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Sewage Treatment

Sewage Treatment. Reducing Water Pollution through Sewage Treatment. Septic tanks and various levels of sewage treatment can reduce point-source water pollution. Reducing Water Pollution through Sewage Treatment. Primary and Secondary sewage treatment. Figure 21-16.

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Sewage Treatment

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  1. Sewage Treatment

  2. Reducing Water Pollution through Sewage Treatment • Septic tanks and various levels of sewage treatment can reduce point-source water pollution.

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

  4. 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.

  5. Primary • Removes suspended and floating particles, such as sand and silt, by mechanical processes such as screening and gravitational settling. The solid material that is settled out is called primary sludge. Bar screens, grit chambers, primary clarifiers, digesters and pre-aeration

  6. Secondary • Uses microorganisms to decompose the suspended organic material in wastewater. • Trickling filters – where wastewater trickles through aerated rock beds that contain bacteria and other microorganisms, which degrade the organic material in the water.

  7. Secondary (Cont.) • Activated sludge process • wastewater is aerated and circulated through bacteria-rich particles • bacteria degrade suspended organic material. • After several hours, the particles and microorganisms are allowed to settle out, forming secondary sludge.

  8. Tertiary • Includes a variety of biological, chemical and physical processes used to remove phosphorus and nitrogen • Can also be used to purify wastewater so that it can be reused in communities where water is scarce. • Use chlorine as a disinfection and then chlorine is removed by SO2 so it can be released into river.

  9. Municipal Water Purification Plant

  10. Coagulation • Rachel Casiday, Greg Noelken, and Regina Frey, Washington University (http://wunmr.wustl.edu/EduDev/LabTutorials/Water/PublicWaterSupply/PublicWaterSupply.html) isis.csuhayward.edu/alss/Geography/ mlee/geog4350/4350c4f01.ppt

  11. Sedimentation • Rachel Casiday, Greg Noelken, and Regina Frey, Washington University (http://wunmr.wustl.edu/EduDev/LabTutorials/Water/PublicWaterSupply/PublicWaterSupply.html) isis.csuhayward.edu/alss/Geography/ mlee/geog4350/4350c4f01.ppt

  12. Filtration • Rachel Casiday, Greg Noelken, and Regina Frey, Washington University (http://wunmr.wustl.edu/EduDev/LabTutorials/Water/PublicWaterSupply/PublicWaterSupply.html) isis.csuhayward.edu/alss/Geography/ mlee/geog4350/4350c4f01.ppt

  13. Adsorption • Rachel Casiday, Greg Noelken, and Regina Frey, Washington University (http://wunmr.wustl.edu/EduDev/LabTutorials/Water/PublicWaterSupply/PublicWaterSupply.html) isis.csuhayward.edu/alss/Geography/ mlee/geog4350/4350c4f01.ppt

  14. Reducing Water Pollution through Sewage Treatment • Natural and artificial wetlands and other ecological systems can be used to treat sewage. • California created a 65 hectare wetland near Humboldt Bay that acts as a natural wastewater treatment plant for the town of 16,000 people. • The project cost less than half of the estimated price of a conventional treatment plant.

  15. Septic Tanks • 30% of US population • Suitability determined by soil type, depth to water table, depth to bedrock and topography • Commonly fail due to poor soil drainage • Potential contaminants: bacteria, heavy metals, nutrients, synthetic organic chemicals (e.g. benzene)

  16. Drinking Water Quality

  17. DRINKING WATER QUALITY • Centralized water treatment plants and watershed protection • can provide safe drinking water for city dwellers in developed countries. • Simpler and cheaper ways can be used to purify drinking water for developing countries. • Exposing water to heat and the sun’s UV rays for 3 hours can kill infectious microbes.

  18. 2 million plastic bottles,dumped every 5 minutes. Is Bottled Water the Answer?

  19. Is Bottled Water the Answer? • Some bottled water is not as pure as tap water and costs much more. • 1.4 million metric tons of plastic bottles are thrown away. • Fossil fuels are used to make plastic bottles. • The oil used to produce plastic bottles in the U.S. each year would fuel 100,000 cars.

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