Mass transfer limitation of sulfate in methanogenic aggregates

The role of mass transfer limitation of sulfate as a factor governing the competition between sulfate reducing and methane producing bacteria in methanogenic aggregates was theoretically evaluated by the calculation of steady‐state sulfate microprofiles using a reference set of parameters obtained from the literature. The shooting method was used as a numerical technique for solving the mathematical model. The effect of the parameters on mass transport limitation was tested by varying each reference value of the parameters with a factor of 3. Sulfate limitation within granules prevailed at moderate (0.1 kg m −3 ) and low sulfate concentrations in the bulk liquid, at high maximum sulfate utilization rates (3.73 × 10 −5 kg SO   4 2−kg −1 VSS S −1 or biomass concentrations (40 KG VSS m −3 ), and in large aggregates (radius of 7.5 10 −4 m). The effective diffusion coefficient of sulfate and the affinity constant were less determinative for the penetration depth of sulfate within a granule. © 1994 John Wiley & Sons, Inc.