Waste Water Treatment Sewage Treatment - GEOCITIES.ws

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.