2. Contents of Unit-IVContents of Unit-IV
• L-20 Miscellaneous methods of
dissolved solids removal
• L-21 Sludge disposal methods
3. Types of dissolved solidsTypes of dissolved solids
• The dissolved solids are of both organic
and inorganic types. A number of
methods have been investigated for the
removal of inorganic constituents from
waste water. Four methods which arewaste water. Four methods which are
finding wide application in advanced
waste treatment are
• 1. Ion-exchange,
• 2. Electrodialysis and
• 3. Reverse osmosis and 4. Evaporation
4. • . For the removal of soluble organics
from waste water the most commonly
used method is adsorption on
activated carbon.
• Solvent extraction is also used to
recover certain organic chemicals likerecover certain organic chemicals like
phenol an d amines from industrial
waste waters.
6. 1. Evaporation1. Evaporation
• “Evaporation” is a process of bringing
wastewater to its boiling point and
vaporizing pure water.
• The vapor is either used for power
production, condensed and used forproduction, condensed and used for
heating, or simply wasted to the
surrounding atmosphere.
• .
7. • The mineral solids concentrate in the
residue may be sufficiently concentrated
for the solids either to be reusable in the
production cycle or to be disposed easily.
• This method of disposal is used for
radioactive wastes, and paper mills haveradioactive wastes, and paper mills have
for a long time been evaporating their
sulfate cooking liquors to a degree where
they may be returned to the cookers for
reuse
8. 2. Ion exchange2. Ion exchange
• This technique has been used
extensively to remove hardness, and
iron and manganese salts in drinking
water supplies.
• It has also been used selectively to• It has also been used selectively to
remove specific impurities and to
recover valuable trace metals like
chromium, nickel, copper, lead and
cadmium from industrial waste
discharges.
9.
10. 2R-NA + Ca(HCO3)2 -> R2CA + 2NaHCO3
Sodium
Ion
Exchange
Resin
+
Calcium
Bicarbonate
in Water
->
Calcium
Ion
Exchange
Resin
+
Sodium
Bicarbonate
in Water
Fully charged
resin
Fully charged
resin
Ion exchanged
resin
Ion exchanged
resin
11. • The process takes advantage of the ability
of certain natural and synthetic materials
to exchange one of their ions.
• A number of naturally occuring minerals
have ion exchange properties.
• Among them the notable ones are• Among them the notable ones are
aluminum silicate minerals, which are
called zeolites.
• Synthetic zeolites have been prepared
using solutions of sodium silicate and
sodium aluminate.
12. Hard water
flows over Ion
Resin is
exhausted.
Counter-flow
Resin is
fully
charged.
flows over Ion
Exchange
media.
Hardness
mineral Ions
are
exchanged for
Sodium or
Potassium
Ions.
exhausted.
Hardness
minerals
are
passing by
the Resin.
Regenerati
on process
is needed.
Counter-flow
regeneration
of Resin with
Brine
solution.
Hardness
minerals are
driven off the
Resin.
Resin is
fully
charged
again ready
for use.
17. • Reverse osmosis (RO) is a membrane-
technology filtration method that removes many
types of large molecules and ions from
solutions by applying pressure to the solution
when it is on one side of a selective membrane.
• The result is that the solute is retained on the
pressurized side of the membrane and the purepressurized side of the membrane and the pure
solvent is allowed to pass to the other side. To
be "selective," this membrane should not allow
large molecules or ions through the pores
(holes), but should allow smaller components of
the solution (such as the solvent) to pass freely.
18. • Commonly used membrane is Cellulose
Acetate
• Pre-treatment of wastewater is needed to
avoid membrane fouling.
• High COD and BOD can also affect
membrane.membrane.
• Flushes away impurities and does not
collect them.
• It can remove almost everything. It allows
only water (H2O) to pass
• Very efficient but Cost is high
22. Applications of ROApplications of RO
• Applications include treatment and recycle of
wastewaters generated from metal finishing and
plating operations; printed circuit board and
semiconductor manufacturing (treatment and
recycle of rinse waters used in electroplating
processes); automotive manufacturingprocesses); automotive manufacturing
(treatment and recycle of water used for
cleaning and painting); food and
beverage (concentration of wastewater for
reuse and reduction of BOD prior to discharge);
groundwater and landfill leachate (removal of
salts and heavy metals prior to discharge).
23. 4. Electrodialysis4. Electrodialysis
• Electrodialysis is an electrochemical
process whereby electrically charged
particles, ions, are transported from a raw
solution (retentate, diluate) into a more
concentrated solution (permeate,
concentrate) through ion-selective
membranes by applying an electric field.
• When a salt solution is under the influence
of an electric field, as is the case in an
electrodialysis module, the charge carriers
in the solution come into motion.
24.
25. • This means that the negatively charged
anions migrate towards the anode and
the positively charged cations towards
the cathode.
• In order to separate salts from a solution,
ion-selective membranes, through whichion-selective membranes, through which
only one type of ion can permeate in an
ideal case, are arranged in the solution
perpendicular to the electric field.
26. • Thus negatively charged particles (anions)
can pass through an anion exchange
membrane on their way to the anode but
are selectively retained by the upstream
cation exchange membrane.
• This separation stage results in a• This separation stage results in a
concentration of electrolytes in the so-
called concentrate loop and a depletion of
charge carriers in the so-called diluate
loop.
29. • Some of the methods used are:
• (1) lagooning in oxidation ponds;
• (2) activated-sludge treatment;
• (3) high-rate aerobic treatment (total oxidation);
• (4) trickling filtration;
• (5) spray irrigation;• (5) spray irrigation;
• (6) wet combustion;
• (7) anaerobic digestion
• (8) subsurface disposal; and
• (9) the Bio-Disc system (RBC).
• (10) Adsorption
30. AdsorptionAdsorption
• One of the most commonly used
techniques for removing organics involves
the process of adsorption, which is the
physical adhesion of chemicals on to the
surface of the solid.surface of the solid.
• The effectiveness of the adsorbent is
directly related to the amount of surface
area available to attract the particles of
contaminant.
31. • The most commonly used adsorbent is a
very porous matrix of granular activated
carbon, which has an enormous surface
area (~ 1000 m2/g).
• Adsorption on activated carbon is perhaps
the most economical and technicallythe most economical and technically
attractive method available for removing
soluble organics such as phenols,
chlorinated hydrocarbons, surfactants,
and colour and odour producing
substances from waste water.
32. • adsorbate: material being adsorbed.
• Adsorbent:material doing the
adsorbing. (examples are activated
carbon or ion exchange resin).
• Generally some combination of
physical and chemical adsorption isphysical and chemical adsorption is
responsible for activated carbon
adsorption in water and wastewater.
33. Physical adsorption:Physical adsorption:
• Van der Waals attraction between
adsorbate and adsorbent.
• The attraction is not fixed to a specific
site and the adsorbate is relativelysite and the adsorbate is relatively
free to move on the surface.
• This is relatively weak, reversible,
adsorption capable of multilayer
adsorption.
34. Chemical adsorption:Chemical adsorption:
• Some degree of chemical bonding
between adsorbate and adsorbent
characterized by strong attractiveness.
Adsorbed molecules are not free to move
on the surface.on the surface.
• There is a high degree of specificity and
typically a monolayer is formed.
• The process is seldom reversible.
35. Objective questionsObjective questions
1. Pick out the odd one
i. Microfiltration, filtration, Nanofiltration,
adsorption.
2. _______________ membrane is commonly
used in RO process.used in RO process.
3. ____________ ________ is excellent
adsorbent because of its very high surface
area.
4. For RO, pretreatment is needed to avoid
________ _________.
36. Theory QuestionsTheory Questions
Q1. Write Short note on
1. Removal of Inorganic Dissolved Solids
(May 2010)
2. Removal of Organic Dissolved Solids2. Removal of Organic Dissolved Solids
3. Electrodialysis
4. Reverse Osmosis
5. Ion Exchange
Q2. Differentiate between Physical
adsorption and Chemical Adsorption
