AWWA ACE59870

The City of Winnipeg (pop. 630,000) obtains its drinking water from Shoal Lake, whichborders the Canadian provinces of Manitoba and Ontario, and the state of Minnesota,USA. The raw water supply is chlorinated at the intake for pathogen, taste and odor,slime, and zebra mussel control. The water then flows through a 159-km long aqueductto the Deacon Reservoir in Winnipeg. Water for distribution is rechlorinated at the outletof the reservoir, sent to two covered distribution system reservoirs, and then delivered toconsumers.The City completed an intensive Phase 2 pilot water treatment program in 1997. Phase 2tested the most suitable treatment processes for Winnipeg's water quality, resulting in arecommendation for a baseline water treatment process, which included conventionaldissolved air flotation (DAF). In November 2002, a Value Engineering review teamidentified high-rate DAF as a potential cost savings alternative for consideration by theCity. In 2003, the City contracted a consultant team from Earth Tech and CH2M HILLto determine the suitability and limits of the high-rate DAF process. The pilot systemconsisted of ferric chloride coagulation, high-rate DAF, intermediate ozonation, and deepbed filtration, and was evaluated under cool, cold, and warm water conditions. The high-rateDAF pilot tests were conducted in 2003 and the suitability of high-rate DAF wasdetermined by comparing the process performance with data from the conventional DAFprocess tested in 1997. The key parameters investigated were the DAF loading rates,post-filter turbidity and particle counts, total organic carbon (TOC) removal, and unit filter run volumes. Thepotential for the freeze/thaw dewatering of plant residuals was also examined.High-rate DAF testing with and without lamella plates installed in the DAF tank wasconducted during the warm and cold water test periods to determine their effect on theDAF loading rate. Without the lamella plates installed, successful test results wereachieved at DAF loading rates of 45 and 40 m/h in the warm and cold water test periods,respectively. With the lamella plates installed, DAF loading rates as high as 50 and 45m/h were reached in warm and cold water conditions, respectively. In 1997, theconventional DAF process was limited to loading rates of 20 and 15 m/h in the warm andcold water test periods. During the high-rate DAF pilot trials, filter run volumes were ashigh as 900 m3/m2, and post-DAF and filter turbidities were consistently less than 1.0 and0.1 NTU, respectively. On average, filtered water particles were less than 10 /mL (totalparticles>2 um) and the TOC reduction through the high-rate DAF was between 60 and70%. Based on the success of the high-rate DAF pilot trials, conventional DAF wasreplaced with high-rate DAF as part of the final water treatment process. Includes tables, figures.

Product Details

Edition:

Vol. - No.

Published:

06/17/2004

Number of Pages:

12

File Size:

1 file , 370 KB