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
