World Water Day 2017: Wastewater
Globally, the vast majority of all the wastewater from our homes, cities, industry and agriculture flows back to nature without being treated or reused – polluting the environment, and losing valuable nutrients and other recoverable materials.
Instead of wasting wastewater, we need to reduce and reuse it. In our homes, we can reuse greywater on our gardens and plots. In our cities, we can treat and reuse wastewater for green spaces. In industry and agriculture, we can treat and recycle discharge for things like cooling systems and irrigation.
By exploiting this valuable resource, we will make the water cycle work better for every living thing. And we will help achieve the Sustainable Development Goal 6 target to halve the proportion of untreated wastewater and increase water recycling and safe reuse.
> Read more: www.worldwaterday.org/theme/
Wastewater: Towards a green solution to the problem of combined sewer overflows in Ontario
Our chapter wastewater campaign advocates low impact approaches to development, amply successful in other cities and the elimination of by-passes and overflows of sanitary sewage.
One of the impacts of urbanization on the flow of water is that roads and buildings are impervious, thus reducing percolation and increasing both the velocity and peaking of the storm-water. In addition, the storm-water picks up contaminants from roads and therefore needs to be treated. Since the 1930s, this treatment is provided in above-ground ponds that are attractive, green and fairly low-cost. In such systems which are found in most newer communities such as Scarborough, North York, Oakville etc, the wastewater (sanitary sewage) from homes and industries flows to a sewage treatment plant (STP) where sophisticated treatment deals with E. coli and other harmful substances. There are different levels of sewage treatment ranging from the lowest or primary, to secondary and tertiary. Most Canadian cities including Toronto use secondary treatment, which is not perfect but is the minimum acceptable standard for sewage treatment.
In older parts of most cities, such as Toronto, Hamilton, Kingston, and Niagara Falls, the sewage collection system is much older – sometimes over a hundred years old. Both the sanitary sewage and the storm-water are collected in one pipe called the combined sewer and flow to the STP. As a result, during intensive rainfall events, there are overflows (combined sewer overflows or CSOs) at points along the system and by-passes at the STP. In Ontario, there are over 100 such communities, some of which are small rural communities. In Toronto, to take a familiar example, the problem is exacerbated because in the 19th century the sanitary sewage was led to ravines such as Garrison Creek and Taddle Creek and the engineering solution at the time was to bury these streams in pipes. So today, the STPs have to treat all the water in these streams – no wonder that by-passes and overflows occur to the point that untreated sewage is occasionally found in our basements, ravines and parks; and our beaches are closed to swimming most of the days in summer when it rains.
To alleviate the problem, engineers have built or have planned to build containment storage along the sewer lines in some cities. This storage reduces the frequency of overflows and by-passes but perpetuate the problem rather than solve it. What is needed is a careful disconnection of the sanitary sewage flow from the storm-water flow such as in most parts of Scarborough and in North York. Even tiny East York had a policy to disconnect the two flows such that no rain was allowed in the sanitary drain except for flows from the weeping tiles in the foundation drains. The Council of Canadian Ministers of the Environment (CCME) has announced a policy for long term plans to reduce combined sewer overflows in the ‘Canada-Wide Strategy for the Management of Municipal Wastewater Effluent’ framed in 2009. Many North American cities, such as Vancouver, BC and Minneapolis, MN have already undertaken sewer separation programs; i.e. complete separation of storm pipes from sanitary sewer. These source control measures and above ground green facilities for the treatment of storm-water are substantially economical compared to the cost incurred towards the end-of-the-pipe solutions, such as building containment storage and the indirect cost incurred due to the risk to human health and the environment. In British Columbia, the Province requires that all CSO’s be eliminated by the year 2050.