| The use of off-farm materials as amendments in anaerobic digestion of manure is an option that is being explored more extensively, due to the benefits of boosting biogas production, and making the process more economical for the farmer. The addition of varying amounts of glycerol, which is a by-product in the biodiesel industry, was used as an amendment to anaerobic digestion of hog manure in lab-scale tests. Four bench-scale anaerobic digesters were operated under mesophilic conditions (35°C) at an SRT of 17.5 days. They were tested to determine how the anaerobic digestion process, and the biogas production, would be affected by the addition of glycerol.;The use of 2% glycerol produced the greatest amount of methane and biogas, however stabilization time was quite high, and the digestion of nutrients in the manure appeared to decrease. The addition of 4% glycerol resulted in an overloading of COD and digester failure. The addition of 1% glycerol resulted in a doubling of the methane and biogas production and the acclimation period was quite short, while the effluent quality remained good. There appeared to be no detrimental effects of using crude, industrial-based glycerol compared to pure, chemical-grade glycerol. Batch tests also confirmed that using smaller additions of glycerol (0.5% and 1%) produced the highest biogas and methane yields, and were recommended as good co-substrates to be used in anaerobic digestion with hog manure. |
