OPTIMIZATION MODELING OF ANAEROBIC BIOFILM REACTORS

A rigorous steady state model of acetate-utilizing methanogenic biofil ms is developed accounting for the mass transfer of neutral and ionic species, pH changes within the biofilm, pH-dependent Monod kinetics, c hemical equilibrium, electroneutrality, gas production within the biof ilm, and the presence of a concentration boundary layer (CBL). In cont rast to traditional biofilm models where the pH is assumed to be const ant within the biofilm, an increase in pH in acetate-utilizing methano genic biofilms is predicted. Furthermore, significant differences can exist between the flux predictions using the traditional models and wh en pH changes within the biofilm are taken into account. The optimum p H for acetate-utilizing biofilms is less than the optimum defined for suspended-growth systems. The biofilm model is coupled to a model of a completely-stirred tank reactor (CSTR), and strategies for the optimi zation of biofilm reactor performance are examined. For a fixed set of operating conditions, an optimum influent pH can be defined that corr esponds to the maximum removal efficiency and flux of acetate into the biofilm.