Phyllanthus emblica residues (PER) are unsuitable as a single substrate for biogas production because they usually
contain residual tannins which are methanogenic inhibitors. In addition, the ratio of total chemical oxygen
demand (tCOD) to nitrogen of 14:1 w/w in the PER is much lower than the value that is usually recommended.
It is shown that a mixed substrate of PER and food waste has a tCOD to N ratio that is closer to recommended
values and that co-digestion with this mixed substrate improves the yield of biogas. In this study, three labscale
bioreactors were used to investigate (1) the single digestion of food waste, (2) the single digestion of the
PER and (3) the co-digestion of food waste and PER at a mixing ratio of 11:1 g tCOD food waste/g tCOD PER.
The organic loading rates (OLRs) of the co-digestion were 2.13, 2.83 and 4.26 g tCOD/L·day at hydraulic retention
times (HRTs) of 40, 30 and 20 days, respectively. The OLR of the co-digestion was chosen to be equal to
the sumof the OLRs of the single digestions. The methane production of the co-digestionwas found to be greater
than the sumof themethane production of the two single digestions by 12% atHRTs of 40 days and by 22% at HRT
of 30 days. In addition, th emethane yield of the co-digestionwas higher than that of each of the single digestions.
The co-digestion strategy was also applied to a pilot-scale 2000 liter-bioreactor that was usually used for treating
food waste. It was found that the methane production was increased by 34% when the substrate was switched
from food waste to the mixed food waste and PER co-substrate, and no signs of inhibition were observed.
Phyllanthus emblica residues (PER) are unsuitable as a single substrate for biogas production because they usually
contain residual tannins which are methanogenic inhibitors. In addition, the ratio of total chemical oxygen
demand (tCOD) to nitrogen of 14:1 w/w in the PER is much lower than the value that is usually recommended.
It is shown that a mixed substrate of PER and food waste has a tCOD to N ratio that is closer to recommended
values and that co-digestion with this mixed substrate improves the yield of biogas. In this study, three labscale
bioreactors were used to investigate (1) the single digestion of food waste, (2) the single digestion of the
PER and (3) the co-digestion of food waste and PER at a mixing ratio of 11:1 g tCOD food waste/g tCOD PER.
The organic loading rates (OLRs) of the co-digestion were 2.13, 2.83 and 4.26 g tCOD/L·day at hydraulic retention
times (HRTs) of 40, 30 and 20 days, respectively. The OLR of the co-digestion was chosen to be equal to
the sumof the OLRs of the single digestions. The methane production of the co-digestionwas found to be greater
than the sumof themethane production of the two single digestions by 12% atHRTs of 40 days and by 22% at HRT
of 30 days. In addition, th emethane yield of the co-digestionwas higher than that of each of the single digestions.
The co-digestion strategy was also applied to a pilot-scale 2000 liter-bioreactor that was usually used for treating
food waste. It was found that the methane production was increased by 34% when the substrate was switched
from food waste to the mixed food waste and PER co-substrate, and no signs of inhibition were observed.
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