Colour

December 4, 2016 4:30 pm

Natural color exists in water primarily as negatively charged colloidal particles. Because of this fact, its removal can usually be readily accomplished by coagulation with the aid of a salt having a trivalent metallic ion, such as aluminum or iron.

Color caused by suspended matter is referred as apparent color and is differentiated from color due to vegetable or organic extracts that are colloidal and which is called true color.

Range

Public Health Significance

The natural coloring materials, however, give a yellow-brownish appearance to the water, somewhat like that of urine & there is a natural reluctance to the part of water consumers to dink such waters because of the associations involved.

Disinfection by chlorination of waters containing natural organics results in the formation of chloroform, a problem of current concern.

Where waters are not aesthetically acceptable, consumers often shun safe domestic supplies and use waters from uncontrolled springs or private wells which may serve as foci for dissemination of pathogenic organisms. For this reason, waters intended for human use should not have a color exceeding 15 units.

Methods of Determination

Standard color solution

Water containing natural color are yellow-brownish in appearance. It has been found that solutions of potassium chloroplatinate (K2PtCl6) tinted with small amounts of cobalt chloride yield colors that are very much like the natural colors. The shading of the color can be varied to match natural hues very closely by increasing or decreasing the amount of cobaltchloride.

Methods applicable to Domestic and Industrial Wastewaters

Many industrial wastes are highly colored, and some contain colored substances that are quite resistant to biological destruction. Regulations concerning the color of effluents that may be discharged to streams are becoming more common. A system adopted by the International Commission on Illumination utilized characterization and measurement of color by spectrophotometric means is recommended in “Standard Methods.”

Interpretation & application of color data

Many industrial processes require the use of color free water. Removal of color is an expensive matter when capital investment and operating costs are considered. Therefore the water engineer, when developing or looking for new supplies, is always searching for a suitable supply with a color low enough so that chemical treatment will not be required. This “prospecting” may or may not be successful. If it is, he will use color data as one of the parameters to satisfy his client that expensive chemical treatment is not necessary. If it is not successful, he will use color data along with other information to prove that expensive chemical coagulation and sand filtration are needed to produce an acceptable supply.

Before a chemical treatment plant is designed, research should be conducted to ascertain the best chemicals to use and amounts required. In dealing with colored waters, color determinations serve as the basis of the decisions. Such data must be obtained proper selection of chemical feeding machinery and the design of storage space.

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

Conclusion

In water analysis it is important to differentiate between apparent and true color. Color intensity generally increases with increase in pH. For this reason recording pH along with color is advisable.

Disclaimer

The details given are for general understanding. References should be taken from respective authorized agencies.