DETERMINATION OF TURBIDITY

AIM: To determine turbidity of the given sample of water by using Nephelo turbidity meter.

APPARATUS: Nephelo turbidity meter, glass tubes, beakers

INTRODUCTION: Turbidity is the specialized term referring to the cloudness of a solution and it is a subjective characteristic which is imparted by solid particles obstructing the transmittance of light passing through a water sample. Turbidity regularly demonstrates the presence of suspended solids like earth material, silt, clay, organic matter green growth and different microorganisms.

PRINCIPLE: Turbidity is depends on the comparison of the intensity of light scattered by the sample under characterized conditions with the power of the light scattered by a standard reference suspension under the similar conditions. The turbidity of the sample is thus estimated from the amount of light scattered by the sample taking a reference with standard turbidity suspension. The higher the power of scattered light the more is the turbidity. For the primary standard reference suspension formazin polymer is used.The unit of turbidity is expressed on NTU (Nephelometric Turbidity Unit).

REAGENTS: 1) Hydrazine sulfate

 2) Hexamethelenetetramine

PREPARATION OF STOCK SOLUTION:

Step 1: First of all dissolve 1 gm hydrazine sulphate, (NH₂)₂ ·H₂SO₄, in distilled water after than dilute to 100 mL in a volumetric flask.

Step 2: Moving further dissolve 10 gm hexamethylenetetramine, (CH₂)₆N₄, in distilled water dilute to 100 mL in a volumetric flask.

Step 3: At last in a flask mix up both above solutions. Let stand for 24 h at 25 ± 3⁰C. This result in a 4000 NTU suspension. Transfer the stock suspension to the glass or other UV light blocking bottle for the storage purpose. The stock suspension is stable for the till one year if it is properly stored.

Preparation of standard solution from known turbidity of 4000 NTU is prepared previously. By dilution technique with distilled water prepared some other known reference standard solution with different various turbidity values for the purpose of calibration of Nephelo turbidity meter.

Stock suspension  (mL)	Distilled water Required to mix (mL)	Total Volume (mL)	Resulting Turbidity (NTU)
10.0	90.0	100	400
2.5	97.5	100	100

PROCEDURE:

 1.      Switch the instrument “ON” and permit 10-15 minutes warm up.

2.      Select (200 or 2000) RANGE on instrument.

3.      Set STANDARDIZE control to maximum.

4.      Insert curette with distilled water into cell holder and cover with light shield.

5.      Moving further “SET ZERO” control adjust the meter indication to read zero.

6.      Remove the curette and replace with curette containing standard solution (100 NTU or 400 NTU) aligning it as per the marking on cell holder.

7.      Adjust “STANDARD CONTROL” such that meter indicates “100” in accordance with a standard solution of the selected range.

8.      Replace test tube containing unknown solution and record the turbidity reading of the solution.

APPLICATION OF TURBIDITY DATA:

Ø  In water supply turbidity data information can be helpful to know the effectiveness and adequacy of the treatment delivered with various coagulants and the necessary doses.

Ø  Faulty operation of filter can be checked by estimating the turbidity of filtered water.

Ø  The effective removal of suspended solid from the waste can be known from the measurements of treated wastewater turbidity.

Ø  To produce great quality effluent by using least amount of chemical, the dose of chemical can be adjusted or balanced by turbidity information.

OBSERVATION TABLE:

Sr No.	Sample of description	Turbidity in ( NTU)

NOTE: According to  IS 10500:1991 maximum limit of turbidity is 10 NTU and upto 5 NTU water is acceptable and above 5 NTU the consumer acceptance decreases. Hence 0.1 NTU as a goal; less than 1 NTU as a standard and 5 NTU as a special case of consumable water. Turbidity is an indicator of poor treatment plant efficiency, filter run timing, contamination of distribution system and can fix the measurements of coagulants.