Wastewater Treatment Notes
¼ of U.S. Homes use __SEPTIC TANKS________ ______________
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Rural and suburban
Underground tank
__BACTERIA_____________ decompose organic wastes
__SLUDGE____________ settles on the bottom
__EFFLUENT_____________ flows out and into ground
Urban areas use sewage treatment plants: raw sewage treatment:
1. __PRIMARY______________: physical process that removes solids
 Removes approx. 60% of solids
 Removes approx. 30 to 40% organic wastes
 Passed through bars/screens and allowed to settle
 Does NOT remove nitrates, phosphates, salts, radioisotopes, or
pesticides
2. __SECONDARY________: biological process where aerobic bacteria
remove biodegradable wastes
 Removes up to 90% of organic wastes
 Passes water through a bed of gravel covered by aerobic bacteria
OR
 Passes water through aeration tank (feed oxygen to the bacteria to
aid in decomposition)
Primary and Secondary remove (approx.):
 95 – 97%: SOLIDS AND ORGANICS
 70%: TOXIC METALS AND SYNTHETIC ORGANICS
 70%: PHOSPHATES
 50%: NITRATES
 5%: SALTS
Primary and Secondary do NOT remove:
 Radioisotopes
 Some persistent pesticides
3. _TERTIERY________: (or advanced): chemical and physical processes
that remove “what’s left”
 Mostly removes phosphates and nitrates
 Expensive: only used to treat about 5% of U.S. wastewater
Before water is discharged from ANY treatment facility: water undergoes:
 _BLEACHING____________ : to remove water discoloration
 _DISINFECTION__ : to kill disease-carrying bacteria and some (but
not all) viruses. The usual method for this is _CHLORINATION_.
But chlorine can react with organic materials in water to form small
amounts of chlorinated hydrocarbons which can cause adverse
health affects. So other disinfectants can be used such as
___OZONE__ and _ULTRAVIOLET LIGHT (UV)________ are
used.
The “leftovers”….. Or SLUDGE:
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Sludge: SLIMY MIXTURE THAT IS DRIED
o BACTERIA-LADEN SOLIDS
o OFTEN TOXIC CHEMICALS AND METALS
o HOUSEHOLD/INDUSTRIAL WASTE
o CAN BE USED AS FERTILIZER; OTHERWISE DUMPED
IN LANDFILLS OR INCINERATED
Drinking water vs. Reclaimed water:
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Reclaimed water is similar to drinking water but NOT INTENDED
for drinking.
Reclaimed water has higher levels of ___PHOSPHORUS__ and
___NITROGEN_____ for plant growth
Used for:
o IRRIGATION
o BACK UP FIRE PREVENTION
o COOLING TOWERS FOR POWER PLANTS
Solutions??
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Prevent toxic/hazardous chemicals from reaching treatment plants
Treat sewage naturally: living machines (intro to chapt. 22)
1. sewage goes to ___SEDIMENTATION TANKS_____; solids
settle as sludge
2. liquid pumped into __OXIDATION PONDS________;
bacteria break down remaining wastes
3. water then released into ___ARTIFICAL MARSHES_____;
plants and bacteria further filtrate and cleanse
Wastewater garden removes 99.9% of fecal coliform and more
than 80% nitrates and phosphates!!!