Compared with aerobic activated sludge process, aerobic granule process has several advantages, such as good settling ability, high biomass retention, strong microbial structure, resistance of high loadings and variation influent concentration. There are many factors affecting granule growth, including selection pressure, starvation time, pH value, temperature, dissolved oxygen, and filamentous fungi, etc. Aerobic granules might disintegrate and are washed out from the reactor with effluent. It has been attributed to the reason that oxygen cannot penetrate the granule core, causing anaerobic condition in the granule core. In this study, aerobic granules are operated under high pressure environment, i.e., high pressure granulation process, to overcome the aforementioned problem. High pressure granulation process along with ambient pressure process were studied under three organic loading conditions (5, 10, 20 kgCOD/m3-d). The characteristics of aerobic granules were compared.
After a three-week granulation under three loading, the result shows that both reactors have few filamentous.But the filamentous bacteria in high pressure reactor are not only less than those in the ambient pressure reactor but also having better settling ability, resulting in less total suspended solids in the effluent of the high pressure reactor. Under the same organic loading, COD removal efficiencies are much better in the high pressure reactor than in the ambient pressure reactor. Regardless of the high pressure reactor and ambient pressure reactor, COD removal efficiencies under high loading are worse than those under medium and low loading. In addition, the amount of EPS is not affected by oxygen concentration, and is decided by the starvation time.