1. Protecting the Environment by Separating Mixtures
Sewage treatment
Protecting the Environment by Separating Mixtures

2. The mixture of water and waste you flush down the sink or toilet
Sewage treatment
Sewage:
The mixture of water and waste you flush down the sink or toilet

3. What happens after you flush?
Passes through drain to sewage treatment plant
Primary Treatment
Secondary Treatment
Tertiary Treatment

4. Primary treatment
Half the solids in the sewage are removed from the mixture
First: sewage passes through a metal grid
Filters out objects that don’t easily decompose (Example- fabric or plastic)

5. Primary treatment [cont’d]
Second: sewage poured into large pool and allowed to settle for several hours
Most solids settle to the bottom; floating parts (Ex., oil and grease) rise to the top
Third: solids removed, treated; used as fertilizer, burned, or sent to landfill

6. Secondary treatment
First: remaining dirty water passes through tanks containing bacteria
Bacteria break down any remaining human waste and plant material
Second: water allowed to settle again
Third: bacteria settle to the bottom and are removed

7. Tertiary treatment
First: pollutants like phosphorous and nitrogen removed
Second: water may also pass through filters, have ozone bubbled through it, or be exposed to ultraviolet radiation
Finally: chlorine is added to the water to kill any remaining organisms

8. Then what?
Water is clean enough to be returned to the ocean, lake, or river

9. Keeping our water clean
Contaminants in the water:
Sewage
Waste produced by manufacturing or processing factories
Fertilizers, pesticides, or salt from farms, golf courses, or roads
Accidental spills and leaks

10. Petroleum (oil) and water
Petroleum/petroleum products are shipped around the world
An oil spill from a sinking or leaking cargo ship is difficult to clean up/difficult to separate
Some parts of the petroleum float and spread across the surface affecting wildlife
Other substances in the petroleum sink and contaminate the lake or sea bed