Turbidity and Colour PDF

Turbidity and Colour Turbidity Turbidity is the measure of relative clarity of a liquid. It is an optical characteristic of water and is a measurement of the amount of light that is scattered by material in the water when a light is shined through the water sample. Both the size and surface characte...

Turbidity and Colour Turbidity Turbidity is the measure of relative clarity of a liquid. It is an optical characteristic of water and is a measurement of the amount of light that is scattered by material in the water when a light is shined through the water sample. Both the size and surface characteristics of suspended materials influence the absorption and scattering of light through a water sample. The higher the intensity of scattered light, the higher the turbidity. The erosion of soil and the presence of excessive vegetable fibres and micro-organisms may cause turbidity. Usually, domestic and industrial wastewater contains soap, detergent and other emulsifying agents which produce stable colloids, and thus cause turbidity. Effects of Turbidity Turbidity of water is not only aesthetically displeasing, but also not acceptable to environmental engineers because of the fact that the colloidal materials associated with turbidity provide absorption sites for chemicals as well as micro-organisms that may be harmful. Turbidity reduces the efficiency of chlorination in water treatment plants and may interfere with the light penetration and photosynthesis in natural water bodies. 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, the causes of high turbidity can promote re-growth of pathogens in the water, leading to waterborne disease outbreaks, which have caused significant cases of intestinal sickness throughout the world. For use in textile processing, water must be clear. Turbidity may be due to large or small particles suspended in the water. The suspended matters are undesirable as they can adversely affect the quality of dyeing and finishing in wet processing. In boilers and cooling systems, they promote deposition of objectionable scale and increased carryover of solids in steam. Estimation of turbidity Turbidity makes water cloudy or opaque. The water collected in a bottle will be used to find out the turbidity, which is measured by shining a light through the water and is reported in Nephelometric turbidity units (NTU). The instrument used for measuring it is called nephelometer or turbidimeter, which measures the intensity of light scattered at 90 degrees as a beam of light passes through a water sample. The most widely used measurement unit for turbidity is the Formazin Turbidity Unit (FTU). ISO refers to its units as FNU (Formazin Nephelometric Units). ISO 7027 provides the method in water quality for the determination of turbidity. It is used to determine the concentration of suspended particles in a sample of water by measuring the incident light scattered at right angles from the sample. The scattered light is captured by a photodiode, which produces an electronic signal that is converted to turbidity. The unit used in the ancient times was JTU (Jackson Turbidity Units), measured with the Jackson candle turbidimeter. This unit is no longer in standard use. In lakes the turbidity is measured with a secchi disk. This is a black and white disk that is dropped in the water attached to a rope. The depth that the disk reaches before it disappears from sight is recorded. This provides an estimation of the turbidity level in the lake. A turbidity measurement could be used to provide an estimation of the TSS (Total Suspended Solids) concentration, which is otherwise a tedious and difficult parameter to measure. Normal range for turbidity in water Many drinking water utilities strive to achieve levels as low as 0.1 NTU. The European standards for turbidity state that it must be no more than 4 NTU. The World Health Organization establishes that the turbidity of drinking water should not be more than 5 NTU, and should ideally be below 1 NTU. Colour Natural water is normally colourless. However, occasionally it possesses objectionable colour due to dissolved or finely dispersed organic matters, and rarely due to mineral salts. Organic matters like algae, fungi and bacteria may build up during long storage. A tintometer may be used to measure colour in Hazen units by comparing it with a color of a standard solution. A Hazen unit is the color produced by dissolving 1 ppm platinum in the form of chloroplatinic acid, in the presence of 2 ppm cobalt chloride. Generally little is known about the composition of such colouring matters and these may create various problems in wet processing. Colour can also be measured in terms of absorbance values (optical density) at several wavelengths across the visible spectrum (at 50 to 100 nm intervals). The samples are to be filtered through a 0.45 mm filter before measurement. A peak at 500 nm denotes a red coloration, which usually causes public complaint.