The Influence of Total Solid Contents on Biogas Yield from Cattle Manure Using Rumen Fluid Inoculum

Problem statement: Anaerobic digestion was a biological method used to convert organic wastes into biogas and a stable product for land application without adverse environmental effects. The biogas produced could be used as an alternative renewable energy source. The aim of this study was to analyze the influence of total solid contents on biogas yield from cattle manure using fluid rumen inoculums. Approach: A series of laboratory experiments using 400 mL biodigester were performed in batch operation mode. Given 100 g of fresh cattle manure was fed to each biodigester and mixed with fixed 50 mL of rumen fluid and different volumes of tap water resulting six different Total Solid (TS) contents i.e., 2.6, 4.6, 6.2, 7.4, 9.2, 12.3 and 18.4%. Results: The results showed that the best performance for biogas production was the digester with 7.4 and 9.2% of total solid i.e., gave biogas yield 184.09 and 186.28 mL gVS^-1, respectively after 90 days observation. While the other TSs content of 2.6, 4.6, 6.2, 12.3 and 18.4% gave the biogas yield 115.78, 122.33, 172.34, 137.99 and 54.87 mL gVS^-1, respectively. Conclusion: These results suggested that, based on TS content effects to biogas yield, rumen fluid inoculum exhibit the similar effect with other inoculums. In all cases, there was no variation of pH, fat, protein and ash content in sludge after digestion at several variation of pH. During digesting, pH tends to increase to neutral pH i.e., optimum pH for methanogenic bacteria. The effect of rumen fluid concentration to biogas production will need to be studied in the next step research.