ABSTRACT
Although SBRAS systems are often treated as if special design techniques are required, they actually operate according to the same principles as other activated sludge processes, as discussed in Section 7.8.2, and can be designed according to them. Consequently, the mass of MLSS in the system is defined by Eq. 9.11, the overall daily solids wastage rate is given by Eq. 9.12, the total daily heterotrophic oxygen requirement is given by Eq. 9.13, and the total daily autotrophic oxygen requirement by Eq. 10.16, provided that the effective SRT is used in their computation. The three primary differences between SBRAS and other activated sludge systems are that the oxygen requirement must be distributed to each of the discrete operating cycles and then apportioned within each cycle in a manner consistent with the length of the fill period, the fraction of each operating cycle that is not devoted to biological reaction must be accounted for in the design, and the interaction between the bioreactor and the secondary clarifier must be analyzed differently because biological reaction and sedimentation occur in the same vessel (although at different times in the cycle). The first of these can be accomplished by the same techniques used to apportion steady-and transient-state oxygen requirements in the various continuous-flow activated sludge systems. The second can be accounted for through use of the effective HRT, Te, and the effective SRT, 0cc, when using the CMAS equations listed above. The third can be considered through simple procedures to be presented below.
