1- Turbidity
1. Scope
This procedure applies to all type of water samples either drinking water and wastewater samples to measure turbidity.
2. Definition
Turbidity: is a measure of an optical property that causes light to be scattered rather than transmitted in straight lines through a sample.
3. Principle
Suspended matter such as clay, silt, finely divided organic and inorganic matter, Planktons and microscopic organisms cause turbidity in water.
This method is based on a comparison of intensity of light scattered by a standard reference suspension under the same conditions. The higher the intensity of scattered light, the higher the turbidity. Formazin polymer is used as the primary standard reference suspension.
4. Interference
Turbidity can be determined for any water sample that is free of debris and rapidly settling coarse sediment. Dirty glassware and the presence of air bubbles give false results. ‘‘True color,’’ i.e., water color due to dissolved substances that absorb light, causes measured turbidities to be low. This effect usually is not significant in treated water .
5. Equipments
- HACH Model 2100 NTU Turbidimeter . - Turbidity tube with cover.
6. Chemical and reagents
a. Dilution water: High-purity water will cause some light scattering, which is detected by nephelometers as turbidity
b. the laboratory-formazin standards 1, 20, 200, 1000 and 4000 NTU
7. Procedure
Calibrate the Turbidimeter with formazin standards each according to instrument manual instructions: 1- Switch On the Instrument from the I/O switch.
2 – Select: * Measurement unit : NTU
7.1 Measurement
1 – Fill the sample cell to the line (approximately 10 mL), cap the sample cell.
2 – Hold the sample cell by the cap, and wipe to remove water spots and fingerprints.
3 - Gently mix the sample cells by inversion to homogenize the sample, be sure to eliminate the air bubbles.
4 – Apply a thin bead of silicone oil from the top to bottom of the cell just enough to coat the cell with a thin layer of oil. Using the oiling cloth provided spread the oil uniformly, then wipe off the excess. The cell should appear nearly dry.
5 – Insert the cell in the cell holder, and press the key.
6 – The instrument displays the turbidity measure of the sample in NTUs (Nephelometric turbidity units) Note: The instrument’s response time is 8 seconds.
8. Calculations
Sample results are read directly from the meter display.
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