1. Sewage Treatment

2. Wastewater Treatment Utilizes a variety of strategies:
Physical (mechanical)
Biological
Chemical
The federal government requires the monitoring of sewage discharge and sets limits on pollutant levels:
Clean Water Act (‘72, ‘77, ‘87)

3. Primary treatment Pollutants
Large objects: rocks, gravel, twigs, litter, female hygiene products, big food scraps, condoms, etc.
Smaller: sand, grit, human or animal fecal material
Even smaller (& water insoluble): fats and grease
Removal methods
Filtration, screening, sieving, nets
Inflow is slowed in a settling tank. Solids settle to the bottom and are collected (sludge).
Allowed to float to surface in settling tank and are then skimmed off (sludge).

4. Secondary treatment Pollutants
Dissolved/suspended organics substances (eg fecal matter, soaps, detergents, food particles)
Removal methods
Effluent is pumped into aeration tanks where aerobic microorganisms break down the organic matter
There is secondary settling and filtration.
This sludge is pumped into an enclosed tank with anaerobic decomposers.

5. Advanced secondary treatment (sometimes called tertiary)
Pollutants
Phosphate
Nitrates/ammonia
Removal methods
biological removal, chemical binders
Denitrifying bacteria in anaerobic tank

6. Final step: Disinfection
Usually done with chlorine which kills pathogens (eg E. coli and other coliform bacteria, Giardia, Cholera, viruses)
What is the negative effect of this?
Sometimes done with UV radiation or ozone

7. Sewage treatment summary
Multi-staged approach to cleaning up waste water
Utilizes mechanical, biological, and chemical strategies
Products are
Clean(er) water
Sludge
Solid waste (from primary treatment filters)
A last step includes disinfection with chlorine (for fecal coliform and other harmful bacteria)
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8. The solid waste of the waste
Sent to already overtaxed landfills
May contain toxins, heavy metals, POPs, etc that could potentially contaminate groundwater through leaching
Contributes to the production of methane during decomposition

9. The sludge waste Often used as fertilizer
If not properly disinfected, could contaminate soils with bacteria
May contain toxins, heavy metals, POPs that could contaminate groundwater, soil, and plants
This could lead to an accumulation of heavy metals in food chains
Field runoff could result in surface water contamination, leading to our old friend eutrophication if high in nitrates or phosphates.

10. Sewage sludge as fertilizer
Odors
Odors may cause illness or indicate presence of harmful gases
Dust Particles
Particles of dried sludge carry viruses and harmful bacteria that can be inhaled, infect cuts or enter homes.
Exposure
Children may walk or play in fertilized fields.
Livestock Poisoning
Cows may die after grazing on sludge-treated fields.
Sludge
Groundwater
Contamination
Harmful chemicals and pathogens may leach into groundwater and shallow wells.
Surface Runoff
Harmful chemicals and pathogens may pollute nearby streams, lakes, ponds, and wetlands.

11. Constructing Wetlands to Treat Sewage
(1) Raw sewage drains by
gravity into the first pool
and flows through a long
perforated PVC pipe into
a bed of limestone gravel.
(3) Wastewater flows through
another perforated pipe
into a second pool, where
the same process is repeated.
Sewage
Treated
water
Wetland type
plants
Wetland type
plants
45 centimeter
layer of limestone
gravel coated with
decomposing bacteria
First concrete pool
Second concrete pool
(2) Microbes in the limestone gravel
break down the sewage into
chemicals that can be absorbed
by the plant roots, and the gravel
absorbs phosphorus.
(4) Treated water flowing from the
second pool is nearly free of
bacteria and plant nutrients.
Treated water can be recycled
for irrigation and flushing toilets.

12. Household Wastewater: Septic Tanks
trap greases & large solids & discharge
the remaining wastes over drainage field
© Brooks/Cole Publishing Company / ITP