Lab Turbidity

7/17/2019 Lab Turbidity

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Abstract

This experiment consisted of measuring the turbidities of a variety of samples using the

nephelometer .These recorded turbidities were then analyzed and a reasonable explanation

for each value is made.

INTRODUCTION

urbidity is the cloudiness or haziness of a fluid caused by large numbers of

individual particles that are generally invisible to the naked eye, similar to

smoke in air. The measurement of turbidity is a key test of water quality.

Turbidity is a measurement of how cloudy water appears. Technically, it is a

measure of how much light passes

through water, and it is caused by suspended solid particles that scatter

light. These particles may be microscopic plankton, stirred up sediment or

organic materials, eroded soil, clay, silt, sand, industrial waste, or sewage.

Bottom sediment may be stirred up by such actions as waves or currents,

bottom-feeding fish, people swimming, or wading, or storm runoff.

Clear water may appear cleaner than turbid water, but it is not necessarily

healthier. ater may be clear because it

has too little dissolved o!ygen, too much acidity or too many contaminants

to support aquatic life. ater that is turbidfrom plankton has both the food and o!ygen to support fish and plant life.

"owever, high turbidity may be a symptom of

other water quality problems.

he method is based upon 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. he higher the intensity of scattered

light, the

higher the turbidity. #eadings, in $ %&s, are made in a nephelometer

designed according tocertain specifications. ' primary

standard suspension is used to calibrate the instrument.

(ormazin polymer is used as a primary turbidity suspension for water

because it is more reproducible than other types of standards



previously used for turbidity analysis.

EQUIPMENT AND SUPPLIES

The turbidimeter shall consist of a nephelometer, with light sourceforilluminating the sample, and one or more photo-electric detectorswith areadout device to indicate the intensity of light scattered at rightangles to thepath of the incident light. The turbidimeter should be designed sothat littlestray light reaches the detector in the absence of turbidity andshould be freefrom signicant drift after a short warm-up period.

Experimental procedres

'. )ackson Turbidimeter

*. +lace a clean )ackson turbidimeter tube in the receptacle on the stand.

+lace a

candle in the device and insure that the spring in the candle holder is

released

and keeping the top of the candle at a distance of . cm below the bottom

of the

tube. f the water is relatively clean use the longer tube, otherwise use the

shorter

tube.

/. 'dd a small amount of well-mi!ed sample to the tube and light the candle.

Be

sure to add a small amount of sample B0(1#0 lighting the candle to prevent

cracking the tube.

2. 'dd well-mi!ed sample to the tube until the light field becomes uniform.

$ote the

reading from the side of the calibrated tube.



3. 0mpty the tube. 0!tinguish the flame. 4i! the sample again, add a few m5

to the

tube and light the candle. Then add 6 of the volume of sample added in 7tep

2.

Then add sample slowly until a uniform light field is observed. #ecord the

reading

B. $ephelometer

*. 7elect a standard that compares with the turbidity of the sample. Turn on

the unit

and select the range corresponding to the standard. nsert the standard and

replace the cover. 'd8ust the calibration knob to provide the correct reading

on

the meter. #emove the standard.

/. (ill the sample tube about 6 full of well-mi!ed sample and wipe the

outside of the

tube with 9imwipes if any spillage occurred. nsert the tube and replace the

cover. f the reading is offscale, switch the range of the meter until the

reading is

on scale. #ecord the reading and report it as $T%.

2. f the sample reading is significantly outside of the range in which the

meter was

calibrated, repeat the e!ercise calibrating with a standard in the appropriate

range.

Reslts

Turbidity:

The following data was collected during this experiment:

SAMPL T!"#$%$T&'(T!)

Drinking water 1.2Distilled water 0.8

coffee 78

*a*+, Errortoo high!

"ugar dissol#ed $n water %%should &e &etween 0'1!



"and ( water )7.*

"oil ( water 1)+

"ilt ( water 2+*

DISCUSSION AND CONCLUSION' direct measurement of suspended solids is not usually performed on

samples from natural bodies of water or on potable water supplies. The

nature of the solids in these waters and the secondary effects they produce

are more important than the actual quantity. (or such waters a test for

turbidity is commonly used.

7and and water mi!ture gave less turbidity than that of silt and water which

is logical. 7ilt is a much smaller particle than sand and thus more surface

area for pollutants to settle e!ist leading to higher turbidity. 1n the other

hand, comparing coarse soil and fine sand we see that coarse soil and water

had a higher turbidity of *3:, this result seems illogical because coarse soil

has a larger grain size than the fine sand, yet this result may be due to the

fact that coarse particles have more bumps and irregularities resulting in a

larger surface area. 's for distilled and drinking water, the results obtained

are also logical and acceptable. Calcium carbonate gave an error implying

that the sample has a very high turbidity that cannot be measured using the

$ephelometer .To find the turbidity of this sample we should dilute it by a

known ratio, measure the turbidity of the diluted sample and deduce the

original;s turbidity.1n the other hand, the cold coffee sample gave a turbidity

of <$T% which is larger than that of water . hen Coffee cools, its

solubility decreases and the coffee precipitates out to become a suspension,and then cause that turbidity we found.

(rom our e!periment we conclude that absorption and scattering and thus

turbidity are influenced by both size and surface characteristics of the

suspended material, and that turbidity is not a direct quantitative

measurement of suspended solids .(or e!ample a small pebble in a glass of



water would produce virtually no turbidity .f this pebble were crushed into a

thousand particles of colloidal size,a measurable turbidity would result even

though the mass of solids is still the same.

APPENDI!

*.decribed above

/.7uspended solids absorb light and scatter it leading to a decrease in light

intensity and thus the turbidity reading is deacreased.7econdly, Turbidity is

not color related, but relates rather to the loss of transparency due to the

effect of suspended particulate, colloidal material, or both. ' lack of turbidityresults in clarity or clearness because it is, in part, the effect of these

various suspended materials on light passing through a liquid.The presence

of bubbles on the other hand will affect turbidity by scattering light.

2.all three devices rely on the principle of Tyndall or light scattering by

colloidal and suspended particles ."owever these devices differ greatly in

their accuracy, where the )ackson turbidity meter is less accurate than the

nephelometer because it relies on naked eye sight and no measurable data.

This e!periment is prone to many errors of which we list=

-0!istence of fingerprints and other microorganisms on the e!ternal vial

walls leading to a fluctuation in the turbidity values.

-'ir bubbles inside the sample that can be only e!tracted through de-airing.

-The coffee and sugar samples are cold thus solubility is reduced and some

particles will settle leading to increased turbidity.



Re"erences

-0nvironmental engineering +eavey #ow

http=>>www.water-research.net>inde!.php>stream-water-quality-importance-of-

total-suspended-solids-turbidity

Lab Turbidity

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