Aim:

→ To determination of turbidity of given wastewater sample by nephelometrimeter. 

Principle:

→ Turbidity may be defined us interference to the passage of light by suspended particles in water.

→ It can be measured by its effect on the transmission which is termed as Turbidimetry by its effect on the scattering of light, which is termed as Nephelometay.

→ Turbidimeter can be used for sample with moderate tumbidity & Nephelometer for sample with low turbidity 

→ Higher the intensity of scattered light higher the turbidity.

→ The original standard choosen for turbidity was Sio2,

 1 mg SiO2/1 = 1 unit of Tumbidity 

→ The SiO 2 was originally used to calibrate the Jackson candle turbidity meter.

→ But Jackson candle turbidimetric unit (JTU) has been removed as standard method of turbidity measurement. 

→ The formazine standard of 40 NTV is equivalent to 40 JTU.

→ The lowest turbidity measured by Jackson candle tumbidikmeter is 25 JTU.

  • Light Source
  • Shit
  • Sample
  • Phototube 

Turbidimeter 

Interferences:

→ Dissolved material that imparts a colour to the wester may cause serious errors in nephelometric readings. 

→ Floating or suspended large particles & entrained air bubbles will give false or unstable results.

→ Certain turbulent motions also create unstable read- ing condition of nephelometer. 

Precautions:

→ Scratches, finger marks, or dist on the wall of the sample cell give erroneous readings. 

→ Cells should be kept scrupulously clean both inside & outside & discard when their is a scratch. 

Storage of Sample:

→ Determine the turbidity on the day the sample is taken. 

→ If this is not feasible, store the sample in the dasil for up 24h & refrigerate at 4°s if possible, but do not freeze.

 → Prolonged storage is not recommended because of irreversible changes. 

Preparation of Sample:

→ Bring the sample to room temperature & shake sample vigorously for at least one min.

→ Let the sample stand 2 to 3 min to allow air bubbles to disappear, then gently invent the sample several times Lor swirl, mix before examination.

Apparatus & Reagents:

1. Nephelometer: Range 0.05-40 NTV to as low as 0.05-1 NTU. 

2. Formazine Turbidity Suspension Stock: A stock turbidity suspension for formazine polymer is prepared by seating bydrazine sulphate with hexamethylene tetramine unden camefully controlled conditions. 

(a). Solution - I : Dissolve 1 g hydrazine sulphate [(NH2)2 H2SO4 ] & dilute to mark in 100 ml volumetric flask. 

(b) Solution - II : Dissolve 10.0 g hexamethylene tetramin & dilute to mark in a 100 mL volumetric flask.

(c) Solution-III: Mix 5 mL of solution - I & II, Allow to stand for 24 h at 25-to 28°c & dilute to 100 mL after reaction. 

→ This mixed solution will have turbidity of 400 units (NTU).

→ This 400 NTU stock to be prepared monthly. 

3. Formazine Turbidity suspension, standard (40 NTU) : 

→ Pipet 10 mL of 400 NTU stock into a 100 ml volume tric flask & dilute to 100 mL with water.  


Turbidity Summary: 

Caused by:

Suspended & colloidal matter such as clay, slit, organic e inorganic particulate plankton & other micro-organisms. 

Concentration Expected:

From almost Zero (0.05 NTU) in distilled water to over 1000 NTV in highly turbid waiter

Indicator of:

→ Necessity of treatment, potential contamination by pathogen: poor treatment plant efficiency-coagulant dosage, filter run timing contamination in distribution system. 

Test:

→ A physical & microbiological parameter, sample, inexpensive. mandated by public health regulation; expressed in the Nephelometric turbidity unit (NTU). 

NTU:

→ Turbidity unit measured by Nephelo metric standard method. 

Regulation:

0. I NTU a goal ; less than 1 NTU as a standard; 5 NTU as an exception for potable water. 

Application Of Turbidity Data:

(1) Water Supply: Turbidity measurements are used to determine the effectiveness of the treatment, produced with different coagulants & the dosages needed.

Turbidity measurements of the filtered water are needed to check on faulty filter operation.

(2) Domestic & Industrial Wastewater Treatment: 

→ To determine the effectiveness of suspended solids removal. 

→Chemical dosages can be adjusted to use the minimum amount of chemical while producing a high-quality effluent.