physical, chemical & bacteriological contamination of water and water quality standards
TRANSCRIPT
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