2. The role of chemical treatment unit process in
wastewater treatment
The principal chemical unit processes used for
wastewater treatment are:
chemical coagulation, chemical
precipitation,
chemical disinfections, chemical
oxidation,
advanced oxidation processes ion exchange
chemical neutralization.
Chemical treatment processes
3. Removal of ammonia
Removal of heavy metals
Removal of organic compounds
Ion exchange
pH control
Chemical
neutralization
Disinfections with chlorine, ozone etc.
Chemical
disinfections
Removal of persistent organic pollutants and
refractory organic compounds
Advanced oxidation
BOD removal
Ammonia removal
Odor control
Chemical oxidation
Enhancement of TSS and BOD removal in the
primary sedimentation
Phosphorous removal
Heavy metals removal
Chemical
precipitation
Removal of COD, BOD and Oil & Grease
Chemical
coagulation
Application
Process
Application of Chemicals for Wastewater Treatments
4. Chemicals used in wastewater treatment
666.7
162.1
400
278.0
56 as CaO
Al2(SO4)3-18H2O
FeCl3
Fe2(SO4)3-3H2O
FeSO4-7H2O
Ca(OH)2
Alum
Ferric chloride
Ferric sulfate
Ferrous sulfate
(copperas)
Lime
Molecular
weight
Formula
Chemical
10. Heavy metals precipitation
Most of the heavy metals are precipitated during the process of chemical
coagulation.
The achievable effluent concentrations of heavy metals
Hydroxide precipitation at pH 11
0.1
Zinc
Hydroxide precipitation at pH 10
0.12
Nickel
Alum co-precipitation
Ferric hydroxide co-precipitation
0.001-0.01
0.0005-0.005
Mercury
Hydroxide precipitation
0.02-0.07
Copper
Hydroxide precipitation at pH 10-11
Co-precipitation with ferric hydroxide
0.05
0.05
Cadmium
Sulfate precipitation
0.5
Barium
Ferric hydroxide co-precipitation
0.005
Arsenic
Types of precipitation and technology
Achievable effluent
concentration,
mg/L
Metal
11. Advanced wastewater Treatment
The need for advanced treatment is based on a
consideration of one or more of the following factors:
-The need to remove organic matter and total suspended
solids beyond what can be accomplished by
conventional methods
-The need to remove more specific inorganic
constituents like heavy metals
-The need to remove more specific organic constituents
like refractory organic compounds
12. Theory of advanced oxidation
• Advanced oxidation process involve the generation and use of the
hydroxyl free radical (•
OH.)
0.90
1.23
Oxygen (molecular)
0.93
1.27
Chlorine dioxide
1.00
1.36
Chlorine
1.10
1.49
Hypochlorite
1.30
1.78
Hydrogen peroxide
1.52
2.08
Ozone
1.78
2.42
Oxygen (atomic)
2.05
2.80
Hydroxyl radical
2.25
3.06
Fluorine
EOP relative to
chlorine
Electrochemical oxidation
potential (EOP), V
Oxidizing agent
Comparison of the oxidizing potential of various oxidizing agents
14. Ozone/UV
Production of the hydroxyl free radical is presented in the following equations:
O3 + UV (hv, λ<310 nm) O2 + O
H2O2
•OH + •OH
O + H2O H2O2
Ozone/hydrogen peroxide
• The overall reaction for the production of hydroxyl
radicals using hydrogen peroxide and ozone is as follows:
H2O2 + 2O3 •OH + •OH + 3O2
15. Hydrogen peroxide/UV
The formation of hydrogen radicals possible when water -
containing
H
2O2 is exposed to UV light (200 to 280 nm). The following
reactions can be used to describe the photolysis of H2O2:
H2O2 + UV (hv, λ ≈ 200-280 nm) •OH + •OH
16. Fenton's reaction
• The Fenton's Reaction has been known since 1894 and is currently one of
the most powerful oxidizing reactions available.
• The reaction involves hydrogen peroxide and a ferrous iron catalyst.
• The peroxide is broken down into a hydroxide ion and a hydroxyl free
radical.
H2O2 + Fe2+ Fe3+ + HO- + •OH
How does the Fenton's reaction work?
Once the hydroxyl radicals have been generated they start to attack
organic molecules by the following mechanisms:
17. Radical addition. The addition of hydroxyl radical to an unsaturated
aliphatic or aromatic compound results in the production of a radical
organic compound.
RH = the reacting organic compound.
RH + •OH RHOH
Hydrogen abstraction. The hydroxyl radical can be used to remove a
hydrogen atom from the organic compounds.
RH + •OH •R + H2O
Requirements of the reaction:
pH adjustment to 3-5: if the pH is too high the iron precipitates as
Fe(OH)3 and will decompose the H2O2 to oxygen.
Addition of Iron and H2O2 result in significant drop in the pH , FeSO4
catalyst, and the H2O2 addition, is responsible for the fragmentation of
organic material into organic acids.
18. Addition of the iron catalyst as a solution of FeSO4: The typical range
for the iron dose is 1 part of Fe per 15 parts of H2O2.
Adding slowly the H2O2: in order to control the increasing of the pH
and the temperature during the reaction it's better to complete the
reaction step by step with a continuous adjustment.
Applications of the Fenton's reaction:
Nowadays, the Fenton's reaction is used to treat a large variety of
water pollution such as phenols, formaldehyde, pesticides,
This process may be use to treat wastewater, contaminated soils and
sludge with the following actions:
Organic pollutant destruction
Toxicity reduction
Biodegradability improvement
BOD/Cod removal
Odour and colour removal
Destruction of resin in radioactive contaminated sludge
