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Safe Drinking water : Building block for sustainability
More than 5 million people die each yearly due to diseases caused by unsafe
drinking water (WHO & Johannesburg Summit 2002)
California think - 76 million children could die worldwide from water-borne
diseases by 2020 if adequate safeguards are not taken
Delhi water supply- Carcinogenic substances in potable water five times higher
than WHO standards.
Disinfection - Health point and to control the spread of diseases
Chlorine- popular disinfectant (Good or Bad?) & Disinfection by- products (DBP’s)
• To determine the concentration of selected parameters of chlorinated
compounds in drinking water with the help of spectrophotometer
• Free chlorine, Total chlorine, Monochloramine & Chlorine dioxide
• Comparing the obtained results with the standards given by Govt. of India,
WHO & USEPA.
Chlorine water reactions
Free available chlorine-
Cl2 + H2O HOCl + H+ + Cl-
HOCl H+ + OCl- (Hypochlorite ions)
Free available chlorine = Hypochlorous acid and Hypochlorite ions
Combined available chlorine
Cl2 + H2O HOCl + HCl
NH3 + HOCl NH2Cl + H2O (Monochloramine)
NH2CL + HOCl NHCl2 + H2O (Dichloramine)
NHCl2 + HOCl NCl3 + H2O (Trichloramine)
Source: CPHEEO Manual, 1999 & B K Bhole 2000
Equipment's & Materials
(HACH) DR 2400 spectrophotometer and distilled water
Chlorine demand free glassware.
Pipettes for 0.1ml, 1ml and 10 ml capacity and conical flasks.
Analytical balance GF series GF 300 & Vensar make pH meter.
DPD (N, N-diethyl-p-phenylenediamine) method
• Given by AWWA, APHA & 4500 Cl (G)
• Chlorine (hypochlorite ion, hypochlorous acid) and chloramines
stoichiometrically liberate iodine from potassium iodide at pH 6.2 to 6.5
• The liberated iodine reacts with N, N-diethyl-p phenylenediamine (DPD) to
produce a pink or red colored solution.
• Wavelength range 515 nm.
• Parameters Can be tested- Free, Combine & Total Chlorine.
Source: Standard methods, 4500 Cl , (G) and DPD Method, APHA, AWWA
Calibration of Spectrophotometer
By the use of potassium permanganate solution as equivalent to Chlorine
Standards are made by serial diluting (0.891 gm. to 1000 ml deionized water
[1000 mg /l as cl2])
The color is produced by adding Buffer & DPD indicator
Standards from 0.05 - 2 mg/l
0.0 0.5 1.0 1.5 2.0 2.5
Concentration Vs. Absorbance
Source: Standard methods, 4500 Cl (G), DPD Method, Calibration of Spectrophotometer, APHA, AWWA
Flow sheet for determination of free chlorine by spectrophoometer
0.5 ml phosphate buffer to
10 ml cuvette.
0.5 ml N, N Diethyl-p-
10 ml water sample to the
cuvette and mix.
10 ml water sample to the
cuvette as a blank with no
addition of reagents.
Development of Colour
Flow sheet for determination of Total chlorine by spectrophotometer
Add 0.5 ml phosphate buffer to 10 ml cuvette to adjust the pH
to 6.2 -6.5
Add 0.5 ml N, N Diethyl-p-phynelenediamine [DPD] indicator
to the spectrophotometer cuvette.
Add 0.1 gm. Potassium iodide or KI crystals to the cuvette.
Place10 ml water sample to the cuvette. Mix well & Wait for 2
Fill another 10 ml sample as a blank with no addition of
Add 0.5 ml phosphate buffer to 10 ml cuvette to adjust the
pH to 6.2 -6.5
Add 0.5 ml N, N Diethyl-p-phynelenediamine [DPD]
indicator to the spectrophotometer cuvette.
Place10 ml water sample to the cuvette. Mix well & Wait
for 2 min. Fill another 10 ml sample as a blank with no
addition of reagents
Read the reading for blank as 0.00mg/l. Place the prepared
sample in the spectrophotometer and read concentration of
Continue by adding the 0.1 mg Potassium Iodide or KI
crystal. Read the reading for blank as 0.00mg/l and read
the concentration of Monochloramine
Flow sheet for determination of Monochloramine by spectrophotometer
DPD (N, N-diethyl-p-phenylenediamine) method for
• Given by AWWA, APHA & 4500 ClO2 (D)
• Chlorine dioxide reacts with DPD (N, N-diethyl-p-phenylenediamine) to
the extent of one-fifth of its total available chlorine content corresponding
to reduction of chlorine dioxide to chlorite to form a pink colour.
• The colour intensity is proportional to the ClO2 in the sample.
• Chlorine interference is eliminated by adding glycine, which converts free
chlorine to chloroaminoacetic acid, but has no effect on chlorine dioxide at
the test pH.
• Wavelength range 515 nm
Source: Standard methods, 4500 ClO2 (D), DPD Method , APHA, AWWA
Flow sheet for determination of Chlorine dioxide by spectrophotometer
Add 10 ml water sample to the cuvette and
add 0.2ml glycine then mix.
Add 0.5 ml phosphate buffer and DPD
indicator to another the cuvette and mix well.
Add glycine treated sample to the buffer/
indicator cuvette and mix well. Wait for 30
sec for proper mixing and colour
Fill another cuvette with the 10 ml sample as
a blank with no addition of reagents. &
Read blank sample.
Sampling of Potable Water
Area under Greater Mumbai Municipal Corporation
Standard sampling procedure [CPHEEO, 1999]
Brown amber 350 ml glass sampling bottles
3 samples from each station
Sample no.1- Residential areas
Sample no.2 - Commercial areas
Sample no 3 - Public places (Railway stations)
• The water is supplied to the Mumbai is from the Bhandup water treatment
• The capacity of Bhandup water treatment plant is about 1950 MLD
• The free chlorine concentration is go on continuously decreasing as the
water passes through water treatment plant to the distribution system
• The chlorine concentration is higher in the Bhandup, Mulund, Kanjurmarg
area and after it is go on decreasing up to CST Mumbai
• The Bhandup water treatment plant(WTP) is using chlorine for disinfection
• The water supply pipelines in Mumbai are very old age and there are
leakages in the water supply pipelines and are increasing day by day
• There are chances of leakages in the water distribution system which
causes the contamination of organic matter through it & chances of
ammonia formation are there
• Hence chances of formation of Monochloramines in the water cannot be
Parameter Concentration as per
HACH reagents (mg/l)
Concentration as per
Prepared reagents (mg/l)
Free Chlorine 0.10 0.16
Total Chlorine 0.40 0.47
Monochloramine 0.02 0.09
Chlorine Dioixide 0.01 0.06
Cost comparison for prepared and HACH reagents
(Cost of analysis per sample)
Parameter HACH Reagents (Rs.) Prepared reagents (Rs.)
Free Chlorine 21/- 1.20/-
Total Chlorine 21/- 1.30/-
Monochloramine 104/- 1.30/-
Chlorine Dioixide 35/- 1.50/-
• Difference - due to the presence of interfering agent
• The prepared reagents- obtaining a rough idea about the presence of
• Reasonable accuracy of the results with the great saving in cost
• Periodic calibration of the prepared reagents is important for accuracy of
laboratory results are acceptable
Chlorine compounds or disinfection by-products levels less than the
Central Public Health and Environmental Engineering Organisation
(CPHEEO), World health organisation (WHO) and US Environmental
protection agency (USEPA) standards.
Quality of potable water from central suburbs are comparatively better than
The amount of free chlorine reduces as the distance from Bhandup water
treatment plant increases.
Laboratory chemicals as given by the standard methods are fairly accurate.
The cost of sample analysis for prepared reagents is much lower.
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Standard Potassium Permanganate Solution (Equivalent to