Treatment Processes

The plant's water treatment process consists of the following:
 

  • 278.4 m3 Raw water well
  • Three low lift pumps rated at 22,910 m3/d
  • 4.65 m3/d rapid mix tank
  • 595 m3/d flocculation tanks
  • 458.3 m2 Clarifiers
  • 1,650 m3 clearwell
  • Three high lift pumps rated at 20,945 m3/d
  • Wastewater clarifiers that discharge settled sludge to the sanitary sewer


Raw Water Source


The source of water treated by the Petawawa water plant is the Ottawa River at a widening in the river called Allumette Lake. The 760 mm diameter intake pipe extends 490m into the river at approximately 6m +1- under the surface and 1.5m off of the bottom of the river.  This raw water intake pipe has a capacity of 21,500 cubic meters per day, gravity fed to the raw water well, and is supported at the end with a concrete and timber crib.


Screening


A vertical stainless steel coarse screen in the Raw water well of the low lift area of the building removes any large debris such as weeds, fish, etc.


Low Lift Pumps


There are three low lift pumps that lift the water from river level via a 400 mm header to the flash mix tanks.  From there the water flows via gravity through the various plant processes.


Chemical Feed System


Pre-hydroxylated Aluminum sulphate (PAS-8) and a polyelectrolyte are used to create a 'floc'. The floc captures suspended particles (colour, dirt, etc.) which may be found in the raw water.  This 'capture' process aids in their removal. The pH adjustment is achieved by the addition of Sodium Bicarbonate, pre and post treatment.


Flash Mix Tank


This 50 m3 tank provides the necessary mixing or blending of the raw water and the added coagulants.


Contact Tanks


Following the mixing and coagulation in flash mix tank it is necessary to gently agitate the chemically treated water in the flocculation tanks to promote particle collision and formation of larger floc.


Clarification


The floc created by the coagulation is settled in the clarifiers.  The rectangular clarifiers rely on slow longitudinal flow to allow enough time for the particles to settle. These particles are collected by a tracvac sludge vacuum system.  This system transfers the settled sludge to two wastewater tanks for water separation and disposal.


Filters


The plant is equipped with three dual media (sand/antharcite) filters.  The filters remove particles (suspended solids) that are present in the raw water, as well as compounds that cause taste and odours. Filters are washed regularly on a backwash cycle to prevent any buildup on the filters.


Pre Chlorination


Pre-chlorination of chlorine gas and water is added to the clarifier effluent channel to assist in the removal of color, help control tastes and odour, and/or to oxidize organic and inorganic elements.


Post Chlorination


Chlorine gas is added to the water as it enters the clearwell.  Sufficient amounts of chlorine is used to disinfect the treated water and to provide a chlorine residual which remains in the distribution system.  This ensures water quality protection to the customers' location.


The clearwell provides water storage for the high lift pumps and has 1650 cubic meters of total storage capacity.


High Lift Pumps


There are three high lift pumps that discharge the treated water into a 500 mm header that connects into a 400 mm line and a 500 mm line leaving the plant and connecting into the distribution system.


Standby Power


A 325 kW diesel generator is located at the water treatment plant to provide power to essential equipment to ensure a continuous supply of water during power failures.


Elevated Tank


There are four functional towers in the Town of Petawawa, as of August 2010.  A 2,250 m3 tower located on DND south townsite, and a 4,500 m3 tower located on Woodland Crescent. The third tower is located on Tower Road, having a capacity of 2,250 m3.  A fourth tower has been commissioned on the property of CFB Petawawa that has a capacity of 3,785 m3, totaling 12,785 m3 or approximately 1,000,000 gallons of water storage.  Once the new tower is fully operational, maintained by OCWA staff, the south townsite elevated tank will  be decommissioned.


Distribution System


Approximately 11,475 people are supplied with water from the Petawawa Water Treatment Plant.