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CHEM115 Environmental Chemistry
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CHAPTER 13
WATER POLLUTION &
TREATMENT
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Definition
It refers to the degradation of water quality at
which the watercannot be used for its existing,
intendedandpotentialpurpose anymore.
It is usually due to anthropogenic activities.
A pollutant is any biological, physical and chemicalsubstance that is known to be harmful to other
desirable living organisms.
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Point source pollution
Point source pollution refers to
contaminants that enter a waterway
through a discrete conveyance, such as a
pipe or ditch. Examples of sources in this
category include discharges from a
sewage treatment plant, a factory, or a citystorm drain.
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Non-point source pollution
Non-point source (NPS) pollution refers to diffusecontamination that does not originate from a single
discrete source.
NPS pollution is often accumulative effect of small
amounts of contaminants gathered from a large area. The leaching out of nitrogen compounds from
agricultural land which has been fertilized is a typical
example.
Nutrient runoff in stormwater from "sheet flow" over anagricultural field or a forest are also cited as examples of
NPS pollution.
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CHEM115 Environmental Chemistry
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Water Pollutants
Waste effluent (Industrial)
Urban run-off (sewage)
Agricultural run-off (pesticides) Oil spillage (petroleum)
Acid precipitation (SO2, NOx)
Suspended solids
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CHEM115 Environmental Chemistry
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Pollution Category
According to UK Environment Agency, pollution can becategorized into 3 categories based on the severity.
Category 1 involves one of the following:
Closure of a source of water abstractionExtensive fish kill
Potential or actual persistent on water quality or
aquatic life
Major effect on the amenity value of receivingwater
Extensive subsequent remedial measures.
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CHEM115 Environmental Chemistry
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Category 2is less severe and may cause
Necessity to notify downstream abstractors
Significant fish kill
Render water unfit for livestock
Measurable effect on animal life in water
Contaminate the bed of river
Reduce the amenity value of water to their
owners or to the general public.
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CHEM115 Environmental Chemistry
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Category 3 isrelatively minorand has no
significant or lasting effect on the receiving
water.
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CHEM115 Environmental Chemistry
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The New River flows at 200 cfs as it
enters California. The water at this
point is three colors: dark green, white
(foam), and milky brown/green.
Point source pollution
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Water Treatment
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CHEM115 Environmental Chemistry
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Primary treatment involves eliminating parts of thesolids from the WW. Normally, physical treatmentis involved.
Secondary treatment involves removal of organicmatterand remaining suspended material.Normally, biological treatment is required.
Advanced treatment involves removal ofsuspended and dissolved materials. (Usually,chemical treatment is applied)
Level of Water Treatment
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CHEM115 Environmental Chemistry
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Water Treatment
Water treatment is basically categorized into physical andchemical treatment. Biological treatment is integrated insome of the treatment processes.
Physical treatment Chemical treatment
Screening Coagulation
Sedimentation Disinfection
Filtration Ion exchange
Mixing Adsorption
Flocculation Chemical Oxidation
Aeration Chemical Precipitation
Membrane Filtration
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CHEM115 Environmental Chemistry
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Physical Process - Screening
First treatment process
Course Screens:Easily separate and remove large matter carried
along by the raw water, which might negatively affect theefficiency of later treatment procedures or make their
implementation more difficult.
Fine Screens:Remove floating and suspended material
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CHEM115 Environmental Chemistry
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Physical Process - Sedimentation
-A detention process to allow the settlement
of flocculated/suspended particles.
-Suspended material may be particles, such
as clay or silts, originally present in the
source water.
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CHEM115 Environmental Chemistry
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Physical Process - Filtration
To remove residual solids that remain in
water after settling.
Filter bed is made oflayers of sand, gravels
andcharcoal.
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CHEM115 Environmental Chemistry
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Chemical Process- Chemicals
Mixing
Coagulants:
To coagulate suspended solids andmaterials.
Lime-soda ash:
To treat water hardness
Rapid mixing removes dissolved gases
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Flocculation
in the field of chemistry, is a process where
in colloids come out ofsuspension in the form of
floc or flakes by the addition of a clarifying agent.
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CHEM115 Environmental Chemistry
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Chemical process - Flocculation
and Coagulation
A process where small and suspended particles
arejoined to form larger particles so that they can
settle at the bottom of the treatment tank.
Alum (Al3+) is usually used. Iron salts or synthetic
organic polymers can also be used.
Al2O3, FeSO4..
Colourmay be removed through this process.
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CHEM115 Environmental Chemistry
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Chemical Process - Disinfection
To destroy the pathogenic organisms
present in the water.
Types of disinfection include Chlorination,
Ozone andUV radiation.
Colourand odourmay be removed through
this process.
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CHEM115 Environmental Chemistry
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Chemical Process - Ion Exchange
It is basically used forsoftening water.
The hardness in the water exchanges withions from the ion-exchange material.
When the ion-exchange material becomessaturated,. hardness will not be removed
anymore
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CHEM115 Environmental Chemistry
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The ion exchange material can either be
zeolites orsynthetic resins.
The zeolites and resins are characterized by
the amount ofhardness they can remove
per volume of resin material and amount of
salt needed for regeneration.
Chemical Process- Ion Exchange(contd)
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CHEM115 Environmental Chemistry
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Synthetically made resins have higher
exchange capacity and require less salt for
regeneration compared to zeolites.
They virtually remove 100% of water
hardness which is not desired.
Chemical Process- Ion Exchange(contd)
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Chemical Process - Adsorption
Adsorption is a process where a substanceis transferred from liquid to the surface of asolid.
Has been used since 1950 at US
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AdsorptionAdsorption is used to treat odor, taste, synthetic
organic chemicals (SOCs), volatile organiccompounds (VOCs), semi-volatile organic
compounds (SVOCs), THMs precursors and
Disinfection by-products (DBPs).
Able to remove contaminants until < 10 ppm.
Able to be reused by regeneration process with
acid. High efficiency, most common chemical
treatment technique.CHEM115 Environmental Chemistry
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CHEM115 Environmental Chemistry
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Chemical Process - Membrane
Process
A membrane is a thin layerof material that is
able to separate materials as a function of
their physical and chemical properties when
a driving force is applied across themembrane.
The membrane type depends on the target
compounds.
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CHEM115 Environmental Chemistry
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The membraneacts like a barrier
and only allows
certain substanceto pass through.
Feed Permeate
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CHEM115 Environmental Chemistry
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Removal of phosphorus, heavy metals.
Ferric chloride (FeCl3) and alum arecommonly used (can be added in aeration
tank).
Settling tanks are required for settlement of
precipitates.
Chemical Process - Chemical
Precipitation
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CHEM115 Environmental Chemistry
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Remove ammonia.
It can be done by raising the pH to convertthe ammonium ion into ammonia and be
stripped from the water by passing large
quantities of air through the water.
Chemical Process-Ammonia
stripping
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Disinfection
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Chlorination
Chlorine may be used as element (Cl2),
sodium hypochlorite (NaOCl), or calcium
hypochlorite [Ca(OCl)2)].
When chlorine is added to water, a mixture
ofhypochlorous acid (HOCl) and
hydrochloric acid (HCl) is formed.
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CHEM115 Environmental Chemistry
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Chlorine Dioxide
It is a very strong oxidant. It is formed by
combining chlorine and sodium chlorite.
It does not persist long enough as a
distribution-system disinfectant.
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CHEM115 Environmental Chemistry
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Ozonation
It is a powerful oxidant which is more
effective than chlorine in destroying viruses
and cysts in water.
However, it does not persist in waterand
decay back to oxygen in minutes.
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CHEM115 Environmental Chemistry
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UV radiation
UV light disrupts the genetic material in cells ofpathogenic organisms, causing them unable toreproduce and cannot cause an infection.
It is effective in destroying Cryptosporidium,Giardiaand viruses.
Turbidity may affect the performance of UVdisinfection system.
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Bonus (0.5)
CHEM115 Environmental Chemistry
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