1. Advanced Oxidation Processes for water treatment
Santi Esplugas
Chemical Engineering Department.
University of Barcelona SPAIN
Tarragona, 20 December 2011

2. Structure of the Presentation
Introduction
Advanced Oxidation Processes
- Ozone based
- Fenton
Photochemical Oxidation Processes
- UV Photolysis
- H2O2/UV
- Ozone/UV
- TiO2 Photocatalysis
- PhotoFenton
Conclussions and Recommendations
Photocatalysis

3. REMOVAL OF POLLUTANTS FROM WATER
*PHYSICAL METHODS (non destructive ):
Mechanical separation
Sedimentation
Filtration
Adsorption and ion exchange
Reverse osmosis
cost
*CHEMICAL METHODS (destructive ):
Precipitation
Ion exchange
Chemical Oxidation (and reduction):
biochemical oxidation
chlorine
hydrogen peroxide
ozone
hydroxyl radical (OH •) AOPs

4. Classical Oxidants
Oxygen: moderate oxidant with small solubility in water that needs high investments in installations, but its low operation costs may do the process attractive.
Chlorine: strong oxidant and cheap. Possibility of producing chlorinated organic compounds, more toxic than the initial ones. It has good enough solubility in water.
Permanganate: strong enough oxidant, but expensive. It is selective, no easy to handle and not desirable manganese is added to the treated water.
Hydrogen peroxide: multipurpose oxidant soluble in water that could be applied directly or with a catalyst (without it some organic compounds are not attacked).
Ozone: strong oxidant that as oxygen and hydrogen peroxide does not introduce new ions to the medium. It is more soluble in water than oxygen. Its difficult handling. Necessary to generate it on-site. Process, normally, is controlled by mass transfer.

5. OH• Characteristics (redoxpotential)
* very powerful oxidation compound (F2 > OH• > O3 > )
* oxidation power related to chlorine (Eº = 1.36 V)
Rate constants of °OH radical with organics: x 107 mol-1 L s-1

6. OH• Characteristics (no especific oxidant)
Compounds that can be oxididez by OH radicals
Acids
Formic, gluconic, lactic, malic, propionic, tartaric
Alcohols
Benzyl, tert-butyl, ethanol, ethylene glycol, glycerol, isopropanol, methanol, propenediol
Aldehydes
Acetaldehyde, benzaldehyde, formaldehyde, glyoxal, isobutyraldehyde, trichloroacetaldehyde
Aromatics
Benzene, chlorobenzene, chlorophenol, creosote, dichlorophenol, hydroquinone, p-nitrophenol, phenol, toluene, trichlorophenol, xylene, trinitrotoluene
Amines
Aniline, cyclic amines, diethylamine, dimethylformamide, EDTA, propanediamine, n-propylamine
Dyes
Anthraquinone, diazo, monoazo
Ethers
tetrahydrofuran
Ketones
Dihydroxyacetone, methyl ethyl ketone

7. OH• Characteristics (no especific oxidant)
Scavenger effect (at high concentration)
Inorganic ions: Sulfate, chloride, carbonate,..
Alcohols: methanol, terbutanol,..
Hydrogen Peroxyde 7

8. Biodegradability enhancement by AOPs
dyes WO
pulp&paper
Fenton
textil O3
surfactants

9. AOP classics homogeneous heterogeneous radiation UV-VIS Photolysis
O3/UV
TiO2/UV
Fe+3/UV/H2O2
O3/H2O2 O3
sonolysis
electrochem
Se divide principalmente en dos partes, una primera parte donde se estudiaran los procesos llamados homogéneos, y son aquellos procesos donde todos los reactivos son líquidos o en disolución. Y una segunda parte dedicada a los procesos heterogéneos, se trata de reacciones gas-liquido, donde el reactante gaseoso es el ozono. Los tratamientos estudiados en la primera parte son la fotolisis mediante radiación ultravioleta, y el proceso que combina radiación ultravioleta y un oxidante ( en este caso se utilizaron peróxido de hidrogeno y sales de hierro III). En cuanto a la segunda parte se estudiaron los procesos de ozonización. Ozonización combinada con radiación UV, y ozonización combinada con peróxido de hidrogeno, también se realizaron experimentos combinando ozono, radiación y peróxido a la vez.
Todos estos tratamientos, están basados principalmente en el poder oxidativo del radical ·OH, considerado uno de los oxidantes más potentes.
Radical ·OH
(light conditions) atmospheric pressure and room temperature Glaze 1987.

10. AOP modern (hot AOP) ELECTRON BEAM CAVITATION WET OXIDATION
SUPERCRITICAL WATER OXIDATION
Se divide principalmente en dos partes, una primera parte donde se estudiaran los procesos llamados homogéneos, y son aquellos procesos donde todos los reactivos son líquidos o en disolución. Y una segunda parte dedicada a los procesos heterogéneos, se trata de reacciones gas-liquido, donde el reactante gaseoso es el ozono. Los tratamientos estudiados en la primera parte son la fotolisis mediante radiación ultravioleta, y el proceso que combina radiación ultravioleta y un oxidante ( en este caso se utilizaron peróxido de hidrogeno y sales de hierro III). En cuanto a la segunda parte se estudiaron los procesos de ozonización. Ozonización combinada con radiación UV, y ozonización combinada con peróxido de hidrogeno, también se realizaron experimentos combinando ozono, radiación y peróxido a la vez.
Todos estos tratamientos, están basados principalmente en el poder oxidativo del radical ·OH, considerado uno de los oxidantes más potentes.

11. WET OXIDATION
* Wet oxidation is a flameless radical oxidation process brought about when an organic and/or oxidizable inorganic-containing liquid is mixed thoroughly with a gaseous source of oxygen at temperatures of 150 to 325 ºC and gauges pressures of 0.2 to 2.06 Mpa (2 – 20 atm).
- High Pressure High operating Need to optimize the
and Temperature costs process
* WO is a process specially suited to treat effluents that are too concentrated to be treated biologically and too diluted to be incinerated. The common COD level of the emissary effluent to be treated by WAO is between 20 g/L and 200 g/L.
* Advantage: During the process neither NOx, SO2, HCl, dioxides nor other harmful products are generated.

12. Lab WO installation
thermostatic bath
stirrer
reactor
controller

13. Lab WO installation PO2 = 5 - 20 bar stirrer = 700 rpm V = 0.3 L
T = C
1) power supply, 2) controller, 3) oxygen cylinder, 4) heater, 5) stirrer, 6) reactor, 7) sample extraction, 8) gas draining

14. WO reactor Drop band with screw Split ring pair with screws Bomb head
Dip tube
Cooling loop
Stirrer
Bomb cylinder

15. Suitability of water treatment according to COD10
100
1000
Classical AOP
Wet Oxidation
Incineration
COD (g.L-1) 20
200
autothermic 2
Andreozzi, R., Caprio, V., Marotta, R. (1999) Advanced Oxidation Processes (AOP)
for water purification and recovery”, Catalysis Today 53 (1) 51-59

16. Suitability of water treatment according to TOC
TOC (mg.L-1)
Flow rate (m3.h-1)
Hancock,F.E. (1999) “Catalytic strategies for industrial water reuse”
Cat. Today 53, 3-9

17. COD removal - AOPs Applications
AOPs application regions with regards to economic consideration
From these examples of applications and considering all others we know today from different sources we can draw out a figure of the use of AOP for COD removal in waste water treatment. With regards to economic consideration it appears than ranging few 10 mg/L to few 100mg/L the UV based systems and O3/H2O2 combination are set out. The Fenton process and pressurised Fenton processes are much more dedicated to COD ranging 800mg/l to 30000mg/L while the WAO process since to get interest for COD of 30000mg/L up to mg/L. Above this value incineration should be the ultimate solution. It is clear than higher is the COD and lower is the quantity of flow which is really economically acceptable. To complete this purpose about waste water treatment we can mention the case of concentrate coming from gas treatment for hydrophilic COV with a chemical washing process. In such case in which we get dirty water which contains few g/l of COV (case of formaldehyde and phenols) and with a small volume (few m3/d) AOPs can be used to recover the washing water with the same figure.
Suty,H., Coste, M. “The AOPs tools in the treatment of waste water effluents”
3rd European Meeting on Solar Chemistry and Photocatalysis :Environmental
Applications Barcelona, 30 June and 1, 2 July 2004

18. Ozone O3
1785: M. van Marun . Oxygen with electric discharges gives a peculiar odor (irritant).
1840: Schönbein discovered Ozone, a different substance based on Oxygen (from greek ozein, smell)
1856: Thomas Andrews demonstrate that Ozone is only formed by Oxygen
1863: Soret found the relation Oxygen-Ozone (three volumes of oxygen produces two volumes of ozone)
3 O2 ↔ 2 O3
Thermodinamically unstable  have to be produced “in situ”
ozone% explosion limit = 30%

19. Ozone generation
UV (185 nm) irradiation (air oxygen)
Electric discharge
Electrolitic
only 5-10% of electric energy leads to ozone production

20. Ozone reactivity O3 ───® 3/2 O2 DH°= - 34.61 kcal/mol
O3 + 2 H+ + 2 e- ───® O2 + H2O E° = 2.07 V
organics :direct and indirect attack
Moxidized O3
HO· M
Initiators
Promoters
M’oxidized
Inhibition
metallic ions oxidation

21. Ozone mass transfer Generation (air, oxygen) Mass transfer
water treatment with ozone

22. Ozone /Hydrogen Peroxyde
Ozone via hydroxyl radical
Ozone at high pH
Ozone /UV
Ozone /Hydrogen Peroxyde
Catalytic Ozonation
C, TiO2, oxides and salts of Fe, Mn, Ce, Cu, Co..

23. Ozone Material & operating conditions

24. Ozone Material & operating conditions
Ozonation Set-up

25. Ozone/Hydrogen Peroxyde
(Peroxone)

26. Fenton = Fe+2- H2O2 Fe 2 + + H 2 O 2 → Fe 3 + + OH· + OH-
* Developed 1894 by Henry John Horstman Fenton as an analytical
reagent
Fenton HJH (1894). "Oxidation of tartaric acid in Presence of iron" J. Chem Soc, Trans. 65 (65): doi : /ct
* Suggested by Haber and Weiss in the 1932
Haber, F. and Weiss, J. (1932). "Über die des Hydroperoxydes KATALYSE" Naturwissenschaften . doi : /BF
Fe H 2 O 2 → Fe OH· + OH-
Fe H 2 O 2 → Fe OOH· + H+

27. H2O2 Hydrogen Peroxide Discovered by Thenard 1818
by reacting barium peroxide with nitric acid
Hydrogen peroxide is a clear liquid, slightly more viscous than water, colorless. pure hydrogen peroxide have a pH of 6.2, pH can be as low as 4.5 when diluted at approximately 60%.

28. mechanism through de Fe(IV) ??
Fenton
Fenton = Fe+2- H2O2 T mV pH H 2 O OH Fe 3+ 2+
mechanism through de Fe(IV) ?? 28

29. Fenton mechanism 29

30. Fenton like Fe+2- H2O2 at not acidic pH
Me+2- H2O2 at basic or neutral pH
Heterogeneous Fenton by using solids containing metalic oxids- H2O2
……. 30

31. Fenton Advantages Disadvantages Operation pH 2-4 (optimal =3)
Very cheap
Simplicity  (easy maintenance). Robustness. Flexibility
Disadvantages
Operation pH 2-4 (optimal =3)
Generation of sludge through the removal of iron ions.
Exploration of Fenton at different pH (neutral and basic) under research (iron complexes, Cu,..)
Possibility of supporting Fe ions on a solid under research 31

32. Photochemical Oxidation Processes
PHOTOCHEMICAL PROCESSES
WAVELENGTH
UV (photolysis)
< 190 nm
H2O2/UV
< 300 nm
O3/UV
< 320 nm
O3/H2O2/UV
TiO2/UV (photocatalysis)
< 400 nm
Fe+2/H2O2/UV (photoFenton)
< 550 nm
Fe+2/e-/UV (photoelectroFenton)

33. PHOTOCHEMISTRY 33

34. Energy of photon with wavelength  E = h.c/
PHOTOCHEMISTRY
Energy of photon with wavelength 
E = h.c/
h (Planck) = J.s
c (light) = m/s
= m
Einstein = 1 mol of photons
Quantum yield  (stoichiometric coefficient)
 = mol reacted/mol of photons absorbed 34

35. PHOTOCHEMISTRY UV radiation ~ 100 - 400 nm visible ~ 400 - 700 nm
near infrared ~ nm
far infrared nm
UVA – 400 nm
UVB – 320 nm
UBC – 280 nm
UV-VIS ENERGY ENERGY
200 nm kcal.mol kJ.mol-1
700 nm kcal.mol kJ.mol-1
wavelength, nm UV
VISIBLE 35

36. SOLAR PHOTOCHEMISTRY
4 - 7% UV radiation ( <400 nm) 36

37. PHOTOREACTOR DESIGN mass balance momentum balance energy balance
global
j componet
momentum balance
energy balance

38. PHOTOREACTOR DESIGN radiation balance for every wavelength
UR = radiation internal energy , Einstein/m3
qR = radiant energy flux density vector , Einstein/(m2.s)
E = radiant energy emission , Einstein/(m3.s)
A = radiant energy absorption , Einstein/(m3.s)
c = light speed, m/s
Iw* = radiation intensity (escalar and by solid angle) in the vectorial direction w, Einstein/(m2.s.srad)

39. PHOTOREACTOR DESIGN for not emitting media
Iw* = radiation intensity (escalar and by solid angle) in the vectorial direction w, Einstein/(m2.s.srad)
I = radiation intensity (escalar), Einstein/(m2.s)
x = position according the bundle moviment, m
s = lineal cordinate in w direction w (optical way),m
 = adsorption radiation coefficient, m-1
 = scattering coefficient, m-1
P(w*,w) = phase function of dispersion w*  w. Indicates the probability of a bundle in the direction w* takes the direction w after dispersion.
 = solid angle, srad

40. PHOTOREACTOR DESIGN photon balance x
q =photon flow density vector, Einstein/(m2.s)
= absorbance, cm-1
x = position, cm
0,01
0,9900
0,0100
0,1
0,9048
0,0952 1
0,3679
0,6321 3
0,0498
0,9502 9
0,0001
0,9999 40

41. Tubular Photoreactors

42. Multitubular Photoreactors

43. Multitubular Photoreactors

44. Helioman-PSA – Almeria
Solar Photoreactors
Helioman-PSA – Almeria

45. Solar Photoreactors
Parabolic
CPC-PSA – Almeria

46. Experimental Devices c0: 200 ppm cp: 0 - 1 g/L pH: free T: 30 ºC
VR: 1,26 - 0,078 L
L = cm
d = 4 - 1,95 cm
VT: 6 - 1,5 L
Smirror: cm2
41º inclination (Barcelona
Latitude) and faced South.

47. Experimental Devices 6 tubes Vtubo: 0,135 L Ltubo = 60 cm
dtubo = 1,75 cm
VR = 0,808
5 codos
VC = 0,034L
VTC = 0,170 L
VTR = 0,978 L
c0: 50 ppm
cp: 0,4 g/L
pH: free
VT: 10 L
T: 30 ºC
q: 1,95 L/min

48. WATER PHOTOLYSIS O-H bond strength in H2O: ca. 497 kJ mol -1
(corresponding wavelength = 240 nm)
240 nm
H2O + hν → °OH + H°
Φ = 0.42 at 172 nm
H° + O2 → HO2°
Termination reactions:
2 °OH → H2O2
2 H° → H2
HO2° + °OH → H2O + O2
2 HO2° → H2O2 + O2 48

49. WATER PHOTOLYSIS VCV lamps ( = 180 nm) Excimer lamps
Advantage: no gaseous, liquid or solid additive
Disadvantage: very limited penetration depth of the photons
high cost of 180 nm radiation (Xe lamp)
ozone production
Potential application: microelectronics, gas treatment 49

50. UV/ H2O2 (WATER PHOTOLYSIS)
380 kJ/mol or 90 kcal/mol
210 kJ/mol or 50 kcal/mol

51. H2O2 PHOTOLYSIS H2O2 + hν → 2 °OH pKa = 11.6 HO2- + hν → °OH + O°-
O°- + H2O → °OH + OH-
ε254: 18.6 for H2O2 ; 240 L mol-1 cm-1 for HO2- 51

52. UV/ H2O2 tubular photoreactor
UVC-lamps
photoreactor
punp
rotameter
tubular
photoreactor
4 low-pressure 15 W mercury lamps nm
Volume 1.5 L
Went,
13.9 Einstein.s-1

53. UV/ H2O2

54. H2O2 PHOTOLYSIS Drawbacks Advantages handling/safety precautions
no residues
H2O2 is miscible with H2O
H2O2 is readily available, transportable, storable
handling/safety precautions
very weak absorption except at high pH (several tens of kW-lamps) ; inner filter effect by organics
needs UVC (254 nm). Gemicidal
°OH scavenging by H2O2 (°OH + H2O2 → HO2° + H2O)
Drawbacks
Advantages 54

55. OZONE/UV Absorbs < 320 nm (UVB-UVC) ε254: 18.6 for O3 L mol-1 cm-1
Relative absorbance
wavelength, nm
320 nm
ε254: 18.6 for O3 L mol-1 cm-1 55

56. OZONE/UV mechanism
hydroxyl radical
hydroperoxyl radical
scavenger 56

57. Ozone/UV

58. Ozone/Hydrogen Peroxyde/UV

59. OZONE/UV Advantages Disadvantages no residues
easy O3 dosification
UV absorption higher than that of H2O2 (0.1 kW-lamps)
Disadvantages
need to produce O3 (but bactericidal use of O3)
necessity of destroying residual gaseous O3
efficiency limited by O3 hydrosolublity, gas-liquid transfer and scavenging of °OH (°OH + O3 → HO2° + O2)
Problems
Unwanted stripping of VOCs
Br- + 3 O3 → BrO O2 (overall reaction) 59

60. Photocatalysis Heterogeneous photocatalysis
Semiconductor based catalyst:
* TiO2 , ZnO, ...
* CdS
Homogeneous photocatalysis
Photosensitizers
(ruthenium(II) poly(pyridyl),...)
PhotoFenton
Fe+3/UV/H2O2 60

61. Zeolite with photosensitizers
Fe2+ N
[Fe(bpy)3] (1 nm)
2,2‘ - bipiridin (bpy)
Zeolite 61

62. Zeolite with photosensitizers
Absorbance UV
Visible 62

63. TiO2/UV
good UV absorption
low quantum yield (  < 0.03) 63

64. TiO2/UV Advantages Disadvantages
No consumable additive
Use of Solar UV
Simplicity  (easy maintenance). Robustness. Flexibility
Much lower sensitivity to pH than UV-AOPs based on H2O2 , O3
Reduction of some pollutants: Mn+, CCl4
Disadvantages
Separation of the catalyst from the solution
UV irradiation is poorly utilized by TiO2 despite high absorption
Poisoning of catalyst by organic matter.
Low quantum yield 64

65. PhotoFenton Fe+3/UV/H2O2
Fe2(SO4)3
UV lamps
(360 nm)
Fe(III) in the presence of UV :
Fe3+(aq) + H2O + hn OH· + Fe2+ +H+
quantum yield for the formation of Fe(II)
at 313 nm
0.017 at 360 nm
Faust, B. C.; Hoigne, J., Atmos. Environ. 24A (1990) pp
Magnetic Stirrer 65

66. PhotoFenton Fenton Fe(III) in the presence of UV :
Fe3+(aq) + H2O + hn OH· + Fe2+ +H+
Fenton 66

67. °OH radicals are not the only active species
PhotoFenton
Additional reactions in Photo-Fenton
Fe3+ + H2O2 → H+ + Fe(HO2)2+
Fe(HO2)2+ + hν → Fe(HO2)2+*
Fe(HO2)2+* → FeIII-O° ↔ FeIV=O + °OH
Fe(HO2)2+* → FeII + HO2°
°OH radicals are not the only active species
UV-visible photodegradable compounds 67

68. Solar PhotoFenton
parabolic CPC PSA – Almeria 68

69. PhotoFenton Advantages Disadvantages Operation pH 2-4 (optimal =3)
Very cheap
Simplicity  (easy maintenance). Robustness. Flexibility
Increase mineralization (TOC reduction)
Use of visible radiation
Disadvantages
Operation pH 2-4 (optimal =3)
Generation of sludge through the removal of iron ions.
Cost of UV-visible lamps
Waters with suitable UV light transmission
Fouling of the surface of UV tubes 69

70. Strategy to combine AOPs with Biological treatments
* Decrease the treatment cost
* Increase biodegradability
* Eliminate toxicity
CHEM
BIOL
CHEM
BIOL
DOMESTIC WASTEWATER
Biodegradability (BODn/COD) =
Metcalf and Eddy (1985)

71. Strategy to combine AOPs with Biological treatments Wastewater
Wastewater
Biodegradability
High
Partially biodegradable
Low
Organic
level
Chemical
process
Yes
Biodegradability
Chemical
process
Non-biodegradable NO
Biodegradable
Biological
process

72. Coupling Ozone with Biological and Menbrane Treatments
SOSTAQUA (
NOVEDAR (
MBR
activated sludge
Bioreactor
etc..
Ultrafiltration
Reverse
Osmosis
AOPs
(ozonation,UV/H2O2)
AOPs
(ozonation,UV/H2O2)

73. Ozone/UV with Biological treatment
UV Lamp
Volcanic stones
27ºC
Neutralizing stage O3
killer
1.5L Vessel
Thermostatic Bath
Air
Stirrer

74. UV sequencing photoreactor + bioreactor H2O2 FeSO4 UV lamps
Thermostatic Bath
Air
27ºC
Volcanic stones
Neutralizing stage
H2O2
FeSO4 UV
UV lamps
Magnetic Stirrer 74

75. sequencing photoreactor + bioreactor
Photoreactor 1.5 L
Black blue lamps (3 x 8W, 360 nm) = 6 Einstein/s 75

76. SUMMARY Chemical Oxidation Processes
Advantadges
- High oxidizing power
- Not selective oxidant
- No residues (except homogeneous Fenton and O3 catalytic)
- Increase biodegradabilty
- Decrease toxicty
Disadvantages
- Cost of UV-Visible radiation and chemicals (H2O2, O3)
- Mass Transfer control for ozone
- UV light transmission of waters
- Rate decreases due to °OH scavenging by the
sensitizer (H2O2, O3)
products (HCO3-/CO32-, SO42-, HxPO43-x)
reactant (Fe2+)
Good chance for coupling AOP with biological treatment 76

77. AOPs application fields
Agriculture
wastewaters
Site waters
Abandoned-
waters
Cooling
Domestic
Drinking
water
Well-waters 77

78. Thank you

79. Thank you