1 respectively. When compared with those from cow dung, a 58% increase in cumulative biogas yield was obtained through an increased Substrate/Inoculum ratio from 1:1 to 2:1 from food waste.