Removing pharmaceuticals and endocrine-disrupting compounds from wastewater by photocatalysis

Journal of Chemical Technology and Biotechnology J Chem Technol Biotechnol 82:121–134 (2007)

ReviewRemoving pharmaceuticals andendocrine-disrupting compounds fromwastewater by photocatalysisOmatoyo K Dalrymple,∗ Daniel H Yeh and Maya A TrotzDepartment of Civil and Environmental Engineering, University of South Florida, Tampa, Florida, USA

Abstract: Widespread concerns continue to be raised about the increasing presence of emerging contaminants inthe environment. Such compounds include a wide range of persistent organic chemicals, including pharmaceuticalsand endocrine-disrupting compounds whose effects are poorly known, often because they have only begun to enterthe environment and are showing up in wastewater treatment plants. The occurrence and behavior of thesecompounds in wastewater are key issues with regard to water reclamation and reuse. Treatment plants are nowfaced with the challenge of removing the compounds from their effluent before they enter natural waterways.In this regard, photocatalysis is a promising technology for wastewater treatment that offers many advantagesover conventional and some advanced treatment options. The application of photocatalysis for the removal ofpharmaceuticals and endocrine-disrupting compounds for wastewater is comprehensively surveyed in this paper.This treatment technology is not intended to replace conventional systems but to supplement for higher-qualityeffluent. The assessment places emphasis on the process fundamentals, advantages, and disadvantages of thetechnology. It also focuses on the current limitations and future research needs. 2007 Society of Chemical Industry

Keywords: hormones; pharmaceuticals; photodegradation; titanium dioxide; wastewater treatment

INTRODUCTIONMany synthetic and naturally occurring chemicals,which are not commonly monitored in the envi-ronment, but have the potential to cause known orsuspected adverse ecological and/or human healtheffects, are ending up in natural waters from the efflu-ent streams of wastewater treatment plants.1–4 Theseemerging contaminants are often present in trace con-centrations and include pharmaceuticals (both humanand veterinary medicine), natural and synthetic hor-mones, and many persistent organic wastewater con-taminants. They are the result of production, use, anddisposal of numerous chemicals which offer improve-ments in industry, agriculture, medical treatment, andeven common household conveniences.1–3 The effectsor presence of most of the compounds are poorlyknown, often because they have only begun to enterthe environment and/or analytical methods to detectthem have improved.5 Treatment plants are now facedwith the challenge of developing new techniques toremove these contaminants from effluent streams inanticipation of stricter regulations as new informationon their transport, fate, and effects is released.6

Two broad categories of emerging environmentalcontaminants are pharmaceuticals and endocrine-disrupting compounds (EDCs).2,4,7 After use of the

compounds, especially pharmaceuticals by humans,the constituents are excreted unchanged or as metabo-lites through urine and feces and are subsequentlyincorporated into the influent of wastewater treat-ment plants. They then pass through the treatmentplants into effluent streams practically unaffected andare discharged into surface waters.2,8 The same phar-maceuticals and hormones designed to stimulate aphysiological response in humans, plants, and animalspose significant threats to the aquatic environment dueto their inherent lipophilic nature, tendency to inter-act with living tissues, and continued extensive use.4,9

Pharmaceuticals and EDCs may also induce potentialchanges to the microbial ecology both at the treat-ment plant and in surface waters.2,10,11 Furthermore,some of the compounds (or the metabolites thereof)are not easily biodegradable, and therefore are notefficiently removed by conventional treatment meth-ods, leading to an unfavorable accumulation in theenvironment.8,12,13 In some cases, the traditional acti-vated sludge process is now assumed to generate EDCsin the form of free estrogens (such as alkylphenols andsteroid estrogens) which are the result of incompletedegradation of respective parent compounds.14

Many advanced treatment options are availableand heterogeneous photocatalysis is a promising

∗ Correspondence to: Omatoyo K Dalrymple, Department of Civil and Environmental Engineering, University of South Florida, 4202 E Fowler Ave., Tampa, FL33647, USAE-mail: [email protected](Received 26 July 2006; revised version received 8 September 2006; accepted 8 November 2006)Published online 12 January 2007; DOI: 10.1002/jctb.1657

2007 Society of Chemical Industry. J Chem Technol Biotechnol 0268–2575/2007/$30.00

OK Dalrymple, Daniel H Yeh, MA Trotz

technology. The main objective of this review isto critically assess the available information onthe application of photocatalysis for the removalof pharmaceuticals and EDCs from wastewater.The technique has been shown to be effective atdegrading the compounds and eliminating endocrine-disrupting capabilities. The current limitations andfuture research needs associated with the treatmenttechnology are also discussed with regard to thecontaminants of interest.

PHARMACEUTICALS AND EDCS INWASTEWATERPharmaceutical compounds occurring in wastewaterand the environment include human and veterinaryantibiotics (e.g., sulfamethoxazole, erythromycin, androxithromycin); prescription analgesic drugs such ascodeine and anti-epileptic drugs inclusive of car-bamazepine; and non-prescription drugs such asacetaminophen and ibuprofen.1,2,15,16 Environmen-tal effects include the development of antibiotic-resistant microbes in water treatment processes andin the aquatic environment;2,17 retardation of nitriteoxidation10 and methanogenesis;10,11 and the poten-tial increased toxicity of chemical combinations andmetabolites.18 The potential effects on people andaquatic ecosystems, however, are not clearly under-stood.

EDCs are a special group of chemicals that canupset normal endocrine functions directly or indirectlythrough interaction with receptor-mediated processessuch as steroid hormone receptors, even at a lowconcentration (µg L−1 and ng L−1 range), due to theirsteroid-like structures.19,20 Thus, they tend to mimicendogenous hormones and/or inhibit normal hormoneactivities and metabolism.21 The effects, however,are not confined to steroidal systems; they can alsoinfluence thyroid hormone secretion patterns, withassociated physiological consequences.19,20 Abnormalsexual development in animals21,22 and a decrease inthe average numbers of human spermatozoa20,23 havebeen reported.

Important EDCs include bisphenol A (investigatedin the 1930s as a synthetic estrogen24), which leachesfrom food cans, polycarbonate water jugs, and den-tal composites; dioxin, which is a near-ubiquitousbyproduct of combustion from incinerators, paperbleaching and foundries; nonylphenols, which areadded to polyvinylchloride (PVC) plastic and arealso a byproduct of industrial detergents and pesti-cide decomposition; polychlorinated biphenyls (PCB)associated with adhesives and electrical transform-ers; and vinclozolin, a common fungicide.25 EDCsalso include natural and synthetic hormones such ashuman and animal steroids (estradiol, estrone, andestriol) and contraceptives (e.g., ethynylestradiol).

It is becoming increasingly important to assesswastewater treatment processes with regard to theirpotential to remove micro-pollutants. Apart from their

impact on the aquatic environment, the occurrenceand behavior of these compounds in wastewater arealso key issues when it comes to water reclamationand reuse.26 A number of advanced treatment optionsare available and these include membrane filtra-tion technologies,27,28 advanced oxidation processes(AOPs),13 ultraviolet (UV) irradiation, and hybridsystems.29 Hydrophobic adsorption and size exclusionplay important roles in the removal of pharmaceuticalsand EDCs with membrane filtration. Nanofiltrationmembranes retained many EDCs and pharmaceuti-cals due to both hydrophobic adsorption and sizeexclusion, while the ultrafiltration membranes retainedtypically hydrophobic EDCs and pharmaceuticals duemainly to hydrophobic adsorption.27 The release ofpollutants retained by the membrane, however, doesnot eliminate the risk to the environment.27,28,30

Among the advanced oxidation treatment options,heterogeneous photocatalysis in the presence ofsemiconductor metal oxides is a fast-growing fieldof basic and applied research and a promising toolfor water treatment. Effective degradation of majorpharmaceuticals and EDCs has been observed withoutformation of harmful intermediates in some cases.31–38

Other advantages include low chemical input, energyefficiency, and the capacity to use renewable andpollution-free solar energy.39

PHOTOCATALYSISPhotocatalysis is the acceleration of a photochemicaltransformation by the action of a catalyst; the catalystmay accelerate the photoreaction by interaction witha substrate in its ground or excited state and/orwith a primary photoproduct, depending on themechanism of the photoreaction.40 By definition,the catalyst participates and accelerates the chemicaltransformation of the substrate, itself remainingunaltered at the end of each catalytic cycle. Mostphotocatalysts are semiconductor metal oxides whichcharacteristically possess a band gap. The bandgap is a void region that extends from the topof the electron-filled valence band to the vacantconduction band. In photocatalysis, absorption ofphoton energy (hv) produces electron excitation inthe catalyst and electrons gain sufficient energy tochange levels from the valence to the conductionband. Conversely, an electron vacancy or hole (h+)is created in the valence band. The electron–hole pairmigrates to the photocatalyst’s surface where it eitherrecombines or participates in redox reactions withcompounds adsorbed on the photocatalyst (Fig. 1).Furthermore, the interaction of the hole with waterand/or hydrogen peroxide (H2O2) produces hydroxylradicals (OH·) which act as powerful oxidants andprovide an additional pathway for the oxidationof compounds.41,42 The chemical and adsorptionproperties of the substrate and the chemical reactionconditions largely determine which mechanism willdominate.

122 J Chem Technol Biotechnol 82:121–134 (2007)DOI: 10.1002/jctb

Removing pharmaceuticals from wastewater by photocatalysis

UV (λ < 400 nm)

adsorption

reduction (ox + ne- → red)

oxidation (red → ox + ne-)

adsorption

valenceband

conductionband

e-

e-

e-

h+

Energy (eV)

Redox Potential (V)

Eg

Ef

+3.1

+2.0

+1.0

-0.1

When illuminated with photons energy higher than the band gap, electrons and holes areformed in the semiconductor and are capable of initiating chemical reactions

Figure 1. Scheme of photocatalytic process over TiO2 surface.

Other reactive oxygen species are formed andinclude the superoxide radical (O−

2 ·), resulting fromreactions with oxygen (O2). Superoxide and hydrogenperoxide contribute to the oxidation of organic andinorganic electron donors by acting as direct electronacceptors, or in the case of H2O2 as a direct source ofhydroxyl radicals due to homolytic scission.43 A simplekinetic model for the photo-induced redox process canbe presented as follows:44,45

TiO2 + hvg→e− + h+

e− + Ake→ A− → Reduction products

h+ + Dkh→ D+ → Oxidation products

e− + h + krec→ TiO2 → Recombination

A− + D + k′rec→ A + D

where e− and h+ are conduction band electronsand valence band holes, respectively. A and Drepresent molecules which are reduced and oxidized,respectively. The intermediate species, A− and D+,precede the reaction toward reduction and oxidationproducts. The photo-induced electron and holerecombine with each other and diminish in the solid.

Photocatalysts include titanium dioxide (TiO2),zinc oxide (ZnO), zinc sulfide (ZnS), ferric oxide(Fe2O3), silicon (Si), tin oxide (SnO2), and cadmiumsulfide (CdS), among others. Over the past twodecades, however, TiO2 has been the most widelyused photocatalyst in the literature and most emergingcatalysts are measured against it as a benchmark.46

There are three forms of TiO2: anatase, rutile, and

brookite. Of these three, anatase is often used as thephotocatalyst of choice and is commonly mixed withrutile (which is a much less catalytically active formof TiO2) to help reduce the rate of recombinationof electron–hole pair.47,48 The band gap energy ofanatase is 3.2 electron volts (eV) and hence absorbsphotons within the near-UV range (∼380 nm) of theelectromagnetic spectrum.

There is a wide range of photoreactivity withinspecimens of mixtures containing variable contents ofanatase and rutile. Degussa P25 TiO2, however, hasset the standard for photoreactivity in environmentalapplications. It is a non-porous 70% to 30% anataseto rutile mixture.44,48 P25 is available as highsurface area (50 ± 15 m2 g−1) nanoparticles with anaverage individual particle size of 20–30 nm, eventhough particle agglomeration in solution can reach300–500 nm.48,49 The small size of the nanoparticlescan provide high efficiency of surface trapping ofphoton-generated electrons and holes, thus increasingthe probability of a photocatalytic process on thesurface of the catalyst.

Heterogeneous photocatalysis has been applied tomore than 90 organic and 25 inorganic compoundscatalogued on the US Environmental ProtectionAgency’s (USEPA) priority list of contaminants.50

These include benzene, trichloroethane, acetone,aniline, MTBE, and atrazine, among others. Inaddition to the USEPA priority list, Blake50 andBhatkhande et al.44 provide exhaustive lists of otherorganic compounds degraded by photocatalysis. Theprocess has also been successfully applied for theremoval of organic and inorganic compounds presentat low concentrations in aqueous solutions.48,51–53

J Chem Technol Biotechnol 82:121–134 (2007) 123DOI: 10.1002/jctb


PHARMACEUTICALS AND EDCS STUDIEDSnyder54 narrowed emerging contaminants to a list ofroughly 30 compounds. These include chemicals thatthe researchers expect have the highest toxicity levelsor that are most likely to occur in drinking water.The list of pharmaceuticals and EDCs being studiedfor removal by photocatalysis continues to increase.Focus has been given to the most prescribed drugsand other compounds most likely to be present indrinking water and wastewater in an active form andespecially those that carry potential health risk at lowconcentrations.32,33,35,55–61 Tables 1 and 2 summarizethe most common pharmaceuticals and EDCs foundin wastewater which have been investigated andgives information on the photocatalyst used andintermediates detected. Comments are also providedin some instances to give additional insights along withthe relevant references. The chemical structures of thecompounds are illustrated in Figs 2 and 3.

The tables indicate successful removal of thecompounds with TiO2. In some cases, however,other catalysts have proven more efficient underthe specific conditions reported in the literature.In the cases of tetracycline and ranitidine, Merckappeared more active than P25 for the degradationof the pharmaceutical compounds, while destructionof sulfamethazine was further advanced with ZnOafter 60 min of irradiation compared to 60% with P25.These observations highlight the difficulty in removingmost of the compounds with only one catalyst andsuggest the need for possible combination of catalyststo target a wide range of compounds.

REACTION KINETICSThe rate and efficiency of the photocatalytic reactiondepend on a number of factors. One such importantfactor is adsorption of the substrate onto the surfaceof the catalyst. In these reactions, the contaminantsubstrate is oxidized by the photo-generated holesor by reactive oxygen species such as the OH• andO−

2 · radicals formed on the surface of the catalyst.This mechanism requires that the contaminantadsorbs on the catalyst surface as a prerequisitefor efficient oxidation. The adsorption–desorptionprocess is characterized by the transfer of thereactants in the aqueous phase to the surface;adsorption of the reactants; reaction in the adsorbedphase; desorption of the products; and removalof the products from the interface region.62 Mostresearchers observe a Langmuir adsorption isothermand describe the adsorption–desorption process andthe reaction rate constant based on the associatedLangmuir–Hinshelwood (L-H) model, which isrepresented as follows:

r = kθ = −dCdt

= k(

KC1 + KC

)

where r is the rate of mineralization, k is the reactionrate constant, C is the concentration, K is the

adsorption coefficient and θ is the fractional sitecoverage for the reactant.42

In general, adsorption studies are done in the darkand sometimes the adsorption capacity cannot betransferred quantitatively into irradiated systems.63–65

Researchers note that increased adsorption to thecatalyst surface translates to increased reactionrates.35,65–67 Doll et al.35 however, found that withlittle difference in adsorption of carbamazepine on thesurface of P25 and Hombikat UV100, the reactionrate was much higher with P25 as the catalyst. Theysuggest that photo-adsorption of the drug on P25 wasprobably much better. Turchi and Ollis68 propose amodel in which the rate parameter is independentof the organic reactant and the kinetic parametersfor the photocatalytic degradation may be estimatedfrom data on the photocatalyst’s physical properties,the knowledge of electron–hole recombination andtrapping rates, and the values of second-order reactionrate constants for hydroxyl radicals.

Although the L-H model seems to adequatelydescribe the macroscopic kinetics when dealing withvery dilute aqueous solutions of photodegradablecontaminants, some of the inherent assumptions ofthe model may not be valid at the microscopiclevel, which includes its failure to account forsimultaneous adsorption (or desorption) of parent andintermediate compounds.63 Clearly, many differenttypes of microscopic mechanisms could lead to theoverall L-H type kinetic expression, but the derivedkinetic parameters represent fundamentally differentreactions and properties.68,69

Since most pharmaceuticals and EDCs are presentin trace concentrations, generally below 1 µmol L−1

(KC � 1), the L-H equation simplifies to a pseudo-first-order kinetic equation as follows:

r = −dCdt

= krC or C(t) = Coe−krt

where kr is the pseudo-first-order photocatalyticreaction rate constant. This pseudo-first-order rateconstant is often determined by observing the relativeaqueous concentration changes of the contaminantas a function of time during experiments. Tables 1and 2 indicate some values of kr (min−1) for selectedcompounds from the literature. The reaction rates ofpharmaceuticals with hydroxyl radicals, during bench-scale experiments for AOPs applied in drinking watertreatment, were found to be two to three times fasterwhen compared with other important micro-pollutantssuch as methyl tert-butyl ether (MTBE) and atrazine.70

EFFECT OF LIGHT INTENSITY ON REACTIONRATEThe oxidation of organics is directly proportional tothe concentration of positively charged holes formedby absorption of UV radiation.45 The concentration ofphoto-generated holes is determined by recombinationand reaction with organic compounds. Therefore, the



Tab

le1.

Sel

ecte

dlis

tof

com

mon

was

tew

ater

pha

rmac

eutic

als

stud

ied

und

erp

hoto

cata

lysi

s

Com

poun

dFo

rmul

aC

atal

ystu

sed

Inte

rmed

iate

san

dde

grad

atio

nco

mpo

unds

Firs

t-or

der

rate

cons

tant

(min

−1)

Com

men

tsR

efer

ence

s

Linc

omyc

inC

18H

34N

2O

6S

P25

TiO

2N

otan

alyz

ed0.

022

31S

ulfa

met

hazi

neC

12H

14O

2N

4S

P25

TiO

2H

ydro

xyla

min

e0.

056

Afte

r60

min

ofirr

adia

tion,

dest

ruct

ion

88Zn

Ow

as>

90%

with

ZnO

;>60

%w

ithTi

O2

P25

;and

>35

%w

ithan

atas

eA

nata

seTi

O2

Car

bam

azep

ine

C15

H12

N2O

P25

TiO

210

,11-

Dih

ydro

carb

amaz

epin

e-10

,11-

epox

ide,

hydr

ocar

bam

azep

ine,

dihy

droc

arba

maz

epin

e,ac

ridin

e,ac

ridin

e-9-

carb

oxal

dehy

de,

hydr

oxya

crid

ine-

9-ca

rbox

alde

hyde

and

hydr

oxya

crid

ine-

9-ca

rbox

yalc

ohol

0.28

2O

fthe

inte

rmed

iate

sid

entifi

ed,a

crid

ine

iskn

own

asa

wat

erpo

lluta

ntw

ithm

utag

enic

and

carc

inog

enic

activ

ity

35,1

06

Clo

fibric

acid

C10

H11

ClO

3P

25Ti

O2

4-ch

loro

-cat

echo

l1.

038

35,1

06Io

mep

rol

C17

H22

I 3N

3O

8P

25Ti

O2

Not

iden

tified

0.31

535

Dic

lofe

nac

C14

H11

Cl 2

NO

2P

25Ti

O2

Not

anal

yzed

0.02

2A

lso

stud

ied

sola

rph

oto-

Fent

on,w

hich

occu

rred

ata

fast

erre

actio

nra

te61

,84,

106

Tetr

acyc

line

C22

H24

N2O

8M

erck

TiO

2an

dP

25N

otan

alyz

edC

ompl

ete

min

eral

izat

ion

obse

rved

56,5

7R

aniti

dine

C13

H22

N4O

3S

Mer

ckTi

O2

and

P25

Not

anal

yzed

Mer

ckw

asm

ore

activ

eth

anP

25fo

rth

ede

grad

atio

nof

tetr

acyc

line

and

rani

tidin

e

56

Nap

roxe

nC

14H

14O

3P

25Ti

O2

Not

anal

yzed

0.09

961

Ibup

rofe

nC

13H

18O

2P

25Ti

O2

sec-

But

ylac

etop

heno

nean

dse

c-bu

tylp

hene

thyl

alco

hol

0.04

9561



Tab

le2.

Sel

ecte

dlis

tof

com

mon

was

tew

ater

ED

Cs

stud

ied

und

erp

hoto

cata

lysi

s

Com

poun

dFo

rmul

aC

atal

ystu

sed

Inte

rmed

iate

san

dde

grad

atio

nco

mpo

unds

Firs

t-or

der

rate

cons

tant

(min

−1)

Com

men

tsR

efer

ence

s

Est

rone

C18

H22

O2

TiO

2im

mob

ilized

onTi

-4V

-6A

lallo

yN

otan

alyz

ed0.

086

Est

roge

nic

activ

ityof

17β

-est

radi

ol,

estr

one

and

17α

-eth

inye

stra

diol

was

elim

inat

edat

the

sam

era

tedu

ring

phot

ocat

alys

is

34

17β

-Est

radi

olC

18H

24O

2P

25Ti

O2

10e

–17

β-d

ihyd

roxy

-1,4

-est

radi

en-3

-on

ean

dte

stos

tero

ne

0.10

6D

egra

datio

nof

this

com

poun

dcl

oses

mat

ches

mos

tphe

nolc

ompo

unds

32,3

3,38

,67

17α

-Eth

inyl

estr

adio

lC

20H

24O

2P

25Ti

O2

Not

anal

yzed

0.23

132

,34

Est

riol

C18

H24

O3

P25

TiO

2N

otan

alyz

ed0.

156

32B

isph

enol

AC

15H

16O

2Ti

O2

anat

ase

pow

der

Com

plet

eox

idat

ion

toC

O2

and

inte

rmed

iate

san

alyz

ed11

.2×

10−6

fragm

ents

did

note

xhib

itS

/Nle

vels

high

enou

ghto

iden

tify

the

inte

rmed

iate

com

pone

nts

prec

isel

y

37,1

00

Res

orci

nol

C6H

6O

2P

25Ti

O2

Not

anal

yzed

0.30

011

42,

4-D

ichl

orop

heno

lC

6H

4C

l 2O

P25

TiO

2N

otan

alyz

ed0.

250

114

Non

ylph

enol

C15

H24

OP

25Ti

O2

Inte

rmed

iate

sco

uld

notb

ede

tect

edby

anal

ysis

0.06

211

5

Eth

oxyl

ate

met

abol

ites

C17

H28

O2

0.04

4(n

onyl

phen

ol,n

onyl

phen

olC

17H

26O

30.

016

mon

oeth

oxyl

ate,

and

nony

lphe

noxy

acet

icac

id)

Est

roge

nco

njug

ates

C24

H30

O8

TiO

2N

otan

alyz

ed0.

0036

Est

roge

nco

njug

ates

dono

thav

e11

6(e

stra

diol

-3-g

lucu

roni

de,

C24

H32

O8

0.01

50es

trog

enic

activ

ities

,but

serv

eas

-17-

gluc

uron

ide,

C24

H30

O8

0.00

34ho

rmon

epr

ecur

sors

byes

tron

e-gl

ucur

onid

ean

dsu

lfate

)C

18H

22O

5S

Not

repo

rted

deco

njug

atio

ndu

ring

was

tew

ater

trea

tmen

twith

activ

ated

slud

geA

traz

ine

and

s-tr

iazi

nehe

rbic

ides

C8H

14C

lN5

(atr

azin

e)P

25Ti

O2

Cya

nuric

acid

,am

mel

ine,

2,4-

diam

ino-

6-ch

loro

-1,3

,5-t

riazi

ne,

amm

elid

e,2,

4-di

amin

o-6-

chlo

ro-N

-(1

-met

hyle

thyl

)-1,

3,5-

tria

zine

Not

repo

rted

Cya

nuric

acid

reco

gniz

edas

the

final

degr

adat

ion

prod

ucto

fall

the

herb

icid

esan

dis

oflo

wto

xici

ty

105



Figure 2. Structures of selected pharmaceuticals.

reaction rate of h+ can be expressed in the followingmanner:

d[h+]dt

= −kh[h+] − krec[e−][h+] + g

where [h+] is the density (cm−3) of valence bandholes in the semiconductor particle; g representsthe generation rate of photo-induced e− − h+ pairs(cm−3 s−1), which can be calculated from the fluxof the incident light (I), absorption coefficient of thesystem, and the density of the semiconductor material;

kh is the rate of hole transfer (s−1); and krec (s−1) is therecombination rate. The decay rate is also affected bythe organic molecules adsorbed on the surface of thecatalyst.

Since light intensity determines the rate of gener-ation of the photo-induced electron and holes in thecatalyst, Egerton and King71 were able to show that thereaction rate should be directly proportional to inten-sity at low fluxes and proportional to the square root ofintensity at relatively high flux levels. When the deple-tion of the surface reactant is included, the dependenceof reaction rate on light intensity undergoes transition



Figure 3. Structures of selected EDCs.

from linearity to a non-linear dependence (I1/2) asintensity increases.71–73 Okamoto et al.72 showed thatthe reaction rate for the degradation of phenol onTiO2 was directly proportional to intensity up toabout 1 × 10−5 mol m−2 s−1 and proportional to thesquare root of intensity above 2 × 10−5 mol m−2 s−1.This conclusion is also supported by Parsons et al.74

A similar observation is made for the degradation of

17β-estradiol, which was found to be proportional tothe square root of light intensity.32 It appears thatat high light intensity the recombination of the elec-tron–hole pair is enhanced while at low fluxes organicoxidation can compete with recombination.45,71,73

Further, the rate becomes independent of light inten-sity at higher fluxes and the expected rate-limitingfactor becomes the mass transfer.32



SOLAR VERSUS UV LAMPSThe preference to use solar or UV lamps as theirradiation source depends largely on illuminationintensity and the cost of the light-producing or light-collecting equipment. UV lamps are conventionallyused for photocatalysis, but more efficient, longer-life and safe UV light-emitting diodes (LEDs) areprospective replacements. The costs still remain achallenge, however, and much focus has been givento sunlight as the initiator of the photochemicalreaction. Solar photochemical systems are based onthe collection of only high-energy short-wavelengthUV or near-UV sunlight (300–400 nm) to promotephotochemical reactions especially with TiO2 asthe catalyst.75,76 Given the linear dependence ofthe reaction rate on low intensity, there is aninherent kinetic advantage in using low or non-concentrating solar reactors.73,77 A useful overviewof solar photocatalysis and solar collectors is providedby Malato et al.75

Solar systems have been used with much success forthe degradation of both common water pollutants77–83

and pharmaceuticals and EDCs with reaction ratescomparable to UV lamp systems.31,84,85 Solar photo-catalytic treatment with TiO2 as a catalyst, however,poses some challenges. Solar photocatalysis uses onlythe UV portion of sunlight and as much as 50% ormore of this may be present in diffused form. Aswould be expected, local variability in cloud coverand other factors may change actual levels. The useof compound parabolic collectors (CPC: static col-lectors with a reflection surface following an involutearound a cylindrical reactor tube) solves this difficultysince most of the UV radiation arriving at the CPCaperture area (not only direct, but also diffused) canbe collected and is available for the process in thereactor.75,86 Even under the limitations of solar appli-cations, by far the greatest advantage is the cleanness,cheapness, and abundance of the energy source.

PHOTOCATALYST CONCENTRATIONThe addition of catalyst has proven to increase thedegradation rate within a range of concentrations.The dosage of the catalyst reaches an optimum value,however, after which there is no marked increasein the reaction efficiency. The solution becomessaturated and only a portion of the particles receiveirradiation. Although more area is available, theadditional catalyst does not participate in the reactionand the reaction rate does not increase with growingcatalyst load beyond the optimum level.87 Kaniouet al.88 investigated the influence of TiO2 dosageon the degradation of sulfamethazine and found atwofold increase in the photonic efficiency of thereaction when the catalyst concentration was raisedfrom 0.1 to 4 g L−1. This behavior is consistentwith observations made by other researchers.35,48,61,89

The optimum catalyst concentration depends on thegeneral characteristics of the material being adsorbed.

Based on the literature, 0.2–1 g L−1 of catalyst appearsas an adequate range for the degradation of mostpharmaceuticals and EDCs.

With slurry-type systems, however, one of the chal-lenges of creating an economically viable technologylies in the solid–liquid separation after treatmentsince the photocatalytic particles tend to be finepowders, especially in the case of TiO2. Expensivepost-treatment separation methods are often neededto recover the catalyst. As a result, researchers havestudied ways to increase the size of the catalyst par-ticle so that they are easier to filter or better to packinto a fixed column, and have investigated methodsto change the magnetic properties of the catalyst par-ticle so that they can easily be recovered.90,91 Manyresearchers have attempted to immobilize TiO2 onsolid surfaces such as silica, glass and carbon fibers,woven fiber cloth, and ceramic materials, or aroundthe casing of the light source.92,93 Various methodssuch as simple impregnation, the sol–gel method, andsurface grafting have been used to combine the cata-lyst with mesoporous silicas to develop new catalyticfunctions for the materials.94–96

Nevertheless, it does not seem to be easy to replicateand exceed the photocatalytic performance of slurry-type systems which use pure and well-crystallizedhigh-surface TiO2 particles such as the commerciallyavailable P25. Apart from low crystallinity of the TiO2

particles on such supports, the main limitation is theTiO2 loading level (approx. 10% by weight). A numberof researchers have demonstrated rapid temporalremoval of the biological activity in aqueous solutionsof pharmaceuticals and EDCs by photocatalysis overan immobilized TiO2 catalyst with 1.5 mg cm−2

loading33,34 and enhanced photocatalytic activity fordecomposition of 4-nonylphenol with well-crystallizedP25 TiO2 particles (60 wt%) deposited directly intosurfactant-templated mesoporous silica particles.97

EFFECTS OF PHThe pH of the reaction can have significant impacton the adsorption of the substrate to the catalyst byaffecting the surface charge and state of ionization ofthe compound. Coleman et al.33 and Malygina et al.67

studied the effects of pH on 17β-estradiol and noteda general increase in the rate of photocatalysis withincreasing pH up to 7, at which point there was asharp drop to pH 10 followed by a rise to pH 12. 17-β-Estradiol is phenol based and the pH effect matchesclosely that of other phenols under photocatalytictreatment.98 There is, however, a difference in theoxidation mechanism of the steroid and other phenolsbecause its adsorption at high pH is more likely to bea result of its alcoholic group and not the phenolicmoiety. Phenolic compounds exhibit poor adsorptionby TiO2 at high pH.67

The pH also affects the nature of the metal oxidecatalyst surface in terms of its surface charge. Surfacegroups of a metal oxide are known to be amphoteric.



‘Titanol’ (represented as >TiOH) represents theprimary hydrated surface functionality of TiO2. It is aneutral surface species predominant over a broad rangeof pH. Below pH 6, however, the TiO2 accumulatesa net positive charge due to the increasing fractionof total surface sites present as >TiOH+. At highpH, TiO2 is deprotonated and the surface has anet negative charge due to a significant fraction oftotal surface sites present as >TiO−.43,99 The rate ofthe photocatalytic process is therefore affected by theabsorption of different solutes to the surface of thecatalyst. At low pH, negatively charged ions such asCl− and HCO−

3 are attracted to the positively chargedsurface of TiO2 and may reduce the efficiency of thereaction. However, at high pH these anions have littleor no effect because of the negatively charged surface.Consequently, repulsion of OH− may also reduce thegeneration of hydroxyl radicals.33

With the effects on surface charge of the catalyst andspeciation of the substrate, it follows that changingpH will result in changing reaction mechanisms andmolecular interactions as intermediates are formed.The degradation of bisphenol A shows a strongdependence on pH with different oxidation productsformed at pH 3 and 10.100 Further, the degradationintermediates formed at pH 10 were found to be verystable to further photocatalytic oxidation, while thoseintermediates formed at pH 3 were more susceptibleto degradation. In each case, the toxicity of theintermediates was found to be less than that ofbisphenol A as the parent molecule.37,100

REMOVAL OF TOXICITY AND ESTROGENICACTIVITYThe ultimate goal of any treatment techniqueemployed for pharmaceuticals and EDCs is to removetoxicity and endocrine-disrupting capabilities. It isdesirable that intermediates and/or final productsbe less toxic and estrogenic in nature than theparent compound in order to reduce the risk tothe environment and humans. There are methods forevaluating toxicity of pharmaceuticals in wastewater101

and determining the estrogenic activity of EDCs.102,103

In the latter, yeast cells are transformed with plasmidsencoding the human estrogen receptor (hER) and anestrogen-responsive promoter linked to a reporter geneis used to assess estrogenic activity. The estrogenicactivity of the hormonal compounds is evaluated basedon its interaction with the hER.

Photocatalytic treatment with TiO2 has been shownto remove estrogenic activity of 17β-estradiol,34,38

17α-ethinylestradiol, and estrone.34 Ohko et al.37

found that the estrogenic activity of bisphenol A wasreduced to less than 10% of the initial activity after 6 hof treatment with UV illumination with TiO2. Theyalso determined that no increase in estrogenic activityoccurred during the course of the photocatalytictreatment. The phenol moiety of natural and syntheticestrogens appears to play the most important role

in determining estrogenic activity as it interacts withthe hER.102 Since the majority of known syntheticestrogens are phenolic chemicals and benzene rings arerapidly photodegraded by preferential hydroxyl radicalattack,37,104 it stands to reason that estrogenic activitymay be lost almost completely if the photocatalyticdegradation of the compounds commences with thephenol moiety as demonstrated by Ohko et al.38 Inthe case of atrazine and other s-triazine herbicides,the end product of all photodegradation was cyanuricacid, which is of low toxicity.105

There are very limited studies on the post-treatmenttoxicity of most pharmaceuticals in photocatalyticexperiments. The few studies aimed at assessing phar-maceutical toxicity indicate poor overall reduction106

and increased toxicity in some cases from intermediatecompounds.35,88 Merely 9% reduction in toxicity wasachieved for the photocatalytic oxidation of a mixtureof pharmaceuticals which included carbamazepine,diclofenac, clofibric acid, ofloxacin, sulfamethoxazoleand propranolol.106 The researchers used the methoddefined by Ferrari et al.101 for evaluation of toxicity.

It is difficult to assess whether the successful degra-dation of some compounds reported in other sectionsof the literature was also successful at removing tox-icity because of the unidentified and/or undetectedintermediate products. In the case of sulfonamides(e.g., sulfamethazine and sulfamethoxazole), how-ever, the formation of hydroxylamine could be oftoxicological concern as it is associated with hyper-sensitivity reactions to this class of antibiotics.15 Inaddition, acridine, a well-known air and water pol-lutant with mutagenic and carcinogenic activity,107 isanother example of a toxic byproduct resulting fromthe photodegradation of carbamazepine.35,108 Chloro-catechols (certainly 4-chlorocatechol) were identifiedas intermediate compounds from the photodegrada-tion of clofibric acid.35 Chlorocatechols are toxic tobacteria and higher organisms but the mode of actionis not yet clearly understood. Acute toxicity, however,increases with the increasing degree of chlorination.109

LARGE-SCALE APPLICATIONMost of the work on photocatalysis so far hasbeen limited to laboratory-scale experiments and afew pilot-scale plants with individual compounds.Pilot studies include work by Doll and Frimmel110

which investigated the combination of semiconductorphotocatalysis with cross-flow microfiltration. Thesystem allowed the separation and reuse of TiO2

after the photocatalytic degradation of clofibric acid,carbamazepine, and iomeprol. The majority of otherpilot studies have been restricted to experimentswith solar-type pilot plant apparatus, specificallythose conducted at the Plataforma Solar de Almerıa(PSA) located in Europe. Malato et al.75 describedthe experimental systems necessary for performingpilot-plant-scale solar photocatalytic experiments andoutlined the basic components of these pilot plants



and the fundamental parameters related to solarphotocatalysis reactions. The pilot plant has been usedsuccessfully to treat pharmaceuticals and EDCs alongwith other organic contaminants in wastewater.82,84,111

Large-scale applications are few but are evolving,and particular interest is being given to the develop-ment of a simple, efficient, and commercially compet-itive water treatment technology, based on compoundparabolic solar collectors and TiO2 photocatalysis.76

The efficiency achieved at laboratory scale and pilotscale, however, has not been achieved in larger sys-tems. The performance of large-scale plants is par-ticularly affected by the complexity of the incomingwastewater to be detoxified. Therefore, it is importantto take into account the effect of other compounds notoften accounted for in small-scale studies. In large-scale systems the competition to adsorb to active siteson the catalyst surface will increase such that com-pounds with higher adsorption affinity may have theadvantage of being degraded much faster and morecompletely.

When treating compounds present in low concen-tration, it may be necessary to have pretreatmentprocesses prior to employing photocatalysis and/orcombining the process with strong absorbents such asactivated carbon. Also, coupling photocatalysis withmembrane separation for wastewater is a viable optionfor some applications.31,112 In this case, the tech-nique essentially becomes an ‘end-of-pipe’ treatmentoption to remove residual compounds which oftenpass through the treatment plant. Conversely, as apretreatment option, the photocatalytic oxidation ofpharmaceuticals and EDCs can be coupled with bio-logical systems to reduce toxicity to biomass and toenhance biodegradability of some compounds.

Investigations with complex mixtures whichincluded natural organic matter (NOM) among phar-maceuticals of interest showed that the efficiencyof the process is not particularly affected for somecompounds.35 Doll and Frimmel,59 however, showedthat the presence of carbamazepine and NOMretarded the photodegradation of clofibric acid. Thepresence of cations and anions also reduce the absorp-tion capacity of substrate compounds when the surfacecharge on the catalyst is favorable.43,67

ANALYSIS AND IDENTIFICATION OFDEGRADATION PRODUCTSPotential post-treatment increase in toxicity andestrogenic activity of pharmaceuticals and EDCsdemand that the degradation products be detectedand identified in order to evaluate their formationkinetics, stability, and toxicity. For EDCs in particular,characterization of both biologically active and inactivespecies and accounting for the conjugated anddeconjugated forms of the compounds are importantto the overall assessment.113 With the developmentof sophisticated and modern analytical instrumentsand techniques, however, the limits of detection for

trace compounds can be reduced. It is difficult toassess the true success of the photocatalytic processin the absence of identified intermediate compoundsand end products. In this regard, hyphenatedtechniques offer much promise by increasing detectionsensitivity and compound specificity. Some of the mostcommon combinations used for improved analyticalspecificity are gas chromatography coupled withmass spectrometry (GC-MS), liquid chromatographycoupled with mass spectrometry (LC-MS) and, insome cases, LC with two stages of mass spectrometry(LC-MS-MS).1,35,59,84 The high sensitivity of theseinstruments combined with the high selectivity allowsdetection and quantification at very low levels.

CONCLUSIONSThe available literature on photocatalytic degradationof pharmaceuticals and EDCs demonstrates thatphotocatalysis is a promising technology to reduce theeffects of these compounds even though they may bepresent at low concentrations. The possibility of usingsolar energy also increases the economic viability ofthe process. Much more research is needed, however,to identify degradation compounds and evaluatetheir post-treatment toxicity and estrogenic potency.While many studies report successful photocatalyticdegradation, toxicity assays will determine the finalefficiency of the treatment process for this class ofpollutants.

REFERENCES1 Kolpin DW, Furlong ET, Meyer MT, Thurman EM, Zaugg

SD, Barber LB, et al, Pharmaceuticals, hormones, andother organic wastewater contaminants in US streams,1999–2000: a national reconnaissance. Environ Sci Technol36:1202–1211 (2002).

2 Kummerer K, Drugs in the environment: emission of drugs,diagnostic aids and disinfectants into wastewater byhospitals in relation to other sources: a review. Chemosphere45:957–969 (2001).

3 Daughton CG, Non-regulated water contaminants: emergingresearch. Environ Impact Assess Rev 24:711–732 (2004).

4 Halling-Sorensen B, Nors Nielsen S, Lanzky PF, Ingerslev F,Holten Lutzhoft HC and Jorgensen SE, Occurrence, fateand effects of pharmaceutical substances in the environment:a review. Chemosphere 36:357–393 (1998).

5 Kavlock RJ, Daston GP, DeRosa C, Fenner-Crisp P, Gray LE,Kaattari S, et al, Research needs for the risk assessment ofhealth and environmental effects of endocrine disruptors: areport of the US EPA-sponsored workshop. Environ HealthPerspect 104:1–26 (1996).

6 Velagaleti R and Gill M, Regulatory oversight for the envi-ronmental assessment of human and animal health drugs:environmental assessment regulations for drugs, in Phar-maceuticals and Personal Care Products in the Environment:Scientific and Regulatory Issues, ed. by Daughton CG andJones-Lepp TL. Symposium Series 791. ACS/Oxford Univer-sity Press, Washington, DC, pp. 304–319 (2001).

7 Daughton CG and Jones-Lepp TL (eds), Pharmaceuticalsand Personal Care Products in the Environment: Scientificand Regulatory Issues. Symposium Series 791. ACS/OxfordUniversity Press, Washington, DC (2001).

8 Ivashechkin P, Corvini PF and Dohmann M, Behaviour ofendocrine disrupting chemicals during the treatment of



municipal sewage sludge. Water Sci Technol 50:133–140(2004).

9 Bound JP and Voulvoulis N, Pharmaceuticals in the aquaticenvironment: a comparison of risk assessment strategies.Chemosphere 56:1143–1155 (2004).

10 Dokianakis SN, Kornaros ME and Lyberatos G, On the effectof pharmaceuticals on bacterial nitrite oxidation. Water SciTechnol 50:341–346 (2004).

11 Fountoulakis M, Drillia P, Stamatelatou K and Lyberatos G,Toxic effect of pharmaceuticals on methanogenesis. WaterSci Technol 50:335–340 (2004).

12 Carballa M, Omil F, Lema JM, Llompart M, Garcia-Jares C,Rodriguez I, et al, Behavior of pharmaceuticals, cosmeticsand hormones in a sewage treatment plant. Water Res38:2918–2926 (2004).

13 Petrovic M, Gonzalez S and Barcelo D, Analysis and removalof emerging contaminants in wastewater and drinking water.Trends Anal Chem 22:685–696 (2003).

14 Johnson AC and Sumpter JP, Removal of endocrine-disruptingchemicals in activated sludge treatment works. Environ SciTechnol 35:4697–4703 (2001).

15 Huber MM, Canonica S, Park GY and von Gunten U, Oxi-dation of pharmaceuticals during ozonation and advancedoxidation processes. Environ Sci Technol 37:1016–1024(2003).

16 Hirsch R, Ternes T, Haberer K and Kratz K-L, Occurrenceof antibiotics in the aquatic environment. Sci Total Environ225:109–118 (1999).

17 Wise R, Hart T, Cars O, Streulens M, Helmuth R, Huovi-nen P, et al, Antimicrobial resistance. Br Med J 317:609–610(1998).

18 Eljarrat E and Barcelo D, Priority lists for persistent organicpollutants and emerging contaminants based on their relativetoxic potency in environmental samples. Trends Anal Chem22:655–665 (2003).

19 Hansen LG, Stepping backward to improve assessment of PCBcongener toxicities. Environ Health Perspect 106:171–189(1998).

20 Jegou B, An introduction to endocrine disruption science.Toxicol Lett 95:16–17 (1998).

21 Roepke TA, Snyder MJ and Cherr GN, Estradiol andendocrine disrupting compounds adversely affect develop-ment of sea urchin embryos at environmentally relevantconcentrations. Aquat Toxicol 71:155–173 (2005).

22 Rhind SM, Are endocrine disrupting compounds a threat tofarm animal health, welfare and productivity? Reprod DomestAnim 40:282–290 (2005).

23 Spano M, Toft G, Hagmar L, Eleuteri P, Rescia M, Rignell-Hydbom A, et al, Exposure to PCB and p,p′-DDE inEuropean and Inuit populations: impact on human spermchromatin integrity. Hum Reprod 20:3488–3499 (2005).

24 Dodds E and Lawson W, Molecular structure in relation tooestrogenic activity: compounds without a phenanthrenenucleus. Proc R Soc Biol Sci Ser B 125:222–232 (1938).

25 Colborn T, Dumanoski D and Myers JP, Our Stolen Future:Are We Threatening our Fertility, Intelligence, and Survival? AScientific Detective Story. Dutton, New York (1996).

26 Drewes JE and Shore LS, Concerns about pharmaceuticalsin water reuse, groundwater recharge, and animal waste, inPharmaceuticals and Personal Care Products in the Environment:Scientific and Regulatory Issues, ed. by Jones-Lepp CGDTL.Symposium Series 791. ACS/Oxford University Press,Washington, DC, pp. 206–229 (2004).

27 Yoon Y, Westerhoff P, Snyder SA and Wert EC, Nanofiltra-tion and ultrafiltration of endocrine disrupting compounds,pharmaceuticals and personal care products. Journal of Mem-brane Science 270:88–100 (2006).

28 Wintgens T, Gallenkemper M and Melin T, Removal ofendocrine disrupting compounds with membrane processesin wastewater treatment and reuse. Water Sci Technol 50:1–8(2004).

29 Zhou H, Nusier OK and Smith DW, Advanced technologiesin water and wastewater treatment. J Environ Eng Sci1:247–264 (2002).

30 Weber S, Gallenkemper M, Melin T, Dott W and Hollender J,Efficiency of nanofiltration for the elimination of steroidsfrom water. Water Sci Technol 50:9–14 (2004).

31 Augugliaro V, Garcıa-Lopez E, Loddo V, Malato-Rodrıguez S, Maldonado I, Marcı G, et al, Degradationof lincomycin in aqueous medium: coupling of solarphotocatalysis and membrane separation. Solar Energy79:402–408 (2005).

32 Coleman HM, Abdullah MI, Eggins BR and Palmer FL,Photocatalytic degradation of 17[beta]-oestradiol, oestrioland 17[alpha]-ethynyloestradiol in water monitored usingfluorescence spectroscopy. Appl Catal B, Environ 55:23–30(2005).

33 Coleman HM, Eggins BR, Byrne JA, Palmer FL and King E,Photocatalytic degradation of 17-[beta]-oestradiol on immo-bilised TiO2. Appl Catal B, Environ 24:L1–L5 (2000).

34 Coleman HM, Routledge EJ, Sumpter JP, Eggins BR andByrne JA, Rapid loss of estrogenicity of steroid estrogensby UVA photolysis and photocatalysis over an immobilisedtitanium dioxide catalyst. Water Res 38:3233–3240 (2004).

35 Doll TE and Frimmel FH, Removal of selected persistentorganic pollutants by heterogeneous photocatalysis in water.Catal Today 101:195–202 (2005).

36 Nakashima T, Ohko Y, Kubota Y and Fujishima A, Photocat-alytic decomposition of estrogens in aquatic environmentby reciprocating immersion of TiO2-modified polytetraflu-oroethylene mesh sheets. J Photochem Photobiol A, Chem160:115–120 (2003).

37 Ohko Y, Ando I, Niwa C, Tatsuma T, Yamamura T,Nakashima T, et al, Degradation of bisphenol A in waterby TiO2 photocatalyst. Environ Sci Technol 35:2365–2368(2001).

38 Ohko Y, Iuchi K, Niwa C, Tatsuma T, Nakashima T, Iguchi T,et al, 17 Beta-estradiol degradation by TiO2 photocatalysis asa means of reducing estrogenic activity. Environ Sci Technol36:4175–4181 (2002).

39 Kabra K, Chaudhary R and Sawhney RL, Treatment ofhazardous organic and inorganic compounds throughaqueous-phase photocatalysis: a review. Ind Eng Chem Res43:7683–7696 (2004).

40 Serpone N and Emeline AV, Suggested terms and definitionsin photocatalysis and radiocatalysis. Int J Photoenergy4:91–131 (2002).

41 Wong CC and Chu W, The hydrogen peroxide-assistedphotocatalytic degradation of alachlor in TiO2 suspensions.Environ Sci Technol 37:2310–2316 (2003).

42 Herrmann J-M, Heterogeneous photocatalysis: fundamentalsand applications to the removal of various types of aqueouspollutants. Catal Today 53:115–129 (1999).

43 Hoffmann MR, Martin ST, Choi W and Bahnemann DW,Environmental applications of semiconductor photocatal-ysis. Chem Rev 95:69–96 (1995).

44 Bhatkhande DS, Pangarkar VG and Beenackers AACM, Pho-tocatalytic degradation for environmental applications: areview. J Chem Technol Biotechnol 77:102–116 (2002).

45 Kaneko M and Okura I (eds), Photocatalysis: Science andTechnology (1st edn). Springer, Tokyo (2002).

46 Rajeshwar K, Chenthamarakshan CR, Goeringer S and Dju-kic M, Titania-based heterogeneous photocatalysis: materi-als, mechanistic issues, and implications for environmentalremediation. Pure Appl Chem 73:1849–1860 (2001).

47 Mills A and Le Hunte S, An overview of semiconductorphotocatalysis. J Photochem Photobiol A, Chem 108:1–35(1997).

48 Wold A, Photocatalytic properties of titanium dioxide (TiO2).Chem Mater 5:280–283 (1993).

49 Chae SY, Park MK, Lee SK, Kim TY, Kim SK and Lee WI,Preparation of size-controlled TiO2 nanoparticles andderivation of optically transparent photocatalytic films. ChemMater 15:3326–3331 (2003).



50 Blake DM, Bibliography of work on the heterogenousphotocatalytic removal of hazardous compounds from waterand air: update number 1 to June, 1995. National RenewableEnergy Laboratory, Golden, CO, November (1995).

51 Chen PH and Jenq CH, Kinetics of photocatalytic oxidationof trace organic compounds over titanium dioxide. EnvironInt 24:871–879 (1998).

52 Le-Clech P, Lee EK and Chen V, Hybrid photocataly-sis/membrane treatment for surface waters containinglow concentrations of natural organic matters. Water Res40:323–330 (2006).

53 Nakajima T, Xu Y-H, Mori Y, Kishita M, Takanashi H,Maeda S, et al, Combined use of photocatalyst andadsorbent for the removal of inorganic arsenic(III) andorganoarsenic compounds from aqueous media. J HazardMater 120:75–80 (2005).

54 Snyder S, Toxicological significant of trace endocrine disrup-tors and pharmaceuticals in water, in Annual WateReuseAssociation’s Symposium, Denver, CO, 18–21 September(2005).

55 Adams CD, Control of total chloro-s-triazines in conventionaldrinking water treatment plants. Practice Periodical ofHazardous, Toxic, and Radioactive Waste Management7:281–288 (2003).

56 Addamo M, Augugliaro V, Di Paola A, Garcia-Lopez E,Loddo V, Marci G, et al, Removal of drugs in aqueoussystems by photoassisted degradation. J Appl Electrochem35:765–774 (2005).

57 Di Paola A, Addamo M, Augugliaro V, Garcia-Lopez E,Loddo V, Marci G, et al, Photolytic and TiO2-assistedphotodegradation of aqueous solutions of tetracycline.Fresenius Environ Bull 13:1275–1280 (2004).

58 Doll TE and Frimmel FH, Kinetic study of photocatalyticdegradation of carbamazepine, clofibric acid, iomeproland iopromide assisted by different TiO2 materials:determination of intermediates and reaction pathways. WaterRes 38:955–964 (2004).

59 Doll TE and Frimmel FH, Photocatalytic degradation ofcarbamazepine, clofibric acid and iomeprol with P25 andHombikat UV100 in the presence of natural organic matter(NOM) and other organic water constituents. Water Res39:403–411 (2005).

60 Liu B, Liu X-L and Deng N-S, The photocatalytic degradationof 17alpha-ethynylestradiol (EE2) with Anabaena. ActaHydrobiol Sin 27:390–395 (2003).

61 Tungudomwongsa H, Leckie J and Mill T, Photocatalyticoxidation of emerging contaminants: kinetics and pathwaysfor photocatalytic oxidation of pharmaceutical compounds.J Adv Oxidation Technol 9:59–64 (2006).

62 Serpone N and Pelizzetti E, Photocatalysis: Fundamentals andApplications. Wiley, New York (1989).

63 Cunningham J and Al-Sayyed G, Factors influencing efficien-cies of TiO2-sensitised photodegradation. Part 1. Substi-tuted benzoic acids: discrepancies with dark-adsorptionparameters. J Chem Soc Faraday Trans 86:3935–3941(1990).

64 Xu Y and Langford CH, Variation of Langmuir adsorptionconstant determined for TiO2-photocatalyzed degradationof acetophenone under different light intensity. J PhotochemPhotobiol A, Chem 133:67–71 (2000).

65 Xu Y and Langford CH, UV- or visible-light-Induced degra-dation of X3B on TiO2 nanoparticles: the influence ofadsorption. Langmuir 17:897–902 (2001).

66 Rudder JD, Wiele TVD, Dhooge W, Comhaire F and Ver-straete W, Advanced water treatment with manganese oxidefor the removal of 17[alpha]-ethynylestradiol (EE2). WaterRes 38:184–192 (2004).

67 Malygina T, Preis S and Kallas J, The role of pH in aqueousphotocatalytic oxidation of β-estradiol. Int J Photoenergy7:187–191 (2005).

68 Turchi CS and Ollis DF, Photocatalytic degradation of organicwater contaminants: mechanisms involving hydroxyl radicalattack. J Catal 122:178 (1990).

69 Mandelbaum PA, Regazzoni AE, Blesa MA and Bilmes SA,Photo-electro-oxidation of alcohols on titanium dioxide thinfilm electrodes. J Phys Chem B 103:5505–5511 (1999).

70 Huber MM, Canonica S, Park GY and von Gunten U, Oxi-dation of pharmaceuticals during ozonation and advancedoxidation processes. Environ Sci Technol 37:1016–1024(2003).

71 Egerton TA and King CJ, Influence of light intensity onphotoactivity in titanium dioxide pigmented systems. J OilCol Chem Assoc 62:386–391 (1979).

72 Okamoto K, Yamamoto Y, Tanaka H and Itaya A, Kinetics ofheterogeneous photocatalytic decomposition of phenol overanatase TiO2 powder. Bull Chem Soc Japan 58:2023–2028(1985).

73 Turchi CS, Effect of light intensity on photocatalyticreaction, in Potential Applications of Concentrated SolarEnergy:Proceedings of a Workshop, ed. by Araj KJ. Com-mission on Engineering and Technical Systems (CETS),Washington, DC, pp. 16–19 (1991).

74 Parsons CA, Peterson MW, Thacker BR, Turner JA andNozik AJ, Single quantum well electrodes for photoelec-trochemistry. J Phys Chem 94:3381–3384 (1990).

75 Malato S, Blanco J, Vidal A and Richter C, Photocatalysis withsolar energy at a pilot-plant scale: an overview. Appl Catal B,Environ 37:1–15 (2002).

76 Malato S, Blanco J, Vidal A, Fernandez P, Caceres J, Trin-cado P, et al, New large solar photocatalytic plant: set-upand preliminary results. Chemosphere 47:235–240 (2002).

77 Parra S, Malato S, Blanco J, Peringer P and Pulgarin C,Concentrating versus non-concentrating reactors for solarphotocatalytic degradation of p-nitrotoluene-o-sulfonic acid.Water Sci Technol 44:219–227 (2001).

78 Ajmera AA, Sawant SB, Pangarkar VG and BeenackersAACM, Solar-assisted photocatalytic degradation of benzoicacid using titanium dioxide as a photocatalyst. Chem EngTechnol 25:173–180 (2002).

79 Dhodapkar RS, Chaturvedi V, Neti NR and Kaul SN, Het-erogenous solar photocatalysis of two commercial reactiveazo dyes. Ann Chim 93:739–744 (2003).

80 Gautam S, Kamble SP, Sawant SB and Pangarkar VG, Pho-tocatalytic degradation of 4-nitroaniline using solar andartificial UV radiation. Chem Eng J 110:129–137 (2005).

81 Herrera Melian JA, Dona Rodriguez JM, Viera Suarez A,Tello Rendon E, Valdes do Campo C, Arana J, et al,The photocatalytic disinfection of urban wastewaters.Chemosphere 41:323–327 (2000).

82 Kositzi M, Poulios I, Malato S, Caceres J and Campos A,Solar photocatalytic treatment of synthetic municipalwastewater. Water Res 38:1147–1154 (2004).

83 Malato S, Caceres J, Fernandez-Alba AR, Piedra L, Her-nando MD, Aguera A, et al, Photocatalytic treatment ofdiuron by solar photocatalysis: evaluation of main inter-mediates and toxicity. Environ Sci Technol 37:2516–2524(2003).

84 Perez-Estrada LA, Maldonado MI, Gernjak W, Aguera A,Fernandez-Alba AR, Ballesteros MM, et al, Decompositionof diclofenac by solar driven photocatalysis at pilot plantscale. Catal Today 101:219–256 (2005).

85 Saravanan P, Mandal B and Saha P, Solar photocatalytictreatment of phenolic wastewater, in CHEMCON, NewDelhi (2005).

86 Robert D and Malato S, Solar photocatalysis: a clean processfor water detoxification. Sci Total Environ 291:85–97 (2002).

87 Parra S, Olivero J and Pulgarin C, Relationships betweenphysicochemical properties and photoreactivity of fourbiorecalcitrant phenylurea herbicides in aqueous TiO2

suspension. Appl Catal B, Environ 36:75–84 (2002).88 Kaniou S, Pitarakis K, Barlagianni I and Poulios I, Photocat-

alytic oxidation of sulfamethazine. Chemosphere 60:372–380(2005).

89 de Lasa H, Serrano B and Salaices M, Photocatalytic ReactionEngineering (1st edn). Springer, New York (2005).



90 Chen F, Xie Y, Zhao J and Lu G, Photocatalytic degradationof dyes on a magnetically separated photocatalyst undervisible and UV irradiation. Chemosphere 44:1159–1168(2001).

91 Beydoun D, Amal R, Low GKC and McEvoy S, Novel photo-catalyst: titania-coated magnetite. Activity and photodisso-lution. J Phys Chem B 104:4387–4396 (2000).

92 Alexiadis A and Mazzarino I, Design guidelines for fixed-bedphotocatalytic reactors. Chem Eng Proc 44:453–459 (2005).

93 Pirkanniemi K and Sillanpaa M, Heterogeneous water phasecatalysis as an environmental application: a review.Chemosphere 48:1047–1060 (2002).

94 Reddy EP, Davydov L and Smirniotis P, TiO2-loaded zeo-lites and mesoporous materials in the sonophotocatalyticdecomposition of aqueous organic pollutants: the role of thesupport. Appl Catal B, Environ 42:1–11 (2003).

95 Davydov L, Reddy EP, France P and Smirniotis PG,Transition-metal-substituted titania-loaded MCM-41 asphotocatalysts for the degradation of aqueous organics invisible light. J Catal 203:157–167 (2001).

96 Mohseni M, Gas phase trichloroethylene (TCE) photooxida-tion and byproduct formation: photolysis vs. titania/silicabased photocatalysis. Chemosphere 59:335–342 (2005).

97 Inumaru K, Kasahara T, Yasui M and Yamanaka S, Directnanocomposite of crystalline TiO2 particles and mesoporoussilica as a molecular selective and highly active photocatalyst.Chem Commun (Camb) 16:2131–2133 (2005).

98 Wei T-Y and Wan C-C, Kinetics of photocatalytic oxidationof phenol on TiO2 surface. J Photochem Photobiol A, Chem69:241–249 (1992).

99 Kormann C, Bahnemann DW and Hoffmann MR, Photolysisof chloroform and other organic molecules in aqueous TiO2

suspensions. Environ Sci Technol 25:494–500 (1991).100 Chiang K, Lim TM, Tsen L and Lee CC, Photocatalytic

degradation and mineralization of bisphenol A by TiO2 andplatinized TiO2. Appl Catal A, Gen 261:225–237 (2004).

101 Ferrari B, Paxeus N, Giudice RL, Pollio A and Garric J,Ecotoxicological impact of pharmaceuticals found in treatedwastewaters: study of carbamazepine, clofibric acid, anddiclofenac. Ecotoxicol Environ Saf 55:359–370 (2003).

102 Coldham NG, Dave M, Sivapathasundaram S, McDonnellDP, Connor C and Sauer MJ, Evaluation of a recombinantyeast cell estrogen screening assay. Environ Health Perspect105:734–742 (1997).

103 Collins BM, McLachlan JA and Arnold SF, The estrogenicand antiestrogenic activities of phytochemicals with thehuman estrogen receptor expressed in yeast. Steroids62:365–372 (1997).

104 Watanabe N, Horikoshi S, Kawabe H, Sugie Y, Zhao J andHidaka H, Photodegradation mechanism for bisphenol A atthe TiO2/H2O interfaces. Chemosphere 52:851–859 (2003).

105 Pelizzetti E, Maurino V, Minero C, Carlin V, Tosato ML,Pramauro E, et al, Photocatalytic degradation of atrazineand other s-triazine herbicides. Environ Sci Technol24:1559–1565 (1990).

106 Andreozzi R, Campanella L, Fraysse B, Garric J, Gonnella A,Giudice RL, et al, Effects of advanced oxidation processes(AOPs) on the toxicity of a mixture of pharmaceuticals.Water Sci Technol 50:23–28 (2004).

107 Kirpnick Z, Homiski M, Rubitski E, Repnevskaya M,Howlett N, Aubrecht J, et al, Yeast DEL assay detectsclastogens. Mutat Res 582:116–134 (2005).

108 Vogna D, Marotta R, Andreozzi R, Napolitano A andd’Ischia M, Kinetic and chemical assessment of theUV/H2O2 treatment of antiepileptic drug carbamazepine.Chemosphere 54:497–505 (2004).

109 Schweigert N, Hunziker RW, Escher BI and Eggen RIL,Acute toxicity of (chloro-)catechols and (chloro-)catechol-copper combinations in Escherichia coli corresponds totheir membrane toxicity in vitro. Environ Toxicol Chem20:239–247 (2001).

110 Doll TE and Frimmel FH, Cross-flow microfiltration withperiodical back-washing for photocatalytic degradation ofpharmaceutical and diagnostic residues-evaluation of thelong-term stability of the photocatalytic activity of TiO2.Water Res 39:847–854 (2005).

111 Fernandez-Alba AR, Hernando D, Aguera A, Caceres J andMalato S, Toxicity assays: a way for evaluating AOPsefficiency. Water Res 36:4255–4262 (2002).

112 Ollis DF, Integrating photocatalysis and membrane technolo-gies for water treatment. Ann NY Acad Sci 984:65–84(2003).

113 Lee YM, Oleszkiewicz JA, Cicek N and Londry K, Endocrinedisrupting compounds (EDC) in municipal wastewatertreatment: a need for mass balance. Environ Technol25:635–645 (2004).

114 Coleman HM, Chiang K and Amal R, Effects of Ag andPt on photocatalytic degradation of endocrine disruptingchemicals in water. Chem Eng J 113:65–72 (2005).

115 Ike M, Asano M, Belkada FD, Tsunoi S, Tanaka M andFujita M, Degradation of biotransformation products ofnonylphenol ethoxylates by ozonation and UV/TiO2 treat-ment. Water Sci Technol 46:127–132 (2002).

116 Mitamura K, Narukawa H, Mizuguchi T and Shimada K,Degradation of estrogen conjugates using titanium dioxideas a photocatalyst. Anal Sci 20:3–4 (2004).


Documents

Removing pharmaceuticals and endocrine-disrupting compounds from wastewater by photocatalysis