2. Outline
Introduction to Water Quality
Water Quality Parameters
WQ Examination and Potable Water Standards
Preliminary Water Treatment Process
Sedimentation
Coagulation and Flocculation
Filtration
Softening
Disinfection
3. Introduction to Water Quality
Water quality refers to the chemical, physical,
biological, and bacteriological characteristics of water.
It is a measure of the condition of water relative to the
requirements of biotic species and or to any human
need.
It is not a simple thing to say
“that water is good” or
“that water is bad”
Scientific measurements are used to define water
quality.
4. Introduction to Water Quality
Determination of water quality is typically made
relative to the purpose of the water:
◦ is it for drinking?
◦ is it to wash a car?
◦ is it to mix a concrete?
◦ or for some other purpose?
Poor water quality can pose a health risk for people,
ecosystems.
Absolutely pure water is never found in nature and
contains number of impurities in varying amounts.
Normal
Rapid
hardening
Low heat
Composition: %
Lime 63.1 64.5 60
Silica 20.6 20.7 22.5
Alumina 6.3 5.2 5.2
Iron Oxide 3.6 2.9 4.6
5. Introduction to Water Quality
Before supplying to the public, raw water should be
treated and purified for the safety of:
◦ public health
◦ economy and
◦ protection of various industrial processes
The water work engineer has to thoroughly check,
analyze and do the treatment of the raw water
obtained from the sources, before its distribution.
The water supplied to the public should be strictly
according to the standards laid down from time to
time.
6. Introduction to Water Quality
Important requirements of water for domestic use:
1. Colorless and sparkling clear
2. Tasteless and free from odor
3. Reasonably soft (Ca2+
, Mg2+
4. Free from disease producing bacteria or organisms
5. Free from objectionable dissolved gases such as H2S
6. Have sufficient quantity of dissolved oxygen (DO)
7. Free from harmful salts
8. Free from objectionable minerals like Iron, Manganese, Lead,
Arsenic and other poisonous minerals
9. Reasonably free from phenolic compounds, Cl2, fluorides, iodine
10.Not lead to scale formation and should be non-corrosive
7. Introduction to Water Quality
Common impurities in water
Impurities in water are classified into three heads:
i. Suspended impurities
◦ Are those impurities which normally remains in
suspension
◦ They are microscopic and make water turbid
◦ Sources:
Living organisms: bacteria, algae, protozoa
Inorganic: clay, silt, sand
Organic: plant and animal particles, vegetable, industrial and
domestic by-products
8. Introduction to Water Quality
ii. Dissolved impurities
◦ Are not visible but they are large in quantity since
water is a good solvent.
◦ They cause bad taste, hardness, salinity and alkalinity.
◦ Sometimes they are harmful.
◦ Sources:
a. Salt
Ca and Mg: bicarbonates, carbonates, sulphates and chlorides
Na: bicarbonates, carbonates, sulphates, chlorides, and fluorides
b. Metals and compounds: Iron oxide, Mn, Pb, As, Ba, Cd,
Cy, Br, Se, Nitrates
c. Vegetable dyes
d. Gases: O2, CO2, H2S
9. Introduction to Water Quality
iii. Colloidal impurities
◦ Are electrically charged impurities.
◦ Usually very small in size and remains in constant
motion and don’t settle.
◦ Sources:
Clay, amino acids, organic waste products, silica, Iron oxides,
manganese oxides
10. Introduction to Water Quality
Fig. 1: Size range of particles of concern in water treatment
12. Physical Parameters
Characteristics of water that respond to the sense of
sight, touch, or smell.
◦ Turbidity
◦ Color
◦ Taste and odor
◦ Temperature
13. Turbidity
is a measure of resistance of
water to the passage of light
through it.
is caused due to presence of
suspended and colloidal solids.
Sources (s):
i. Inorganic compounds: clay, silt,
sand
ii. Organic compounds: plant fiber,
human waste
14. Turbidity
The amount and character of turbidity depend upon:
◦ The type of soil (land use) over which the water has run
◦ Point source pollution and effluent
◦ Resuspension
◦ The velocity of the water (Groundwater is normally clear)
Can vary seasonally according to:
◦ biological activity in the water
◦ surface run-off
carrying soil particles
15. Turbidity
When the water becomes quite:
◦ the heavier and larger suspended particles settle quickly
◦ the lighter and more finely divided ones settle very
slowly
◦ very finely divided clay may require months of complete
quiescence for settlement
Low inorganic turbidity (silt and clay) may result in a
relatively high organic turbidity.
◦ low inorganic turbidity permits sunlight to penetrate
freely into the water and stimulates a heavier growth of
algae, photoplankton
16. Turbidity
Effects (s):
◦ Aesthetics
◦ Adsorption point/center for chemical and
micro-organism
◦ Health aspect
Turbidity is measured by:
1. Turbidity rod or Tape
2. Jacksons Turbid meter
3. Bali’s Turbid meter
measured photometrically by determining
the percentage of light of a given intensity
that is either absorbed or scattered.
test
tube
17. Turbidity
Turbidity is expressed as NTU (Nephelometric
Turbidity Units) or PPM (parts per million) or (mg/l).
Drinking water should not have turbidity more than 10
NTU.
The maximum times that samples may be held before
analysis --- 48 hrs
Turbidity test is useful to determine:
◦ the detention time in settling for raw water and
◦ the dosage of coagulants required
Sedimentation with or without chemical coagulation
and filtration are used to remove turbidity.
18. Color
is caused by materials in solution or colloidal
conditions.
should be distinguished from an apparent (not true)
color (which is due to turbidity).
True color is caused by dyes derived from
decomposing vegetation.
Colored water:
◦ is undesirable because of consumer objections
◦ may discolor clothing and adversely affect industrial
processes
19. Color
Before testing the color of water:
◦ total suspended solids should be removed by centrifugal
force in a special apparatus
The color produced by one milligram of platinum in a
liter of water has been fixed as the unit of color.
The permissible color for domestic water is 20 ppm on
platinum cobalt scale.
The maximum times that
samples may be held before
analysis --- 48 hrs
20. Temperature
Temperature increase may affect the potability of water
Temperature above 15°C is objectionable to drinking
water.
The maximum times that samples may be held before
analysis --- immediately after sampling
Effect (s):
i. disturb biological activities
ii. most chemical reactions that occur in natural water
systems
iii. has pronounced effect on the solubility of gases in water
21. Tastes and Odor
Substances that produce an odor in water will almost
in variably impart a taste as well.
The converse is not true, as there are many mineral
substances that produce taste but no odor.
Source (s):
i. Inorganic compounds: minerals, metals, salts
ii. Organic compound: petroleum and/or degradation of organic
matter
Inorganic substances are more likely to produce tastes
unaccompanied by odor.
Organic material is likely to produce both taste and
odor.
22. Tastes and Odor
Alkaline material imports a bitter taste to water
Metallic salts may give salty or bitter taste
A multitude of organic chemicals may cause taste &
odor problems
Biological decomposition of organics may also result in
taste and odor producing liquids and gases in water.
Effect(s):
i. aesthetic
ii. health problems
23. Chemical Parameters
Electrical conductivity
Total Solids
Alkalinity
pH
Dissolved Oxygen (DO)
Oxygen Demand (BOD, COD, TOC, TOD)
Nitrogen
Hardness
Chloride
Fluoride
Metals and other chemical substances
24. Total Solids
Forms of solids present in water:
Solids
Suspended solids
remain floating in
water
Dissolved solids
remain dissolved in
water
Colloidal solids
remaining either in
solution or in
suspension
Settleable solids
settles out, if water is
allowed to remain
undisturbed for a
period of 14 minutes
25. Total Solids
Determination of suspended solids are important as
pollutants and pathogens are carried on the surface of
particles.
The quantity of suspended solids is determined by:
◦ filtering the sample of water through fine filter (0.45m) …
(1m) , drying and weighing
Filter paper
26. Total Solids
The quantity of dissolved & colloidal solids is
determined by:
◦ evaporating the filtered water obtained from the suspended
solid test and weighing the residue …. (phase change)
The total solids in a water sample can be directly
determined by:
◦ evaporating the water (@105°C oven dry for 24 hrs) and
weighing the residue
oven
27. Total Solids
When the residue of total solids is fused in a muffle
furnace (@550°C for 1 hour … (15 – 20 min))
◦ the organic solids will decompose where as only inorganic
solids will remain
◦ the inorganic solids can be determined by weighing
Organic solids = total solids – inorganic solids
Effect (s):
◦ cause taste, colour and odour problems
◦ health aspect
◦ small amount of TDS – water becomes corrosive to attain
equilibrium
◦ high levels of TSS will increase
water temp & decrease DO levels
muffle furnace
28. Alkalinity
The quantity of ions in water to neutralize acid or a
measure of water strength to neutralize acid.
Main constituents are:
◦ carbonate (CO3
2-)
◦ bicarbonate (HCO3-)
◦ hydroxide (OH-)
Effects:
◦ Non-pleasant taste
◦ Reaction between alkaline constituent and cation (+ ion:
Ca2+
, Mg2+
, … ) produces precipitation in pipe
29. pH
is a measure of the concentration of free hydrogen ion
in water.
It expresses the molar concentration of the hydrogen
ion as its negative logarithm.
◦ pH = -log [H+]
pH + pOH = 14
In neutral solutions at equilibrium [OH] = [H]
◦ pH = pOH = 7
Low pH is associated with high acidity, high pH with
caustic alkalinity.
30. pH
The maximum times that samples may be held before
analysis --- immediately after sampling
pH is measured by using a pH meter
Effects:
◦ water treatment process
◦ a number of waste treatment processes (on the rate of microbial
growth)
◦ Corrosion
◦ pH below 6.5 metal corrosion
can become a problem
◦ pH above 8.5 (alkaline) scaling of
pipes may occur
31. Dissolved oxygen (DO)
What is Dissolved Oxygen?
◦ DO refers to the level of free, non-compound oxygen
present in water or other liquids.
◦ Non-compound oxygen, or free oxygen (O2), is
oxygen that is not bonded to any other element.
◦ DO is the presence of these free
O2 molecules within water.
◦ The bonded oxygen molecule in
water (H2O) is in a compound
and does not count toward
dissolved oxygen levels.
32. Dissolved Oxygen (DO)
The oxygen content of natural waters varies with:
◦ Temperature (Inverse relation)
◦ Salinity (Inverse relation)
◦ Turbulence (water movement and mixing)
◦ Photosynthetic activity of algae and plants
◦ Respiration by aquatic plants and animals
◦ Atmospheric pressure
◦ Depth of water
In fresh-waters dissolved oxygen (DO) at sea level
ranges from 15 mg/l @ 0°C to 8 mg/l @ 25°C.
CO2 + H2O → (CH2O) + O2
33. Dissolved Oxygen (DO)
• Oxygen saturated waters have pleasant taste.
• The presence of oxygen in the water in dissolved form
keeps it fresh.
• Drinking water is thus aerated if necessary to ensure
maximum DO.
Effects:
• waters lacking in DO have an insipid tastes
• more quantity of DO causes corrosion to the pipe
materials
34. Dissolved oxygen (DO)
The DO content of water is generally determined by:
Winkler's method
◦ an oxidation-reduction process carried out chemically
to liberate iodine in amount equivalent to the quantity
of dissolved oxygen originally present.
DO meter
• The maximum times that samples
may be held before analysis ---
immediately after sampling
35. Oxygen Demand
Organic compounds are generally unstable to be
oxidized biologically or chemically to stable, relatively
inert end products such as CO2, H2O & NO3.
Indicators used for estimation of the oxygen
demanding substance in water are:
◦ BOD, COD, TOD and TOC
An indication of the organic content of water can be
detected by:
◦ measuring the amount of oxygen required for stabilization
36. Oxygen Demand
BOD is the quantity of oxygen required for the
biochemical oxidation of the decomposable organic
matter at specified temperature within specified time.
(20°C and 5 day).
Chemical Oxygen Demand (COD) is a measurement of
the oxygen required to oxidize soluble and particulate
organic matter in water.
Bio-degradable Non
biodergradable
Inorganic
Organic
BOD
COD
37. Nitrogen
The forms most important to water quality include:
a. Organic – nitrogen: in the form of protein, amino acids
and urea
b. Ammonia – nitrogen: nitrogen as ammonium salts. eg.
(NH4).CO3
c. Nitrite- nitrogen: an intermediate oxidation stage. Not
normally present in large quantity.
d. Nitrate- nitrogen: final oxidation product of nitrogen.
e. Gaseous nitrogen (N2)
The presence of nitrogen compounds in surface waters
usually indicates pollution.
38. Nitrogen
Excessive amount of ammonia and organic nitrogen
may result from recent sewage discharges or runoff
contamination by relatively fresh pollution.
Effect (s):
◦ NO3
- poisoning human and animals babies (human below
6 month old) … blue baby syndrome
NO3
- > NO2
- (in acidic condition) – will substitute O2 in blood
vessel
◦ High nitrate levels in drinking water:
May increase cancer risks (nitrosamines/des) (Mirvish 1991)
Cause disruption of thyroid function
Cause birth defects
◦ Excessive algae breeding and aquatic plants
39. Phosphorus
A mineral nutrient that is essential for all forms of life.
Exist in a form of “orthophosphate”, “condensed
phosphate”, and “organic phosphate”.
Source (s):
◦ readily present in soil (weathering of rocks)
◦ fertilizers
◦ human wastes (“organic phosphate”)
◦ domestic wastes (element in detergent)
Effects (s)
◦ algae breeding and aquatic plants
◦ > 0.2 mg/l – disturb coagulation
processes in WT plants
40. Hardness
Hard water is formed when water percolates through
deposits of calcium and magnesium containing
minerals such as limestone, chalk and dolomite.
Hardness is caused by:
◦ Measure of “multivalent” cations in
water such as Ca2+, Mg2+, Fe2+, Mn3+
◦ Ca2+ and Mg2+ are the major constituents
Hardness is defined as the concentrations of calcium
and magnesium ions expressed in terms of calcium
carbonate (CaCO3).
43. Hardness
A generally accepted classification of hardness is as
follows:
Generally a hardness of 100 to 150 mg/liter is desirable.
Water hardness more than 600mg/lit have to be
rejected for drinking purpose.
Soft < 50 (75) mg/1 as CaCO3
Moderately hard 50 (75) – 150 mg/1 as CaCO3
Hard 150 – 300 mg/1 as CaCO3
Very hard > 300 mg/1 as CaCO3
44. Hardness
Excess of hardness leads to the following effects:
i. Large soap consumption in washing and bathing
ii. Fabrics when washed become rough & strained with
precipitates.
iii. Is not fit for industrial use like textiles, paper making, dye and
ice-cream manufactures.
iv. It forms scales in the boiler tubes and reduces their efficiency
v. The precipitates clog the pores on the skin & makes the skin
rough
vi. Precipitates can choke pipe lines and valves
vii. Very hard water is not palatable
viii. May cause kidney stones are generally composed of calcium
salt and usually occur as calcium oxalate.
45. Chloride
Chlorides are widely distributed in nature as salts of
sodium (NaCl), potassium (KCl), and calcium (CaCl2).
Source (s):
◦ mines and sea dissolve sodium chloride
◦ mixing of saline water and sewage in the water
Effect (s):
◦ Excess of chlorides is dangerous and unfit for use
◦ When it is in excess of 250mg/l:
can give rise to detectable taste in water
adverse physiological effect
46. Fluoride
Fluoride is a naturally occurring mineral that protects
teeth from tooth decay.
Source (s):
◦ minerals
Effect (s):
◦ concen. of 1 mg/l is good for the growth of children teeth
◦ discoloration of teeth if it is taken in high concentration
◦ excessive concentration (> 5mg/l) – problem in bone
growth (bone fluorosis and other skeletal abnormalities)
discoloration of teeth
bone fluorosis
47. Metals - non toxic and toxic
Non – toxic: Ca2+, Mn2+, Na+, Fe2+, Mg2+, Al3+, Cu2+, Zn2+
◦ dangerous for health if the concentration is high
Source (s):
◦ minerals, readily available from nature
Effect (s):
◦ color, odor, taste
◦ deteriorate health (at high concentration)
◦ discoloration of clothes during washing (Fe2+ & Mn2+)
◦ incrustation in water mains due to deposition of ferric
hydroxide and manganese oxide
48. Metals - non toxic and toxic
Toxic – As2+, Ba2+, Cd2+, Cr2+, Pb2+, Hg2+
◦ stored up in food chain
Source (s):
◦ human activities such as mining and industries
Effect (s):
◦ dangerous disease such as cancer, abortion and deformation
in newborn baby
Arsenic, Selenium are poisonous, therefore they should
be removed totally.
50. Biological Characteristics
microorganism that bring diseases are called
“pathogen”.
Their quantities are very small compared to other
microorganisms.
The experiments to determine the presence of all
pathogens takes a long time and very expensive.
The presence of pathogenic microorganism is shown
by indicator microorganism
51. Biological Characteristics
Properties of indicator microorganism :
◦ Can be used for all types of water
◦ Always present when pathogen is present
◦ Always absent when pathogen is absent
◦ Easily experimented and give reliable results
Typical indicators used are coliform group
◦ Coliform group:
Fecal coliform e.g. E.Coli
Total coliform e.g. fecal coliform,
soil coliform and others
52. Algae
These are small, chlorophyll bearing generally one–
celled plants of varying shapes and sizes which live in
water.
When present in large numbers:
◦ may cause turbidity in water and an apparent color.
◦ cause trouble in water works by undue clogging of filters
◦ their most troublesome characteristics in the taste and
odor that they may cause.
53. Bacterium, Protozoa
Bacterium:
◦ Many are found in water.
◦ Some bacteria are indicator of pollution but are harmless;
other few in number are pathogenic.
◦ Bacterial-born diseases include: typhoid fever, cholera,
and bacterial dysentery
Protozoa:
◦ They are the lowest and simplest forms of animal life.
◦ Protozoa–born diseases include giardiasis and amebic
dysentery.
54. Examination of Water Quality
The purposes of analysis of raw water and purified
water:
◦ To classify the water with respect to general level of
mineral constituents
◦ To determine the degree of clarity
◦ To determine the chemical & bacteriological pollution of
water
◦ To determine the presence of an excess of any particular
constituent
◦ To determine the level of organic impurities
◦ To set the outlines of purification process and specify
various stages
◦ To ascertain whether purification of water has reached to
the required standards or not.
55. Examination of Water Quality
There are two aspects of water analysis that we need to
consider:
What substances or organisms are we interested in testing
for …. and why?
√ What procedures and equipment do we use to make the
measurements and … how do they work?
56. Water Quality Standard
Public water supplies are obliged to provide a supply
of wholesome water which is suitable and safe for
drinking purposes.
Water quality standards may be set regional, national,
or international bodies.
Guidelines for drinking water quality have
established by the World Health Organization (WHO)
as shown in the table below.
57. Water Quality Standard
Table 1: WHO guideline for drinking water quality
Parameter Unit Guideline value
Microbial quality
Fecal coli forms Number/ 100 ml Zero*
Coli form organisms Number /100 ml Zero*
Arsenic mg/1 0.05
Cadmium mg/1 0.005
Chromium mg/1 0.05
Cyanide mg/1 0.1
Fluoride mg/1 0.5 - 1.5(3)
Lead mg/1 0.05
Mercury mg/1 0.001
Nitrate (as nitrogen) mg/1 10
Selenium mg/1 0.01
Magnesium mg/l 30
58. Water Quality Standard
Parameter Unit Guideline value
Calcium mg/l 75
Aluminum mg/1 0.03
Chloride mg/1 250
Color True color unit 5(15)
Copper mg/1 1
Hardness mg/1(as CaCO3) 300
Iron mg/1 0.3(3)
Manganese mg/1 0.3
pH ---- 6.5 - 8.5
Sodium mg/1 200
Total dissolved solids mg/1 500
Sulfate mg/1 250
Taste and odor ---- Non objectionable
Turbidity NTU 5(10)
Zinc mg/1 5
Alkalinity mg/l 300
59. Sources of Water Pollution
Domestic Sewage
Industrial Wastes
Catchment Area
◦ agricultural activities and extensive use of fertilizers and
insecticides are main factors
Distribution System
◦ If there are cracks in pipes or if joints are leaky, the flowing
water gets contaminated by the surrounding substances
Oily Wastes
Radioactive Wastes
Travel of Water
60. Question
1. Explain the general characteristics of the following water
sources in terms of impurities/wqp.
i. Pure water-salts
ii. Rainwater-gases,radioactivefall out,vapours,particulate.
iii. Surface runoff water-
nitrate,phosphate,biocides,particulate,organic matter
iv. River water-organic water,waste water,particulates.
v. Lake and reservoir water-algae,odours,tastes
vi. Groundwater-carbonate,chloride,iron manganese.
2. Explain the effects of impoundment on water quality.
3. Explain the effects of storage and direct sunlight on water
bottles made of PET (polyethylene terephthalate).
