Sewage Treatment Plants
Our sewer systems collect wastewater from industry, commercial businesses and homes. From there, it is sent to one of our three wastewater treatment plants:
How does wastewater treatment work?
We treat wastewater to remove the major contaminants (carbon, nitrogen and phosphorus) and harmful bacteria, such as E. coli. To do this, we send the raw sewage through several processes in our plants. Bacteria called activated sludge plays a major role in the treatment process. The activated sludge bacteria use the contaminants in the sewage as food to reproduce. Once this treatment cycle is completed, the activated sludge is removed, the treated water is disinfected, and it is sent to the river.
This process has been used worldwide since 1914 and has been used in Winnipeg since 1964, when we commissioned our first activated sludge plant at the NEWPCC to remove carbon. In 2008, the WEWPCC activated sludge process was upgraded to remove not only carbon but also nitrogen and phosphorus. The SEWPCC and NEWPCC are now being upgraded to also remove all three contaminants.
Screens are used to remove plastics, rags, and other debris from the incoming raw wastewater. After screening, sand and grit settles to the bottom. The sand and grit are removed and trucked away to the Brady Road Resource Management Facility for disposal.
Next the wastewater moves into sedimentation tanks, where approximately 65% of the suspended material settles to the bottom of the tank. In addition to material that settles in the bottom of the tanks, grease and oil that floats to the surface is removed by paddles or skimmers. Primary treatment takes several hours before the wastewater moves to the next stage of treatment.
After Primary Treatment, the wastewater flows into bioreactors which contain a mixture of micro-organisms that feed on the carbon in the wastewater. Oxygen is fed into the bioreactor so the micro-organisms can metabolize the carbon they’re feeding on. This process also takes several hours. The activated sludge, or biomass, must be separated from the treated wastewater. The separation takes place in another group of sedimentation tanks called Secondary Clarifiers.
In the final clarifier tanks, the biomass from the bioreactors settles out by gravity. About 25 to 50% of the settled biomass is returned to the head of each bioreactor to begin the process again.
The biomass that is reused provides a constant source of micro-organisms to the incoming wastewater for treatment. Because the biological growth within the bioreactors produces more biomass than is needed, some of it must be removed.
This excess biomass, called Waste Activated Sludge, is pumped to the Digesters, where it decomposes. All the material that settles in the Primary Clarifiers is also pumped to the Digesters.
Digestion, Dewatering and Solids Disposal
During digestion, the anaerobic bacteria break down the solids over the course of about 15 days. About half of the solids are destroyed during this process.
In the Digesters, a different type of bacteria, called anaerobes, feed on the carbon in the solids to produce bio gases mainly carbon dioxide and methane. Methane is recovered at the NEWPCC and used to heat the Digesters and other buildings.
Once digestion is complete, excess water must be removed from the digested sludge. Dewatering is accomplished using high speed mechanical centrifuges. The liquid produced during dewatering is returned to another activated sludge process designed specifically to remove ammonia and nitrogen produced during digestion.
Digested material contains about 2% solids but is thickened to about 25% before being transported. The thickening process significantly reduces the volume of material that must be transported for final disposal.The thickened solids, now called biosolids, are trucked to the Brady Road Resource Management Facility. On average, Brady Road receives 36,000 kg of biosolids each day for final disposal.