Oxidation case studies
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Transcript Oxidation case studies
Oxidation
Case Studies
J(Hans) van Leeuwen
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Disinfection applications
Introduction
Summary
and
explanation
Simple calculations
Show some
applications
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DISINFECTION KINETICS
Chick’s Law
dN
dt
=
-kN
N is the number of microorganisms at time t,
and k is a constant (dimension : t-1).
This constant applies only for a fixed
concentration of a certain disinfectant
INTEGRATION OF CHICK’s LAW
Integrating for N, N=No at t = 0
ln N/N0 = -kt
N/N0 = e-kt
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Watson’s Law
Cnt = constant
Simplified:
Ct = constant
Applies only for
• a fixed rate of “kill”
• a certain organism
• a specific disinfectant
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Example
Ct value for ozone is 1.0 mgL-1min.
We could achieve that with
1 mg/L ozone residual for 1 minute
Or: 0.4 mg/L for 2.5 minutes
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CHLORINE RESIDUALS
Free
– HOCl and OClCombined – NH2Cl, NHCl2
Total
= Free + combined
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CHLORINE REACTIONS WITH AMMONIA
Cl2 + H2O
HOCl + H+Cl-
HOCl + NH3
NH2Cl + HOH
HOCl + 2NH2Cl N2 + 3H+Cl- + H2O
Net reaction: 2 x 2nd + 3rd :
3 HOCl + 2 NH3 N2 + 3H+Cl- + 3H2O
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CHLORINE REACTIONS WITH AMMONIA
Cl2 + H2O
HOCl + H+Cl-
HOCl + NH3
NH2Cl + HOH
HOCl + 2NH2Cl N2 + 3H+Cl- + H2O
Net reaction: 3 x 1st + 2 x 2nd + 3rd :
3 Cl2 + 2 NH3
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N2 + 6H+Cl-
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MEASUREMENT OF CHLORINE
(OR CHLORAMINES)
DPD – pink color develops
KI solution – I-1 oxidized to I, forms I2
Color of DPD or I2 can be measured,
or I2 titrated with FAS solution
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formation
Other
oxidation
reactions
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DISINFECTION BYPRODUCTS
• THMs - CHX3, e.g. CHCl3
• Chlorite and chlorate,
ClO2ClO3• Bromoform - CHBr3
• Bromate - BrO3-
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ClO2 made from Sodium Chlorite
Acidification of Chlorite
5 ClO2- + 4 H+ 4 ClO2 + 2 H2O + ClOxidation of Chlorite by Chlorine
2 NaClO2 + Cl2 2 NaCl + 2 ClO2
Oxidation of Chlorite by Persulfate
2 NaClO2 + Na2S2O8 2 ClO2 + 2 Na2SO4
From Sodium Hypochlorite and Sodium Chlorite
NaOCl + 2 NaClO2 + 2 HCl 2 ClO2 + 3 NaCl + H2O
Electrochemical oxidation of chlorite
ClO2- ClO2 + eDry chlorine/chlorite (laboratory method)
NaClO2 + 1/2 Cl2 --> ClO2 + NaCl (solid)
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OZONE
PRODUCTION
• Electron bombardment
• UV irradiation at < 200 m
• Electrolytically
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Corona Discharges in
Ozone Generation
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Large Ozone Generators
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1000 10000
100
10
1
0.1
Ozone concentration ppm
Toxicity of ozone to humans
0.1
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10
100
1000
Exposure time (minutes)
10000
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COMPONENTS OF AN OZONATION SYSTEM
INFLUENT
OZONE GENERATOR
AIR/OXYGEN PREPARATION
AIR
OZONE
CONTACT
CHAMBER
OZONE DESTRUCTOR
VENT
OTHER OXYGEN APPLICATIONS
EFFLUENT
Alternative paths for enriched oxygen recycle
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BUBBLE
COLUMN
CONSTRUCTION
DETAILS
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50m
50 m
Deep Shaft
Ozonation
System
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0.8
0.7
OZONE RESIDUAL (mg/l)
Ozone dose A
0.6
0.5
0.4
0.3
Ozone dose B
0.2
0.1
0
0
1
2
3
4
5
TIME (min)
6
7
8
9
10
Ozone
Disinfection
Pre-ozonation
Raw Water
Screening
Clarification
Filtration
G
A
C
Distribution
Residual
Disinfection
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OTHER USES OF OZONE
IN WATER TREATMENT
•
•
•
•
Iron and Mn removal
Color removal
Geosmin and 2-MIB
Cyanotoxins – cylindrospermopsin,
microcystin, anatoxin*
• Microflocculation
• Biodegradability
*Produced by Cylindrospermopsis, Microcystis and
Anabena genera
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Scarce Water Resources near Mines
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Further Applications of Ozone in
The Water Technology Field
•
•
•
•
•
•
•
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Wastewater treatment
Effluent disinfection
Cooling water treatment
Swimming pools
Ozonated ice
Ozonated air
AOP (advanced oxidation processes)
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Mine Water Cooling
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Case Study: Mining Application
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DUST
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POSSIBLE INHIBITORS
High temperatures
Heavy metals
Disinfectant byproducts
or residues
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Ozonation Bubble Column
Sand Filters
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Oxidation of cyanides, thiocyanate
and TOC in the Reclamation of
Water in Steel Processing
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BHP near Wollongong, Australia reuses
wastewater after biological and activated
carbon treatment
Cyanides interfere with biological treatment
and need to be lowered to 200 mg/L before
activated sludge
Cyanates are incompletely removed if over
250 mg/L
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BHP Ozonation Investigations
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Ozone was tested to observe efficacy to
remove CN- and SCNOzone requirements due to competitive
reactions observed
Ozone needs to replace or enhance
activated carbon treatment
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CYANIDE REMOVAL FROM COG
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CYANIDE REMOVAL FROM BHP
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CYANATE REMOVAL FROM BHP
200,0
180,0
BHP
160,0
SCN, mg/L
140,0
120,0
100,0
80,0
60,0
40,0
20,0
0,0
0
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250
500
750
Ozone consumed, mg/L
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1000
1250
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TOC AND COLOR REMOVAL FROM
ACTIVATED SLUDGE EFFLUENT
TOC mg/L or PCU
140
120
Color
100
80
60
TOC
40
20
0
0
10
20
30
40
50
60
70
Time, min
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Cost Implications: CN
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Capital cost of ozone
installation $ 0.64 million
Amortisation, maintenance
operation $16,000 per month
Present alternative,
formaldehyde costs $ 7000 per
month, more COD
Ozone not cost effective
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Cost implications: SCN-
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Capital required $ 2.0 million
Monthly costs $ 76 000
No other method SCN- removal There will
be a much smaller risk in achieving treatment
objectives
Ozone not economical
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SYNTHETIC
ORGANIC
REMOVAL BY
INTEGRATED
OZONOLYSIS/
ACTIVATED
SLUDGE
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CONVENTIONAL PREOZONATION + ACTIVATED SLUDGE
-
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AirAir
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POST-OZONATION: Remove degradables first
More
Treatment
required
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Since ozonolysis results in
biodegradable byproducts,
more biological treatment
required after post-ozonation
This requirement can be resolved
in two possible ways:
¶ another biological treatment stage
¶ recirculation to biological treatment
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Biological
treatment
before and
after
ozonation
Using a
large
ozonated
recycle
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Ozonated Recycle
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O3
THE SOLUTION INVESTIGATED
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Experimental Set-up
Activated sludge with wastewater
containing methylene blue
ozonated
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Results
MeBl removal in ozonated
activated sludge 95%
vs. 40% in control
COD removal in ozonated
activated sludge 80.5%
vs. 79.5% in control
Better biomass settling
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Control
Ozonated
after settling
mixed liquor
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Conclusions
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Ozone can be dosed within an
activated sludge system for the
ozonolysis of non-biodegradables
Effect on biomass beneficial, if minimal
Byproducts mainly biodegradable
Economical integrated procedure
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Pilot Scale Implementation at
Van Diest Supply Company, Iowa
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