Determination of the pore size distribution and porosity of aerobic granules using size-exclusion chromatography

The pore size distribution and porosity of aerobic granules with different diameters were evaluated using size-exclusion chromatography, in which polyethylene glycols and distilled water were, respectively, used as solute and mobile phase. The porosity of the aerobic granules varied from 68% to 93% and the exclusion limit, expressed as molecular mass, showed a significant difference. For the small-size granules with a diameter of 0.2–0.6 mm, molecules greater than 137,000 Da could not penetrate the pores, while the exclusion limits of the middle-size granules with a diameter of 0.6–0.9 mm and large-size ones with a diameter of 0.9–1.5 mm were 76,000 and 29,000 Da, respectively. The extracellular polymeric substances of the granules might clog the pores and might be responsible for the reduced porosity. A correlation between the bioactivity and available porosity of the aerobic granules was found. The experimental results show that the size-exclusion chromatography was appropriate for elucidating the pore size distribution and porosity of the aerobic granules.