| A laboratory study was conducted using an aerobic upflow sludge blanket (AUSB) reactor to achieve high-rate biological treatment through maintenance of high biomass concentration (7–10 g VSS/L) together with high oxygen flux. Emphasis of the study was placed on evaluating the treatment performance under different organic loading rates, and different pressurizations/flow recirculations, which were employed to provide a needed oxygen flux. That is, the AUSB reactor was not aerated directly, but oxygenation was provided in an external chamber with or without flow recirculation. In most operation, the oxygenation was provided under pressure of up to 25 psig. Thus, the AUSB operation was also under pressure. The flow recirculation rate was varied from 400% to 1500% in order to ensure adequate oxygen supply.; It was found that the AUSB process was able to handle a volumetric loading of as high as 3.83 kg TOC/m3-day (10 kg COD/m3-day) with the organic removal efficiency of 92% (equivalent to a volumetric removal rate of 3.58 kg TOC/m3-day). Out of this, about 20% of the organic removal was achieved in the oxygenation chamber. Despite the high upflow velocity through the reactor, the effluent suspended solids was mostly below 70 mg/L, which could be polished further for SS removal without using a conventional secondary clarifier. The AUSB sludge showed a high specific oxygen uptake rate (SOUR) of up to 180–250 mg O2/g VSS-hr, mainly due to a higher fraction of active biomass in the sludge flocs. Because of this, the biomass endogenous respiration rate was about 15 mg O2/g VSS-hr, which was also 3 to 4 times higher than that of the activated sludge flocs. The sludge yield in the AUSB system was around 0.3 to 0.4 g VSS/g COD removed without recirculation. However, with recirculation, the yield was only 0.09 to 0.18 g VSS/g COD removed. The low sludge yield was mainly caused by “enhanced auto-oxidation” of bio-solids in the oxygenation chamber, which had a very high DO and provided 10–30 minute HRT. |
