3. Results and discussion
3.1. Influence of water dilution on biogas generation
The influence of water volume on cumulative biogas yield and daily rate of biogas generation were shown in Fig. 2 and Fig. 3, respectively. Feed to water ratio of 1:6 w/v gave the best cumulative yields. Although, the four tested ratios all gave greater yields than the control digester that had no water. Peak biogas production rates recorded for feed to water dilutions ratios of 1:4, 1:6 and 1:8 w/v were 130,150 and 143 mL/day, respectively. Also, the yield of 4 mL/day occurred at day 3 for control while 1:10 gave maximum yield of 50 mL/day at day 4, as shown in Fig. 3. Using brewer's spent grains; Onwosi [22] reported an improved biogas production at the dilution of 1:4 w/v but biogas production decreased as the dilution increased to 1:10 w/v. Report by Fernando [23] showed that excess dilution does not encourage bacterial cluster formation, which is needed for excellent biogas production.