3.2. Physical characteristics of mature aerobic granules
Samples of aerobic granules were taken from the two reactorson day 85 at the end of the experiment. The physical and chemicalcharacteristics were analyzed in terms of size distributions, settlingvelocity, specific gravity, the integrity coefficient, and the moisturecontent of mature aerobic granules.The granule size distributions of aerobic granulation on day 85in R1 and R2 in triplicate are shown in Fig. 3. The volume percent-age of aerobic granules in the two reactors with size in the range1.5–2.5 mm was about 50%; i.e., there was little difference in thevolume percentage between the two reactors. Moreover, 66.4% ofgranules in R1 were in the size range 1–2.5 mm, and 6.6% of gran-ules were larger than 3 mm. In contrast, 76.8% of granules in R2fell in the size range 1.5–3 mm while 13.1% of granules were largerthan 3 mm. Similar results were obtained in other studies [16,29].It can be inferred that ZVI augmentation promotes aerobic gran-ulation, resulting in a larger diameter of granules. The result alsoimplies that the microbial community structure differed betweenthe two reactors. The granule microstructure and microbial diver-sity are strongly dependent on the composition and loading rateof the carbon source available via the selection and enrichment ofdifferent bacterial species [12]. In this research, the influent of thetwo reactors had the same composition and loading rate of the car-bon source (1200 mg L−1COD). The difference between the reactors