Sewage Treatment

lameubiquityMechanics

Feb 21, 2014 (3 years and 7 months ago)

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Sewage Treatment

What’s In Sewage?

Brainstorm a List

Comes from sinks, toilets,
shower, bathtub in your house

What’s In Sewage?


Water


Urine





Feces


Toilet paper


Tampons


Soap


Food Wastes


Oil and Grease


Bacteria and viruses

Now Add Materials in
Storm Drain

They are the drains in
the curbs on the street

Wastewater from Storm Drains


Water


Dirt


Water


Oil


Fertilizers


Pesticides


Grass clippings


Now Add Industrial Wastewater


Toxic chemicals


Organic wastes


Heavy metals

Where Does It Go?

Small Scale


Septic Tanks

Septic Tanks


Sewage and wastewater
pumped into settling tank


Grease and oil rises to top


Solids fall to bottom and are
decomposed


Partially treated wastewater
discharged into drainage field


Soil and bacteria partially filter it

Large Scale


Sewage
Treatment Plant

How Do We Filter and
Treat It?

Basic Processes


Physical/Mechanical


removes
large substances like trash, rocks,
sand, tampons, etc.


Biological


decomposes organic
matter such as feces, food scraps,
grass clippings, toilet paper


Chemical


kills bacteria and some
viruses and tries to remove nitrates,
phosphates, heavy metals, toxic
chemicals, etc

Steps to Sewage
Treatment

3 Major Steps


Primary


Mostly mechanical


Removes big stuff


Secondary


Physical and biological


Decompose organic matter


Tertiary


Mostly chemical and physical


Kills pathogens


Tries to remove toxic chemicals

Primary Treatment


Influent sewage water strained
to remove large objects such as
rocks, sticks, tampons, etc.


Physically done with
mechanical rake bar screen


Solids collected in a dumpster
and are sent to the landfill




Mechanical Rake Bar Screen

Primary Sewage Treatment


Also usually includes a sand or grit
chamber


Wastewater passed through
chamber at highly controlled speed


Sand and grit settle out


Other wastes remain suspended


Sand and grit sent to landfill

Sand/Grit Chamber

Residue Trucked to Landfill

Primary Sedimentation


Sewage moves from grit
chamber to sedimentation tank


Sludge settles to the bottom


Oil and grease rise to top and
are skimmed off


Produces homogeneous liquid
for biological decomposition


Sludge treated separately

Settling tanks have mechanical
scrapers that push sludge into
storage hoppers

Secondary Treatment


Goal is to degrade organic matter
such as feces, food scraps, grass
clippings, toilet paper, etc.


Based on aerobic cellular
respiration by bacteria


Held in large aeration tanks full of
bacteria


Bacteria “eat” organic matter for
energy


Use oxygen to decompose it


Aeration Chamber

Secondary Sedimentation/Clarifier


Final step in secondary treatment


Settle out biological floc or filter
material


Remaining water contains very low
levels of organic material and
suspended matter


Sludge sent to drying bed

Tertiary Treatment


Uses a variety of chemical,
biological and physical
processes to further upgrade
water quality before release


Not always required


Tertiary Treatment Methods


Send filtrate over activated carbon
to remove toxins


Use ponds or lagoons with plants
and fish to remove fine particulates


Use bacteria to remove nitrogen
(remember nitrogen cycle)


Remove phosphorus

Tertiary Treatment Methods


Disinfection to remove
microorganisms such as bacteria,
protozoans, viruses


Traditional method is the addition of
chlorine but can precipitate out of
solution and become carcinogenic


U.V. light treatment


Ozone treatment


What do you do with the
sludge?


Most often sent to landfill


Can be composed and used as
“fertilizer” in agricultural use


Very rich in nutrients


Could contain toxins and would
then leach into groundwater
and be incorporated into crops

Using Wetlandsfor
Sewage Treatment

Using Wetlands for
Sewage Treatment


Use natural or man
-
made
wetlands


Costs half of conventional
methods


Provides quality wildlife habitat


Let’s nature do the recycling

Wetland Sewage Treatment


1
st

sewage goes to settling
tanks to remove big stuff


Liquid pumped to oxidation
ponds for bacterial
decomposition


Water released to marshes


Plants and bacteria finish
filtration and cleansing


Clean water released into river