In order to improve water quality of Hakata Bay, which is a closed water basin, the authors are promoting the advanced wastewater treatment system for simultaneous removal of nitrogen and phosphorus. The authors intend to adopt two systems, one is the carrier-added anaerobic-anoxic-oxic
(A2/O) process and the other is the three-steps-feed biological nitrogen removal process with coagulant addition. This study was intended to verify treatment performances and provide information crucial on facility design and operation. The target water qualities, specifically
T-N 9.0 mg/L, T-P 0.4mg/L, could be achieved in both experiments. Concerning the removal ratio of nitrogen, the difference between theoretical and actual figures were not large each other, but the authors found that denitrification rates were lower than the value used as the standard
in Japan. As for phosphorus removal in the A2/O process, the removal efficiency was adversely affected by rain, making the addition of coagulant necessary as a backup to constantly achieve water quality targets. The step-feed recycled process, which always requires coagulant
addition, was observed as being able to attain water quality target with the addition of aluminum (as PAC) in a molar ratio of 1.5 ~2.0 to PO4-P in the influent.
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