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8/12/2019 Sewage Lecture
http://slidepdf.com/reader/full/sewage-lecture 1/22
CE C-342
WATER AND WASTEWATER
TREATMENT
To
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WHAT IS SEWAGE?
SEWAGE IS THE WASTEWATER GENERATEDFROM DOMESTIC OPERATIONS (HOUSE HOLD/
OFFICES/COMMERCIAL COMPLEXES/ HOTELS/
ETC.)
DOMESTIC OPERATIONS INCLUDE:
• BATHING
• CLOTHES WASHING
• KITCHEN (VEGETABLE WASHING/ UTENCIL
WASHING)• TOILETS/ URINALS
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Purpose Quantity Drinking 3
Bathing 30
Toilets/Flushing 45
Laundry 30
Kitchen/ Dish
washes
22
Leakages 15
Total 145
WATER REQUIREMENT
Water usage Quantity (l/head/day)*
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SEWAGE QUANTITY
ABOUT 80% OF WATER SUPPLIED FINDS ITS WAY
INTO DRAIN
HENCE SEWAGE QUANTITY CAN BE ASSUMED AS
FOLLOWS:
FOR RESIDENCES : 120 l/head/day
FOR INDUSTRIES/ OFFICES/ : 40 l/head/day
COMMERCIAL ESTABLISHMENTS:FOR HOTELS : 150 l/room/day
RESTAURANTS : 15 l/head/day
FOR HOSPITALS : 200 l/bed/day
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Characterisation of Waste water
Physical Characteristics
Chemical Characteristics
Biochemical Characteristics
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Physical Characteristics
Colour
Odour
Insoluble Substances-Settleable,
Suspended solids
Temperature Range etc….
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Chemical Characteristics
Chemical Oxygen Demand -
COD
pH
Acidity/AlkalinityHardness
Total Organic Carbon
Total Dissolved Solids
Surfactants
Phenols etc...
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Biochemical Characteristics
Biochemical oxygen demand- BOD
Dead and Decaying plants and animals
Presence of pathogenic bacteria
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1. Colour: The colour of sewage normally be detected
by normal eye and indicates the freshness of
sewage.
Yellowish, grey or light colour Fresh Sewage
Black or dark brown colour Stale or septic
sewage
Note: When industrial waste water is mixed with
sewage, may also add colour to it.
2. Odour: Fresh sewage is practically odourless. But
however, in 3 to 4 hours, it becomes stale with alloxygen present in sewage being practically
exhausted. It then starts omitting offensive odours,
especially that of hydrogen sulphide gas, which is
formed due to decomposition of sewage.
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3. Turbidity: The turbidity of waste water depends on the
quantity of solid matters present in suspension state.
Turbidity is a measure of light-emitting properties of waste
water, and turbidity is used to indicate the quality of wastedischarges with respect to colloidal matter. The turbidity
depends upon the strength of sewage or waste water.
The stronger or more concentrated the sewage , the
higher is turbidity.4. Total Solids: Sewage 99.9%water +0.1% solids
Total solids in waste water exist in three different forms.
Suspended SolidsColloidal Solids
Dissolved Solids
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Type of suspended solids
Settleable Solids
Non- settleable Solids
Dissolved Solids = 0.001 to 0.00001 micron
Colloidal Solids = 0.001 to 1.0 micron
Suspended or non settleble solids > 1.0 microns
Removable by coagulation = 0.000001 to 10 micron
Settleable > 10 micron
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5. Temperature : Generally , the temperature of waste
water is higher than the water supply, due to addition
of warm water from the house holds and from theindustries.
Effect of temperature
Viscosity
Bacterial activity
Solubility of gases
Growth of aquatic life
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Chemical Characteristics
1. pH: The pH of sewage indicates the logarithm of
reciprocal of hydrogen ion concentration present in
sewage.
Importance of pH in the Sewage Treatment
2. Chlorides Content : Chlorides are mineral salts and
therefore, are not affected by biological action of sewage.
The normal chloride content of domestic sewage is 120
mg/l.
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3.Nitrogen Contents: The presence of nitrogen in the
sewage indicates the presence of organic matter, and
may occur in one or following forms:
Free Ammonia
Albuminoid Nitrogen
Nitrites Nitrates
The free ammonia indicates the very first stage of
decomposition of organic matter.
Albuminoid Nitrogen indicates the quantity of nitrogen
present in sewage before the decomposition of
organic matter.
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Nitrites indicate the presence of partly decomposed ( not
fully oxidised) organic matter.
Nitrates: The presence of nitrates indicate the moststable form of nitrogenous matter contained in sewage,
thus indicating the well oxidised and treated sewage. If
nitrates > 45 ppm in potable water, this may cause nitrate
poisoning in infants.
4. Fats, Oils and Grease: These are derived in sewage
from the discharge of animals and vegetable matters or
from industries like garrages, kitchens of hotels and
restaurants etc.
5. Surfactants: These come from synthetic detergents
and these are discharged from bathrooms, kitchens,
washing machine etc Surfactants are large organic
molecules which cause foaming in waste water treatment
.
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6. Phenols, Pesticides and Agricultural Chemicals:
Phenols are found in Industrial Waste Water and this may
impart taste problem in drinking water.
Pesticides and agricultural chemicals are a result of
surface runoff from agricultural vacant and park lands,
specially in a combined sewage.
7. Toxic Compounds: Cu, Pb, Ag, Cr, As, Ni etc. Thesemay be present due to mixing of Industrial Wastewater in
Sewage. Measured by AAS methods. Their presence may
hinder performance of Waste Water Treatment Plant.
8. Sulphates, Sulphides and Hydrogen Sulphide Gas:Sulphides and sulphates are formed due to decomposition
of various sulphur containing substances present in
Sewage. This decomposition also leads to evolution of
hydrogen sulphide gas, causing bed smells and odours,besides causing corrosion of concrete pipes.
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9. Other Gases: Nitrogen , Oxygen , Carbon Di Oxide,
Methane gases may be present in Sewage.
10. Oxygen Consumed: This is the oxygen requires for the
oxidation of carbonaceous matter.
11. Dissolved Oxygen: DO is the amount of oxygen in the
dissolved state in the waste water.
While discharging the treated wastewater in to receiving
body , it is essential to ensure that at least 4ppm of DO is
present in it .
If DO is less, aquatic animals will be killed near the vicinity
of disposal.
The presence of DO in wastewater is desirable because it
prevents the formation of noxious order.
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12. Chemical Oxygen Demand: Amount of oxygen required
to oxidise biologically active as well as biologically inactive
organic matter.
Biochemical Characteristics
1.Biochemical oxygen demand (BOD): The BOD is a
measure of the Oxygen required to oxidise the organic
matter present in a sample, through the action of
micro-organisms contained in a sample of wastewater.
The BOD may be defined as the oxygen required forthe micro-organisms to carry out the biological
decomposition of dissolved o organic matter in the
wastewater under aerobic conditions at standard
temperature.
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2. Aquatic Plants & Animals:
Aquatic Plantso Spermophyta: Water weeds
o Bryophyta: Mosses and lever words
o Pteridophyta: Ferns and horsetailsoThallophyta: Algae
Animals:
Vertebrate: Fish and amphibians
Arthophoda: Insects, spiders, mites.Mollusca: Mussels, snails etc.Worms: Earthworms, thread worms, rotiferaMetazoa: Hydra, polyzoaProtozoa: Endameba histolytica etc.
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Bacteria:
Saprophytic bacteria
Parasitic bacteria
Pathogenic bacteria
Non-pathogenic bacteria