oxidation technologies at ambient conditions for...

Oxidation Technologies at ambient conditions for Wastewater Treatment

and Recovery

A. B. PanditInstitute of Chemical Technology

INDIA

Scope of the Lecture

Individual process

Basics

Equipments and optimization

Problems in large scale application

Hybrid processes

Combination of different techniques

Model hybrid scheme useful for CETP

Processes covered

Individual process

Cavitation

Photocatalytic Oxidation

Fenton Oxidation

Chemical Disinfection using hydrogen peroxide and ozone

Hybrid processes

Ultrasound in combination with ozone/hydrogen peroxide

Photocatalytic oxidation in combination with ozone/hydrogen peroxide

Ozone/hydrogen peroxide

Sonophotocatalytic oxidation

Photo-Fenton oxidation

Cavitation

Mechanism of Oxidation of pollutants

Free radical theoryGeneration of highly reactive free radicals

Hot-Spot theoryGeneration of local hot-spots resulting in

breakage of chemical bonds

• Use of Snapping Shrimp for actually visualizinghydrodynamic cavitation technique

• Study carried out at University of Twente, TheNetherlands, indicated that the Snapping shrimp throwsa cavity, which travels a certain distance and collapses.

Top ViewFrontal View

Nature also utilizes cavitation!

Measurements using hydrophone indicated that the pressure pulsegenerated at the collapse is capable of carrying out physical or chemicaltransformations (Versluis et al., Science, Vo. 289, 2114-2117 (2000))

Confirmation by Experiments

• Aim of hydrodynamic cavitation reactors will be to replicatethis natural phenomena but at multiple locationssimultaneously

• Earlier investigations dealing with hydrodynamic cavitationhave been mainly directed towards avoiding it e.g.cavitation erosion of propeller blades of ships

• Concentrated efforts by few research groups worldwidehave led to harnessing the positive effects ofhydrodynamic cavitation

Replicate Nature !!!

Fluctuating Pressure field Oscillating cavity

Nuclei Maximum radius

Bang!Adiabatic Collapse

phase

Expansion phase

Generation Expansion CollapseWhat is Cavitation?

How is cavitation done?

Turbulent fluctuating pressure field

Hydrodynamic cavitation

Orifice plate

Ultrasonic pressure field

Acoustic cavitation

Ultrasonic bath

High Magnitude Pressure Pulse, 100 to 5000 atm

Extremely High Temperatures, 1000 to 15000 K

Velocities in excess of 2 to 3 times that of Sound in the case of Compressible Media

High Energy Densities, 1 to 10 X 1018 kW/m3

Effects of Cavitation

Engineers Job

Control the Phenomena

and

Use the Effects in Positive Way

CAVITATION

AcousticUltrasound

Hydrodynamic

OpticHigh intensity laser

ParticleHigh energy elementary particle beams

High velocity flow, rotating machinery

Generation of Acoustic Cavitation

Types of Equipments used

Sonochemical Reactors

Reaction Mixture

Generator

Ultrasonic horn

Formic acid solution

TRANSDUCERS

Ultrasonic bath

Immersion type reactor Transducers at bottom

Very low active volume Volume dependent on number and arrangement of transducers

Sonochemical reactors

Thermocouple

Dual Frequency Flow Cell

Cooling water-in

Cooling water-out

Cooling pipe

25 kHz 40 kHz

Transducers

Rectangular flow cell with opposite faces housing Multiple frequency multiple transducers

Sonochemical reactors: Triple frequency flow cell

Ultrasound

T1T2

T3T5

T6 Quartz tube

Hexagonal Reactor with 10 cm sides also stirred continuously with the help of an agitator (not shown in the figure)

Transducers

annular part in batch modeEffluent in Hexagonal

T4

Optimum design parameters

Use higher frequencies of irradiation.

Use higher power dissipation per unit volume till optimum value.

Dissipate same power through higher areas of cross-section.

Use lower operating temperatures.

Reaction rates are enhanced in the presence of:

Solid catalyst such as CuO, CuSO4, TiO2.

Air, inert gases such as argon or mixture of gases.

Adjust the physicochemical properties of liquid medium for obtaining lower initial sizes of the nuclei (Diffusional size).Use low vapor pressure, viscosity, surface tension.

Hydrodynamic Cavitation Principle of generation

Adjust the geometry of constriction such that local pressure falls below the vapor pressure of the medium

Hydrodynamic cavitation can also be generated in rotating machinery e.g. high speed homogenizer

Flowdirection

ConstrictionPipe

r

x

Different geometries used as constriction in the pastThrottling valveSingle hole orificeMultiple orifice plate

Types of Equipments

High Speed/Pressure Homogenizer

Reactor capacity is 1500 ml; operated in re-circulating mode with the flow rate of circulation deciding the intensity of cavitation generated.

Feed tank

Plunger Pump

1st stage

2nd stage

Non return valve

P1

P2

BYE PASSLINE

TANK

P1, P2 - PRESSURE GAGES

V1

V2 V3

V1,V2,V3 - CONTROL VALVES

CENTRIFUGALPUMP

CW out

Orifice plate setup

Orifice Plate Configuration

Setup has a capacity of 50 liters and is operated in recirculation mode

Tremendous flexibility in controlling the intensity of cavitation

plate1 plate2

•1. Schematic of the hydrodynamic cavitation setup

•2. Schematic of cavitating device

•3. Rotating cylinder

•4. Cylinder with casing (side view)SPR Cavitation.flv

•Inlet •Outlet

•Hydrodynamic cavitation setup

Methanol water degradation

0 5 10 15 20

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

1800 2000 2200 2700 2850

me

tha

no

l co

nc.

(g

/l)

Time (min)

•Concentration of methanol (g/l) vs. time (min) at different speed of rotation

•Maximum (80 %) reduction •in concentration was •observed at 2200 RPM

Methanol water degradation

0 5 10 15 20

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

TiO2(0.4 %) FeO (500 ppm) CuO (500 ppm) ZnO (500 ppm) 2mm gap

me

tha

nol c

on

c. (

g/l)

Time (min)

•Concentration of methanol (g/lit) vs. time (min) at 2200 RPM for various metal oxidizing agents

•Maximum reduction in •concentration of methanol•was for FeO. (81%). But its•marginal increase compared•to earlier case where no•oxidizing agents were used.

Wastewater experiments

0 5 10 15 20

18000

20000

22000

24000

26000

28000

30000

32000

34000

36000

38000

40000

1800 2000 2200 2400

CO

D (

mg

/lit)

Time (min)

•Effect of speed of rotation:

•Reduction in COD (mg/lit) vs Time (min) at different speed of rotation


0 5 10 15 20

15000

20000

25000

30000

35000

40000

4.4 sec 6.25 sec 7.5 sec

CO

D (

mg

/lit)

Time (min)

•Effect of residence time:

•Reduction in COD (mg/lit) vs. Time (min) at 2200 RPM.

•Residence time was changed •throttling the outlet valve of the •cavitating device

•In 1st case valve is full open•In 2nd case valve is half open•In 3rd case valve is 1/3rd open

•Maximum reduction was 56 %, •Observed when valve was half•closed.


•Reduction in COD (mg/lit) vs. Time (min) at 2200 RPM, outlet valve is half open

•Effect of H2 O2 concentration:

•Almost 83 % reduction •In COD value when 5 g/lit of•H2 O2 was used.

Wastewater experiments•Effect of H2 O2 concentration:

•Reduction in COD (mg/lit) vs. Time (min) at 2200 RPM, outlet valve is half open

•Maximum reduction In •COD after 20 min was 92 %•After 30 min it was 94 %

Degradation of ImidaclopridEffect of Inlet Pressure

-0.14

-0.12

-0.1

-0.08

-0.06

-0.04

-0.02

0

0 50 100 150ln

C/C

0

Time in minutes

P= 5 bar

P = 10 bar

P = 15 bar

P = 17.5 bar

P = 20 bar

Pressure in

bar

%degradati

on

k X 104 min-

1 R²

Cavitation

Number, Cv

5 17% 7.46 0.899766 0.192

10 21% 8.5 0.984386 0.0993

15 26 % 11.14 0.985979 0.066

17.5 25% 11.79 0.985925 0.0587

20 25% 11.12 0.990375 0.0506

Effect of operating pH:

-0.16

-0.14

-0.12

-0.1

-0.08

-0.06

-0.04

-0.02

0

0 50 100 150

lnC

/C0

Time in Minutes

pH=2

pH=2.7

pH=3

pH=4

pH=6

pH=7.5

pH % degradation k X 104 , min-1 R²

2 26.5 12.54 0.920108

2.7 26 11.14 0.985979

3 24 10.76 0.956269

4 2.6 1.33 0.828179

6 2.4 1.06 0.902135

7.5 3.0 1.14 0.911896

Optimisation of Hydrodynamic Cavitation

Cavitation number should be less than 1 for maximum benefits though cavitation can occur at Cv > 1.5 in the presence of gases

Operate with higher inlet pressures which results in more intense cavitation.

Use plates with smaller size of the orifice holes and large in number to get maximum benefits of the shear layer.

System specific:Compromise between number of cavities and pressure pulse generated by collapse of individual cavity

Low percentage free area of the orifice on the plates is preferred.

Comparison of Reactors in terms of Energy Efficiency

•Hydrodynamic cavitation reactors are more energy efficient as compared to sonochemical reactors•Flow cell and ultrasonic bath (wider dissipation of energy) are better among the sonochemical reactors

Energy efficiency Energy dissipated into the system

Electrical energy supplied to the system

0

10

20

30

40

50

60

70

Ace h

orn

Dakshin

horn

Dakshin

bath

Flo

w c

ell

Hig

h S

peed

hom

ogenis

er

Hig

h p

ressure

hom

ogenis

er

Orific

e P

late

hydro

dynam

ic

cavita

tion s

et

up

Energ

y e

ffic

iency (

%)

Comparison in terms of cavitational effects

Equipment Cavitational yield per unit power density

g/(J/ml)

Dakshin horn 3.53 E-9

Dakshin bath 5.83 E-7

Ace horn 5.25 E-9

Flow cell 7.06 E-7

High pressure homogenizer 7.38 E-5

High speed homogenizer 6.64 E-7

Pilot plant scale (Orifice plates) 2.48 E-4

Cavitational yield = Desired chemical change per unit power density

Case Study: Degradation of Potassium iodide

Conclusions

The equipment based on acoustic cavitation are less energy efficient and offer lower cavitational yields

Reactors based on the hydrodynamic cavitation show aconsiderable optimization possibility due to the presence ofmultiple pressure oscillation frequencies present asturbulent and chaotic flow (depending on thegeometry), unlike acoustic equipments, which operate at afixed frequency

Hydrodynamic cavitation (pilot plant scale) has the twinadvantage of greater energy efficiency and higher cavitationaleffects at least for the model reactionMoreover, the scale up of these reactors is relatively easy

The results are valid for the model reaction considered in the present work. Similar results have been obtained for decolorization of Rhodamine B solution ( a typical pollutant observed in the effluent from Dyes/Textile industry)

Some preliminary work indicated that existing hydrodynamic cavitation setup was not able to give degradation of chemicals such as p-nitrophenol

Modifications in the hydrodynamic cavitation setup such as using number of orifice plates in sequential manner may result in generation of intensities equivalent to acoustic cavitation

Cavitation zone

Pressureindicator

Pressure indicator

Temperature indicator

Centrifugal pump

CavitationReactor reservoir

Water bath

Cooling coil

Refrigerant coil

Contaminantflow

Orifice Plate

Intensification of cavitating conditions with the use of multipleOrifice plates in Hydrodynamic Cavitation Reactors

Problems for large scale applications

Not much information on the operating design strategies

Higher cost of operation

Scale up of sonochemical reactors is difficult

Uneven distribution of cavitating events

High frequency high power dissipation operation is difficult

Hydrodynamic cavitation reactors though offer promise for scale up are hampered by less intense cavitation which restricts the applicability

Photocatalytic oxidation

Mechanism of oxidation of pollutants

Generation of highly reactive free radicals and itssubsequent attack on the pollutants

Two methods:

Photochemical oxidation

UV + Hydrogen peroxide

Photocatalytic oxidation

Use of solid photocatalyst such as TiO2

Rate of generation of free radicals is much faster when

catalyst is used

Semiconductor catalyst + h e – + h+

H2O + h+ OH + H+

Pollutant (in adsorbed state) + OH Intermediates

Intermediates (also in adsorbed state) + OH CO2 + H2O

Adsorption of the pollutant molecules on the catalyst surface is the rate-controlling step

Mechanism of Free radical generation

Typical Scheme of photocatalytic process over TiO2

UV ( < 400 nm)

Energy (eV)

Ef- 0.1

1

2

3.1

Redox Potential

Eg

Conduction band

Valence band

e-

h+

e-

Adsorption

TiO2 Particle

e-

Adsorption

Reduction (ox + ne- red)

Oxidation (red ox + ne-)

When illuminated with light of energy higher that the band gap, electrons and holes are formed in a semiconductor and are capable of initiating chemical reactions.

Typical catalysts

Titanium dioxideZinc oxideSelenium oxideZinc sulfideCadmium sulfide

Most beneficial is Titanium dioxide Hybrid mixture of Rutile and Anatase forms

Using mixture of two forms helps in restricting the Electron-hole recombination reaction

Typical equipments used

Slurry Reactors

Problem of fine particle separation

Opacity of the slurry

Supported photocatalyst reactors

Thin layer of photocatalyst supported on a support

Stability of the crystal structure and the support in flow conditions is a key parameter.

Schematic representations

Air

Bubbler

Cooling coilmagnetic needle

UV source

Simple Suspended type reactors(UV source may also be used at top for direct irradiation or can be immersed directly in the solution surrounded by quartz tube)

U.V. tube

Quartz tube

Effluent in the annular space

Hexagonal annular photoreactorDifferent outer reactor configurationshave also been used., Catalyst can be in suspendedform or also can be immobilized on the quartz tube

Conventional approaches

Feed introduced at the topeof the vessel through 5 different portsfor avoiding channeling

21 U shaped lamps placed oneafter the another

Section of Novel Tube light reactor usedBy Ray and Beenackers (1998)

Novel approaches

Schematic representations

Inlet

Outlet

Light Source

Reflector

LensTitanium dioxide coatedhollow glass tubes

Multiple tube reactor

Optimum operating parameters

1. Use catalyst concentration till an optimum value depending on type of effluent and reactor

2. Degussa P-25 TiO2 catalyst is the best

3. Reactor design should be such that uniform irradiation of the entire catalyst surface should be achieved at near-incident intensity

4. Operate at ambient conditions; use cooling if temperature is expected to increase beyond 80°C

5. Operating pH should be equal to the zPc of the catalyst

6. Aeration is a must

Class of Organics Examples

Haloalkanes/haloalkenes

chloroform, trichloroethylene, perchloroethylene, tribromomethane,dichloromethane, CCl4

Aliphatic alcohols Methanol, ethanol, 1-octanol, 2- propanol

Aliphaticcarboxylic acids

Formic, Glycolic, citric

Amines alkylamines, alkanolamines, heterocyclic and aromaticN-compounds

Aromatics Toulene, Benzene, Xylene, 2 chlorobiphenyl

Phenoliccompounds

Phenol, 2-, 4-, chlorophenol, 2-4 dichlorophenol

Aromaticcarboxylic acids

Malic, chlorobenzoic acids, phenoxy acetic acid, 2,4dichlorophenoxyacetic acid

Surfactants Sodium dodecasulphate, polyethylene glycol, sodium dodecylbenzene sulphonate, trimethyl phosphate

Herbicides Atrazine, S-trizine herbicides, bentazone

List of pollutants successfully degraded

Problems for large scale operation

1. Problem of uniform distribution of the incident light2. Processing capacity is restricted due to the fact that

only a thin film of catalyst can be used and lower rates of photocatalytic reactions

3. Ultra-fine separation is a problem for slurry type of reactors

4. Applications to real industrial effluents is lacking in the literature

5. Fouling of the catalyst results in a decrease in the rates of degradation

6. Severe mass transfer resistances

Fenton Oxidation


Use of Fenton’s reagent (Fe ions in combination with hydrogen peroxide) results in formation of oxidizing species though the exact mechanism is not yet understood

Hydroxyl radicals either in ‘free’ or ‘caged’ form

Aquo or organo complexes of the high valence ferryl ions

Typical scheme of reactions

Fe++ + H2O2 Fe+++ + OH + OH

The hydroxyl radicals as well as R radicals formed in this way undergo a series of radical chain reactions before undergoing complete/partial mineralization depending on the conditions existing in the reactor.

R-H + OH R + H2O

R + Fe+++ R+ + Fe++

Typical reactor usedA simple stirred reactor

Treatment flowsheet used for Fenton oxidation

Effect of Fenton reagent

-1.8

-1.3

-0.8

-0.3

0.2

0 5 10 15 20 25 30

lnC

/C0

Time in Minutes

FeSO4 . 7H2O : H2O2= 1:50

FeSO4 . 7H2O : H2O2= 1:40

FeSO4 . 7H2O : H2O2= 1:30

FeSO4 . 7H2O : H2O2= 1:20

only fenton

Only HC

Sr. No. Process k X 103 , min-1 R2

1 Only HC 1.114 0.985

2 Only Fenton

FeSO4 . 7H2O : H2O2 1:40 29.3 0.6544

3 Fenton + HC

FeSO4 . 7H2O : H2O2 1:50

85.5 0.996

FeSO4 . 7H2O : H2O2 1:40

108.9 0.9896

FeSO4 .7H2O : H2O2 1:30

190.2 0.9417

FeSO4 . 7H2O : H2O2 1:20

244.1 0.99

Optimum operating conditions

1. Operating pH of 3

2. Higher ferrous ion concentration though optimum may

exist

3. Use higher concentration of hydrogen peroxide but

there should be no residual concentration

4. Use lower initial concentration of the pollutant

5. Use acetic acid/acetate buffer for the adjustment of pH

6. Use ambient conditions of temperatures

7. Chemical coagulation step is recommended after

Fenton oxidation so as to keep TDS within limits

Problems for large scale operation

1.Fenton chemistry is not a universal solution as there are many chemicals refractory towards Fenton’s reagent such as acetic acid, carbon tetrachloride, methylene chloride

2.Degree of oxidation conditions is limited i.e. oxidant dose cannot be increased beyond a certain limit

3.Applicability to real industrial effluents still a unanswered question

Chemical Disinfection

1. Use of ozone

2. Use of hydrogen peroxide


1. Direct attack of the oxidants

2. Formation of free radicals in the presence of additional energy dissipation by ultrasound or UV light

Reactors used for Ozonation

Water outlet

ContactChamberSpray header

Raw water inlet

Film Layer Purifying Chamber Process

Residual Ozone underpressure

Ozone reinjection

Raw water inlet Water outlet

Torricelli Apparatus

Reactors used for Ozonation

Spent gas

Water inlet

Water outlet

Pressurized ozone inlet

Counter current bubble column

To Destaurator for separation ofwater

Ozone Inlet

Raw water inlet

Self contactcolumn

Tube for dissolving under pressure

Otto Apparatus

Novel Design in terms of Use of Static Mixers

Optimum operating parameters for Ozonation

1.Use alkaline conditions but pH must be less that pK value for the pollutant

2.Higher ozone partial pressures gives higher degradation rates but is associated with an increase in the cost of generation. Increase the ozone transfer into the medium by increasing the contact time and the available gas-liquid surface area

3.Optimize the operating temperature as the effect is two-fold (increase in temperature increases the intrinsic rates of degradation but at the same time decreases ozone solubility)

4.Presence of catalyst such as Mn(II), Fe (II), TiO2

supported on alumina beads is beneficial

Reactors used for Hydrogen peroxide

Introduction of hydrogen peroxide into the waste stream in critical due to lower stability

An optimum addition point should give large residence time and it also depends on the rate of reaction between the pollutant and oxidant

Other optimizing parameters can be size of the holding tank, injection rate, catalyst and the temperature

Simplest, faster and cheapest method for injection is the gravity feed system

Effect of H202

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

0 20 40 60

lnC

/C0

Time in minutes

IMID: H2O2 1:1

IMID: H2O2 1:5

IMID: H2O2 1:10

IMID: H2O2 1:20

IMID: H2O2 1:30

IMID : H2O2 1:40

imid:H2O2 1: 50

IMID: H2O2 1:60

Sr. No. Process k X 103 , min-1 R²

1 Only HC 1.114 0.985

2 Only H202

Imid : H202 1:40

1.317 0.508

3 HC + H202

Imid : H202 1:01 8.597 0.978831

Imid : H202 1:05 18.94 0.956005

Imid : H202 1:10 28.47 0.890898

Imid : H202 1:20 40.01 0.921202

Imid : H202 1:30 40.09 0.932452

Imid : H202 1:40 59.3 0.946486

Imid : H202 1:50 48.59 0.8177

Imid : H202 1:60 36.51 0.9139

Problems for large scale applications

1.Limited applicability of the oxidants i.e. many compounds are refractory towards direct attack of both ozone and hydrogen peroxide

2.Severe mass transfer limitations

3.Higher cost of ozone generation makes the overall economics unfavorable for the process

4.Concentration of hydrogen peroxide cannot be increased indefinitely as residual amount gives an increase in the COD and also may produce detonable mixtures with some of the organic compounds

Hybrid Methods

Increase the rates of degradation and possible elimination of drawbacks of the individual operations

Ultrasound in conjunction with H2O2/ozone

Mechanism for synergism

Increased mass transfer due to the acoustic streaming (liquid circulation) induced by ultrasonic irradiation

Production of enhanced free radicals due to dissociation of hydrogen peroxide/ozone.

Use of catalyst such as CuO may further increase the synergistic effects

Optimum concentration of hydrogen peroxide exists due to scavenging action on the unutilized free radicals

Magnitude of optimum concentration strongly depends on the type of the effluent stream

Precautions

Use of Hydrogen peroxide:

Use of Ozone:

Optimum concentration of ozone exists at higher frequencies of irradiation possibly due to shorter lifetime of cavities

UV irradiation in conjunction with H2O2/ozone


Production of enhanced free radicals due to dissociation of hydrogen peroxide/ozone.

Synergistic effects will be observed only when the free radical attack is the controlling mechanism for the degradation and for pollutants requiring more intense oxidation conditions

Precautions

Use of Hydrogen peroxide:

Optimum concentration of hydrogen peroxide exists to be determined for the specific pollutant in question

Presence of radical scavengers needs to be tackled either by adjusting the operating pH or with pre-treatment such as carbon adsorption

Use lower initial concentrations of the pollutants and acidic conditions

Precautions

Use of Ozone:

Use higher ozone partial pressures; extent of enhancement needs to be optimized against increased costs of generation

Use lower initial concentration of pollutants

Operating pH should be neutral or slightly alkaline

Optimize the operating temperature

Nullify the effect of radical scavengers

Ozone in combination with Hydrogen peroxide


Production of additional oxidizing species in terms of the free radicals due to dissociation of hydrogen peroxide in the presence of ozone

Dual oxidation schemes (direct attack of oxidants as well as free radical attack) exists

Precautions

1.Combination technique helpful for pollutants showing less reactivity towards ozone and for the systems where no radical chain reaction initiators are present

2.Use optimum conditions i.e. lower initial concentration of pollutants, proper dose of oxidants, near neutral pH

3.Use of proper mixing conditions in the reactor (static mixer will be optimum)

4.Use multistage oxidation systems where the dosage of oxidants in adjusted in steps

Combination of US + UV + hydrogen peroxide

Combination of all the above factors for both the combinations

Ultrasound coupled with UV irradiation


Increase in the surface area of the catalyst

Continuous cleaning of the catalyst

Enhanced mass transfer rates

Enhancement in the number of free radicals

Hot spots resulting in an increase in the rates of chemical reactions

Reactors used

Sonophotochemical reactors: Batch reactors

Air

Bubbler

Cooling coil

UV source

Stirrer

Transducers

A ultrasonic bath type reactor simultaneously irradiated by UV light either directly or indirectly

Dye Solution

Immersed UV Lamps

Outlet

Cover

Ultrasonic transducers

Sonophotochemical reactors: Batch reactors

Air

Bubbler

Ultrasonicprobe

Cooling coilmagnetic needleUV source

Ar Gas

Al foilcovering

O rings

Cell holder

Ultrasonic probe

CoolantPyrex Glass reactor

A ultrasonic horn type reactor simultaneously irradiated by UV light either directly or indirectly

Sonophotochemical reactors: Continuous reactors

Effluent in

Effluent out

Ultrasound

T1T2

T3T5

T6

UV light source

Quartz tube

Hexagonal Reactor with 10 cm sides

Transducers

U.V. tube

Quartz tube

annular partEffluent in Hexagonal

Immobilisedcatalyst (or slurry)

T4

Ti indicates transducer

Triple frequency Hexagonal flow cell

Sonophotochemical reactors: Continuous reactors

1

2

3

1: Cell holder (stainless steel)2: O- rings 3: Ar gas

Ultrasonic Probe(titanium)

Reactor of pyrex glass ReactionSolution In

UV light

A ultrasonic horn type reactor operated continuously andsimultaneously irradiated by UV light indirectly

Combination of Hydrodynamic cavitation withPhotocatalytic oxidation (CAV-OX process)

HydrogenPeroxide addition

Ground water

Equalisation tank

Influent holding tank

Low energyUV reactor

High energyUV reactor

To effluent storagetank

Hydrodynamiccavitation

List of chemicals degraded using CAV-OX process

• Trichloroethane

• Aromatic compounds like Benzene, toluene, xylene

• Phenolic compounds like Phenol, Penta-chlorophenol (PCP),

• Ethyl benzene, atrazine

• Inorganic compounds like cyanides e.g. sodium cyanide

The removal efficiency is in the range of 20 to 90% depending on the constituents of the effluent stream

Precautions

Simultaneous operation is more beneficial as compared to sequential operation (ultrasonic irradiation followed by UV irradiation)

Stability of the catalyst molecules as well as the support used for binding the catalyst has to be adjusted so as to sustain the turbulence generated by acoustic streaming

Use of continuous aeration is a must

Use acidic conditions

Use additives such as Hydrogen peroxide, Fe2+ ions and ozone for increasing the severity of oxidation conditions

Photo-Fenton system


Additional oxidation scheme by formation of aqua / organo complexes of ferryl ions, which are resistant towards the action of radical scavengers

Enhancement in the number of hydroxyl radicals generated

Reaction pathways of the Photo-Fenton Process

Photolysis of FE (III)-complexes

Fenton’s reaction

Oxidation of organic compounds

h

Fe (II)

Fe (III)

OH•Radical recombination

CO2 + Water + …

OH•

Step 1:a) Fe (II) productionb) OH•production

Step 2:c) OH•production

Step 3:d) Mineralization

Combining Hydrodynamic cavitation and Photofenton

-2.5

-2

-1.5

-1

-0.5

0

0 20 40 60 80 100 120

lnC

/C0

Time in minutes

Photofenton

HC

HC + Phofenton

Type of process k x 103 min-1 R2

HC 1.114 0.986

Photofenton 43.157 0.92617

HC+ Photofenton 128.99 0.98

Comparison of Fenton and Photofentonprocesses with and without HC

Process % degradation in 15 min

Only HC 4.9

Fenton 64

HC + Fenton 97.77

Photofenton 81

HC + PhotoFenton 99.22

Photocatalytic degradation (with and without HC)

-0.4

-0.3

-0.2

-0.1

0

0 50 100 150ln

C/C

0Time in minutes

only UV

photocatalytic

Photocatalytic + HC

HC

Type of process k x 103 min-1 R2

HC 1.114 0.987

UV only 1.545 0.975

UV + Nb2O5 2.112 0.989

UV + Nb2O5 + HC 2.969 0.989

Precautions1.Use of sunlight offers a cheaper alternative but the dose of oxidant should be adjusted properly to account for lower oxidation rates as compared to the use of UV light2.Use appropriate dilution factors for treatment of highly loaded effluents3.Use of aeration is a must and air can be safely used instead of pure oxygen with similar rates of degradation4.Select appropriate combination of Fe ions and the counter-ion depending on the operating conditions such as pH, type and intensity of irradiation5.Use acidic conditions

Model Hybrid System

Effluent

Mixingvessel

Pump(open impeller slurry type)

1

Ultrasonicpredispersion

Air

Periodic U.S. treatment

Photosonic Reactor withconcentrating Reflectors.

Treated effluent may beSubjected to biologicaloxidation

catalyst desorption

catalyst recycle

Filtration

Solar

1: Annular UV tube for intermittent irradiation2: Ozone addition depending on contaminant load

Reflectors

HydrodynamicCavitation setupWith orifice plate

Addition of Fe (III) ions + H2O2

2

TiO2 addition+

Acid or alkali for pH adjustment

Bypass

1. Initial analysis of the effluent stream

2. Loading of ozone gas should be kept to minimum

3. Time of ultrasonic irradiation also needs to be optimized

4. Solar concentrators need to be critically designed so thatentire surface is uniformly irradiated

5. Loading of hydrogen peroxide and Fe2+ ions should beoptimized depending on the effluent stream

6. Distance between the hydrodynamic cavitation reactor andsonochemical reactor should be adjusted in such a way thatnuclei are available for acoustic cavitation

Optimum considerations

Optimization of the

Model Hybrid System

is the Key to the

Success of CETP

oxidation technologies at ambient conditions for...

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