Integrated Coagulation-ultrafiltration Process For Purification Of Source Water In Southern China

Through lab scale study, integrated coagulation-ultrafiltration process was used to purify source water (reservoir and river) in southern China. This study found a set of optimal conditions for river source water in southern China. The removal efficiencies of turbidity, dissolved organic matter (DOM), nutrients and endocrine disrupting chemicals (EDCs) were examined, the membrane operating characteristics and cleaning methods were also investigated in this paper. The result showed that:This study used a sequencing batch reactor with polyaluminium chloride and external pressure type hollow fiber ultrafiltration membrane module to purify reservoir water. The results indicated that the pollutant removals by integrated process were better than conventional process. The turbidity of effluent was less than 0.02 NTU, removal efficiencies of COD_Mn, DOC, UV₂₅₄ were 38% on average, removal efficiencies of DOM fluorescent substances were better than conventional process. Removal efficiencies of natural organic matter (NOM) with molecular weight (MW) 1000～2000 were above 48% while removals of NOM with MW 500～1000 were about 10%. The removal efficiencies of NH₃-N,NO₃^--N,TP were 19%～29%. It suggested that combined alkaline-acid cleaning and combined alkaline-EDTA cleaning can perform better cleaning effect.Orthogonal test analysis indicated that the factors which influence the pollutant removals of integrated process by effect decending were: coagulant type > stirring speed > coagulant dosage > sedimentation time > pH. The optimal conditions were (1)coagulant is polyferric sulfate; (2)dosage is 4.2 mg/L (Fe³⁺); (3)stirring speed is 400 rpm; (4)pH is 7; (5)sedimentation time is 30 min.Under optimal conditions, the integrated process purified river water was discussed in this research. The turbidity of effluent was less than 0.02 NTU, removal efficiency of DOC and UV₂₅₄ was 64% on average. Removal efficiency of natural organic matter (NOM) with molecular weight (MW) 1000～2000 was 70% while removal of NOM with MW 500～1000 was 11%. The removal efficiencies of NH₃-N,NO₃^--N,TP were 45%～94%. Removal efficiencies of DOM fluorescent substances were better than the removal rate which measured in treating reservoir water by integrated process. Comparing with conventional process, the removal efficiencies of endocrine disrupting chemicals (EDCs) by integrated process performed the similar effect. Removal efficiencies of 17α-estradiol, estrone, estriol, ethynyl estradiol and nonylphenol were 64%, 73%, 55%, 29%, 27% respectively.