2Lecture;Wastewater Flow Rates

8/17/2019 2Lecture;Wastewater Flow Rates

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CE 4312- Water andWastewater Engineering

LECTURE 2-Wastewater Flow Rates

Nadeeka [email protected]

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Learning OutcomesOn completion of this unit you should be able to:

• Understand the importance of water and wastewatertransfer and treatment.

• Understand the principles of unit processes in water andwastewater treatment including: physical, chemical, andbiological treatment principles and the impacts of waterpollutants on human health and the environment.

• Apply the fundamental principles of water andwastewater treatment in designing water and wastewatertreatment schemes to remove pollutants.

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ContentWastewater collection and treatment

• Introduction and Terminology

• Wastewater flow rates

• Wastewater characteristics

• Wastewater composition

• Wastewater characterization studies

•

Primary and secondary treatment of wastewater 3


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Wastewater flow ratesTopics

• Introduction• Components of wastewater flows• Variation of wastewater Flow• Analysis of wastewater flow rates• Reduction of wastewater flow rates• Practice Questions

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Introduction

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Wastewater Quality Monitoring is needed toprovide EFFECTIVEwastewater treatmentfacilities.

The accurate assessment of wastewater flowcharacteristics and pollutant concentrations

ARE IN CRUCIAL IMPORTANCE

WHY?


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Insufficient data on Wastewater FlowRates LEEDS

Improper Design Considerations such as• hydraulic characteristics,• sizing and operational considerations of the

treatment system components.• Equipment Selection

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Un estimated Costs associated with design,

construction and functioning of Treatment Plants.

Inequitably of facilities when serve more than onecommunity or district.


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Difficulties in Obtaining Wastewaterflow Rates

• The complexity of human activities in recreationalareas makes estimating water usage and wastewatergeneration a difficult task

• Direct field measurements of wastewater flow ratesare not possible.

• Actual wastewater flow rate data are not available.

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Components of

wastewater flows

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Domestic Industrial

Public

Services

Infiltration/Inflow UnaccountedLosses andLeakages


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• Over one-third of the water used in a municipalwater supply system is for domestic purposes such aswashing, bathing, culinary, land yard watering etc.

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Domestic Wastewater


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• Principal sources of wastewater generated in acommunity:

• residential areas,• commercial districts,• institutional facilities and recreational facilities.

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Domestic Wastewater contd:


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A v e r a g e W a t e r C o n s u m p t i o n


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Sources :• canneries,•

chemical plants, and• refineries. Etc.

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Industrial Wastewater


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• Sources :• public buildings,• fire fighting,• irrigating public parks

and greenbelts,• system maintenance

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Wastewater from Public Services


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Extraneous flows in sewers called Infiltration/Inflow

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Infiltration/Inflow (I/I)

I/I that occurs on a relatively continuous basis

The quantity of water from bothinfiltration andinflow without

distinguishingthe source

OR


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Infiltration

• defective pipes (Broken and damaged pipes),• pipe joints, connections, and

•

manhole walls.

Water other than wastewater that enters a sewer system(including sewer service connections and foundationdrains) from the ground through:


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• Infiltration is expected to present in wastewaterflow through out the year

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• Infiltration is depended on length of sewer,local construction standards, soil types andlocation of water table

Infiltration Contd:

• Directly influence by groundwater fluctuations

• Infiltration is not depended on population of thearea

•

Can be incorporated into per capita flow


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The amount of flow that can enter a sewer fromgroundwater, or infiltration, may vary between ;

200 - 28,000 L / ha.day8,600 - 24,000 L / km.day9.4 - 940 L / mm.km.day

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Infiltration Contd:


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• Inflow is largely result from stormwater runoff

(wet weather flow)

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• High Impact on sewer systemIncreasesthewastewaterflow

• The effect on sewersystem is varying with thetype of inflow sourcesexist in the system


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Components of Inflow

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I/I Wh I Th A P bl ?


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I/I Why Is There A Problem?• The sanitary sewers are meant to carry only

wastewater, which comes from fixtures such as sinks,

toilets, bathtubs, showers and washers.• This wastewater then enters the septic tank, where

the liquid portion is pumped out and conveyed toTreatment Facility.

• When infiltration and inflow enter the sanitary sewer,they take up pipe space that is required for thewastewater.

• The infiltration and inflow can cause sewer backupsand overflows into the environment during wetweather.

•

They can also cause overloading at the treatmentfacilit .22


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What Is The Solution?

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Wastewater collection systems must be properly sized toconvey the wastewater discharged to the collectionsystem.

Inflow that is connected to the sanitary sewer systemmust be diverted to an acceptable location. This flowbelongs on the ground surface or in drainage ditches.

Infiltration can be reduced by repairing existing leaky

pipelines, manholes and septic tanks.


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Unaccounted system losses are mainly attributed to

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Unaccounted Losses and Leakages

Unauthorized usesIncorrect meter calibration or readingsImproper meter sizingInadequate system control

Leakages are mainly attributed to

System ageType of material of constructionLack of system maintenance


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A large city has measured high flow rates during the wet season of the year. The flow rates during the dry period of the year, whenrainfall is rare and groundwater infiltration is negligible, averages128,000 m 3/d. During the wet period when groundwater levels areelevated, the flow rate averaged 240,000 m 3/d excluding those daysduring and following any significant rainfall events. During a recentstorm, hourly flow rates were recorded during the peak flow periodas well as several days following the storm. The flow rate plots areshown in the accompanying figure. Compute the infiltration and

inflow and determine if the infiltration is excessive. Excessiveinfiltration is defined by the local regulatory agency as rates over0.752 m 3/d. mm-km of the sewer. The composite diameter-length of the sewer system is 270,000 mm-km.

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Example 2


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1. Determine the infiltration and inflowcomponents during the wet season.

a) As the infiltration is low during dry periods, highgroundwater infiltration is computed aspeak flow rate – Base (Dry weather) flow rate

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Infiltration = (240,000-128,000) m 3/d

Infiltration = 112,000 m 3/d

Answer-Example 2


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b) The maximum hourly inflow is graphically

determined from the Figure

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Example 2 Contd:

180

80

33.8

Maximum hourly wet weather flow rate

Preceding day flow rate

180

80

33.8


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2). Determine if the infiltration is excessive.

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Example 2 Contd:

Infiltration per unit diameter-length of thesewer system.

−

= 112,0003

/270,000 −

= . . −


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According to regulatory AuthorityIf the infiltration rate > 0.752 m 3/d.mm-km -

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Example 2 Contd:

Excessive

Therefore, The infiltration found in this city isnot excessive

The infiltration found in this city is0.415 m 3/d.mm-km


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Example 3

A small community water supply agency furnisheswater to 147 customers from a well supply. Waterrecords are kept showing the amount of waterpumped to the system. The agency recently installedmeters for all customers and total water sales recordsare also kept. The following data are obtained.


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Example 3 Contd:

Determine the amount of water consumed

(gal/capita.d) and the amount of water that isunaccounted system loss (as a percent of production).The average household size as determined by thelocal planning agency is 2.43 persons per service.


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Determine the average daily per capita waterconsumption for the period of record.

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Answer-Example 3

Use the sales records because that provides the actualamount of water measured as used by the customers.

=35,046 /

147 (2.43 )

= 98.


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• Determine unaccounted system losses.

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Answer-Example 3 Contd:

The difference between the production rate and salesrepresents unaccounted system losses and leakage.

Unaccounted system losses

=(46,116 − 35,046 )

46,116× 100% = 24%

Comment: metering errors often account for a large percentage of

system losses and records of meter calibration need to be checked.Differences in production and consumption as large as those in theabove example are significant and require investigation. If water

production records are used without investigating unaccountedlosses, the computed consumption rates may be in error.


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Variation of wastewater Flow

A considerable portion of the water produced doesnot reach the sanitary sewer system

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WHY?

Product water by manufacturing establishments,For landscape irrigation, system maintenance, andextinguishing fires,Water used by consumers whose facilities are notconnected to sewers, andLeakage from water mains and service pipes (unaccountedfor losses).

Considerable amount of water used as


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Variations in Water Use

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Variation of wastewater Flow Contd:

Variations in water consumption also effectthe rate of wastewater flow


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Water Usage Patterns

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V i ti i W t t fl t


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Variations in Wastewater flow rates

Daily indoor water use pattern for single-familyresidence

General terms :Daily and Hourly Flow Rates

Variations in Wastewater flow rates Contd:


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Wastewater flow can vary significantly from day today or Hour to Hour. Minimum hourly flows of zeroare typical for residential dwellings. Maximumhourly flows as high as 100 gallons (380 L/hr).

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This is due to the variability of typical fixture andappliance usage characteristics and residential wateruse demands.

Hourly flows exceeding this rate can occur in casesof plumbing fixture failure and appliance misuse(e.g., broken pipe or fixture, faucets left running).



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Peak Flow Rates

• The peak flow rate from a residential dwelling is afunction of the fixtures and appliances present and their

position in the plumbing system configuration. 42

Peak wastewater flows for single-family home



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• The peak discharge rate from a given fixture or applianceis typically around 5 gallons/ minute (19 liters/minute),

with the exception of the tank-type toilet and possiblyhot tubs and bathtubs.• The use of several fixtures or appliances simultaneously

can increase the total flow rate above the rate forisolated fixtures or appliances.

• However, attenuation occurring in the residentialdrainage system tends to decrease peak flow ratesobserved in the sewer pipe leaving the residence.

• Although field data are limited, peak discharge rates froma single-family dwelling of 5 to 10 gallons/minute (19 to38 liters/minute) can be expected.

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This variability can affect treatment systems by potentiallycausing hydraulic overloads of the system during peak flowconditions.



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f f


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1

•

K e y F

l o w

P a r a m

e t e r s 2

•

D e s i g n F

l o w

P a r a m e t e r s 3

•

S t a t i s t i c a l A n a

l y s i s

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Analysis of wastewater flow rates



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Key Flow parameters


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Analysis of wastewater flow rates Contd:

The determination of the ADWF, PDWF andPWWF should be based on:

• Actual system performance;• The data based on Sewerage Code in

particular catchment;• The historical catchment approach where

typically.

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Key Flow parameters Contd:


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PDWF = C2 x ADWF where C2 = 4.7 x (EP) -0.105

PWWF = (5 x ADWF) or (C1 x ADWF) whichever is thelarger and C1 = 15 x (EP) -0.1587

(Note: the minimum value of C1 = 3.5)

In the above formulae, EP is the total equivalent

population in the catchments gravitating to a pumpstation.

Analysis of wastewater flow rates Contd:Key Flow parameters Contd:


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Calculate the PDWF for a given wastewaterflow by considering Equivalent population15 000, and ADWF =180 L/EP.day.

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Example 4


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Answer- Example 4PDWF ?

Given ADWF =180 L/EP.day

PDWF = C2 x ADWF

C2 = 4.7 x 15 000 -0.105

= 4.7 x 0.364

= 1.71PDWF = 15 000 EP x 180 L/EP.d x 1.71

= 4 617 kL/d


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Design Flow parameters Contd:• The average daily flow (Volume per unit time)The average of the daily volumes to be received for a continuous12 month period of the design year.

Average flow rate is used in evaluating treatment plant capacity and in developing flow rate ratios used in design. And also, theaverage flow may be used to estimate pumping and chemicalcosts, sludge generation and organic loading rates.

• The maximum daily flowThe largest volume of flow to be received during a continuous 24-hour period.It is employed in the calculation of retention time for equalizationbasin and chlorine contact time.


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Design Flow parameters Contd:• The peak hourly flowThe largest volume received during a one hour period, based on annualdata.

It is employed in the design of collection and interceptor sewers, wetwells, wastewater pumping stations, wastewater flow measurements,grit chambers, settling basins chlorine contact tanks and pipings.

• The design peak flowThe design peak flow is the instantaneous maximum flow rate to bereceived.

The peak Daily / Hourly flow is commonly assumed as threetimes the average Daily / Hourly flow.


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Design Flow parameters Contd:• The minimum daily flowThis the smallest volume of flow received during 24-hour period.This is important in the sizing of conduits where solids might be

deposited at low flow rates.

• The minimum hourly flowThe smallest hourly flow rate occurring over a 24-hour period based on

annual data.This is important to the sizing of wastewater flowmeters, chemical-feedsystems and pumping systems.


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Estimate the average and maximum hourly flow fora community of 10,000 persons. Assume averagewater consumption is 200 L/c.d and assume 80% of

water consumption goes to the sewer.

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Example 5


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Answer- Example 5

Average Wastewater flow= 200 L/(c.d)×0.80×10,000 persons×0.001 m 3/L

Average Wastewater flow= 1600m3

/d

STEP2

STEP1

Compute Average Hourly Flow Rate

Average hourly flow Rate= 1600m 3/d × 1d/24 h

Average hourly flow Rate= 66.67 m 3/h


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STEP 3

Answer- Example 5 Contd:

Estimate the Maximum ( peak) Hourly Flow Rate

Assumption :The peak hourly flow rate is three times the average hourl flow rate

Therefore;

Maximum Hourly Flow Rate = 66.67 m 3/h × 3

Maximum Hourly Flow Rate = 200 m 3/h


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The following data is given:Sewered population = 50,000.Average domestic wastewater flow = 100 gal/c.dAssume infiltration flow rate = 500 gal/(d.mile) per inch of pipediameter

Sanitary sewer systems for the city:• 4-in house sewers = 66.6 miles• 6-in building sewers = 13.2 miles• 8-in street laterals = 35.2 miles• 12-in submains = 9.8 miles• 18-in mains = 7.4 miles

Estimate the infiltration flow rate and its percentage of the

average daily and peak daily domestic wastewater flows. 58

Example 6


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Calculate the Average Daily Flow (Q) and Peak DailyFlow (Q p)

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Answer- Example 6Step 1

Assume Q p=3Q

Average Daily Flow (Q) = 100 gal/(c.d)× 55,000 persons

Average Daily Flow (Q) = 5500,000 gal/dPeak Daily Flow (Q p) = 5500,000 gal/d × 3

Peak Daily Flow (Q p) = 16500,000 gal/d


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Compute total Infiltration flow, I

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Step 2

I = infiltration rate × length× diameter

I = 500 gal/(d.mile.in) × (66.4×4 + 13.2 × 6+ 35.2×8+9.8×12 + 7.4×18) mile.in

I = 439,000 gal/d

S 3


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Compute percentages of infiltration to daily average

and peak daily flows

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Step 3

I/Q = (439,000 gal/d)/ (5,500,000 gal/d ) ×100

I/Q = 8.0 %

I/Q p = (439,000 gal/d)/ (16,300,000 gal/d ) ×10I/Q p = 2.66 %


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Statistical Analysis of Flow RatesDetermination of statistical parameters used to quantify aseries of measurements.Commonly used statistical measures include the

mean,median,mode,

standard deviation andcoefficient variation

Based on the assumption that data are distributed normally.


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How to determine the type of Distribution?

plotting the data on both arithmetic-probabilityand log-probability paper.

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Note whether the data can be fitted with a straightline or not.

How to plot the Data?


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Plotting of Data

Arrange the measurements in a data set in orderof increasing magnitude and assign a rank serialnumber.

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Compute a corresponding plotting position for eachdata point using following formula.

Plotting position (%) = m/(n+1) × 100Where m= rank serial number

n= number of observationsThe plotting position represents the percent orfrequency of observations that are equal or less

than the indicated value.


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The Resultant Table

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Rank Serial Number(m)

Flow Rate Plotting Position %

1 2000

2 3000

3 32504 4000

Prepared in AscendingOrder of the Values (just setof example values)

C o n t i n u

i n g

n

Number ofObservations

Plot the data on arithmetic-probability and log-


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probability paper.

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A r i t h m e

t i c - p r o

b a

b i l i t y

p a p e r

A r i t h m e t i c S c a

l e

Log Scale


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L o g - p r o

b a

b i l i t y p a p e r

Log Scale

L o g S c a l e

The probability scale is labeled “ percent of


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values equal to or less than the indicated value”

If the data plotted onarithmetic probability paper andif the data set fit with a straightline then the data are assumed

to be normally distributed

Can calculate statisticalmeasures Which include

mean,median,mode,standard deviation andcoefficient variation

IF NOT

If h d i fi i i h


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If the data is not fitting to a straightline (which is called as Skewness)the data is re-plotted on the log-

probability paper. The implicationhere is that the logarithm of the

observed values is normally

distributed .Have to go for the measures such asGeometric Mean, GeometricStandard Deviation etc

Scope : we are dealing with arithmetic- probability papers Only. i.e We are looking at

Normally distributed data sets only.


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Using the following weekly flow rate data obtained

from an industrial discharger for a calendar quarter ofoperation, determine the statistical characteristicsand predict the maximum weekly flow rate that willoccur during a full year’s operation.

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Example 7


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Example 7 Contd:


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Determine the statistical characteristics of Data Set Setting up data analysisAnswer- Example 7 Cond:


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Determine the statistical characteristics of Data Set- Setting up data analysistable to obtain the values needed to determine the statistical characteristics

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Flow Ratem3/wk

− (

−)2

2,900 -578 334,0843,040 -438 191,8843,135 -343 117,6493,180 -298 88,8043,265 -213 45,3693,360 -118 13,9243,450 -28 7843,540 62 3,8443,675 197 38,8093,770 292 85,264

3,810 332 110,2244,015 537 288,3694,080 602 362,40445,220 1,681,372

Answer- Example 7 Cond:


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Determine the statistical characteristics using

the parameters given in The Table

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I . ean

=

=45,220

13

= 3478 3 /


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II. Median The Middle Most Value )

Looking at the Table

Median = 3450 m 3/wk

III . Mode

= 3 − 2

= 3 3450 − 2478

= 3394 3 /


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III Standard Deviation

=

( −) 2

−1

=

1681,372

12= 374.3 3 /


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Answer Example 7 Cond:


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Determine the probable annual maximum weekly flow rate

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Determine the probability factor

=+ 1

= 525 2 + 1

= 0.981

Determine the flow rate from the graphobtained for the 98.1 percentile value

Peak Weekly Flow Rate = 4500 m 3 /wk


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Reduction of wastewater flow rates• Because of the importance of conserving both resources and

energy, various means for reducing wastewater flow rates andpollutant loadings from domestic sources are gaining increasingattention.

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• The reduction of wastewater flow rates from domestic sourcesresults directly from the reduction in interior water use.

• Therefore, the terms " interior water use " and " domestic wastewater flow rates " are used interchangeably.

Flow Reduction Devices and Appliances


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Faucet aerators

• Faucet aerators mix air and water as the water leaves the spout.•

They reduce both the flow rate and splashing, while increasing areasof coverage and wetting efficiency. This conserves water and improvesfaucet performance at the same time.

• Aerators will not reduce the amount of water needed to fill a sink orwater jug, but will reduce the amount of water needed for a thoroughrinsin .


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• The greatest savings on kitchen and bathroom faucets comesfrom proper operation . Do not leave the faucet running whenwashing, shaving, brushing teeth, or washing dishes. This oneprecaution can save five or 10 times the water of an efficientfaucet or aerator alone.

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Low flush toilet


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Pushing the handle on dual-flushtoilet down uses 1.6 gallons; pushingit up uses just 1.1 gallons.


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