Reducing Water Pollution through Sewage Treatment

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.

10. Municipal Water Purification Plant

11. 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

12. 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

13. 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

14. 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

15. 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.

16. 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)

18. Drinking Water Quality

19. 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.

20. 2 million plastic bottles,
dumped every 5 minutes.
Is Bottled Water the Answer?

21. 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.