3.4. Effects of different nitrogen sources on biogas production
The influence of different nitrogen sources (urea and poultry
droppings) on cumulative biogas yield and on biogas production
rate is shown in Figs. 4 and 5, respectively. From the results in Fig. 4,
the supplementation of the rice husk with urea reduced the biogas
yield when compared with the control while addition of poultry
droppings (PD) improved biogas production. The maximum values
of biogas production rate were 30 and 69 mL/day for the control
and poultry droppings, respectively, on day 2, while urea gave the
maximum biogas yield of 8 mL/day on day four (Fig. 5). The higher
biogas production rate from PD could be attributed to the fact that
the poultry droppings contained some remnants of their unconsumed
feed which made poultry droppings to have higher carbon
content than the urea N. In biogas production, it is necessary to
maintain a proper composition of the feedstock for efficient plant
operation so that C:N ratio in feed remains within desired range.
Thus, to meet this requirement, microbes need a 25e30:1 ratio of C
to N with the largest percentage of the carbon being readily
degradable [45,46]. Vermeullen [47] reported that high concentration
of N reduced the biogas production rate and this was
improved by the addition of paper, which contributed to increase in
C/N ratio.