To optimize the sequencing batch reactor (SBR) process for nitrogen and phosphorus (N/P) removal at small scale wastewater treatment plants, an experimental study was performed using a 30 L SBR designed for oxygen tension variations. Modeling was carried out using Monod kinetics, mass balances, and fundamental mechanisms of simultaneous N/P removal. During the sludge acclimation period, the microorganisms only for N/P removal could be selectively cultured owing to changes of oxygen conditions. After 100-day-sludge acclimation period, at the steady state, the system was operated with a sequence of anaerobic (2 - 3 hr) - aerobic (2 - 5 hr) - anoxic (2 - 4 hr) phases. Optimum pH range and rpm (revolution per minute) in such a sequence were from 6.5 to 7.5 and 280, respectively. DO (Dissolved oxygen) was below 0.2 ppm in anaerobic and anoxic step and above 4.0 ppm in aerobic phase. Comparatively high rpm showed high removal rate of N and P in this reactor configuration partly because high rpm could keep DO as low as 0.2 ppm. System operation temperature was kept at 28℃ according to the Bergey's manual. Using anaerobic - aerobic - anoxic sequences, percent removals were up to 50 - 60% for nitrogen and phosphorus, and more than 95% for BOD. When the sequences were switched to aerobic - anoxic - aerobic for providing more carbon sources to the denitrification phase, the removal efficiencies were improved to 60 - 80% for N and P. System performance was evaluated by operations using real wastewater. Nitrification in the real wastewater was a little low because of ammonifications, but the phosphorus removal was maintained the same as synthetic wastewater. In order to understand full process of the system and decide optimum HRT (Hydraulic Retention Time), models were studied and established and suggested the guideline for scale-up by simulations.
