WATER QUALITY
ASSESSMENT AND
POLLUTION
CONTROL
WMA 318
Prof. O. Martins and Dr O.Z. Ojekunle
Dept of Water Res. Magt. & Agromet
UNAAB. Abeokuta. Ogun State
Nigeria
oojekunle@yahoo.com
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COURSE CODE: WMA 318
COURSE TITLE: Water Quality Assessment and
Pollution Control
COURSE UNITS: 2 Units
COURSE DURATION: 2 hours per week
COURSE DETAILS
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Course Cordinator: Prof. O. Martins B.Sc., M.Sc., PhD
Email:ola_sumbo@yahoo.co.uk
Office Location: Room B208, COLERM
Other Lecturers: Dr. O.Z. Ojekunle B.Sc., M.Sc., PhD
COURSE CONTENT
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Solvent properties of water; principles of physicochemical analysis, major ionic components of natural
water. Chemistry of natural waters, water quality
requirements, standards for potable water, irrigation
and livestock. Types of water, lithological control of
surface and ground water.
Water Pollution Studies: Sources, fate, pathways and
effects of water pollution, Chemical, Mechanical and
Biological methods of maintaining and improving water
quality.
Pre-requisite:
CHM 202
COURSE REQUIREMENT
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This is a required course for students in the
College of Environmental Resources
Management. They are supposed to passed
CHM 202 before registering for this course. As a
school regulation, a minimum of 75%
attendance is required of the students to enable
him/her write the final examination
READING LIST
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Eidon D. Enger, Bradley F. Smith 2003. Environmental Science: A study of
Interrelationships (Ninth Edition) McGraw-Hill International Edition
Publication.
William P. Cunningham, Mary Ann Cunningham 2008. Principles of
Environmental Sciences, Inquiry and Applications (Fifth Edition) McGrawHill International Edition Publication.
William P. Cunningham, Mary Ann Cunningham 2008. Environmental
Sciences, A Global Concern (Eleventh Edition) McGraw-Hill International
Edition Publication.
PROPERTIES OF WATER
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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. The reason for these and other departures from
“normal” behaviour can be gained by more detailed consideration of the
molecular structure of the compound.
MOLECULAR STRUCTURE OF
WATER
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The spheres representing the ions coalesce to some extent, and the molecule might be
thought of as a sphere having two rather prominent bubbles of “blisters” attached to it.
Te 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.
Although this representation of the molecule is somewhat empirical it helps to explain
some of the abnormal features of the behaviour of water. 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. They
hold molecule together in a fixed pattern in the solid state. In contrast to the orderly
arrangement of molecules in crystal of ice, the molecules of liquid water are in a
chaotic condition of disorder. Hydrogen bonds still remain an important force but
their arrangement is continually shifting
The cohesive forces represented by the hydrogen bonds impact to liquid water is high
heat of vaporization. The forces also tend to prevent the passage to electric currents
and impart to the fluid its high dielectric constant. The attraction between molecules
of a liquid is shown at a liquid surface by the phenomenon called Surface tension.
The surface of water is 75.6 dynes per centimeter at 0oC and 71.8 dynes per
centimeter at 25oC, which are very high values compared with the many other liquids
PROPERTIES OF WATER
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Chemical Constitution of Water
1 Ionic and Non Ionic
Ionic
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Anion
Cations
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2 Major Anions
 Bicarbonate, Chloride, Sulphate
Major Cations
 Sodium, Potassium, Calcium, Magnesium
Non-Ionic
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SiO2, Dissolved gases, oily Substance, Synthetic detergent, etc
CHARACTERISTICS OF WATER
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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-, CO32-,
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.
PHYSICAL CHEMICAL
PARAMETER
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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-
PHYSICAL CHEMICAL
PARAMETER (Cont)
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Temperature: Measurement is relevant
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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
pH: Controlled by CO2/HCO3-/CO32- 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
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PHYSICAL CHEMICAL
PARAMETER (Cont)
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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
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
MEASUREMENT & RELATIONSHIP OF PHYSICAL
CHEMICAL PARAMETERS
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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. Thermistor are
reliable, accurate, and durable temperature sensors that require
little maintenance and are relative inexpensive. The preferred
water-temperature scale for most scientific work ids the Celcius
scale. measure temperature to plus or minus 0.1 degree celcius
(oC)
MEASUREMENT & RELATIONSHIP OF
PHYSICAL CHEMICAL PARAMETERS (Cont)
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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 25oC. Specific conductance 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.
MEASUREMENT & RELATIONSHIP OF
PHYSICAL CHEMICAL PARAMETERS (Cont)
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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.
Before developing the PSS, salinity was reported in part per
thousand/million. Salinity expressed in the PSS is a
dimensionless value, although by convection, it is reported as
practical salinity unit.
MEASUREMENT & RELATIONSHIP OF
PHYSICAL CHEMICAL PARAMETERS (Cont)
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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. Occasion of
super saturation (greater than 100 percent DO saturation) often are related to
excess photosynthetic production of oxygen by aquatic plants as a result of
nutrient (nitrogen and Phosphorus) enrichment, sunlight and warm water
temperature.
DO may be depleted in inorganic oxidation reaction or by biological and
chemical processes that consume dissolved, suspended or precipitated organic
matter.
The DO Solubility in saline environments is dependent on salinity as
well as temperature and barometric pressure. DO in water that have
specific conductance values of greater than 2000 microsiemens/centimeter
should be corrected for salinity.
The newest technology for measuring DO is the Luminescent sensor that is
based on dynamic fluorescence quenching.
MEASUREMENT & RELATIONSHIP OF
PHYSICAL CHEMICAL PARAMETERS (Cont)
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pH: The pH of aqueous solution is controlled by the interrelated chemical
reactions that produce or consume hydrogen ions. The pH of a solution is a
measure of the effective hydrogen-ion concentration. More specifically, pH is
a measure that represents the negative base-10 logarithm of hydrogen-ion
activity of a solution, in moles per liter. Solutions having a pH below 7 are
described as acidic, and solutions with pH greater than 7 are described as
basic or alkaline. 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.
A correctly calibrated pH sensor can accurately measure pH to -+ 0.2 pH
units; however, the sensor can be stretched, broken or fouled easily. If the
streamflow rates are high, the accuracy of the pH measurement can be
affected by streaming-potential effects.
MEASUREMENT & RELATIONSHIP OF
PHYSICAL CHEMICAL PARAMETERS (Cont)
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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. Submersible turbidity sensors
typically direct a light beam from light-emitting diode into water sample and
measure the light that scatters or is absorbed by suspended particles in water.
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.
WATER QUALITY
ASSESSMENT AND
POLLUTION
CONTROL
WMA 318 PART 2
Note
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For any water body to function adequately in
satisfying the desired use, it must have
corresponding degree of purity.
Drinking water should be of highest purity. As
the magnitude of demand for water is fast
approaching the available supply,
the concept of management of the quality of
water is becoming as important as its
quantity.
Contaminant
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Are physical, chemical, biological or radiological
substances found as unwanted residue in or on a
substance.
Pathogens: Are micro organisms that can cause
diseases e.g bacteria
Metals (Metals that are harmful in relatively
small amounts are labeled toxic)
Disease caused by contaminants
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Salmonella Typhi
Typhoid fever
Vibro Cholera
Cholera
Entameoba histolytica Amoeba Dysentery
Escherichia Coli (E. Coli) Gastroenterits
Enterovirus
Polio
Hepatitis
Infestious Hepatitis
Heavy Metal
Cancer
Water Purification Process
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Abstraction: Abstraction involves pumping and transportation of raw water, a process
with high rate of electrical energy consumption. It occurs at the intake.
Screening: Is defined as the process whereby relatively large and suspended debris is
removed from the water before it enters the plant.
Aeration: Aeration (Air Stripping) is a physical treatment process whereby air is
thoroughly mixed with water to removed dissolved gasses and odour.
Coagulation: Addition of chemical to remove suspended solids.
Flocculation: A chemical flocculent, such as aluminium sulphate, is mixed rapidly with
the water to remove mud.
Sedimentation: Also known as clarification- is the gravity-induced removal of particles.
Filtration: Involves the removal of suspended particles from water by passing it
through a layer or bed of a porous granular material e.g sand. The filter water the
passed through nozzles, the nozzles and sand in the filter beds must be cleaned
periodically (This is known as back washing).
Chlorination: After filtration, the water looks much more cleaner than it was in the
dam or river but it may not yet be healthy to drink because it may contain unseen
micro-organism (bacteria) that are dangerous to the human body and can serious
illness (such as diahorrea)
4.5 liters – 1 Gallon. 1 Liter – 100cl. 1 m3 – 5 drums or 200 liter volume.
WATER QUALITY OBJECTIVES
AND REQUIREMENT
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A major advantage of the water quality objectives
approach to water resources management is that it
focuses on solving problems caused by conflicts
between the various demands placed on water
resources, particularly in relation to their ability to
assimilate pollution. The water quality objectives
approach is sensitive not just to the effects of an
individual discharge, but to the combined effects
of the whole range of different discharges into a
water body. It enables an overall limit on levels of
contaminants within a water body to be set according
to the required uses of the water.
WQ Criteria
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For some other water quality variables, such as
dissolved oxygen, water quality criteria are set at
the minimum acceptable concentration to
ensure the maintenance of biological functions.
Examples of the development of national water quality
criteria and guidelines in Nigeria
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In Nigeria, the Federal Environmental
Protection Agency (FEPA) issued, in 1988, a
specific decree to protect, to restore and to
preserve the ecosystem of the Nigerian
environment. The decree also empowered the
agency to set water quality standards to protect
public health and to enhance the quality of
waters
Background Information
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FEPA approached this task by reviewing water quality
guidelines and standards from developed and
developing countries as well as from international
organisations and, subsequently, by comparing them
with data available on Nigeria's own water quality.
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The standards considered included those of Australia,
Brazil, Canada, India, Tanzania, the United States and
the World Health Organization (WHO). These sets of
data were harmonised and used to generate the Interim
National Water Quality Guidelines and Standards for
Nigeria
Background Information (Cont)
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These sets of data were harmonised and used to
generate the Interim National Water Quality Guidelines
and Standards for Nigeria. These address drinking
water, recreational use of water, freshwater aquatic life,
agricultural (irrigation and livestock watering) and
industrial water uses. The guidelines are expected to
become the maximum allowable limits for inland
surface waters and groundwaters, as well as for nontidal coastal waters. They also apply to Nigeria's
transboundary watercourses, the rivers Niger, Benue
and Cross River, which are major sources of water
supply in the country.
THE NATIONAL ENVIRONMENTAL
STANDARDS AND REGULATIONS
ENFORCEMENT AGENCY (NESREA)
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Prior to the dumping of toxic waste in Koko village, in Delta
State, in 1987, Nigeria was ill equipped to manage serious
environmental crisis, as there were no institutional arrangement
or mechanisms for environmental protection and enforcement
of environmental laws and regulations in the country.
Arising from the Koko toxic episode, the Federal Government
promulgated the Harmful Waste Decree 42 of 1988, which
facilitated the establishment of the Federal Environmental
Protection Agency (FEPA) through Decree 58 of 1988 and 59
(amended) of 1992. FEPA was then charged with the overall
responsibility of environmental management and protection. It is
on record that by the establishment of FEPA, Nigeria became
the first in African country to establish a national institutional
mechanism fir environmental protection.
NESREA (Cont)
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In the wisdom of Government, FEPA and other relevant
Departments in other Ministries were merged to form the
Federal ministry of Environment in 1999, but without an
appropriate enabling law on enforcement issues. This situation
created a vacuum in the effective enforcement of environmental
law standards and regulations in the country.
To address this lapse, the Federal Government in line with
Section 20 of the 1999 constitution of the Federal Republic of
Nigeria, established the National Environmental Standard and
Regulations Enforcement Agency (NESREA), as a parastatal of
the federal Ministry of Environment. By the NESREA Act 2007,
the Federal Environmental Protection Agency Act Cap F10 LFN
2004 has been repealed (NESREA 2007).
Table 1 Definition Related to Water
Quality and Pollution Control
Water quality criteria for individual use categories
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Water quality criteria have been widely established for a
number of traditional water quality variables such as pH,
dissolved oxygen, biochemical oxygen demand for
periods of five or seven days (BOD5 and BOD7),
chemical oxygen demand (COD) and nutrients. Such
criteria guide decision makers, especially in countries
with rivers affected by severe organic pollution, in the
establishment of control strategies to decrease the
potential for oxygen depletion and the resultant low
BOD and COD levels.
Development of criteria for Aquatic DO
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Numerous studies have confirmed that a pH range of
6.5 to 9 is most appropriate for the maintenance of fish
communities.
Low concentrations of dissolved oxygen, when
combined with the presence of toxic substances may
lead to stress responses in aquatic ecosystems because
the toxicity of certain elements, such as zinc, lead
and copper, is increased by low concentrations of
dissolved oxygen.
High water temperature also increases the adverse
effects on biota associated with low concentrations
of dissolved oxygen.
Criteria for Aquatic Life DO
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The water quality criterion for dissolved oxygen,
therefore, takes these factors into account. Depending
on the water temperature requirements for particular
aquatic species at various life stages, the criteria values
range from 5 to 9.5 mg/l, i.e. a minimum dissolved
oxygen concentration of 5-6 mg/l for warm-water
biota and 6.5-9.5 mg/l for cold-water biota. Higher
oxygen concentrations are also relevant for early
life stages. More details are given in Alabaster and
Lloyd (1982) and the EPA (1976, 1986).
BOD Requirement
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In Nigeria, the interim water quality criterion for
BOD for the protection of aquatic life is 4 mg
O2 l-1 (water temperature 20-33 °C), for
irrigation water it is 2 mg O2 l-1 (water
temperature 20-25 °C), and for recreational
waters it is 2 mg O2 l-1 (water temperature 20-33
°C) (FEPA, 1991).
Drinking Water Criteria
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Quality criteria for raw water generally follow drinking-water
criteria and even strive to attain them, particularly when raw
water is abstracted directly to drinking-water treatment works
without prior storage. Drinking-water criteria define a quality of
water that can be safely consumed by humans throughout their
lifetime. Such criteria have been developed by international
organisations and include the WHO Guidelines for Drinking water
Quality (WHO, 1984, 1993) and the EU Council Directive of 15 July
1980 Relating to the Quality of Water Intended for Human Consumption
(80/778/EEC), which covers some 60 quality variables. These
guidelines and directives are used by countries, as appropriate, in
establishing enforceable national drinking-water quality standards.
Irrigation
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Poor quality water may affect irrigated crops by
causing accumulation of salts in the root one, by
causing loss of permeability of the soil due
to excess sodium or calcium leaching, or by
containing pathogens or contaminants
which are directly toxic to plants or to those
consuming them.
Irrigation
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Even when the presence of pesticides or
pathogenic organisms in irrigation water does
not directly affect plant growth, it may
potentially affect the acceptability of the
agricultural product for sale or consumption.
Criteria have been published by a number of
countries as well as by the Food and Agriculture
Organization of the United Nations (FAO)
Irrigation Criteria Takes into
Account
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Water quality criteria for irrigation water generally take into
account, amongst other factors, such characteristics as crop
tolerance to salinity, sodium concentration and phytotoxic
trace elements.
The effect of salinity on the osmotic pressure in the unsaturated
soil zone is one of the most important water quality
considerations because this has an influence on the
availability of water for plant consumption.
Sodium in irrigation waters can adversely affect soil structure
and reduce the rate at which water moves into and through
soils. Sodium is also a specific source of damage to fruits.
Phytotoxic trace elements such as boron, heavy metals and
pesticides may stunt the growth of plants or render the crop
unfit for human consumption or other intended uses.
Livestock watering
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Livestock may be affected by poor quality water causing
death, sickness or impaired growth. Variables of
concern include nitrates, sulphates, total dissolved
solids (salinity), a number of metals and organic
micropollutants such as pesticides. In addition,
bluegreen algae and pathogens in water can present
problems.
Some substances, or their degradation products,
present in water used for livestock may occasionally
be transmitted to humans.
The purpose of quality criteria for water used for
livestock watering is, therefore, to protect both the
livestock and the consumer.
Livestock Water Standard
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Criteria for livestock watering
usually take into account the
type of livestock, the daily
water requirements of each
species, the chemicals added
to the feed of the livestock to
enhance the growth and to
reduce the risk of disease, as
well as information on the
toxicity of specific substances
to the different species
Recreational use
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Recreational water quality criteria are used to assess the safety of
water to be used for swimming and other water-sport activities.
The primary concern is to protect human health by preventing
water pollution from faecal material or from contamination
by microorganisms that could cause gastro-intestinal
illness, ear, eye or skin infections.
Criteria are therefore usually set for indicators of faecal pollution,
such as faecal coliforms and pathogens. There has been a
considerable amount of research in recent years into the
development of other indicators of microbiological pollution
including viruses that could affect swimmers. As a rule,
recreational water quality criteria are established by government
health agencies.
Amenity use
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Criteria have been established in some countries aimed
at the protection of the aesthetic properties of water.
These criteria are primarily orientated towards visual
aspects. They are usually narrative in nature and may
specify, for example, that waters must be free of
floating oil or other immiscible liquids, floating debris,
excessive turbidity, and objectionable odours. The
criteria are mostly non-quantifiable because of the
different sensory perception of individuals and because
of the variability of local conditions.
Commercial and sports fishing
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Water quality criteria for commercial and sports
fishing take into account, in particular, the
bioaccumulation of contaminants through
successive levels of the food chain and their
possible biomagnification in higher trophic
levels, which can make fish unsuitable for
human consumption.
In India, the Central Pollution Control Board (CPCB) has
developed a concept of designated best use.
Designated Best Use
Class
Criteria
Drinking Water Source without
conventional treatment but after
disinfection
A
1.Total Coliforms Organism MPN/100ml shall be 50 or less
2. pH between 6.5 and 8.5
3. Dissolved Oxygen 6mg/l or more
4. Biochemical Oxygen Demand 5 days 20 C, 2mg/l or less
Outdoor bathing (Organised)
B
1.Total Coliforms Organism MPN/100ml shall be 500 or less
2. pH between 6.5 and 8.5
3. Dissolved Oxygen 5mg/l or more
4. Biochemical Oxygen Demand 5 days 20 C, 3mg/l or less
Drinking water source after
conventional treatment and
disinfection
C
1. Total Coliforms Organism MPN/100ml shall be 5000 or less
2. pH between 6 and 9
3. Dissolved Oxygen 4mg/l or more
4. Biochemical Oxygen Demand 5 days 20 C, 3mg/l or less
Propagation of Wild life and
Fisheries
D
1. pH between 6.5 and 8.5
2. Dissolved Oxygen 4mg/l or more
3. Free Ammonia (as N)
4. Biochemical Oxygen Demand 5 days 20 C, 2mg/l or less
Irrigation, Industrial Cooling,
Controlled Waste disposal
E
1. pH between 6.0 and 8.5
2. Electrical Conductivity at 25 C micro mhos/cm, maximum 2250
3. Sodium absorption Ratio Max. 26
4. Boron Max. 2mg/l
Below-E
Not meeting any of the A, B, C, D & E criteria
A colour coding frequently used to
depict the quality of water on maps
Blue water
This water can be directly used for drinking, industrial use, etc.
Green water
Water contained in soil and plants is termed as green water
White water
Brown or grey water
Atmospheric moisture is white water
Various grades of wastewater are shown by brown or grey colour
Water Quality Criteria
Characteristics
Designated best use
A
B
C
D
E
Dissolved Oxygen (DO)mg/l, min
6
5
4
4
-
Biochemical Oxygen demand (BOD)mg/l, max
2
3
3
-
-
Total coliform organisms MPN/100ml, max
50
500
5,000
-
-
6.5-8.5
6.5-8.5
6.0-9.0
6.5-8.5
6.0-8.5
Colour, Hazen units, max.
10
300
300
-
-
Odour
Un-objectionable
-
-
pH value
Taste
Tasteless
-
-
-
-
Total dissolved solids, mg/l, max.
500
-
1,500
-
2,100
Total hardness (as CaCO3), mg/l, max.
200
-
-
-
-
Calcium hardness (as CaCO3), mg/l, max.
200
-
-
-
-
Magnesium hardness (as CaCO3), mg/l, max.
200
-
-
-
-
Copper (as Cu), mg/l, max.
1.5
-
1.5
-
-
Iron (as Fe), mg/l, max.
0.3
-
0.5
-
-
Manganese (as Mn), mg/l, max.
0.5
-
-
-
-
Cholorides (as Cu), mg/l, max.
250
-
600
-
600
Sulphates (as SO4), mg/l, max.
400
-
400
-
1,000
Suspended particulate matter and
sediment

The attempts in some countries to develop quality
criteria for suspended particulate matter and sediment
aim at achieving a water quality, such that any sediment
dredged from the water body could be used for soil
improvement and for application to farmland.
Another goal of these quality criteria is to protect
organisms living on, or in, sediment, and the related
food chain. Persistent pollutants in sediments have
been shown to be accumulated and biomagnified
through aquatic food chains leading to unacceptable
concentrations in fish and fish-eating birds.

NOTE: SEE VARIOUS TABLE FOR DATA

WATER QUALITY
ASSESSMENT AND
POLLUTION
CONTROL
WMA 318 PART 3
TYPES OF WATER

Water is commonly described either in terms of
its nature, usage, or origin. The implications
in these descriptions range from being
highly specific to so general as to be nondefinitive. Ground waters originate in
subterranean locations such as wells, while
surface waters comprise the lakes, rivers, and
seas.
TYPES OF WATER (Cont)


Fresh Water (precisely less than 0.5%)
Fresh water may come from either a surface or ground
source, and typically contains less than 1% sodium chloride. It
may be either "hard" or "soft," i.e., either rich in
calcium and magnesium salts and thus possibly
forming insoluble curds with ordinary soap. Actually,
there are gradations of hardness, which can be
estimated from the Langelier or Ryznar indexes or
accurately determined by titration with standardized
chelating agent solutions such as versenates.
TYPES OF WATER (Cont)



Brackish Water
Brackish water contains between 0.5 or 1 and 2.5%
sodium chloride, either from natural sources around
otherwise fresh water or by dilution of seawater.
Brackish water differs from open seawater in certain
other respects. The biological activity, for example, can
be significantly modified by higher concentrations of
nutrients. Fouling is also likely to be more severe as a
consequence of the greater availability of nutrients.
The main environmental factors responsible,
singly or in combination, for these differences are
the salinity, the degree of pollution, and the
prevalence of silt.
TYPES OF WATER (Cont)


Seawater
Seawater typically contains about 3.5% sodium chloride,
although the salinity may be weakened in some areas by dilution
with fresh water or concentrated by solar evaporation in others.
Seawater is normally more corrosive than fresh water
because of the higher conductivity and the penetrating power of
the chloride ion through surface films on a metal. The rate of
corrosion is controlled by the chloride content,
oxygen availability, and the temperature.
Saline




Water is classified as "saline" when it becomes a risk for
growth and yield of crops. Saline water has a relatively high
concentration of dissolved salts (cations and anions). Salt is
not just "salt" as we know it - sodium chloride (NaCl) - but can
be dissolved calcium (Ca2+), magnesium (Mg2+), sulfate (SO42), bicarbonate (HCO3-), Boron (B), and other compounds.
Water can be both saline and sodic, or saline-sodic. If water
has an EC greater than 4 (2 for horticulture) and a Sodium
Adsorption Ration (SAR) greater than 12, it is considered
saline-sodic
The concentration is usually expressed in parts per million
(ppm) of salt.
If water has a concentration of 10,000 ppm of dissolved salts,
then one percent (10,000 divided by 1,000,000) of the weight
of the water comes from dissolved salts.
Classification of Salinity





Slightly saline water contains around 1,000 to 3,000
ppm. 0.1-0.3%
Moderately saline water contains roughly 3,000 to
10,000 ppm. 0.3-1%
Highly saline water has around 10,000 to 35,000 ppm
of salt. 1-3.5%
Seawater has a salinity of roughly 35,000 ppm,
equivalent to 35 g/L. 3.5-5.0%
Brine Greater 50,000 ppm. 5.0% above
Salinity in Different Water Bodies
Water salinity based on dissolved salts in parts per thousand (ppt)
Fresh water
Brackish water
Saline water
Brine
< 0.5
0.5 – 30
30 – 50
> 50
Relationship between Tidal and Salinity

Salinity variations of the tidal water irrigating the rice fields at
Warri mangrove swamp were studied for one calendar year. It
was found that the mean pH is 7.24 for low tides and 7.14 for
high tides, and pH is highest in July for both high and low
tides. Sodium, calcium and magnesium, the major cationic
constituents of the soluble salts in the saline tidal irrigation
water, as well as potassium a minor ionic constituent were all
found to be highest in June at both low and high tides. Also,
both the Electrical Conductivity (EC) and the derived Sodium
Adsorption Ration (SAR) were highest in June. Salinity at
both high and low tides is highest in June but lowest in
September for high tides and in October for low tides. The
indications are that the adverse effects of salinity are largely
responsible for the poor initial growth and survival of the rice
variety during early seedling stage. From salinity point of view,
it would appear that October is the most favourable month to
transplant rice at the Warri mangrove swamp.
Effects of Salinity

Saline water reduces plant growth to varying degrees, with
grass and grain crops generally showing less sensitivity and
field crops being most sensitive. Aside from biomass reduction,
salinity can have additional effects on plants. For example, in a
study by Bauder et al., both inoculated and non-inoculated
alfalfa were grown with irrigation waters of progressively
higher salinity levels

Correction of Salinity
There are no amendments, chemicals, or additives available
commercially that can be added to saline water to make the
salt go away. Dilution with a non-saline water or salt
precipitation with an evaporation process which leaves the salt
behind and traps the evaporated water can be used. Dilution of
saline irrigation water is only possible if there is a source of
non-saline water with which to dilute the saline water

TYPES OF WATER (Cont)

The combination of high
conductivity and oxygen
solubility is at a maximum at
this point (oxygen solubility
is reduced in more
concentrated salt solutions).
The corrosion of numerous
metals in a wide range of
saline waters is reported in
the following Table.
Effect of velocity on the corrosion of
metals in seawater
TYPES OF WATER (Cont)


Distilled or Demineralized Water
The total mineral content of water can be
removed by either distillation or mixed-bed ion
exchange. In the first case, purity is described
qualitatively in some cases (e.g., triple-distilled
water), but is best expressed, for both
distilled and demineralized water, in terms
of specific conductivity. Water also can be
demineralized by reverse osmosis or
electrodialysis.
TYPES OF WATER (Cont)


Steam Condensate
Water condensed from industrial steam is called
steam condensate. It approaches distilled water
in purity, except for contamination (as by DO or
carbon dioxide) and the effect of deliberate
additives (e.g., neutralizing or filming amines).
TYPES OF WATER (Cont)


Boiler Feedwater Make-up
The feedwater make-up for boilers is always softened
and subsequently deaerated. It may vary in quality
from fairly high dissolved solids (e.g., Zeolite-Treated),
to very pure demineralized feed for high-pressure
boilers. It tends to be highly corrosive, because of
its softness, until thoroughly deaerated. This term is
more precise than “boiler feedwater”, which may
include recirculated steam condensate in various ratios
to fresh make-up water.
TYPES OF WATER (Cont)


Potable Water
Potable water is fresh water that is sanitized with
oxidizing biocides such as chlorine or ozone to
kill bacteria and make it safe for drinking
purposes. By definition, certain mineral
constituents are also restricted. For example, the
chlorinity will be not more than 250 ppm
chloride ion in the United States or 400 ppm on
an international basis.
TYPES OF WATER (Cont)


Process or Hydrotest Water/Firewater
These terms are essentially non-definitive, since
the water employed may be of almost any
chemistry, ranging from demineralized
water to quite saline fresh water or even
seawater in some cases. “Produced water” is
that which originates in oil and gas production,
emanating from geological sources with the
hydrocarbons.
TYPES OF WATER (Cont)


Cooling Water
Cooling water is another undefined term,
although it implies that any necessary
treatment against excessive scaling or
corrosion has been applied, or corrosionresistant material selected. This may include
anything from fresh water to seawater, and may
comprise either an open- or closed-loop system,
or a once-through system.
TYPES OF WATER (Cont)


Waste Water
By definition, waste water is any water that is discarded
after use. Sanitary waste from private or industrial
applications is contaminated with fecal matter, soaps,
detergents, etc., but is quite readily handled from a
corrosion standpoint. Industrial wastes from chemical
or petrochemical sources can contain strange and
specific contaminants which greatly complicate
materials selection, especially in the uses of plastics and
elastomers.
WATER QUALITY
ASSESSMENT AND
POLLUTION
CONTROL
WMA 318 PART 4
SOURCES OF WATER
POLLUTION


The surface water and groundwater systems
Surface water is the water we see in streams,
rivers, wetlands, and lakes across the country.
Every square mile of ground drains into one of
these bodies of water. The area drained is
known as a watershed. As smaller creeks and
rivers feed into larger ones, the size of the
watershed increases.
SOURCES OF WATER
POLLUTION (Cont)


While surface water is found in the form of rivers and
lakes, groundwater is stored in aquifers. Aquifers are
formations of cracked rock, sand, or gravel that hold
water and yield enough water to supply wells or springs.
More than 95 percent of the world’s usable water
resources are stored in its groundwater.
Approximately third-quarter of all Nigerians depends
on groundwater for their drinking water. In most times,
80 percent of all Nigerians depend on groundwater for
their drinking water, and more than 97 percent of all
rural Nigerians, depend on groundwater for their
drinking water supplies.
SOURCES OF WATER
POLLUTION (Cont)


As people pump and use water from these underground aquifers,
the water must be replaced. Aquifers are replenished or
recharged by water seeping down through the soil from surface
water supplies. In some parts of the country, groundwater
supplies are very deep, and pollutants may be filtered out by
layers of soil, sand, and gravel.
In parts of Nigeria, there are more direct links to the
groundwater. In some parts of north-central and south of
Nigeria, the groundwater supply may come within a few meters
of the soil surface. That’s why this area of south is covered with
wetlands and prairie potholes. In these areas, there is much less
filtration by the soil and a greater risk of contamination by
animal wastes, pesticides, and other pollutants. In other parts of
the country, like the east and some part of the south west corner,
limestone sits just below the soil surface. This limestone layer, or
karst, can crack, erode, and form caverns that allow water and
any pollutants to travel with little filtering from the soil.
SOURCES OF WATER
POLLUTION (Cont)

Non-point source pollution refers to
pollutants that come from a widespread area and
cannot be tracked to a single point or source.
Soil erosion, chemical runoff, and animal waste
pollution are all examples of non-point source
pollution. Non-point source pollution is major
water quality problem by sheer volume and in
terms of current and future economic costs to
the nation.
SOURCES OF WATER
POLLUTION (Cont)

Point source pollution – also known as “the end of
the pipe pollution”– can be traced to a specific source,
such as a leaking chemical tank, effluents coming from
a waste treatment or industrial plant, or a manure spill
from a hog confinement lagoon. Although this may
seem easy to control, there are economic, political, and
other factors involved. For known point source
pollution threats, households, communities, industry,
and agribusiness must deal with the problem of
disposing of wastes and by-products.
TREATMENT OF POLLUTANTS








TREATMENT METHODS
There are various levels of treatment that prevent dumping raw
waste products from being dumped into surface waters.
Industrial wastes may require special treatment to remove
harmful chemicals before reentering the water system.
For the more common problem of organic wastes, the three
main treatment methods for treating waste water are
septic systems, lagoons, and sewage treatment plants.
Each method must be properly sized so that the treatment
system is able to handle the volume of waste entering it.
Septic systems are designed for individual households,
lagoons may meet the needs of small towns, and
sewage treatment facilities are necessary for controlling
pollution.
TREATMENT OF POLLUTANTS
(Cont)

Septic systems

Septic systems are generally used in rural areas to handle
household wastes. They usually use a large tank buried in the
ground to contain and break down household sewage. Attached
to the tank is a series of perforated pipes that are buried in a
drain field and are usually surrounded by crushed rock or gravel
to facilitate drainage. Fats, oils, and grease, as well as large waste
particles, are stored and later pumped out of the holding tank,
while the water and suspended solids in the water flow into the
soil through the perforated pipes. The soil around the septic
system filters many harmful compounds, and bacteria break
down organic matter.
TREATMENT OF POLLUTANTS
(Cont)



STANDARD: Septic systems are most popular in rural and
suburban areas and must be located in soils that meet standards
for percolation or the ability to drain away water. standards
require a maximum percolation rate of one inch of water in 60
minutes. A slow percolation rate allows soil bacteria to break
down wastes as they move into soil layers.
CONCERN: Septic systems are generally a greater source of
concern for groundwater pollution than for surface water
pollution. However, septic systems are a real concern for surface
water pollution when they are located near lakes, rivers, and
streams. Of particular concern are lakes with high concentrations
of tourist homes.
Note: 1 Cube Inch is equal 16.34 cm3, Multiple inch by 2.54 to get Centimetre
TREATMENT OF POLLUTANTS
(Cont)

Lagoons

Many communities, feedlot operators, and industries use lagoons
to control wastes. A lagoon is simply one or a series of shallow
holding pits into which wastes are pumped and treated. In a welldesigned lagoon system, the material is aerated so bacteria can
break down the organic matter.
STANDARD: In municipal lagoons, the water generally stays in
the lagoon for at least 30 days for this process to be completed.
Then the water is removed and treated with chlorine as needed
to destroy remaining bacteria. The remaining solids must be
disposed of by spreading on farm fields or burying.
CONCERN: Lagoons are inexpensive to construct and operate
compared to other systems. However, poorly constructed
lagoons and lagoons built where the water table is very high have
been found to leak. The most often found contaminant tends to
be nitrates.


TREATMENT OF POLLUTANTS
(Cont)





Treatment plants
We require two levels of sewage treatment.
Primary sewage treatment simply filters out unwanted items such as sticks,
stones, garbage, and other debris that arrive at the treatment plant and allows
time for the solid materials to settle out.
Secondary treatment uses aeration and aerobic, or oxygen-using, bacteria
to break down organic wastes. The water is then treated with chlorine to kill
bacteria and discharged into adjacent rivers and streams.
Treatment plants remove approximately

90 percent of the organic waste and suspended solids,
less than 70 percent of the toxic metals and synthetic organic chemicals,
50 percent of the nitrogen in the form of nitrates, and

30 percent of the phosphorus in the form of phosphates.



CONCERN: This remaining discharge is still high in nutrients and is not pure
water entering the surface water. More advanced treatment systems are
available, but they are rarely used due to their high cost. The remaining sludge
is sent to a landfill as waste or applied to the land as a soil additive.
Wastewater Treatment Process
TREATMENT OF POLLUTANTS
SUMMARY









Runoff pollution is difficult to control. The best method of control is limited
use of chemical pesticides.
The speed and amount of movement depends on whether
the pesticide is water-soluble,
the soil type,
the amount of rain, and
the proximity of the water table to the surface.
Over time, nearly all pesticides break down to other chemicals as they are
exposed to sunlight and air. Generally, it is these base chemicals that are
detected in groundwater.
Some agricultural drainage wells provide direct pathways for pollutants
to enter groundwater.
The forms of nitrogen that cause problems as pollutants are the nitrate
and ammonium forms. The nitrate form is water-soluble and moves
with the water into surface water or groundwater. The ammonium form
attaches to soil particles.
MAINTAINING AND
IMPROVING WATER QUALITY




Cultural,
Mechanical,
Biological and
Chemical Control
The best solution is prevention




Just as there is no single source of water pollution, there is no
single answer to solve the problem. Once water has become
contaminated, it is very difficult, if not impossible, to clean. Surface
water flows quickly, and a pollutant will generally be diluted as it enters larger bodies of water.
However, even large bodies of water, such as the Gulf of Mexico near the mouth of the
Mississippi River, cannot tolerate many years of eroded soils, increased nutrients, and chemical
pollution.
Groundwater, however, moves very slowly. In heavy clay layers or in bedrock, water might only
move several inches per year. Even in gravel and sand aquifers, groundwater may move only
several hundred to a thousand feet per year. Once the water is polluted, it will
spread out slowly over a period of many years.
Some problems, such as hazardous waste sites, require massive, expensive clean-up procedures.
With other problems, such as large manure spills, little can be done but let the wastes become
diluted as they reach larger bodies of water.
However, there are steps to take to reduce some of the most
serious problems such as siltation from erosion is passed
legislative law to warn deterrent
Other Methods Are

No-till and minimum-till farming: Most of the crop residues
- the stalks and leaves of the harvested crop - are left on the
surface of the field with no-till and minimum-till farming. Crops
are planted into the crop residue the next year. This may reduce
soil loss by up to 90 percent. The residue helps keep raindrops
from directly hitting the soil and breaking it into small erodible
particles.

With no-till or minimum-till farming, crop residue remains
to protect the soil from rain or wind.

Contour farming: Contour farming involves planting crops in
rows that circle around a hill in contours rather than in straight
rows that go up and down the hill. These contours help break
the water flow. With conventional farming methods, straight
rows encourage the water to run down the row and wash along
soil.
Other Methods Are (Cont)


Terraces: For very steep hillsides, terraces may be required.
Terraces are constructed by planting a short slope with grass or
other cover crops and then planting the level area with crops.
This pattern of short slopes and planting areas follows the
hillsides. This practice breaks up the steep hill into a series
of shorter slopes and level areas and slows down the water
flow. Since the terraces are planted in grass, they hold the
slope in place and reduce erosion. Terracing provides good
protection for steeper slopes, especially if combined with
low-till or no-till farming.
Grassed waterways: Where concentrated water runoff occurs
due to the sloping of several hills or along bottom slopes,
planting grass or hay is recommended. As water collects and runs
along these erosion-prone areas, the denser root systems of the
grasses help hold the soil in place to prevent these areas from
washing out and forming gullies.
Other Methods Are (Cont)

Grasses and filterstrips: Stream banks and
road ditches also need to be protected. Plants
growing on banks and slopes help hold the soil.
Along stream and river banks, filter-strips of
grasses and trees help slow down water run-off
and help prevent soil from washing into
waterways.

Filter strips help reduce erosion along
stream and river banks.
Good pest management depends

Since polluted groundwater is nearly impossible to
clean, prevention is the only solution. For pesticides, this
means reducing the use of chemicals and focusing on
an integrated pest management program that controls
weeds and insects by more natural means whenever
possible and resorting to pesticides only as a last resort.

Good pest management depends on four
methods of s control: cultural, mechanical,
biological, and chemical.
CULTURAL CONTROL





Cultural control relies on planting factors such as crop
rotation and planting after weeds have been killed following
germination. Good management starts with scouting fields
on a regular basis. Keeping records of past problem areas helps
control pests, as well as the need for chemical means of
controlling pests.
The first step is to determine the seriousness of the
infestation of weeds or insects. This is where trade-offs take
place.
Will the potential loss of crop yield be greater than the cost of
chemical treatment?
Are there other options that might be cheaper and less
environmentally dangerous?
There are no set answers since each farm is different and each
year brings new challenges.
MECHANICAL CONTROL



Mechanical weed control or cultivation is one of the
oldest forms of control. Tools like the rotary hoe are
used when plants are small, while a cultivator is used on
larger plants. Although mechanical control requires the
use of fuel to pull the implement across the fields,
it results in reduced chemical control.
Most farmers substituting mechanical control for
herbicides estimate that it costs them about half of
what their neighbors spend on chemical control.
BIOLOGICAL CONTROL





Biological control introduces insects and plant diseases that
target specific weed or other pest populations. One example in
the Midwest is the introduction of the musk thistle weevil which
feeds on musk thistles. Thistles are tough weeds to control, and
the weevil appears promising in controlling pest populations.
Insect control is best suited for pasture land rather than
crop land Cultivation tends to disrupt the life cycle of the
insects.
Researchers are also developing microbial controls. These
microbes are essentially plant diseases that occur naturally. The
microbes are cultured in labs and sprayed on fields where they
select the weeds but not the crops.
One major advantage of biological control is that the
diseases can adapt to changing weeds so they can’t build
up resistance or tolerances, which has occurred with
herbicides and insects.
Musk thistle weevils are used as a biological control on
thistles.
CHEMICAL CONTROL



Farmers using other controls methods must occasionally resort
to chemical control for tough cases. However, even when
chemical control is required, it’s possible to reduce the amounts
of chemicals used.
Careful calibration or setting of the sprayer is essential to not
over-apply chemicals.
In addition, many farmers use banding techniques that spray
chemicals in a narrow band over the crop row and rely on
cultivation for the weeds between rows. An Iowa State
University research study shows that this method reduces the
amount of chemicals used by 50 to 67 percent, while maintaining
the corn yield on 99 percent of the fields tested.
Controlling nitrate pollution



General management practices may help ease the
problem of nitrate pollution, but they also rely on tradeoffs that protect both the economic interests of the
farmer and the natural environment.
The bottom line is not to apply more nitrogen based
fertilizers, either artificial or natural animal byproducts,
than the crops need for that growing season.
Since ammonia may be lost to the air and nitrates may
be moved with the water, it is economical for the
farmer to apply only the amount of nitrogen needed
and only at the time it is needed by the plants.
SUMMARY

Storm water, drainage systems in town and
city are also considered to be dispersed
sources of many pollutant, because, even
though the pollutant are often convene into
streams or lakes in drainages pipes or storm
sewer, they are usually many of these
discharges scattered over a large area.
SUMMARY (Cont)

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.
SUMMARY (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
SUMMARY (Cont)




Domestic Sewage is a primary source of the first three types of
pollutant.
Pathogen or diseases causing micro-organism are excreted in the
feaces of infected person and may be carried into water receiving
sewage discharges. Sewage from communities with large
population is very likely to contained pathogen of some type.
Sewage also carries oxygen demanding substance—the organism
waste that exert a biochemical oxygen demand as they are
decomposed by microbes. BOD changes the ecological balance
in a body of water by depleting the Dissolved Oxygen DO
content.
Nitrogen and phosphorus, the major plant nutrients are in
sewage, too, as well as in runoff from farm and from suburban
lawns.
SUMMARY (Cont) SOLUTION

Conventional Sewage treatment processes significantly
reduce the amount of pathogens and BOD in sewage,
but do not eliminate them completely. Certain virus, in
particular, may be somewhat resistant to the sewage
disinfection processes. (A virus is an extremely small
pathogenic organism that can only be seen with
electron microscopes). To decrease the amount of
Nitrogen and Phosphorus in sewage, usually some form
of advanced sewage treatment must be applied.
Toxic Chemical

Toxic organic chemical, primary pesticide may be carry
into the water in the surface runoff from agricultural
areas. Perhaps the most dangerous type is the family of
chemical called Chlorinated hydrocarbons. Common
examples are known by there common chemical names
as chlordane, Dieldrin, Heptachlor, and the famous
DDT., which has been banned all over the world. They
are very effective poison against insect that demand
agriculture crops. Unfortunately, they can kill fish, birds,
and animals, including humans. And they are not very
biodegradable, taking more than 30 years in some cases
to dissipate from the environment.
Inorganic and Oil


Poisonous inorganic chemical, specifically those of the
heavy metal group, such as lead, mercury, and
chromium, also usually originate from industrial
activities and are considered hazardous waste.
Oil is washed into surface water in ruoff from road and
parking lot, and groundwater can be polluted from
leaking underground tanks, accidental oil spills from
large transport tankers at a sea occasional occur,
causing significant environmental damage. Blow out
accident at offshore oil wells can release many thousand
of tonnes of oil in a short period of time. Oil spills at
sea may eventually move towards shore, affecting
aquatic life and damaging recreational areas.
CALCULATIONS
EXPRESSING CONCENTRATION




The properties of solutions, suspensions and colloids depend to large extent on their
concentrations. A dilute or weak solution has a relatively small amount of solute
dissolved in the solvent. It has a characteristic different from those concentrated or
strong solution of the same substances, in which a relatively large amount of solute is
present. 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.
MASS PER UNIT VOLUME: One of the common types of concentration is
milligram per liter (mg/L). For example, if a mass of 10 mg of oxygen is dissolved in a
volume of 1 L of water, the concentration of that solution is expressed simply as
10mg/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).
Very dilute solutions are more conveniently expressed in term of micrograms per liter
(g/L). 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).



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)
Neglecting the small changes in the density of water as
substances are dissolved in it, we can say that, in general, a
concentration of 1 mg per liter is equivalent to one part per
million: 1mg/L=1ppm. Conversion is very simple; for example,
a concentration of 17.5 mg/L is identical to 17.5ppm
The expression mg/L is preferred over ppm just as the
expression g/L is preferred over its equivalent of ppb. But both
types of units are still used and the student should be familiar
with each.



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).
The concentration of salts in seawater is about 35000mg/L. To
convert to percent salts, divide by 10,000 obtaining 3.5 percent.
The concentration of wastewater sludge may be about 3 percent
solids. To convert this to mg/L, multiply by 10,000 getting
30000mg/L solids.
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


U.S CUSTOMARY UNITS: The expression grains
per gallon (gpg) are sometimes used for concentrations
of certain substances in water. One grain per gallon is
equivalent to a concentration of 17.1 milligrams per
liter: 1gpg=17.1mg/L
The expression pounds per million gallon is also used
in US customary unit of concentration for water
treatment applications. Since 1 gallon of water weighs
8.34lb, 1 gal/mil gal is the same as 8.34 lb/mil gal. Or
we can say that 1mg/L = 8.34 mil gal to convert from
mg/L to lb/mil gal, multiply by 8.34; to go from lb/mil
gal to mg/L. divide by 8.34












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
EXAMPLE: How many pounds of chlorine gas should be dissolved in 8 mil gal of
water to result in a concentration of 0.2 mg/L
Solution
0.2 mg/L X 8.34 = 1.67 lb/mil gal
And 1.67 lb/mil gal X 8 mil gal = 13 lb


BIOCHEMICAL OXYGEN DEMAND: Bacteria and other
microorganisms use organic substance for food. As they metabolize organics
are broken down into simpler compounds, such as CO2 and H2O, and the
microbes use the energy released fro growth and reproduction.
When this process occurs in water, the oxygen consumed is the DO. If
oxygen is not continually replaced in the water by artificial or natural means,
then the DO level will decrease as the organic are decomposed by the
microbes. This need for oxygen is called Biological Oxygen Demand. In effect,
the microbes “demand” the oxygen for use in the biochemical reactions that
sustain them. Organic waste in sewage is one of the major types of water
pollutants. It is impractical to isolate and identify each specific organic
chemical in these wastes and to determine its concentration. Instead, the
BOD is used as an indirect measure of the total amount of biodegradable
organics in the water. The more organic material there is in the water; the
higher the BOD exerted by the microbes will be.


In addition to being used as a measure of the amount of organic pollutant in streams
or lakes, the BOD is used as a measure of the strength of sewage. This is the most
important parameters for design and operation of water pollution control plant. A
strong sewage has a high concentration of organic material and a correspondingly high
BOD. The complete decomposition of organic material by microorganisms takes time,
usually 20d or more under ordinary circumstances. The amount of oxygen used to
completely decompose or stabilize all the biodegradable organics in a given volume of
water is called Ultimate BOD, or BODL for example, if a 1-L volume of municipal
waste requires 300 mg of oxygen for complete decomposition of the organics, the
BODL would be expressed as 300mg/L. One liter of waste from an industrial or food
processing plant may require as much as 1500 mg of oxygen for complete stabilization
of the waste. In this case, the BODL would be 1500mg/L, indicating a much stronger
waste than ordinary municipal or domestic sewage. In general, then, the BOD is
expressed in terms of mg/L of oxygen.
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
The rate at which oxygen is consumed is expressed by the
constant k. the value of this rate constant depend on the
temperature, the type of organic material, and the types of
microbes exerting the BOD. For the ordinary domestic sewage
at a temperature of 20oC, the value of k is usually about 0.15/d









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.
This is particularly true when the BOD data are used to monitor the efficiency of a
water pollution control plant. It has been found that more than two-third of the
BODL is usually exerted within the first 5d of decomposition. For instance, in the
preceding example, the 5d BOD is 180/260 = 0.69, or 69% of the ultimate BOD. For
practical purposes, the 5d BOD, or BOD5, has been chosen as a representation of the
organic content of water or waste water. For standardization of results, the test must
be conducted at a temperature of 20oC.
In summary, the parameter of BOD5 is the amount of dissolved oxygen used by
microbes in the 5 d to decompose organic substances in water at 20oC.




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 20oC. 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 20oC. 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.
Very clean bodies of surface water usually have a BOD5 of about 1 mg/L due
to the presence of naturally occurring from decaying leaves and animal wastes.
BOD5 values in excess of 10 mg/L, however usually indicate the presence of
sewage pollution.

EXPERIMENTATION: When measuring the BOD5 of
sewage, it is necessary to first dilute the sample in the BOD
bottle. Domestic sewage usually has a general BOD value of 200
mg/L. If the sample were not diluted, the entire DO will be
completely depleted and it would not be possible to get a DO
reading on the fifth day. Computation of the BOD5, using this
dilution method in a 300-ml BOD bottle, is done by using the
following equation:
BOD 5



DO0 _DO5 X 300
V
Where DO0 = Initial DO at t = 0
D05 = DO at t = 5d
V = Sample volume, mL







EXAMPLE: A 6.0-ml sample of wastewater is diluted to 300
mL with distilled water in a standard BOD bottle. The initial DO
in the bottle is determined to be 8.5 mg/L, and the DO after 5d
at 20oC is found to be 5.0 mg/L.
Determine the BOD5 of the wastewater and compute its BODL.
Assume that k = 0.1/d
SOLUTION:
BOD5 = ((8.5-5.0) X 300)/ 6.0 = 3.5 X 300/6.0 = 180 mg/L
Now applying BODt = BODL X (1 – 10-kt)
180 = BODL X (1 – 10-0.1X5) and
BODL = 180/0.684 = 260mg/L
CHEMICAL OXYGEN DEMAND



The BOD test provides a measure of the biodegradable organic material in
water, i.e., of the substance that microbe can readily use for food. There
might also be non biodegradable or slowly biodegradable substance that will
not detected by the convectional BOD test.
The Chemical Oxygen Demand, COD is another parameter of water quality
which measures all organics, including the non biodegradable substances. It is
a chemical test using a strong oxidizing agent (Potassium Dichromate),
sulphuric acid and heat. The result of the COD test can be available in just
2hours, a definite advantage over the 5d required for the standard BOD test.
COD values are always higher than BOD values for the same sample, but
there is generally no consistent correlation between the two tests for different
wastewater. In other word, it is not feasible to simply measure the COD and
then predict the BOD. Because most waste water treatment plant are
biological in their mode of operation, the BOD is more representative of the
treatment process and remains a more commonly used parameter than the
COD.


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.

( A - B) X 1000
TDS ≡
C



Where A = equal to weigh of dish plus residue. Mg
B = Weight of empty dish
C = Volume of sample filtered mL.

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
( A - B) X 1000
(40.545 - 40.525) X 1000
= 200mg/L
TDS ≡





C
TDS ≡
100
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

Hardness is usually expressed in term of milligram per
liter of calcium carbonate, CaC03; grains per gallon are
also used to express hardness concentration. Water
with more than 300mg/L of hardness is generally
considered to be hard, and water with less than
75mg/L is considered to be soft. Very soft water is
undesirable in public supply because it tends to increase
corrosion problem in metal pipes; also, some health
official believe it to be associated with the incident of
the heart disease.
Dilution







In water pollution control, it is often necessary to predict the BOD
concentrations and the DO levels downstream from a sewage discharge point.
One of the first computations needed for this involves the effect of dilution.
Assuming that pollutant is completely mixed in the streamflow (at a point just
below the end of the mixing zone), one can calculate the diluted
concentration of any water quality parameter using the following mass
balance equation:
cd = (csQs + cwQw)/(Qs + Qw)
where cd = diluted concentration or temperature
cs = original stream concentration or temperature
cw = waste concentration or temperature
Qs = stream discharge
Qw = waste discharge



A fundamental concept in science is the law of conservation of matter. This means that when there is
no appreciable conversion of mass into energy, the sum of the masses of substances entering into
a reaction must always equal the sum of the masses of products of reaction. Even if there in no
chemical reaction occurring, the law of conservation underlies the concept of mass balance (also
called material balance), and is useful in environmental technology
Mass balance calculations play an important role in the design and operation of water, sewage, air
and solid waste treatment processes. In treatment systems, the physical, chemical, and biological
processes usually occurs in vessel or tanks called reactors, and the particular reactions or processes
are referred to as unit processes. In the simplest case, it can be said that the input must equal the
output, or, in other words, “what goes in must go out.” If this does not occur, there must be an
accumulation (depletion) of the material in the reactor equal to the difference between the input
and output, or accumulation = input-output. Since, in this kind of situation, the composition of
material in the reactor changes with time, it is referred to as an unsteady-state operation. In the steady
state operation, it can be assumed that the rates of input and output are constant, as is the
composition of the completely mixed reactor.
Suppose, for example, two pipes containing salt solutions discharge into a tank in which the two
solutions are completely mixed, and the third pipe carries the mixture out of the tank


The solution in the first pipe has a concentration of c1 mg/L and that in the
second pipe has a concentration of c2 mg/L. the flow rate of the pipes are
Q1 and Q2 respectively. The concept of mass or material balance can be
applied to determine the concentration of the mixed solution discharged from
the tank because under steady-state conditions, the total amount of salt
entering the tank must be equal to the total amount leaving the tank. In other
words, since the salt neither decays nor reacts with other substance (in this
example), the concentration of salt in the mixture in the tank stay constant
over time.
The product of concentration of volume flow rate equals the mass flow rate
because mg/L X L/d = mg/d where the volume flow rate in this example is
expresses in terms of liter per day, or L/d. for convenience here, consider that
the time interval is 1 day. Then the product of c1 X Q must equal the mass of
salt entering the vessel in 1 d from the first pipe. Similarly, c2 X Q equals the
mass of salt entering the tank from the second pipe. The total mass of salt
entering the tank in 1 d, that is, the input, must be equal to the sum from the
two pipes, or input = c1 X Q1 + c2 X Q2.





The total mass of salt leaving the tank equals the product of the
concentration in the mixture c3 and the volume flow rate leaving
the tank. Because water is actually incompressible, however, that
flow rate must be Q1 + Q2. Therefore, the output of salt is c3 X
(Q1 + Q2). Because the concept of mass or material balance
applies here and output = input, the following relationship is
obtained:
c3 X (Q1 + Q2) = c1 X Q1 + c2 X Q2
Solving the above equation for c3 by dividing both sides by (Q1
+ Q2), we obtained the following mass balance equation
c3 = (c1 X Q1 + c2 X Q2)/Q1 + Q2
Mass balance calculation can be applied to the natural
environmental systems, such as streams, rivers, lakes and even
the atmosphere e.g Stream pollution.










EXAMPLE: The BOD5 of an effluent from a municipal sewage treatment plants is
25mg/L and the effluent discharge is 4 ML/d. the receiving stream has a BOD5 of 2
mg/L and the stream flow is 40 ML/d. compute the combined 5-day BOD in the
stream just below the mixing zone.
SOLUTION: Applying cd = (csQs + cwQw)/(Qs +Qw)
cd = (2 X 40 + 25 X 4)/ 40 X 4 = 180/44 = 4.1mg/L
Where cd represent the diluted BOD5 in the combined flow
EXAMPLE: A river has a dry-weather discharge of 100 cfs and a temperature of
25oC. Compute the maximum discharge of cooling water at 65oC that can be
discharged from a power plant into the stream. Assume the legal limit on the
temperature increase in stream is 2oC
SOLUTION: The maximum allowable stream temperature is 25 + 2 = 27oC
Applying mass balance equation cd = (csQs + cwQw)/(Qs +Qw)
27 = (25 X 100 + 65 X Qw)/100 + Qw
200 = 38Qw : Qw = 5.3 cfs
The discharge of warm water cannot be exceed 5.3 ft3/s if the stream temperature is
not to increase more than 2oC
COMPUTATION OF MINIMUM DO


It is important to be able to predict the minimum dissolved oxygen level in a
polluted stream or river. For Example, if a new sewage treatment plant is to
be discharge its effluent into a trout stream, it is possible that conventional
(secondary) treatment levels will not remove enough BOD to prevent
excessively low DO downstream. To determine if some form of advanced
treatment is required to preserve the stream for trout spawning and survival, it
is necessary to compute the minimum DO caused by the sewage effluent and
to compare it to the allowable value for trout streams.
One technique used to describe and predict the behaviour of a polluted
stream uses the so-called Streeter-Phelps equation. This equation is based on
the assumption that the only two processes taking place are deoxygenation of
BOD and the reaeration by oxygen transfer at the surface, as previously
discussed. Two key formulas from the Streete-Phelps model of stream
pollution and oxygen sag follow. Figure 5.11 illustrate some of the variables in
these equations. The minimum DO in the stream is the difference between
the saturation DO level and the critical oxygen deficit. The formulas are
COMPUTATION OF MINIMUM DO (Cont)


_k
Tc= k 1_ k X log[ kk X (1_ D ) X k kXBOD
]
Dc= k XBOD
_ 10
) + D X (10
)
k _ k X (10
Where tc = Time it takes for the critical oxygen deficit
or minimum DO to develop, d
Dc = Critical oxygen deficit, mg/L
Di = Initial oxygen deficit at time t = 0 just below the
point of waste discharge into the stream, mg/L
BODL = Ultimate BOD in the stream just below the
point of waste discharge, mg/L
k1 = Deoxygenated rate constant, d-1
k2 = The reaeration rate constant, d-1
2
2
1
1
1






L
2
2
i
1
_ k1tc
1
1
L
_ k 2t c
_ k 2t c
i
COMPUTATION OF MINIMUM DO (Cont)


The value of k1 if generally taken to be the same as the rate constant for the
BOD reaction in this equation BODt = BODL X (1-10-kt); it can be
determined in the laboratory. The value of k2 depends on the velocity and the
depth of the flow and can be determined from field studies or by an
appropriate formula. The reaeration rate constant k2 can be vary from about
0.1 for the sluggish to about 4.0 for a swallow turbulent stream. Both rate
constants, k1 and k2 depend on temperature.
The equation tc and Dc look complicated, and they are. They are presented
here to illustrate the power of mathematics as a tool for modeling the
environment and helping solve water pollution problems. But as complicated
as they may appear, the Streeter-Phelps equations are not completely accurate
representations of the oxygen profile in a polluted stream or river. Other
factors that affect the oxygen balance include photosynthesis and respiration
of rooted plants and algae and the oxygen demand of benthic (bottom)
deposits. Equations that have been developed to include these factors are
even more complicated than the equation tc and Dc
COMPUTATION OF MINIMUM DO (Cont)







EXAMPLE: The BODL in a stream is 3 mg/L and the DO is 9.0 mg/L. The
streamflow is 15mgd. A treated sewage effluent with BODL =50mg/L is
discharged into the stream at a rate of 5 mgd. The DO of the sewage effluent
is 2 mg/L. Assuming that k1 = 0.2, k2 = 0.5, and the saturation DO level is
11 mg/L, determine the minimum DO level in the stream. For a stream
velocity of 0.5 ft/s, how far downstream does the minimum DO occur?
SOLUTION: First, it is necessary to compute the diluted BODL and DO
using the Mass Balance Equation
BODL = (15 X 3 + 5 X 50)/15 + 5 = 295/20 = 14.8mg/L
DO = (15 X 9 + 5 X 2)/15 + 5 = 145/20 = 7.3 mg/L
Now compute the initial oxygen deficit as
Di = saturation DO – Initial DO = 11.0 – 7.3 = 3.7mg/L
Applying the Streeter-Phelps Model Equations for tc
COMPUTATION OF MINIMUM DO (Cont)

Tc=

It will take about 0.64 d (roughly 15hours) for the minimum
DO to occur.
Now applying next Streeter-Phelps Model Equation for Dc
gives



Dc=
=
1
0.5
0.5 _ 0.2
X
log[
X
(
1
_
3
.
7
X
0.5 _ 0.2
0.2
0.2 _ 14.8 )]
1
0.3 X [2.5 X (1 _ 0.375)]
0.2 X 14.8
_ 0.2 X 0.64
_ 10 _ 0.5 X 0.64 ) + 3.7 X 10 _ 0.5 X 0.64
0.5 _ 0.2 X (10
=(0.33)log 1.56 = 0.64 d
= 9.87 X (0.745 – 0.479) + 3.7 X
0.479 = 2.63 + 1.78 = 4.4 mg/L
The minimum DO in the stream is the difference between saturation
DO and the critical oxygen deficit, or 11.0 – 4.4 = 5.6 mg/L. At a
velocity of 0.5 ft/s, in 0.64 d the distance downstream for the minimum
DO is 0.64 d X 24 h/d X 3600 s/h X 0.5 ft/s = 27659 ft approximately 5
million.