Abstract
Methane gas yields and production processes were studied in laboratory experiments on the codigestion of cattle manure with organic cosubstrates using digesters with an effective volume of 6 liters maintained at a mesophilic temperature of 37°C and with a hydraulic retention times of 30 days. Butter, breadcrumbs and protein supplements were used as cosubstrates. We found that lipids, carbohydrates and proteins contribute differently when used as cosubstrates for cattle manure digestion. The maximum loading rates of the cosubstrates before they inhibit methanogenesis were 2.2gVS/L per day for breadcrumbs, 2.4gVS/L per day for butter and 0.8gVS/L per day for protein. We measured methane gas (CH4) yields per amount of volatile solids (VS) for each cosubstrate. Butter showed the highest yield (0.82L/gVSlipid at 68 percent concentration). The yield of breadcrumbs was second highest (0.42L/gVScarbo at 57 percent). Protein yield ranked third (0.31L/gVSprotein at 64 percent) and was only 54 percent of the theoretical methane yield of protein. NH4-N generated by protein codigestion seemed to inhibit methanogenesis even at low loading rates.
