1. Power & Industrial Systems R&D Laboratory, Hitachi, Ltd., 7-2-1 Omika, Hitachi, Ibaraki, Japan (E-mail: misaki.sumikura.mf@hitachi.com; masataka.hidaka.ej@hitachi.com)
2. Public & Industrial Systems Div, Hitachi, Ltd., 13-18-1 Sotokanda, Chiyoda, Tokyo, Japan (E-mail: hiroshi.murakami.dc@hitachi.com)
3. Information & Control Systems Div, Hitachi, Ltd., 5-2-1 Omika, Hitachi, Ibaraki, Japan (E-mail: yoshihiro.nobutomo.yz@hitachi.com)
4. R&D Dept, Japan Sewage Works Agency, 5141 , Shimo-sasame, Toda, Japan (E-mail: murakamit@jswa.go.jp)