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Abstract
Factors of pretreatment coagulation/flocculation units were studied using raw water of low temperature and low turbidity. Aluminum sulfate (AS) and selected polyaluminium chlorides (PACls) were all effective in the DAF process when used under favorable conditions of coagulant addition, coagulation, flocculation and flotation units. Compared with the AS coagulant, PACls, at lower dosage, could give the same effective performance even with shorter coagulation/flocculation time or lower recycle ratio during the treatment of cold water. This is attributed to the higher-charged polymeric Al species, and the lower hydrophilic and more compact flocculated flocs of PACl coagulant. Based on results of pilot experiments, the goal of FRD system can be achieved by combining a DAF heterocoagulation reactor with PACl coagulant (F), an efficient flocculation reactor (R), as well as an economical auto-dosing system (D).
ACKNOWLEDGMENTS
This research was supported by a state key special project (No. 96–909–03–02), which was funded by the National 9th Five-year Plan of China. The authors would like to express their thanks to the 9th water plant of Beijing for providing raw water data, laboratory and experimental materials, and also appreciate its technicians for their contributions in building this pilot system. Professor Luan Zhaokun, Qu Jiuhui, associate professor Li Dapeng, Lei Pengju, Master Li Ke, Li Guiping and Lü Chunsheng et al., are all acknowledged for their help in the experiments.