Transcript water quality assessment and pollution control

WATER QUALITY
ASSESSMENT
WMA 509
Prof O. Martins, Dr O.Z. Ojekunle and Dr. G.O. Oluwasanya
Dept of Water Res. Magt. & Agromet
UNAAB. Abeokuta. Ogun State
Nigeria
[email protected]
• COURSE CODE: WMA 509
• COURSE TITLE: Water Quality
Assessment
• COURSE UNITS: 3 Units
• COURSE DURATION: 3 hours per week
COURSE DETAILS
• Course Cordinator: Prof. O. Martins B.Sc.,
M.Sc., PhD
• Email:[email protected]
• 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
COURSE CONTENT
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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.
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
READING LIST
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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) McGrawHill 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
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
History of Water Quality
The Problem and its Science
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
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
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.
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.
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,
Properties which Affect Quality of
Water
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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-,
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
• 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
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
PHYSICAL CHEMICAL
PARAMETER (Cont)
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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
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
PHYSICAL CHEMICAL
PARAMETER (Cont)
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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
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 (oC).
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
25oC. 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
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Multiparameter monitoring systems should contain automatic temperature
compensation circuits to compensate specific conductance to 25oC.
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.
Effect of Some Physical Parameter
and their Measurement (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.
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
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 hydrogenion electrode, commonly is used in continuous water-quality
pH sensors
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.
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 01000 and an accuracy of -+5 percent or
2NTU, whichever is greater. Some
sensors can report values reliably up to
about 1500 NTU.
WATER SAMPLING/ WATER
POLLUTION
Part 1a
• Grab Sampling
• Composite Sampling
Water Sampling
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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.
Physical Analysis
• The physical analysis which can be
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.
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
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.
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, -Oxygendemanding substances, -Plant nutrients Toxic organics, -Inorganic chemicals, Sediments, -Radioactive substances, Heat, -Oil
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.
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).
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.
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
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
PHYSICAL PARAMETERS
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Turbidity
Temperature
Colour
Taste and Odour
CHEMICAL PARAMENTER OF
WATER QUALITY.
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DISSOLVED OXYGEN
BIOCHEMICAL OXYGEN DEMAND
CHEMICAL OXYGEN DEMAND
NITRATE
PHOSPHATE
IRON
MANGANESE
COPPER
ZINC
TDS
TSS etc
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
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)
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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.
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.
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
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• Where A = equal to weigh of dish plus residue. Mg
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B = Weight of empty dish
• 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
TDS ≡
200mg/l
( A - B) X 1000
C
TDS ≡
(40.545 - 40.525 ) X 1000
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
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B represent the weight of the clean filter
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C represent the volume of the sample filtered
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.
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.
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.
examples
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BACTERIA:
ALGAE:
PROTOZOA:
VIRUESE:
COLIFORM:
AEROBIC AND ANAEROBIC
DIGESTION AND
TYPES OF DECOMPOSITION
• 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.
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.
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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.
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.
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Path of Aerobic Digestion
Aerobic Decomposition
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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.
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.
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.
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.
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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
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.
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.
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.
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.
• 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
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.
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.
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.
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).
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.
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.
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.
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).
Wastewater Treatment Process
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%.