Optimal scheduling of a single anaerobic digester with multiple feedstocks

Biomass to methane via anaerobic digestion conversion has the potential of supplying 25% of the annual US national demand for natural gas. However, the economic viability of this technology is contingent upon managing the production facilities in a cost effective manner. Biomass in storage is subject to declining viability and the rate of methane yield in the batch digester also declines with time. Typically lots, each of a known quantity of batches, of possibly different feedstocks arrive at the digester facility over time. The problem is to determine the batch production sequence as well as the batch residence times in the digester so as to maximize total gas production over a given planning horizon. This paper presents a branch and bound algorithm for the problem of scheduling a single anaerobic digester with multiple feedstocks. An example is also given to illustrate the solution procedure.