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Photodegradation ofPhotodegradation of

WaterpollutantsWaterpollutants

presentedpresented byby

MatthMatthus Hamulskius Hamulski

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What is Photodegradation ?

Photodegradation and

Photokatalysis are usually

oxidations of organic compounds

in exoergic processes, in whichthe absorption of light energy is

the driveing reaction force.

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Direct photochemical degradation.Direct photochemical degradation.

In direct photochemical degradation the electrones ofan organic compound are excited. This can lead to

decomposition of the organic molecule into two

radicals, which are extremly reactive. More often the

excited point of the molecule is attacked by oxygene

molecules, which then oxidise the organic compound.

As the reactivity of ground state triplet oxigene withthe singlet ground state of the most compounds is very

low, the excitetion of oxigene to singlet is even more

important for the oxidation of organic compounds.

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Direct photochemical degradation.Direct photochemical degradation.

Degradation of phenol by singlet oxigene to maleinate

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Addvanced oxidation process:Addvanced oxidation process:

As the photodegradation of many

microorganisms and compounds is very

slow and lead to oxidation or

degradation of organic compounds, the

addvanced oxidation process bycombining UV illumination with ozone

or supply is much more effective

often leading to complettemineralisation.

This is achieved especially by the

photolytic reaction of .

22OH

22OH

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IndirectIndirect photochemicalphotochemical oxidationoxidation::In the indirect photochemical oxidation radicals are are

formed by photolysis, which then attack the organiccompounds. As an example the reaction of is drown:

22OH

OHOH h 222

As hydroxide radicals need an electon to obtain an octate,they are very electrophilic and thatfor attack electron rich

areas of any molecules.

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PhotocatalystsPhotocatalysts

A couple of semiconductive materials can be used as

photocatalites. Most popular is because of it`s chemicalstability and high efficiency.

has a band gap of 3.2 eV, equivalent to about 400nm.

By this reason can be excited by illumination in the

range of 300 to 400 nm.

Driving force for catalysis of photochemical reactions is theexcess of free energy in the electron-hole thus produced.

2TiO

2TiO

2TiO

+

+vbcb

h

heTiO

2

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PhotocatalystsPhotocatalystsBy this reaction centers act as electron holes while

partially go to the surface, where they can be taken up by othermolecules.

Exaples for possible reactions forming highly reactive radicals:

+3Tie

++++

OHHOHh 2

+ 22 OeO

2TiO

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SensitizerSensitizer DyesDyesSensitizer dyes are photoactive organic

compounds like for example methyleneblue, which are resistent to

photodegradation by releasing the

absorbed energy to neighboring

molecules and in this way activeting

them.

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ProcessingProcessing

Photokatalysts can be used as particles dispersed in thewater. In this way the surface of the catalyst is used most

efficiently but the dispersed particles disturb

illumination. Additionally the particles have to beremoved after the treatment.

Another method is a fixed bed covered with .

For the dye sensitization most popular are granulated

polymeres careing the dye.

2TiO

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ComperanceComperance withwith otherother oxidationoxidation

methodesmethodes

Ozonation:

Effective to many organic compounds, but ineffective to

halomethanes, triazine herbicides and other compounds.

Ozone combination with or UV illumination can

overcome this problem.

Biodegradation:

Most important purification method for purification ofmunicipal wastewater. However, xenobiotics as methyl vinyl

ketone, pentachlorophenol and 2,4-dichlorophenol can

inhibite the respiratory activity of activated sludge. In thiscase aclimation of microorganisms is necessary.

22

OH

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ComperanceComperance withwith otherother oxidationoxidation

methodesmethodes

Chlorinaton:

Chlorination is the major factor of prevention of water borne

diseases.

Chlorination may cause the formation of trihalomethane as

carcinogenic chloroforme.

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DirectDirect UVUV disinfectiondisinfection::Classicly photoreactions

has been used fordesinfection of drinking

water and it still being

the easiest and chaepest

way to disinfect water.

The illuniation with

sunlight for five houreskills most coliform

MOs.

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DirectDirect UVUV desinfectiondesinfection::

Direct desinfection by denaturisationof DNA and photolytic reactions on

the surface

Indirect desinfection by oxidation ofcellwalls or cell membranes and throu

this destruction of cellwall/ -

membrane properties or even cell

lysis. This effect is acheaved by

radical production.

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DirectDirect UVUV disinfectiondisinfection::

Such reactors are used inthe drinking water

disinfection in addition to

chlorination in the BlackMountain Irrigation

District.

UV reactor for disinfection

of drinking water disinfection

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EnhancedEnhanced UVUV disinfectiondisinfection::

At the Japan Gulch Water

Treatment Plant the

drinking water disinfection

is done by a chain of UV

reactors with supply.

Beside the disinfection by

the addvanced oxidation

process, chlorine

reconfiguration is achieved.

22OH

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OtherOther applicationapplication examplesexamples::Disinfection of water, rainwater,

drinking water in containers, tanks,

small wells, open systems

Protection of germ build up of

surfaces (e.g. on watersoluble

lacques)

Disinfection of tanks before filling

Underground water tank with animersion lamp and airation

Disinfections in air washers

for air conditioning systems(coolant recovery)

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PhotochemicalPhotochemical detoxinationdetoxination

degradation: is used in previous

metal processing, for example to recover

gold-mill tailing.

is usually oxidized by alkaline

chlorination or with but the

hexacyanoferat(II) and hexacyanoferat (III)from gold-mill tailing are resistent to the

treatment.

CN

22OH

CN

CN

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PhotochemicalPhotochemical detoxinationdetoxination

Also they undergo photodegradation by

relaesing and recombining after the end of

the illumination.

Degradation can be achieved by addition of

to alkaline solution (pH 10) and illumination by

sun for 1.5 h.

CN

2TiO

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PhotochemicalPhotochemical detoxinationdetoxinationCr(VI) is very stable, good water soluble, carcinogenic and

extremly toxic. Cr(III) is much less toxic and precipitating inneutral and alkaline solutions.

Chrome polutions origins e.g. from chrome plating, leather tanning

and metallurgical processes.

Photocatalitic reduction of chrome in alkaline solution by to

which strongly addsorbs to and thus is removed from

solution by removeing the catalist.

In presence of oxygene the reduction is inhibited because of

competiton with molecules for conduction-band electrons.

2TiO

3)(OHCr2

TiO

2O

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PhotochemicalPhotochemical detoxinationdetoxination

Main reaction:

+++ OHadsOHCreOHaqCrOh 5)()(34)( 32

2

4

- purging necessery because of production:2N 2O

OHOhOH 22 244 +++

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ConclusionsConclusions

TheThe addvancedaddvanced oxidationoxidation processprocess isis highlyhighly suitablesuitable

forfor desinfectiondesinfection forfor drinkingdrinking waterwater purposespurposes

AsAs groundwatergroundwater hashas usuallyusually lowlow loadload ofofpolutantspolutants thethe

addvancedaddvanced oxidationoxidation processprocess withwith oror withoutwithout

photocatalitesphotocatalites isis alsoalso suitablesuitable forfor detoxificationdetoxification ofofherbizideherbizide contaminatedcontaminated waterwater

AsAs seenseen onon cyanidescyanides andand chromechrome removalremoval somesome

photochemicalphotochemical methodesmethodes requirerequire specialspecial conditionsconditionsnotnot suitablesuitable forfor drinkingdrinking waterwater purposespurposes..

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ConclusionsConclusions

As photodegradation and photodetoxination are not

suitable for highly diferenciated waste water and highloads it can be used for partial waste water streamscontaining special contamination.

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ReferencesReferences

1. Martin M. Halmann Photodegradation of WaterPollutants

2. pyros-bremen.de

3. bmid.ca

4. crd.ca

5. sondis.ch

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Thank You for Your Attention !!!Thank You for Your Attention !!!