[Air drying process of granules and characteristics of their structure]

Filamentous granules were cultivated using a sequencing batch reactor. The yellowish bacteria dominated granules, black fungi dominated granules and Microthrix parvicella dominated white smooth granules occurred in the reactor on the day 18, 23 and 27 respectively. Distribution of surface related free water and capillary water were analysis using air drying method. It was found that the surface related free water in the black and white filamentous granules was 79% and 83%, respectively, and that in the conventional bacteria granules were 64%, suggesting that the surface area opening ratio of surface and porosity decreased in the order of white, black and yellowish granules. According to the air drying rate in different phases of granules, it can be inferred that the white and black filamentous granules could rapidly exchange the substrates on the surface and consequently prone to be big and loose, which discourages the stability of granules. Additionally, the section image showed that filamentous granules were more porous than the black bacteria granules. Filamentous granules exhibited encouraging COD and nitrogen removal efficiencies. The black and white filamentous granules showed higher bioactivity with the oxygen up-take rate (SOUR) of 1.29 and 1.26 fold of the conventional yellowish granules.