Transcript Lecture 8 (2014)

Philadelphia University
Faculty of Engineering
Department of Civil Engineering
First Semester, 2013/2014
ENVIRONMENTAL
ENGINEERING
343
Lecture 8:
Water Treatment 2
SELECTION OF TREATMENT PROCESSES
Selection of the set of Treatment Processes will be based
on :
 Sources of water intake
 Characteristic of water
Detailed raw water quality analysis for a minimum
of one year, or longer, at periods of high, low and
medium flows. The parameters to be looked at all
those listed in the legislative standards
 Cost
 Suitability of the processes for removing
particulate impurities. Example:
 Turbidity; suitable process might be coagulation
, sedimentation or filtration
 For pathogen, pre or post chlorination, UV,
ozone, or chloramines
COAGULATION & FLOCCULATION
Effective removal of particles < 50um is difficult in normal settling
operations.
Colloidal particles are difficult to separate from water because
they do not settle by gravity and are so small that they pass
through the pores of filtration media.
To be removed, the individual colloids must aggregate and grow in
size.
The objective of coagulation (and subsequent flocculation) is to
turn small particles into larger particles called flocs. The flocs are
readily removed in subsequent processes such as settling,
filtration or other methods.
Coagulation means the addition of one or more chemicals to
condition the small particles for subsequent processing by
flocculation
Flocculation is the process of aggregation of the destabilized
particles and precipitation products.
WATER TREATMENT -COAGULATION
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Colloids possess a negative charges that repels other
colloidal particles before they colloid with one another .
In order to destabilize the colloids, we must neutralize the
charge by addition of an ions of the opposite charge for the
colloids
Positive ions is added to water to reduce the surface charge
to the point where the colloids are not repelled from each
other.
Coagulants tend to be positively charged. Due to their
positive charge, they are attracted to the negative particles
in the water
The combination of positive and negative charge results in
a neutral , or lack of charge
FILTRATION
Filtration is a process for separating suspended or
colloidal impurities from water by passing
through a porous medium, usually a bed of sand
or other medium.
Settled water (Sedimentation effluent) turbidity
range 1-10 TU – due to residue of flocs particles.
So turbidity need to be reduce to less than 0.3
Common materials for granular bed filters:
Sand (slow, rapid or high)
 Anthracite coal
 Dual media (Coal plus sand)
 Mixed media (coal, sand & garnet)
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DISINFECTION
Disinfection is used in water treatment to reduce
pathogens (diseases-producing microorganisms) to
an acceptable level
 Treatment of water with chemicals to kill
bacteria”
 Two objectives:
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Primary disinfection : Kill any pathogen in water
Secondary (residual) disinfection : Prevent pathogen
re-growth in the water.
Method use :
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Should be harmless and unobjectionable to the
consumer
Should be able to retain a residual disinfecting effect
for a long period
DISINFECTION- PROPERTIES
1.
2.
3.
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5.
6.
7.
8.
9.
Destroy bacteria / pathogens within a practicable
period of time, over an expected range of water
temperature
Effective at variable compositions, concentration and
conditions of water treated.
Neither toxic to humans and domestic animals nor
unpalatable
Not change water properties
Have residual in a sufficient concentration to provide
protection against recontamination
Can be determined easily, quickly, and preferably
automatically.
Dispensable at reasonable cost
Safe and easy to store, transport, handle and supply
Not form toxic by-products due to their reactions
with any naturally occurring materials in water.
DISINFECTION- METHODS
1.
2.
3.
Chlorination- chlorine
Ultra violet Radiation
Ozonation