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Evaluation of a photocatalytic reactor membrane pilotsystem for the removal of pharmaceuticals andendocrine disrupting compounds from water

Mark J. Benotti*, Benjamin D. Stanford, Eric C. Wert, Shane A. Snyder

Southern Nevada Water Authority, P.O. Box 99954, Las Vegas, NV 89193-9954, United States

a r t i c l e i n f o

Article history:

Received 18 July 2008

Received in revised form

10 October 2008

Accepted 16 December 2008

Published online 13 January 2009

Keywords:

Pharmaceuticals

Endocrine disrupting compounds

(EDCs)

Photocatalysis

Titanium dioxide (TiO2)

Yeast estrogen screen (YES) assay

Water treatment

Estrogenic activity

Advanced oxidation process (AOP)

* Corresponding author. Tel.: þ1 702 856 368E-mail address: mark.benotti@snwa.com

0043-1354/$ – see front matter ª 2009 Elsevidoi:10.1016/j.watres.2008.12.049

a b s t r a c t

A photocatalytic reactor membrane pilot system, employing UV/TiO2 photocatalysis, was

evaluated for its ability to remove thirty-two pharmaceuticals, endocrine disrupting

compounds, and estrogenic activity from water. Concentrations of all compounds

decreased following treatment, and removal followed pseudo-first-order kinetics as

a function of the amount of treatment. Twenty-nine of the targeted compounds in addition

to total estrogenic activity were greater than 70% removed while only three compounds

were less than 50% removed following the highest level of treatment (4.24 kW h/m3). No

estrogenically active transformation products were formed during treatment. Additionally,

the unit was operated in photolytic mode (UV only) and photolytic plus H2O2 mode

(UV/H2O2) to determine the relative amount of energy required. Based on the electrical

energy per order (EEO), the unit achieved the greatest efficiency when operated in photo-

lytic plus H2O2 mode for the conditions tested.

ª 2009 Elsevier Ltd. All rights reserved.

1. Introduction particularly problematic as this pathway represents a vector

The presence of pharmaceuticals and endocrine disrupting

compounds (EDCs) in the environment has been a topic of

concern (Daughton and Ternes, 1999). Most environmental

data focus on the occurrence, fate, and transport of these

compounds in wastewater (Carballa et al., 2005; Conn et al.,

2006; Metcalfe et al., 2003; Sole et al., 2000) or receiving waters

(Kolpin et al., 2002). Their presence in source waters (Heberer

et al., 1997) and drinking water (Skutlarek et al., 2006; Snyder

et al., 2007; Stackelberg et al., 2004; Ternes et al., 2002) is

4; fax: þ1 702 856 3647.(M.J. Benotti).er Ltd. All rights reserved

for human exposure.

Another major concern over the presence of pharmaceu-

ticals and EDCs in the environment is the ability for some

compounds to act as endocrine disruptors and adversely

affect natural ecosystems. Several natural and synthetic EDCs

have been shown to impact aquatic organisms at low ng/L

concentrations, both as single compounds and as complex

mixtures (Brian et al., 2007; Brion et al., 2004; Labadie and

Budzinski, 2006). While direct links to human health through

drinking water exposure have not been proven, public fear

.

Table 1 – General water quality parameters of ColoradoRiver water.

Parameter Concentration/value

TOC (mg/L) 2.6

Alkalinity (mg/L) 137

pH 8.0

UV254 (1/cm) 0.036

w a t e r r e s e a r c h 4 3 ( 2 0 0 9 ) 1 5 1 3 – 1 5 2 21514

over pharmaceuticals and EDCs in potable water is high. A

recent report by Snyder et al. (2007) found detectable

concentrations of various pharmaceuticals and EDCs in the

finished water of 20 full scale drinking water utilities. Based on

the reported occurrence of these compounds in wastewaters,

source waters, and finished drinking waters, the lack of

evidence proving or disproving public health implications,

and the known impact of such compounds on environmental

species, scientists, utilities, and regulators are interested in

new technologies which can improve their removal from

water.

Several promising options for the pharmaceutical and EDC

removal from water are available, and many technologies

employ an advanced oxidation process (AOP). AOPs have been

shown to be better suited for removing recalcitrant pharma-

ceuticals and EDCs from water as compared to conventional

treatment processes (Kim et al., 2008; Oh et al., 2006; Snyder

et al., 2007; Vogna et al., 2004). Photocatalysis is one type of

AOP in which an electron of a semiconductor is promoted, by

light, from the valence band to the conduction band resulting

in the formation of superoxide (O2� �) and hydroxyl (�OH) radi-

cals. Additionally, the site on the TiO2 surface vacated by the

electron, termed the ‘‘electron hole’’, can directly oxidize

dissolved compounds. TiO2 is the most commonly used pho-

tocatalyst as it is relatively inexpensive, readily available, and

otherwise unreactive. The energy required for electron

promotion, commonly referred to as band-gap energy, is

3.2 eV for the anatase form of TiO2, and must be in the form of

UV light.

UV/TiO2 photocatalysis has been shown to remove

a variety of organic contaminants from water, most

commonly in bench-top, statically mixed experiments. For

example, nonylphenol concentrations of 0.2, 0.5, and 1.0 mg/L

were removed to less than 25% of their starting concentration

within 30 min (Ike et al., 2002). Micromolar concentrations of

17b-estradiol were entirely removed after 3 h (Ohko et al.,

2002), and the measured half-life of the pseudo-first-order

kinetics was 40 min (Coleman et al., 2000). The degradation of

low mg/L concentrations of carbamazepine, clofibric acid,

iomeprol, and iopromide was observed in aqueous TiO2 slur-

ries irradiated with simulated solar light. Half-lives of the four

compounds varied with the TiO2 concentrations, as well as the

type of TiO2 powder used: half-lives ranged from 0.5 to

7000 min (Doll and Frimmel, 2004). UV/TiO2 photocatalysis

has also been used in bench-top systems to remove other

pharmaceuticals and EDCs, such as sulfonamide antibiotics

(Hu et al., 2007; Kaniou et al., 2005), fluoroquinolone antibi-

otics (Paul et al., 2007), tetracycline (Reyes et al., 2006), chlor-

amphenicol (Chatzitakis et al., 2008), as well as gemfibrozil

and tamoxifen (Yurdakal et al., 2007).

While researchers have demonstrated that bench-scale

UV/TiO2 systems can remove pharmaceuticals and EDCs from

water, a major limitation to scaling up this technology has

been the difficulty in separating the TiO2 following treatment.

Doll and Frimmel (2005) have shown that a microfiltration

membrane can be employed to separate TiO2 from water

allowing the technology to be utilized in a flow-through

system. Here, we present data detailing the removal of thirty-

two of pharmaceuticals and EDCs at environmentally relevant

concentrations, as well as estrogenic activity through a pilot-

scale water treatment plant, employing UV/TiO2

photocatalysis.

2. Methods

2.1. General water quality

Colorado River water from Lake Mead, NV was used as the

source water for the pilot-scale testing. The Colorado River

water received at the pilot plant had been prechlorinated with

a 0.8 ppm dose of free chlorine (to control Quagga Mussel

growth in the intake structures) and contained a residual less

than 0.2 ppm by the time it reached the testing site. For all

experiments, a feed tank was filled and recirculated for 24 h to

remove some of the remaining chlorine residual prior to the

addition of pharmaceuticals and EDCs. Water quality param-

eters known to scavenge �OH radicals are shown in Table 1.

There were no changes in these parameters through any of

the experiments.

2.2. Photocatalytic reactor membrane mode(UV/TiO2) experiment

The pilot unit (Photo-Cat�) system was set up to operate from

a 3000 gallon polyethylene water tank (American Tank

Company, Windsor, CA). It was manufactured by Purifics ES,

Inc. (London, Ontario, Canada), and is referred to in this

manuscript as a ‘‘photocatalytic reactor membrane pilot’’,

which is a patented process employing treatment by UV/TiO2

photocatalysis as well as filtration and recycling of the pho-

tocatalyst by a ceramic microfiltration membrane. A general

schematic of the unit is presented in Fig. 1, and a compre-

hensive description of the unit is available in the Supple-

mentary Information. Briefly, as water enters the unit at a flow

rate of 24 liters per minute (Point 1), it is passed through a pre-

filter consisting of both a bag (Point 2) and cartridge filter

(Point 3) having a nominal pore size of 10 mm. It is then mixed

with a 2 liter per minute nanoparticle TiO2–water slurry (Point

5), and passed through the reactor (Point 6) within 3 mm of 32

UV lamps aligned in series, which can be individually turned

on or off to alter the amount of treatment. The total amount of

time which the slurry is exposed to the UV lamps is 1–30 s,

depending on the number of lamps in operation. The spectral

output of these lamps includes bands at 254 and 185 nm. The

reactor has a thin film reactor geometry, and its mixing is very

turbulent due to the plug-flow design and 3 mm containment

sleeve. As such, comparisons with other commercially

Fig. 1 – General schematic of photocatalytic reactor membrane pilot system.

w a t e r r e s e a r c h 4 3 ( 2 0 0 9 ) 1 5 1 3 – 1 5 2 2 1515

available UV reactors cannot be made. The unit’s flow-

through design is enabled by a TiO2-recovery system. After

exposure to the UV lamps, a cross-flow ceramic membrane

(Point 8) removes the TiO2 from the flow stream and the

treated water exits the unit (Point 9). Every 60 s the membrane

is back-pulsed to prevent catalyst buildup. The rejected TiO2 is

mixed with influent (Point 5) prior to the UV reactor. Thus, the

unit recycles and reuses all of the TiO2, allowing for long-term

operation. The TiO2 used in this pilot was Degussa P-25 con-

sisting of 80% anatase and 20% rutile TiO2. The surface area of

Degussa P-25 is 50 m2/g.

The efficacy of the photocatalytic reactor membrane pilot

was evaluated by spiking the feed tank with ng/L concentra-

tions of thirty-two pharmaceuticals and EDCs (Table 2). Their

removal was determined as a function of the treatment

energy applied. Compounds were spiked without the use of

organic solvents to prevent addition of organic matter and

radical quenching. For all experiments, the unit was operated

at 24 liters per minute and samples were collected after the

pre-filter (Point 4 in Fig. 1) and following treatment with 0, 1, 2,

4, 6, 8, 16, and 32 UV lamps (Point 9 in Fig. 1). The unit was

allowed to equilibrate for at least 40 min between each sample

collection. The TiO2 concentration in the UV reactor was

approximately 50 ppm.

Two treatment energies were calculated for each level of

treatment. The first is the treatment energy based upon the

amount of energy output for the lamps (Elamps), providing an

indication of the energy used in the photocatalytic (or

photolytic) process. The second treatment energy is calcu-

lated from the total energy consumption of the photocatalytic

reactor membrane (Etotal), providing an indication of the

operating cost of the unit. Methods for calculating both values

are presented in the Supplementary Information. Etotal values

are presented in the Supplementary Information (Table S10) to

provide the actual power consumed during treatment. Elamps

values are used for the purposes of data interpretation and

discussion in the manuscript text.

2.3. Photolytic (UV) and photolytic plus H2O2 (UV/H2O2)mode experiments

To determine treatment efficacy of the unit under different

operational parameters, the unit was also operated without

TiO2 (photolytic mode) and without TiO2 but with peroxide

(photolytic plus H2O2 mode). Though these experiments are

UV and UV/H2O2 processes, care must be taken not to directly

compare these modes of operation with conventional UV or

UV/H2O2 systems due to differences in reactor design and

efficiency. All subsequent discussions of UV/TiO2, UV, and

UV/H2O2 efficiencies in this manuscript pertain only to the

Photo-Cat� unit operated in these modes.

Treatment efficacy was determined by the relative energy

requirement for equivalent degrees of contaminant destruc-

tion. Photolysis plus H2O2 mode was evaluated using H2O2

doses of 10 and 20 ppm, supplied by a system-integrated

dosing pump from a 15% H2O2 solution. Residual H2O2 was

measured in the effluent indicating that contaminant

destruction was not H2O2 limited. Nine pharmaceuticals and

EDCs were spiked into the tank (Table 3) and removal was

determined as a function of treatment. Effluent samples were

collected after exiting the UV reactor (Point 7 in Fig. 1). The

TiO2-recovery system was turned off for these experiments,

and there was no recycle flow. The amount of treatment and

the flow rate was otherwise similar to that employed for the

photocatalytic reactor membrane experiment.

2.4. Analytical methods

Four separate analytical methodologies were employed to

monitor removal of pharmaceuticals, EDCs, and estrogenic

activity for the photocatalytic reactor membrane mode

experiment. The 32 targeted pharmaceuticals and EDCs are

presented in Table 2 with their method reporting limits

(MRLs). In addition, although perfloroctanoic acid (PFOA) was

not spiked into the tank, its concentration was monitored as it

Table 2 – C0, MRLs, calculated first-order removal constants, EEOs, and the number of detections for 32 pharmaceuticals andEDCs for the photocatalytic reactor membrane mode experiment.

C0 (ng/L; n¼ 2) MRL (ng/L) Removal const.(m3/kW h)

EEOa (kW h/m3) n

Atenolol 83 (�24) 1.0 1.1 (�0.066) 2.0 (�0.12) 7

Atorvastatin 120 (�7.1) 0.5 22 (�10) 0.10 (�0.048) 3

Atrazine 140 (�0) 0.25 0.49 (�0.026) 4.7 (�0.24) 8

Benzophenone 330 (�7.1) 50 0.71 (�0.036) 3.2 (�0.16) 7

BHA 190 (�14) 1.0 40 0.048 2

Bisphenol A 270 (�92) 5.0 15 (�1.7) 0.16 (�0.018) 3

Caffeine 490 (�21) 5.0 0.73 (�0.081) 3.2 (�0.35) 8

Carbamazepine 220 (�7.1) 0.50 1.1 (�0.080) 2.1 (�0.15) 8

DEET 1500 (�71) 1.0 0.58 (�0.056) 4.0 (�0.38) 8

Diazepam 250 (�14) 0.25 0.63 (�0.080) 3.7 (�0.46) 8

Diclofenac 280 (�50) 0.5 8.2 (�1.6) 0.21 (�0.040) 4

Dilantin 98 (�2.8) 1.0 1.0 (�0.054) 2.2 (�0.11) 8

Estradiol 18 (�0.71) 0.5 12 (�2.2) 0.19 (�0.37) 3

Estrone 26 (�2.1) 0.2 13 (�2.2) 0.18 (�0.031) 3

Ethynylestradiol 140 (�14) 1.0 9.8 (�1.6) 0.23 (�0.039) 4

Fluoxetine 54 (�16) 0.5 1.3 (�0.097) 1.7 (�0.13) 7

Gemfibrozil 170 (�14) 0.25 0.80 (�0.086) 2.9 (�0.31) 8

Ibuprofen 170 (�14) 1.0 0.79 (�0.084) 2.9 (�0.31) 8

Iopromide 530 (�71) 10 1.3 (�0.071) 1.8 (�0.095) 7

Meprobamate 345 (�7.1) 0.25 0.34 (�0.048) 6.8 (�0.98) 8

Musk Ketone 0 (�0) 25 na na 0

Naproxen 210 (�0) 0.5 5.4 (�0.46) 0.43 (�0.037) 6

Octylphenol 55 (�24) 25 na na 0

PFOS 330 (�92) 1.0 0.044 (�0.068) 53 (�81) 8

Primidone 510 (�21) 0.50 0.59 (�0.066) 3.9 (�0.43) 8

Progesterone 56 (�2.1) 0.5 1.1 (�0.14) 2.2 (�0.29) 7

Sulfamethoxazole 270 (�14) 0.25 1.7 (�0.70) 1.3 (�0.54) 8

TCEP 1300 (�0) 10 0.063 (�0.017) 37 (�9.8) 8

TCPP 1300 (�140) 100 0.13 (�0.036) 17 (�4.7) 8

Testosterone 280 (�14) 1.0 1.3 (�0.043) 1.8 (�0.062) 8

Triclosan 16 (�19) 1.0 20 0.11 2

Trimethoprim 360 (�14) 0.25 1.6 (�0.28) 1.5 (�0.27) 8

a EEO values were calculated using the calculated energy output of the UV lamps (Elamps). EEO values would be markedly greater if they were

calculated using the total energy consumption of the pilot-unit (Etotal). See Supplementary Information.

w a t e r r e s e a r c h 4 3 ( 2 0 0 9 ) 1 5 1 3 – 1 5 2 21516

has been predicted to be a significant oxidation product of

polyfluorinated compounds (Dimitrov et al., 2004). All

compounds were obtained from Sigma-Aldrich (St. Louis, MO,

USA). Analytical methods (both solid phase extraction and

LC–MS/MS analysis) to measure pharmaceuticals and non-

steroidal endocrine disruptors were slightly modified from

published methods (Vanderford and Snyder, 2006). A similar

extraction was used for steroid hormones and PFOS/PFOA, but

Table 3 – C0, MRLs, and calculated first-order removal constantphotolytic plus H2O2 mode experiments.

C0 (ng/L; n¼ 3) MRL (ng/L) kUV (m3

Atenolol 1300 (�20) 10 1.6 (�Atrazine 960 (�30) 25 0.69

Carbamazepine 870 (�40) 10 0.98

Dilantin 940 (�60) 10 1.1 (�Meprobamate 700 (�20) 10 0.35

Primidone 1100 (�0) 10 0.62

TCEP 3100 (�200) 400 0.063

TCPP 4000 (�300) 400 0.11

Trimethoprim 1000 (�90) 10 2.9 (�

different LC–MS/MS methods were used for each. The

Supplementary Information contains more detailed descrip-

tions of each method.

Total estrogenic activity was determined using a yeast

estrogen screen (YES) assay (Routledge and Sumpter, 1996;

Stanford, 2008). The human estrogen receptor-transfected

yeast strain was used under agreement from John P. Sumpter of

Brunel University, Middlesex, UK. The YES assay is well-suited

s for nine pharmaceuticals and EDCs for the photolytic and

/kW h) kUV=H2O2�10ppm (m3/kW h) kUV=H2O2�20ppm (m3/kW h)

0.12) 5.1 (�0.94) 7.2 (�0.96)

(�0.038) 2.0 (�0.26) 2.7 (�0.11)

(�0.21) 5.7 (�1.1) 7.9 (�0.57)

0.26) 2.3 (�0.62) 7.9 (�0.50)

(�0.023) 2.3 (�0.37) 3.3 (�0.15)

(�0.052) 3.8 (�0.51) 5.4 (�0.31)

(�0.026) 0.24 (�0.051) 0.35 (�0.057)

(�0.042) 0.59 (�0.16) 0.84 (�0.17)

0.36) 5.5 (�0.53) 7.2 (�0.54)

w a t e r r e s e a r c h 4 3 ( 2 0 0 9 ) 1 5 1 3 – 1 5 2 2 1517

to measuring overall estrogenic activity as the human estrogen

receptor-transfected yeast employed for this study have been

shown to be resistant to interference from androgens (Sohoni

and Sumpter, 1998) and are able to respond to molecules

capable of binding with the estrogen receptor site. As such, the

assay is able to detect any loss of parent molecules in addition

to the formation of estrogenically active transformation prod-

ucts. Estrogenic activity was determined from the concentra-

tion of estradiol or the relative concentration of the sample

extract needed to induce 50% of the maximum response,

written as the EC50. Further information pertaining to the YES

assay methods used in this study, is available elsewhere

(Stanford, 2008).

A separate analytical method was employed to monitor

concentrations of the nine emerging contaminants through

the photolytic and photolytic plus H2O2 mode experiments.

This method employs an online solid phase extraction

(Symbiosis, Spark Holland, Emmen, The Netherlands), fol-

lowed by LC–MS/MS analysis. Although less time-consuming,

this method is not as sensitive as offline extraction methods,

and it was necessary to spike at slightly higher concentra-

tions. Spiked concentrations and method reporting limits

(MRLs) for the compounds targeted in this photolytic and

photolytic plus H2O2 mode experiments are presented in Table

3. Additional details of this method are provided in Supple-

mentary Information.

2.5. Experimental design

To spike the feed tank, approximately 5 mg of each compound

was transferred to a 2000 mL flask where most dissolved into

DI water. The contents of the flask were added to the 3000

gallon tank when it was full, and the flask was flushed with

volumes of water to transfer all of the undissolved material.

The tank was then topped off and its contents were circulated

for two days to homogenize. Samples were collected prior to

treatment at the start and finish of the experiment to ensure

homogenization. These samples also indicate that any

observed removal was due to photocatalysis, photolysis, or

photolysis plus H2O2, and not due to chemical insolubility,

slow dissolution, particle adsorption, adsorption to the tank

wall, or reaction with free chlorine present in the feed water.

Tables 2 and 3 list the mean concentrations of spiked

compounds in the feed water. Only one compound (musk

ketone) was entirely lost during homogenization of the tank,

perhaps due to the fact that it is a fragrance compound, and

therefore volatile. The low standard deviations of influent

concentrations (C0) measured throughout each experiment

illustrate that all spiked compounds were well-mixed in the

feed water. Raw data are available in the Supplementary

Information.

Additional samples were collected with zero UV lamps in

operation to determine whether or not compounds were

adsorbed to the TiO2 nanoparticles or the ceramic membrane

(for the photocatalytic reactor membrane experiment) or

reacted with the H2O2 (for the photolytic plus H2O2 mode

experiments). In these cases, the effluent concentrations

without any UV lamps in operation were similar to influent

concentrations, thus loss due to adsorption or direct reaction

with H2O2 was not observed.

2.6. Mathematical treatment to determine removalconstants and associated error

First-order removal constants (k) and their associated error

were calculated from the raw data using the Regression

Statistics associated with Microsoft Office’s Data Analysis

feature. The range of x-data data for this analysis were the

treatment energies (Elamps), the range of y-data were the

natural log of the concentration of a compound at a particular

energy (Ce) divided C0, and the regression was forced through

the origin. The standard deviation of the rate was calculated

from the standard error and number of observations associ-

ated with the slope of the regression. Removal constants and

their standard deviations are presented in Table 2 for the

photocatalytic reactor membrane mode experiment and in

Table 3 for the photolytic and photolytic plus H2O2 mode

experiments.

3. Results and discussion

3.1. Removal of pharmaceuticals and EDCs during thephotocatalytic reactor membrane mode experiment

The concentrations of most compounds decreased regularly

as a function of the amount of treatment (Fig. 2). Concentra-

tions reported as below MRLs in the raw data are considered

zero for the purposes of plotting and are not included in the

mathematical determination of removal constants. Eleven of

the 32 compounds were easily removed, with concentrations

below or approaching MRLs with 0.53 kW h/m3 (4 lamps) of

treatment: estrone, estradiol, ethinylestradiol, bisphenol A,

octylphenol, butylated hydroxyanisole (BHA), atorvastatin,

triclosan, diclofenac, sulfamethoxazole, and naproxen.

Conversely, PFOS, tris(2-chloroethyl) phosphate (TCEP), and

tris(1-chloro-2-propyl) phosphate (TCPP) were largely resis-

tant to the photocatalytic reactor membrane experiment,

exhibiting concentrations following the maximum treatment

(4.24 kW h/m3 or 32 lamps) that were greater than 50% of their

starting concentration. Their refractory nature through

treatment is consistent with their chemical design: all three

are used as flame-retardants or in applications requiring

resistance to chemical oxidation. The remaining 17

compounds were removed, although it took higher amounts

of treatment (0.80–4.24 kW h/m3 or 6–32 lamps) to achieve

a greater than 70% reduction in compound concentration.

Additionally, no formation of PFOA was observed.

Removal of each compound appeared to be pseudo-first-

order with respect to treatment for the given set of operational

parameters. Results from bench-scale UV/TiO2 studies have

shown that the efficiency of removal of organic contaminants

can rely on other parameters such as type (Bahnemann et al.,

2007) or concentration of TiO2 catalyst (Bahnemann et al.,

2007; Chen et al., 2007), pH (Bahnemann et al., 2007), and

presence of other water constituents such as inorganic salts

(Guillard et al., 2005). Thus, it is possible that improvements in

removal efficiency could be realized by optimizing some of the

operational parameters.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

PrimidoneGemfibrozilDiclofenacIbuprofenTrimethoprimSulfamethoxazoleNaproxenMeprobamate

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 1 2 3 4 5 0 1 2 3 4 5

AtenololIopromideCaffeineFluoxetineDilantinCarbamazepineDiazepamAtorvastatin

0

0.2

0.4

0.6

0.8

1

1.2

1.4

TestosteroneProgesteroneEstroneEstradiolEthynylestradiol

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 1 2 3 4 5 0 1 2 3 4 5

PFOSTCPPTCEP

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Bisphenol ABenzophenoneOctylphenolBHAMusk Ketone

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 1 2 3 4 5 0 1 2 3 4 5

AtrazineDEETTriclosan

Ce/C

0C

e/C

0C

e/C

0

Energy per volume treated (kWh/m3)Energy per volume treated (kWh/m

3)

Pharmaceuticals Pharmaceuticals, cont.

Steroid hormones Flame retardant-like compounds

Non-steroidal EDCs Miscellaneous

A B

C D

E F

Fig. 2 – Removal of 32 pharmaceuticals and EDCs as a function of treatment energy by the photocatalytic reactor membrane

mode experiment separated by A) and B) pharmaceuticals, C) steroid hormones, D) flame retardant-like compounds, E) non-

steroidal EDCs, and F) miscellaneous.

w a t e r r e s e a r c h 4 3 ( 2 0 0 9 ) 1 5 1 3 – 1 5 2 21518

3.2. Removal of estrogenic activity during thephotocatalytic reactor membrane mode experiment

Data from the YES assay showed a rapid loss of estrogenic

activity during the photocatalytic reactor membrane mode

experiment that paralleled the loss of individual estrogenic

analytes. Fig. 3A shows that most of response to estrogenic

activity occurred for treatments using 6 or less lamps. Total

estrogenic activity, report as the equivalent concentration of

estradiol (EEQ), was rapidly removed (Fig. 3B). The removal

constant derived from the YES data was 13 m3/kW h

(R2¼ 0.904) which is in excellent agreement with the analyte-

specific removal constants for estrone (13 m3/kW h) and

estradiol (12 m3/kW h), though less for ethinylestradiol

(9.8 m3/kW h). The EEQ response of 122 (�41) ng/L is slightly

lower than the combined presence of estrone (26 ng/L),

estradiol (18 ng/L), and ethinylestradiol (140 ng/L) in the test

water, though such discrepancies between instrumental- and

bioassay-derived values have been reported elsewhere (Aerni

et al., 2004; Cespedes et al., 2004). As such, the agreement

between the instrumental and YES assay analyses indicate

that the photocatalytic reactor membrane system is able to

0

20

40

60

80

100

120

140

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 1 2 3 4 50 0.001 0.1 10

EE

Q (n

g/L

)

Energy per volume treated (kWh/m3)

A550-A

660

Concentration Factor

0 lamps 2 lamps

6 lamps

A B

Fig. 3 – Removal of estrogenic activity by the photocatalytic reactor membrane mode experiment by A) YES dose–response

curve and B) EEQ loss.

0

0.2

0.4

0.6

0.8

1

1.2

energy (kWh/m3)

Ce/C

0

0

0.2

0.4

0.6

0.8

1

1.2

energy (kWh/m3)

Ce/C

0

0

0.2

0.4

0.6

0.8

1

1.2

0 1 2 3 4 5

0 1 2 3 4 5

0 1 2 3 4 5

energy (kWh/m3)

Ce/C

0

AtenololAtrazineCarbamazepineDilantinMeprobamate

PrimidoneTCEPTCPPTrimethoprim

A

B

C

Fig. 4 – Removal of nine emerging contaminants as

a function of treatment by the unit operated in A)

photolytic mode, B) photolytic plus 10 ppm H2O2 mode, and

C) photolytic plus 20 ppm H2O2 mode.

w a t e r r e s e a r c h 4 3 ( 2 0 0 9 ) 1 5 1 3 – 1 5 2 2 1519

reduce individual analytes and total estrogenic activity as has

been shown in a bench-top, stirred-cell system (Coleman

et al., 2004). Additionally, results from the YES assay show that

no estrogenically active transformation products were

generated during treatment.

3.3. Removal of pharmaceuticals and EDCs during thephotolytic and photolytic plus H2O2 mode experiments

The concentrations of the nine compounds analyzed in the

photolytic and photolytic plus H2O2 mode experiments

decreased regularly as a function of treatment (Fig. 4).

Removal appeared to follow pseudo-first-order kinetics, and

the concentrations of most were almost entirely removed

following the highest level of treatment. Of the nine

compounds, all but TCEP and TCPP were removed to less than

25% of their starting concentration following the highest level

of photolytic treatment (4.24 kW h/m3), although only atenolol

and trimethoprim were below MRLs. For the photolytic plus

H2O2 treatment with 10 ppm H2O2, only TCEP was detected

following the highest level of treatment (39% of its initial

concentration). For the photolytic plus H2O2 with 20 ppm

H2O2, only TCEP was detected following the highest level of

treatment (25% of its initial concentration). First-order

removal constants, as well as associated error are presented

in Table 3.

3.4. Relative energy consumption of photocatalyticreactor membrane mode, photolytic mode, and photolyticplus H2O2 mode experiments

The energy required for photocatalytic reactor membrane

mode can be compared to the energy required for photolytic

and photolytic plus H2O2 treatments using electrical energy

per order (EEO) values. The EEO is the amount of energy

required to reduce the concentration of a compound by one

order of magnitude, and is directly calculated from the

removal constant, k, by the following equation:

EEO ¼ lnð1Þk

(1)

EEOs were calculated for each compound during the photo-

catalytic reactor membrane mode experiment and are

0.1

1

10

100

EE

O (kW

h/m

3)

UV/TiO2 photocatalysisUV photolysisUV/H2O2 (10ppm)UV/H2O2 (20ppm)

Aten

olol

Atra

zine

Car

bam

azep

ine

Dila

ntin

Mep

roba

mat

e

Prim

idon

e

TCEP

TCPP

Trim

etho

prim

Fig. 5 – EEOs for the unit operated in photocatalytic reactor membrane mode, photolytic mode, photolytic plus 10 ppm H2O2

mode, and photolytic plus 20 ppm H2O2 mode.

w a t e r r e s e a r c h 4 3 ( 2 0 0 9 ) 1 5 1 3 – 1 5 2 21520

presented in Table 2. Additionally, EEOs were calculated for

the nine compounds investigated in the photolytic or photo-

lytic plus H2O2 experiments. Fig. 5 compares EEOs’ values for

nine compounds between photocatalytic reactor membrane

mode, photolytic, photolytic plus 10 ppm H2O2, and photolytic

plus 20 ppm H2O2. Although photocatalytic reactor membrane

mode is an effective technology for removing these nine

compounds, it takes a similar amount of energy as compared

to photolytic mode to reduce analyte concentrations by one

order of magnitude. Additionally, both photolytic plus H2O2

mode experiments were much more efficient at contaminant

destruction as compared to the photocatalytic reactor

membrane mode experiment. It is important to note that, like

the rate, EEOs are dependant on the set of operational

parameters used during the experiment and will change

under different conditions. For example, it is possible that

lower energy UVA lamps may be employed increasing the

energy efficiency of the unit, though this would need to be

evaluated. UV/TiO2 photocatalysis with H2O2 was not evalu-

ated, though it may provide the highest level of efficiency of all

the possible modes of operation.

Not included in the comparison of EEOs is the cost of

peroxide. This cost can be calculated following the approach

used in Rosenfeldt et al. (2006), and assuming an energy cost of

$70 per MW h and $0.60 per kg 50% H2O2. Given these values,

and converting the EEOs in Fig. 5 to dollar amounts, the cost of

H2O2 is 1–30% of the total treatment costs in both H2O2

experiments. The corrected cost of photolytic plus H2O2

operation is still well below the cost of operation in either

photocatalytic reactor membrane mode or photolytic mode.

The cost to destroy residual H2O2 is not presented.

The reason the unit exhibited similar efficiencies during

photocatalytic reactor membrane mode and photolytic mode

is not known, though it may be due to the relatively low TiO2

concentration (50 ppm) and/or the relatively fast passage

times through the reactor. Other researchers have shown TiO2

concentration has an effect on photocatalytic efficiency. For

example Mendez-Arriaga et al. (2008) showed that ibuprofen

was most efficiently degraded using photocatalysis at TiO2

concentrations of 1000 ppm, whereas diclofenac and

naproxen were most efficiently degraded at TiO2 concentra-

tions of 100 ppm. The concentration of TiO2 used in this work

was based on the manufacturer’s recommendation, and is

markedly lower than the TiO2 concentration used in most

bench-top applications as well as another pilot-scale study.

Doll and Frimmel (2005) utilized a TiO2 concentration of

1000 ppm, though their pilot had markedly lower flow rates.

Though higher concentrations of TiO2 may increase the effi-

ciency of the UV/TiO2 photocatalysis within the system, the

effect of a higher TiO2 load would have decreased the

membrane flux or increased the transmembrane pressure.

Additionally, bench-top UV/TiO2 systems haven typically

taken minutes to hours for the photocatalytic process to

achieve significant contaminant destruction (Coleman et al.,

2000; Ike et al., 2002; Ohko et al., 2002). In the system described

in this manuscript, water is exposed to the UV lamps for less

than a minute. Thus, increasing the time which the water is

exposed to the UV lamps may increase photocatalytic effi-

ciency of the unit.

4. Conclusions

This study adds to the growing literature on treatment tech-

nologies which are able to remove pharmaceuticals and EDCs

from water. Variable removal rates for thirty-two compounds

were observed when the unit was operated in photocatalytic

reactor membrane mode, indicating that photocatalysis may

be a viable AOP for water treatment at larger scales. Addi-

tionally, the concomitant decrease in total estrogenic activity

and concentrations of individual steroid hormones illustrates

that no estrogenically active byproducts are formed during

photocatalytic transformation. The similar EEOs observed

during photocatalytic reactor mode operation and photolytic

mode operation highlight the need for process optimization.

In terms of energy, the unit was least efficient when operated

in photocatalytic reactor mode under the conditions investi-

gated, though operation in this mode does offer other

advantages not investigated in this work (e.g. the ceramic

membrane provides as additional barrier against pathogenic

w a t e r r e s e a r c h 4 3 ( 2 0 0 9 ) 1 5 1 3 – 1 5 2 2 1521

microbes). Results from this study will be of interest to those

interested in the removal of pharmaceuticals and EDCs from

water, especially in areas with sensitive receiving waters as

the photocatalytic reactor membrane contains no chemical

residual in the treated water. In short, the photocatalytic

reactor membrane is a useful treatment technology for water

treatment as determined by pharmaceutical and EDC

destruction as well as the removal of estrogenic activity.

Acknowledgements

The authors gratefully acknowledge the WateReuse Founda-

tion’s financial, technical, and administrative assistance in

funding and managing the project through which this infor-

mation was discovered (Grant 06-012). The authors would also

like to thank Tony Powell and Brian Butters of Purifics ES, Inc.,

for use of the Photo-Cat� unit and the staff at the SNWA

Water Quality Research and Development Laboratory for the

analysis of trace contaminants.

Supplementary Information

Supplementary data associated with this article can be found

in the online version, at doi:10.1016/j.watres.2008.12.049.

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