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COLOR & TURBIDITYCOLOR & TURBIDITY

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C O L O RC O L O R

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General Considerations

Color is important from the standpoint of aesthetics. If water looks colored , people instinctively avoid using it, even though it might be perfectly safe from the public health aspect.

Color is often caused by organic substances such as algae or humic compounds.

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apparent color:apparent color:color caused by suspended matter.

true color:true color:color caused by colloidal, such as vegetable or organic extracts.

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Methods of Determination

Natural color is caused by a wide variety of substances, and it has been necessary to adopt an arbitrary standardfor its measurement.

Samples PretreatmentSamples PretreatmentSamples require pretreatment (centrifugation not

filtration is recommended for adsorption reason) to remove suspended matter in order to determine its true color.

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(1)(1) Standard Color Solutions MethodStandard Color Solutions Method

(2) Dilution Multiple Method(2) Dilution Multiple Method

(3) (3) SpectrophotometricSpectrophotometric MethodMethod

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Waters containing natural color are yellow-brownish in appearance.

Solutions of potassium chloroplatinate (K2PtCl6) tinted with small amounts of cobalt chloride yield colors that are very much like the natural colors. In this method, the color produced by 1 mg/l of platinum (as K2PtCl6) and 0.5mg/l of cobalt (as CoCl2•6H2O)is taken as the standard one unit of color.

(1) Standard Color Solutions(1) Standard Color Solutions

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Usually, a stock solutionstock solution of K2PtCl6 that contains 500mg/l500mg/l of platinum is prepared, which has a color of 500 units. Then, a series of working standards may be prepared from it by dilution.

ColorColor--comparison tubescomparison tubes are usually used to contain the standards. A series ranging from 0 to 70 color units is employed and samples with color less than 70 units are tested by direct comparison with the prepared standards.

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For samples with a color greater than 70 units, a dilution is made with distilled waterdistilled water to bring the resulting color within the range of the standards. In this case, the final result should be corrected using a dilution factordilution factor.

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(2)Dilution Multiple Method(2)Dilution Multiple Method

Color of most domestic and industrial waste-waters are not yellow-brownish hue.

Other systems of measurement have to be used to measure and describe colors that do not fall into this classification.

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For dilution multiple method, color is measured by successive dilutionssuccessive dilutions of the sample with colorcolor--free free waterwater until the color is no longer detectable comparing with distilled water. The total dilution total dilution multiplemultiple is calculated and used to express the color degree.

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Significance and Application of Color Measurement

Many people are reluctant to drink colored water.

Some colored wastes are quite resistant to resistant to biological attackbiological attack and persistpersist for great distances after disposed of into natural watercourses.

Why to measure color

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Color caused by natural organics results in the formation of chloroform, other trihalomethanes, and a range of other chlorinated organicschlorinated organics, leading to problems of much current concern.

Many industrial processes require the use of color-free water. Removal of color is an expensive matter.

U.S. EPA secondary standard or WHO guideline U.S. EPA secondary standard or WHO guideline of color units for drinking water is 15. of color units for drinking water is 15.

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In dealing with colored waters, color In dealing with colored waters, color determinations serve as the basis of the decisions.determinations serve as the basis of the decisions.Before a chemical treatment plant is designed, research should be conducted to ascertain the best chemicals to use and amounts required.

When to measure color

Once operation of the treatment facilities has begun, color determinations on the raw and finished wastes serve to govern the dosages of chemicals usedgovern the dosages of chemicals used, to ensure economical operation, and to produce a low-color water that is well within accepted limits.

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ProblemsProblems

Discuss briefly the causes of color in water.Discuss briefly the causes of color in water.

Differentiate between Differentiate between ““apparentapparent”” and and ““truetrue”” Color.Color.

What limit is generally placed on color and why are What limit is generally placed on color and why are

such standards set?such standards set?

What is used as the standard unit of color?What is used as the standard unit of color?

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TURBIDITYTURBIDITY

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Turbid means waters containing suspended matter that interferes with the passage of light through the water or in which visual depth is restricted.

Turbidity is an expression of the optical propertyoptical propertythat causes light to be scattered and absorbed rather than transmitted in straight lines through the sample.

General ConsiderationsGeneral Considerations

Definition of TurbidityDefinition of Turbidity

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Turbidity in water may be caused by a wide variety of suspended mattersuspended matter, such as clay, silt, finely divided organic and inorganic matter, solublesoluble colored organic compounds, and other organisms.

Under flood conditions, great amounts of topsoil topsoil are washed to receiving streams. As the rivers pass through urban areas, the domestic and industrial wastewaters wastewaters may be added.

Causes for TurbidityCauses for Turbidity

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Environmental SignificanceEnvironmental Significance

Turbidity is an important consideration in public water supplies.

People: People will automatically associated turbidity in the drinking water with possible wastewater pollution and the possible wastewater pollution and the health hazardshealth hazards occasioned by it.

Water treatment facilities:When turbidity increases, filtrationfiltration of water get more difficult and costly. When turbidity increases, disinfectiondisinfection of water may become ineffective.

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Regulation of U.S. EPARegulation of U.S. EPATurbidity in treated drinking water must never

exceed 0.3 NTU in 95 percent0.3 NTU in 95 percent of daily monitoring in one month.

Guideline of WHOGuideline of WHO5 NTU5 NTU is suggested as The turbidity limit for

drinking water, while 1 NTU1 NTU is recommended to achieve the adequate disinfecting safety.

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Standard Unit of TurbidityStandard Unit of Turbidity

Because of the wide variety of materials that cause turbidity in natural waters, it has been necessary to use an arbitrary standardarbitrary standard. The original standard chosen was

1 mg SiO2/l =1 unit of turbidity

and the silica used had to meet certain specifications as to particle size.

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Standard suspensions of pure silica were used originally to calibrate the Jackson candle Jackson candle turbidimeterturbidimeter, the former standard instrument for turbidity measurement.

The Jackson candle turbidimeter is reported in Jackson candle Jackson candle turbidimeterturbidimeter units (JTU)units (JTU) .

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The Jackson candle Jackson candle turbidimeterturbidimeter has been replaced by more reliable, sensitive, and easier to use instruments that depend upon the principle of nephelometrynephelometry.

As a standard reference material, SilicaSilica has been replaced by formazinformazin polymerpolymer. The formazin suspensions were first calibrated against the Jackson candle turbidimeter.

The standard nephelometry procedure is now reported in nephelometricnephelometric turbidity units (NTU)turbidity units (NTU)..

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Because the basic principles difference for Jackson candle turbidimeter method and nephelometric method, results got from the two methods can vary widely.

In order to avoid any confusion this may cause, turbidity measurements by the standard nephelometryprocedure are now reported in nephelometric turbidity units(NTUNTU), and the other one is reported in Jackson candle turbidimeter units(JTUJTU).

40 NTU are about equivalent to 40 JTU.40 NTU are about equivalent to 40 JTU.

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A particular formazin polymer suspension is used as a standard.

Method of Determination

Light Light ScourceScource

Sample Sample tanktank

detectordetector readoutreadout

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The current standard method for measurement of turbidity depends upon instruments that employ the principles of nephelometry. In the instrument, a light source illuminates the sample and one or more photoelectric detectors are used with a readout device to indicate the intensity of scattered light at right angles to the path of the incident light.

A particular formazin polymer suspension is used as a standard.

Method of Determination

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Turbidities as low as 0.02 NTU0.02 NTU can be determined by this procedure. Samples with turbidities greater than 40 NTU are diluted with turbidity-free water until values within the range of 30 to 40 NTU are obtained. The turbidity is then determined by multiplying the measured turbidity by the dilution factor.

The instruments can be automated to provide a automated to provide a continuous readingcontinuous reading of water turbidityof water turbidity for process control.

LOD of MethodLOD of Method

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Application of Turbidity Data

Turbidity measurements are of particular particular importance in the field of water supplyimportance in the field of water supply. They have limited use in the field of domestic and industrial waste treatment.

Designing a water treatment plant: Turbidity result is used in conjunction with other information to determine whether a supply requires special treatment special treatment by chemical coagulation and filtrationby chemical coagulation and filtration before it may be used for a public water supply.

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evaluating the treatment efficiency: Turbidity measurements are used to determine the effectiveness the effectiveness of the treatmentof the treatment produced with different chemicals and the dosages needed.

routine monitoring: Turbidity measurements also help to gauge the amount of chemicals needed from gauge the amount of chemicals needed from day to dayday to day in the operation of treatment works.

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Online Turbidity Analyzer

Portable Turbidimeter

HACH Turbidity Meter

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ProblemsProblemsDiscuss the nature of materials causing turbidity in Discuss the nature of materials causing turbidity in polluted river water.polluted river water.What limit is placed on turbidity in water supplies by What limit is placed on turbidity in water supplies by the present standards and why has such a limit been the present standards and why has such a limit been set?set?In what field that turbidity measurements are often used?In what field that turbidity measurements are often used?WhatWhat’’s the usage of the measurement of turbidity in s the usage of the measurement of turbidity in water treatment process?water treatment process?