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| Construction of the Lapinière water treatment plant and pumping station. |
By Yvan Savoie, ITT Flygt, Montréal
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| Construction of the Lapinière water treatment plant and pumping station. |
Over the past 20 years, extensive efforts have been made to improve water sanitation in Laval, including the infusion of almost half a billion dollars in funding from the Québec government through its Programme d'assainissement des eaux, initiatives by other agencies involved in rehabilitating networks, the construction of new facilities, such as interceptors and pumping stations, or improving the operation of existing ones.
At the heart of these efforts is the desire of operating staff to continuously improve the performance of existing stations.
The ultimate objective is to ensure that the quality of the water being returned to the Des Milles-Iles and Des Prairies rivers is good enough to protect the wildlife habitats and ecotourism potential of these bodies of water, the quality of life of local residents, and the capacity of treatment facilities to produce better-quality drinking water.
History of Reunification and Standardisation
The City of Laval was created in 1965 after the merger of the 14 municipalities located on this island measuring 32 by 12 km, whose current population is 345,000. In the years since, in addition to operating drinking water treatment facilities, Laval has also constructed three wastewater treatment plants.
The first plant with its Fabreville pumping station was built in 1984. This station used Flygt model 3305 submersible pumps with a pumping capacity of 78,000 m3/day and a maximum lift height of 9 m; the plant utilizes a physico-chemical process.
The second facility at Auteuil was opened in 1993 and designed to use Archimedes screw pumps with a total pumping capacity of 160,000 m3/day at 33 rpm and a height of 12.65 m. Four Flygt model 7050PL pumps are used in this plant's biological treatment process.
La Pinière, the third wastewater treatment facility, uses a physico-chemical process; 16 275-hp model CP3312 Flygt pumps ensure that the wastewater is lifted to a velocity head of 33 m for a total capacity of 8000 L/sec.
This makes La Pinière the largest lift station using submersible pumps in North America in terms of capacity and dynamic load. The diameter of the station is 20 m.
The 2.45 m (8-ft.) feed pipes that transport wastewater from the city to the La Pinière station are located 22.7 m (75-ft.) below the level of the Des Prairies River and buried under Route 440, one of the main highways running through the city. Construction of the facility required the excavation of 200,000 m3 of earth and the use of 30,000 m3 of concrete and 3,000 tons of reinforcing steel. Because the station was built using the caisson technique, underground water is drawn by gravity into an outfall located in the central ring of the station, then pumped by the 16 pumps situated around the ring.
The volume of this lift station is impressive; it is equivalent to 400 7.5 m swimming pools. After lifting, the water is forced by gravity to the pretreatment block, where it is subject to fine screening and degritting. Next, the water moves to six settling tanks for removal of phosphorous and suspended solids.
Before being ejected back into the river, the water passes through a disinfection block, which eliminates any viruses, bacteria, or pathogenic organisms still present, using ultraviolet rays from 320 UV lamps. Next, the sludge is dried and granulated.
Construction began in 1996 on this $107 million station designed to serve a population of approximately 282,000 with an average capacity of 240,000 m3/day, and the facility began operating in August 1998.
By processing approximately 75% of the island's total wastewater, mainly from the south end, the operation of this station has a major environmental impact, because it has finally made possible the purification of waste entering the Des Prairies River (waste entering the Des Milles-Iles River is already processed at the Auteuil and Fabreville plants). Positive effects on the Des Prairies River were already evident in the fall of 1998 in terms of the quality of the water pumped at the intake to the drinking water processing facility.
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