4.7 Water Treatment and
Disposal
Page 220-221
Water Treatment

Filters remove particles but not solutes or bacteria

Sand, gravel, and charcoal are cheap and effective filters

Alum or ammonium aluminum sulphate “flocculate” or clump small particles together so
they settle

Chlorine is added to water (chlorination) to kill microorganisms

Ozone or ultraviolent light may also be used to kill organisms
Sewage Treatment

In urban areas, household sewage flows through sanitary sewers to a sewagetreatment facility

Primary treatment removes only floating and suspended solids, usually by filtration,
before returning the effluent (treated sewage) to a water body

Secondary treatment uses biological methods, such as biological decomposition to
treat the waste

Tertiary treatment removes all bacteria and organic components from the sewage, and
chlorine is added as a disinfectant

The remaining solids, called sludge, can be used as a farm fertilizer or dried and
incinerated. The ash is buried in landfill
Septic Tanks

In rural areas, a single home’s sewage flows into a septic tank

Solids settle on the bottom of the tank or are degraded by bacteria

Overflow wastewater flows away from the tank in “weeping tiles” and filters though
the soil to the ground water
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