Role of Mass Transfer Resistance in Overall Substrate Removal Rate in Upflow Anaerobic Sludge Bed Reactors

A kinetic model (incorporating intrinsic Haldane kinetics) and an empirical model (incorporating apparent Haldane kinetics) for phenol degradation in upflow anaerobic sludge bed (UASB) reactors were used. UASB-reactor performance data were also generated for model verification. From the independent batch study together with statistical analyses, the apparent Haldane kinetic constants $k^{\prime }$ and $K_i^{\prime }$ did not differ from the intrinsic $k$ and $K_i$ , but the apparent $K_s^{\prime }$ was significantly larger than the intrinsic $K_s$ (i.e., greater internal mass transfer resistance). From the calculated results (of overall effectiveness factor, Thiele modulus, and Biot number) together with parametric sensitivity analyses, the internal mass transfer resistance would play a more influential role than the external mass transfer resistance on the overall substrate removal rate in UASB reactors. The simulated residual phenol concentrations using the empirical model were in good agreement with the experimental data; the simulated results using the empirical model were also close to those using the kinetic model. Accordingly, the empirical model that can properly describe the overall substrate removal rate should be acceptable for process design of UASB reactors.