A new application of size-exclusion chromatography is described for assessment of the permeability and internal pore distribution of anaerobic sludge granules. The fractionation range and adsorption characteristics were investigated for a series of standard proteins and dextrans. To determine possible adsorption of solutes and stability of the sludges, the pH and salt concentration of the mobile phase were varied. Good results were obtained using dextrans as solutes and tap water as the mobile phase. To inhibit the sludge activity without affecting the granule characteristics the experimental arrangement was operated at 4 ° C. Three granular sludge types were investigated. The permeability of the granular sludges varied from 7% to 96%. The exclusion limit expressed as molecular mass also showed large differences. For two sludges, molecules greater than 80 000 Da cannot penetrate the pores; for one sludge the exclusion limit is 1300 Da. Experiments using acetic acid as an indicator of permeability gave corresponding results.

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