Waste Water Treatment Sewage Treatment - GEOCITIES.ws

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Feb 22, 2014 (3 years and 6 months ago)

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Waste Water Treatment


(Sewage Treatment)

Outline


Objectives


Outline of treatment process (flow diagram)


Preliminary treatment


Primary treatment (sedimentation)


Secondary treatment (activated sludge, filtration)


Sludge treatment


Disinfection


Tertiary treatment

O
bjective of Sewage Treatment


To prevent pollution of the receiving water


To prevent offensive odour in the water


To prevent the destruction aquatic life


If the sewage has to be disposed of on land,
the soil will become sewage sick after some
time and cannot take any more sewage


Outline of Sewage Treatment


Preliminary treatment


Primary treatment


Secondary treatment


Disinfecting


Tertiary Treatment


Preliminary Treatment



Waster water contains floating suspended
solids such as rags, wood, metal, plastic, etc.


these suspended impurities have to be
removed as they interfere with the treatment
processes or mechanical equipment.



Primary Treatment


consists of mainly the sedimentation
process to remove suspended organic solids


Chemicals are sometimes added in primary
clarifier to assist in the removal of finely
divided and colloidal solids or to precipitate
phosphorous


Secondary or Biological
Treatment




Activated sludge process


Filtration

Activated sludge process


the sewage is biologically treated.

Filtration


is done in contact beds or intermittent sand
filters or tricking filters.


It removes finely divided suspended matter.

Sludge & Effluent


The semi
-
solid that settles down at the
bottom after treatment,is called sludge



liquid to be discharged is called effluent.


Disinfecting


Disinfecting

is

carried

out

if

necessary

by

chlorination

to

kill

the

bacteria

which

remain

in

the

effluent

of

sewage


Tertiary Treatment



If

the

receiving

water

provides

only

little

dilution

or

there

is

a

need

to

preserve

a

particularly

high

quality

of

effluent,

tertiary

treatment

can

be

used
.


PRELIMINARY TREATMENT


Objectives



Remove

coarse

suspended

and

floating

matter

such

as

rags,

plastic,

pieces

of

wood,

etc
.
,

by

means

of

screening


Remove

grit,

sand,

broken

glass,

etc
.
,

in

grit

chambers


Remove

grease,

and

oil

substances

by

floatation

in

skimming

tanks


Processes


Screening



Silt

and

grit

removal


Oil

and

grease

removal


PRIMARY TREATMENT


PRIMARY TREATMENT


Primary

sedimentation

tank



(Secondary

sedimentation

tank)

-

sedimentation

after

activated

sludge

process


Advantages


The

advantages

of

coagulation

over

plain

sedimentation

are
:


Sedimentation

by

coagulation

is

more

effective


BOD,

colour

and

turbidity

are

reduced


Less

capacity

of

sedimentation

tanks


The

process

is

simple

Disadvantages


The

disadvantages

are
:


Chemicals

destroy

the

bacteria

that

digest

the

sludge


Chemicals

increase

the

cost

of

sedimentation


Skilled

supervision

is

required


Large

quantity

of

sludge

is

produced


SECONDARY TREATMENT


SECONDARY TREATMENT


The secondary treatment converts the
remaining organic matter into stable form
by putting aerobic and anaerobic bacteria
into action

Processes


Filtration


Activated

sludge

process


Filtration


Aerobic bacteria need a contact surface to
live and carry out their activities

Filtration


Contact

beds


Intermittent

sand

filters


Trickling

filters


Contact Beds


A

contact

bed

consists

of

filtering

medium
.



When

the

sewage

is

passed

over

the

medium,

a

thin

film

is

produced

around

the

particles
.



The

bacteria

present

in

the

film

oxidise

the

organic

matter
.


Intermittent Sand Filter


the

filtering

medium

consists

of

sand
.



The

action

of

the

filter

is

due

to
:


Mechanical

straining

and


Bacterial action

Trickling Filters


A trickling filter is an artificial bed of stone
or broken brick material


waste water is distributed an applied in
drops, films or spray


A zoogleal film is formed on the surface
media.

ACTIVATED SLUDGE
PROCESS


is

a

biological

sewage

treatment

process


a

mixture

of

sewage

and

activated

sludge

is

agitated

and

aerated
.



The

activated

sludge

is

subsequently

separated

from

the

treated

sewage

by

sedimentation

What is ACTIVATED SLUDGE



is

that

sludge

which

settles

down

after

the

sewage

has

been

freely

aerated

and

agitated

for

a

certain

time
.


How Activated Sludge works


Activated

sludge

contains

numerous

bacteria

and

other

microorganisms
.

When

it

is

mixed

with

raw

sewage

saturated

with

oxygen,

the

bacteria

perform
:


Oxidise

the

organic

solids


Promote

coagulation

and

flocculation

and

convert

the

colloidal

and

suspended

solids

into

settable

solids

Steps in Activated Sludge
process


Treat

raw

sewage

in

the

primary

settling

tank


mix

sewage

with

the

activated

sludge

and

aerated

for

4
-
10

hours


final

(secondary)

settling

tank



dispose

of

effluent


return

some

sludge

to

the

aeration

tanks



dispose

of

the

rest

of

the

sludge


Advantages


Gives

clear

sparkling

treated

effluent


Effluent

free

from

offensive

odour



Degree

of

purity

can

be

varied

as

desired


Cost

of

installation

lesser

than

for

a

trickling

filter


Small

loss

of

head

in

the

process

Disadvantages


Skilled

supervision

and

constant

check

on

the

return

sludge

is

necessary


When

there

is

change

in

the

quality

or

quantity

of

sewage,

the

process

is

upset


The

process

does

not

work

for

some

industrial

wastes


Large

volume

of

sludge

increases

difficulty

in

disposal

Methods of Aeration


The

success

of

the

activated

sludge

process

depends

on

the

aeration

provided
.



Diffused

air

aeration


Mechanical

aeration


Combination

of

the

above

two

methods


TERTIARY TREATMENT

TERTIARY TREATMENT


MICROSTRAINERS


RAPID GRAVITY SAND FILTERS


UPWARD
-
FLOW “MEDUIM” SAND
FILTERS


SLOW SAND FILTERS


PEBBLE
-
BED CLARIFIERS


SETTLEMENT


GRASS PLOTS


LAGOONS

SLUDGE TREATMENT AND
DISPOSAL


Sludge


Sludge

is a semi
-
liquid


Sludge produced by plain sedimentation


Sludge produced by chemical
precipitation


Trickling filter


Activated sludge

Methods of Disposal



Disposal

on

land


Drying

on

drying

beds


Dumping

into

the

sea


Heat
-
drying


Incineration


Lagooning

or

ponding


Sludge

Digestion

Sludge Digestion


It transforms a portion of solids into
liquids and gases, thereby reducing the
sludge volume to be dealt with





It breaks the organic matter of sludge
into simpler compounds by the action of
anaerobic bacteria.