CHAPTER – IV QUALITY OF WATER 4.1 Impurities in water, their classification and effects 4.1.1 Suspended Impurities E.g. sand, silt, algae, virus Characteristics:
They develop colour. They make turbidity high. Suspended impurity is measured in terms of turbidity. They develop taste. They invite diseases. They are macroscopic or can be microscopic.
Removed by: Sedimentation or Chemical Treatment 4.1.2 Colloidal Impurities
Microscopic. Their size is between 10-3 mm to 10-6 mm. Not removed by sedimentation Develop charges (anions) Cause colour in water and these impurities cause epidemics. Have much less weight They come in motion due to repulsion.
Removed by: +ve charge for neutralization and settlement 4.1.3 Dissolved Impurities Dissolved impurities make bad taste, hardness and alkalinity. The concentration is measured in PPM (parts per million) or mg/l and obtained by weighing the residue after evaporation of the water sample from a filtered sample. a. Salts of Ca and Mg b. Minerals c. Gases Constituents a. Calcium and Magnesium i. Bicarbonate ii. Carbonate iii. Sulphate iv. Chloride b. Metals and Compounds i. Lead
Effects Alkalinity Alkalinity and hardness Hardness Hardness, corrosion Cumulative poisoning
ii. iii. iv. v. vi. vii. viii. ix. x. xi.
Arsenic Iron Oxide Manganese Barium Cadmium Cyanide Boron Selenium Silver Nitrates
Toxicity, poisoning Taste, red colour, corrosiveness, hardness Black or brown colour Toxic effect on heart, nerves Toxic, illness Fatal Affects central nervous system Highly toxic to animals and fish Discoloration of skin, eyes Blue baby condition, infant poisoning, colour and acidity
c. Gases i. Oxygen ii. Carbon iii. Hydrogen Sulphide
Corrosive to metals Acidity, corrosiveness Odour, acidity and corrosiveness
4.2 Hardness and Alkalinity Water is said to be ‘hard’ when it contains relatively large amounts of bicarbonates, carbonates, sulphates and chlorides of calcium and magnesium dissolved in it. It is the property that prevents lathering of soap. 4.2.1 Types of Hardness
Types of Hardness
Permanent Hardness
Temporary Hardness
Permanent hardness is due to the presence of sulphates, chlorides and nitrates of calcium and magnesium and is also known as ‘non-carbonate hardness’ (NCH). Permanent hardness can’t be removed by simple boiling but requires special treatment of softening. Temporary hardness is known as ‘carbonate hardness’ (CH) and due to the presence of carbonates and bicarbonates of calcium and magnesium. It can be removed by boiling or by adding lime. On boiling, CO2 escapes and insoluble CaCO3 gets precipitated. So, temporary hardness causes deposition of Ca scales in boilers. Total Hardness (TH) = CH + NCH
Where, ion = Mg, Ca, Sr (Strontium) Eq. wt. of Mg = 12.2, Eq. wt. of Ca = 20, Eq. wt. of Sr = 43.8, Eq. wt. of CaCO3 = 50 Effects of Hardness: 1. Wasteful consumption of soap while washing and bathing. 2. Modifies colour if used in dyeing work and washing clothes. 3. Produces scale in steam boiler and its pipe which reduces heat transfer and finally causes leak. 4. Causes corrosion and incrustation of pipelines and fittings. 5. Scale formation further causes corrosion, caustic brittleness, decreases efficiency and danger of burst of pipe line and boiler. 6. Makes food tasteless, more fuel consumption and causes bad effects to our digestive system. Measurement of Hardness in Water: Hardness of water is measured in ppm or mg/l of calcium carbonate present in water. Range (mg/l) Hardness Level
0 – 50 Soft
50 – 100 100 – 150 150 – 250 > 250 Moderately Slightly Hard Moderately Hard Soft Hard The hardness of water is also expressed as the degree of hardness. It may be Clark Scale, French Scale or American Scale. Clark’s Scale: 1° Cl = Power of soap destroying is equivalent to the effect of 14.254 mg of calcium carbonate present in one litre of water which causes wastage of about 0.6 gm of soap in 1 litre of water (i.e. 14.254 ppm). French Scale: 1° Fr = Power of soap destroying is equivalent to the effect of 10 mg of calcium carbonate present in one litre of water. American Scale: 1° Am = Power of soap destroying is equivalent to the effect of 17.15 mg of calcium carbonate present in one litre of water. 4.2.2 Types of Alkalinity Alkalinity is a measure of the acid-neutralizing capacity of water. It is an aggregate of the sum of all titratable bases in the sample. When pH of water is > 7, it is said to be alkaline. Alkalinity --
-
in most natural waters is due to the presence of carbonate (CO3 ), bicarbonate (HCO3 ), and -
hydroxyl (OH ) anions.
Alkalinity
Alkalinity due to Bicarbonate
Alkalinity due to Carbonate [ [
] ]
Alkalinity caused by hydroxides is called hydroxide alkalinity or caustic alkalinity, caused by carbonate is carbonate alkalinity and caused by bicarbonate is called bicarbonate alkalinity. 4.2.3 Relation between Hardness and Alkalinity 1.
When Total Hardness > Total Alkalinity CH = Total Alkalinity NCH = TH – CH
2. When Total Hardness ≤ Total Alkalinity CH = TH NCH = 0 Problem: The analysis of water from a well shows the following results in mg/l. ++ ++ + + --Ca = 65, Mg = 51, Na = 100, K = 25, HCO3 = 248, SO4 = 220, Cl = 18, CO3 = 240
Find Total Hardness (TH), Carbonate Hardness (CH) and Non-Carbonate Hardness (NCH). Solution:
Here, TA > TH Hence, Carbonate Hardness (CH) = Total Hardness (TH) = 371.52 mg/l
Non-Carbonate Hardness (NCH) = 0
1.
++ ++ The analysis of a water sample shows the following results in mg/l. Ca = 7, Mg = + + -12, Na = 20, K = 25, HCO3 = 68, SO4 = 7, Cl = 40. The concentration of Sr is equal
to hardness of 2.52 mg/l and the carbonate alkalinity in water is zero. Calculate TH, CH and NCH. 2. Total hardness obtained from the analysis of water is found to be 117 mg/l. The analysis further showed that the concentrations of all the three principle cations causing hardness are numerically same. If the value of CH = 57 mg/l, calculate: i. NCH. ii. The concentration of principle cation (Ca, Mg, Sr) iii. Total Alkalinity (TA) 4.3 Living Organisms in Water a. b. c. d.
Algae Bacteria Virus Helminthes or Worms
(Refer descriptions in any book.) 4.4 Water Related Diseases 4.4.1 Water borne Diseases Water borne diseases are caused due to drinking water contaminated with pathogenic microorganisms. Some of the most common water borne diseases are typhoid fever, dysentery (amoebic and bacillary), gastro-enteritis, infectious hepatitis, schistosomiasis, etc.
Water borne diseases
Bacterial diseases
Protozoal diseases
Virus diseases
Helminthic (worm) diseases
a. BACTERIAL DISEASES: Botulism, Cholera, E. coli infection, Dysentery, Typhoid fever b. PROTOZOAL DISEASES: Amoebiasis, Giardiasis c. VIRUS DISEASES: SARS (Severe Acute Respiratory Syndrome), Hepatitis A, Poliomyelitis
d. HELMINTHIC DISEASES: Schistosomiasis, Swimmer’s itch 4.4.2 Water washed/hygiene Diseases Water washed diseases are caused by poor personal hygiene and skin or eye contact with contaminated water. Examples of water washed diseases include scabies, trachoma and flea, lice and tick-borne diseases. 4.4.3 Water based Diseases Water-based diseases are caused by parasites found in intermediate organisms living in contaminated water. Examples include dracunculiasis, schistosomiasis and other helminthes. These diseases are usually passed to humans when they drink contaminated water or use it for washing. ** Schistosomiasis is a water-based disease which is considered the second most important parasitic infection after malaria in terms of public health and economic impact. 4.4.4 Water vector Diseases
Due to vector like mosquitoes
E.g. malaria (mosquito injects protozoa), filariasis (elephantiasis) – mosquito carrier, no circulation of blood in joints, swelling of body parts 4.4.5 Transmission Routes Transmission routes refer to the ways in which a healthy person gets attacked by diseases. a. Faecal-oral route b. Penetration of skin c. Due to vector
4.4.6 Preventive Measures
Improve the quality of drinking water at source, at the tap, or in the storage vessel Interrupting the routes of transmission Protecting food from flies interrupts the faeces-flies-food route (at a household level). Chlorination of water interrupts the faeces-fluids-food and drinking water route (at the community level). Increase the quantity of water available. This allows better hygiene and can thus prevent disease transmission from contaminated hands, food or household utensils. Changing hygiene behaviour. Care in disposing of faeces. Safe and protective measures should be adopted to avoid contamination and to destroy infectious organisms while handling and disposing of infant and toddler faeces. Proper use and maintenance of water supply and sanitation systems. Good food hygiene.
4.5 Examination of Water 4.5.1 Physical Examination of Water (tests for temperature, colour and turbidity)
1. Test for temperature The temperature of water to be supplied should be between 10°C to 20°C. Temperature higher than 25°C is considered objectionable. Temperature of water can be measured with ordinary thermometers graduated in 0.1°C, range from 0 to 50°C. At depths greater than 15m, a thermocouple may be used.
2. Test for colour Colour can be measured against various standards or scales such as Hazen or Platinic Chloride Scale, Burgess Scale or Cobalt Scale using a tintometer. In older days, test for colour of water was performed solely through visual inspection. Test for Colour by Tintometer: 1. First, the apparent colour of water due to turbidity is removed by centrifuging. 2. A tintometer has an eye-piece with two holes. 3. A slide of the standard coloured water is seen through one hole, while the slide of the water to be tested is seen through the other hole. 4. A number of slides of standard colour in water are kept ready for comparison. 5. The intensity of colour in water is measured in terms of arbitrary unit of colour on the cobalt scale. 3. Test for Turbidity Turbidity is a measure of resistance of passing of light through water. It is imparted by the colloidal matter present in water. Units of turbidity in older days:
i. ii. iii. iv.
ppm in silica scale JTU (Jackson Turbidity Unit) FTU (Formagen Turbidity Unit) NTU (Nephelometric Turbidity Unit)
Equipment: Turbidity Meter 4.5.2 Chemical Examination of Water (tests for pH, suspended, dissolved and total solids) 1.
Test for pH
The hydrogen-ion concentration or pH value of water is a measure of degree of acidity or alkalinity of water. For water at 21°C, +
-
(H ) x (OH ) = 10
-14
Water becomes acidic when concentration of H ions is increased and alkaline when concentration of H ions is decreased. ( )
( )
For pure water, pH = 7. For water with maximum acidity, pH value is zero, while for water with maximum alkalinity, pH value is 14. For potable waters, the pH value should between 6 and 9, and preferable between 7 and 8.5. 2. Tests for Solids in Water Total Solids - all solids in water. Total solids are measured by evaporating all of the water out of a sample and weighing the solids which remain. Dissolved Solids - solids which are dissolved in the water and would pass through a filter. Dissolved solids are measured by passing the sample though a filter, they drying the water which passes through. The solids remaining after the filtered water is dried are the dissolved solids. Suspended Solids - solids which are suspended in the water and would be caught by a filter. Suspended solids are measured by passing sample water through a filter. The solids caught by the filter, once dried, are the suspended solids. Settleable solids - suspended solids which would settle out of the water if given enough time. Settleable solids are measured by allowing the sample water to settle for fifteen minutes, then by recording the volume of solids which have settled to the bottom of the sample. Nonsettleable solids - suspended solids which are too small and light to settle out of the water, also known as colloidal solids. Nonsettleable solids are measured by subtracting the amount of settleable solids from the amount of suspended solids.
The amount of total solids should preferable be less than 500 ppm. 4.5.3 Biological Examination of Water (multiple tube and membrane fermentation method), most probable number
MULTIPLE TUBE FERMENTATION TECHNIQUE The coliform group of bacteria is defined as all aerobic and facultative anaerobic, gramnegative, rod-shaped bacteria that ferment lactose with gas and acid formation within 48 hours at 35°C. 1.
Presumptive Phase
This test is based on the ability of coliform group (E-coli) to ferment the lactose broth and producing gas. Procedure: i.
ii. iii.
Definite amount of diluted samples of water are taken in multiples of ten, such as 0.1 ml, 1.0 ml, 10 ml etc. Then, the samples are placed in standard fermentation tubes containing lactose broth and then kept in the incubator at a temperature of 37°C for a period of 48 hours. If gas formed is seen in the tubes, it is the indication of presence of E. coli group and result is +ve. If no gas is formed, the result is _ve. –ve result in presumptive test indicates the water is fit for drinking.
2. Confirmed Phase The other bacteria than E. coli present also may ferment in presumptive test so the confirmed test to indicate E. coli is necessary. This test consists of growing cultures of coliforms on media which suppress the growth of other organisms. Procedure: i.
ii.
Small amount of incubated sample showing gas in presumptive test is carefully transferred to another fermentation medium containing brilliant green lactose bile broth and placed in the incubator at 37°C for a period of 48 hours. If the gas is formed, there is presence of E. coli and then step 2 is followed. Again the small portion of incubated material showing gas in presumptive test is marked as streaks on the plates containing Endo or Eosin-methylene blue agar and the plates are kept in the incubator at 37°C for a period of 24 hours. If colonies of bacteria are seen after this period, it indicates the presence of E. coli and completed test is necessary.
3. Completed Phase This test is based on the ability of the culture grown in the confirmed test to again ferment the lactose broth.
Procedure: i. ii.
iii.
The bacterial colonies or cultures grown in the confirmed test are kept into lactose broth fermentation tubes and agar tubes. The tubes are then kept in the incubator at 37°C for a period of 24 to 48 hours. If gases are seen in tubes after this period, it indicates the presence of E. coli and the test is +ve and it contains the pathogens, then detailed tests are necessary for pathogens. If result is –ve, it indicates the absence of E. coli and hence absence of pathogens.
Example: If we take 10 test tubes out of which 3 test tubes are positive after third test and in each test tube, 1 ml of sample is kept, No. of positive tubes = 3 ml of sample in negative tubes = 7 ml of sample in all tubes = 10
√
MEMBRANE FILTRATION TECHNIQUE The coliform group may be defined as comprising all aerobic and many facultative anaerobic, gram -ve, rod-shaped bacteria that develop a red colony with a metallic sheen within 24 hours at 35°C on an Endo-type medium containing lactose.
Take 50 ml sample of water and a filter paper. The water is filtered through the filter paper. Filter paper is kept in petidions glass plate along with M. Endo medium. Incubate at 35°C for 20 hours. We can observe colonies of coliform.
where, x = sample
Problems:
In water treatment plant, the pH values of incoming and outgoing waters are 7.3 and 8.5 respectively. Assuming a linear variation of pH with time, determine the average pH value of time. There are two samples A and B of water, having pH values of 4.4 and 6.4 respectively. Calculate how many times sample A is acidic than sample B. Find out the pH of a mixture formed by mixing the following two solutions. Vol. 300 ml - pH = 7, Vol. 700 ml - pH = 5.
4.6 Water Quality Standard for Drinking Purpose (refer from any book)
