Experimental Analysis on the Effects of Bio-char Addition in Bio-gas Production Process and Comparison of Biogas Yields

Abstract

The addition of pyrolytic biochar to anaerobic digestion of food waste with four different percentage ratios was investigated to evaluate the effect of biochar addition on biogas production as a functional additive and to compare the biogas yields with a control (No) BC addition for optimizing the biogas production by biochar additive. The biochar addition was tested with the ratio of 5%, 10%, 15% and 20% (w/w) and was investigated for 40 days in plastic biogas digester with initial volume of 300 ml. The results indicate that, the maximum cumulative %CH4 and biogas volume yields of the five tests, 0%, 5%, 10%, 15% and 20% BC were 56.07%, 60.0%, 56.33%, 50.99%, 50.0% and 420, 530, 490, 425, 396 (ml) respectively. The addition of 5% and 10% biochar shortened the lag phase of the AD by 5.26% and the 15% and 20% BC by 7.89%. The 5% and 10% BC had more positive effects on cumulative %CH4, biogas volume and conversion efficiency on the AD relative to the control (0%) BC and both increase the cumulative values by 10.25% and 12.13%, 110.0ml and 86.0ml, 6.71% and 4.02% respectively. On average the 5% and 10% BC increase the methane, biogas volume and conversion efficiency by 1.89%, 47.62ml, 3.52% and 0.56%, 36.54ml, 1.76% consecutively. While, the 15% and 20% BC additions decrease the %CH4 and conversion efficiency by 5.13%, 7.4% and 2.56%, 4.82% respectively. But, 15% increase the volume by 4.99ml, while 20% decrease by 6.62ml. The overall effect of the given biochar additive ratio on methane quality (%) and biogas volume quantity indicates, the 5% BC increases the CH4 quality by 363.92ml (2.4%) and the 10% BC increases by 252.89ml (1.09%) per digester. While, the 15% BC decreases by 110.17ml (5.11%) and the 20% BC decreases by 268.14ml (8.83%) per digester. On the total biogas volume, the 5%, 10% and15% BC increases by (619, 475, 64.8) ml, respectively. While, 20% BC decreases by 86ml/digester. The comparison of all results indicates that, the 5% and 10% BC additions had more positive effects, while the 15% and 20%BC had more negative effects on %CH4, biogas volume and conversion efficiency. The results were less as compared to other treatments of biochar additives due to the pretreatment case on both substrate and additive. It can be concluded that, a small dose of biochar additive has advantage over more dose for enhancement of biogas production as the effectiveness of biochar addition depends on the additive ratio