Treatment of Organic Micropollutants in Water and Wastewater by UV-Based Processes: A Literature...

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Treatment of Organic Micropollutants in Water and Wastewater by UV-basedProcesses: A Literature ReviewWenbo Yang a , Hongde Zhou a & Nazim Cicek ba School of Engineering , University of Guelph , Guelph , ON , Canadab Department of Biosystems Engineering , University of Manitoba , Winnipeg , MB , CanadaAccepted author version posted online: 06 Sep 2013.

To cite this article: Critical Reviews in Environmental Science and Technology (2013): Treatment of Organic Micropollutants in Water and Wastewater by UV-basedProcesses: A Literature Review, Critical Reviews in Environmental Science and Technology, DOI: 10.1080/10643389.2013.790745

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Treatment of Organic Micropollutants in Water and Wastewater by UV-based Processes: A Literature Review

WENBO YANG,1 HONGDE ZHOU 1 and NAZIM CICEK 2

1School of Engineering, University of Guelph, Guelph, ON, Canada

2Department of Biosystems Engineering, University of Manitoba, Winnipeg, MB, Canada

ABSTRACT

This paper provides a review of the up-to-date research on the treatment of micropollutants by UV-based processes. More than 140 scientific

publications in the past 10 years were reviewed and analyzed, with emphasis on the peer-reviewed papers in the last 3 years (2009-2011). Previous

studies showed that UV-based advanced oxidation processes (AOPs) could be efficient for the removal of a number of micropollutants in drinking water

and wastewater although direct UV photolysis at disinfection dosages was proven not effective in removing most micropollutants. Among those UV-

based AOPs, UV-oxidation with hydrogen peroxide (H2O2) has attracted great attention and shown numerous advantages as an advanced technology

for micropollutants control. The public concern about the impact of micropollutants on the safety of drinking water and the increasing needs of safe

water reuse will likely facilitate the application of UV-based processes for micropollutants control in drinking water treatment and water reuse.

KEY WORDS: micropollutants, UV, advanced oxidation processes, drinking water, wastewater, water reuse.

Address correspondence to Wenbo Yang, School of Engineering, University of Guelph, Guelph, ON, Canada, N1G 2W1; Email:

[email protected]

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INTRODUCTION

Micropollutants commonly refer to chemical compounds which are detected in the environment at the concentrations of from

µg/L to ng/L or even lower.1, 2 This terminology has been adopted by European organizations including International Water

Association (IWA). Various organizations use different terminology for micropollutants, e.g. microconstituents by Water

Environment Federation (WEF) and trace organic compounds (TOrC) by Water Environment Research Foundation (WERF).

For the treatment of drinking water and wastewater, the micropollutants may include two classes of contaminants: (1) legacy

contaminants of which toxic effects have been established and control measures have been developed; (2) emerging

contaminants that are not currently regulated and are thought to have potential threats to environmental ecosystems or human

health and safety.3,4 Based on their functions or industrial uses, the micropollutants may also be grouped as pharmaceuticals

and personal care products (PPCPs), endocrine disrupting compounds (EDCs), surfactants, pesticides, synthetic fragrances,

flame retardants, industrial additives, and their transformation products.4, 5 The number of such contaminants being found in

the environment is increasing and is driven by analytical technology advancements.

The occurrence of micropollutants in water resources is an increasing safety concern from the scientific community,

regulatory agencies and public because a number of them could have adverse effects on the ecosystems when they are released

into the aquatic environment. One of the most publicly visible effects occurs when their potential to disrupt the endocrine

system of animals is manifest in aquatic biota (multiple-appendaged amphibians, feminization of fish, etc.). In recent years,

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evidence from field research has indicated adverse reproductive and developmental effects in wildlife, possibly via endocrine

disrupting pathways.6 It should be noted that some scientists have reported that the risk to public health might be minimal

because human beings are being exposed to micropollutants in water at extremely trace levels compared to the exposure to

these compounds present in food sources.7 Micropollutants in water are less likely to cause adverse effects on humans than

they are on fish due to the difference in exposures. The very apparent manifestations of effects on aquatic biota are indications

that the risk to the environment is real, because the aquatic biota spends most of their developmental stages in the

contaminated water.

Because existing water and wastewater treatment plants are not designed for treating these contaminants, of which most

have not been regulated, the occurrence of micropollutants has become a potential threat to our water supply networks. The

presence of PPCPs and EDCs in treated drinking water has been reported in a few surveys.8, 9 Therefore, there has been

concern about the effectiveness of existing drinking water treatment technologies to remove these micropollutants and

alternative technologies may need to be considered. Since the majority of micropollutants is anthropogenic in origin, often

heavily consumed by the general public and industry, and subsequently present in wastewater, the study of the fate of

emerging contaminants in wastewater treatment processes is also important. In many cases, the second line of defense in

protecting water supplies will be the treatment of wastewaters (the first line of defense will be keeping the compounds out of

the wastewater in the first place). A number of studies have demonstrated that most micropollutants were not completely

removed in exiting wastewater treatment plants (WWTPs) and remained with fluctuating concentrations in discharged

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effluents.10-12 Efforts are ongoing to understand the occurrence of micropollutants in the effluents, assess environmental and

public health risk (a combination of occurrence and effects), determine acceptable levels at which the compounds can be

present to minimize the risk, and develop effective ways to remove these trace contaminants to acceptable effect levels. In

addition, reclamation and reuse of municipal wastewater is an emerging approach to mitigate the stress from water scarcity in

many regions of the world; however, one of the main concerns in water recycling for indirect potable reuse is the risk resulting

from micropollutants at trace concentrations.5 Micropollutants in wastewater effluents from conventional WWTPs need be

further removed before effluent reuse is possible.

Micropollutants can be removed to certain extents via physical methods, biodegradation and chemical advanced

oxidation.13 Among these technologies, ultraviolet (UV) irradiation and UV-based advanced oxidation processes (AOPs) have

received considerable attention in the past decade. UV is gaining wide application for microbial disinfection in the treatment of

both drinking water and wastewater. In addition to its disinfection effectiveness for inactivating microorganisms, UV can also

degrade organic compounds by direct photolysis as a consequence of UV light absorption or by indirect processes assisted by

the addition of oxidants or photosensitizing agents such as humic substances. In recent years, a number of researchers have

investigated the degradation of selected contaminants by direct UV irradiation or UV-based AOPs. This paper is aimed to

provide a review of the up-to-date research on treatment of micropollutants in water and wastewater by UV-based processes in

the past 10 years, particularly on the studies published in peer-reviewed journals in the last 3 years. Because EDCs and PPCPs

are two major classes of micropollutants that occur ubiquitously in WWTP effluents and subsequently occur in source waters

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for drinking water supply, emphasis will be placed on the degradation of EDCs and PPCPs in water and wastewater by UV-

based processes.

PHOTODEGRADATION OF MICROPOLLUTANTS BY UV IRRADIATION IN LAB-SCALE EXPERIMENTS

Effectiveness in removing micropollutants by direct UV photolysis

UV photolysis has been one of the most widely studied advanced chemical transformation processes for the destruction of

micropollutants. The investigated micropollutants include estrone (E1), 17β-estradiol (E2), 17α-ethinylestradiol (EE2),

bisphenol A (BPA), N-nitrosodimethylamine (NDMA), trichloroethene (TCE), acetaminophen, butylparaben, carbamazepine,

chlorfenvinphos, clofibric acid, cyclophosphamide, diatrizoate, diclofenac, diphenhydramine, ibuprofen, iohexol iopromide,

irinotecan, ketoprofen, metronidazole, naproxen, phenazone, phenytoin, primidone, sulfamethoxazole, tamoxifen, tibetene,

trenbolone etc.. Most of these compounds are EDCs and/or pharmaceuticals. Table 1 summarizes the effectiveness and reaction

conditions for the removal of micropollutants from water or wastewater effluents by direct UV irradiation. In many studies,

direct UV irradiation was used as a control in comparison with UV-based AOPs.

As shown in Table 1, the effectiveness of degradation of micropollutants by direct UV irradiation varied from no

degradation to 100% removal, depending on physicochemical properties of the micropollutants and the UV fluence (dose)

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employed. More specifically, it is the molecular structure that determines the absorption spectrum of a particular

micropollutant, thereby, the quantum yield for conversion of the excited state to a transformed product that determines whether

the micropollutant responds to UV at a given wavelength. The amount of transformation is related to the UV fluence (dose).

Generally, direct UV irradiation at disinfection doses was not effective in removing micropollutants; 18, 23, 28, 34, 45 however,

certain kinds of micropollutants can be effectively degraded at reasonably low doses although they are still higher than the

typical disinfection doses for the treatment of drinking water and/or wastewater. For instance, photodegradation rates of up to

100% were achieved when diclofenac was treated at the UV dose of 230 mJ/cm2, which is about 6 times higher than typically

used to disinfect potable water.38

Factors affecting the removal of micropollutants by direct UV irradiation

Besides the physicochemical properties of micropollutants themselves and the applied UV fluence (dose), the following factors

may affect the degradation efficiency of micropollutants by UV irradiation.

Sources of UV light

The difference in degradation efficiency of EDCs was observed between direct UV irradiation by low-pressure (LP) and

medium-pressure (MP) lamps. LP-UV lamps generate essentially monochromatic radiation at a wavelength of 254 nm; while

MP high-intensity lamps generate polychromatic radiation.64 The efficacy of LP or MP lamps for direct photolysis of

micropollutants varies among compounds with different spectral or physical structures. For instance, direct photolysis of

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NDMA was found to be independent of LP or MP lamp type.65 In contrast, direct photolysis with MP lamps was shown more

effective for degrading BPA, E2 and EE2 as compared to LP lamps.22 It was reported that 14.5%, 17.7% and 21.6%

degradation occurred for BPA, E2 and EE2, respectively, at a UV fluence of 1000 mJ/cm2 from the MP lamp. However, no

more than 5% degradation for all three investigated EDCs was observed using LP lamps. The reason for the low degradation

by LP lamps was that the radiation emitted from these lamps (254 nm) had a very low probability of being absorbed by the

EDCs in the water; i.e., the absorption coefficient was low at 254 compared with the other wavelengths emitted by the MP

lamp. In a more recent study, results confirmed that MP-UV direct photolysis more effectively removed BPA in comparison

with LP-UV lamps.19

pH

A number of studies have shown that degradation rates of certain micropollutants by UV irradiation were pH dependent.35, 44, 55

Lester et al.55 found that the UV photolysis rates of sulphadimethoxine decreased with an increase of pH from 2.5, 6.5 to 10.0.

Similar results were reported in a more recent study by Avisar et al.27 showing that an increase of water pH from 5 to 7 leads to

a decrease in degradation rate of sulfamethoxazole. However, it was found that an increase of water pH from 5 to 7 leads to an

increase in degradation rate of the other two investigated antibiotics oxtetracycline and ciprofloxacin. Another study35 also

showed that the effect of pH on each investigated compound was different. When pH changed from 3 to 9, there was a

significant improvement of removals rates for primidone (4.8% at pH 3 and 9.4% at pH 9), and a very slight improvement for

diatrizoate (91.9% at pH 3 and 96.6% at pH 9). However, the removal rates at pH 3 and 9 were almost the same for

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ketoprophen. The authors explained the difference was due to the reactivity of the compound to UV irradiation. The effect of

pH was less important to the more reactive compound.

In the study by Liu and Liu44, the effect of pH values from 2 to 8 on the photolysis of E1 and E2 was evaluated. The

results showed that the photolysis rates were the lowest at pH value of approximately 5.0. In practice, the pH for the treatment

of wastewater or drinking water may be determined by the process pH that is generally near neutrality.

Temperature

Real et al.35 evaluated the effect of the temperature on the photodegradation of three investigated micropollutants (primidone,

ketoprofen, and diatrizoate sodium) at different pH values (pH = 3.0, 5.0, 7.0 and 9.0). The experiments were conducted at 10,

20 and 40 °C. It was observed that the rate constants increased with the increase of the temperature for all three investigated

compounds under the experimental conditions.

Composition of water matrixes

The co-presence of other substances such as natural organic matter (NOM) with the target micropollutants in water matrixes

could affect the photolysis efficiency of micropollutants by direct UV irradiation. The degradation of micropollutants could

increase in the presence of NOM, primarily due to the production of hydroxyl radicals from reaction of the UV light with

NOM (i.e., a photosensitized reaction). Pereira et al.28 investigated direct photolysis of selected PPCPs in laboratory-grade

water (LGW) and a surface water with 4.2 mgC/L dissolved organic carbon (DOC) using a low-pressure UV batch reactor.

They found the photolysis rate constants of four compounds in surface water were all higher than those in LGW. This was in

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agreement with the observation that the degradation of BPA by solar irradiation in the presence of natural humic substances at

the concentration of 10 mg/L was faster than in pure water.23 Similarly, Neamtu and Frimmel21 reported that the UV

degradation rate of BPA disappearance was slightly higher in wastewater effluent than in purified water, probably due to the

production of reactive oxygen species by various reactions in wastewater effluent between organic molecules and UV light. In

a more recent study, Leech et al.66 reported that the photodegradation of E2 was accelerated by the presence of 2.0–15.0 mg/l

of DOC due to the production of hydroxyl radicals.

Summary

(1) Direct UV irradiation at disinfection dosages was not an effective method to remove most micropollutants, although

some micropollutants, such as boldenone, diclofenac, ketoprofen, sulfamethoxazole can be effectively degraded at reasonably

low dosages (>90% degradation at dose of around 230 mJ/cm2).

(2) The efficacy of LP or MP lamps for direct photolysis of micropollutants varies among compounds with different

spectral or physical structures. Differences in response of different micropollutants by UV irradiation are likely due to the

difference of the absorption spectrum of the various micropollutants and their quantum yield of degradation products.

(3) The optimum pH for degradation of micropollutants by direct UV irradiation could be dependent on the physico-

chemical properties and reactivity of individual compounds.

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(4) Degradation rate constants of certain micropollutants by direct UV irradiation in surface water or wastewater were

found to be slightly higher than pure waters due to the presence of natural organic matter to initiate the production of hydroxyl

free radicals.

DEGRADATION OF MICROPOLLUTANTS IN UV-BASED AOPS

IN LAB-SCALE EXPERIMENTS

A number of researchers have reported that for many compounds, UV as part of AOPs for degrading micropollutants is more

effective than direct UV photolysis treatment.18, 22, 42, 43, 67 AOPs are characterized by the production of hydroxyl radials (·OH),

which are very reactive and able to mineralize intermediate by-products in the final stage of oxidation, although very few

treatments are carried out to such complete degradation as it would be too expensive. Research on the removal of

micropollutants by UV-based AOPs generally falls into two categories: (1) removal effectiveness and optimization of

operational conditions for AOPs and (2) degradation pathways of micropollutants by AOPs. The most investigated AOP

systems were UV/H2O2 and UV/TiO2 processes. Other investigated AOPs include UV/Fenton, UV/O3, UV/O3/H2O2,

UV/H2O2/TiO2, UV/O3/TiO2, UV/HOCl, UV/ClO2 and ultrasound/UV. The ultrasound/UV treatment of micropollutants in

aqueous medium could result in hydrogen peroxide formation and organic and inorganic structure oxidation. In those reactions,

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hydroxyl radical was reported as oxidative reagent.68 Therefore, ultrasound/UV was regarded as a UV-based AOP in this

literature review as well.

Photo-oxidation of micropollutants by UV/H2O2

Hydrogen peroxide (H2O2) is one of the most powerful oxidizers, which is stronger than chlorine and chlorine dioxide.

Irradiated by UV light, H2O2 can be converted into hydroxyl radial (·OH) which possess a high oxidation potential (2.8V) with

reactivity second only to fluorine (3.0V). The formation of ·OH with high redox potential in UV/H2O2 process has led to the

application of UV/H2O2 as a promising process for both water disinfection and oxidation of unwanted contaminants.69 In

recent years, the number of studies on the photo-oxidation of micropollutants in UV/H2O2 process has greatly increased. A

summary of these studies is presented in Table 2. The artificial water refers to Milli-Q/deionized water in the lab spiked with

target compounds.

In terms of removal efficiency and energy consumption, UV/H2O2 process could be a feasible way to remove

micropollutants from drinking water and/or wastewater. Kim et al.61 reported that over 90% removal efficiency could be

accomplished in 39 compounds of the 41 investigated pharmaceuticals by the combination of H2O2 with UV process at UV

dose of 350-923 mJ/cm2. The concentration of H2O2 in UV/H2O2 process could be as low as 5 mg/L to achieve the effective

removal of micropollutants.61, 69, 80

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The performance of UV/H2O2 process for the removal of micropollutants could be affected by experimental conditions,

such as UV light sources (LP and MP), pH and the composition of the water. Chen et al.19 compared the UV-based treatments

of BPA in water with LP and MP lamps via toxicity assessments. The estrogenic activity was quantitatively evaluated by in

vitro yeast estrogen screen (YES) and in vivo Vitellogenin (VTG) assays with Japanese medaka fish. No significant differences

in removal rates between the two lamps under UV/ H2O2 process were reported, although MP-UV direct photolysis more

effectively reduced the concentrations of BPA and associated estrogenic activity compared to LP-UV direct photolysis.

However, in another study29, MP lamps were proved to be more efficient in degrading the selected group of micropollutants by

direct UV photolysis and UV/ H2O2 oxidation. The difference in the impact of LP and MP lamps on the UV/ H2O2 photo-

oxidation of micropollutants likely results from the difference in micropollutants’ spectral and/or physical structures. Different

compounds have various sensitivities to UV photolysis or radical-based oxidation, resulting in the variation of degradation

mechanisms (photolysis and oxidation etc.).

Unlike in the UV direct photolysis of several PPCPs in surface water where the rate constants were slightly higher than in

artificial water, the UV/H2O2 photolysis rate constants obtained in surface water were all lower than in artificial water.28

Similar results were reported by Neamtu and Frimmel 21 showing that the photolysis rate of BPA in the presence of H2O2 was

lower in wastewater effluent than in purified water. The lower efficiency of BPA destruction in wastewater effluent by

UV/H2O2 process was probably due to the competing reaction (scavenging) of hydroxyl radicals by the humic substances and

other scavengers in the water. The overall effect of ·OH radical scavenging from humic acids on the degradation of four PPCPs

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via UV/H2O2 process was investigated in a more recent study.39 It was found that humic acids could act as a ·OH radical

scavenger and hence reduce the destruction rate of PPCPs by UV/H2O2 process.

Most previous studies on the UV/H2O2 oxidation of micropollutants were conducted at near neutral pH conditions.

Olmez-Hanci et al.77 studied the degradation of dimethyl phthalate by UV/H2O2 oxidation at various pH values of 3.5, 6.0 and

9.0. The most effective pH value for the degradation of dimethyl phthalate by UV/H2O2 treatment was found as 6.0. This was

due to the fact that slightly acidic conditions were more suitable for the production of ·OH radicals. In alkaline medium, the

H2O2 becomes highly unstable and rapidly breaks down into water and oxygen. The decomposition of H2O2 reduces its

availability as a source of hydroxyl radicals. Similar results were reported in the study by Ocampo-Pérez etal.34 that the highest

degradation rate of cytarabine after 2 h of irradiation was achieved at pH = 6.0, compared to the degradation rates at pH = 2.0,

4.0, 8.0.

Photo-catalysis of micropollutants by UV/TiO2

Titanium dioxide (TiO2) is a semiconductor which is the most commonly used photocatalyst because it is relatively

inexpensive and readily available. Figure 1 illustrates the primary mechanism of the photocatalytic reaction. When electrons of

TiO2 are promoted by UV light, the electron promotion from valence band to the conduction band can result in the formation

of superoxide radical anion (O2-) and hydroxyl radicals (·OH). These highly reactive oxygen species (ROS) can attack organic

compounds in the presence of or near the surface of TiO2 surface. Additionally, the sites on the TiO2 surface vacated by the

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electrons, termed as “electron holes”, can directly oxidize dissolved compounds such as micropollutants. This photocatalysis

process finally results in the formation of carbon dioxide and water, if the reaction is carried to ultimate completion. This is,

however, rarely needed as the physiological function of the pollutants is reduced by a lesser number of oxidative

transformations. When the TiO2 photocatalyst is irradiated with energy equal to or greater than the band gap, it is thought to

undergo reactions with pollutants described by the following equations: 95

TiO2 + hν → hvb+ + ecb

- (1)

H2O + hvb+ → ·OH + H+ (2)

hvb+ + Pollutant (adsorbed) → Pollutant + (3)

·OH + Pollutant + → CO2 + H2O (4)

O2 + ecb- → O2

- (5)

UV/TiO2 photocatalysis has been proven to remove a variety of organic micropollutants from water or wastewater.

Previous studies on the UV/TiO2 photocatalysis of micropollutants are summarized in Table 3. The majority of previous

studies on the photolysis of micropollutants in UV/TiO2 process were conducted using aqueous solutions prepared with lab

waters. Only a couple of recent studies investigated the photocatalysis of certain micropollutants in wastewater effluents by the

UV/TiO2 process. In the study by Zhang and Zhou, 108 photodegradation aided by a TiO2 catalyst was studied for its removal

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efficiency of EDCs from wastewater. The degradation rate constants for the investigated compounds E1 and E2 were

determined to be 0.01 h-1, which was much lower than those (0.9 -2.7 h-1) from UV photocatalysis. By applying the

photocatalysis treatment to a real WWTP effluent, no target compounds were detected after the treatment. In a more recent

study, 116 a municipal secondary treatment effluent was used as a field sample matrix with comparison to laboratory matrixes

in the study of the photocatalysis of N, N-diethyl-meta-toluamide (DEET) in UV/TiO2 process. The degradation rate constant

for samples in the secondary effluent matrix was shown to be 50% lower than samples prepared in deionized water. The

authors concluded that the decrease in rate was due to the presence of both dissolved organic matter and salts in the

wastewater, which were believed to compete with the oxidation/reduction of target compounds, quench reactive species at the

surface of the TiO2, and prevent efficient charge transfer at the surface by forming at salt layer.

Degradation of micropollutants by other UV-based AOPs

UV-based AOPs can be implemented / facilitated by processes other than UV/H2O2 or UV/TiO2. The processes reported for

the removal of micropollutants include UV/Fenton, UV/O3 UV/O3/H2O2, UV/H2O2/TiO2, UV/O3/TiO2 UV/HOCl, UV/ClO2

and ultrasound/UV. Table 4 listed the studies on the degradation/oxidation of micropollutants in those processes.

Photo-Fenton process is carried out by applying ultraviolet (UV) light to a Fenton process. In a Fenton process, ferrous

ion reacts with hydrogen peroxide to produce hydroxyl radicals. By applying UV light, Fe2+ can be regenerated via photo-

Fenton reaction. Hydroxyl radical is also generated in the reduction process of Fe3+ into Fe2+. Therefore, photo-Fenton process

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facilitates the formation of hydroxyl radicals and is able to promote the degradation and/or oxidation of organic compounds

including micropollutants. It has been found that degradation rates of micropollutants in photo-Fenton process were strongly

influenced by pH, initial concentrations of H2O2 and Fe2+. The weakness of Fenton reactions is that the optimal pH for photo-

Fenton reactions is in the range of 2.5 to 3.0, which are much lower than the process pH for the treatment of drinking water or

wastewater.

The mechanisms of UV/O3 and UV/ultrasound both involve the formation of hydroxyl radicals via photolysis. O3 is a

strong oxidizer and reacts with organic compounds through a direct pathway by molecular ozone and a radical pathway by

means of hydroxyl radicals. The combination of UV radiation with O3 may be a more effective advanced oxidation technique

than using O3 alone for certain target compounds due to the formation of additional H2O2 and •OH radical generation via

photolysis. In the UV/ultrasound process, the propagation of an ultrasound wave in aqueous medium results in the formation of

hydroxyl radicals which are the oxidative reagent in this process.

UV-BASED PROCESSES FOR MICROPOLLUTANTS CONTROL

IN EXISTING/PILOT-SCALE WATER TREATMENT SYSTEMS

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Full-scale application of UV/H2O2 in an existing water treatment plant in North Holland for a running time of more than 2

years has proven that UV/H2O2 treatment was an effective and reliable way to control organic micropollutants. 69 The

optimized conditions for micropollutants control were 6 mg/L H2O2 and UV dose of 540 mJ/cm2, which was much higher than

the dose needed for disinfection in the investigated plant (120 mJ/cm2). Under those conditions, two tested micropollutants

mecoprop and diclofenac were removed by 98%; while the removal of the other 7 compounds varied from 60% to 91%. Figure

2 presents the degradation rates of 4 pesticides and 5 pharmaceuticals using pre-treated lake water under the optimized

conditions. The UV/H2O2 process was installed between the sand filtration and granular activated carbon (GAC) filtration

processes. GAC filters could effectively remove residual H2O2 and at least conceptually, also any byproducts formed in the

oxidation process as well as assimilable organic carbon (AOC) that can feed microbes in biofilm formed within the water

distribution lines.

UV/TiO2 has been shown to be an effective way to remove a variety of micropollutants from water by bench-scale

experiments. However, a major limitation to scaling up this technology is the difficulty in separating and recycling the TiO2

prior to the downstream treatment processes. Benotti et al. 138 reported on a pilot-scale photocatalytic membrane reactor for the

removal of 32 pharmaceuticals and endocrine disrupting compounds in river water. The river water was mixed with

nanoparticle TiO2 and then passes through a reactor with UV lamps aligned in series. After exposure to the UV lamps, the

TiO2-water slurry was separated by a cross-flow ceramic membrane unit. The rejected TiO2 by membranes could be recycled

and reused (Figure 3). Variable removal rates for thirty-two compounds were observed when the unit was operated in UV/TiO2

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mode. Eleven of the 32 compounds were easily removed, with concentrations below detection limits with 0.53 kWh/m3 of

treatment. Conversely, PFOS, tris(2-chloroethyl) phosphate (TCEP), and tris(1-chloro-2-propyl) phosphate (TCPP) were

largely resistant to the photocatalytic membrane reactor with lower than 50% removal at the maximum treatment (4.24

kWh/m3). In addition, the unit was operated in UV only and UV/H2O2 mode to determine the relative amount of energy

required. It was found that the unit achieved the greatest efficiency when operated in UV/H2O2 mode under the tested

conditions.

TREATMENT OF MICROPOLLUTANTS BY UV-BASED PROCESSES

IN EXISTING WWTPS

Most of the previous studies on the fate of micropollutants in UV or UV-based processes were done in the lab by using

aqueous solutions prepared in lab waters, with a few studies using natural river waters or wastewater samples. The fate of

micropollutants in wastewater during UV-based processes has not been well documented. In a study by Cicek et al.139, the

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removal of estrogens in a full-scale WWTP was investigated by sampling at each treatment unit. It was found that the UV

treatment process did not reduce the amount of estrogens. Further research is strongly required to determine the fate of

micropollutants during UV disinfection process in WWTPs. In a recent study evaluating occurrence and treatment efficiency

of five estrogenic hormones and ten beta blockers in WWTPs 140, it was shown that UV could remove 7-30% beta blockers in

secondary effluents.

The reuse of wastewater treatment effluents as an augmentation of a water body utilized for drinking water supplies (a

process known as “indirect potable reuse”) is rapidly gaining attention as a means of achieving a sustainable water supply and

for protection against drought. However, the wastewater effluent must be further treated before recharging into water bodies.

One of the main concerns in indirect potable reuse is the potential health risk resulting from trace micropollutants. 141 Many

micropollutants, such as the nitrosamines (e.g., NDMA), PPCPs, EDCs, and industrial solvents, are not fully removed in

traditional wastewater treatment processes. These chemical contaminants must be removed before the water can safely be

reused.

UV-oxidation process has been demonstrated capable of treating a wide variety of micropollutants for indirect potable

reuse. A particular environmental contaminant of concern is NDMA which is characterized as highly carcinogenic and listed as

a contaminant candidate on the US EPA Drinking Water Contaminant Candidate List 3-Final. Advanced oxidation process

with UV and H2O2 has been implemented in Orange County, California for the treatment of NDMA in wastewater destined for

groundwater replenishment. 142 This is one of the largest water reclamation facilities of its kind in the world using UV/H2O2

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process for micropollutants control. The system effectively reduced NDMA concentration to below the target treatment level

of 10 ppt given an influent concentration of 150 ppt.

A pilot-scale study was conducted to determine the effectiveness of a three-step advanced process (ultrafiltration, reverse

osmosis and UV/H2O2) to produce water suitable for indirect potable reuse from treated wastewater. 143 The project also aimed

to assess the ability of UV/H2O2 to remove selected EDCs and PPCPs. Figure 4 shows the removal rates of 8 spiked

micropollutants by UV/H2O2 process. It was shown that the UV/H2O2 process with 5 ppm H2O2 at an equivalent dose to

achieve 1-log destruction of NDMA achieved greater than 98% removal of all investigated EDCs and PPCPs, with the

exception of tris(2-chloroethyl) phosphate (TCEP).

CONCLUSIVE REMARKS

With the increased awareness of the risks involved with micropollutants in the aquatic environment, control of micropollutants

in drinking water treatment and wastewater treatment (particularly for water reclamation and reuse) processes will be gaining

greater attention in the water industry. UV-based processes may become a feasible and sustainable alternative for

micropollutants control. The main advantage of UV-based processes over other processes, such as activated carbon adsorption,

membrane filtration etc., is that UV-based processes can destroy targeted micropollutants rather than transfer micropollutants

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from one medium to another. For instance, activated carbon adsorption only transfers contaminants in water/wastewater to the

solid phase, but does not destroy them. The disposal of the contaminated carbon requires further treatment.

Although a number of studies have shown that direct UV photolysis at disinfection dosages was not an effective method

to remove most micropollutants, UV-based AOPs have been proven to be efficient for the removal of a variety of

micropollutants in drinking water and/or wastewater. Among those UV-based AOPS, UV/H2O2 process has attracted great

attention as an advanced technology for micropollutants control. One of its main advantages is that UV/H2O2 process is

capable of destroying a great variety of micropollutants and providing simultaneous germicidal disinfection of microorganisms

including Cryotosporidium and Giardia. Full-scale applications of UV/H2O2 in drinking water treatment and water reuse have

demonstrated its effectiveness and feasibility for the control of micropollutants in water and wastewater streams. The public

concern about the impacts of micropollutants on the safety of drinking water and the increasing needs of safe water reuse will

likely facilitate the application of UV/H2O2 process for micropollutants control in drinking water treatment and water reuse.

ACKNOWLEDGMENTS

The authors would like to acknowledge Dr. Bill Cairns and Dr. Mihaela Stefan in Trojan Technologies for their valuable

comments on this literature review.

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Table 1 - Summary of studies on the removal of micropollutants by direct UV photolysis

Target micropollutants UV lamps UV fluence or

irradiation time Degradation efficiency (%) References

Acetaminophen, caffeine, antipyrine, doxycycline, ketorolac

15W LPa mercury lamp (λ=254nm)

0 - 175 min 0 - 100 14

Atrazine diuron, alachlor, pentachlorophenol

LP lamp (λ=254nm) 1500 mJ/cm2 58-86 15

Boldenone 150W MPb lamp < 1min >98 16 UVC lamps (254nm) 50 sec 95 17

BPA 15W LP Hg lamp (λ=253.7nm) 100-5000 mJ/cm2 < 10c 18 1 kW MP lamp 0-5000 mJ/cm2 0-22c 19

UVA, UVB and UVC lamps 0, 100, 500, 1000 mJ/cm2

0-78c 20

15W LP lamp(λ=254nm) 0-120 min 0-25c 21 1 kW MP and 15W LP lamps 1000 mJ/cm2 3c (LP); 14.5 (MP) 22

500W MP lamp(λ>290nm) 0-360 min <6 23 125W lamp (λ≥313nm) 0-160 min No degradation 24

Butylparaben LP UVC lamps 0-90 min 0-99 25 150W MP lamp 0-20 min 0-95 16

LP UVC lamps (254nm) -- -- 26

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Carbamazepine 0.45 kW MP lamp 0-1000 mJ/cm2 0- >99 27

15W LP lamp (λ=254nm) 0-1700 mJ/cm2 <5 28 1kW MP lamp 100 mJ/cm2 minor 29

Chlorfenvinphos 15W LP lamp 0-10 min 0-91c 30 Ciprofloxacine 0.45 kW MP lamp 0-1200 mJ/cm2 0-99 27

Chloromycetin 15W UV lamp (254nm) 0-24 min 0-80a 31 Clofibric acid 10W LP lamp (λ=185nm) 0-30 min 0-100 32

15W LP lamp (λ=254nm) 0-1700 mJ/cm2 0-96 28 Cyclophosphamide 450W UV lamp(λ=254nm) 0-30 min 0-28a 33

Cytarabine MP mercury lamp 120 min 10 34 Diatrizoate 15W LP lamp 10 min 96.6 35

Diclofenac UVC (λ=254nm) 40 mJ/cm2 27 36 400W MP mercury lamp 60 min 95 37

Lamp 1(λ=254nm) and Lamp2 (λ=254nm and 185nm)

230.4 and 232.8 mJ/cm2 100 38

Diphenhydramine 11W LP Hg lamp (λ=254nm) 0-1272 mJ/cm2 0-26.3 39 Doxycycline 15W UVC lamp (254nm) 0-120 min 0-27c 40

E1 UVB lamps 0-480 min 0-83c 41 125W Mercury UVA lamp 0-360 min 0-100d 42

250W metal halide lamp, λ≥313nm

20-160 min Nearly zero 43

30 W Disinfection lamp(254 nm) 10-60 min 48-93c 44 E2 125W Mercury UVA lamp 0-485 min 0-100d 42

30W UV lamp(254nm) 10-60 min 19-60c 44

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1 kW MP and 15W LP lamps 1000 mJ/cm2 5 a (LP); 17.7 (MP) 22

EE2 1 kW MP and 15W LP lamps 1000 mJ/cm2 2a (LP); 21.6(MP) 22 125W Mercury UVA lamp 0-120 min 0-100d 42

250W high-pressure lamp(λ≥313nm)

0-240 min ≤10 45

UV-C (λ=254nm) 40 mJ/cm2 0.4 36 UVB lamps 0-480 min No significant degradation 41

30W UV lamp (254nm) 30 min 64.1-91.6 46 Hydrochlorothiazide 15W LP Hg lamp (λ=254nm) 5 min 30.5-58.9 47

Ibuprofen 11W LP Hg lamp (λ=254nm) 0-1272 mJ/cm2 0-27.4 39 UV (254 nm) and UV/VUV

(254/185 nm) 0 – 60 min 0- 99 48

400W MP mercury lamp 60 min 95 37

Iopromide UV-C (λ=254nm) 40 mJ/cm2 15 36 LP lamp (λ=254nm) 1500 mJ/cm2 90 15

Iohexol 15W LP lamp (λ=254nm) 0-1700 mJ/cm2 0-levels below detection 28 1kW MP lamp 100 mJ/cm2 24 29

Irinotecan 450W UV lamp(λ=254nm) 0-30 min 0-18c 33 Isoproturon LP lamp (λ=254nm) 1500 mJ/cm2 12 15

Ketoprofen 15W LP lamp 10 min >99% 35 UV (254 nm) and UV/VUV

(254/185 nm) 0 – 1.5 min 0- 99 48

Mefenamic acid 15W UVC lamp (254nm) 0-120 min 0-56c 40

Melatonin 8W MP mercury lamp 60 min 18-32 49

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Metoprolol 15W LP Hg vapor lamp 360 min 43-69 50

Metronidazole LP lamp (λ=253.7nm); MP lamp (200-400nm)

5 min 6 (LP) 12(MP)

51

UV-254 lamp and UV-365 lamp 8 h and 24 h 23-98 52

Naproxen 15W LP lamp (λ=254nm) 0-1700 mJ/cm2 0-50 28 1kW MP lamp 100 mJ/cm2 36-50 29

400W MP mercury lamp 60 min 95 37 NDMA --- 10-50 min Fully degraded 53

Norfloxacin 15W UVC lamp (254nm) 0-120 min 0-55c 40, 54 Oxtetracycline 0.45 kW MP lamp 0-2800 mJ/cm2 0-93 27

Phenazone 11W LP Hg lamp (λ=254nm) 0-1272 mJ/cm2 0-95.8 39 Phenytion 11W LP Hg lamp (λ=254nm) 0-1272 mJ/cm2 0-87.8 39

Primidone 15W LP lamp 10 min 9.4 35 Propranolol UV-254 lamp and UV-365 lamp 8 h and 24 h 0-61 52

Sulfadimethoxine 0.45W MP lamp (λ=200-300nm 7000 mJ/cm2 99 55 Sulfamethoxazole UV-C (λ=254nm) 40 mJ/cm2 15 36

10W LP lamp (254nm) 0-40 min 0-100 56 UV lamp(254nm) 60 min 99.4-99.9 57

VUV lamp (90% 254 nm and 10% 185 nm).

40 min 91.2-98.9 57

Hg-Ar lamp (λ= 254 nm) 10 min ~100 58

Tamoxifen 450W UV lamp(λ=254nm) 0-30 min 0-43c 33

TCE LP mercury lamps (λ=254, 300, 350nm)

0-90 min 50-95c 59

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Tibetene 125W Hg lamp(λ=305,313,360 nm)

0-60 min 0-87 60

Trenbolone 150W MP lamp 0-30 min 0-50 16

UVC lamps (254nm) 50 sec 42 17 41 pharmaceuticals 65W LP lamp(λ=254nm) 0-2768 mJ/cm2 18-100 61

30 PPCPs Lamp 1(λ=254nm) and Lamp2 (λ=254nm and 185nm)

230.4 mJ/cm2 (Lamp1) 232.8 mJ/cm2 (Lamp 2)

3-100 (Lamp1) 15-100(Lamp2)

38, 62

7 antibiotics LP lamp (λ=254nm) 3000 mJ/cm2 50-80 63

a - low pressure

b - medium pressure

c - estimated from the figures in references

d - concentrations measured in term of estrogenic activity

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Table 2 - Summary of studies on the photo-oxidation of micropollutants in UV/H2O2 process

Target micropollutants Matrix UV lamp Experimental conditions Reference

Acetaminophen, caffeine, antipyrine, doxycycline, ketorolac

Artificial water and WWTP effluent

15W LP mercury lamp (λ=254nm)

[H2O2]=1.0, 5.0, 10.0 mM; UV irradiation 0 -- 175 min

14

4-Aminoantipyrine Artificial water 15W LP lamp [H2O2]= 0 - 0.392 mol/l ; 70

Anatoxin-a Artificial water LP lamp [H2O2]=30 mg/L; UV dose=250 mJ/cm2 71 Atrazine, sulfamethoxazol, NDMA

Lake water and wastewater

LP mercury lamp [H2O2]=0.2 mM; pH=8; T=20°C; UV dose= 500 -- 11000 J/m2

72

n-Butylparaben, 4-tert-octylphenol

Artificial water LP mercury lamp [H2O2]=0.01M; T=22°C; UV irradiance 11.8 -- 44.4Wm-2

73

BPA, E2, EE2 Artificial water LP- and MP lamps [H2O2]=15/25 ppm; UV dose= 0 -- 1000 mJ/cm2

22

BPA Artificial water LP Hg lamp (254 nm) [H2O2]=10/25/50 ppm; Initial pH=5.3 UV dose = 0 --5000 mJ/cm2

18

BPA Artificial water LP and MP Hg lamp [H2O2]=10/25/50 ppm; room temperature UV dose=0 -- 5000 mJ/cm2;

19

BPA Artificial, surface water and wastewater effluents

15 W LP UV lamp [H2O2]=0.5 mM; 0 -- 120 min irradiation 21

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Carbamazepine Artificial water 17W LP mercury lamp [H2O2]=5.0 mM; pH=5.0; 0 – 60 min irradiation

74

Chlorfenvinphos Natural water 15W LP lamp [H2O2]=2×10-4 M ; pH=7 ; T=20°C 0 -- 180 min irradiation ;

30

Clofibric acid Artificial water and WWTP effluent

10W LP lamp [H2O2]=100 mg/L ; T=10, 20 and 30°C 0-15 min irradiation ;

75

Cytarabine Artificial water MP mercury lamp [H2O2]=0.1 -- 5.0mM ; pH=2-7 34 Diclofenac Artificial water 17W LP lamp [H2O2]=5 mM ; pH = 7.0 ;

0 -- 90 min irradiation 76

Dimethyl phthalate Artificial water LP UV-C lamp [H2O2]=5-40 mM ; 0 -- 60 min irradiation ; pH=3.5/6.0/9.0

77

1,4-Dioxane Artificial water UV-vis lamp (200-400 nm)

[H2O2]=15 mM; 0 -- 60 min irradiation 78

E2, EE2, BPA, NP Artificial and river waters

LP Hg lamps [H2O2]=10ppm; room temperature UV dose=500 -- 2000 mJ/cm2;

79

E2, EE2 Artificial and natural waters

LP and MP lamps [H2O2]=5/10ppm; UV dose= 0 -- 1500 mJ/cm2

80

EE2 Artificial water 30W UV lamp (254nm)

[H2O2]=5, 10, 20, 30, 50 mg/L ; 20-60 min irradiation

46

TCE Artificial water 1 kW MP Hg lamp [H2O2]=10.4 mM; 0 -- 30 min irradiation 81

Melatonin Artificial water 8W MP mercury lamp [H2O2]=3.0, 4.0 mM; pH=3, 4 49

Meprobamate, carbamazepine, dilantin, atenolol, primidone, trimethoprim

Wastewater effluents

LP lamp (254 nm) [H2O2]=0 -- 20 mg/L UV dose = 300, 500 and 700 mJ/cm2

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Methyl-tert-butyl ether (MTBE)

Municipal drinking water

1 kW MP Hg lamp [H2O2]=30 mg/L; UV dose=0 -- 5 kWh/m3

83, 84

Metoprolol Artificial water 15W LP Hg vapor lamp

[H2O2]=0.83, 1.4, 2.8, 5.0 mM 50

Metoprolol, naproxen, amoxicillin phenacetin

Artificial water and natural water

15W LP Hg vapor lamp

[H2O2]=0.05, 0.1 mM ; T=20°C; pH=7 85

Naproxen, carbamazepine, clofibric acid, Iohexol

Artificial and surface water

LP and MP lamps [H2O2]=10 mg/L; UV dose=0 -- 1000 mJ/cm2

28

4-nonylphenol Wastewater 36W LP mercury lamp [H2O2]=10 mg/L 86

Norfloxacin, doxycycline, mefenamic acid

Artificial water 15W UVC lamp [H2O2]=0.59 -- 2.92 mM; T=20°C 54

Ibuprofen, naproxen, diclofenac

Artificial water 400W MP mercury lamp

[H2O2]=1 g/L 37

Ibuprofen, diphenhydramine, phenazone, phenytoin

Artificial water 11 W LP Hg vapor lamp

[H2O2]=0.29/1 mM; pH=7 UV dose=40 mJ/cm2;

39

Paracetamol Artificial water LP UV lamp (254nm) [H2O2]=2.0, 5.0 mM ; pH=5.5 87

Oxytetracycline, doxycycline, ciprofloxacin

Artificial water, surface water and wastewater

11W LP Hg vapor lamp

[H2O2]=0.06, 0.18, 0.29 mM ; pH=8 88

Sulfamethoxazole Artificial water UV and VUV lamps [H2O2]=50 mg/L ; T=20°C 57

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Artificial water 0.45 kW MP lamp H2O2]=5 -- 50 mg/L ; UV irradiation 0-6 min

89

Trialkyl phosphate esters

Artificial water 4 LP Hg UV lamps [H2O2]=6.1/47.1 mg/L; UV dose=0 -- 1000 mJ/cm2

90

30 PPCPs Artificial water 8W LP UV lamps [H2O2]=4.9 mg/L; pH=7; T=20°C 0 – 5 min reaction

62

23 chemicals Natural water LP and MP lamps [H2O2]=10 mg/L ; UV dose 600 mJ/cm2

91

41 pharmaceuticals WWTP effluent LP UV lamps [H2O2]=7.8 mg/L ; HRTa = 5 min 61

16 pharmaceuticals Artificial water -- [H2O2]= 11.03 mM ; T=25 ± 2ºC 92

38 PPCPs WWTP effluent LP UV lamps [H2O2]=1.2/3.1/6.2 mg/L ; HRTa = 5 min

93

30 PPCPs Artificial water and WWTP effluent

8W LP UV lamps [H2O2]=6.0/8.2 mg/L 94

a - Hydraulic retention time

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Table 3 - Summary of studies on the photo-catalysis of micropollutants in UV/TiO2 process

Target micropollutants Matrix UV lamp Experimental conditions Reference

Amoxicillin, ampicillin, cloxacillin

Artificial water

6W UV lamp (365nm) TiO2 in suspensions at 0.5-2.0 g/L; 0-300 min UV irradiation; T= 22±2 °C

97

Amoxicillin, carbamazepine, diclofenac

WWTP effluent

125W black light fluorescent lamp

TiO2 suspension at 0.2, 0.4, 0.8 g/L 98

Benzylparaben Artificial water

125W mercury high pressure UV lamp

TiO2 powder in suspensions at 0.5-3.0 g/L; pH=3 -- 11

99

2,2-Bis(4-hydroxy-3-methylohenyl) propane

Artificial water

250W metal halide lamp (≥365nm)

Nano-TiO2 (particle size 10-20 nm) 100

n-Butyl benzyl phthalate

Artificial water

350 nm black blue fluorescent UV lamps

TiO2 particle in suspension at 0.5-5.0 g/L; T=24±1°C,

101

BPA Artificial water

200W Hg-Xe lamp with a 365nm band-pass filter

TiO2 powder (7nm diameter) in suspensions at 1.0g/L

102

Artificial water

20W black light (359nm) TiO2 immobilized on quartz beads, T=25°C

67

Carbamazepine Artificial water

LP Hg vapor lamp (254nm)

TiO2 suspension at 0.1-2.0 g/L 103

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Clofibric acid Artificial water

MP Hg vapor lamp (intense lines at 254, 313, 366, 405, 436, 546 and 578 nm, with the UV lines below 366 nm being filtered)

TiO2 suspension at 18 mg/L and 1 g/L

104

Diclofenac Artificial water

LP Hg vapor lamp (254nm)

TiO2 concentration 0.5 g/L 105

Artificial water, groundwater and wastewater

9W UVA lamp (350–400 nm)

TiO2 loading 50 -- 1600 mg/L 106

E1, E2 , EE2 Artificial water

125W high pressure Hg TiO2 immobilized on titanium alloy 42

E1, E2 Artificial water

UV lamp (253nm, 238-579nm)

TiO2 at a concentration of 1g/L 107

E1, E2 Wastewater UV lamp (253nm) TiO2 at a concentration of 1g/L 108

E2 Artificial water

Hg-Xe lamp(365nm) TiO2 powder in the solution at 1.0 g/L

109

E2, BPA, 2,4-dichlorophenol

Artificial water

Black-light fluorescent lamps

TiO2 immobilized on PTFE mesh sheets

110

Erythromycin Artificial water

9W UVA lamp (350-400nm)

TiO2 in suspension at 100, 250, 500, 750 mg/L

111

Ibuprofen, clofibric acid, diclofenac, naproxen

Artificial water

150W xenon arc lamp 0.4% TiO2 aqueous suspensions 112

Ibuprofen, carbamazepine

Artificial water

9W UV-A lamp(350-400nm)

TiO2 suspensions at 250 mg/L; UV irradiation 15-120 min

113

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Metoprolol tartrate, Propranolol-HCl

Artificial water

Xe-OP lamp (290–400 nm)

0.05%, 0.2%, 0.4% and 0.5% TiO2 aqueous suspensions

114

Moxifloxacin Artificial water

UV-A (485 W/cm2, main peak at 365 nm)

pH=7; TiO2 concentration (0.25–8.00 g/L)

115

N, N-Diethyl-m-toluamide

Artificial water and WWTP effluent

350nm Hg lamp

TiO2 particle in suspension at 0.25g/L

116

Oxolinic acid Artificial water

black light lamp(<365nm) TiO2 suspension at 0.2-1.5 g/L; pH=7.5-11

117

Oxytetracycline Artificial water

16W UV lamp (254nm) Nano- TiO2 suspension at 1, 5, 10 and 15 wt% loading

118

Paracetamol Artificial water

15W LP UV lamp (254 nm)

TiO2 suspensions at 0.1g/L 119

Artificial water

8W black light UVA lamp, 15W UVC lamp (254nm)

TiO2 suspension at 0.4 g/L 120

Sulfamethoxazole Artificial water

9W UV-A lamp (350–400 nm)

TiO2 suspensions at 250 and 500 mg/L

121

Artificial water

Hg–Ar lamp (λ max = 254 nm)

TiO2 suspension at 0.01 -- 0.5 g/L 58

Sulfonamides Artificial water

4 UV lamps (λmax366 nm) TiO2 powder in suspensions at 2.5g/L

122

Tetracycline Artificial water

15W UV-A lamp and 8W black light lamp

2 mg/L of catalyst TiO2 123

Trimethoprim Artificial water

LP mercury UV lamp (254 nm)

1.25 g/L of TiO2 nanowire membranes

124

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Table 4 - Summary of studies on the degradation of micropollutants in other UV-based AOPs

Target micropollutants AOP UV lamp Experimental conditions Reference

Acetaminophen photo-Fenton UVA (280–200 nm) and UVC (320-400 nm) lamps

H2O2 flow rate=50 mL/h; [Fe(II)]=2 ppm, pH=2.5; T=40 °C,

125

BPA photo-Fenton Xe lamp(>300nm) [H2O2]=0 -- 0.4 mM; [Fe(II)]= 0 -- 0.4 mM; pH=2 -- 4.5

126

E1 photo-Fenton 250W metal halide lamp (≥313nm)

Optimal conditions: [Fe(III)]=20.8µM, [H2O2]=1664µM, pH=3.0

43

E2 photo-Fenton Black light lamps (365nm)

5g/L α-FeOOHR and 9.7mM H2O2 127, 128

Metronidazole photo-Fenton LP (254 nm)and Mp UV lamps

[H2O2]=29.4 µM; [Fe(II)]= 0 -- 11.76 µM; pH=2-4

51

Paracetamol photo-Fenton 8W UV-C lamp (254 nm)

Optimum conditions: pH=3, [H2O2]=60 mg/L, [Fe(II)]= 1 mg/L

129

2,4,6-Trinitrotoluene (TNT)

photo-Fenton LP mercury UV lamps (254 nm)

[H2O2]=0.29 M [Fe(II)]=0.00072 M pH=3.0 130

Doxycycline, norfloxacin

UV/O3 15W LP Hg vapor lamp (254nm)

[O3]=15 ppm, T=20°C 40

E2, BPA UV/O3 Low-pressure mercury UV lamp (254 nm)

0.0076 -- 0.0158 mmol/min O3 pH = 5.25, 6.25

131

40 pharmaceuticals UV/O3 65W LP mercury lamps (254 nm)

[O3]= 6 mg/L; UV fluence 1845 mJ/cm2. 132

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35 PPCPs UV/O3 21.5W and 65W LP mercury lamps (254 nm)

[O3]=2.0, 4.0 ,6.0 mg/L 133

Carbamazepine UV/O3/H2O2 20W UV lamps (254 nm)

[O3]=0 -- 1.2 mg/L; [H2O2]=0 -- 34 mg/L; UV intensity= 0 -- 12.8 mW/cm2

134

Ciprofloxacin, trimethoprim, cyclophosphamide

UV/O3/H2O2 045 kW MP lamp [O3]= 0.5 mg/L; [H2O2]=2 mg/L 135

Amoxicillin, ampicillin, cloxacillin

UV/H2O2/TiO2 6W UV lamp (365nm) TiO2 in suspensions at 1.0 g/L; [H2O2]=50 --300mg/L; T= 22±2 °C

98

Amoxicillin, cloxacillin

UV/H2O2/TiO2 6W UV lamp (365nm) TiO2 in suspensions at 1.0 g/L; [H2O2]=250mg/L; pH=5.0

136

Doxycycline UV/O3/TiO2 15W LP Hg vapor lamp (254nm)

[O3]=15 ppm; 0.5g/L TiO2; T=20°C 40

Desethylatrazine, sulfamethoxazole, carbamazepine, diclofenac, benzotriazole, tolyltriazole, iopamidole, EE2

UV/HOCl and UV/ClO2

40W, 80W and 200W LP lamps (254 nm)

pH=7.0; [HOCl]=0.4-6.1 mg/L; [ClO2]=0.2 – 6.2 mg/L

137

BPA UV/Ultrasound/ /Fe2+

LP mercury lamp (254 nm)

pH=3.0; T= 20°C; Fe(II)]=100 µM 68

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Figure 1. Primary mechanism of photocatalytic reaction. Path 1: formation of charge carries by a

photon. Path 2: recombination to liberate heat. Path 3: production of superoxide by a conduction

band electron. Path 4: production of hydroxyl radical (·OH).95

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Figure 2. Degradation rate of pesticides and pharmaceuticals by UV/H2O2 for drinking water

treatment in pilot-scale experiments; UV dose 540 mJ/cm2, H2O2 dose 6 mg/L 69

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Figure 3. Schematic of a UV/TiO2 photocatalytic reactor membrane pilot system 138

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Figure 4. Removal rates of selected micropollutants by UV/H2O2 for water reuse; UV dose 1104

mJ/cm2, H2O2 dose 5 mg/L 143

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Treatment of Organic Micropollutants in Water and Wastewater by UV-Based Processes: A Literature...

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