A parametric study on a plug-flow anaerobic digester was performed in order to determine the effect of certain design variables on two digester responses: heat requirement and biogas production. Each parameter considered was assigned low, reference, and high values that were based on common digester designs. Using a previously-built simulation that predicted heat requirement and biogas production based on the models presented in Gebremedhin et al. (2005) and Gebremedhin and Inglis (2007), every combination low, reference, and high values was simulated. A Visual Basic program was used to sort the resulting 3 million plus data points in order to determine the rates at which each variable affected heat requirement and biogas production. These rates were then used to compare the design variables? effects on each digester response.

In regards to heat requirement, the insulation variables (floor insulation thickness, insulation conductivity, and wall insulation thickness) had the largest effect. On the other hand, variables that were not associated with digester building materials (hydraulic retention time, manure flow rate, ambient temperature, and digester radius) had a negligible effect. Considering biogas production, hydraulic retention time exhibited a significant negative relationship with the rate of biogas production while the effect of manure flow rate was negligible.