A rain garden. Photo: EPA
Wastewater and stormwater can be treated using a variety of methods, which are organized according to the degree to which they remove these contaminants.
Primary treatment uses mechanical methods that settle or float. Larger solids can be removed via screens, while smaller particles are skimmed or can be removed via a settling process. Only 50-60% of solids are removed at this stage of treatment.
Secondary treatment, in addition to using the methods above, uses biological processes to remove suspended solids and dissolved matter. Bacteria and chlorine are used to remove organic material and small particles. Ninety percent of solids are removed during this stage.
Tertiary treatment uses the methods above and filters the most harmful contaminants. Advanced treatments that fall under this category can disinfect wastewater from viruses and pathogens, making it safe to discharge near places like beaches. Nitrogen and phosphorus, which can harm aquatic ecosystems, can also be removed at this stage, along with persistent organic pollutants. Tertiary treatment methods can also remove over 99% of microplastics.
Following treatment, outflow from wastewater treatment plants, and any remaining contaminants it contains, flows directly into nearby streams, rivers and oceans. This is why advanced treatment is so important.
There are many ways to manage stormwater. Reducing the size of paved areas, using porous surface materials and building rain gardens all allow stormwater to flow into the ground, where it is naturally filtered. Conveyance controls, like storage tanks or special tunnels, can prevent stormwater from flooding wastewater treatment plants. Lastly, end-of-pipe controls like wet ponds can use landscaping and infrastructure to filter contaminants and slow the rate of stormwater flow, preventing flooding and erosion.
McCauley Point outfall, Victoria B.C.
McCauley Point outfall, Victoria B.C.For generations, we have looked at sewage – wastewater and stormwater – simply as a waste product to be rid of. Too often, this waste is discharged into local rivers and oceans, without adequate treatment. The human waste, toxic chemicals and heavy metals contained in sewage end up in local waterways, endangering the health of both humans and marine life.
But is sewage really just a waste product, or is it a resource we’ve been overlooking?
Today, communities around the world are looking at sewage and organic waste differently, recovering resources such as heat, water and biofuels. With this approach to sewage management, communities are ending up with less pollution, and creating products, such as biofuels, that are helping them tackle climate change. Learn more about how sewage is being used as renewable energy resource here.
Iona Island Wastewater Treatment Plant. Photo: Metro Vancouver
Metro Vancouver’s largest wastewater treatment plant, Iona Island, discharges undertreated sewage directly into the Salish Sea. Current plans are for the Iona Plant to be upgraded to the minimum standard of secondary treatment by 2030. There is no question that a higher standard, tertiary treatment, should be implemented as soon as possible to protect local waters.
Tertiary treatment is the best option for Metro Vancouver communities because it will prevent the largest quantity of harmful toxins like nitrogen, ammonia, metals and microplastics from polluting the Salish Sea.
With planning for the upgrade of the Iona Plant underway, there is an exceptionally rare opportunity to incorporate tertiary treatment into the current upgrade. Increasing wastewater treatment at the Iona Plant to tertiary now will be a significant step towards tackling the issue of pollution in the Salish Sea, and support the health of its inhabitants and surrounding communities.
