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| High lift vertical turbine pumps. |
By Marcus Firman, CET and Paula Steel, P.Eng., KMK Consultants Limited
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| High lift vertical turbine pumps. |
A 5,200 m3/d enhanced colour removal membrane microfiltration water treatment plant in the Town of Sioux Lookout is believed to be the first plant of this type in full production in Ontario. The design-build process utilized produced an estimated saving of $500,000.
In 1997 the Town began an Environmental Assessment to determine the best alternative for upgrading their existing water treatment facility. At that time the potable water was taken from Pelican Lake via the Doc Moberly Pumping Station. The water was then screened, but not filtered, chlorinated and fluoride added prior to distribution. This treatment process was in violation of MOE Policy 15-14 which states that surface water must receive a minimum treatment of filtration and disinfection. During the environmental assessment process both Giardia and Cryptosporidium were detected in the raw and treated water and, as a result, the Medical Officer of Health issued a Boil Water Advisory in April of 1997.
A common method of disinfecting drinking water is to dose with chlorine, however research has shown that Giardia and Cryptosporidium are both highly resistant to chlorine. Furthermore, due to their small size, Giardia cysts (8 to 12 microns) and particularly Cryptosporidium oocysts (4 to 5 microns) can be difficult to remove in typical filtration processes. This difficulty arises because this type of contamination is generally linked with an event, such as spring run off, when oocyst concentrations can be extremely high, requiring better than 4 log removal to prevent system breakthrough.
As a result, the environmental study recommended that the existing pumping station be upgraded to a low lift station and that a new microfiltration membrane plant be constructed.
Treatment Process
The upgraded Town of Sioux Lookout Water Treatment Plant is designed to meet a raw water maximum day demand of 5,200 m3/d. Raw water is drawn from the existing water intake structure located in Pelican Lake before entering the Doc Moberly Pumping Station which has now been converted to a low lift station. The raw water is screened and then pumped to the new membrane microfiltration water treatment plant. The low lift pumps are vertical turbines, Model 8W-7000, manufactured by Fairbanks Morse Pumps, and are rated for 31.5 L/s each.
Following an equipment preselection and evaluation process, the ZeeWeed enhanced colour removal membrane microfiltration system by Zenon Environmental Inc. was selected. Raw water enters the treatment plant and is dosed with alum to provide coagulation and sodium hydroxide to adjust the pH to enhance the treatment process. The water then enters one of the two flocculation basins, each equipped with variable speed paddle mixers. From each flocculation chamber the water is distributed to Zeeweed basins. In total there are four basins, each containing two Zeeweed cassettes. The membranes will filter out any object larger than 0.1 microns, which provides a barrier to the Cryptosporidium oocysts which are in the range of 4 to 5 microns.
Permeate pumps, supplied by Zenon, create a low pressure vacuum in the membranes which draws the water, or permeate, through the membranes. The treated water is then again pH adjusted, chlorinated, fluoride added and then stored in clearwells. The high lift pumps then provide potable water to the distribution system and standpipe, as required. The high lift pumps are vertical turbines, Model 10M, also manufactured by Fairbanks Morse Pumps, and are rated for 30.1 L/s each.
The Sioux Lookout design and build project was awarded to KMK Design Build Ltd. at a price significantly less than the engineering budget. The engineer's estimate was $6,400,000; KMK's was $5,900,000.
KMK Design Build's approach is to provide a fully bondable design team who designs projects and then obtains pricing from bona fide contractors, suppliers and sub-trades, providing clients with a complete package to undertake the works.
Plant Performance
To date, the plant is performing extremely well, exceeding all Ontario Drinking Water Objectives. Parameters of particular note are colour reduction from greater than 50 True Colour Units (TCU) to less than 2 TCU and trihalomethanes (THMs) reduced from levels as high as approximately 200 µg/L before construction of the plant to less than 30 µg/L.
Currently data is being collected for a follow up article detailing the performance of the water treatment plant and should be ready for publication early next year.