[Physicochemical characteristics of granules with different size in a granular sludge system for phosphorus removal]

Aerobic granular sludge that could simultaneously remove nitrogen and phosphorus was cultivated in a sequencing batch reactor (SBR). Three groups were divided using 100-, 60- and 40- mesh sieves resulting the size ranges were 150-280 microm, 280-450 microm and > 450 microm, respectively, and the physicochemical properties of different groups were analyzed. Results showed that during the initial period of granulation (7 - 18 d), the compact granules could provide the anaerobic niche for the substrate the competition between GAOs and PAOs; and the compact granules was favorable for the enrichment and growth of PAOs, resulting in different phosphorous fractions in different size of granules: granules with the size of 280 - 450 microm exhibited the highest content of organic phosphorous faction, i.e., 113.25 mg x g(-1). In contrast, these granules showed the lowest content of inorganic phosphorous fraction, i.e., 15.55 mg x g(-1). In a later period, the content of organic phosphorous fraction in granules was similar after 34 d about 50 mg x g(-1), and the inorganic phosphorous fraction became similar after 52 d was 70 mg x g(-1), and the total organic phosphorous fraction of sludge in the reactor were higher than those in the solids effluent. The phosphorous fraction in different size granules was affected by the sludge retention time. The total phosphorous accounted for 11% of total weight of sludge, and the inorganic phosphorous accounted 4.24%. Additionally, the settling velocity, specific weight of bigger granules were higher than the smaller one, and these values were well correlated with total phosphorous. Concerning on denitrification, bigger and smaller granules showed high denitrification efficiency, and the gradient of NO3(-) -N between inside of granules and bulk solution was an important factor for denitrification rate.