高濃度酸素水を利用した水質浄化システム
システムの概要と装置の設計
内湾や湖沼の水質改善手法として，貧酸素化が顕著な水域の底層付近に酸素を供給して溶存酸素量を増加させる方法が用いられている。従来技術である曝気法や微細気泡法は発生できる溶存酸素濃度DOが飽和濃度（飽和度DO%=100％）までに限定され，貧酸素化の解消効果に限界があった。これに対して，酸素飽和度DO％が200％まで達成できる高濃度酸素水の発生装置を開発し，室内実験と現地実験により装置の有効性を実証した。また，本装置の実用レベルの設計方法を確立するために，底質中の微生物量を指標とした室内実験により底質浄化に必要なDOレベルを明らかにした上で，流動・水質数値解析によりスケールが異なる水域モデルを対象にしたDO改善効果の比較を行い，最適放流量の諸元を明らかにした。
| キーワード： | 水質浄化，底質浄化，溶存酸素 |
＊１ 技術センター 土木技術研究所 水域・生物環境研究室
＊２ 国際支店 土木部 土木技術部
Water Purification System Discharging Highly Oxygenated Water
Specifications and Design of the System
Reduced dissolved oxygen in enclosed water leads to an anaerobic environment in which the rate of organic matter biodegradation slows and the elution of eutrophic material from the bottom becomes high. The result is a degradation of water quality. Conventional methods of solving the problem of dissolved oxygen depletion include aeration and micro bubbles. However, there are some problems with these methods: the efficiency of the dissolved oxygen supply cannot be increased because oxygen concentration is limited by saturation and turbidity results from the air bubbles picking up mud. To address these issues, a new type of dissolved oxygen discharge system has been developed. This system uses compressed air and produces highly oxygenated water at 200% of the oxygen saturation level. Furthermore, the water produced by this system contains almost no air bubbles since a buffer water tank removes large bubbles. A high concentration of dissolved oxygen (DO) in the water is achieved, with a DO level of 200% in the air pressure range 0.2-0.3Mpa. The dissolved oxygen purifies the bottom sediment in water. The quantitative effect of dissolved oxygen on bottom sediment quality is studied in a laboratory test measuring bacterial biomass and organic matter decomposition. Furthermore, a numerical simulation is used to determine a suitable discharge rate for the water whose quality is to be improved. Highly oxygenated water produced by the system leads to improvement in the bottom sediment quality of enclosed water.
| Keywords: | water purification, sediment purification, dissolve oxygen |
*1 Hydraulic and Bio Engineering Research Section, Civil Engineering Research Institute, Technology Center
*2 Civil Engineering Department, International Operations Headquarters
