CU-521 ENVIRONMENTAL ENGINEERING-I

ENGR. IFTIKHAR AZIM Department of Civil Engineering, CECOS University Peshawar

CU-521 ENVIRONMENTAL ENGINEERING-I

EXPERIMENT #3 To determine the turbidity of a sample of water.

Prepared by: Engr.Iftikhar

Azim

Turbidity It is defined as a measure of visible materials in suspension in water

Turbidity is not a direct quantitative measure of suspended solids but the turbidity test is actually the relative clarity of water

Turbidity mostly occur in Surface Water

Causes of Turbidity Turbidity in drinking water can be naturally occurring. It is caused by matter such as;

Silt, sand and mud Organic and inorganic matter Bacteria and other germs Chemical precipitates

A clear mountain stream might have a turbidity of around 1 NTU whereas large river like River Kabul has turbidity of 774 NTU. (Source: Pakistan Council of Research in Water Resources)

Why we measure turbidity??

During the rainy season when mud and silt are washed into rivers and streams, high turbidity can quickly block filters and stop them from working effectively.

High turbidity will also fill tanks and pipes with mud and silt, and can damage valves and taps.

Where chlorination of water is practiced, even quite low turbidity will prevent the chlorine killing the germs in the water efficiently.

Continued… Turbidity is an important indicator of the amount of suspended sediments in water, which can have many negative effects on the aquatic life. It can block the sunlight which slows down photosynthesis and hence plant dies, reducing the amount of dissolved oxygen and increasing the acidity, both of which are harmful for aquatic animals

Determination of turbidity is a common component of water quality assessment

Standard guidelines for Turbidity

WHO suggests that water intended for drinking should have turbidity level < 5 NTU (for developing countries)

European Union (EU) Standards = 1 NTU

While in United States, < 1 NTU is recommended for drinking purposes

Units for Measurement of Turbidity:

The unit used to express turbidity depends upon the method used for its evaluation:

Standard Turbidity Unit (mg/l, ppm)

Jackson Turbidity Unit (JTU) Nephelometric Turbidity Unit (NTU)

Measurement of Turbidity

The stepwise procedure is as follows:

Switch on the power supply and check the battery of turbidity meter.

Now we have to calibrate the turbidity meter, for this purpose test tube containing distilled water in the test tube holder and close the test tube holder cover. Make sure that the mark on the test tube coincides with mark on panel.

Now standard Formazine solution of known turbidity is placed in the path of light rays and the scale is brought to the known value of the standard Formazine solution. Gently agitate the sample and wait for the air bubbles to disappear.

Place the sample in turbidity meter and close the cover

Allow the reading for a few seconds to become stabilize and then take it.

Precautions

Remove all moisture from the outside of the sample cell before placing it in the instrument as it will effect the turbidity measurement.

Remove air or other entrained gases in the sample before measurement.

Measure turbidity immediately to prevent temperature changes and particles flocculation and sedimentation due to changing sample characteristics.