This is a compulsory course for students in the Department of Water Resources Management and Agrometeorology with option in Water Resource Management. They are expected to have one hour of practical work in laboratory per week. As a school regulation, a minimum of 75% attendance is required of the students to enable him/her write the final examination

1. WATER QUALITY
ASSESSMENT
WMA 509
Prof O. Martins, Dr O.Z. Ojekunle and Dr. G.O. Oluwasanya
Dr O.Z. Ojekunle and Dr. G.O. Oluwasanya
Dept of Water Res. Magt. & Agromet
Dept of Water Res. Magt. & Agromet
UNAAB. Abeokuta. Ogun State
UNAAB. Abeokuta. Ogun State
Nigeria
Nigeria
oojekunle@yahoo.com

2. • COURSE CODE: WMA 509
• COURSE TITLE: Water Quality
Assessment
• COURSE UNITS: 3 Units
• COURSE DURATION: 3 hours per week

3. COURSE DETAILS
• Course Cordinator: Prof. O. Martins B.Sc.,
M.Sc., PhD
• Email:ola_sumbo@yahoo.co.uk
• Office Location: Room B202, COLERM
• Other Lecturers: Dr. O.Z. Ojekunle B.Sc.,
M.Sc., PhD and Dr. G.O. Oluwasanya B.Sc., M.Sc.,
PhD

4. COURSE CONTENT
• Comparative studies of natural water: River, Lakes, Sea, Ground and
Rainwater. Oxygen demand in aerobic and anaerobic oxidation.
Demineralization and Desalting. Hydro-chemical data analysis. History of
water quality management: The problem and its science. Developing
standards from the traditions of toxicology, classification and environmental
quality assessment; the search for ecologically accurate aquatic metrics. The
role of scale issues in water quality management. Coastal zone water quality
management structuring water management goals by ecological level, effects
of land use on water quality.
•
• Management of water quality in:
•
• A forested landscape
• An agricultural landscape
• An urban landscape.

5. COURSE REQUIREMENTS
• This is a compulsory course for students in
the Department of Water Resources
Management and Agrometeorology with
option in Water Resource Management.
They are expected to have one hour of
practical work in laboratory per week. As a
school regulation, a minimum of 75%
attendance is required of the students to
enable him/her write the final examination

6. READING LIST
• Alan Scragg 1999. Environmental Biotechnology. Pearson Education Limited,
Edinburgh Gate, Harlow. Essex CM20 2JE. England
• Eidon D. Enger, Bradley F. Smith 2003. Environmental Science: A study of
Interrelationships (Ninth Edition) McGraw-Hill International Edition Publication.
• McEldowney, S., Hardman, D.J. and Waite, S. 1993. Pollution: Ecology and
Biotreatment. Longman Scientific and Technical, Harlow, UK.
• William P. Cunningham, Mary Ann Cunningham 2008. Principles of Environmental
Sciences, Inquiry and Applications (Fifth Edition) McGraw-Hill International Edition
Publication.
• William P. Cunningham, Mary Ann Cunningham 2008. Environmental Sciences, A
Global Concern (Eleventh Edition) McGraw-Hill International Edition Publication.
• Wheatly, A. D. 1985. Wastewater treatment and by-product recovery. Critical Reports in
applied Chemistry, 11, 68-106
• OECD, 2003: Assessing microbial safety of drinking water: improving approaches and
methods, IWA, UK, 295pp
• FEPA, 1996: Water quality monitoring and environmental status in Nigeria, FEPA,
Abuja, Nigeria, 235pp

7. History of Water Quality
The Problem and its Science
1.1 History of making water safer
Outbreaks of water borne diseases
High disease burden
Emergence of new pathogens
1.2 The search for ecologically accurate aquatic metrics
Defining the role of the indicator concept
Indicator concept and criteria
1.3 Developing standards
Traditional approach
Current practice
New challenges
The development of water safety plans
Assessment of risk

8. 1.4 Emergence of a new paradigm:
‘Due Diligence’
-HACCP plan
-Water safety plans for drinking water supply
Information needs
Regulation
Water supplier
Public Health Agencies
1.5 The new approach
– Total system approach to risk management
– Decision-making framework
History of Water Quality
The Problem and its Science

9. PROPERTIES OF WATER
• Water is a chemical compound of oxygen and hydrogen and
in the gaseous state can be represented by the molecular
formula H2O. The isotopes of hydrogen and three isotopes of
oxygen exist in nature, and if these are taken into account, 33
varieties of water are possible.
• The physical properties of liquid water are unique in a
number of respects, and these departure from what might be
considered as normal for such a compound are of the greatest
importance with respect to both the existence of life on earth
and the operation of many geochemical processes.
• The boiling point and freezing point of water are both far
higher than would be the theoretically expected,
considering the low molecular weight of the compound, and
the range of temperature over which water as a liquid is wider
than might be expected.

10. MOLECULAR STRUCTURE OF
WATER
• Molecular and crystalline structures are often
studied by the use of models, in which spheres of
various sizes represent the atoms out of which the
structures is built. Much information has been
obtained, especially through the science of
crystallography, as to the distances that separate
the ions in crystals, and the effective size of the ions
themselves
• The bonds connecting the hydrogen’s to oxygen
describe an angle of 105o
, so that the two
hydrogen are relatively close together on one side
of the molecule.

11. MOLECULAR STRUCTURE OF
WATER (Cont)
• The molecule has dipolar properties because the positive charge
associated with the hydrogen are connected on one side of the
molecule, leaving a degree of negativity on the opposite side.
Forces of attraction thus exist between hydrogens of one
molecule and the oxygen bonds.
• Hydrogen bonds still remain an important force but their
arrangement is continually shifting. From Ice to Liquid to Gas
• The attraction between molecules of a liquid is shown at a
liquid surface by the phenomenon called Surface tension.
When in contact with surface to which the liquid particles are
attracted, water is drawn into the small openings with a force many
times that of gravity, induced by the surface tension of the fluid.

12. PROPERTIES OF WATER
• Chemical Constitution of Water
• Ionic and Non Ionic
• Ionic
• Anion
• Cations
– Major Anions
» Bicarbonate, Chloride, Sulphate
– Major Cations
» Sodium, Potassium, Calcium, Magnesium
• Non-Ionic
• SiO2, Dissolved gases, oily Substance, Synthetic
detergent,

13. Properties which Affect Quality of
Water
• All these impart certain quality characteristic of water, which are called its
properties.
• Hardness
• Carbonate (Temporary) Hardness CaCO3
• Non Carbonate (Permanent) Hardness CaSO4
• Concentration of Hydrogen-ion, which are expressed in pH units. It is the—
Log10H+
• Specific Electrical Conductance
• - Increases with temperature: values must therefore be related to the same
temperature (2%)
• Colour
• Alkanity: Ability to neutralize acid; due to the presence of OH-
, HCO3
-
, CO3
2-
,
• Acidity: Water with pH 4.5 is said to have acidity; caused by the presence of free
mineral acids and carbonic acids
• Turbidity: Measure of transparency of water column; indirect method of
measuring ability of suspended and colloidal materials to minimize penetration of
light through water.
• Dissolved gasses: O2, N2, CO2, H2S, CH4, NH3, etc.

14. PHYSICAL CHEMICAL
PARAMETER
• Since water is not found in its pure in nature, it is
important to determine its combined
• physical,
• chemical and
• biological characteristics.
• This is done through monitoring of water for its
quality.
• Physical chemical parameter analyzed in natural
environments; Atmosphere (rainfall), hydrosphere
(river, lakes, and oceans) and Lithosphere
(Groundwater) are similar-

15. PHYSICAL CHEMICAL
PARAMETER (Cont)
• Temperature: Measurement is relevant
• For Aquatic life
• Control of waste treatment plants
• Cooling purposes for industries
• Calculation of solubility of dissolved gases
• Identification of water source
• Agriculture Irrigation
• Domestic uses (Drinking, bathing)
• Instrument of measurement is thermometer

16. PHYSICAL CHEMICAL
PARAMETER (Cont)
• pH: Controlled by CO2/HCO3
-
/CO3
2-
Equilibria in
natural water. Its values lie between 4.5 and 8.5.
It is important
• Chemical and biological properties of liquid
• Analytical work
• Measurement is done in the field. Most
common method of determination is the
electrometric method, involving a pH-meter. It
is important to calibrate the meter with standard
pH buffer solutions

17. PHYSICAL CHEMICAL
PARAMETER (Cont)
• Dissolved Oxygen: Water in contact
with the atmosphere has measurable
dissolved oxygen concentration. It values
depends on
• Partial pressure of O2 in the gaseous
phase
• Temperature of the water

18. PHYSICAL CHEMICAL
PARAMETER (Cont)
• Concentration of salt in the water (the higher
the salt content in water, the lower the
concentration of dissolved oxygen and the
other gases). Measurement is important in
• Evaluation of surface water quality
• Waste-treatment processes control
• Corrosivity of water
• Septicity
• Photosynthetic activity of natural water

19. Effect of Some Physical Parameter
and their Measurement
• Temperature: Temperature affects the density
of water, the solubility of constituents (Such as
oxygen in water), pH, Specific conductance, the
rate of chemical reactions, and biological activity
of water. Continuous water quality sensor
measure temperature with thermistor, which is
a semiconductor having resistance that changes
with temperature. Modern thermistor can measure
temperature to plus or minus 0.1 degree celcius
(o
C).

20. Effect of Some Physical Parameter
and their Measurement (Cont)
• Specific Conductance: Electrical conductivity is a measure
of the capacity of water to conduct an electrical current and is
a function of the types and quantities of dissolved substance
in water. As concentration of dissolved ions increase,
conductivity of the water increases. Specific conductance
is the conductivity expressed in units of Microsiemen per
centimeter at 25o
C. Specific conductances are a good
surrogate for total dissolved solids and total ions
concentrations, but there is no universal linear relation
between total dissolved solids and specific conductance.
• Specific conductance sensors are of 2 types: contact sensors
with electrodes and sensor without electrodes
• Multiparameter monitoring systems should contain automatic temperature compensation
circuits to compensate specific conductance to 25o
C.

21. Effect of Some Physical Parameter
and their Measurement (Cont)
• Salinity: Although Salinity is not measured directly,
some sondes include the capability of calculating and
recording salinity based on conductivity measurement.
Conductivity has long been a tool of estimating the
amount of chloride, a principle component of salinity in
water. Salinity is commonly reported using the Practical
Salinity Scale (PSS), a scale developed to a standard
potassium-chloride solution and based on
• conductivity,
• temperature and
• barometric pressure measurement
• Salinity in practical salinity units is nearly equivalent to
salinity per thousand.

22. Effect of Some Physical Parameter
and their Measurement (Cont)
• Dissolved Oxygen: Sources of DO in surface waters are primarily
atmospheric reaeration and photosynthetic activity of aquatic plants. DO is
an important factor in chemical reactions in water and in the survival
of aquatic organisms. In surface water, DO concentration typically range
from 2-10mg/l. DO saturation decreases as water temperature increases,
and DO saturation increases with increased atmospheric pressure.
• The DO Solubility in saline environments is dependent on
• salinity
• as well as temperature and
• barometric pressure
• The technology most commonly used for continuous water quality sensors
is the amperometric method, which measures DO with temperature
compensated polarographic membrane-type sensor.
• The newest technology for measuring DO is the Luminescent sensor that is
based on dynamic fluorescence quenching.
• The sensor has light emitting diode (LED) to illuminate a specially designed
oxygen-sensitive substrate that, when excited, emits a luminescent light with
a lifetime that is directly proportional to the ambient oxygen concentration

23. Effect of Some Physical Parameter
and their Measurement (Cont)
• pH: In more technical terms, pH is defined as the negative
logarithm of the hydrogen ions concentration. For example in pure
water, the numerical value of hydrogen ions concentration 10-7
The
logarithm, (or exponent) is -7, and the negative of that is 7
• Because the pH scale is based on logarithms to the base 10, each unit
change in pH actually represents a tenfold change in the degree of
acidity or alkalinity of a solution. For instance, a solution with a pH = 5 is
ten times more acidic than the solution with a pH = 6, likewise a solution
with a pH = 4 is 100 times more acidic than the solution with pH = 6.
• Dissolved gases such as carbon dioxide, hydrogen sulphide and
ammonia, apparently affect pH. Dagasification (for example, loss of
carbon dioxide) or precipitation of a solid phase (for example, calcium
carbonate) and other chemical, physical, and biological reactions may
cause the pH of a water sample to change appreciably soon after
sample collection.
• The electrometric pH-measurement method, using a hydrogen-ion
electrode, commonly is used in continuous water-quality pH
sensors

24. Effect of Some Physical Parameter
and their Measurement (Cont)
• Turbidity: Turbidity is defined as an expression of the
optical properties of a sample that cause light rays to be
scattered and absorbed, rather than transmitted in straight
lines through a sample. ASTM further describe turbidity as
the presence of suspended and dissolved matter, such as
clay, silt, finely divided organic matter, plankton, other
microscopic organisms, organic acids, and dyes. Implicit in
this definition is the fact that colour, either of dissolved
materials or of particles suspended in the water also can
affect turbidity.
• Turbidity sensors operate differently from those for
temperature, specific conductance, DO, and pH, which
convert electrical potentials into the measurement of
constituent of interest.

25. Effect of Some Physical Parameter
and their Measurement (Cont)
• Most commercially available sensors
report data in Nephelometric Turbidity
Units (NTU)/ with a sensor range of 0-
1000 and an accuracy of -+5 percent or
2NTU, whichever is greater. Some
sensors can report values reliably up to
about 1500 NTU.

26. WATER SAMPLING/ WATER
POLLUTION
Part 1a

27. • Grab Sampling
• Composite Sampling

28. Water Sampling
• Sampling of most wastewaters and contaminated water is difficult due to
their highly variable nature (Keith, 1988). To obtain an accurate
assessment, samples will have to be taken over a time period, over different
sections of the waterway, and at different depths. There are various
automatic methods of taking samples which can be used. Some industrial
discharges into waterways are intermittent, which will extend the time over
which sampling must be carried out. Where to sample in the waterway
depends on the inflow and outflow of water and on stratification, and the
whole waterway may need to be assessed.
• If a groundwater is to be monitored, wells will have to be drilled and the very
process of drilling can alter or contaminate samples. Contamination can
come from the drilling method, casing material and the sample method.
These types of consideration have to be evaluated when choosing the
sampling methods and analysing the results.

29. Physical Analysis
• The physical analysis which can be

30. WATER POLLUTION
Water, Water Everywhere: Nor Any Drop to Drink---Samuel Taylor
Coleridge
• If pure water does not exist, outside of a chemist’s
laboratory, how can a distinction are made
between polluted and unpolluted water? Infact,
the distinction depends on the type and the
concentration of impurities as well as on the
intended use of the water.
• In general terms, water is considered to be
polluted when it contains enough foreign
materials to render it unfit for a specific
benefit use, such as for drinking, recreation,
or fish propagation. Actually, the term pollution
usually implies that human activities are the
cause of the poor water quality.

31. CLASSIFICATION OF WATER
POLLUTANTS
• First, a pollutant can be classified according to
the nature of its origin as either a point
sources of a Dispersed (Non Point) sources
pollutant

32. CLASSIFICATION OF WATER
POLLUTANTS (Cont)
• Point Sources pollutant are easies to deal with than are
dispersed sources pollutant; those from a point source
have being collected and convened to a single point
where they can removed from the water in the treatment
plant and the point discharges from treatment plant can
easily be monitor by regulatory agencies.
• Pollutants from dispersed sources are much more difficult
to control. Many people think that sewage is the primary
culprit in water pollution problems, but dispersed sources
cause a significant fraction of the water pollution in
Nigeria. The most effective way to control the dispersed
sources is to set appropriate restriction on land use.

33. CLASSIFICATION OF WATER
POLLUTANTS (Cont)
• In addition to being classified by there
origin, water pollutant can be classified into
group of substances base primarily on there
environmental or health effect. e.g., the
following lists identify 9 specific types of
pollutants.
• -Pathogenic organism, -Oxygen-demanding
substances, -Plant nutrients -Toxic
organics, -Inorganic chemicals, -Sediments,
-Radioactive substances, -Heat, -Oil

34. WATER QUALITY EXPRESSION
• EXPRESSING CONCENTRATION
• The properties of solutions, suspensions
and colloids depend to large extent on their
concentrations. Since concentrations need
to be expressed quantitatively, instead of
qualitatively terms like dilute or strong,
concentration are usually expressed in
terms of mass per unit volume, part per
million or billion, or percent.

35. MASS PER UNIT VOLUME:
• One of the common types of concentration is
milligram per liter (mg/L).
• If 0.3g of salt is dissolved in 1500mL of water, then
the concentration is expressed as
300mg/1.5L=200mg/L, where 0.3g = 300mg and
1500mL = 1.5L (1g=1000mg/L; 1L=1000mL).
• For example, a concentration of 0.004mg/L is
preferably written as its equivalent 4g/L. Since
1000g=1mg, e.g., a concentration of 1250g/L is
equivalent to 1.25mg/L.
• In air, concentrations of particulate matter of gases
are commonly expressed in terms of micrograms
per cubic meter (g/m3).

36. PART PER MILLION:
• One liter of water has a mass of 1kg. But 1kg
is equivalent to 1000g or 1 million mg.
therefore, if 1 mg of a substance is dissolved
in 1 L of water, we can say that there is 1 mg
of solute per million mg of water. In other
words, there is one part per million (1 ppm)
• 1mg/L=1ppm.
• MICROg/L is preferred over its equivalent of
ppb.

37. PERCENTAGE
CONCENTRATION:
• Concentrations in excess of 10000mg/L are
generally expressed in terms of percent, for
conveniences. For practical purposes, the
conversion of 1 percent = 10000 mg/L be used
even though the density of the solutions are slightly
more than that of pure water (10000mg/L =
10000mg/1000000mg = 1 mg/100 mg = 1 percent).
• A concentration expressed in terms of percent may
be also computed using the following expression.
Percent = (Mass of Solute (mg)/ Mass of
Solvent (mg)) X 100

38. Work out
• EXAMPLE: A 500-mL aqueous solution has 125mg of salt
dissolved in it. Express the concentration of this solution in
terms of (a) mg/L, (b)ppm, (c)gpg (d) Percent and (e) lb/mil gal
• Solution
• (125mg/500mL)X1000mL/L = 250mg/L
• 250mg/L = 250 ppm
• (250 mg/L X 1gpg)/17.1 mg/L = 14.6 gpg
• Applying this equation Percent = (Mass of Solute (mg)/ Mass
of Solvent (mg))X 100
• Percent = 0.125g/500g X 100 = 0.025 percent Or divide
250mg/L by 10,000 to get 0.025 percent
• 250 mg/L X 8.34 = 2090 lb/mil gal

39. PHYSICAL PARAMETERS
• Turbidity
• Temperature
• Colour
• Taste and Odour

40. CHEMICAL PARAMENTER OF
WATER QUALITY.
• DISSOLVED OXYGEN
• BIOCHEMICAL OXYGEN DEMAND
• CHEMICAL OXYGEN DEMAND
• NITRATE
• PHOSPHATE
• IRON
• MANGANESE
• COPPER
• ZINC
• TDS
• TSS etc

41. CHEMICAL PARAMENTER OF
WATER QUALITY.
• The amount of oxygen used to completely decompose or stabilize all
the biodegradable organics in a given volume of water is called
Ultimate BOD,
• The BOD is a function of time. At the very beginning of a BOD test,
or time = 0, no oxygen will have been consumed and the BOD = 0.
As each day goes by oxygen is used by the microbes and the BOD
increase. Ultimately, the BODL is reached and the organics are
completely decomposed. A graph of the BOD versus time has the
characteristic shape called the BOD Curve.
• The BOD curve can be expressed mathematically by the following
equation:
• BODt = BODL X (1 – 10-kt
)
• Where BODt = BOD at any time t. mg/L
• BODL = Ultimate BOD, mg/L
• k = constant representing the rate of BOD reaction
• t = time, d

42. CHEMICAL PARAMENTER OF
WATER QUALITY.
• Example: A sample of sewage from a town is found
to have a BOD after 5 d (BOD5) of 180mg/L.
Estimate the Ultimate BOD (the BODL) of the
sewage assuming that k = 0.1/d for this waste water.
• Solution
• BODt = BODL X (1 – 10-kt
)
• 180 = BODt = BODL X (1 – 10-kt
) , It implies that
180 = BODL X (1-10-0.1X5
)
• Therefore 180 = BODL X (1- 0.316) ; 180 = BODL
X 0.684
• Rearranging terms to solve for BODL gives
• BODL = 180/0.684 = 260 mg/L Rounded off.

43. Measurement of BOD5
• The traditional BOD test is conducted in the standard 300-
mL glass BOD bottles. The test for 5-d BOD of water sample
involves taking two DO measurements: an initial
measurement when the test begins, at time t = 0, and a
second measurement, at t = 5, after the sample has been
incubated in the dark for 5 d at 20o
C. The BOD5 is simply the
difference between the two measurements.
• For example consider that a sample of water from a stream
is found to have an initial DO of 8.0 mg/L. It is placed directly
into a BOD bottle and incubated for 5 d at 20o
C. After the 5
d, the DO is determined to be 4.5mg/L.The BOD is the
amount of oxygen consumed, or the difference between the
two DO readings. That is, BOD5 = 8.0 – 4.5 = 3.5mg/L.

44. SOLIDS:
• Solids occurs in water either in solution or in suspension. These
2 types of solid are distinguish by passing the water sample
through a glass-fibre filter. By definition, the Suspended Solid
are retain on top of the filter and the Dissolved Solid pass
through the filter with the water.
• If the filtered portion of the water sample is placed in a small
dish and then evaporated, the solid in the water remain as a
residue in the evaporating dish. This material is usually called
Total Dissolved Solid TDS. The concentration of TDS is
expressed in term of mg/L. it can be calculated as follows.
•
• Where A = equal to weigh of dish plus residue. Mg
• B = Weight of empty dish
• C = Volume of sample filtered mL.
C
X
B
A
TDS
1000
)
-
(
≡

45. • Example: The weight of an empty
evaporating dish is determined to be
40.525g. After a water sample is filtered,
100mL of the sample is evaporated from
the dish. The weight of the dish plus dried
residue is found to be 40.545g. Compute
the TDS concentration
200mg/l
C
X
B
A
TDS
1000
)
-
(
≡ 100
1000
)
525
.
40
-
545
.
40
( X
TDS ≡

46. • In drinking water, dissolved liquid may caused taste
problems. Hardness, corrosion, or aesthetic problem may
also accompany excessive TDS concentration. In
wastewater analysis and water pollution control, the
suspended retained on the filtered are of primary
importance and are referred to as TOTAL SUSPENDED
SOLID TSS.
• The TSS concentration can be computed using the TDS
equation,
• where A represent the weight of the filtered plus retained
solid
• B represent the weight of the clean filter
• C represent the volume of the sample filtered

47. TOXIC AND RADIOACTIVE
SUBSTANCES:
• A wide variety of toxic inorganic and organic substances may
be found in water in very small or trace amount. Even in trace
amounts, they can be a danger to public sources, but many
come from industrial activities and improper management of
hazardous waste
• A toxic chemical may be a poison, causing death, or it may
cause disease that is not noticeable until many years after
exposure. A carcinogenic substance is one that causes
cancer; substances that are mutagenic cause harmful effects
in the offspring of exposed people.
• Some heavy metals that are toxic are Cadmium, Cd,
Chromium, Cr, Lead, Pb, Mercury, Hg, and Silver, Ag. Arsenic,
as, Barium, Bar, and Selenium, Se, are also poisonous in
organic elements that must be monitored in drinking water.

48. RADIATION:
• The emission of subatomic particles or energy from
unstable nuclei of certain atoms, referred to as
radiation, poses a serious public health hazard.
Obviously, the consumption of radioactive
substances in water is undesirable, and maximum
allowable concentrations of radioactive materials
have been established for public water supplies.
Potential sources of radioactive pollutants in water
include wastes from nuclear power plants, from
industrial or medical research using radioactive
chemicals, and from refining of uranium ores.
Radon sometimes occurs naturally in groundwater.

49. BIOLOGICAL PARAMETERS OF
WATER QUALITY
• The presence or absence of living organisms in
water can be one of the most useful indicators of its
quality. In the streams, river, and lakes, the diversity
of fish and insect species provide a measure of the
biological balance or health of the aquatic
environment. A wide variety of different species of
organisms usually indicates that the stream or lake
is polluted. The disappearance of certain species
and overabundance of other groups of organisms is
generally one of the effects of pollution.

50. examples
• BACTERIA:
• ALGAE:
• PROTOZOA:
• VIRUESE:
• COLIFORM:

51. AEROBIC AND ANAEROBIC
DIGESTION AND
TYPES OF DECOMPOSITION

52. • Microorganisms , like all living things, require
food for growth . Biological sewage treatment
consists of a step-by-step, continuous,
sequenced attack on the organic compounds
found in wastewater and upon which the
microbes feed.
• In the following sections we will look at the
processes of aerobic and anaerobic digestion
and the decomposition of waste in each
process.

53. Aerobic Digestion
• Aerobic digestion of waste is the natural biological degradation and
purification process in which bacteria that thrive in oxygen-rich
environments break down and digest the waste.
• During oxidation process, pollutants are broken down into carbon
dioxide (CO2), water (H2O), nitrates, sulphates and biomass
(microorganisms). By operating the oxygen supply with aerators,
the process can be significantly accelerated. Of all the biological
treatment methods, aerobic digestion is the most widespread
process that is used throughout the world.
• Aerobic bacteria demand oxygen to decompose dissolved pollutants. Large amounts of
pollutants require large quantities of bacteria; therefore the demand for oxygen will be
high.

54. Advantages of Aerobic Digestion
• Aerobic bacteria are
very efficient in breaking
down waste products.
The result of this is;
aerobic treatment usually
yields better effluent
quality that is obtained in
anaerobic processes. The
aerobic pathway also
releases a substantial
amount of energy. A
portion is used by the
microorganisms for
synthesis and growth of
new microorganisms.
• Path of Aerobic Digestion

55. Aerobic Decomposition
• A biological process, in which,
organisms use available organic
matter to support biological activity.
The process uses organic matter,
nutrients, and dissolved oxygen, and
produces stable solids, carbon dioxide,
and more organisms. The
microorganisms which can only
survive in aerobic conditions are
known as aerobic organisms. In sewer
lines the sewage becomes anoxic if
left for a few hours and becomes
anaerobic if left for more than 1 1/2
days. Anoxic organisms work well
with aerobic and anaerobic organisms.
Facultative and anoxic are basically
the same concept.

56. Anoxic Decomposition
• A biological process in which a
certain group of
microorganisms use
chemically combined oxygen
such as that found in nitrite
and nitrate. These organisms
consume organic matter to
support life functions. They
use organic matter, combined
oxygen from nitrate, and
nutrients to produce nitrogen
gas, carbon dioxide, stable
solids and more organisms.

57. Anaerobic Digestion
• Anaerobic digestion is a complex biochemical
reaction carried out in a number of steps by
several types of microorganisms that require
little or no oxygen to live. During this process, a
gas that is mainly composed of methane and
carbon dioxide, also referred to as biogas, is
produced. The amount of gas produced varies
with the amount of organic waste fed to the
digester and temperature influences the rate of
decomposition and gas production.

58. Anaerobic digestion occurs in
four steps:
• • Hydrolysis : Complex organic matter is decomposed
into simple soluble organic molecules using water to split
the chemical bonds between the substances.
• • Fermentation or Acidogenesis: The chemical
decomposition of carbohydrates by enzymes, bacteria,
yeasts, or molds in the absence of oxygen.
• • Acetogenesis: The fermentation products are
converted into acetate, hydrogen and carbon dioxide by
what are known as acetogenic bacteria.
• • Methanogenesis: Is formed from acetate and
hydrogen/carbon dioxide by methanogenic bacteria.

59. • The acetogenic bacteria grow in
close association with the
methanogenic bacteria during the
fourth stage of the process. The
reason for this is that the
conversion of the fermentation
products by the acetogens is
thermodynamically only if the
hydrogen concentration is kept
sufficiently low. This requires a
close relationship between both
classes of bacteria.
• The anaerobic process only takes
place under strict anaerobic
conditions. It requires specific
adapted bio-solids and particular
process conditions, which are
considerably different from those
needed for aerobic treatment.
Path of Anaerobic Digestion

60. Advantages of Anaerobic
Digestion
• Wastewater pollutants are transformed
into methane, carbon dioxide and smaller
amount of bio-solids. The biomass growth
is much lower compared to those in the
aerobic processes. They are also much
more compact than the aerobic bio-solids.

61. Anaerobic Decomposition
• A biological process, in which,
decomposition of organic matter
occurs without oxygen. Two
processes occur during anaerobic
decomposition. First, facultative acid
forming bacteria use organic matter as
a food source and produce volatile
(organic) acids, gases such as carbon
dioxide and hydrogen sulfide, stable
solids and more facultative
organisms. Second, anaerobic
methane formers use the volatile acids
as a food source and produce
methane gas, stable solids and more
anaerobic methane formers. The
methane gas produced by the process
is usable as a fuel. The methane
former works slower than the acid
former, therefore the pH has to stay
constant consistently, slightly basic, to
optimize the creation of methane.

62. DEMINERALIZATION
• Water, even if it is occurring in nature, consists of lot of
minerals which is harmful for both humans and animals.
The consumption of these harmful minerals can be
avoided by using demineralizer. The minerals present in
water are normally calcium, magnesium, sodium,
alkalinity, chlorides, sulfates, nitrates, and silica which
can also harm industrial pipes, boilers etc by causing
corrosion, scale building, spotting on finished surfaces,
precipitation in chemical products and other related
problems. The demineralizer is designed to sort out
these problems.

63. DEMINERALIZATION
• Dissolved ionic material from water is removed by
demineralization process. This process is followed to
obtain pure water. Demineralization takes place in an ion
exchange unit called as demineralizer or deionizer that
consist of cation bed, an anion bed and a mixed bed in
series. The mixed bed consist of both cation and anion
resins and is called as polisher. The mixed bed provides
the highest ion removal efficiency.
Positively charged ions like calcium, magnesium and
sodium are removed by the cation bed whereas
negatively charged ions like sulfate and chloride are
removed by the anion beds.

64. • It was only after the production of different types of resins
demineralization on large scale began. The popular resin used for
demineralization purpose are:
• Strong Acid Cation
• Weak Acid Cation
• Strong Base Anion
• Weak Base Anion
• Water softening process can be summarized in following chemical
equation:
Softening Process

65. WHAT IS DESALTING
• Water desalting, or desalination, has long been utilized
by water-short nations worldwide to produce or augment
drinking water supplies. The process dates back to the
4th century BC when Greek sailors used an evaporative
process to desalinate seawater.
• Today, desalting plants worldwide have the capacity to
produce over 6.0 billion gallons a day – enough water to
provide over 15 gallons a day for every person in the
United States.
• About 1,200 desalting plants are in operation nationwide.
Most United States plants are used for brackish
(moderately salty) ground water treatment for softening
and organics removal, or to produce highly purified water
for industrial use.

66. Uses of Desalting
• The conversion of salt water to drinking
water is the most publicly recognized
desalting use. Desalting processes are
also used in home water treatment
systems, to treat industrial wastewater, to
produce high-quality water for industrial
purposes, to improve the quality of
drinking water from marginal or brackish
sources, and for the treatment and
recycling of municipal wastewater.

67. The Process
• Water desalting is a process used to remove salt and
other dissolved minerals from water.
• Other contaminants, such as dissolved metals,
radionuclides, bacterial and organic matter may also be
removed by some desalting methods. In addition,
desalting processes are used to improve the quality of
hard waters (high in concentrations of magnesium and
calcium), brackish waters (moderate levels of salt), and
seawater.
• Desalting separates saline water into two products: fresh
water and water containing the concentrated salts, or
brine. Such separation can be accomplished by a
number of processes. The two most widely used are
thermal processes and membrane processes.

68. Thermal (Distillation) Processes
• Nature, through the
hydrologic cycle, provides
our planet with a
continuous supply of
fresh, distilled water.
Water evaporates from
the ocean (salt water) and
other water bodies,
accumulates in clouds as
vapor, and then
condenses and falls to the
Earth’s surface as rain or
snow (fresh water).

69. Thermal (Distillation) Processes
• Distillation desalting processes work in the same way. Over 60% of
the world’s desalted water is produced by heating salty water to
produce water vapor that is then condensed to form fresh water.
Since heat energy represents a large portion of overall desalting
costs, distillation processes often recover and reuse a portion of the
heat required to decrease overall energy requirements. Boiling in
successive vessels, each operated at a lower temperature and
pressure can also significantly reduce the amount of energy
needed.
• Depending on the plant design, distilled water produced from a
distillation plant has salt concentrations of 5 to 50 parts per million
(ppm) Total Dissolved Solids (TDS). Between 25 and 50% of the
source water is recovered by most distillation methods.

70. Membrane Processes
• Both the electrodialysis (ED) and reverse
osmosis (RO) processes use membranes to
separate salts from water. No one desalting
process is “the best.” A variety of factors come
into play in choosing the appropriate process for
a particular situation. These factors include the
quality of the source water, the desired
quantity and quality of the water produced,
pretreatment, energy and chemical
requirements, and concentrate disposal.

71. ELECTRODIALYSIS
• Electrodialysis is an
electrochemical process in which
the salts pass through the
membrane, leaving the water
behind. It is a process typically
used for brackish water. Because
most dissolved salts are ionic
(either positively or negatively
charged) and the ions are
attracted to electrodes with an
opposite electric charge,
membranes that allow selective
passage of either positively or
negatively charged ions can
accomplish the desalting.
Freshwater recovery rates for this
type of unit range from 75 to 95%
of the source water.

72. REVERSE OSMOSIS
• In reverse osmosis, salt water on one
side of a semi-permeable plastic
membrane is subjected to pressure,
causing fresh water to diffuse through
the membrane and leaving behind a
concentrate solution, containing the
majority of the dissolved minerals and
other contaminants. The major energy
requirement for reverse osmosis is for
pressurizing the source, or “feed,”
water. Depending on the
characteristics of the feed water,
different types of membranes may be
used. Because the feed water must
pass through very narrow passages in
the membrane, larger suspended
solids must be removed during an
initial treatment phase (pretreatment).

73. Wastewater Treatment Process

75. Conclusion
• Nanofiltration plants typically operate at 85
to 95% recovery. Brackish water RO
plants typically recover 50 to 80% of the
source water and seawater RO recovery
rates range from 30 to 60%.