With the increase of population, acceleration of economic development and urbanization process, sewage and industrial wastewater emissions is increased year after year, which results in the extremely serious problem of eutrophication of surface water. In order to improve the water environment, and to prevent water eutrophication, the requirements on the sewage plant has become increasingly demanding in terms of effluent quality, operating cost, and energy saving. In recent years, the treatment of the city l...