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This paper discusses results from a 16-month water treatment pilot testing program in Winnipeg, Canada (pop. 650,000) which evaluated a dissolved air flotation (DAF)/ozone/deep bed filtration process. Seasonal raw water temperature ranged from 0.3 to 23 degrees C. Pilot testing determined that the coagulation, flocculation and DAF design parameters were dictated by the cold water period. Cold water poses special challenges to coagulation, flocculation and DAF treatment. For the DAF process, bubble carry-over was a problem at higher loading rates since the higher water viscosity at low temperatures resulted in a lower bubble rise rate. It was found during cold water periods that DAF loading rates had to be reduced and recycle air loading rates had to be increased. Additionally, because coagulation reactions are slower at low temperatures, higher coagulant doses and additional flocculation time was required to form a floatable and filterable floc. It was also found that cold water temperature affected the performance of various coagulants and coagulant aids tested and adversely affected filter ripening times. This paper compares unit process performance at different water temperatures and focuses on cold water test results used to establish several unit process design parameters. Includes 3 references, tables, figures.

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Edition: Vol. - No. Published: 06/01/2001 Number of Pages: 17File Size: 1 file , 510 KB