Planning the optimal site, size, and feed of biogas plants in agricultural districts

In agricultural districts, biogas production through anaerobic co-digestion of residual biomasses is a sustainable way to valorize agro-industry and livestock residues and integrate farm profits. Size and location of a biogas plant as well as co-digestion substrate composition strictly depend on the substrate properties and availability within the rural district. The logistical substrate chain should be optimized to assure the right size and the maximum profitability of the planned biogas plant. A simple method is proposed to site a digester and choose its power output as well as to identify the optimal substrate blend, reducing the complexity of design and management operations. The method, requiring a reduced number of easy-to-survey input parameters, has been verified by its application to an agricultural district of southern Italy. If the planned plant is fed by a prevalent substrate from a single farm, the most economical power output is 300 kW. This size depends also on the Italian subsidy system to renewable energy. However, in the case of a centralized plant, supplied by a blend of substrates, the method gives the optimal plant location, based on the district barycenter, weighed by the biogas potential production of each farm. Secondly, the method suggests the annual amounts of the different substrates in the digester blend, maximizing the plant's annual profit and complying with technical-economic constraints. Thirdly, the most economical power output of the plant is 480 kW. Finally, it indicates the related annual revenues, costs, and profits. The method can also be applied to other agricultural biomasses, such as ensiled crops or energy species available at a competitive cost, as are found in northern Europe. (C) 2017 Society of Chemical Industry and John Wiley & Sons, Ltd