Environmental impacts and economic benefits of manure management chain with biogas production in a large scale dairy farm

The manure management cycle from collection to application in dairy farming was evaluated from environmental and economic aspects for different scenarios including biogas production. For this purpose, manure characteristic is determined regarding the real feed ration composition. Environmental impacts and economic profitability of each scenario was calculated using standards and COMFAR program, respectively. The results showed although biogas production is costly but it is profitable with initial investment of 125 billion Rials (2,777,778 €) and a payback period of about 3 to 4 years. The internal rate of return was calculated as 24% considering a discount rate of 20%. The internal rate of return shows that although this investment is risky, the amount of income is acceptable. Scenario 4 including digestate processing using a mechanical separator followed by composting has the maximum avoided methane emission (-261 kg CO2eq m-3). Emissions mitigation was calculated to be 36% and 17% in scenario 2 and 4, respectively. Solid/liquid separation and sand separation have less impact on emission reduction withy different economic advantages. Regarding the results of this study, a large amount of greenhouse gases and emissions to water and soil has mitigated thank to biogas production