Aerobic granular sludge cultivated under the selective pressure as a driving force

Inoculated with aerobic sludge from a conventional activated sludge wastewater treatment plant, granulation of aerobic sludge was realized in a sequencing batch reactor fed with glucose as carbon substrate. Selective pressure created by means of decreasing sedimentation time and increasing organic loading rate (OLR) enhances the formation of aerobic granular sludge, which follows three consecutive stages: acclimation, granulation. and maturation. Granules started to appear after 67 days operation. On the condition of OLR at 4.8 kgCOD/m(3) day, and superficial gas velocity at 0.0175 m/s, granules were the dominant sludge forms with most of diameter about 6-9 mm, a minimal settling velocity of 32.7 m/h, and a MLSS of 7800 mg/l. Aerobic granular sludge demonstrates high activity and ability to withstand high OLR. The granules were composed of filamentous species with varying degrees of rod- and coccal-type bacteria. Microscopic examination revealed that granules did not exhibit layered microbial distribution and should be less vulnerable to the changes of mixed liquor condition. (C) 2003 Elsevier Ltd. All rights reserved.