Biogas production from different types of cow manure

Animal waste generated in farms of developing countries is usually handled through stockpiling and direct application to soil. However, there are negative environmental impacts associated with those practices, mainly contribution to global warming, eutrophication and odor. Anaerobic digestion is one of the well-established technologies that capture the energy in the waste, including animal waste. In this research, manures from different types of cows typically present in dairy farms were collected and tested for their biochemical methane potential. The test was conducted on five categories of cows, namely: (1) high cows; regularly milked cows, (2) dry cows; pregnant cows, (3) fresh cows; to be milked for the first time after their delivery, (4) young cows (Young-1); cows younger than 18 months, and (5) young cows (Young-2); cows younger than 7 months. Those cows differ in age, weight, digestion/ metabolic processes and feeding diet, which lead to variations in biochemical characteristics, and consequently biogas potential, of the produced manure. The methane yield was found to be highest in the manure of fresh cows (216 L CH4/kg VS), followed by Young-1 (208 L CH4/kg VS), high (196 L CH4/kg VS), dry (160 L CH4/kg VS), and Young-2 (148 L CH4/kg VS) cow manures. The carbohydrates, lipids, and proteins were measured for each manure type to determine their effects on biogas production. Furthermore, those parameters were tested for correlation with the measured biogas production using Kendall's Tau approach. The analysis showed that higher lipid and protein contents lead to lower biogas potential, while higher carbohydrates content resulted in higher biogas production.