Permeabilities of anaerobic CH4-producing granules.

The permeability of anaerobic CH4-producing granules was investigated with both settling and size exclusion chromatography experiments. The experimental results indicate that the two methods could be successfully applied to evaluate the permeability of the CH4-producing granules. An interdependent relationship was found to exist between the two methods for explaining the permeability of the granules. Both methods demonstrate that the porosity of the CH4-producing granules decreased with increasing size, while their settling velocities had an opposite trend. Extracellular polymeric substances yielded by the anaerobic microorganisms might clog the pores within the granules, resulting in a reduction in their porosities. The experimental results also suggest that molecular diffusion appeared to play an important role in the mass transfer in and/or through the granules.