8 Water and Sewage Part 2 Review.docx

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Ryerson University
Environment and Urban Sustainability
EUS 202
Christopher Greene

WASTE & SEWAGE PART 2 Water Quality & Sewage Treatment  Withdrawal and discharge in stream system  Water is withdrawn upstream, removing half of the normal stream discharge=doubled concentration  New concentration poses higher potential to harm aquatic organisms and system  Conventional systems also use potentially hazardous chemicals in the treatment process & ^$$ Sewage Treatment & Injustice  Often located in areas with very little power in the decision-making process Stormwater  storm+wastewater: A source of concern during heavy precipitation events and periods of rapid melting snow  During these events, volume becomes extremely high, stresses the capacity of the treatment plant and can cause overflow  Overflow means pollution directly released to surface waters without treatment  Reduce per capita water use=Less domestic wastewater in the combined system lessens the potential for overflow  Reducing flow rates ensures water is detained longer during treatment=Less water =longer retention times at plants Reduced Water Use and Coastal Groundwater  Coastal cities may have groundwater=vulnerable to saltwater intrusion  ^withdraws of freshwater reduces pressure that allows denser saltwater to migrate  vertical contaminant migration Ounce of Prevention or Pound of Cure Sewage Treatment Plants & Pollution  Primary Treatment: Mechanical or physical separation (settling tanks) WASTE & SEWAGE PART 2  Secondary treatment: Additional settling + biological treatment (microbial) o Effluent still contains high nutrient loads (nitrogen, phosphorous)  Tertiary treatment: Chemical treatment (often chelation)=Removes nutrients, salts, metals, other potential toxic compounds o Highest level of treatment, most expensive, least common  Degradation of aquatic systems/associated ecosystem services  long term $ may be >upfront cost Reclamation and Reuse  Waste to an input to some other process (reduces consumption, financial benefits)  Reducing demand for potable water (and thus minimizing the need to increase capacity required)  Reclaimed wastewater that has been treated can be used for non- potable purposes  Wastewater that does not receive tertiary treatment is also nutrient rich=Can be applied directly as a fertilizer  groundwater recharge Alternatives to Treatment  Natural processes can be used to treat wastewater as an alternative (Wetlands) Solar Aquatic Systems (SAS)  Attempts to imitate water filtration of wetlands in controlled conditions Green Infrasturcture The Importance of Vegetation Stormwater & Green Infrastructure  High impervious cover can increase both rate and volume of stormwater runoff  Vegetation and permeable surface naturally slows the rate, decreases volume of runoff  Vegetated Swales (Bioswales, Grassed Channels): Gently sloped depressions that collect water WASTE & SEWAGE PART 2 o Dense vegetation planted in depressions to slow and filter runoff o Traps sediment, filters pollutants before they can be discharged to streams o Reduces the need for physical infrastructure to manage stormwater  Rainwater Gardens o planted in depressions, more attention to aesthetics o Use soil and flood-tolerant plants and drought tolerant plants to capture and filter runoff  Planter Boxes: Small, compartmentalized, vegetated areas o Allow infiltration to recharge groundwater o Release water back into the stormwater system  Green Roofs: Absorb rainwater and reduce stormwater runoff in addition to other benefits o Intensive (thicker soil, more active) vs. extensive (thinner soil, more functional) o Roofs partially or fully covered/Membrane/Growing medium/Vegetation  Rain Barrels and Cisterns: Used to collect and stormwater from rooftops  Detention Ponds: Primary purpose to manage storm water during peak events (heavy rainfall, spring melt)/Collect water and slow down flow (or to de
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