sewage lecture

8/12/2019 Sewage Lecture

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CE C-342

WATER AND WASTEWATER

TREATMENT

To



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



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)*



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



Characterisation of Waste water

Physical Characteristics

Chemical Characteristics

Biochemical Characteristics



Physical Characteristics

Colour

Odour

Insoluble Substances-Settleable,

Suspended solids

Temperature Range etc….




Chemical Oxygen Demand -

COD

pH

Acidity/AlkalinityHardness

Total Organic Carbon

Total Dissolved Solids

Surfactants

Phenols etc...




Biochemical oxygen demand- BOD

Dead and Decaying plants and animals

Presence of pathogenic bacteria



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.



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



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



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




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.



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.



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

.



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.



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.



12. Chemical Oxygen Demand: Amount of oxygen required

to oxidise biologically active as well as biologically inactive

organic matter.


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.



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.



Bacteria:

Saprophytic bacteria

Parasitic bacteria

Pathogenic bacteria

Non-pathogenic bacteria

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