Sign and symptoms of a polluted water

body
1. Offensive foul odour coming out of the water
body.
2. Unchecked growth of plants and other
aquatic community.
3. Oil and greases floating on the water surface.
4. Decrease in the number of fish and other
aquatic community.

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 Environmental terms
• Pollutant
A substance or chemical species that is present
greater than its natural abundance either by
natural activity or human activity and cause
detrimental effect on living organism.
Example: CO2 in air; CaCO3 in soil and MgCO3 in
water

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 Environmental terms
• Contaminant
Those substances or chemical species that are
not normally present in the environment but
is introduced into the amenities by human
activity. E.g., Cl2 AsH3 PH3 gas in air.
• Contaminants are non-toxic.
• When they show toxicity, they are said to be
pollutant.

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 Environmental terms
• Receptor
The medium which is affected by pollutants.
Animal and plants including man are the
receptors of pollutants
• Sink
The medium in which a pollutant is contained is
converted to other species. E.g., The ocean is
the sink of atmospheric CO2 gas.

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 Environmental terms
• Pathway
The mechanism by which a pollutant is
transported from it source into a receptor.
Example: pathway of Hg pollution

Hg from an industrial plant Ocean Conversion into CH3-Hg+

Human body Fish body Plant body

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 Environmental terms
TLV (Threshold Limit Value)/TL (Tolerance limit)
• The maximum concentration of a pollutant
contained in a place where a healthy worker can
work 8 hours a day without any harmful effect.
The TLV or safe level of atmospheric CO2 in air is 350 ppm

250 - 400 ppm: background (normal) outdoor air level. 400 - 1,000 ppm: typical level
found in occupied spaces with good air exchange. 1,000 - 2,000 ppm: level associated
with complaints of drowsiness and poor air. 2,000 - 5,000 ppm: level associated with
headaches, sleepiness, and stagnant, stale, stuffy air.

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 What is waste water?
• We might understand this question better by first answering the
question; what is water?
• Water is a compound made up of two parts hydrogen and one part
oxygen.
• This is true, however, only for “pure” water.
• The water of our everyday lives contains many substances in
addition to hydrogen and oxygen.
• These substances, since they are not found in “pure” water, may be
considered impurities.
• In fact, the water that we drink every day contains many substances
that can be considered as impurities.
• Wastewater can be defined as a community’s spent water.
Wastewater contains the impurities that were present when the
water was obtained, and any impurities added through human
uses.

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 Source Based Classification of
wastewater
• Wastewater can originate from many sources such as homes, businesses and
industries. Storm water, surface water and ground water can enter the wastewater
collection system and add to the volume of wastewater.
• The source of a wastewater will determine it’s characteristics and how it must be
treated.
• For example, wastewater from homes (domestic wastewater or typically
residential waste water) typically contains pollutants such as; fecal and vegetable
matter, grease and scum, detergents, rags and sediment.
• On the other hand, Non-residential wastewater in small communities is generated
by such diverse sources as offices, businesses, department stores, restaurants,
schools, hospitals, farms, manufacturers, and other commercial, industrial and
institutional entities.
• Wastewater from an industrial process (industrial wastewater) may include; toxic
chemicals and metals, very strong organic wastes, radioactive wastes, large
amounts of sediment, high temperature waste or acidic/caustic waste. Wastewater
could even come from streets and parking lots during a rainstorm (storm
wastewater) that could contain; motor oil, gasoline, pesticides, herbicides and
sediment.

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 Components in waste water
• Waste discharges can be placed into two broad categories: organic
wastes and inorganic wastes.
• Organic Wastes are those substances that contain the element carbon and
are derived from something that was once living. Examples include:
vegetable and fecal matter, grease, proteins, sugars and paper.
• Inorganic Wastes are those substances that do not contain carbon and are
not derived from something that was once living. Examples include:
metals, minerals, salts, acids and bases.
• Another most important component is nutrients. Wastewater often
contains large amounts nitrogen and phosphorous in the form of nitrate
and phosphate, respectively that promotes plant growth. Organisms only
require small amounts of nutrients in biological treatment, so there exist
an excess of available nutrients even in treated water. In severe cases,
excess nitrogen and phosphorous can result in eutrophication, the
nutrient enrichment of water bodies causing excessive growth of aquatic
plants (algae, cyanobacteria, rooted aquatic vegetation, duckweed etc).

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 Characteristics of waste water
• Waster waters are characterized on the basis of various physical, chemical
and biological characteristics apart from flow data details:

1. Physical characteristics: colour, odour, Dissolved Oxygen (DO), Insoluble

substances (settleable solids, suspended solids), corrosive properties,
radioactivity, temperature range, foamability etc.
2. Chemical characteristics: Chemical Oxygen Demand (COD), pH, acidity,
alkalinity, hardness, total carbon, total dissolved solids (TDS), chlorine
demand, known organic and inorganic components such as Cl-, S2-, SO42-,
N, P, Pb, Cd, Hg, Cr, As, surfactants, phenols, hydrocarbons, oils and
greases.
3. Biochemical characteristics: Biochemical Oxygen Demand (BOD),
presence of pathogenic bacteria etc., and toxicity to man, aquatic
organic organisms, plants and other life forms.

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 Suspended solid
• Definition
• The portion of waste water that, when passed
through a filter, remains on the filter, known as
suspended solids (SS).
• Materials that resist settling may remain
suspended in waste water.
• Suspended solids in wastewater must be treated,
or they will clog soil absorption systems or reduce
the effectiveness of disinfection system.

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 Measurement of suspended solid
• Suspended solids are determined by filtering
an aliquot of the sample through a previously
weighed sintered crucible or a tared Gooch
crucible and drying the crucible at 103°C to
105°C to a constant.
• Calculation: The difference in weight indicated
as mg/L gives the suspended solid content of
the sample.

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 Environmental significance of
suspended solid
• In addition to BOD, estimating the amount of
suspended solids in waste water helps to complete
an overall picture of how much secondary treatment
is likely to be required.
• It also indicates wastewater clarity and is important
for assessing the potential impact of wastewater on
the environment.
Suspended solids (mg/L) Pollution strength
100 weak
220 moderate
350 Strongly polluted
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 Settleable solids
• Certain substances such as sand, grit and heavier
organic and inorganic materials settle out from
the rest of the waste water stream during the
preliminary stages of treatment.
• On the bottom of the settling tanks and ponds,
organic materials makes up a biologically active
layer of sludge that aids in treatment.
• Knowing the amount of settleable solids in the
wastewater provides information on how much
sludge will be created in the septic tank.

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 Determination of settleable solids
• The settleable solids content of a
sample is obtained by allowing 1 L
of the sample to settle for about 1h
at 20°C in an imhoff cone, which is
tapered conical tube.
• The volume of settleable matter in
the cone is recorded as ml/L.
• It may also be expressed as mg/L
which can be calculated by the
difference between mg/L
suspended solids minus mg/L non- Imhoff cone
settle matter.

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 Environmental significance of
settleable solids

Amount of settleable solids (ml/L) Quality of water

3 Weakly polluted
5 Moderately polluted
7 Strongly polluted

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 Total solids (TS)
• The term applied to the residue left after evaporation; it
includes the total suspended solids plus total dissolved solids.
• Determination
• The total solids content of a sample is determined by
evaporating a known volume of the sewage or wastewater
sample and drying the residue for 24 hs at 103° to 105°C,
followed by weighing.

TS(mg/L) Environmental significance

450 Weakly polluted
800 Moderately polluted
1250 Strongly polluted

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 Dissolved Oxygen (DO)
• Oxygen dissolved in water is very important for water analysis.
• The DO content is not only important for the survival of fish
and other aquatic communities, but also a measure of its
ability to oxidize organic impurities in water.
• Dissolved oxygen is the presence of free O2 molecules within
water. The bonded oxygen molecule in water (H2O) is in a
compound and does not count toward dissolved oxygen
levels.
• The amount of dissolved oxygen needed varies from creature
to creature. Bottom feeders, crabs, oysters and worms need
minimal amounts of oxygen (1-6 mg/L), while shallow water
fish need higher levels (4-15 mg/L).

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 Assemble of DO in water

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Measurement of DO as a water quality
parameter
Methods of measurement of DO

Winkler Method or Electrometric Method using membrane

Iodometric Method technique

Based on the oxydizing property of DO Based on the rate of dif f usion of

molecular O2 across the membrane

Characteristics of iodometric method Characteristics of electrometric method

Visual method by strach indicator Operated by potentiometer using deep stop

technique or DO meter

Precision equal to ± 50 micro gram/mL Precision equal to ± 5 micro gram /mL

The choice of procedure depends on the interferences present, the

accuracy desired and in some cases convenience or expedience
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Modification of Winkler method based
on the interference present

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 Azide modification method
• Principle
• This method is based on the reduction of
oxygen present in a water sample by using
manganese(II) sulfate to manganese(III)
hydroxide in presence of alkaline-iodide
solution and subsequent liberation of iodine
in presence of acidic medium followed by the
titration of liberated iodine with a standard
solution of thiosulfate.

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 Chemicals and Apparatus
Chemicals Apparatus
Manganese(II) sulfate pentahydrate Reagent bottle with stopper
Alkaline iodide-azide solution(NaOH +KI+ NaN3) Erlenmeyer conical flask with
ground glass joint
Phosphoric acid/sulfuric acid Hot plate
Sodium thiosulphate solution (M/80) Dropper
Starch solution as indicator Condenser with rubber tube
Pipette

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 Working procedure

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 Reactions involved in Winkler method

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