Sewagedisposalunit 8 by K R Thanki

11/22/2016
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Sub.: WATER SUPPLY And SANITARY ENGINEERING (3350603)
UNIT -VIII
Prepared By:
K.R.THANKI
(BE Civil)
LECTURER CIVIL ENGINEERING DEPARTMENT
GOVERNMENT POLY TECHNIC ,
JUNAGADH,GUJARAT-INDIA.

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Characteristics of sewage:
Sewage Charecteristics
Physical Chemical Biological

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Physical
• colour
• Odour
• Temperature
• Turbidity

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PhysicalColour :
Fresh domestic sewage has a soap solution
or grey colour.
With the time of sewer begins to get black
as the decomposition starts.
Colour of septic sewer is more or less
black.
Colour of industrial sewage depends on the
chemical used.

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PhysicalOdour :
Fresh sewage water has slightly soapy or
oily odour.
The stale sewage (unpleasant) has
offensive odour (strong odour) of
hydrogen sulphate and other sulphur
compounds.
In the normal temperature when sewage
passes through the sewers, the offensive
smell will start after 2 hours, which
reaches the climates after 6 hours.

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PhysicalTemperature :
Generally the temperature of the sewage is
slightly higher than the water supply.
When the sewage flows in the close
conduits its temperature further rises,
resulting in the increase of viscosity and
Bacterial activity.

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PhysicalTemperature :
Temperature of sewage varies with the
season also.
If the temperature of the sewage is below
the normal atmospheric temperature, it
will indicate the infiltration of ground
water , but in case of higher temperature
it indicates the addition of industrial
sewage.

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PhysicalTurbidity :
The turbidity of the sewage directly
depends on the quantity of solid matters
present in it in suspension state.
When ever suspended matters increase
strength of sewage increases.

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Chemical

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The Chemical Characteristics of sewage helps
in indicating:
The stage of sewage decomposition.
Its strength, and extent and type of treatment
required for making it safe.
Chemical

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Therefore, chemical analysis is carried out, which includes test
for determining:
 Total solids, suspended solids and settleable solids
 pH value;
 Chloride content;
 Nitrogen content;
 Presence of fats, greases and oils;
 Sulphides, sulphates and H2S gas;
 Dissolved oxygen;
 Chemical oxygen demand(COD);
 Boi-chemical oxygen demand (BOD)
Chemical

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Total solids, suspended solids and settleable solids
Chemical
Solids present in sewage may be in any of these forms:
 Suspended / non-filterable solids
 Dissolved solids
 Colloidal solids / filterable solids
 Settleable solids
Further, the solids in sewage comprise of both:
 Organic solids (45%)
 Inorganic solids (55%)

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pH value
Chemical
It’s determination is important because efficiency of
some of the treatment methods depends upon the
availability of suitable pH value.
It can be measured using potentiometer.

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Chloride content
Chemical
Chlorides found in sewage is derived from kitchen
wastes, urinary discharges, industries.
It can be measured by titrating (calculate the
amount of substance in a solution by measuring the
volume of a stranded reagent) the waste water(i.e.
sewage) with standard silver nitrate solution using
potassium chromate as indicator.

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Nitrogen content
Chemical
 Nitrogen may occur in one of the following forms:
 Free ammonia, called ammonia nitrogen;
 Albuminoid nitrogen, called organic nitrogen;
 Nitrites and
 Nitrates
Nitrates and nitrites are measured by colour
matching techniques.

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Presence of fats, greases and oils
Chemical
They are derived in sewage from the discharge of
animals and vegetable matter, or from the
garages, kitchens of hotels and restaurants, etc.
Such matter form scum on top of the
sedimentation tanks, clogs the void of filter
media and affects the diffusion of oxygen, thus
interfering with the normal treatment methods.

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Sulphides, sulphates and H2S gas
Chemical
They are formed due to the decomposition of
various sulphur containing substances in sewage.
In aerobic digestion of sewage, the aerobic and
faculative bacteria oxidizes sulphur & its
compounds to initially form sulphides, which
ultimately breakdown to sulphates.
In anaerobic digestion, the anaerobic and
facultative bacteria reduce the sulphur and its
compounds to sulphides, with evolution of H2S
along with methane, carbon dioxide.

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Dissolved Oxygen
Chemical
The actual quantity of DO is governed by:
Solubility of oxygen
Temperature
Purity of water
It decreases as temperature increases.
It is also determined by winklers method.

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Chemical oxygen demand(COD)
Chemical
It is the measured amount of oxygen needed to
chemically oxidize the organic matter using a
strong oxidizing agent like potassium dichromate
under acidic condition.
It can be used to measure both biodegradable and
non biodegradable organic matter.

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Chemical
It is defined as the amount of oxygen required by
the microorganisms (mostly bacteria) to carry out
decomposition of biodegradable organic matter
under aerobic conditions.
Boi-chemical oxygen demand (BOD)

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Chemical
•The BOD test is widely used to determine the
pollution strength of domestic and industrial
wastes in terms of the oxygen that they will require
if discharged into natural watercourses. It is the one
of the most important test in stream pollution
control activities.

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Chemical
•This test is of prime importance in regulatory work
and in studies designed to evaluate the purification
capacity of receiving bodies of water.
•It is also useful in design of wastewater treatment
plant and also to measure the efficiency of some
treatment processes.

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Biological

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Biological
• Sewer contains large quantity of bacteria which
come from excremental matter. (solid waste of
animals).
• All the bacteria present in sewage are not harmful,
more quantity of harmless bacteria helps to treat the
sewage and reduce the cost of treatment plants.

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Biological
•All the organisms can be broadly classified as
Macroscopic and Microscopic.
•Followings are the main living organisms in
sewage:
Bacteria
Algae
Fungi
Protozoa

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Biological
• Normally bacteria are harmless to humans they
decompose the complex compounds of sewerage
and convert it into simple, stable and basic
compounds.
• According to Oxygen used they can be classify as,
 Aerobic
 Anaerobic
 Faculative
Bacteria:

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Biological
 Aerobic:
Aerobic Bacteria survive by using free oxygen to
atmosphere or dissolved oxygen of water.
They produce in water based organic substances.
Bacteria:

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Biological
 Anaerobic:
Anaerobic Bacteria survive without using free
oxygen to atmosphere or dissolved oxygen of
water.
They can easily obtain oxygen from Nitrites,
Nitrates and Sulphates.
Bacteria:

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Biological
 Facultative:
Facultative Bacteria survive with or without
using free oxygen to atmosphere or dissolved
oxygen of water.
Bacteria:

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BiologicalAlgae:
 Algae contains chlorophyl and other additional
pigments.
 Algae produces oxygen and release carbon
dioxide by the process of photoshyntasis.

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BiologicalFungi:
 Fungi is NOT Clorophyl or Pigments (which
gives some color).
These are usually colorless and are filamentous
having branches.

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BiologicalFungi:
 They have the property of decomposing starches
sugar, Cellulose, Fats, Protins, Higher alcohols and
Nitrogenous substances.
 When they are present in large number they are
called mycelium and resemble like a Cat’s tail.

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BiologicalProtozoa:
These includes all Unicellular animals.
Normally most of Protozoa survive by eating
Bacteria.
These are of various types like Amoeba,
Flagellates, Free swimming ciliates, etc...

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BiologicalProtozoa:
Amoeba:
A single celled organism that is the first to
develop in sludge.
If they are predominant the sludge is very young.

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BiologicalProtozoa:
Flagellates :
 A large single cell body with a whip like
appendage called a flagellum.
 Number of flagellates decreasing as the sludge
age increased.

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BiologicalProtozoa:
Flagellates :

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BiologicalProtozoa:
Free swimming ciliates :
These are small oval shaped with tiny hairs or also
called as cilia.
Cilia move in a wave-like motion to propel them
in water and bring in food.
Numbers increase as sludge reaches maturity and
achieves its peak settle ability.

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BiologicalProtozoa:
Free swimming ciliates :

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Sampling of Sewage:
Following procedure should be adopted for
collecting sample for various laboratory tests:
The samples of sewage are collected at interval of
1hour during the day.
The capacity of the sampling bottles should be
100cc to 150 cc (Cubic centimeters).
The Date, Time and Place of collection of sample
should be noted on the bottles.

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Sampling of Sewage:
Grab Sample Composite Sample
Types of samples

Grab Sample
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Sampling of Sewage:
This type of sample is taken at that place where all
the particles mixed to gather by the effect of
turbulence .
This type of sample is very useful to find out PH,
Dissolved Oxygen, etc..
For this sampling method there is no perticular
method ; sampling is done by manually.

Grab Sample
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Sampling of Sewage:
When ever the quantity and quality of sewer
changes frequently at that places grab samples
are not sufficient to analyze the sewage.
At that places a regular samples are taken and
mixture of that sample is known as composite
sample.
By using this method one can analyze average
qualities of sewer.
Composite Sample

Grab Sample
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Sampling of Sewage:
For composite sample a grab samples are taken at
every hours.
Composite sample is taken by Automatic sampler
during the day.
Composite Sample

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Sampling of Sewage:
Sampling Tube:
This tube is useful to collect sewage samples and
also it is useful to collect oil , grease etc..
 external diameter of this tube is 40 mm.
Length of tube is 1m.
It is madeup of stainless steel or brass.
One bucket is fitted on one end of length 50mm.

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Sampling of Sewage:
Sampling Tube:
Internal diameter of bucket is 2mm more than
outer diameter.
Both sides 6.5mm diameter brass rods are fitted
for 100mm sampling space.
Open side sampling tube there is rubber stopper
fitted which is removed at the time of sampling.

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Sampling of Sewage:
Sampling Tube:

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Wastewater treatment steps:
Waste water can be treated by:
Artificially
Naturally

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Naturally
Land
Treatment
Dilution

Dilution
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Dilution is the disposal of sewage by discharging
it into large bodies of water like sea, streams, rivers
etc. This method is possible only when the natural
water is available in large quantity near the town.
Proper care should be taken while discharging
sewage in water so that sewage may not pollute
natural water and make it unfit for any other
purposes like bathing, drinking, irrigation etc.

Dilution
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CONDITIONS FAVOURING DILUTION
Where sewage is fresh.
Where favorable currents exits in a stream.
Where sewage is almost free from floating
settleable solids.
Where through mixing is possible.
Where diluting water has high quantities of
dissolved oxygen.
When the city is situated near river or sea.

Dilution
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SELF-PURIFICAION OF STREAMS
The natural process in which the oxygen of water
of streams is consumed by sewage and at the same
time it is filled again by the atmosphere is called
self-purification of streams.

Dilution
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FACTORS HELPING SELF-PURIFICATION OF
STREAMS:-
₪Dilution
₪ Sedimentation
₪Sun-light
₪Oxidation
₪Reduction
₪Temperature
₪Bacteria.

Dilution
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STREAMS:-
₪DILUTION
when sewage is discharged into the stream water ,
the offensiveness of the organic matter is diminished
(reduces in size)by its dispersion through the
diluting water .
The sewage always remains in aerobic condition &
anaerobic conditions never comes because dissolved
oxygen always remains present in the water.

Dilution
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STREAMS:-
₪SEDIMENTATION:
The heavier solids with slow current settle in the
stream bed & start anaerobic decomposition.
An aerobic condition will not develop if dilution is
sufficient & scouring tendency of streams during
floods will wash the deposits.
Settleable solids drop down to the bottom of the
stream in the form of sludge deposits. Hence it is
purified to some extent.

Dilution
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STREAMS:-
₪OXYDATION :
The oxidation of the organic matter starts as soon as
sewage is discharged into the diluting water due to
CHEMICAL REACTION GROWTH & ACTIVITY
OF OXIDISING ORGANISMS.

Dilution
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STREAMS:-
₪OXYDATION :
When the organic matter meets the water; it starts
getting oxidized due to development of oxidizing
organisms in water. The process continues till the
organic matter has been completely oxidized. The
oxygen demand is fully satisfied, the stream
becomes pure. Water always contains some
dissolved oxygen and it is responsible for oxidation
of organic matter.

Dilution
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STREAMS:-
₪ REDUCTION :
when organic matter hydrolyses either chemically or
biologically by anaerobic organisms to form gases
from the liquids, the process is known as reduction.
It also helps for stabilization by oxidation.

Dilution
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STREAMS:-
₪ SUNLIGHT :
It has sterilizing effect on certain bacterias,
bleaching powder & photosynthesis by which
chlorophyll bearing organisms take energy from sun
& convert it into food for other forms of life . Co2 is
absorbed & o2 is evolved in the process.

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Land
Treatment
SUITABILITY OF LAND TREATMENT
METHOD OF SEWAGE DISPOSAL:-
₪ The overall rainfall is very low.
₪The natural water courses are not available.
₪The quantity of sewage is more which pollutes the
natural water courses.
₪The rivers have very small discharge during
summer.

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Land
Treatment
SUITABILITY OF LAND TREATMENT
METHOD OF SEWAGE DISPOSAL:-
₪The water table is very deep and is not likely to be
polluted by adopting the land treatment method of
disposal.
₪The vegetables have good market value as by
adopting land treatment, the income also increases.
₪The soil is porous as it will allow good areation.

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Land
Treatment
APPLICATION OF SEWAGE METHODS:
Flooding method
Surface irrigation method
Zig zag method
Lagooning method
Basin method
Sub-soil irrigation method
Ridge and ferrow irrigation method.

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Land
Treatment
Flooding method
The area to be irrigated is divided into various parts
surrounded by dykes.
The sewage is filled like small ponds in between the
dykes.
The depth of dose varies from 3.0 cms. To 5.0 cms.
Depending on the irrigation requirements.

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Land
Treatment
Flooding method

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Land
Treatment
This method is most suited in sloping area. Here,
parallel drains are constructed in the fields.
All these drains are connected to a distributaries
drain with the help of regulating device so that
sewage may flow in the require drain.
Here when sewage flows over the fields, its large
quantity is absorbed by the field and only excess
quantity reaches another drain.

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Land
Treatment

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Land
Treatment
Zig zag method
In this method the ridges are arranged in a zag-zag
method with corresponding furrows by their side.

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Land
Treatment
Lagooning method
These are used cheaply for sewage disposal. In this
method the sewage is allowed to in a natural
depression available or artificial constructed tanks.
Detention period is about a month. During this
period the sludge is stabilized and dried.
The purified effluent passes way from an outlet
placed at the other end. Lagoons should be shallow
and must be constructed away from the town.

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Land
Treatment
Lagooning method

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Land
Treatment
Basin method
In this method big trees are planted in an isolated
manner, basins are formed around each tree. These
basins are filled with sewage. This method is
suitable for fruit gardens.

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Land
Treatment
Here sewage is applied at the roofs of plants,
through the open jointed agricultural drain-pipes.
These pipes are laid about 1.0 m below the ground
level.
The sewage rises up due to capillary action. Here
soil takes less load but this is an economical
method.

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Land
Treatment

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Land
Treatment
In this method , sewage is supplied in furrows
between crop rows.
Sewage spreads laterally irrigating the area between
two furrows.
The width of furrow varies from 120-150 cm and
the depth from 25-50 cm. The width of the ridge
varies from 125-250 cm and length from 10-30 m.
The percolated effluent is collected in underground
drains flows towards natural drainage for disposal.

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Land
Treatment

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• Includes removal of large objects
some solid materials like debris,
gravel, sand or liquids like fats, oils
and grease from the water.
Primary
Treatment
• Includes degradation of biological
content of the sewage such as are
derived from human waste, food
waste, soaps and detergent.
Secondary
Treament
• Includes a final treatment to
effluent (water) to increase the
water quality, before the water is
discharged to the natural
waterways.
Tertiary
Treatment
Artificially

1
2
3
4
5
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Screening
Grit Chamber Primary Sedimentation
Aeration Tank
Secondary Sedimentation

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Sewage Treatment Plant:
Primary Treatment
This treatment consists of removal of floating
materials .
It also removes heavy settleable inorganic solids.
This treatment reduces BOD about 15 to 30%.

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Primary Treatment
Raw Sewage
Screens
(Remove floating materials)
Grit Chambers(Remove Organic and
inorganic matters)
Skimming Tank(Remove Oil ,
Grease, etc..)
To Primary Treatment Plant

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Primary Treatment
This process is first carried out at a sewage
treatment plant, to trap and remove the floating
matter , such as dead animals, tree branches, metal
containers, plastic containers, etc..
If these matters are not removed, will chock the
pipes, or adversely affect the working of sewage
pumps.
Screening

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Primary Treatment
Types of Screens:
Based on Opening size:
 Coarse screen
 Medium screen
 Fine screen
Based on their Shapes:
 Disc screen
 Drum screen
 Band screen
 Wings screen
 Cage screen
Screening

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Primary Treatment
Types of Screens:
Other Types:
 Racks or Bar- Screens
 Perforated or Fine screens
 Cutting screens
Screening

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Primary Treatment
Types of Screens: Racks or Bar- Screens
Screening

Sewagedisposalunit 8 by K R Thanki

Sewagedisposalunit 8 by K R Thanki

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