Widespread use of the anaerobic-anoxic-oxic process (AAO) has been expected because nutrients (nitrogen and phosphorus) can be removed simultaneously without any chemicals. The authors have been studying the nutrient removal performance of the media-anaerobic-anoxic-oxic process (M-AAO) using pilot plants, the media of which were suspending in an oxic tank (Mishima et al., 1995). The purpose of the M-AAO was to remove nutrients from sewage using a bioreactor half the size of the one used in the AAO process. The average water quality of the treated effluent of the M-AAO was 8.3 mg/l of T-N and 0.6 mg/l of T-P after a retention time of 8-9 hours in the bioreactor. According to the batch experimental results, 93% of nitrification at low water temperatures (below 15°C) was performed by the biofilm on the media. The specific nitrification activity of the biofilm was high showing 5-10 mg-N/g-MLSS/hr at low water temperatures. Media nitrification largely depended on the dissolved oxygen (DO). The denitrification rate of the activated sludge increased almost in proportion to BOD-SS loading. It was suggested that the phosphorus uptake in the anoxic tank was closely linked to denitrification.

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