The objective of this study was to know the effect of C/N ratios of fermentation substrate composed of beef cattle feces and water hyacinth (Eichornia crassipes) mix on the quality of produced biogas and sludge. Experiment was performed based on completely randomized design with three treatments of C/N ratio: i.e., 20, 25, 30, and replicated six times. The result showed that C/N ratios significantly increase the CH4 content. Highest CH4 content was provided by C/N ratio of 30. Ratios of C/N has no significant effect on CO2 content, and results in very low H2 content. The result also indicated that C/N ratios significantly decrease N, P, and K contents of the sludge. Although, C/N ratio of 20 provides the highest concentration of N, P, and K contents, all produced sludge may be used as single source of fertilizer.
Key words: beef cattle feces, water hyacinth, biogas, sludge