Fig. 6 gives the effect of nitrogen source on biogas
production rate while Fig. 7 gives the cumulative biogas yield.
As shown on Fig. 6, the biogas production rate peaked up in
both cases compared to the control. A maximum biogas
production rate of 85 mL/day and 60 mL/day were observed
for the guano supplement in RH and CD respectively. The
biogas production rate dropped to 50 mL/day and 40 mL/day
for RH and CD respectively when poultry droppings was used
as the nitrogen supplement. This could be attributed to a better
balance of C:N ratio from the bat droppings. Ahmadu et al. [38]
and Ojolo et al. [39] noted that the organic matter content of
poultry wastes is a factor that affects the digestion
environment and the microbial habitat, hence this could also
be responsible for the lower yield observed for the poultry
droppings supplement in this study. Table 2 gives the literature
of the effect of nitrogen supplement on the biogas yield for
same or different feedstocks.