WATER QUALITY AND
WATER POLLUTION
IMPURITIES IN HYDROLOGIC CYCLE
Natural Impurities:
Dissolved Solids: TDS:
Ca, Mg, HCO
3
, Fe, Mn,
F, SO
4
, Cl, K, Mn,
Salt Water Intrusion
TDS:NaCl
Detergents-P
Human Waste: Organics,
N,P& Pathogens
Eutrophication
Stream Pollution
Industries:
heavy Metals.
Cr, Cd, Pb, Hg
SS, Pesticides, NOM
Bioaccumulation &
Biomagnification
Salinity
Size Classification of Impurities
10
-3
10
-2
1.0 10
10
2
10
3
Aqueous Salts Virus Protozoa Silt Sand
10
-4
Metal Ions
Trihalomethanes
Bacteria (Coliform)
Clay Cryptosporidium
Pesticides
Humic Acid
10
-1
Micrometer Scale
Precipitation
Oxidation
Reverse
Osmosis
Coagulation & Flocculation
Ultrafiltration &
Nanofiltration
Slow Sand Filtration
Ultrafiltration, Microfiltration
Sand Filtration
Dissolved Suspended Substances Colloids
Presence of impurities in such
quantity and of such nature
as to impair the use of water
for designated purpose
WATER POLLUTION
How Much ?? (mg/L) Organic, Inorganic, Color, Odor
Drinking, Bathing, Industrial use,
Fishing, Recreation
Water
Sectors of
usage
Pollutants
being contributed
Agriculture Pesticides, fertilizers, salts
Municipal Human waste
Power Plant Elevated temperature
Industry Variety of chemicals
Unsuitable for drinking, recreation, agriculture, industry
Diminishes aesthetic quality
Destruction of aquatic life
Eventually affect human health too/ Nobody escapes
Major categories of Water Pollutants
Pathogens Heat (Thermal Pollution)
O
2
Demanding Wastes Heavy Metals
Nutrients Pesticides
Salts Volatile Organic Compounds
Impurities/pollutants in water
Physical : Physical water quality
parameters
Chemical : Chemical water quality
parameters
Bacteriological: Bacteriological water
quality parameters
Biological : Biological water quality
parameters
Physical Water Quality Parameters
Parameters responding to the senses of
Sight: Suspended Solids (SS/TSS),
Turbidity and Color
Touch: Temperature (no source of cold water
emission)
Taste : Taste
Smell : Odor
Suspended Solids
Organic and inorganic particles suspended in water.
Settleable or non-settleable (Colloids)
Organic : Algal cell, bacteria, protozoa, plant fibers etc.,
Inorganic: Clay, Silt etc.,
Sources
storm water
wastes dumping
erosion
Measured by filtering a water sample,
drying (104
o
C,24 h) and weighing the filter, reported
in mg/l
Suspended Solids
Range: 0: Clear groundwater
300 mg/l sewage
1000 mg/l Monsoon rivers
100,000 mg/l Food industry
Problems: aesthetics
sedimentation
may exert oxygen demand
additional filtration/pre-treatment
Turbidity
Turbidity is the cloudiness or haziness of
a fluid caused by individual particles
(suspended solids) that are generally
invisible to the naked eye, similar to
smoke in air. The measurement of
turbidity is a key test of water quality.
Turbidity
Normally used for drinking water.
Imparts opaqueness & color
It is the measure of the extent to which light is absorbed or
scattered by suspended material in water.
Measured in NTU
Removed by Coagulation-Flocculation-Sedimentation and/or
Sand Filtration
Drinking water: less than 1 NTU
NTU: Nephelometric Turbidity Units
Equipment used : Nephelometer
Turbidity
Photomultiplier
Light Source
Sample Cell
Color
By organic debris, leaves, tannins (polyphenols),
humic acids: Natural color
Iron and Manganese: Brown & Blackish Color
Different types of industries impart different colors
Pulp & paper industry; sugar industry; textile industry
Aesthetic problem, color causing substances react
with chlorine and form Trihalomethanes (THM).
Can be removed by Coagulation-Flocculation,
Activated Carbon Adsorption & Ozonation
Measured by Spectrophotometer
Taste & Odor
Alkaline material : Bitter taste
Metallic Salts : Salty taste
Organic Material : Reduced Products of
Sulphur (Rotten Eggs)
Aesthetically displeasing for consumers
Removed by Activated Carbon Adsorption,
Ozonation, RO
Thermal Pollution
A typical nuclear Plant- Warms 150,000m
3
/ h cooling
water by 10 degree C
Life threatening: Trout & Salmon (omega 3 fatty acids)
Beneficial: for some fishes
Within certain limits- promotes fish growth, fishing
may improve
Sudden change in temperatureundesirable
With increase in temperature:
Metabolic rate increases by a factor of 2 for each
10 degree C rise in temp.
DO requirement increases &
Available DO reduces
Chemical Water Quality Parameters
Total Dissolved Solids:
Major Ions (Na
+
, K
+
, Ca
2+
, Mg
2+
, SO
4
2-
, Cl
-
, HCO
3
-
and CO
3
2-
)
Hardness
Fluorides
Metals:
Non Toxic: Ca, Mg,Fe, Mn, Al, Cu, Zn
Toxic: Cr, Cd, Pb, Hg
Organics
Biodegradable
Non-Biodegradable
Nutrients:
Nitrogen
Phosphorus
Nutrients
P, C, S, Ca, N, K, Fe, Mn, B, CO: Essential for growth
Considered Pollutants: These support the excessive
growth of aquatic life
Nutrient Enrichment: Blooms of algae/ die,
decompose / remove DO/water can not support
normal life forms/ add color turbidity, odour, tastes/
reduced acceptability for water supply
Aquatic Species- Three important : C,N,P
Limiting nutrients- Seawater-N
Fresh Water-P
Total Dissolved Solids (TDS) or
Salts
Dissolved solids, or salts, may be present as any
number of ions
cations: Na
+
, K
+
, Mg
2+
, Ca
2+
anions: Cl
-
, SO
4
2-
, HCO3
-
Typically measured as total dissolved solids (TDS)
Water classification
freshwater <1500 mg/l TDS
brackish water 1500 5000 mg/l
saline water >5000 mg/l
sea water 30,000-34,000 mg/l
Salts
Drinking Water - TDS<500mg/l
Irrigation Water - TDS<2100 mg/l
Salinity in Soil
Evaporation of freshwater
Accumulation of salts
Salinity increases - in reservoirs
Effects of TDS
Interfere with wastewater reuse
Crop damage/soil poisoning
Ion Balance (meq/L)
Na
+
, K
+
, Ca
2+
, Mg
2+
SO
4
2-, Cl-, HCO
3
- and CO
3
2-
% IB =
+
meq of Cations meq of Anions
* 100
meq of Cations + meq of Anions
Samples with pH <= 5.5 and ion sum >= 100 ueq/l
|IB| <= 10% Valid No flag
10% < |IB| <= 20% Valid 476 or 276
20% < |IB| Invalid 478 or 278
Samples with pH > 5.5 and ion sum >= 100 ueq/l
IB < -20% Invalid 478 or 278
-20% <= IB < -10% Valid 476 or 276
-10% <= IB <= 20% Valid No flag
20% < IB Valid 476 or 276
Hardness
cause soap scum
Ca
2+
+ (Soap)
-
Ca(Soap)
2 (s)
increase the amount of soap needed
cause scaling on pipes
cause valves to stick due to the formation of
calcium carbonate crystals
leave stains on plumbing fixtures
A term often used to characterize the ability of a water to:
Formation of Hardness
CO
2
+ H
2
O H
2
CO
3
Subsoil
Limestone
CaCO
3
(s) + H
2
CO
3
Ca(HCO
3
)
2
MgCO
3
(s) + H
2
CO
3
Mg(HCO
3
)
2
Precipitation
Topsoil
Fluorides
Occurs in few types of sedimentary or igneous
rocks
Toxic to humans in large quantities:
discoloration of teeth if fluoride> 2mg/l
> 5 mg/l causes bone fluorosis or other
abnormalities.
Can be removed by alum and ion exchange
methods
Metals
Na (non toxic): Bitter taste and health hazard
to cardiac and kidney patients.
Iron & Manganese (non toxic): Impart color
Arsenic, barium, cadmium, chromium, lead
mercury: Hazardous: concentrated by food
chains and greatest danger to the top of food
chain organisms
Heavy Metals
Important ones- Hg, Pb, Cd, As
Toxic Non-degradable
Essential nutrients-Cr, Fe
Cr, Fe in higher doses nervous system / kidney damage,
creation of mutation , induction of tumors
Inhaled / Ingested: Absorption depends on particular
metal and form .
Ex. Liquid Hg- not very toxic
Hg Vapor- Highly Toxic/ enters lungs./ diffused in to
blood stream/ can pass in to the brain / damage the
central nervous system
Kidney/complex filter/ eliminate toxic substance from
body.
Kidney- Contain millions of excretory units-nephrons
chemical toxic to kidney- nephrotoxins
Ex. Of nephrotoxic metals-Cd, Pb, Hg
Pesticides
Volatile Organic Compounds
Most commonly found in contaminated GW
Suspected carcinogens/ Mutagens
Can be removed by aeration
Kill undesirable organisms
Insecticides , herbicides,
Rodenticides,
Fungicides
Characteristics Standard Remarks
Color Colorless Generally cause by decaying vegetation or industries
Odor Unobjectionable (a) Test cold when heated
(b) Test at several dilutions
Caused by biological reactions and sewage
Turbidity 5 NTU
Dissolved solids mg/L,
Max
500 Beyond this palatability decreases and may cause gastro
intestinal irritation From minerals, metals
pH 6.5-8.5 Beyond this range, the water will affect the mucous
membrane and/or water supply system
Total Alkalinity 200 mg/L
Total hardness (as
CaCO
3
) mg/L, Max
300 Encrustation in water supply structure and adverse effects
on domestic use
DRINKING WATER QUALITY STANDARDS
Characteristics Standard Remarks
Chlorides (as Cl) mg/L,
max
250 Beyond this limit, taste, corrosion and palatability are
affected
Fluoride (as F) mg/L,
Max
1.0 Fluoride may be kept as low as possible. High chloride
may cause fluorosis, Less than 1 mg/L help to prevent
dental activities in children.
Sulphate (as SO
4
) mg/L,
Max
200 Beyond this limit, taste/appearance are affected, has
adverse effect on domestic uses and water supply
structures
Nitrate (as NO
3-N
) mg/L,
Max
45 as NO3-N
10 mg/L as
NO3
Beyond this methaemoglobinemia takes place.
(bluish discoloration)
Bacterial Counts: Nil
Biodegradable organics
Oxygen-Demanding Material
Measured in Terms of BOD
BOD (Biochemical Oxygen Demand): amount of
oxygen (DO, Dissolved Oxygen) required for the
biological decomposition of organic matter. The
oxygen consumed is related to the amount of
biodegradable organics.
When organic substances are broken down
into CO2 and water, oxygen is consumed
organic C + O
2
CO
2
Organic C : protein, Carbohydrates, Fats
etc., in Human Waste
Measure of BOD =
Initial oxygen- Final
Oxygen after 5 days
Biochemical Oxygen
Demand Measurement
Take sample of waste; dilute with
oxygen saturated water; add nutrients
and microorganisms (seed)
Measure dissolved oxygen (DO) levels over 5
days
Temperature 20C
In dark (prevents algae from growing)
Final DO concentration must be > 2 mg/L
Need at least 2 mg/L change in DO over 5 days
Example 1: Raw Data
Time
(days)
Diluted
sample
DO (mg/L)
Blank Seeded
Sample DO
(mg/L)
0 7.95 8.15
1 3.75 8.10
2 3.45 8.05
3 2.75 8.00
4 2.15 7.95
5 1.80 7.90
Example 1: Calculations
What is the BOD
5
of the sample?
Plot the BOD with respect to time.
sample diluted
the of ions concentrat DO final and initial DO , DO
(blank) water diluted seeded
the of ions concentrat DO final and initial B , B
volume total sample/ volume factor dilution P
P
P)] )(1 B (B - ) DO [(DO
BOD
f i
f i
f i f i
m
=
=
= =
=
Example 1: Time Concentration
Plot
0
100
200
300
400
500
600
700
0 1 2 3 4 5 6
time (days)
B
O
D
(
m
g
/
L
)
Modeling BOD as a First-order Reaction
0
1
2
3
4
5
6
0 10 20 30
time (days)
C
o
n
c
.
(
m
g
/
L
)
Organic matter oxidized
Organic matter remaining
Modeling BOD Reactions
Assume rate of decomposition of organic
waste is proportional to the waste that is
left in the flask.
demand oxygen us carbonaceo ultimate the is where
: yields equation this Solving
(time constant rate BOD the
t time after left demand oxygen of amount where
1 -
o
kt
o t
t
t
t
L
e L L
k
L
- kL
dt
dL
=
=
=
=
)
Ultimate BOD
0
1
2
3
4
5
6
0 10 20 30
time (days)
C
o
n
c
.
(
m
g
/
L
)
L
t
L
o
L
o
- L
t
BOD exerted
L remaining
BOD
t
Ultimate Biochemical Oxygen
Demand
L
t
= amount of O
2
demand left in sample at
time, t
L
o
= amount of O
2
demand left initially (at time 0,
no DO demand has been exerted, so BOD = 0)
At any time, L
o
= BOD
t
+ L
t
(that is the amount
of DO demand used up and the amount
of DO that could be used up eventually)
Assuming that DO depletion is first order
BOD
t
= L
o
(1 - e
-kt
)
Example 2
If the BOD
5
of a waste is 102 mg/L and the
BOD
20
(corresponds to the ultimate BOD) is
158 mg/L, what is k (base e)?
( )
kt
e L
= 1
0 t
BOD
kt
e
L
=
0
1
t
BOD
kt
L
=
|
|
.
|
\
|
0
1 ln
t
BOD
Example 2 (cont)
t
L
k
|
|
.
|
\
|
=
0
1 ln
t
BOD
day
mg/L
mg/L
5
158
102
1 ln
|
|
.
|
\
|
= k
-1
day 21 . 0 = k
Biological Oxygen Demand:
Temperature Dependence
Temperature dependence of biochemical
oxygen demand
As temperature increases, metabolism
increases, utilization of DO also increases
k
t
= k
20
u
T-20
u = 1.135 if T is between 4 - 20
o
C
u = 1.056 if T is between 20 - 30
o
C
Example 3
The BOD rate constant, k, was determined
empirically to be 0.20 days
-1
at 20
o
C.
What is k if the temperature of the water
increases to 25
o
C?
What is k if the temperature of the water
decreases to 10
o
C?
Example 3
( )
20 25
25
) 056 . 1 ( 20 . 0
=
-1
day k
-1
day 26 . 0
25
= k
( )
20 10
10
) 135 . 1 ( 20 . 0
=
-1
day k
-1
day 056 . 0
10
= k
Oxygen-Demanding Material
Increased Biochemical Oxygen Demand
(BOD) can result in
anaerobic conditions.
Anaerobic conditions lead to fish kills and bad
smell (H2S, NH3).
High oxygen levels necessary for healthy stream
ecology
trout require 5-8 mg/L dissolved oxygen (DO)
carp require 3 mg/L DO
aesthetic problem <1 mg/L
Dissolved Oxygen Depletion
Waste
Non-Biodegradable Organics
Molecules with exceptionally strong bonds (some
polysaccharides) and ringed structures (benzene)
Constituent of woody plants: tannic and lignin acids,
cellulose, phenols,
Petroleum products, pesticides, industrial chemicals:
Toxic to microorganism.
Total (Biodegradable+non Biodegradable) can be
measured in terms of Chemical Oxygen Demand
(COD).
Individual Organics are Analyzed by GC &/or HPLC
and other sophisticated methods
Principal sources are proteins, amines. Ammonia
Nitrogen is formed by the decomposition of these
components.
Although essential for primary production, an excess
of nutrients will result in eutrophication.
Eutrophication will stimulate the growth of algae,
resulting in strong oxygen production during daytime.
Respiration during the night and degradation of dead
algae will lead to anaerobic conditions (fish kills).
Nutrients ( Nitrogen & Phosphorus)
Algae & Algal Blooms
Phosphorus
Phosphorus is typically the limiting nutrient in lakes,
and algae growth is linked to phosphorus inputs.
Problems
aesthetic
taste and odor in drinking water
can be toxic, especially to farm animals
fouling
diurnal DO cycles
Phosphorus
P Sources
fertilizers
detergents
P can exist in a variety of chemical forms, so
total P in normally measured
Nitrogen
Nitrogen is often the limiting nutrient in ocean
waters and some streams
Nitrogen can exist in numerous forms, but
nitrate (NO
3
-
), nitrite (NO
2
-
), ammonia (NH
3
)
are most commonly measured
Sources are primarily from fertilizers and acid
deposition
Biological Water Quality
Parameters
Aquatic Organisms. Single Cell Fish: Trout:
Higher Quality of Water than Carp
Water Body Hosting Large number of species
with well balanced number of individuals :
Healthy System
For Human Use and Consumption: Pathogens:
Capable of infecting or transmitting disease to
humans
Pathogens
Not native to aquatic system: Usually require an
animal host for growth and reproduction.
Transported by natural water: temporary member
of aquatic community.
Able to survive in natural waters and maintain
their infectious capabilities.
Include bacteria, viruses, protozoa, helminthes
(parasitic worms)
Impacts on Human Health
Pathogenic Organisms
Smallest biological structures: Nervous System
disorders: Immunization
Single cell: Rod or spherical in shape:
Gastrointestinal Infections
Salmonella
Typhi
Poliovirus
Pathogenic Organisms
Giardia Lambia
Lowest form animal life, unicellular, complex
functional activity Milder Gastrointestinal Infections
Parasitic Worms
Analysis of Pathogens
Analysis of known pathogens time consuming. Test
for specific microorganisms only when needed.
Generally purity of water is checked by using
indicator microorganisms.
Indicator microorganism should be:
Always present when pathogens are present and always
absent when pathogens are absent
Applicable to all types of water.
Native to intestinal track of humans
For the safety of lab personnel's: not pathogen itself
Indicator Organism
Fecal coliform groups, several strains principal
is E Coli.: Non pathogenic and longer survival
time outside the human body
Simple tests to determine the presence or
absence and enumeration
Membrane filer technique or multiple tube
tests
River Bathing Standards
BOD - BIO-CHEMICAL OXYGEN DEMAND
DO - DISSOLVED OXYGEN
MPN - MOST PROBABLE NUMBER
BOD 3 mg/L (MAXIMUM)
DO 5 mg/L (MINIMUM)
COLIFORM (FECAL) 500 (DESIRABLE)
2500 (MAX. PERMISSIBLE)
PERMISSIBLE LIMIT PARAMETERS
MPN
100 ml
AVERAGE DENSITY OF FECAL COLIFORMS
EXCRETED IN 24 HOURS
(million/100ml)
Human 13.0
Duck 33.0
Sheep 16.0
Pig 3.3
Chicken 1.3
Cow 0.23
Turkey 0.29
Treated Water Quality Standards
INTO WATER BODY ON LAND
BOD (mg/l)
T S S (mg/l)
FECAL (MPN/100 ml)
COLIFORMS
30
50
1000
10000
100
200
(Desirable)
(Maximum)
TSS : Indian Standards: 100 mg/L
NRCP: 50 mg/L
No Indian standards for Fecal coliforms
