The effect of the variation of aeration time on the microorganisms was investigated in sequencing batch reactor (SBRs). The cycling time in four SBRs was adjusted to 12 hours and then included different aerobic times as 1 hr, 2.5 hr, 4 hr and 5.5 hr, respectively. Four SBR systems have been operated and investigated for over 40 days. As the increase of aeration time, the consumption of glycogen within sludge at the 1st non-aeration time a little bit was increased and the production of glycogen at the aeration time was increased. Also, the produced PHB amounts and PHB production rate at the 1st non-aeration time were increased as the decrease of aeration time, which showed the activation of the phosphorus removal. The ratios of nitrifying microorganisms' number and GAOs to the total microorganisms' number in SBRs was decreased as the decrease of the aeration time, however, the PAOs ratio was almost constant irrespective of the variation of aeration time.

The effect of the variation of aeration time on the removal of organics, nitrogen and phosphorus using synthetic wastewater was investigated in sequencing batch reactors (SBRs) which included DNPAOs and DNGAOs. The cycling times in four SBRs were adjusted to 12 hours and then included different aerobic times as 1 hr, 2.5 hr, 4 hr and 5.5 hr, respectively. Four SBR systems have been operated and investigated for over 40 days. Average TOC removal efficiencies were about 71 % in all SBRs. The NH_4^+-N removal efficiency was increased as the increase of aeration time. After changing aeration time, the total nitrogen removal efficiencies of SBRs were shown as 35 %, 85 %, 75 % and 65 %, respectively. Higher phosphorus release and uptake were occurred as the decrease of the aeration time. After all, the overall phosphorus removal efficiency decreased and the deterioration of phosphorus removal was occurred when aeration time was over 4 hr. Denitrification in aerobic conditions was observed, which showed the presence of DNPAOs and DNGAOs. In batch experiments, PAOs were shown as the most important microorganisms for the phosphorus removal in this experiment, and the role of DNGAOs was higher than that of DNAPOs for the nitrogen removal.

Laboratory scale experiments were conducted to investigate the removal characteristics of nitrogen and phosphorus in two sequencing batch biofilm reactors (SBBRs). SBBR1 had a short first non-aeration period and SBBR2 had a long first non-aeration period. The removal characteristics of nitrogen and phosphorus in each SBBR were precisely observed according to the variation of influent TOC concentration, and the operation control parameters (pH, DO concentration, ORP) in each reactor were measured. In biological nitrogen removal, there was little difference between SBBR1 and SBBR2 and the nitrogen removal efficiencies were very low. The nitrogen and phosphorus removal characteristics in high influent TOC concentration were different from those in low TOC. Nitrogen removals by simultaneous nitrification/denitrification (SND) were occurred in both SBBR1 and SBBR2. The P removal in SBBR1 was superior to that in SBBR2. The second P release was observed in SBBR1 which had long second non-aeration period.

This study was carried out to get more operational characteristics of Anoxic(anaerobic)-Oxic-Anoxic-Oxic (AO)2 sequencing batch biofilm reactors (SBBRs) at the low TOC concentration. The operating time in anoxic (anaerobic) time to oxic time was 1：1. Experiments were conducted to find the effects of the aeration time distribution on the organic matters and nutrients removal. Three lab-scale reactors were fed with synthetic wastewater based on glucose as carbon source. During studies, the operation mode was fixed. The first aeration time to the second aeration time in SBBR-1 was 2：3, and those in SBBR-2 and SBBR-3 were 1：4 and 3：2, respectively. The organic removal efficiency didn't show large difference among three reactors of different aeration time distribution. However, from these study results, the optimum aeration time distribution in the first and the second aeration time for biological nutrient removal was shown as 3：2. The release of phosphorus was inhibited at the second non-aeration period because of the low TOC concentration and the nitrate produced by the nitrification at the first aeration period.

This study was conducted to remove organics and nutrients using 2 stage intermittent aeration reactor. First reactor, using suspended microbial growth in intermittent aeration instead of anaerobic reactor in the typical BNR process, used minimum carbon source to release P, and it was possible to reduce ammonia loading going to second reactor. In the second reactor, using moving media intermittent aeration, it was effective to reduce nitrate in non-aeration time by attached microorganisms having long retention time. In aeration time, nitrification and P uptake were taken place simultaneously. From the experiment, two major results were as follows. First, the removal of organics was more than 90%, and optimum aeration/non-aeration time ratio for organic removal was corresponded with aeration/non-aeration time ratio for nitrogen removal. Second, in the first reactor, optimum aeration/non-aeration time ratio was 15/75 (min.) because it was necessary to maintain 75 min. of non-aeration time to suppress of impediment of return nitrate and to lead release of phosphate. In the second reactor, optimum aeration/non-aeration time ratio was 45/90 (min.).