Environmental eng

1. Environmental engineering
“My Lord, Increase me in knowledge”
Al-Quran 20:114
Prof. Md. Mohibul Alam
B.Sc. (Engineering-SUST), M.Sc.(Engineering-Belgium)
Joining as a faculty: February, 2006
Course teacher
Department of Chemical Engineering and Polymer
Science
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2. Water treatment ?
Department of Chemical Engineering and Polymer
Science
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3. Department of Chemical Engineering and Polymer
Science
3
Coagulation/
flocculation
• Charge neutralization processes
• Building large flocs/particles from small
one
Sedimentation
• Separate out solids from water
• e.g., clarification tank or settling tank
Filtration
• Rapid gravity sand filtration
• Membrane filtrtion,MBR
Water treatment steps ?

4. Coagulation/flocculation process?
Department of Chemical Engineering and Polymer
Science
4

5. Sedimentation tank?
Department of Chemical Engineering and Polymer
Science
5

6. Filtration?
Department of Chemical Engineering and Polymer
Science
6

7. Mechanism of Coagulation/flocculation
process?
Department of Chemical Engineering and Polymer
Science
7
Colloidal
particles size:
10−6
mm (1 nm)
to 10−6
mm
(1mm)

8. Colloidal characteristics?
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Department of Chemical Engineering and Polymer
Science
Imperfections in
crystal structure
Adsorption of ions on particles
surface
Ionization of
surface sites
Electrical Charges on
Colloidal Surfaces arises
in 3 main ways:
Silicon atoms in crystalline
material: replaced by atoms with
lower valence (such as aluminum
ion) giving an excess negative
charge to the crystal material
Example :Clay particles
 Many colloidal
particles acquire a
charge as a result of the
preferential adsorption
of either positive or
negative ions on their
surface.
 Colloidal particles in
aqueous media usually
adsorb anions and
acquire a negative
charge.
 Many particles contain
ionogenic groups,such as
hydroxyl, carboxyl groups,
which dissociate in water.
 These ionogenic groups
produce a surface charge
depending on the solution pH.

9. Colloidal stability?
Department of Chemical Engineering and Polymer
Science
9
Attractive Forces:
results from Van der Waal
forces of intermolecular
attraction
Repulsive Forces:
result from electric
double layer (EDL)
Forces acting
on particles

10. EDL theory
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Fixed (stern) layer: negative
ions attract opposite charge ion
from surrounding water to its
surface
Diffusion layer: Outside the
fixed layer: electric potential
decrease exponentially
increasing with distance
Electric double layer: Fixed
layer +Diffusion layer; both layer
contain (+) ve and (-) ve ions
positive ions>>> negative ions
Department of Chemical Engineering and Polymer
Science

11. EDL
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Department of Chemical Engineering and Polymer
Science

12. Zeta potential
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Department of Chemical Engineering and Polymer
Science
The liquid layer
surrounding the particle
exists as 2 parts:
an inner region (Stern
layer) where the ions are
strongly bound and an
outer (diffuse) region
where they are less firmly
associated. Within the
diffuse layer there is a
notional boundary inside
which the ions and
particles form a stable
entity. When a particle
moves (e.g. due to
gravity), ions within the
boundary move it. Those
ions beyond the boundary
stay with the bulk
dispersant. The potential
at this boundary (surface
of hydrodynamic shear) is
the zeta potential

13. Coagulant
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Department of Chemical Engineering and Polymer
Science