Causes. Release of waste water from drains or sewers (toilets, washing machines, and showers) and include human wastes, soaps and detergents.

Transcription

1 Sewage

2 Causes Release of waste water from drains or sewers (toilets, washing machines, and showers) and include human wastes, soaps and detergents.

3 Pollutants in Sewage Raw sewage (mostly water) Flushing from toilets and collection from drains.1% waste, 99.9% water Debris and grit Rags, plastic bags, sand Particulate organic material Fecal matter, food wastes Colloidal and Dissolved Organic Materials Bacteria, urine, soaps, cleaning agents Dissolved Inorganic Material Nitrogen, phosphorus

4 Core Case Study: Using Nature to Purify Sewage Ecological wastewater purification by a living machine. Uses the sun and a series of tanks containing plants, snails, zooplankton, crayfish, and fish (that can be eaten or sold for bait). Figure 21-1

5 Sewage Treatment Prior to 1800s: Disposed of feces straight into water source Late 1800s: Louis Pasteur Need sewage system, used storm drains 1900s: Facilities designed to treat the outflow before entering storm waterways Many developing countries have primitive stage of sewage treatment, with no treatment at all

6 Reducing Water Pollution through Sewage Treatment Raw sewage reaching a municipal sewage treatment plant typically undergoes: Primary sewage treatment: a physical process that uses screens and a grit tank to remove large floating objects and allows settling. Secondary sewage treatment: a biological process in which aerobic bacteria remove as much as 90% of dissolved and biodegradable, oxygen demanding organic wastes.

7 Municipal Sewage Treatment 2012 John Wiley & Sons, Inc. All rights reserved.

8 Municipal Sewage Treatment Primary treatment Removing suspended and floating particles by mechanical processes Secondary treatment Treating wastewater biologically to decompose suspended organic material; reduces BOD 2012 John Wiley & Sons, Inc. All rights reserved.

9 Reducing Water Pollution through Sewage Treatment Primary and Secondary sewage treatment. Figure 21-16

10 Primary Secondary Bar screen Grit chamber Settling tank Aeration tank Settling tank Chlorine disinfection tank Raw sewage from sewers Sludge Activated sludge To river, lake, or ocean (kills bacteria) Air pump Sludge digester Sludge drying bed Disposed of in landfill or ocean or applied to cropland, pasture, or rangeland Fig , p. 511

11 Municipal Sewage Treatment 2012 John Wiley & Sons, Inc. All rights reserved.

12 Reducing Water Pollution through Sewage Treatment Advanced or tertiary sewage treatment: Uses series of chemical and physical processes to remove specific pollutants left (especially nitrates and phosphates). Water is chlorinated to remove coloration and to kill diseasecarrying bacteria and some viruses (disinfect).

13 Reducing Water Pollution through Sewage Treatment Sewage sludge can be used as a soil conditioner but this can cause health problems if it contains infectious bacteria and toxic chemicals. Sewage Sludge Solids remaining after primary and secondary sewage treatment has been completed Preventing toxic chemicals from reaching sewage treatment plants would eliminate such chemicals from the sludge and water discharged from such plants.

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15 Individual Septic System- Septic Tank 2012 John Wiley & Sons, Inc. All rights reserved.

16 Individual Septic System- Drain Field 2012 John Wiley & Sons, Inc. All rights reserved.