Understanding Water Treatment + Wastewater Treatment

Posted in: Water Quality | 0

If you live in Edmonton, there is a strong chance that you already know that your drinking water comes from the North Saskatchewan River and that your wastewater gets discharged into it following treatment. You also probably know that Edmonton has two water treatment plants that the river can pass through on the way to your taps, the E.L Smith and the Rossdale Treatment Plant, and that the wastewater treatment plant is called the Goldbar Wastewater Treatment Plant. 


If you’re like me and most Edmontonians, beyond naming the water treatment facilities, more specific details of the water treatment processes are a mystery. In this blog I will explain the water treatment process in layperson’s terms for both drinking water and wastewater. I hope this blog will help in understanding how our river water becomes our drinking water and how our wastewater is returned to the river! Throughout I also ask some questions that I’d like you to answer in your head. These questions will allow you to connect the water treatment process with your everyday life and to think about how activities going on in these EPCOR plants affect your day. 


From the North Saskatchewan River to your Tap.

Image credit: Screen capture from EPCOR Treatment Handout. 


  1. Pre- Water Treatment: Water intake of the River

The intakes for the water treatment plants are in the deepest parts of the North Saskatchewan River. This is so that oil (naturally occurring and from human activity) and floating debris on the river’s surface do not come near the intake and obstruct it. The intake depth is also helpful during winter when the surface of the river is ice, so water below can still come into the intake. The intake structure at the E.L. Smith water plant has a fish return so the fish are gently deposited downstream if they come near the intake. There are also screens with small holes just before the low-lift pumps to strain out debris which may enter the plant such as sticks, fish and leaves. 


  1. Chemical Addition + Rapid Mix + Flocculation 

Once the water is in the treatment plant via the low-lift pumps, the first chemical treatment is the addition of Alum (aluminum sulphate) and powdered activated carbon. These chemicals are added from feed pumps, and are adjustable to supply the correct dosages based on the river water properties. Alum is added to remove suspended solids and powdered activated carbon is added to absorb taste, odour and colour-causing compounds. 

The rapid mix is necessary to mix alum and carbon chemicals thoroughly with the water to treat the water. Rapid mix is the process of the water and chemicals being rapidly mixed or shaken together in an enclosed basin. 

After the rapid mix, a polymer is added to the water to encourage the formation of “flocs”. The polymer acts like a glue to bind particles together and when Alum, polymer and dirt combine they become heavy and settle to the bottom of a basin. This mixture is then called sludge. This process, which removes dirt, silt and micro-organisms from the raw water supply drawn in from the river, is known as flocculation. At this stage up to 99% of the sediment has been removed from our drinking water.


  1. Sludge gets the Residuals Treatment

After the floc is formed, it settles to the bottom of the clarifying basin as sludge.

The sludge is removed from the basin and clear water is decanted from the surface. The sludge is treated in residuals treatment, where as much water as possible is recycled, and the remaining silt and debris collected are sent to the landfill. The clear water, which has undergone the clarification process by the removal of sludge, moves on to disinfection.


  1. Clear Water gets Disinfected

Free chlorine is added to the clear water after clarification to kill any remaining harmful bacteria and microbes. Ultraviolet (UV) disinfection also occurs to render the microorganisms harmless. The UV light is similar to what shines down from the sun or a tanning bed, it disrupts processes (such as DNA) in the microorganisms rendering them unable to do any cellular functions. Humans exposed to UV light without protection can also experience cellular damage, so be sure to follow sun safety when you’re outside.

Ammonia is then added to the water, to combine with the chlorine to form a disinfectant called monochloramine. Monochloramine can destroy harmful bacteria in the water system and keeps the water safe from any bacteria that happens to enter the water or pipes.


  1. Clear Water undergoes Filtration

The clear and disinfected water is then filtered by moving it through a layer of anthracite coal and a layer of sand, where any remaining particles in the water will get stuck. The coal and sand filters are cleaned regularly by pumping air and water back up through the sand and coal to dislodge any particles that have been stuck, and they are removed for disposal. After the water is filtered, fluoride is added. Flouride is the only chemical added to drinking water in Canada for medical treatment. A concentration of 0.7 mg/L is recommended by Health Canada guidelines for dental health. Fluoride has been a federal recommendation since 1967!


  1. Last additions + Dechlorination

Caustic soda is added to the water near the end of the treatment process to raise the pH of the water, making it more alkaline than acidic. The pH is raised to minimize corrosion problems in the distribution system and customers home piping system. It can also help deter lead, iron, and copper from entering the water from plumbing pipes and fixtures. 


  1. Reservoir Storage + High lift pumping for distribution

After filtration, the water will move to on-site reservoirs where it will be stored until it is needed. This is to allow the treatment plant to handle variations in water demand all day. High-lift pumps move the water into pipes to homes, and businesses based on need.


Connection Questions

  • What were three new things you learned, or are curious to learn more about in your water treatment process? I encourage you to explore on the internet, and share your thoughts with your family and friends. 
  • Did you know that fluoride was added to your water to protect your, and your families dental health? Further reading on water fluoridation in Canada. 
  • When you use your tap water to make morning coffee, how many hours before turning on your faucet do you think the water was in the North Saskatchewan River? 7-15 hours!
  • Did it surprise you that the treatment plant adjusted the pH of the water to protect your home piping system? 
  • Can you think of the two highest times for water demand during a day? It is the morning before work and then mid-afternoon when everyone gets home from work to make dinner, and spent time at home.
  • Do you ever notice a smell to your tap water in Edmonton? EPCOR conducts regular odour tests of their water, and adjust their treatment processes accordingly with the odour. They especially do so during spring run-off!


Now that we know how the water moves from the North Saskatchewan River to your tap, let’s cover what happens when you flush your toilet. Where does the water go and how is it treated?


From your Toilet, Sink or Shower to the River.

In Edmonton, the Gold Bar wastewater treatment plant houses complex processes that remove contaminants from the water, allowing it to be released as effluent into the North Saskatchewan River. 


Image credit: EPCOR Goldbar Treatment Plant Website.

Image Credit: EPCOR Website


  1. Pre-Treatment

In this stage, the wastewater from homes and businesses enters the plant. The plant equipment is protected as large materials (such as wood, sticks or leaves) are removed to limit the wear and tear on the plant, while also improving the quality of organic solids to be treated. This eases the wastewater treatment process later on. Wastewater moves through large tanks that slow down the flow, so solids can settle to the bottom. Grit (sand-like particles mixed with debris and mud) drop to the bottom of the tank and are removed. The wastewater exits the tanks through screens so plastic, rags and wood are trapped. These trapped materials and the grit will be disposed of at a local landfill. Once through the aerated tanks, the wastewater moves to the primary clarifiers.


  1. Primary Treatment

This step is a physical process that relies on waste settling via gravity. Similar to the water treatment process outlined above, alum and polymer are added to attach to dirt and debris to form flocs. The process of flocculation catches small debris that could not be caught in pre-treatment or through the screens. Heavier particles will sink to the bottom and lighter particles will float to the top. There is a rake that will move the flocs and particles along the bottom to a collection point, and then rake will also come to the top and remove the floating scum to a collection point. 

The solids and scum are piped away for solids handling and the primary effluent (the water left over) moves on to secondary treatment.


  1. Secondary Treatment 

The remaining organic matter in the water will not settle out by gravity, therefore the effluent is moved into fermenter and digester tanks for treatment which create “biosolids”. The digesters used are microorganisms (bacteria, fungi, and protozoa) and organic matter. Microorganisms feed on the dissolved organic matter and nutrients such an ammonia and phosphorus, breaking them down. It is important the microorganisms remove nutrients from the treated wastewater as high nutrient concentrations could harm the fish in the river or cause uncontrolled algae growth. 

Following digestion, the water goes through a settling process in the clarifiers where the well- fed microorganisms bind together as ‘flocs’. These flocs will sink and be raked away to be moved to solids treatment. At the end of this stage 95-97% of the organic impurities have been removed. 


  1. Tertiary Treatment 

The final water treatment step is disinfection and the removal of any leftover phosphorus and ammonia. 

Around 5% of the water bypasses UV light treatment, and instead passes through porous synthetic strands, which allows water to pass but acts as a barrier to even the smallest bacteria. This produces high-grade process water for industry, as this water will have zero bacteria or contaminants present in it due to the membrane filtration process. 

The other 95% of the water undergoes high intensity Ultraviolet (UV) light to disinfect the water in a few short minutes. This chemical-free disinfection treatment allow the wastewater to be safe for contact in recreational activities when it leaves the plant outfall. 


The sludge, known as biosolids, that are generated in the processes can be digested in a chamber without any oxygen (anaerobically) to reduce the organic components in the solids. This process produces biogas, which the Goldbar Treatment Plant uses for their boiler and heating systems, which saves the plant money. The remaining sludge is hauled to the Cloverbar sludge lagoon. After the solids and liquids separate the solids can be used for composting material or as fertilizers for farms and gardens in the Edmonton area.


Edmonton still has combined sewers in older neighbourhoods built before 1960. During wet weather conditions, such as this summer, the combined sewers often capture more runoff from the rain that they can handle and this can result in wastewater overflowing into the river. In recent years there has been work to enhance the primary treatment capacity so the plant can take in more in seasonal flows, reducing untreated overflow into the river. The Goldbar Wastewater Treatment Plant has one of the river’s major combined sewer outfalls, and actually undergoes the primary treatment processes outlined above before entering the river!


Connection Questions: 

  • Were you surprised by any of the processes outlined, or motivated to explore something you read further? I encourage you to look up things you found interesting, or programs you could engage in such as the biosolids fertilizer for your garden!
  • Did you know that Edmonton had combined sewers, especially in older neighbourhoods, that in heavy rainfall bring diluted sewage into the river? What do you think of this? In recent years EPCOR has worked on this in their primary treatment area of the plant, even with the heavy rainfalls we have had this year it is improving!
  • Did the lack of heavy chemicals in the wastewater treatment process surprise you? It sure surprised me! I think it is very interesting how the treatment plant uses limited chemicals, natural microorganisms, UV light and synthetic screens to purify the wastewater!
  • How much of the water that you flush and send down the drain makes it back to the river? As much as 90%!
  • Did you know that microorganisms played such a large role in purifying your wastewater? Where else do you think microorganisms play a role in your everyday life? Microorganisms are great for breaking down organic matter, they multiply fast and by mixing oxygen in the digesters, can be very productive at their job of digesting waste. Microorganisms are used in making dairy products, bread and many beverages. This is just one example among many of how microorganisms play a role in your everyday life.  


Every time you turn on a tap, take a shower or flush the toilet you are interacting with the water treatment processes outlined above. In the questions I shared I hope you learned something new and considered how water treatment process affects your life. I hope this blog drew you to consider how essential water treatment facilities are, and to appreciate the processes in which tap water arrives at your house or how wastewater is whisked away. Share this article with friends and family to educate and inspire them to learn more about water treatment. 











Cover Image by kubinger from Pixabay 

Leave a Reply

Your email address will not be published. Required fields are marked *