of glycerol co-digestion with digestate, as compared to digestate
alone. The hydraulic retention time for co-digestion was determined
to be 32 days using Eq. (1) and when the glycerol was
loaded at 33% of the total OLR of the reactor, no inhibitory effects
were evident. The maximum Biological Methane Potential (BMP)
for glycerol co-digested with digestate samples was 766 ± 42
ml/gVS as shown in Fig. 1. The digestate alone reached a maximum
methane production of 112 ± 14 ml/gVS. The average difference
between the two samples was 608 ml/gVS, which is 7 times as
much as the gas production of digestate alone. This indicates that
glycerol adds significant methane production when co-digested
with digestate, and does not show short term toxicity effects when
loaded at 33% of the total OLR. Crude glycerol co-digestion with
various substrates has been reported to increase gas output in
BMP and CSTR tests (Astals et al., 2011; Heaven et al., 2011).