chapter 2 water demand.pdf

8/12/2019 Chapter 2 Water Demand.pdf

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Environmental Engineering(VCB 3033)

Water demand

and overview of

water treatmentplant

AP Dr. AmirhosseinMalakahmadCivil Engineering DepartmentUniversiti Teknologi PETRONAS

CO1: To identify thesources of water and itsimpurities and to performcomplex design of watertreatment plant to meetthe standard limits.


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Unit Objectives

At the end of this session you will be able to:

Estimate the water demand and waterusage rate.

Forecast the population growth rate for

future developments.

Outline the water treatment plant unitprocesses.


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Demand factor range


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Example1: Using Historical Records to Estimate DemandFactors and Household Water Usage Rate

For a small water treatment plant, estimate the

following, using data gathered from the annual

water reports:

Maximum and minimum day demand factors.

Average household usage rate.

The average residential water usage is approximately 101 gpd/household.

So it appears this community is averaging approximately 1.5 individuals per

household. Give your opinions on how to tackle this matter.


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Estimation of water demand

Total water demand of acommunity will comprise ofpublic, domestic, industrial,and commercial demand.

Q= Total quantity of water

requiredP= population

q= rate of demand(consumption) per capita/ day

Q= P q 365


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A population equivalentis a method of

converting the water use (or wastewatergeneration) of commercial or industrial

users into the equivalent amount of water

used by a population number. For example,

an industrial unit may use the waterequivalent of 150 people in a residential

area. The projected equivalent population

(real population plus population

equivalents) is estimated to determine thefuture water demand.


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Population design

Before a water supply system can bedesigned, it is necessary to determine thewater amount need to be served to

present and future population.This requires not only the design period

but also a population estimation (forecast).

To approach population estimation

appropriately, information on economicbasis, trade territory and, industrialexpansion plans of the city are essential.


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Arithmetic method

This method is based on constant growth rate. This method is applicable if the projection period is

relatively short ( 5-10 years) and social and economic

activities in the area do not change drastically.

Pn= future population

P= present populationia= constant growth rate per decade

n = duration over which the projection is made, decade

Pn= P + nia


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Example 2:Given that the population of a townin 1990, 2000, and 2010 are 90 000, 100 000,

110 500, respectively. Estimate the population

in 2020 using the arithmetic method.


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Geometric method

This method is based on growth rate proportional topopulation size.

This method is applicable to growing towns and cities,where economic activities are growing and large landareas are still available for development or there is

unlimited scope of expansion.

Pn= future population

P= present population

ig= % increment of population

n= duration over which the projection is made, decade

Pn= P (1 + ig/100)n


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Example 3:Population of a town in 2014 is

67,300 while it was 33,300 in 1990.

i. Estimate the population in 2040 using the

geometric method.

ii. Compare the annual water demand at

present and in 2040 if per capita water

demand to be 280 L/capita.day. Explain

your comparison.


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Overview of water treatment process

Typical water treatment unit processes and their arrangement, These processes are

typically used for: (a) treatment of surface water and (b) treatment of water with high

levels of dissolved constituents.


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Treatment of surface waters mostly requires theremoval of particulate matter and pathogens.Removing particles also assists in pathogen removal,because most pathogens either are particles or areassociated with particles.

If the water source contains dissolved constituents,then additional unit processes can be added toremove them as well.

Treatment of water with high levels of dissolvedconstituents will become more important in the futureas increases in population and demand, along withclimate change, force society to search for waters ofpoorer quality. These sources are sometimes high inTDS and are present as brackish ground- water,seawater, and reclaimed water.

Overview of water treatment process


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Unit processes that remove a significant

amount of raw-water constituents

chapter 2 water demand.pdf

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