Conceptual design and economic evaluation of an integrated anaerobic digestion system for sustainable dairy manure management

The sustainable management of livestock waste is a growing environmental and energy challenge, especially in regions with concentrated dairy farming. This study presents the conceptual design and techno-economic analysis of a medium-scale anaerobic digestion (AD) plant for the treatment of dairy cow manure. The proposed plant processes 250 ton of manure per day and integrates four main units: a pretreatment system, a continuously stirred tank reactor (CSTR) digester, a biogas upgrading system, and a digestate management unit. Biogas is purified using iron sponge beds, cooling systems, and activated carbon filters to meet the specifications of a combined heat and power generation system, which produces 352 kWe of electricity and 327 kWth of heat, 254 kW of which is reused to maintain digester temperature. The system avoids the release of 3439 ton of fossil-derived CO2 annually and reduces water consumption by 10 ton per day through internal recycling, with the static and dynamic payback periods of 7.22 and 9.18 years, respectively. When benchmarked against real-world plants, the design demonstrates competitive energy efficiency and cost-effectiveness for its scale. This study highlights the viability of medium-scale AD plants as a practical solution for renewable energy generation, nutrient recovery, and climate-resilient manure management.