The raw water of the Guanjinggang water plant comes from the Guanjinggang River, which is located to the south of the plant. The water source is polluted by organic substances and metals, NH 3 -N, COD Mn , total nitrogen, total phosphorus, dissolved oxygen, iron and manganese all exceed the acceptable limits of class III water according to the "Environment quality standards for surface water" (GB3838-2002). In particular, the seasonal high ammonia-nitrogen in winter is a major problem during the purification process. Figure 1 shows the flow chart of the first phase project layout of the Guanjinggang water plant.Each step of the treatment process aims to eliminate the targeted pollutants. First, the biological pretreatment aims to degrade the ammonia nitrogen then the intermediate high density sedimentation tank removes turbidity; subsequently, the biological activated carbon advanced treatment eliminates organics; finally, the sand filter ensures that the biosecurity and level of turbidity reach the standard.
KEY ISSUESThe key issues during the process selection and design for the second phase project of the Guanjinggang water plant are the seasonal high ammonia-nitrogen, biosecurity, pH control of outlet water and energy saving.
Seasonal high ammonia-nitrogenThe changes of the ammonia nitrogen in the raw water, pretreatment, precipitation, oxidation, carbon filter and sand filter effluent are shown in Figure At the early stages of the first phase project, the ammonia nitrogen concentration in the raw water is generally below 2mg/L , which means the whole process including comprehensive biological pretreatment-strengthening coagulation and sedimentation-biological activated carbon-advanced filtration with biological-physical-chemical synergism, can meet the standard of outlet water quality. However, after the second half of 2008, the raw water quality changed because the amount of COD Mn , ammonia nitrogen, total phosphorus, total nitrogen, iron and manganese rose significantly. In particular, the worsening of the pollution caused by ammonia nitrogen and the filler deposition in the biological pretreatment ABSTRACT: The Guanjingang water plant has a capacity of 300,000m 3 /d and is one of the main water plants of Jiaxing City in Zhejiang Province, which is located in the southern suburban area of this city. Its second phase with an augmentation of capacity of 150,000m 3 /d was put into operation in September, 2012. The raw water for this plant is the surface water that purified by the artificial wetlands and goes through the combined treatment of a biological preprocess, with both conventional and advanced process, to ensure the water quality meets the standard. This paper mainly focuses on the three key problems: the seasonal high ammonia-nitrogen, biological security and pH control of outlet water. And it aims to optimize and analyze the combined processes including the artificial wetlands, biological pretreatment, sand filtration and advanced treatment with ozone-activated carbon. Subsequently, the new treat...