The wastewater treatment process

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Pretreatment is achieved by screening, pumping, grit removal and flow monitoring.  Screens remove large debris which could damage equipment in the plant.  Grit treatment removes sand and gravel which causes plugging and abrasive problems in pumps and other mechanical devices.

Wastewater flows into two primary clarifiers where settlement occurs.  Removal of 30-40% of contaminants is expected during this stage.

Secondary treatment begins as the flows enter the oxidations ditches.  The primary treated wastewater is mixed with sludge from the secondary clarifiers.  This secondary sludge, also called activated sludge, is rich in microorganisms which thrive on organic material in the wastewater.  In order for them to accomplish their task of consuming the organic material, they must have sufficient oxygen and be well mixed.  These requirements are accomplished by the use of disc-type rotary aerators.  After the wastewater entering the oxidations ditches has passed through the circular channels, it discharges by gravity to the secondary clarifiers.  Chemical addition is provided ahead of both clarifiers for polymer addition - a coagulant agent which promotes particle growth and settling.  The final clarifier provides a quiet zone for settlement of solids known as sludge.  A portion of the sludge is returned to the head of the oxidation basins to seed the activated sludge process.  The excess sludge is pumped to the anaerobic digesters for further solids treatment.   

The water from the final clarifier is disinfected by chlorine in the chlorine contact chambers.  Excess chlorine is removed from the water before the final effluent is discharged by gravity to the Montreal River.

Solids handling is necessary due to the accumulation of settled solids at the primary and final clarifier stages.  The digesters serve several important functions.  The sludge stored in the digesters is cut off from any oxygen source (anaerobic digestion).  The organisms requiring oxygen die off and the methane producing bacteria are cultivated.  The sludge is heated and thoroughly mixed using compressed methane gas and the bacterial action proceeds to digest the organic material in the sludge, producing methane gas, water and carbon dioxide as primary by-products.  The methane gas is then burned to provide heat for the digester contents.  The digested sludge is thickened in digester #3 and pumped to the solids processing building for further dewatering.

The finished treated product resulting from solids removal is a sludge cake ranging from 21-25% total solids content.  The cake is nearly pathogen free, has minimal odor, and is comparable to compost.  The product is land-applied to local farm sites in a safe and effective manner.  This improves soil texture and structure, saves on valuable landfill space, and recycles the nutrients to enhance a variety of crop growth.

All stages of the treatment process are monitored through regular sampling in the laboratory facility located in the administration building.