Water Demand, Water treatment Aeration

1. Subject: Water Supply Engineering
Unit-II
Water Demand, Water Treatment,
Aeration
Prepared by
Prof. H. N. Wagh
Assistant Professor, Department of Structural Engineering
Sanjivani College of Engineering, Kopargaon, 423603
Mail- waghharshadast@sanjivani.org.in, 7588026776

2. UNIT –II
Treatment of water
a) Water Demand
b) Water treatment
c) Aeration of water

3. Various Types of Water
Consumption/Demands
• Domestic consumption
• Industrial and commercial demand
• Public demand
• Fire fighting demand.

4. •Domestic consumption: the water required for
actual household activities is known as domestic
demand. It includes water required for drinking,
cooking, bathing, washing flushing of toilets etc.
Details of Domestic consumption
Purpose
Drinking
Cooking
Cleaning of utensils and house
Washing of clothes
Flushing of water closets(W.C.)
Bathing
TOTAL
5
5
20
20
30
55
135

5. • Industrial and Commercial Demand: Industry requires large
quantity of water for manufacturing, cooling operation, steam
generation, for processing and sanitation. This is known as
industrial demand. Commercial demand includes water
required for private offices, restaurants, cinema halls motor
garages and small scale industries. This demand can be
expressed per capita demand ,by dividing the industrial demand
by the population of the area.
Details of Industrial and commercial
Demand
ACTIVITY DEMAND(lit/capita/day)
Factories
Offices
Restaurants/seat
Hotels/person
Cinema/seat
30-45
45
70
180
15

6. • Public Demands: It includes water required for washing
of roads, cleaning of public sewers, watering of parks,
gardens water fountains, swimming pools, flushing of
water closets and urinals, hospitals, hotels, schools and
colleges. This demand is about 5 percentage of total
demand.
Details of Public Demands
ACTIVITY DEMAND
Public gardens
Street washing
Sewer cleaning
Hospitals
Hotels
Schools(without boarding)
Schools(with boarding)
1.4 lit/m2/day
1.0 lit/m2/day
4.5 lit/head/day
340 - 450 lit/bed/day
135 lit/head/day
45 lit/head/day
135 lit/head/day

7. Fire fighting Demand

8. Factors affecting per capita demand in a
community
• People's habits
• Industrialization
• Public Services
• Climatic conditions
• Systems of water supply
• Meter system
• System of drainage
• Availability of supplementary sources
• Distribution pressure
• Cost of water

9. Population forecasting
1. Arithmetic Increase Method:
• This method is generally applicable to large and old
cities.
• In this method average increase of population per
decade is calculated from the past records and
added to the present population to find out
population of next decade.
• This method gives a low value and is suitable for
well settled and established cities.
Pn = P + n x i
Pn = Population after n decade
P = Present population, n = Nos of decades
i = Average increase in population

10. 2. Geometric increase method
• In this method percentage increase in population from
decade to decade remains constant.
• Therefore, the average value of percentage increase in
population is calculated and the future population are
calculated at this rate.
• This method gives much higher value and mostly
applicable for growing towns and cities having vast scope
for expansion.
Pn = P( 1 + r/100)n
Where r = Average percentage rate of population increase
P = Present population
Pn = Population after n decade

11. 3. Incremental Increase method
• This method is the combination of arithmetic
increase method and geometric increase method.
• Hence ,combines the advantages of both methods
and gives satisfactory results.
• In this method, average increase per decade is first
calculated and to this average of net incremental
increase once for every future decade is added.
Pn = P + n x i + n(n + 1)/2 x I
Where I = Average incremental increase
i = Average increase per decade
n = Nos of decades

12. • Decreasing rate of increase method
• Graphical comparison method
• Graphical extension method

13. Layout and components of water treatment plant

14. Functions of Water treatment Units
Sr. No Unit Treatment Function(Removal)
1 Screening Removal of Floating matter
2 Aeration Removal of colour, odour,
bad taste
3 Sedimentation Suspended matter
4 Coagulation and flocculation or
clariflucculator
Colloidal matter
5 Filtration Colloidal matter and
bacteria
6 disinfection Pathogenic bacteria, organic
matter
7 softening Removal of hardness

15. Components of water treatment plants
Intake well, Jack well and Pump house:
Screen chamber: To remove floating matters. e.g.
polythene bags, tree leaves, branches of trees, paper
pieces etc.
Aerator: Increase O2 and to remove CO2,H2S,Fe,Mn etc.
Clariflocculator: Remove suspended and colloidal
impurities.
Filter: To remove very fine particles and colloidal matter
which is not removed by Clariflocculator.
Disinfection : To kill or inactivate pathogenic micro-
organism.
Clear water tank:
ESR:
Distribution:

16. Aeration
Aeration : It is the process of exposing the large sheet of
water to the atmospheric air.
Objectives of Aeration
To increase dissolved oxygen content.
To expel foul gases such as H2S,CO2,causing bad taste and
odour.
To oxidize the iron and manganese, so that they can be
precipitated and removed.
To destroy bacteria to some extent ,by agitation of water
during aeration.
It is also used for mixing chemical with water.
Classification: 1)Free fall- Cascade, Inclined apron, Slat
tray and gravel bed or trickling bed.
2. Spray aerator 3. Air diffuser basins.

17. Cascade aerators
§ Series of three to six steps.
§ Water falls through a
h e i g h t o f 1 m t o 3 m
depending upon capacity.
§ Constructed in room or
open air.
§ CO2 reduction is about 50
to 60 %.
§ Tread- about 0.5m - 1.5m
and rise 0.2 – 0.3m
Straight steps

18. Inclined Apron Aerator with riffle plates

19. Trickling bed or multiple bed aerator
§ Three or four trays arranged
one over the other.
§ Sand, coke, broken slag,
gravel, stones are filled in
trays.
§ Thickness of bed in each
tray is 0.5 -0.6m.
§ Vertical distance between
the trays is 0.5m.
§ Sometimes air is blown
from bottom in upward
direction.
§ Effective in removal of CO2
than other methods.

21. THANK YOU