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Sewage Treatment.

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Presentation on theme: "Sewage Treatment."— Presentation transcript:

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) START HERE THURSDAY

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

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