Optimum design parameter determination of biogas digester using human faeces feedstock

Biogas digester operation depends majorly on C/N ratio, hydraulic retention time, pH, temperature, and mixing ratio of the domestic waste used. Temperature of 15 to 45°C, C/N ratio of 20 to 30, Hydraulic retention time of 1 to 30 days, mixing ratio of 10 to 20 %w/v and pH of 6.5 to 8 were considered for the analysis. Analysis of Variance (ANOVA) was used to test whether there are statistically significant differences between two or more independent groups using Design Expert Software. The R-square values are 0.933, 0.943 and 0.919 for mean, standard deviation and coefficient of variance respectively. These values were found to be in reasonable agreement with standards. Retention time is the only factor that is not involved in the interactions among the four significant factors selected out of the five factors under consideration. The maximum biogas yield was 86.24% at retention time of 30 days, temperature of 45°C, pH value of 6.5, mixing ration of 10%w/v, and carbon to nitrogen ratio of 20 respectively.   Key words:  Biogas, experiment, analysis of variance (ANOVA), faeces, digester, yield.