Introduction to Environmental Engineering

Environment: The non living and living Organisms(things) which surrounds us; that which can be

seen, hear, touch, smell and taste is Environment. Environment is of two types

(i)Natural Environment : Consists of all non living and living things occurring naturally in the area.

(ii) Built Environment: It refers to the human made surroundings that provide for the settling of

human activities like; buildings, parks, cities, and supporting structures like transport water

supplies, energy supplies etc.

Environmental Science : An integrative applied science that draws upon nearly all of the

natural sciences to address environmental quality and health issues.

Environmental Engineering: the application of science and Engineering principles to protect

and utilize natural resources, control environmental pollution, improve environmental quality to

enable healthy ecosystem and comfortable habitation to human. It is based on multiple disciplines

like Chemistry, Physics, Mathematics, Medicines, Hydrology, Geology and economics etc.

Environmental engineering requires a sound foundation in the environmental sciences consists of;

1. Provision of safe, palatable and ample water supplies

2. Proper disposal of or recycling of wastewater and solid wastes

3. Control of water, soil and atmospheric pollution.

4. Industrial Hygiene and Environmental Sustainability

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Water Quantity

The various demands for water quantity are

Domestic; commercial and Industrial; Public use and unaccounted water

Domestic : water uses are for drinking, cooking, meeting of sanitary need in

houses and hotels and irrigating lawns etc. Residential water use rates fluctuate

regularly. Average daily winter consumption is less than annual daily average,

whereas summer consumption average are greater. Similarly, peak hourly demand

is higher than maximum. No universally applied rule for prediction.

Commercial and Industrial: It includes factories, offices and commercial places

demand. It based on either having a separate or combined water supply system.

Demand of water based on unit production, No. of persons working and floor area.

Public Use: Schools, hospitals, fire fighting etc

Losses and waste : unauthorized connections, leakage in distribution system,

Hydrant flushing, Major line breakage and cleaning of streets, irrigating parks

Total consumption is sum of the above demand

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Water demand for dif ferent purposesAverage Annual Daily Demand (AADD):

The total quantity of water supplied for a period of one year divided by the No. of days in a

year. If this demand is based on a single person then it is average per capita.

q = Q / (365 * P) where q = discharge rate (lpcd)

Q = Total quantity of water in liters and P = Population residing in an area

Avg. Daily Demand (ADD) = Q / (365 * P) Max. Daily Demand (MDD) = ADD * 1.80

Max. weekly Demand (MWD) = ADD * 1.48; Max. hourly Demand (MHD) = ADD * 1.50

Max. Monthly Demand (MMD) = ADD * 1.28; Min. rate of Demand (MRD) = (0.25 -0.50)

ADD

Peak hourly Demand (PHD) = ADD * 1.5 * 1.8* = 2.70 * ADD

Average daily Consumption: ADD is based on location, time, season etc.

A rough estimate is Use

Use % Use %

Domestic 44 Commercial 15

Industrial 24 public 09

Losses and waste (Unaccounted) 8

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Factors affecting water use• The ADD is based on a number of factors l ike

• Size of community; Industries and commerce; Characteristics of population; Climatic Conditions; Distribution Pressure; Cost of water (metering system); system of supply; Quality of water; Air

conditioning; Efficiency of the department ; Sewerage facility and conservation practices.

• Fire Demand : Fire demand of water is often the determining factor in the design of mains. Although the actual use of water is less, the rate of use is high. Hydrant pressure should be more

than 140 KPa where motor pump is used and more than 690 K Pa if pump is not used. The

Insurance Services Office (ISO) use the formula

• F = 320 * C (A)0.5; Where F = required flow in m3/ day; A = total floor area excluding the

basement; C = coefficient related to constructed materials C=1.5 for wood frame; 1.0 for ordinary

construction, 0.90 for heavy timber type building, 0.80 for non combustible construction and 0.60

for fire resistive structure.

For high value area communities of population equal to or less than 200,000 the National Board of

Fire Underwriter (NBFU) recommended the following the flow rate F = 3.86 (P)0.5 (1-0.01 (P)0.5

Where P = Population in Thousands and Discharge in m3/minute; flow time = 4 - 10 Hrs

• Table 2.3 Page 15 of Terence provide information about distance between units

and discharge.

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Fire Demand and Population Forecasting

Example: A 4-story building of heavy timber type of 715 m2 of ground area. Calculate the water fire

requirement.

Solution: Using the Equation F = 320 * C (A)0.5 = 320 * 0.90 (4*715)0.5 = 15401.94 m3/day

Example: Assuming a high-value residential area of 100 ha. has a housing density of 10

houses/ha with 4 persons per household. The average daily demand is 340 lpcd. Determine the

water demand, including fire in this residential area.

Solution: Step 1: Estimate Population=( 4 capita/house )* 10 houses/ha) (100 ha) = 4000 persons

step2: Estimate Maximum daily flow = ADD* 1.8 = 340 lpcd* 1.8 * 4000 persons = 2448000

l/day =2448 m3/day (Note: In case of Fire demand the f low must be at maximum

demand and the durat ion of f ire f low wil l be from 4 to 10 hours depending on f ire

nature)

step3: Estimate fire demand F = 3.86 (P)0.5 (1-0.01 (P)0.5 = 3.86 (4)0.5 (1- 0.01 (4)0.5 ) = 7.57 m3/min. =

4542 m3/day

step4: Total water demand = Maximum demand + Fire demand = 2448 + 4542 =6990 m 3/day

6

Population forecasting

Population Forecast ing: Prior to design of a water supply scheme, it is necessary to forecast

the future population. The future prediction of population on the basis of previous census record using mathematical, statistical or graphical methods are known as population forecasting.

The knowledge of forecasting is important for design of any water supply scheme. It based on

design period of population. The design period estimates will be 1 to 50 years.

It is difficult to estimate the population growth due to economic and social factors involved.

However, a few methods have been used for forecasting population.

Arithmetic Method: Based of hypothesis that population rate of increase is constant.

Mathematically dP / dt = Ka (1) where dp / dt= rate of growth of population ;

and Ka= Arithmetic growth rate constant.

If P0 is the population at time t0 and Pf is the future population at time t f

then rearranging and taking integration of equation (1) we have

∫ dp = Ka∫ dt

= Pf – Po = Ka(tf – to ) where tf – to = ∆t or just “t” in years

The population in future is then estimated as

Pf = Po + Kt similarly Ka =(Pf – Po )/ t

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Uniform Percentage or Geometric and Logist ic methods of Populat ion Forecast ing

Geometric Growth method : According to this method it is assumed that the rate of increase of population growth in a community is proportional to the present population.

Mathematically dP / dt α P => dp / dt = Kg* P where Kg = Geometric growth constant. If Po is the

population at any time to and Pf is the population at time t f then ∫ dp/ p = Kg ∫dt = Ln (Pf / Po = Kg

(tf / to ) => Ln (Pf / Po = Kg ∆t => Ln Pf = Ln P0 + Kg ∆t => Pf / P0 = (e) Kg ∆t

and Pf = P0 (e) Kg ∆t

This method gives somewhat larger value as compared to arithmetic method and be used for new cities with rapid growth. In normal practice arithmetic and geometric growth average is taken.

Logist ic Method: When the growth rate of population due to birth, death and migration are

under normal situation and not subjected to extraordinary changes due to unusual situation like war, epidemic, earth quake and refuges etc. then this method is used. According to this method

P = P sat/ (1+ ea+ b ∆t). where P sat is the saturation population of the community and a, b are

constants. P sat , a and b can be determined from three successive census populations and the

equations are P sat = 2 P0 P1 P2 - P12 (P0 + P2) / (P0 P2 - P1

2)

a = ln P sat - P2 / P2 and b = 1/n [ ln {P0 (Psat – P1)} / {P1(Psat- P2}] n = time interval between succeeding

censuses.

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Population Forecasting• Curvi l inear or Comparat ive method: In this method it is assumed that the population of a

city will grow in the same manner as in other cities in the past. This similarity between the cities includes geographical proximity, similarity of economic base, access to similar transportation

system etc. In practice it is difficult to find similar cities.

• Ratio method: Ratio method of forecasting is based on the assumption that the population of a certain area or a city will increase in the same manner to a larger entity like a province, or a

country. It requires calculation of ratio of local to required population in a series of census years.

Projection of the trend line using any of the technique and application of projected ratio to the estimated required population of projected ratio to the estimated required population in the year

of interest. This method of forecasting does not take into account some special calculations in

certain area but have the following advantages.

Declining Growth method: This method like logistic assume that the city has some limiting

saturation population and that its rate of growth is a function of population deficit.

Mathematically dp/dt (P sat- P). Where P sat is the saturation population computed on some rational

basis. Now dp/dt = Kd (P sat- P). Where Kd is the declining growth constant. The value of which will

be Kd = 1/n Ln (P sat- P)/ (P sat- P0) where n= census interval between P0 and P

Future population can be estimated as Pf= P0 + (P sat- P0) ( 1-e Kd t)