Suitability of Canola Meal forAnaerobic Co-digestion with Dairy Manure

Abstract

Due to the renewed interest in biogas production, co-digestion of livestock manure, especially dairy manure, and other agro-wastes has emerged as an appropriate practice in enhancing the economic viability of anaerobic digestion. In this study, various ratios of canola meal and dairy manure (100% canola meal, 10% canola meal and 90% manure, 20% canola meal and 80% manure, 40% canola meal and 60% manure, and 100% manure) by volume basis were co-digested in 0.5 L batch bioreactors at a temperature of 35°C ±1°C for 25 days and a loading of 7.5% total solids (TS). Pre- and post-digestion samples were collected and analyzed for TS, volatile solids (VS), nutrients, pH, volatile fatty acids (VFAs), fiber, and chemical oxygen demand (COD). Biogas yield was measured daily using the water displacement method, and gas composition (mainly methane, CH4) was analyzed weekly within 72 h of collection using a gas chromatograph (HP 5890 Series II) equipped with a flame ionization detector (FID). Results indicated that 0% canola meal (100% manure) and 100% canola had specific methane yields of 352 and 83 L CH4 kg-1 VS, respectively. Addition of canola meal in the dairy manure resulted in decreased cumulative biogas and specific methane yield. This is suspected to be caused by the elevated levels of VFAs of more than 4000 mg L-1 in canola meal and dairy manure mixtures. Alternative methods should be explored to alleviate the inhibition in biogas production caused by elevated VFAs.