The Hangu multiple cell stabilization ponds with the daily treatment capability of 50 000 tons of wastewater was constructed in 1993 and put into operation in 1995.Establishment of this system is important for controlling the red tide and improving water environment in the Bohai Sea.The investigations on the relationship between self purification efficiency and variation in biodiversity of protozoan community in various levels of ponds were carried out.The results indicated that the main pollutants were ...