Enve 208 Experiment 2.2

7/29/2019 Enve 208 Experiment 2.2

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1. PURPOSE:

The purposes of this experiment are to explain the use of light scattering properties of

suspended matter in finding out their concentration and to show the principles of

nephelometric methods.

2. PROCEDURE:

Turbidity measurements:

1. For turbidimeter calibration prepare different dilutions of your 4000NTU formazin

standard (Table 2).

Table 2:

NTU mL of stock suspension diluted to 100

mL with turbidity- free water4000 100

1000 25

200 5

20 0.5

0 0

2. The sample size for all turbidity measurements should be 25(+or1) mL. Variations in

sample volume can affect the accuracy of the determinations.

3. When through with the measurements, best performance will be gained from the

photomultiplier tube by

Removing the sample cell from the cell holder Closing the sample compartment door, and Leaving the range switch in the 4000 position.

4. From the stock kaolinite solution, we take 10, 30, 80 and 70 mL (unknown sample) and

dilute to 100 mL volume using turbidity free water. Before any measurement, or any

solution preparation, we mix samples thoroughly.

5. We calibrate the turbidimeter with standard turbidity solutions.

6. We measure the turbidity of samples of all the kaolinite suspensions at the appropriate

turbidity range of the instrument calibrated.

7. We measure the turbidity of unknown sample before and after addition of

phenolphthalein.

3. THEORY:

A turbidity in water is caused by finely- or coarse-dispersed particles and undissolved

materials. The particle size of the present substances ranges between 1 to 300 m. The

turbidity can be measured by a decrease in the intensity of the radiation passed through the

liquid or by the intensity of the stray light. (URL 1)


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In water, turbidity is caused by suspended matter, such as clay, silt, finely divided organic

and inorganic matter, soluble colored organic compounds, and plankton and other

microscopic organisms. Turbidity is an expression of the optical property that causes light

to be scattered rather than transmitted in straight lines through the sample. Correlation of

turbidity with the weight concentration of suspended matter is difficult because the size,shape, and refractive index of the particulates also affect the light-scattering properties of

the suspension.

Interferences:

1. The presence of floating debris and coarse sediments which settle out rapidly will give

low readings. Finely divided air bubbles can cause high readings.

2. The presence of true color, that is the color of water which is due to dissolved

substances that absorb light, will cause turbidities to be low, although this effect is

generally not significant with drinking waters. Also, this interference is minimized by the

use of a ratiometric optical design which compares the transmitted and scattered signals.

3. Light absorbing materials such as activated carbon in significant concentrations can

cause low readings. (URL 2)

The major impacts of turbidity;

The main impact is merely esthetic: nobody likes the look of dirty water. But also, it is essential to eliminate the turbidity of water in order to effectively

disinfect it for drinking purposes. This adds some extra cost to the treatment of

surface water supplies.

The suspended particles also help the attachment of heavy metals and many othertoxic organic compounds and pesticides. (URL 3)Turbidity units are a measure of the cloudiness of water. If measured by a nephelometric

(deflected light) instrumental procedure, turbidity units are expressed in nephelometric

turbidity units (NTU) or simply TU. Those turbidity units obtained by visual methods are

expressed in Jackson turbidity units (JTU), which are a measure of the cloudiness of water;

they are used to indicate the clarity of water. There is no real connection between NTUs

and JTUs. The Jackson turbidimeter is a visual method and the nephelometer is an

instrumental method based on deflected light. (URL 4)

Historically, the standard method for determination of turbidity has been based on the

Jackson candle turbidimeter; however, the lowest turbidity value that can be measured

directly on this device is 25 Jackson Turbidity Units (JTU). Because turbidities of water

treated by conventional fluid-particle separation processes usually fall within the range of 0

to 1 unit, indirect secondary methods were developed to estimate turbidity. Electronic

nephelometers are the preferred instruments for turbidity measurement.

Most commercial turbidimeters designed for measuring low turbidities give comparatively

good indications of the intensity of light scattered in one particular direction,

predominantly at right angles to the incident light. Turbidimeters with scattered-light

detectors located at 90 to the incident beam are called nephelometers. Nephelometers arerelatively unaffected by small differences in design parameters and therefore are specified

as the standard instrument for measurement of low turbidities. Instruments of different


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make and model may vary in response. However, interinstrument variation may be

effectively negligible if good measurement techniques are used and the characteristics of

the particles in the measured suspensions are similar. Poor measurement technique can

have a greater effect on measurement error than small differences in instrument design.

Turbidimeters of nonstandard design, such as forward-scattering devices, may be moresensitive than nephelometers to the presence of larger particles. While it may not be

appropriate to compare their output with that of instruments of standard design, they still

may be useful for process monitoring.

An additional cause of discrepancies in turbidity analysis is the use of suspensions of

different types of particulate matter for instrument calibration. Like water samples,

prepared suspensions have different optical properties depending on the particle size

distributions, shapes, and refractive indices. A standard reference suspension having

reproducible light-scattering properties is specified for nephelometer calibration.

Its precision, sensitivity, and applicability over a wide turbidity range make thenephelometric method preferable to visual methods. Report nephelometric measurement

results as nephelometric turbidity units (NTU).

Nephelometric Method

a. Principle: This method is based on a comparison of the intensity of light scattered by the

sample under defined conditions with the intensity of light scattered by a standard

reference suspension under the same conditions. The higher the intensity of scattered light,

the higher the turbidity. Formazin polymer is used as the primary standard reference

suspension. The turbidity of a specified concentration of formazin suspension is defined as

4000 NTU.

b. Interference: Turbidity can be determined for any water sample that is free of debris and

rapidly settling coarse sediment. Dirty glassware and the presence of air bubbles give false

results. True color, i.e., water color due to dissolved substances that absorb light, causes

measured turbidities to be low. This effect usually is not significant in treated water.

4. DATA ANALYSIS AND CALCULATIONS:

Table 1. Data

Concentration of kaolinite

suspension(mg/L)Read-out Turbidity (NTU)

0 0.030

50 mg/L 22.5

150 mg/L 37.6

400 mg/L 149

500 mg/L 232

70 mL->(350mg/L) without

With indicator

132

138

500 mg/L sample*10 mL /100mL=50 mg/L 500 mg/L sample*30 mL /100mL=150 mg/L 500 mg/L sample*80 mL /100mL=400 mg/L 500 mg/L sample*100 mL /100mL=500 mg/L


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500 mg/L sample *70/100 mL=350 mg/L

1. Turbidity units (NTU) = A*(B+C)/C

Where, A=turbidity units found in diluted samplesB=volume of dilution water used in (mL)

C= sample volume in (mL) taken for dilution

For sample 10 mL: ((22.5-0.030)*(90mL+10 mL)) /10mL=224.7 NTU

For sample 30 mL: ((37.6-0.030)*(70mL+30 mL)) /30mL=125.23 NTU

For sample 80 mL: ((149-0.030)*(20mL+80 mL)) /80mL=186.21 NTU



2.

y=0.4192x

135=0.4192x x= 322 mg/L

Error = (350-322)/350*100= 8% error

5. DISCUSSION AND CONCLUSION:

1. A comparison of the dilute solution approximation and the condensed phase theory

yielded different predictions for the increase in turbidity as a function of an increase in the

size of the scattering units. Even greater differences are found when a change in theconcentration of the scattering units is considered. The dilute solution approximation

y = 0.4192x

R = 0.9672

0

50

100

150

200

250

0 200 400 600

T

u

rb

i

d

i

t

y

N

T

U

Concentration of kaolinite suspension mg/L

Concentration vs. NTU

Series1

Linear (Series1)


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would predict a proportional increase in turbidity with increasing concentration of the

scattering units. (URL 6)

Therefore we expect our graph will be linearly but our graph do not increase linearly

because we did not read-out suitable turbidity in nephelometre.

2. Turbidity is not color related, but relates rather to the loss of transparency due to the

effect of suspended particulate, colloidal material, or both. A lack of turbidity results in

clarity or clearness because it is, in part, the effect of these various suspended materials on

light passing through a liquid. (URL 7)

3. Excessive turbidity, or cloudiness, in drinking water is aesthetically unappealing, and

may also represent a health concern. Turbidity can provide food and shelter for pathogens.

If not removed, turbidity can promote regrowth of pathogens in the distribution system,

leading to waterborne disease outbreaks, which have caused significant cases of

gastroenteritis throughout the United States and the world. Although turbidity is not a

direct indicator of health risk, numerous studies show a strong relationship betweenremoval of turbidity and removal of protozoa. The particles of turbidity provide shelter

for microbes by reducing their exposure to attack by disinfectants. Microbial attachment to

particulate material or inert substances in water systems has been documented by several

investigators and has been considered to aid in microbe survival. Fortunately, traditional

water treatment processes have the ability to effectively remove turbidity when operated

properly. (URL 8)

Also, simply stated, turbidity is the measure of relative clarity of a liquid. Clarity is

important when producing drinking water for human consumption and in many

manufacturing uses. Once considered as a mostly aesthetic characteristic of drinking water,

significant evidence exists that controlling turbidity is a competent safeguard against

pathogens in drinking water. (URL 9)

4. The Disadvantages;

The presence of floating debris and coarse sediments will give high readings. Air bubbles will cause high results. Colored samples will cause low results.

Also, the sample tubes to be used with the available instrument must be clear, colorless

glass. They should be kept scrupulously clean, both inside and out, and discarded when

they become scratched or etched. They must not be handled at all where the light strikes

them, but should be provided with sufficient extra length, or with a protective case, so thatthey may be handled. Differences in physical design of turbidimeters will cause

differences in measured values for turbidity even though the same suspension is used for

calibration. To minimize such differences, design criteria should be observed.

The Advantages;

The turbidimeter shall consist of a nephelometer with light source for illuminating the

sample and one or more photo-electric detectors with a readout device to indicate the

intensity of light scattered at right angles to the path of the incident light. The turbidimeter

should be so designed that little stray light reaches the detector in the absence of turbidity

and should be free from significant drift after a short warm-up period. (URL 8)


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6. REFERENCES:

1. URL 1. Determination of Turbidity in Waste Water, retrieved 11 December 2012 from,

http://analitica.inycom.es/es-es/notas-de-aplicacion/Documents/UV_ALL_23_01_e.pdf

2. URL 2. Determination of Turbidity by Nephelometry, Thermo Scientific Orion Method

AQ4500, retrieved 11 December 2012 from,

http://www.thermo.com/eThermo/CMA/PDFs/Various/File_51982.pdf

3. URL 3.

http://www.lenntech.com/turbidity.htm#How%20do%20we%20measure%20turbidity?#ixz

z2Elu5a03w

4. URL 4. http://www.owp.csus.edu/glossary/turbidity-units-tu.php

5. URL 5. Standard Methods for the Examination of Water and Wastewater, retrieved 11

December 2012 from, http://www.umass.edu/tei/mwwp/acrobat/sm2130turbidity.PDF

6. URL 6. Effect of Change in Concentration upon Lens Turbidity as Predicted by Random

Fluctuation Theory, retrieved from 11 December 2012 from,

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1329010/pdf/biophysj00223-0035.pdf

7. URL 7. What is Turbidity and how is it measured? Retrieved 11 December 2012 from,

http://www.optek.com/Turbidity.aspTurbidity Overview

8. URL 8.Standard Operating Procedure for GLNPO Turbidity: Nephelometric Method.,

retrieved 12 December 2012from, http://www.epa.gov/glnpo/lmmb/methods/turbid.pdf

9.URL 9. http://www.epa.gov/ogwdw/mdbp/pdf/turbidity/chap_07.pdf

Enve 208 Experiment 2.2

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