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Liquid Waste
Liquid waste, often but not necessarily
containing water, is called wastewater
Sources of Liquid Waste
• Municipalities (houses, businesses, institutions):
from sinks, tubs, showers, toilets
• Agricultural activities: rainfall and irrigation runoff
from farms contains fertilizer, pesticides,
manure, and soil; runoff from ranches and
feedlots contains nutrients, organic matter,
bacteria, growth hormones, and drugs
• Industry: Industrial wastewater may contain
petroleum products, metals, acids and other
chemicals, nutrients, and sediments
Municipal Wastewater
Municipal wastewater
is divided into two
1) Storm water
2) Sewage
Storm Water
• Includes rain and
melting snow that run
off roads, driveways,
roofs and lawns into
storm sewers.
• May contain
sediments, organic
matter, and
• It often runs directly
into water systems.
Connected or Separate?
• In many Canadian cities, storm water sewers are
connected to sanitary sewers, and all this water is
treated. Heavy rains may overload the system, causing
raw sewage to back up into houses and natural
• Having separate storm and sanitary sewers prevents this
problem. However, storm water flowing into natural
waterways can:
- erode stream banks
- increase the temperature of the receiving water,
reducing available oxygen
- introduce chemicals that can harm aquatic life.
Material that is rinsed down the drain or
flushed down a toilet into the sewage
Contains wash water (showers, baths,
laundry, dishes) and organic matter, like
food particles, urine, and feces.
Also contains hundreds of chemicals,
including: plasticizers, medicines,
pesticides, flame retardants
Sewage Treatment
• Liquids cannot be disposed of in a landfill
because they increase leaching and
destabilize the landfill structure
• Sewage must be treated before the water
it contains can be returned to the natural
• 14% of Canadian homes are on a septic system
• Wastewater drains into a septic tank. Grease and oils
rise to the top, solids sink to the bottom
• Clarified liquid waste runs from the tank through pipes
embedded in gravel below the soil surface of the septic
• The pipes have small holes, allowing water to drain into
the gravel and soil, from which it leaches or evaporates
• The tank must be pumped out occasionally
Municipal Sewage Treatment
Sanitary sewers take municipal sewage to a
water treatment plant.
1. Primary
• Primary treatment
removes solids and
suspended sediments
• First, a screen removes
large debris
• In a grit tank, heavier
particles like sand and
gravel settle out
• In a primary
sedimentation tank,
about half the organic
solids settle to the
bottom. This semi-solid
material is called sludge.
2. Secondary Treatment
Secondary treatment breaks down the organic material
biologically in one of the following ways:
1) Aeration tank digestion: sewage is aerated and mixed
with aerobic bacteria, which digest the organic matter.
The sewage then goes into a final settling tank, and
the sludge is removed.
2) Trickling filter bed: Sewage drips from perforated
pipes or overhead sprayer through a stone bed or
corrugated plastic sheets. Bacteria on the bed
decompose the organic material.
3) Sewage lagoon: Outdoor lagoons expose sewage to
sunlight, algae and air, which break down the organic
material (a slower but cheaper method)
After secondary treatment, the fluid is disinfected with
chlorine, UV light, or ozone to kill harmful bacteria.
3. Tertiary Treatment
• After secondary treatment, sewage still
contains nitrates, phosphates, and other
inorganic substances.
• It is passed through a natural wetland or
artificial filtering system to filter out these
nutrients, or chemical flocculants are
added to bind to the nutrients so they
settle out.