4. Conclusions
Apple waste was anaerobically treated with swine manure in
both batch and continuous modes. The AW was found to be a potential
substrate for co-digestion with the SM for biogas production.
Biogas production in the batch test improved when using a
mixture of AW and SM (AW:SM = 33: 67,% VS basis) as opposed
to SM only. The biogas production from mixed feed was significantly
higher under thermophilic conditions than under mesophilic
conditions, but there was no significant difference in
methane production. The modified Gompertz model fitted the
experimental results better than a first-order kinetic model. The
results of the continuous tests showed positive synergetic effects
on biogas production when the AW content in the feed was increased
from 25% to 33% (VS basis) at an OLR of 1.6 g VS/L/d and
a HRT of 30 days, but a further increase in AW content from 33%
to 50% had a negative synergetic effect due to the rapid accumulation
of TVFA and the drop in pH.