Section 4: Wastewater discharges
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Canada has one of the largest renewable water supplies in the world, an average of 3,472 km3 per year. 1 Rivers, lakes and marine areas are used to dispose of wastewater and industrial waste, which can have a negative impact on water quality. This section will examine discharges of municipal and industrial wastewater.
Water discharged into drains or sewers, water received by water treatment plants or water discharged directly to the environment is all considered wastewater. Wastewater includes all return flows of water to the environment, regardless of quality. 2
Municipal wastewater is liquid waste and can be divided into two categories:
- sanitary sewage from homes, businesses, institutions and industries;
- stormwater from rain or melting snow that drains off rooftops, lawns, roads, and other urban surfaces.
Wastewater is collected by sewer systems and in most cases is treated before being released to the environment (see Textbox: Municipal wastewater). 3
Most households in Canada are connected to a municipal sewer system. In 2009, 82% of households lived in dwellings connected to municipal sewer systems, while 13% used private septic systems and 1% used communal septic systems. 4
Municipal wastewater can contain grit, debris, suspended solids, disease-causing pathogens, decaying organic waste, nutrients and about 200 different identified chemicals. It is a leading source of suspended solids, nutrients, organic chemicals and metals discharged into Canadian waters. 5
When discharged, municipal wastewater can cause aesthetic problems such as odours and discolouration. Disease-causing pathogens such as bacteria and viruses can make water unfit for human use. Excess nutrients can overstimulate the growth of aquatic plants. Decaying organic waste can use up dissolved oxygen and threaten the survival of aquatic life. Toxic chemicals can harm aquatic organisms. Additionally, excessive sedimentation 6 can smother fish feeding and spawning grounds.
Contaminant levels can be high in untreated sewage, stormwater, and combined sewer 7 overflows. Even treated sewage may still contain some harmful substances, although in smaller quantities than in raw sewage.
In 2006, municipalities across the country generated a daily average of 668 L of wastewater per person served by sanitary sewers. 8 Residential sources accounted for close to two-thirds of the flow into municipal sewer systems, while the industrial, commercial, and institutional sector produced 18% of municipal wastewater flows. Stormwater accounted for 9% of sewer flows and the remainder (8%) was the result of groundwater infiltration into sewer systems (Chart 4.1).
In smaller communities, wastewater is primarily produced by the residential sector, whereas in larger communities their share decreases. For example, in communities of less than 1,000 people, 71% of wastewater flow was from residential sources, whereas in those communities with 50,000 to 500,000 people, only 53% was produced by the residential sector in 2006.
Municipal wastewater treatment and discharge destination
Municipal wastewater can be treated to various degrees before release to the environment. Secondary mechanical treatment is considered the conventional treatment process in Canada (see Textbox: Wastewater treatment levels). Of Canadians served by sanitary wastewater collection systems in 2006, wastewater was treated at the secondary level or better for 79% of the population. Almost 2% were not served by wastewater treatment facilities at all. 9
Surface freshwater was the main destination for 91% of municipal wastewater discharge in 2006, while 6% was discharged into marine water and 3% was disposed of using other methods, including infiltration, irrigation, and evaporation processes. Smaller municipalities were more likely to use these alternative discharge methods.
Wastewater treatment levels
Municipal wastewater can be treated to various levels, each of which includes specific activities or technologies as described below:
Primary treatment removes insoluble matter only.
Secondary treatment removes biological impurities from water treated at the primary level.
Advanced or tertiary treatment removes nutrients and chemical contaminants remaining after the secondary treatment.
Local governments across Canada spent $3.9 billion for sewage collection and disposal in 2006. 10
Industrial wastewater is liquid waste discharged from industrial activities such as manufacturing, mining and power generation (see Textbox: Industrial Water Use Survey: Coverage).
Industrial Water Use Survey: Coverage
Unless otherwise specified, Section 4.2 Industrial wastewater uses data from the Industrial Water Use Survey. 11 The target population covered manufacturing and thermal-electric power generation as well as selected mining industries (coal, metal ore, and non-metallic mineral mining). The survey did not include wastewater from oil and gas extraction activities or support activities for mining and oil and gas extraction.
Wastewater discharge for manufacturing, mineral extraction 12 and thermal-electric power generation was 29.9 billion cubic metres in 2009. Thermal-electric power producers accounted for 86% of wastewater discharge, followed by manufacturing industries (12%) and mining industries (2%) (Table 4.1).
Industrial wastewater treatment and discharge costs
Industrial wastewater treatment and discharge costs were $532.2 million, approximately 37% of total industrial water costs in 2009 (Table 4.2).
Manufacturing industries spent $452.2 million on wastewater treatment and discharge, 41% of their total water costs (Table 4.2). The paper industry accounted for the largest share of this total at $189.3 million, while the food manufacturing industry spent $91.7 million, the chemical manufacturing industry spent $72.7 million and the primary metals manufacturing industry spent $49.3 million on wastewater treatment and discharge.
Mineral extraction industries spent $70.6 million on wastewater treatment and discharge, 43% of their total expenditure on water.
Thermal-electric power producers use large quantities of water for cooling, condensing and steam. The industry spent relatively little ($9.5 million or 6%) on water treatment and discharge as a proportion of their total water costs in 2009.
Industrial wastewater discharge destination and treatment
Manufacturing industries discharged most of their wastewater (75%) to surface freshwater bodies, tidewater (11%) and to public and municipal sewers (10%). The balance was discharged to groundwater or other points. Of the water discharged by manufacturers, 38% was not treated before being released. Seventeen percent of the total discharge received primary treatment, 37% underwent secondary or biological treatment and 8% underwent tertiary or advanced treatment.
Mining industries discharged most of their wastewater (73%) to surface freshwater, while discharging another 11% to tailing ponds and 9% to groundwater. Metal mines accounted for the largest proportion of wastewater discharged to tailing ponds. Of the total water discharged by mining operations, 60% was not treated before discharge, 31% underwent primary or mechanical treatment and 9% underwent tertiary or advanced treatments.
Thermal-electric power generation industries discharged 95% of their wastewater to surface freshwater bodies. Almost 59% of this water was not treated before being discharged.
Industrial water recirculation
Water recirculation is defined as the process of using the same water more than once in a system. The water must leave the system and re-enter it again or be used in a different system. Water recirculation reduces the need for industries to take in new water. 13
In 2009, 7,770.9 million cubic metres of water was recirculated by the manufacturing, mining and thermal electric power generation industries. The recirculation rate, defined as the amount of recirculated water as a percent of water intake, was 25%.
Manufacturing industries recirculated 2,003.3 million cubic metres of water, 53% of their total water intake. The primary metal manufacturing industry had a recirculation rate of 98%.
Mining industries reported the use of 1,547.7 million cubic metres of recirculated water in 2009, a recirculation rate of 311%. Almost all of the recirculated water (98%) was used for process activities by the mining industry.
Thermal-electric power producers recirculated 4,220.0 million cubic metres of water, resulting in a recirculation rate of 16%.
Industrial water pollutant discharges
Ammonia and nitrate made up 90% of the total tonnage of substances released into water by industrial facilities in Canada in 2009 according to the NPRI database (Table 4.3).
In 2008, $114.7 million in capital expenditures was invested in pollution abatement and control processes and technologies to reduce emissions to surface water, while capital expenditures on pollution prevention processes and technologies totalled $178.8 million (Table 4.4).
The paper manufacturing industry spent the greatest portion (34%) of their total capital expenditures on pollution abatement and control to reduce emissions to surface water, followed by the food manufacturing (19%) and chemical manufacturing (17%) industries. The mining and quarrying industry spent the greatest portion (62%) of their total capital expenditures on pollution prevention to reduce emissions to surface water.