PHYSICAL, CHEMICAL & BACTERIOLOGICAL

CONTAMINATION OF WATER AND WATER QUALITY

STANDARDS

Distribution of water on earth

Ocean and sea - 97%

Snow and ice caps - 2%

Rivers,lakes, Ground water - 1%

UNIVERSAL SOLVENT

QUALITY DEMERIT

45 LAC WELLS AND

50 LAC SEPTIC TANKS ( ?)

contamination

Geological

Human activities

. Organic waste Industrial waste

Aquifiers

Safe drinking water

Free from pathogenic organisms Clear Not saline Free from offensive taste or

smell Free from compounds that may

have adverse effect on human health

Free from chemicals that cause corrosion of water supply systems

WATER QUALITY PARAMETERS Physical parameters Chemical Bacteriological

Colour

May be due to the Presence of organic matter,metals(iron, manganese) or highly coloured industrial waste

Aesthetically displeasing Disirable that drinking water be

colourless Disirable limit, 5 Hazen unit Permissible limit 25 Hazen Unit

Taste and Odour

Mainly due to organic substances, ,Biological activity, industrial pollution

Taste buds in the oral cavity specially detect inorganic compounds of metals like magnesium, calcium, sodium, copper, iron and zinc

Water should be free from objectionable taste and odour.

Turbidity

Caused by suspended matter High level turbidity shield and

protect bacteria from the action of disinfecting agents

Disirable limit-5NTU should be below 1 NTU when

disinfection is practiced Permissible limit-10NTU

pH

It is the measure of hydrogen ion concentration

Neutral water pH-7 Acidic water has pH below 7 Basic water has pH above 7 Disirable limit 6.5-8.5 Beyond this

limit the water will affect the mucous membrane and water supply system

Substances that change pH of water

Acidic Industries Sugar - 5 – 6 Distillery 3 - 4 Electro- Plating unit 2.5-4 Pickle 2 - 3

Basic

Paper 8 – 10

Textile 8.5-11

Fertiliser 6.5- 9

Oil Refine- ries 6.5-

9.5

Battery acids

<1.0 Milk 6.7

Carbonated Beverages

2 – 4 Rain water 6.5

Lemon juice

2.3 Blood 7.5

Orange juice

4.2 Sea water

8.0

Vinegar 3 Ammonia solution

11.3

Domestic sewage

6.5-8.5 Ground water

7.5-8.5

HARDNESS

Capacity of water for reducing and destroying the lather of soap

It is total concentration of calcium and magnesium ions

Temporary hardness – Bicarbonates of Calcium and Magnesium

Permanent hardness – Sulphates, chlorides and nitrates of calcium and magnesium

Hardness – contd…

0 – 50 mg/l - soft 50 – 150 mg/l - moderately hard 150 – 300 mg/l - hard 300 above - very hard Surface water is softer than ground

water Causes encrustations in water supply

structures

ALKALINITY Capacity to nutralise acid Presence of carbonates, bi-

carbonates and hydroxide compounds of Ca, Mg, Na and K

Alkalinity = hardness, Ca and Mg salts

Alkalinity > hardness - presence of basic salts, Na, K along with Ca and Mg

Alkalinity < hardness – neutral salts of Ca & Mg present

IRON One of the earth’s most plentiful

resource

High iron causes brown or yellow staining of laundry, household fixtures

Metalic taste, offensive odour, poor tasting coffee

Cause iron bacteria

Acceptable limit – 0.3 mg / l

CHLORIDE Causes Dissolution of salt deposit Discharge of effluents Intrusion of sea water Not harmful to human beings Regarding irrigation – most

troublesome anion Acceptable limit - 250 mg/l

NITRATE

Increasing level of nitrate is due to

Agricultural fertilizers, manure,animal dung, nitrogenous material ,sewage pollution

(blue baby diseases to infants)

Maximum permissible limit 45 mg / l

FLOURIDE Occurs naturally Long term consumption above

permissible level can cause – dental flurosis (molting of teeth) Skeletal flurosis Acceptable limit – 1 mg / l Maximum permissible limit – 1.5 mg /

l Remedy – 1) Deflouridation 2) Mixing Fluride free

water 3) Intake of vitamin C,D,

calcium,antioxidants

FLOURIDE CAUSES

Three types of Fluorosis

1. Dental Fluorosis

2. Skeletal Fluorosis

3. Non-skeletal Fluorosis

ARSENIC

Occur in ground water from arseniferous belt

Industrial waste, agricultural insecticide

High arsenic causes 1) various type of dermatological lesions, muscular weakness, paralysis of lower limbs, can also cause skin and lung cancer

Acceptable limit – 0.05 mg / l

Heavy Metals

Present as mineral in soil and rocks of earth

Human activities Battery – Lead & Nickel Textile - Copper Photography – Silver Steel production – Iron

Pesticides

Cancer Birth defects Blood disorder Nervous disorder Genetic damage

Essential bacteriological Standards

Characteristics Number / 100 ml

Treated water in distribution system

Feacal coliform zero Total coliform not more than 10 Total coliform should not be detectible in two consecutive samples

RESIDUAL CHLORINE

Chlorine added to water forms hypochlorite ions and hypochlorite acids

Chlorine demand – Quantity required for killing micro organisms and reacting with ammonia, organic compounds etc.

Free residual chlorine – To take care of post contamination

Desirable – 0.2 mg / liter

Common problems contd

Visible effects Reasons

water turns black,smell

Waste water

Acidic taste Low pH

Alkaline taste High pH

Boiled Rice hard and yellow

High Alkalinity

White deposits on boiling

Hardness

Common problems

Visible effects Reason

Iron taste, change in colour after exposure to atmosphere, change in colour of cloths,utensils Oily appea- rance on top of water body

Iron

Soap not lathering hardness

Brownish black streaks on teeth

`Fluride

Growth of Algae Nitrate, phosphate

Fish kills Low pH less DO

Salty taste chloride

Measures of Water Quality

Some of the Most basic and Important Measures

Dissolved OxygenBiochemical Oxygen DemandSolidsNitrogenBacteriological

Dissolved Oxygen (DO)

Typically Measured by DO probe and Meter

Electrochemical Half Cell Reaction

Biochemical Oxygen Demand (BOD)

Amount of oxygen used by microorganisms to decompose organic matter in a water

Theoretical BOD can be determined by balancing a chemical equation in which all organic matter is converted to CO2

Calculate the theoretical oxygen demand of 1.67 x 10-3 moles of glucose (C6H12O6):

C6H12O6 + O2 CO2 + H2O general, unbalanced eqn

C6H12O6 + 6 O2 6 CO2 + 6 H2O

1.67x 10-3moles glucose/L x 6 moles O2/ mole glucose x 32 g O2/mole O2

= 0.321 g O2/L = 321 mg O2/L

BOD Test

Dark

20oC

Time

Standard – 5 days

Ultimate

BOD = I - F

I = Initial DOF = Final DO

If all the DO is used up the test is invalid, as in B above

To get a valid test dilute the sample, as in C above. In this case the sample was diluted by 1:10. The BOD can then be calculated by:

BOD = (I – F) D D = dilution as a fraction

D = volume of bottle/(volume of bottle – volume of dilution water)

BOD = (8 – 4) 10 = 40 mg/L

For the BOD test to work microorganisms have to be present.Sometimes they are not naturally present in a sample so we have to add them. This is called “seeding” a sample

If seed is added you may also be adding some BOD. We have to account for this in the BOD calculation:

BOD = [(I – F) – (I’ – F’)(X/Y)]D

Where:I’ = initial DO a bottle with only dilution water and seedF’ = final DO of bottle with only dilution water and seedX = amount of seeded dilution water in sample bottle, mlY = amount of seeded dilution water in bottle with only

seeded dilution water

Example

Calculate the BOD5 of a sample under the following conditions. Seeded dilution water at 20oC was saturated with DO initially. After 5 days a BOD bottle with only seeded dilution water had a DO of 8 mg/L. The sample was diluted 1:30 with seeded dilution water. The sample was saturated with DO at 20oC initially. After five days the DO of the sample was 2 mg/L.

Since a BOD bottle is 300 ml a 1:30 dilution would have 10 ml sample and 290 ml seeded dilution water.

From the table, at 20oC, DOsat = 9.07 mg/L

BOD5 = [(9.07 – 2) – (9.07 – 8)(290/300)] 30 = 174 mg/L