Effect of Organic Loading Rate on Aerobic Granulation. II: Characteristics of Aerobic Granules

Abstract

Four sequential aerobic sludge blanket reactors, Reactors R1, R2, R3, and R4, were operated at organic loading rates (OLRs) of 1, 2, 4, and 8kg chemical oxygen demand (COD)/m3day, respectively. Aerobic granules were not detected at the low OLRs in R1 and R2. Aerobic granules first appeared on Day 14 in Reactor R3, operating at a moderate OLR of 4kg COD/m3day. Aerobic granules were initially observed on Day 18 in R4, operating at the highest OLR tested of 8kg COD/m3day. These granules were unstable and disintegrated within 2 weeks after their first appearance. Under the OLR of 4kg COD/m3day, the process of aerobic granulation could be clearly divided into three phases of acclimation, multiplication, and maturation, with specific granular growth rates (νφ) of 0.1081, -0.0064, and -0.0008day-1, respectively. The values of νφ became smaller with time, and indicated that the aerobic granules had stabilized. Compared to the looser and more amorphous flocs, the compact granules in Reactor R3 possessed a higher specific gravity of 1.064, a higher strength with an integrated coefficient of 99.5%, a higher cell surface hydrophobicity of 75%, and a higher ratio of polysaccharides (PS) to proteins (PN) at 5.0mg PS per mg PN.