Municipal wastewater effluents are the largest single effluent discharges,
by volume, in the country
Pollution Entering Canadian Waters
Across Canada, a high proportion of the population is served by wastewater collection and treatment systems. The level of treatment ranges from no treatment to very sophisticated and thorough treatments. Wastewater effluents are released to a wide variety of receiving environments: lakes, ponds, streams, rivers, estuaries and oceans. Effluents released from wastewater systems do contain pollutants of concern since even advanced treatment systems are unable to remove all pollutants and chemicals. Furthermore, some sewer collection and treatment systems are combined with stormwater collection systems that can become overloaded during heavy rainfalls, resulting in the release of partially treated or even untreated effluents. The solid material (biosolids and sludges) collected during treatment is disposed of on land, incinerated or sent to landfills. Treatment of wastewater also releases emissions to air mostly in the form of carbon dioxide and methane.
The 2001 report "The State of Municipal Wastewater Effluents in Canada" describes the sources and the nature of contaminants entering municipal sewer systems, levels of wastewater treatment across Canada, the impacts that wastewater effluents can have on water quality, plant and animal life and human health and beneficial water uses, such as shellfish harvesting and recreation.
The Effect of the Release of Wastewater Pollutants on Ecosystems and Human Health
Releases to surface waters
Several environmental and health impacts resulting from insufficient wastewater treatment have been identified in the scientific literature and actions need to be taken to reduce these impacts. These impacts can include negative effects on fish and wildlife populations, oxygen depletion, beach closures and other restrictions on recreational water use, restrictions on fish and shellfish harvesting and consumption and restrictions on drinking water consumption.
Some examples of pollutants that can be found in wastewater and the potentially harmful effects these substances can have on ecosystems and human health include:
- decaying organic matter and debris can use up the dissolved oxygen in a lake so fish and other aquatic biota cannot survive;
- excessive nutrients, such as phosphorus and nitrogen (including ammonia), can cause eutrophication, or over-fertilization of receiving waters, which can be toxic to aquatic organisms, promote excessive plant growth, reduce available oxygen, harm spawning grounds, alter habitat and lead to a decline in certain species;
- chlorine compounds and inorganic chloramines can be toxic to aquatic invertebrates, algae and fish;
- bacteria, viruses and disease-causing pathogens can pollute beaches and contaminate shellfish populations, leading to restrictions on human recreation, drinking water consumption and shellfish consumption;
- metals, such as mercury, lead, cadmium, chromium and arsenic can have acute and chronic toxic effects on species.
- other substances such as some pharmaceutical and personal care products, primarily entering the environment in wastewater effluents, may also pose threats to human health, aquatic life and wildlife.
Releases to Air
The process of collection and treatment of wastewater also results in the release of certain volatile chemicals into the air. The chemicals tyically released in the largest volume include; methane, carbon dioxide, oxides of nitrogen, hydrogen sulfide, mercaptans, chlorine (if used in the treatment process) and various other chemicals can be released to a smaller extent.
Releases to Land
The process of removing both inorganic and organic suspended solids from the wastewater results in large quantities of solid waste. In typical treatment facilities, the inorganic solids (grit, debris) and other non-biodegradable materials are sent to landfill. Many secondary treatment facilities collect the organic solids and process them in a digester to recover methane gas for energy production. Once the organic solids have been completely digested (no further methane production), various options are available to the treatment facility. These solid wastes can be land applied as a soil fertilizer/conditioner, incinerated for further energy recovery, sent to landfill, or to deep well injection.
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