SEWAGE TREATMENT

Protecting the Environment by Separating Mixtures

SEWAGE TREATMENT

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

WHAT HAPPENS AFTER YOU FLUSH?

Passes through drain to sewage treatment

plant

Primary Treatment

Secondary Treatment

Tertiary Treatment

PRIMARY TREATMENT Half the solids in the sewage are

removed from the mixture

First: sewage passes through a metal gridFilters out objects that don’t easily

decompose (Example- fabric or plastic)

PRIMARY TREATMENT [CONT’D]

Second: sewage poured into large pool and allowed to settle for several hoursMost 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

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

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

THEN WHAT? Water is clean enough to be returned to

the ocean, lake, or river

KEEPING OUR WATER CLEAN

Contaminants in the water:SewageWaste produced by manufacturing or

processing factoriesFertilizers, pesticides, or salt from farms,

golf courses, or roadsAccidental spills and leaks

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