each set-up included 1.5 L bottle that served as the anaerobic
digester, an inverted 50 mL graduated burette containing
acidified water as the biogas collector, and a rubber container
which was used to collect the water discharged from the
biogas collector. A rubber pipe was used to convey the gas
produced in the digester to the collector. The anaerobic
digestion was maintained in the mesophilic range in that the
room temperature was 31±1oC [18-21]. It has been reported
that stratification can lower the production rate of biogas [22,
23], thus this was avoided by mixing each digester once daily
for 30 days. The water displacement method used in [24] was
utilised in recording the biogas production rate for each
anaerobic digester.