A Critical Review

Journal of Cleaner Production 258 (2020) 120694
Contents lists available at ScienceDirect
Journal of Cleaner Production

journal homepage: www.elsevier.com/locate/jclepro
Review
A critical review on application of photocatalysis for toxicity reduction

of real wastewaters
Rueda-Marquez a, *, Irina Levchuk b, Pilar Ferna
Juan Jose ndez Iban
~ ez c, Mika Sillanpa
€a€a
a
Laboratory of Green Chemistry, Lappeenranta University of Technology, Sammonkatu 12 (Innovation Centre for Safety and Material Technology, TUMA),
50130, Mikkeli, Finland
b
Water and Wastewater Engineering Research Group, School of Engineering, Aalto University, PO Box 15200, FI-00076, Aalto, Finland
c
Nanotechnology and Integrated BioEngineering Centre, School of Engineering, Ulster University, Northern Ireland, BT37 0QB, United Kingdom
a r t i c l e i n f o a b s t r a c t
Article history: Advanced oxidation processes (AOPs) such as photocatalysis are widely studied for degradation of
Received 6 November 2019 organic pollutants of contaminants of emerging concern (CECs). However, degradation of organic pol-
Received in revised form lutants leads to formation of by-products, which may be more toxic than parental contaminants. The
18 February 2020
toxicity of wastewater treated by photocatalysis is topical issue. In this review paper recent studies
Accepted 19 February 2020
Available online 22 February 2020
concerned with photocatalytic detoxification of real industrial and municipal wastewater were assem-
bled and critically discussed. Such issues as challenges for application of photocatalytic wastewater
Handling editor. Prof. Jiri Jaromir Klemes detoxification, feasibility of various toxicity tests, reuse of photocatalysts, cost estimation, etc. were
considered. Based on reviewed literature it can be suggested that photocatalysis might not always be a
Keywords: promising treatment method for degradation of organic pollutants in real wastewaters and/or waste-
Real wastewater water detoxification from the application point of view.
Photocatalysis © 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND
Advanced oxidation processes (AOP) license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Toxicity
Bioassays
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Photocatalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Technical challenges and toxicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1.1. Photocatalytic materials and their possible contribution to toxicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1.2. Radiation sources and type of wastewater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1.3. Toxicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Declaration of competing interest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction compounds, pesticides, polycyclic aromatic hydrocarbons (PAHs),

polychlorinated biphenyl (PCBs and other contaminants of
Pharmaceuticals, personal care products, endocrine disrupting emerging concern are present in trace concentrations in industrial
and municipal wastewater effluents (Lara-Martín et al., 2014;
Pintado-Herrera et al., 2014). Wastewater treatment plants do not
provide complete elimination of contaminants of emerging
* Corresponding author.
E-mail address: juan.rueda.marquez@lut.fi (J.J. Rueda-Marquez). concern, which leads to its discharge to receiving environment
https://doi.org/10.1016/j.jclepro.2020.120694
0959-6526/© 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
2 J.J. Rueda-Marquez et al. / Journal of Cleaner Production 258 (2020) 120694
(Gracia-Lor et al., 2012). Even trace concentrations of these con- using following keywords: "photocatalysis", "toxicity", "bioassays",
taminants in aquatic bodies negatively affect aquatic organisms "wastewater". After that the generated literature list was checked
(François et al., 2015; Quinn et al., 2009, 2011). manually (reading materials and methods and results) in order to
Advanced Oxidation Processes (AOPs) are known as promising exclude studies, in which (i) real or synthetic wastewater was not
methods for removal of contaminants of emerging concern from used; (ii) toxicity assessment of wastewater before and after pho-
wastewater effluents. Among AOPs, photocatalysis is widely stud- tocatalytic treatment was not conducted. Moreover, literature re-
ied for wastewater treatment. Thus, during the last ten years, more views were not considered. It should be noticed that only relevant
than 16,000 scientific articles containing "photocatalysis" or articles published during the period 2009e2019 were included to
"photocatalyst" were published (Scopus) and each year the number this review. Moreover, relevant studies found during screening
of publications is increasing. These data are not surprising because other studies were included to the list during literature identifying
the photocatalytic properties of semiconductors are studied for step. The literature search was limited to articles published in peer-
wastewater treatment, surfaces with self-cleaning and antifogging reviewed journals in English language. Reports published in other
properties (Li and He, 2013), purification of outdoor air, indoor air languages as well as books were excluded from the literature
deodorization, cancer therapy, etc. (Rao et al., 2003). Number of search.
scientific publications devoted to photocatalytic wastewater puri- Prepared list of scientific articles was critically analysed through
fication and detoxification is shown in Fig. 1. It is well known that extracting relevant information using the list of questions shown
during photocatalytic decomposition of target pollutants in water, below:
generation of more toxic by-products can occur. Thus, it is of high
importance to evaluate toxicity of treated wastewater effluent. Which type of photocatalytic nanoparticles was used?
Among these, there are also a number of studies investigating the Was the release of ions from photocatalyst studied?
photocatalytic degradation of model pollutants and the toxicity of Was the issue of separation of photocatalytic nanoparticles (in
their TPs (transformation products). Nevertheless, these studies do case these were used) from treated wastewater addressed?
not represent the real scenario of industrial or urban wastewaters Which type of photocatalytic thin films was used?
as they use higher pollutants’ concentrations than found in real Was the detachment of nanoparticles from thin films studied?
cases. In this review, only those studies on detoxification of real Which type of wastewater was used?
wastewater (urban or industrial) are considered. By contrast, all Which irradiation source was applied for photocatalytic
studies focused on reduction of toxicity by photocatalysis in model wastewater treatment?
solutions were excluded from this review. The aim of this work is to Was the pre-treatment of wastewater, for instance pH modifi-
systemize and analyse research results on detoxification of real cation, performed prior photocatalytic treatment?
industrial and municipal wastewater (IWW and MWW) by photo- Which type of toxicity tests were applied?
catalysis, with implications in the toxicity effects (see Table 1). Was the toxicity assessment conducted during photocatalytic
treatment of wastewater?
What was the scale of performed experiments?
2. Method
Was the intensity of irradiation source available?
Was the treatment time realistic, applicable in real world cases?
The methods applied in this literature review included identi-
Was the sensitivity of toxicity tests compared?
fication of the relevant studies and preparing set of questions to be
Was the issue of photocatalyst reuse addressed?
addressed to selected literature relevant to the scope of this review.
Identification of relevant literature was performed by searching in
Science Direct, Scopus and Google Scholar and NCBI databases
Fig. 1. Number of scientific publications per year containing keywords (Scopus): "Photocatalysis", "wastewater" and "toxicity" in the title and/or keywords of article (blue). Number
of articles in which real wastewater matrix was used (orange). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this
article.)
J.J. Rueda-Marquez et al. / Journal of Cleaner Production 258 (2020) 120694 3
Table 1
Toxicity bioassays applied for assessment of wastewater detoxification after photocatalysis, photocatalytic ozonation and photocatalysis-based AOPs.
AOP Process and Experimental conditions Type of the water Toxicity assessment Main outcomes
Reference
TiO2 photocatalysis Laboratory scale (UVC 20 W/m2; Real pharmaceutical industry WW. E.Coli DH-a strain (Kirby- Based on toxicity assessment it was
(Talwar et al., 2018) commercial TiO2 (Degussa) COD 12425 mg/L; BOD 1727 mg/L; Bauer method suggested that photocatalytically
Optimal conditions: TiO2 0.6 g/L, pH
pH 5.8; TDS 1600 mg/L; TSS treated pharmaceutical wastewater
3.2, time 455 min 3180 mg/L; TS 4780 mg/L; BOD5/ was not toxic.
COD 0.178.
TiO2 photocatalysis Laboratory scale (UVA-LEDs 375 W/ Municipal WW effluent spiked with Vibrio fischeri Vibrio fischeri bioluminescence
(Degussa P25) m2; TiO2) ibuprofen (6 mg/L, 6 mg/L or 213 mg/ inhibition rate of municipal (spiked
Jallouli et al. (2018) Optimal conditions: natural pH and L): DOC 215 mg/L; pH 7.3; with 213 mg/L of ibuprofen) and
TiO2 loading 2.5 g/L for both conductivity 610 mS/cm. pharmaceutical WW before
municipal and pharmaceutical Pharmaceutical industry WW was photocatalysis was 78.3% and 73.9%,
wastewater also used: DOC 170 mg/L; pH 7.9; respectively. After 240 min of
conductivity 3770 mS/cm; (optimal conditions) toxicity of both
concentration of ibuprofen 213 mg/ types of water significantly
L. decreased leading to inhibition rates
of 40.8% and 30.3% for municipal and
pharmaceutical WW,
correspondently.
TiO2 photocatalysis (Vela Pilot scale (CPC plant; commercial Sewage WW effluent spiked with Vibrio fischeri Initial value of Vibrio fischeri
et al., 2018b) TiO2: Degussa P25 and Krono vlp malathion, fenotrothion, inhibition (60%, untreated
7000). quinalphos, vinclozoline, wastewater) dropped to 27 ± 6%
Optimal conditions: TiO2 200 mg/L dimethoate, fenarimol phtalate (after treatment with vlp 7000) and
and Na2S2O8 250 mg/L. (0.3 mg/L of each one). COD 33.1 mg/ 15 ± 4% (after treatment with P25)
L; DOC 10.8 mg/L; BOD5 5 mg/L; SS after 240 min. For both
3.6 mg/L; turbidity 1.1 UNT; pH 7.2. photocatalysts significant increase
of toxicity was observed after about
90 min of treatment, which was
associated with generation of some
stable intermediates.
TiO2 photocatalysis Laboratory scale (MP lamp intensity Treated WW from citrus fruit Ames test (S.typhimurium High level of genotoxicity was
(Saverini et al., 2012) of irradiation reaching solution (320 transformation factory was used for strain TA100), viability of V79 observed for both types of WW
e390 nm) 10 mW/cm2; photocatalytic experiments TOC Chinese hamster cells and (before and after treatment with
TiO2:Degussa P25) 21 mg/L. Comet assay activated sludge). Results of Comet
Optimal conditions: TiO2 0.4 g/L, assay demonstrated that 30% of
V79 cells (after 1h treatment with
100 mL of wastewater) were
damaged. Exposure of
S.typhimurium to water samples
collected within 2h of photocatalytic
test indicate relatively high level of
genotoxicity, which significantly
decreased after 2h of photocatalysis.
TiO2 coated sand (He Laboratory scale (Xenon lamp 159 Effluent from urban WWTP spiked Pseudokirchneriella Spiked PhACs inhibited growth of all
et al., 2016) lux) with PhACs (propranolol, diclofenac, subcapitata, tested microorganisms, among
Optimal conditions: depth of water carbamazepine, ibuprofen with Anabaena flos-aquae and which green algae was the most
column 0.1 m and 96 h of concentration 5 mg/L each). BOD Vibrio fischeri sensitive (almost 100% of inhibition
irradiation. 6 mg/L; COD 35.2 mg/L; DOC before treatment).After 96 h of
12.2 mg/L; pH 7.3. treatment, growth inhibition of
green algae decreased from almost
100%e60%. Significant toxicity
decline was observed for blue-green
algae (from 70% of growth inhibition
to 20%). No significant changes of
Vibrio fischeri growths inhibition
were observed during and after
treatment.
Photocatalysis with TiO2 Laboratory scale (mercury vapor Textile mill WW effluent Daphnia similis Based on results obtained with
and TiO2 modified lamp; TiO2 and HT/Fe/TiO2). Optimal (secondary). COD 78 mg/L; DOC D. similis the toxicity of wastewater
with hydrotalcite and conditions: TiO2 (2 g/L and pH 4) and 25.7 mg/L; turbidity 15 TU; pH 9; effluent was relatively low (EC50
iron oxide (HT/Fe/ HT/Fe/TiO2 (2 g/L and pH 10) conductivity 1608 mS/cm. 70.7%). After photocatalytic
TiO2) treatment with TiO2, the toxicity of
Arcanjo et al. (2018) effluent decreased and EC50 was
95%. Interestingly, when HT/Fe/TiO2
was applied, the toxicity of treated
effluent was higher (EC50 78.6%)
than in case of TiO2.
ZnO photocatalysis (Vela Pilot scale (CPC plant; UVC, UVB, Sewage WW effluent spiked with Vibrio fischeri The inhibition of V. fischeri exposed
et al., 2018a) UVA, VIS þ NIR were 0.2 ± 0.1 W/m2, endocrine disruptors. COD 33.1 mg/ to WW before treatment was 70%.
2.1 ± 0.6 W/m2, 29.2 ± 4.1 W/m2, L; DOC 10.8 mg/L; BOD5 5 mg/L; SS Slight increase of V. fischeri
1011.6 ± 66.2 W/m2, 3.6 mg/L; turbidity 1.1 UNT; pH 7.2. inhibition was detected after
respectively).Optimal conditions: 30 min. After solar photocatalysis at
ZnO 200 mg/L and Na2S2O8 250 mg/ optimal conditions (240 min)
(continued on next page)
Table 1 (continued )
Reference
L. Concentration of oxygen 8 inhibition of Vibrio fischeri

e10 mg/L. significantly decreased (11 ± 5%).
ZnO photocatalysis Laboratory scale (mercury vapor Effluent from leather industry Artemia salina L. The LC50 of Artemia salina L. was
(Hasegawa et al., 2014) lamp 1850 mW/cm2; ZnO). (filtered and diluted in distilled 14.9% after 24h of exposure to raw
Optimal conditions: ZnO 1 g/L; pH 8.0 water). COD 15 023 ± 60 mg/L; TOC wastewater. After photocatalytic
and irradiation time 4h. 4685 mg/L; BOD5 4374 ± 0.1 mg/L; treatment at optimal conditions the
turbidity 331.0 ± 0.02 NTU; pH LC50 was 56.82%. Results indicate
3.5 ± 0.7. that toxicity of wastewater was
decreased after photocatalysis with
ZnO.
TiO2 and ZnO Laboratory scale (16 UVA lamps Two WW effluents from dyeing and Daphnia magna When TiO2 was applied for
photocatalysis (Çifçi 5.62 mW/cm2; TiO2 and ZnO) finishing textile industry (WW1 and treatment of WW1 at optimal
and Meriç, 2015) Optimal conditions: TiO2: pH 5, TiO2 WW2). WW1: total COD conditions, the toxicity of water
2 g/L, reaction time 3h; ZnO: pH 9, 370 ± 74 mg/L, soluble COD drastically increased at 120 min of
ZnO 2 g/L, reaction time 3h. 230 ± 15 mg/L, TOC 61 mg/L, pH contact time. This was attributed to
7.94, conductivity 5.15 mS/cm, formation of long chain byproducts
alkalinity 436 mg CaCO3/L. WW2: after decomposition of aromatic
total COD 90 ± 9 mg/L, soluble COD compounds. After 180 min no
70 ± 4 mg/L, TOC 60 mg/L, pH 7.65, toxicity was observed. When ZnO
conductivity 4.50 mS/cm, alkalinity was used for treatment of WW2 at
246 mg CaCO3/L. optimized conditions, slight
increase of toxicity occur at 150 min
of reaction (similar reason as in case
of TiO2). No toxicity was detected
after 180 min of photocatalytic
treatment.
Photocatalysis with TiO2, Laboratory scale (mercury vapor Textile effluent from jeans industrial Artemia salina Values of LC50 of Artemia salina
ZnO and Nb2O5 (Souza lamp; TiO2 Kronos, TiO2 Degussa laundry. COD 558.50 ± 5.05 mg/L, before and after photocatalytic
et al., 2016) P25, ZnO Dynamic and Nb2O5, BOD5, 20 170 mg/L, turbidity treatment (300 min, pH 3 and
BCMM). 113.0 ± 2.7 NTU concentration of photocatalyst
Optimal conditions: pH 3, 0.25 g/L) were as follow: Effluent:
concentration of photocatalyst 27.59%; TiO2eP25: 90.86%; TiO2
0.25 g/L, 300 min Kronos: 61.62%; ZnO: 66.56%;
Nb2O5: 77.52%. Results indicate that
toxicity of textile wastewater
effluent significantly decreased after
photocatalytic treatment.
Photocatalysis with Laboratory scale (300 W Osram Textile WW. COD 1111.04 mg/L; Artemia salina. Results demonstrated 96.7% of
polypyrrole (Lima lamp 108 kJ/m2s; polypyrrole) TOC 156.75 mg/L. Artemia survival after treatment,
et al., 2015) Optimal conditions: polypyrrole indicating that treated water is
5 mg/mL; 120 min relatively not toxic. Interestingly
toxicity tests were not shown for
wastewater before treatment.
Photocatalytic ozonation
O3/UV/TiO2 (Tichonovas Laboratory scale (LP lamp; TiO2 Furniture industry WW after Daphnia magna TiO2/UV/O3 process (most efficient):
et al., 2017) (Aeroxide P25, Evonik) deposited on primary treatment. WW diluted mortality (%) of Daphnia magna for
glass rods; O3 concentration 1.3 mg/ 124.4 times: TOC 50 mg/L; COD initial wastewater was 13% after
L, air flow rate 11 L/min) 130 mg/L; conductivity 186 mS/cm; 72h. It drastically increased during
The best conditions among tested pH 6.7 treatment, thus, reaching almost
AOPs: the most efficient AOPs were 100% (48h and 72h) from 20 to
as follows TiO2/UV/O3 ˃ UV/O3 ˃ TiO2/ 40 min. During 80e100 min,
UV. The mortality drastically decreased
reaching zero after 60 min (24h of
exposure), 100 min (48h of
exposure) and about 13% of
mortality after 100 min for 72h of
exposure.
UV/O3/ZnO (Biglari et al., Laboratory scale (UV lamp 254 nm, WW effluent (pulp and paper Daphnia It was reported that treated
2017) 1020 mW/cm2; ZnO) industry). COD 4751 mg/L, BOD wastewater was safe based on
Optimal conditions: ZnO 0.1 g/L, pH 386 mg/L, pH 6.2e8.7, iron 0.28 mg/ conducted toxicity assessment with
5, O3 9.2 mg/min, irradiation time L, bicarbonate 280 mg/L, phenol daphnia.
30 min. 61 ± 2 mg/L
UV and solar Laboratory scale (MP lamp and sun; Secondary WW effluent (spiked MTT assay with Vero cells Significant toxic effect was observed
photocatalytic TiO2 and modified TiO2 with 5000 mg/L of phenol). pH 6.8, for untreated WW effluent (cell
ozonation (Mecha photocatalysts) COD 42 mg/L, DOC 20 mg/L. viability 28.7%). After application of
et al., 2017) photocatalytic ozonation the
toxicity significantly decreased,
leading to cell viability of 76% (UV/
O3/TiO2) and 80% (UV/O3/TiO2eFe).
After solar photocatalytic ozonation
the cell viabilities were 58% (solar/
O3/TiO2) and 69% (solar/O3/TiO2
eFe).
Reference
O3/H2O2 Laboratory scale (gas flow 0.19 N/ Effluent from secondary clarifier Pseudokirchneriella P. subcapitata bioassay: the toxicity
O3/UV m3h, O3 concentration 22 g/Nm3; LP from municipal WWTP spiked with subcapitata, Vibrio fischeri and increased after 15 min of treatment
O3/Xe/CeeTiO2 (6.01 ± 106 E/L) and Xe-arc 500 ng/L of galoxilide and tonalide Daphnia magna by photolysis (UV and Xe lamps), O3/
O2/Xe/CeeTiO2 (1.05 ± 106 E/L) lamps) was used. pH 7.79, COD 28 mg/L, H2O2 and Xe/CeeTiO2
(Santiago-Morales Optimal conditions: H2O2 (when NPOC 8.1 mg/L, CaCO3 219 mg/L. photocatalysis. After 15 min of O3,
et al., 2012) applied) 30 mL/L, concentration of O3/UV and O3/CeeTiO2 treatment,
photocatalytist (when applied) toxicity of water decreased. Daphnia
200 mg/L magna: For all tested processes
toxicity decreased. Immobilisation
observed in raw WW was about 15%,
after majority of tested processes
this value was about 5%. Vibrio
fischeri: Toxicity of waster increased
after 15 min of photolysis and Xe/Ce
eTiO2 process. Decrease of toxicity
was observed after applied O3/UV,
O3/Xe and O3/CeeTiO2.
Hybrid photocatalysis-based processes
Combination of Laboratory (UVA lamps 23 ± 2 W/ Real effluent from pharmaceutical E.coli (The Kirby-Bauer The Kirby-Bauer method: The
photocatalysis, photo- m2) and pilot scale experiments industry. COD 4800 mg/L; BOD method) and zebra fish. biggest inhibition zone against E.coli
Fenton and iron oxide (mean intensity of solar UV þ Visible 830 mg/L; TDS 1320 mg/L; TSS was reported for untreated WW.
catalysis using Fe light 788W/m2) 620 mg/L; turbidity 742 NTU; pH During treatment, the inhibition
eTiO2 composite beds Optimal conditions: H2O2 dose: 5.07; chloride 25 mg/L; sulfate zone was decreasing, which
(Bansal et al., 2018) 1155 mg/L, pH 3e3.5, process time 526 mg/L. corresponds to decrease of toxicity.
6h and dose of FeeTiO2 equal to Zebra fish bioassay: After 96h of
102% area of reactor bed covered bioassay zebra fish survival level
with composite beds (under was 100. The zebra fish toxicity
artificial radiation source). assay was not conducted for
untreated wastewater.
Solar-induced Fenton- Bench (UVA lamp 1.232$104 E/min) Synthetic effluent simulating the Vibrio fischeri, Sorghum V. fischeri (5 min): 87% of inhibition
assisted TiO2 and pilot scale (solar radiation) actual grey WW. DOC 93 mg/L; pH saccharatum, Lepidium (before treatment) and 10% (after
photocatalytic hybrid Optimal conditions: TiO2 0.5 g/L, 3.36; conductivity 47.6 mS/cm sativum, Sinapis alba 247.34 min); V. fischeri (15): 91% of
3þ
process H2O2 0.5 g/L, Fe 0.0035 g/L inhibition (before treatment) and
(Tsoumachidou et al., 18% (after 247.34 min). The EC50
2017) values (15 min) significantly
increased during treatment process.
Sinapis alba was more sensitive to
raw wastewater than other tested
plants.
TiO2/UV and Fe2O3/UV Laboratory scale (UV lamp with Bleach kraft pulp mill secondary Vibrio fischeri Kraft pulp mill effluent: toxicity of
TiO2/H2O2/UV and Fe2O3/ emission peak at 312 nm; WW effluent: COD 391 ± 2 mg/L, pH water after photocatalytic treatment
H2O2/UV (Nogueira commercial TiO2 and Fe2O3). 8.8 ± 0.05. Acid mine drainage: pH with TiO2 (0.5 g/L and 0.75 g/L) and
et al., 2017) Optimal conditions: for pulp mill 2.58 ± 0.07, S 402.3 ± 1.8 mg/L, Cu Fe2O3 (0.25 g/L and 1.0 g/L) slightly
effluent: pH 3.0, TiO2 0.75 g/L; Fe2O3 1.0 ± 0.05 mg/L, Zn 48.0 ± 1.6 mg/L, decreased. But the increase of
0.75 g/L, concentration of H2O2 As 1.2 ± 0.15 mg/L, Al 74.0 ± 0.7 mg/ toxicity was observed when other
75 mM). For mining WW: TiO2 1 g/L; L, Pb 13.5 ± 1.05 mg/L, Cd concentrations of TiO2 (0.25 g/L and
Fe2O3 1 g/L. 56.2 ± 1.5 mg/L 1.0 g/L) and Fe2O3 (0.5 g/L and
0.75 g/L) were applied. Photocatlysis
in combination with H2O2 was more
efficient for removal of toxicity with
best results attributed to Fe2O3 and
75 mM of H2O2. Mining effluent:
toxicity decreased when
photoctalytic treatment was applied
using TiO2 and Fe2O3. Addition of
H2O2 led to decrease of toxicity,
except in case of 5 min exposure
when toxicity increased.
Solar photocatalysis and Pilot scale (average UV intensity Municipal WW effluent after Vibrio fischeri, Daphnia magna, The EC50 values obtained for
photo-Fenton (Brienza 70 W/m2) biological treatment. TOC Pseudokirchneriella V. fischeri, D. magna, P. subcapitata,
et al., 2016) Optimal conditions: TiO2 (Evonik 26.3 ± 0.6 mg/L; conductivity subcapitata, Brachionus and B. calyciflorus for initial WW
P25)0.7 g/L; solar photo-Fenton was 669 ± 21 mS/cm; pH 7.2 ± 0.2. calyciflorus, estrogenic tests were 80%, 90%, 98% and 90%,
conducted with 100 mM of iron (HELN ERa cell line); In vitro respectively (non-toxic). Estrogenic
sulfate, 200 mM of monopersulfate genotoxicity assessment (LS activity was detected in raw WW
and sulfuric acid (initial pH of water 174T cell line) even when estrogen was not
was adjusted to 2.6). possible to analyse by chemical
analysis. Estrogenic activity did not
decrease after solar photolysis,
while after photocatalysis and
photo-Fenton it was reduced.
Genotoxicity before and after
applied treatments was not
detected.
(continued on next page)
Reference
Catalytic ozonation
Heterogeneous catalytic Laboratory scale Lurgi coal gasification WW after Daphnia magna Changes in acute toxicity were
ozonation (Zhuang Optimal conditions: sewage sludge biological treatment was used. COD monitored on the course of catalytic
et al., 2014) based AC impregnated with Mn and 130e180 mg/L, BOD5/COD 0.05 ozonation. Residual ozone was
Fe (1 g/L) and ZnCl2 as activation e0.07, TOC 45e60 mg/L, eliminated before toxicity
agent was used. O3 flow 500 mL/ bicarbonate 40e60 mg/L, pH 6.5 assessment. Inhibition rate observed
min, O3 concentration 15 mg/L. e7.5. for WW prior catalytic ozonation
was about 65%. Toxicity was
decreasing during treatment
reaching highest detoxification
(15%) with Mn impregnated
catalyst. During zonation slight
increase of toxicity was detected in
the beginning of the treatment.
Catalytic ozonation was more
efficient than ozonation for
wastewater detoxification.
Heterogeneous catalytic Catalyst: iron shavings (38CrMoAl WW effluent from dyeing and Photobacterium phosphoreum The inhibition of bacteria for
ozonation (Wu et al., steel) 20 g/L; O3 10.8 mg/L finishing industry. COD 142 ± 6 mg/ wastewater effluent before catalytic
2016) L, DOC 44 ± 1 mg/L, BOD5 ozonation was 51%, whereas after
1.0 ± 0.5 mg/L, pH 7.37 ± 0.14. treatment it was 33%. Results
suggested decrease of wastewater
effluent toxicity.
Heterogeneous catalytic Pilot scale (catalyst: iron shavings). WW effluent from dyeing and Photobacterium phosphoreum After treatment of wastewater by
ozonation (Ma et al., Optimal conditions: O3 dosage 10.2 finishing industry. COD catalytic ozonation at optimal
2018) O3/min, hydraulic retention time 165 ± 20 mg/L, DOC 76 ± 6 mg/L. conditions, the toxicity slightly
30 min. decreased. Thus, the inhibitory
effect for untreated wastewater was
29.3 ± 3% and for treated affluent
25 ± 2%
3. Photocatalysis of oxidation and reduction reactions on the surface of photo-

catalytic material. The increase or decrease of the reaction rate is
Usually photocatalysis is defined as the chemical reaction often associated with an enhanced or suppressed electron-hole
induced by the absorption of photons by solid material (photo- recombination, respectively (Ohtani, 2013). According to a recent
catalyst) (Ohtani, 2011). However, there is still some debate review in the field (Ohtani, 2013), no direct evidence of electron-
regarding the definition of the photocatalytic process (Mills and Le hole recombination during photocatalytic process was presented
Hunte, 1997). It should be mentioned that the photocatalyst does so far.
not undergo any chemical changes during and after the reaction. In Photocatalytic ozonation takes place in the presence of photo-
the literature, the term "photocatalyst" is often used interchange- catalyst, UVevis radiation and ozone. Aside from occurring pho-
ably with term "catalyst". It can be probably explained by the fact tocatalytic reaction, caused by the photoexcitation of the
that some photocatalytic materials are sometimes used in catalytic photocatalyst’s surface, molecules of ozone adsorbed on the surface
reactions as catalysts. However, in terms of thermodynamics, the of photocatalyst. This leads to the formation of active oxygen rad-
concept of catalysis and photocatalysis is different. Thus, energy- icals. It was demonstrated that water molecules react with active
storing reactions can be driven by photocatalysis (DG>0) while oxygen radicals to form hydroxyl radicals (Huang and Li, 2011).
catalysis is limited to thermodynamically possible reactions (DG<0) Moreover, active oxidising species are produced when ozone ab-
(Ohtani, 2010). The reaction rate (absolute or relative) of the pho- sorbs a wavelength shorter than 300 nm (Mehrjouei et al., 2015).
tocatalytic process is usually referred as photocatalytic activity
(Ohtani, 2011). Usually five steps are distinguished during photo- O3 þ hv / O þ O2 (1)
catalysis (Herrmann, 1999):
transfer of pollutants to the photocatalyst’s surface; 3.1. Technical challenges and toxicity
adsorption of pollutants on the surface;
photonic activation and decomposition of adsorbed molecules; A plethora of studies has been conducted on the photocatalytic
reaction product’s desorption; treatment of wastewater effluents at lab and pilot scale (Berberidou
removal of reaction products from the photocatalyst’s surface. et al., 2017; Karaolia et al., 2018; Levchuk et al., 2015; Spasiano et al.,
2015; Talwar et al., 2018). In many cases, the complete minerali-
The main principle of photocatalysis can be explained according sation of pollutants present in wastewater was not achieved and/or
to the widely accepted theory. The electron-hole pairs are gener- was not expected. In such cases, conventional chemical analysis,
ated when photocatalytic material is exposed to the light with which allows to detect and quantify target compounds and their
equal or larger energy than that of photocatalyst’s band gap. by-products, is limited because it is neither able to evaluate the
Formed electron-hole pairs dissociates into electrons (e) in con- possible toxicity of the formed compounds nor their potential
duction band and holes (hþ) in valence band. The e and h þ lead to synergetic effect. Therefore, a toxicity assessment is of crucial
the reduction and oxidation of molecules adsorbed on the surface importance when wastewater is treated by photocatalysis, espe-
of photocatalytic material. Nevertheless, the electron-hole recom- cially if the complete mineralisation of contaminants is not an
bination often takes place, which may lead to the non-occurrence objective.
3.1.1. Photocatalytic materials and their possible contribution to is the photocatalyst’s efficiency loss during its reuse (deactivation)
toxicity reported by various researchers (Li et al., 2009; Ollis, 2000; Sun
3.1.1.1. In the form of powder. In the majority (˃60%) of studies et al., 2003). The deactivation of a photocatalyst can be reversible
devoted to the photocatalytic detoxification of real wastewater, and irreversible (Sauer and Ollis, 1996). As suggested by Ollis
TiO2 in the form of nanoparticles was used as an aqueous suspen- (2000), the probable reasons for deactivation are: (1) accumula-
sion in the contaminated water, also called ‘slurry’. This can be tion of resistance to photocatalysis by-products on the surface of
explained by the fact that TiO2 possess almost all the characteristics photocatalyst and (2) generation of surface species possessing
of ideal photocatalytic material (Carp et al., 2004) and it is one of higher adsorption capacity than reactants. The deactivation of
the most studied materials for photocatalytic applications. The photocatalyst is usually not observed when experiments are con-
nanoparticles of ZnO were applied for photocatalytic wastewater ducted with model pollutants in water (Ahmed and Ollis, 1984; Al-
treatment in less than 25% of the studies reviewed in this article. Sayyed et al., 1991; Hidaka et al., 1986; Levchuk et al., 2016a,b). For
ZnO was widely studied for photocatalytic applications, it benefits instance, the deactivation of TiO2 was not observed after 14 cycles
from relatively high photocatalytic activity, easy production pro- of the photocatalytic degradation of 2,4,5-trichlorophenoxyacetic
cess, low cost, environmentally friendliness, etc. (Qi et al., 2017). acid (Barbeni et al., 1987). However, in more complex water ma-
However, the possible photocorrosion of ZnO should be mentioned trix and/or in the presence of salts (for instance, coagulants), the
as an important drawback (Kudo and Miseki, 2009). Interestingly, deactivation of photocatalyst occurs (Ferna ndez-Iba n
~ ez et al.,
the photodissolution of Zn was reported during the photocatalytic 2003). Only in 17% of articles on photocatalytic detoxification and
treatment of sewage wastewater effluent with ZnO and it was also purification of wastewater, photocatalytic activity during the reuse
suggested to be one of the factors leading to the increase of toxicity of materials was studied. For instance, Arcanjo and co-authors have
(Vibrio fischeri bioassay) (Vela et al., 2018a). Thus, the elevated reused HT/Fe/TiO2 five times for textile wastewater effluent treat-
toxicity was observed when the highest concentrations of Zn2þ ment and observed approx. 17% of its efficiency loss (based on color
(186 ± 8 mg L-1) were detected in treated water (Vela et al., 2018a). removal) (Arcanjo et al., 2018). The photocatalytic activity of
In comparison with ZnO, the dissolution of Ti4þ in similar waste- FeeTiO2 composited beds was reported to be very similar even
water was reported to be significantly lower (6.1 ± 1.3 mg L-1). These after 70 cycles (based on COD removal) of the hybrid photocatalysis
results are in agreement with other studies, which have demon- process (Bansal et al., 2018). Lima and co-authors (Lima et al., 2015)
strated that dissolution of metal from metal-containing nano- reported the deactivation of polypyrrole of approx. 67% after six
particles can play key role in enhancement of their toxicity (Boyle cycles of textile wastewater decontamination. Interestingly, when a
and Goss, 2018; Brunner et al., 2006; Franklin et al., 2007; polymer was washed with HCl solution after reaction, the efficiency
Ka€kinen et al., 2016, Wang, et al., 2009). It should be noted that the loss was significantly lower (approx. 16% after six cycles) (Lima
dissolution and/or photodissolution of photocatalysts is not often et al., 2015). It should be noted that there are only few studies
monitored during treatment; while it is an important parameter concerned with such an important topic as the regeneration of
which can significantly affect the toxicity of the water especially if photocatalytic materials. The following strategies were tested for
toxic metals such as cadmium are used for the synthesis of pho- the regeneration of photocatalysts used for water/wastewater
tocatalysts. It is noteworthy that TiO2 was demonstrated to be more treatment:
efficient for the reduction of toxicity (based on Artemia salina
bioassay) of textile wastewater effluent than ZnO (Souza et al., alkaline treatment (NaOH and NH4OH) (Miranda-García et al.,
2016). Moreover, TiO2 P25 was reported to be more efficient for 2014);
the elimination of toxicity (Vibrio fischeri bioassay) of sewage thermal regeneration (Carp et al., 2004);
wastewater effluent than other commercially available TiO2 (Vela exposure to UV in aqueous media or air (Wang et al., 2015);
et al., 2018b). It can be expected that more studies will focus on oxidation of by-products bounded to the surface by H2O2/UV
comparison of various photocatalysts for toxicity elimination in the (Miranda-García et al., 2014);
future. Besides TiO2 and ZnO, rather few photocatalysts were tested washing with deionised water (Kabra et al., 2004);
in the last ten years for the reduction of wastewater toxicity such as refluxing in water at 100 C with oxygen bubbling (Pan et al.,
TiO2 modified with hydrotalcite and iron oxide (Arcanjo et al., 2013).
2018), polypyrrole (Lima et al., 2015), Nb2O5 (Souza et al., 2016),
Fe2O3 (Nogueira et al., 2017), graphitic carbon nitride (Moreira Miranda-García and co-authors compared the thermal, alkaline
et al., 2019). and H2O2/UV approaches for the regeneration of immobilised TiO2
Despite the relevantly high efficiency of photocatalysts used in (based on photocatalytic degradation of emerging pollutants)
the form of dispersed powder for the degradation of emerging (Miranda-García et al., 2014). Thermal and H2O2/UV treatment
organic pollutants and reduction of toxicity, the practical applica- were reported to be more efficient. Interestingly, after NaOH
tion of this process is hardly feasible due to the technical challenges regeneration, TiO2 was partially removed leading to the decrease of
arising when photocatalyst should be separated from water for photocatalyst’s efficiency (Miranda-García et al., 2014). It can be
further reuse. The separation step is currently among the major expected that more research devoted to separation/recovery and
limitations for the application of photocatalysis in practice (Chong reuse of photocatalytic materials will be conducted in the future,
et al., 2010; Ferna ndez-Iban
~ ez et al., 2003; Iglesias et al., 2016). taking into account its significant importance for the practical
Relatively few studies have been reported on the separation of application. Beyond the technical challenges of the separation and
photocatalysts from treated water such as accelerated sedimenta- reuse of photocatalysts, the possible risks to aquatic organisms due
tion (Ferna ndez-Iba n
~ ez et al., 2003), coagulation with chemical - to the release of some nanoparticles to water should be mentioned
(Kagaya et al., 1999) and plant-based coagulants (Patchaiyappan as well as the generation of sludge, containing nanoparticles of
et al., 2016), and different filtration methods (Doll and Frimmel, photocatalysts. When nanoparticles are introduced to aquatic
2005; Ganiyu et al., 2015; Zhao et al., 2002). Among the works environment their fate (aggregation and its reversibility) is strongly
considered in the scope of this review, a particle agglomeration dependant on pH, quality and quantity of natural organic matter,
process of materials after treatment (Souza et al., 2016) as well as type of released nanoparticles and their surface properties, dis-
the magnetic separation of TiO2 modified with hydrotalcite and solved and particulate inorganic compounds etc. (Bundschuh et al.,
iron (Arcanjo et al., 2018) was conducted. Another point of concern 2018). Studies on fate of nanoparticles in the environment are
emerging (Boxall et al., 2007; Klitzke et al., 2015; Metreveli et al., photocatalytic films from substrate or the possible photo-
2015; Tso et al., 2010), and behaviour of nanoparticles in complex dissolution of immobilised photocatalysts used for real wastewater
environmental conditions is not fully understood (Bundschuh et al., treatment and its possible effect on water toxicity.
2018). Studies devoted to the risk assessment of nanomaterials
used for photocatalytic water treatment to aquatic organisms are 3.1.2. Radiation sources and type of wastewater
available (Lee et al., 2009; Nogueira et al., 2015; Vevers and Jha, 3.1.2.1. Radiation sources. The photocatalytic wastewater treat-
2008). Thus, adverse effects on invertebrates and fish by TiO2 ment process occurs mostly under UV radiation. The UV generation
nanoparticles were reported (Blaise et al., 2008). Lethal toxicity was by conventional UV lamps is relatively expensive and causes the
reported for Chironomus riparius (widely used organism for the generation of highly toxic waste (during utilisation). From the
assessment of sediment toxicity) exposed for 10 days to artificial economic and environmental point of view, solar energy can be
sediments mixed with residual (after photocatalytic treatment) considered as the best radiation source for photocatalysis. How-
nanoparticles of TiO2 and Fe2O3 used for the treatment of olive oil ever, in countries with a moderate or low availability of natural
mill wastewater and Fe2O3 used for the treatment of kraft pulp mill solar energy, alternative radiation sources can be used. Taking into
effluent (Nogueira et al., 2015). Interestingly, toxicity depended not consideration the Minamata Convention on Mercury (United
only on the type on nanoparticles, but also on the type of con- Nations, 2018) signed by 128 countries, the use of light emitting
taminants adsorbed on the NPs surface. For instance, TiO2 and diodes (LEDs) is becoming more attractive. The number of studies
Fe2O3 NPs after the treatment of mine drainage did not promote on photocatalytic water treatment in which alternative UV sources,
any negative effects on Chironomus riparius (Nogueira et al., 2015). such as solar energy and light emitting diodes (LEDs) are used is
It is not surprising that many studies focus on toxicity assessment increasing (Blanco-Galvez et al., 2006; Levchuk et al., 2015;
of nanoparticles in presence of different contaminants (organic and Spasiano et al., 2015; Vilhunen et al., 2011). Thus, many photo-
inorganic) (Ahamed et al., 2019; Canesi et al., 2015; De La Torre catalysts active in solar and/or visible light have been developed
Roche et al., 2018; Hartmann et al., 2012; Martín-de-Lucía et al., recently (Booshehri et al., 2017; Bouhadoun et al., 2015; Iwase et al.,
2019) as nanoparticles may possibly play role of carrier 2013; Morawski et al., 2017; Ratova et al., 2019; Rosman et al., 2018;
(Hartmann and Baun, 2010) of organic and/or inorganic pollutants Sano et al., 2008). It is worth making a point that majority of these
into cells and/or organisms (Kahru and Dubourguier, 2010). For photocatalytic materials possess relatively low photocatalytic ac-
instance, it was reported that metal uptake in various freshwater tivity and quantum efficiency. Hence, photo-Fenton is often applied
organisms increases in presence of TiO2 nanoparticles (Canesi et al., as alternative, despite its pH aggressiveness and requirements for
2015; Fan et al., 2017; Hartmann et al., 2012). More detailed in- consumables.
formation devoted to toxicity of nanoparticles can be find in Pilot scale reactors for photocatalytic water treatment with LEDs
excellent reviews (Du et al., 2018; Menard et al., 2011; Turan et al., as a radiation source are appearing in the market (Apria Systems,
2019). 2018). Taking into account, the fast development of LEDs, it can
be expected that LEDs can reach the level of industrial imple-
3.1.1.2. Thin films. Photocatalytic slurry systems have been widely mentation in the near future. In approx. 35% of the articles, the
studied for treatment of urban and industrial wastewaters experiments were conducted under solar radiation. For the simu-
(Belgiorno et al., 2007; Biancullo et al., 2019; Fenoll et al., 2019; lation of solar radiation, xenon arc lamps are often used (approx.
Moreira et al., 2018; Talwar et al., 2018; Threrujirapapong et al., 12% of the articles) (He et al., 2016). To the best of our knowledge
2017). Despite high efficiency and relatively low price of slurry only one article reported the detoxification and purification of real
photocatalytic systems, it did not lead to many practical applica- wastewater using UVA-LEDs as a radiation source in the last ten
tions in wastewater treatment. This can be mainly explained by years (Jallouli et al., 2018). Considering the fast development of LED
costly separation of photocatalyst from water after treatment technology and advances achieved in this field in recent years it
(Bideau et al., 1995; Shan et al., 2010). Therefore, immobilisation of may be expected that more research will be conducted on the
photocatalyst on inert supports/substrates in a form of thin films photocatalytic detoxification and purification of real wastewater
could significantly simplify the separation procedure and enhance using LEDs as a radiation source.
applicability of photocatalytic process. Immobilisation of photo- Conventional lamps are still utilised in research with various
catalysts allows to avoid the possible release of NPs to water, sludge optical filters in order to study photocatalytic reaction under UVC,
generation and also significantly decrease the cost of the treatment UVB and/or UVA radiation. It should be noted that in some articles
by eliminating the photocatalyst recovery step. However, relatively the radiation intensity of the lamp is not provided and photo-
high preparation costs together with generally reported lower ef- catalytic activity is shown as a function of time. Such representation
ficiency of immobilised photocatalyst (Levchuk et al., 2016a) are the of the experimental results, especially in the absence of lamp in-
main barriers for practical application of photocatalytic thin films. tensity, makes it extremely difficult to compare the results with
Interestingly, it was reported that immobilised photocatalyst can other studies. If the electrical consumption of a lamp is provided, it
achieve a similar level of photocatalytic activity as commercial TiO2 can be possible to estimate the total energy supplied for the
(P25) for industrial wastewater (IWW) treatment (Barndo ~k et al., removal of one ppm of TOC or COD, but it is a tedious procedure
2016). Sordo et al. (2010) demonstrated that the efficiency of given the actual conditions of reporting in the scientific literature.
fixed-bed reactor filled with TiO2 immobilised on glass beds is
similar to that of slurry photocatalytic system. Several studies were 3.1.2.2. Types of wastewater. When working with matrices of real
conducted with immobilised photocatalytic materials for waste- wastewater (urban and/or industrial) a few issues should be taken
water treatment (Barndo ~k et al., 2016; Gholami et al., 2018; Vaiano into consideration. On the one hand high concentration of dis-
and Iervolino, 2018). However, to our knowledge, only a few studies solved organic carbon (DOC) should be considered as it is
were reported for real wastewater detoxification with immobilised competing for the oxidising radicals generated by applied AOP. In
thin films in the last ten years (Barndo ~ k et al., 2016; He et al., 2016; order to avoid this problem, biological treatment followed by AOP is
Tichonovas et al., 2017). The TiO2 (He et al., 2016; Tichonovas et al., often suggested to be applied for wastewater containing CECs,
2017) and FeeTiO2 (Barndo ~ k et al., 2016) were used as a photo- which are not highly toxic for biological process (Oller et al., 2011).
tcatalysts. As far as the authors are aware, in the last ten years there In case when pollutants present in wastewater possess high toxicity
were no works investigating such phenomena as the detachment of for biological treatment, it is often proposed to apply first AOP and
then continue with a biological treatment when the toxicity level of contaminants was relatively high, DOC was as high as 215 mg L-1
the wastewater treated by AOP allows it. For wastewaters with (Jallouli et al., 2018). Taking into account relatively low levels of
extremely low concentrations of CECs nanofiltration (for pre- COD, TOC, emerging pollutants (mg L1 or ng L1) concentrations
concentration of CECs) can be applied, after which reject water with and disinfection in MWW effluents, it may be considered as a viable
high concentration of CECs can be treated by AOP (Miralles-Cuevas source for water reuse, e.g. for recreational and/or agricultural
et al., 2014). On the other hand, there are other issues, such as high irrigation, although health risk assessment should be conducted
levels of carbonates in wastewater, which generally decrease the due to potential presence of pathogens/CECs in treated water
efficiency of applied AOP (possible solution e acidification of (Malchi et al., 2014). However, no studies on photocatalytic MWW
wastewater), phosphates and sulphates can poison and/or coagu- effluent purification and detoxification considered the possible
late catalysts, etc. reuse of MWW effluent by now.
As shown in Fig. 2, the majority of studies on the detoxification
and purification of real wastewaters in the last ten years using
photocatalysis and hybrid processes were conducted with indus- 3.1.3. Toxicity
trial wastewaters. In more than 60% of the studies on photocatalytic Different approaches for acute and chronic toxicity evaluation
wastewater detoxification, pre-treatment such as pH adjustment, were applied so far for photocatalytically treated wastewater ef-
decreasing concentration of carbonates in water, etc. was applied fluents such as bioassays with bacteria (He et al., 2016; Nogueira
prior to the photocatalytic process. Both raw and treated industrial et al., 2017; Talwar et al., 2018), seawater invertebrates
wastewater was studied. Therefore, the concentrations of TOC, COD (Hasegawa et al., 2014; Lima et al., 2015; Souza et al., 2016),
and BOD strongly varied depending on the type of industry, type of freshwater invertebrates (Çifçi and Meriç, 2015), microalgae (He
the pre-treatment (if applicable), etc. It was reported that photo- et al., 2016), plants (phytotoxicity) (Tsoumachidou et al., 2017),
catalytic treatment can be successfully applied as a pre-treatment mammalian cells (genotoxicity) (Saverini et al., 2012), etc. As re-
method (before biological treatment) for raw industrial waste- ported in the majority of the studies, after the photocatalytic
water leading to an increase of its biodegradability and decrease of treatment, the toxicity of wastewater generally decreases. In
toxicity (Talwar et al., 2018) as well as the post-treatment method approx. 44% of the studies on photocatalytic wastewater treatment,
(after biological treatment) for industrial wastewater effluents the toxicity was monitored on the course of photocatalytic treat-
allowing decomposing toxic pollutants (Saverini et al., 2012). ment. Interestingly, in some studies a drastic increase of toxicity
To the best of our knowledge, no studies were reported in the was reported during the treatment of MWW effluents (Vela et al.,
last ten years on the photocatalytic detoxification and purification 2018a, 2018b) as well as industrial wastewater (Çifçi and Meriç,
of industrial wastewater and/or wastewater effluents for water 2015; Saverini et al., 2012; Tichonovas et al., 2017). Such behav-
reuse and/or recycling. Approx. 40% of revised articles were iour was observed when Vibrio fischeri (Vela et al., 2018a, 2018b),
devoted to the purification and detoxification of municipal waste- Daphnia magna (Çifçi and Meriç, 2015) and Ames test (Saverini
water (MWW) effluents. Among these studies, MWW was mostly et al., 2012) bioassays were applied. Generally, this phenomenon
used as a matrix for spiking emerging pollutants. Depending on the can be attributed to possible photodissolution of photocatalyst
MWW effluent, the level of COD and dissolved organic carbon (Vela et al., 2018a), possible generation of more toxic by-products
(DOC) concentrations were approx. 33e55 mg L-1 and 10e13 mg L-1, than parental compounds (Vela et al., 2018b) and/or synergetic
respectively. However, when the concentration of spiked toxic effects appearing due to the presence of many individual
contaminants in water. An additional toxic effect can be produced
Fig. 2. Schematic presentation of types of wastewater used for detoxification by photocatalysis in last ten years.
in case of hybrid photocatalysis processes, requiring the addition of chromatography - mass spectrometry) (Brienza et al., 2016). These
chemical agents such as H2O2, which is toxic for aquatic organisms. results suggest that the estrogenic toxicity test is a very promising
In case residual H2O2 concentrations after treatment are relatively tool for MWW effluents. Genotoxicity (LS 174T cell line) of not
high, the elimination of H2O2 will be required for the safe discharge spiked MWW effluent was not detected neither before no after
or reuse of treated wastewater. For this purpose, filtration through photocatalytic treatment (Brienza et al., 2016). The phytotoxicity of
granular activated carbon (GAC) can be successfully applied synthetic greywater before and after hybrid photocatalytic process
(Rueda-Ma rquez et al., 2015). Therefore, it would be interesting to was tested using the seeds of Sorghum saccharatum, Lepidium sat-
check the toxicity of treated wastewater before and after filtration ivum, Sinapis alba (Tsoumachidou et al., 2017). The Sinapis alba was
through GAC without the preliminary removal of H2O2 from water the most sensitive among the tested plants. A phytotoxicity assay
samples. Toxicity assessment is an important tool for the optimi- might be a valuable tool if MWW effluent is planned to be reused
sation of photocatalytic wastewater treatment when complete for the purpose of irrigation.
mineralisation is not a goal. The results of toxicity assessment Photocatalytic ozonation was efficient for the detoxification of
during the process can clearly indicate at which moment more IWW as well as MWW effluents. Interestingly, in the majority of
toxic by-products are generated and when these are decomposed. reviewed studies devoted to wastewater detoxification by photo-
Therefore, it can be suggested that the evaluation of toxicity on the catalytic ozonation, bioassays with freshwater invertebrate
course of photocatalytic wastewater treatment is of high signifi- (Daphnia) were implemented. Other bioassays (Vibrio fischeri,
cance and should be conducted especially if the practical applica- Pseudokirchneriella subcapitata) as well as genotoxicity and cyto-
tion of photocatalysis is planned. toxicity tests were also used. In general, photocatalytic ozonation
Toxicity tests applied for the photocatalytic detoxification of was efficient for the decrease of wastewater toxicity and all the
industrial wastewater were: Daphnia magna, Daphnia similis, Arte- implemented bioassays were efficient. Tichonovas and co-authors
mia salina, Vibrio fischeri, Ames test (S.typhimurium) and Kirby- assessed toxicity (Daphnia magna) of IWW during photocatalytic
Bauer method (zone inhibition using E.coli). In general, the ozonation (Tichonovas et al., 2017). They reported a drastic increase
toxicity of industrial wastewater is higher than that of MWW ef- of Daphnia magna mortality during the process followed by a sig-
fluents. Therefore, all the tested bioassays were reported as an nificant decrease (reaching zero) at the end of the treatment. These
efficient tool for the toxicity assessment of industrial wastewaters. results were explained by the higher acute toxicity of degradation
In the reviewed articles devoted to photocatalytic wastewater by-products than parental pollutants.
detoxification, the following toxicity tests were applied for the Taking into account the possible practical application of pho-
assessment of MWW effluents and synthetic greywater during tocatalytic wastewater treatment, a preliminary cost evaluation
photocatalytic treatment: Vibrio fischeri bioluminescence’s assay, should be performed. For instance, the operational cost of the
Daphnia magna immobilisation test, Pseudokirchneriella sub- hybrid photocatalytic process was reported to be $45.17 m-3 (Bansal
capitata, Anabaena flos-aquae, Brachionus calyciflorus, estrogenic et al., 2018). Energy consumption can also be very valuable infor-
test (HELN ERa cell line), genotoxicity assessment (LS 174T cell line) mation, based on which a cost estimation can be conducted. The
and phytotoxicity test. The bioluminescence’s assay with Vibrio photocatalytic ozonation is often considered to be expensive for
fischeri was among most widely used toxicity tests for MWW ef- wastewater treatment (Mehrjouei et al., 2015). In the reviewed
fluents. Interestingly, the inhibition of Vibrio fischeri growth was articles, estimations of energy required for the detoxification of
reported for MWW effluents spiked with contaminants at envi- WW were suggested. Thus, photocatalytic ozonation was reported
ronmentally relevant (ng L1 e mg L1) (Vela et al., 2018a, 2018b) to be the most energy efficient treatment among those studied with
and irrelevant concentrations (mg L1 e g L1) (Jallouli et al., 2018). the energy requirements 4.49e41.08 MJ/g-TOC (Tichonovas et al.,
However, in some cases, the very low sensitivity of Vibrio fischeri 2017). Another study suggested that the required energy for pho-
was observed even when MWW effluents spiked with the con- tocatalytic ozonation varies from 7.3 to 22.0 kWh/m3 (Mecha et al.,
centration of pollutants at the mg L1 level (Brienza et al., 2016; He 2017).
et al., 2016). In spite of a large number of pollutants detected in not
spiked MWW effluent, the EC50 value for Vibrio fischeri of 80% was
reported (Brienza et al., 2016), which is non-toxic according to 4. Conclusions
(Calleja et al., 1986). Therefore, for the toxicity assessment of real
MWW effluents, Vibrio fischeri bioluminescence’s assay may not be In this work, the feasibility of photocatalysis for toxicity elimi-
very sensitive. It was shown that a toxicity assay with P. subcapitata nation from real wastewaters is critically discussed. Such aspect of
is not very sensitive for MWW effluent (EC50 98%), while its photocatalysis detoxification of real wastewater as photocatalytic
sensitivity drastically increases when MWW effluents are spiked materials and its reactivation, types of wastewater and bioassays
with pollutants at mg L1 level (Brienza et al., 2016; He et al., 2016). were discussed. Main outcomes of this work are as follows:
Similar behaviour was reported for Daphnia magna and Brachionus
calyciflorus (Brienza et al., 2016). In spiked MWW effluent, the While photocatalytic wastewater detoxification and purification
growth inhibition of Anabaena flos-aquae was reported to be shows potential, most works (˃70%) considered in the scope of
approx. 70% and 20% (growth stimulation) before and after this review were conducted on the laboratory scale.
treatment, respectively (He et al., 2016). The growth stimulation Most studied photocatalytic materials for real wastewater
was attributed to the presence of organic matter, which is the detoxification both in form of powder and thin films are TiO2
nutrition source for Anabaena flos-aquae as well as the decompo- and ZnO.
sition of toxic contaminants (He et al., 2016). Therefore, the toxicity Studies devoted to separation and/or recovery and reuse of
assay with Anabaena flos-aquae and other cyanobacteria may not be photocatalytic materials used for real wastewater detoxification
very representative for MWW due to relatively high organic load are lacking.
serving as a source of nutrition. The very high sensitivity of the Only few studies were conducted on real wastewater detoxifi-
estrogenic toxicity test was reported for not spiked MWW effluent, cation using photocatalysts in a form of thin film. There is lack of
more specifically, estrogenic activity was detected in MWW information on behaviour of thin films (detachment of photo-
effluent when it was not possible to detect any known estrogenic catalyst, photodissolution, etc.) during photocatalytic detoxifi-
compound using sophisticated chemical analysis (liquid cation of real wastewater.
The evaluation of the photocatalytic treatment costs for real Appl. Catal. B Environ. 44e52.
Belgiorno, V., Rizzo, L., Fatta, D., Della Rocca, C., Lofrano, G., Nikolaou, A., Naddeo, V.,
wastewater detoxification by photocatalysis is not always
Meric, S., 2007. Review on endocrine disrupting-emerging compounds in urban
available. wastewater: occurrence and removal by photocatalysis and ultrasonic irradia-
Based on this revised literature, it can be suggested that stan- tion for wastewater reuse. Desalination 1, 166e176.
dard tests with species such as Daphnia magna, Vibrio fishceri, Berberidou, C., Kitsiou, V., Lambropoulou, D.A., Antoniadis, А., Ntonou, E.,
Zalidis, G.C., Poulios, I., 2017. Evaluation of an alternative method for waste-
Pseudokirchneriella subcapitata and Brachionus calyciflorus might water treatment containing pesticides using solar photocatalytic oxidation and
not be sensitive enough when detoxification of municipal constructed wetlands. J. Environ. Manag. 133e139.
wastewater is studied. Biancullo, F., Moreira, N.F.F., Ribeiro, A.R., Manaia, C.M., Faria, J.L., Nunes, O.C.,
Castro-Silva, S.M., Silva, A.M.T., 2019. Heterogeneous photocatalysis using UVA-
In some cases, toxicity assessment may be even more sensitive LEDs for the removal of antibiotics and antibiotic resistant bacteria from urban
than chemical analysis. It is expected that future studies devoted wastewater treatment plant effluents. Chem. Eng. J. 304e313.
to the detoxification of wastewater by photocatalysis will Bideau, M., Claudel, B., Dubien, C., Faure, L., Kazouan, H., 1995. On the “immobili-
zation” of titanium dioxide in the photocatalytic oxidation of spent waters.
implement batteries of bioassays (including biosensors) for a J. Photochem. Photobiol., A 2, 137e144.
more comprehensive evaluation of water toxicity. Biglari, H., Afsharnia, M., Alipour, V., Khosravi, R., Sharafi, K., Mahvi, A.H., 2017.
The use of TiO2 and other photocatalysts for real wastewater A review and investigation of the effect of nanophotocatalytic ozonation pro-
cess for phenolic compound removal from real effluent of pulp and paper in-
treatment has not been investigated as deep as with other AOPs
dustry. Environ. Sci. Pollut. Control Ser. 4, 4105e4116.
due to the clear reasons, i.e. efficiency of the process strongly Blaise, C., Gagne , F., Fe
rard, J.F., Eullaffroy, P., 2008. Ecotoxicity of selected nano-
decreases in presence of complex mixture of organic pollutants materials to aquatic organisms. Environ. Toxicol. 5, 591e598.
Blanco-Galvez, J., Ferna ndez-Iba n~ ez, P., Malato-Rodríguez, S., 2006. Solar photo-
and high levels of DOC, etc. It can be expected that future studies
catalytic detoxification and disinfection of water: recent overview. J. Sol. Energy
devoted to development of nanomaterials for similar applica- Eng. 4e15.
tions might consider issues related to real wastewater matrix. Booshehri, A.Y., Polo-Lopez, M.I., Castro-Alfe rez, M., He, P., Xu, R., Rong, W.,
Malato, S., Ferna ndez-Ib an~ ez, P., 2017. Assessment of solar photocatalysis using
The existing gap between materials research and application
Ag/BiVO4 at pilot solar Compound Parabolic Collector for inactivation of path-
studies for real wastewater is an actual barrier, which limits ogens in well water and secondary effluents. Catal. Today 124e134.
further development of application of photocatalysis for real Bouhadoun, S., Guillard, C., Dapozze, F., Singh, S., Amans, D., Boucle , J., Herlin-
wastewater treatment. Boime, N., 2015. One step synthesis of N-doped and Au-loaded TiO2 nano-
particles by laser pyrolysis: application in photocatalysis. Appl. Catal. B Environ.
367e375.
Declaration of competing interest Boxall, A.B., Tiede, K., Chaudhry, Q., 2007. Engineered Nanomaterials in Soils and
Water: How Do They Behave and Could They Pose a Risk to Human Health?.
Boyle, D., Goss, G.G., 2018. Effects of silver nanoparticles in early life-stage zebrafish
The authors declare that they have no known competing are associated with particle dissolution and the toxicity of soluble silver.
financial interests or personal relationships that could have NanoImpact 1e8.
appeared to influence the work reported in this paper. Brienza, M., Mahdi Ahmed, M., Escande, A., Plantard, G., Scrano, L., Chiron, S.,
Bufo, S.A., Goetz, V., 2016. Use of solar advanced oxidation processes for
wastewater treatment: follow-up on degradation products, acute toxicity,
Acknowledgments genotoxicity and estrogenicity. Chemosphere 473e480.
Brunner, T.J., Wick, P., Manser, P., Spohn, P., Grass, R.N., Limbach, L.K., Bruinink, A.,
Stark, W.J., 2006. In vitro cytotoxicity of oxide nanoparticles: comparison to
Authors would like to express sincere gratitude to Professor
asbestos, silica, and the effect of particle solubility. Environ. Sci. Technol. 14,
Manuel Manzano (University of Cadiz) for fruitful discussions and 4374e4381.
valuable advices during preparation of this review. D.Sc. Juan Jose Bundschuh, M., Filser, J., Lüderwald, S., McKee, M.S., Metreveli, G., Schaumann, G.E.,
Rueda-Marquez is thankful for financial support from Academy of Schulz, R., Wagner, S., 2018. Nanoparticles in the environment: where do we
come from, where do we go to? Environ. Sci. Eur. 1, 1e17.
Finland within the project ʺCombination of Advanced Oxidation Calleja, A., Baldasano, J., Mulet, A., 1986. Toxicity analysis of leachates from haz-
Processes and Photobiotreatment for Sustainable Resource Recov- ardous wastes via Microtox and Daphnia magna. Environ. Toxicol. 1, 73e83.
ery and Wastewater Reuseʺ (No. 322339, 2019-2022). D.Sc. Pilar Canesi, L., Ciacci, C., Balbi, T., 2015. Interactive effects of nanoparticles with other
contaminants in aquatic organisms: friend or foe? Mar. Environ. Res. 128e134.
Fernandez Iban
~ ez acknowledges the financial support of the Global Carp, O., Huisman, C.L., Reller, A., 2004. Photoinduced reactivity of titanium dioxide.
Challenges Research Fund (GCRF) UK Research and Innovation Prog. Solid State Chem. 1e2, 33e177.
(SAFEWATER; EPSRC Grant Reference EP/P032427/1). Chong, M.N., Jin, B., Chow, C.W.K., Saint, C., 2010. Recent developments in photo-
catalytic water treatment technology: a review. Water Res. 10, 2997e3027.
Çifçi, D.I., Meriç, S., 2015. Optimization of suspended photocatalytic treatment of
References two biologically treated textile effluents using TiO2 and ZnO catalysts. Global
NEST Journal 17 (4), 653e663.
Ahamed, M., Akhtar, M.J., Alhadlaq, H.A., 2019. Preventive effect of TiO2 nano- De La Torre Roche, R., Pagano, L., Majumdar, S., Eitzer, B.D., Zuverza-Mena, N., Ma, C.,
particles on heavy metal Pb-induced toxicity in human lung epithelial (A549) Servin, A.D., Marmiroli, N., Dhankher, O.P., White, J.C., 2018. Co-exposure of
cells. Toxicol. Vitro 18e27. imidacloprid and nanoparticle Ag or CeO2 to Cucurbita pepo (zucchini):
Ahmed, S., Ollis, D.F., 1984. Solar photoassisted catalytic decomposition of the contaminant bioaccumulation and translocation. NanoImpact 136e145.
chlorinated hydrocarbons trichloroethylene and trichloromethane. Sol. Energy Doll, T.E., Frimmel, F.H., 2005. Cross-flow microfiltration with periodical back-
5, 597e601. washing for photocatalytic degradation of pharmaceutical and diagnostic
Al-Sayyed, G., D’Oliveira, J., Pichat, P., 1991. Semiconductor-sensitized photo- residueseevaluation of the long-term stability of the photocatalytic activity of
degradation of 4-chlorophenol in water. J. Photochem. Photobiol. Chem. 1, TiO2. Water Res. 5, 847e854.
99e114. Du, J., Tang, J., Xu, S., Ge, J., Dong, Y., Li, H., Jin, M., 2018. A review on silver
Apria Systems, S.L., 2018. Advanced Oxidation Equipment through UV Photo- nanoparticles-induced ecotoxicity and the underlying toxicity mechanisms.
catalysis for R&D Activities. Regul. Toxicol. Pharmacol. 231e239.
Arcanjo, G.S., Mounteer, A.H., Bellato, C.R., Silva, L.M.M.d., Brant Dias, S.H., Fan, X., Wang, P., Wang, C., Hu, B., Wang, X., 2017. Lead accumulation (adsorption
Silva, P.R.d., 2018. Heterogeneous photocatalysis using TiO2 modified with and absorption) by the freshwater bivalve Corbicula fluminea in sediments
hydrotalcite and iron oxide under UVevisible irradiation for color and toxicity contaminated by TiO2 nanoparticles. Environ. Pollut. 712e721.
reduction in secondary textile mill effluent. J. Environ. Manag. 154e163. Fenoll, J., Garrido, I., Flores, P., Hellín, P., Vela, N., Navarro, G., García-García, J.,
Bansal, P., Verma, A., Talwar, S., 2018. Detoxification of real pharmaceutical waste- Navarro, S., 2019. Implementation of a new modular facility to detoxify agro-
water by integrating photocatalysis and photo-Fenton in fixed-mode. Chem. wastewater polluted with neonicotinoid insecticides in farms by solar photo-
Eng. J. 838e848. catalysis. Energy 722e729.
Barbeni, M., Morello, M., Pramauro, E., Pelizzetti, E., Vincenti, M., Borgarello, E., Fernandez-Ib ~ ez, P., Blanco, J., Malato, S., de las Nieves, F.J., 2003. Application of
an
Serpone, N., 1987. Sunlight photodegradation of 2,4,5-trichlorophenoxy-acetic the colloidal stability of TiO2 particles for recovery and reuse in solar photo-
acid and 2,4,5,trichlorophenol on TiO2. Identification of intermediates and catalysis. Water Res. 13, 3180e3188.
degradation pathway. Chemosphere 6, 1165e1179. François, G., Melanie, D., Marle ne, F., Michel, F., 2015. Effects of a municipal effluent
Barndo~ k, H., Hermosilla, D., Han, C., Dionysiou, D.D., Negro, C., Blanco, A., 2016. on the freshwater mussel Elliptio complanata following challenge with Vibrio
Degradation of 1,4-dioxane from industrial wastewater by solar photocatalysis anguillarum. J. Environ. Sci. 91e99.
using immobilized NF-TiO2 composite with monodisperse TiO2 nanoparticles. Franklin, N.M., Rogers, N.J., Apte, S.C., Batley, G.E., Gadd, G.E., Casey, P.S., 2007.
Comparative toxicity of nanoparticulate ZnO, bulk ZnO, and ZnCl2 to a fresh- Lima, C.S., Batista, K.A., García Rodríguez, A., Souza, J.R., Fernandes, K.F., 2015.
water microalga (Pseudokirchneriella subcapitata): the importance of particle Photodecomposition and color removal of a real sample of textile wastewater
solubility. Environ. Sci. Technol. 24, 8484e8490. using heterogeneous photocatalysis with polypyrrole. Sol. Energy 105e113.
Ganiyu, S.O., van Hullebusch, E.D., Cretin, M., Esposito, G., Oturan, M.A., 2015. Ma, J., Chen, Y., Nie, J., Ma, L., Huang, Y., Li, L., Liu, Y., Guo, Z., 2018. Pilot-scale study
Coupling of membrane filtration and advanced oxidation processes for removal on catalytic ozonation of bio-treated dyeing and finishing wastewater using
of pharmaceutical residues: a critical review. Separ. Purif. Technol. 891e914. recycled waste iron shavings as a catalyst. Sci. Rep. 1, 7555.
Gholami, N., Ghasemi, B., Anvaripour, B., Jorfi, S., 2018. Enhanced photocatalytic Malchi, T., Maor, Y., Tadmor, G., Shenker, M., Chefetz, B., 2014. Irrigation of root
degradation of furfural and a real wastewater using UVC/TiO2 nanoparticles vegetables with treated wastewater: evaluating uptake of pharmaceuticals and
immobilized on white concrete in a fixed-bed reactor. J. Ind. Eng. Chem. the associated human health risks. Environ. Sci. Technol. 16, 9325e9333.
291e301. Martín-de-Lucía, I., Gonçalves, S.F., Legane s, F., Fernandez-Pin ~ as, F., Rosal, R.,
Gracia-Lor, E., Sancho, J.V., Serrano, R., Herna ndez, F., 2012. Occurrence and removal Loureiro, S., 2019. Combined toxicity of graphite-diamond nanoparticles and
of pharmaceuticals in wastewater treatment plants at the Spanish Mediterra- thiabendazole to Daphnia magna. Sci. Total Environ. 1145e1154.
nean area of Valencia. Chemosphere 5, 453e462. Mecha, A.C., Onyango, M.S., Ochieng, A., Momba, M.N., 2017. Ultraviolet and solar
Hartmann, N.B., Baun, A., 2010. The nano cocktail: ecotoxicological effects of photocatalytic ozonation of municipal wastewater: catalyst reuse, energy re-
engineered nanoparticles in chemical mixtures. Integrated Environ. Assess. quirements and toxicity assessment. Chemosphere 669e676.
Manag.: Int. J. 2, 311e313. Mehrjouei, M., Müller, S., Mo € ller, D., 2015. A review on photocatalytic ozonation
Hartmann, N.B., Legros, S., Von der Kammer, F., Hofmann, T., Baun, A., 2012. The used for the treatment of water and wastewater. Chem. Eng. J. 209e219.
potential of TiO2 nanoparticles as carriers for cadmium uptake in Lumbriculus Menard, A., Drobne, D., Jemec, A., 2011. Ecotoxicity of nanosized TiO2. Review of
variegatus and Daphnia magna. Aquat. Toxicol. 1e8. in vivo data. Environ. Pollut. 3, 677e684.
Hasegawa, M.C., Feijo de Souza Daniel, J., Takashima, K., Batista, G.A., da Silva, S.M., Metreveli, G., Philippe, A., Schaumann, G.E., 2015. Disaggregation of silver nano-
2014. COD removal and toxicity decrease from tannery wastewater by zinc particle homoaggregates in a river water matrix. Sci. Total Environ. 35e44.
oxide-assisted photocatalysis: a case study. Environ. Technol. 13, 1589e1595. Mills, A., Le Hunte, S., 1997. An overview of semiconductor photocatalysis.
He, Y., Sutton, N.B., Rijnaarts, H.H.H., Langenhoff, A.A.M., 2016. Degradation of J. Photochem. Photobiol., A 1, 1e35.
pharmaceuticals in wastewater using immobilized TiO2 photocatalysis under Miralles-Cuevas, S., Audino, F., Oller, I., Sa nchez-Moreno, R., Sa nchez Pe rez, J.A.,
simulated solar irradiation. Appl. Catal. B Environ. 132e141. Malato, S., 2014. Pharmaceuticals removal from natural water by nanofiltration
Herrmann, J., 1999. Heterogeneous photocatalysis: fundamentals and applications combined with advanced tertiary treatments (solar photo-Fenton, photo-Fen-
to the removal of various types of aqueous pollutants. Catal. Today 1, 115e129. ton-like Fe(III)eEDDS complex and ozonation). Separ. Purif. Technol. 515e522.
Hidaka, H., Kubota, H., Graa €tzel, M., Pelizzetti, E., Serpone, N., 1986. Photo- Miranda-García, N., Su arez, S., Maldonado, M.I., Malato, S., Sa nchez, B., 2014.
degradation of surfactants II: degradation of sodium dodecylbenzene sulpho- Regeneration approaches for TiO2 immobilized photocatalyst used in the
nate catalysed by titanium dioxide particles. J. Photochem. 2, 219e230. elimination of emerging contaminants in water. Catal. Today 27e34, 0.
Huang, H., Li, W., 2011. Destruction of toluene by ozone-enhanced photocatalysis: Morawski, A.W., Kusiak-Nejman, E., Wanag, A., Kapica-Kozar, J., Wro bel, R.J.,
performance and mechanism. Appl. Catal. B Environ. 3e4, 449e453. Ohtani, B., Aksienionek, M., Lipin ska, L., 2017. Photocatalytic degradation of
Iglesias, O., Rivero, M.J., Urtiaga, A.M., Ortiz, I., 2016. Membrane-based photo- acetic acid in the presence of visible light-active TiO2-reduced graphene oxide
catalytic systems for process intensification. Chem. Eng. J. 136e148. photocatalysts. Catal. Today 108e113.
Iwase, M., Yamada, K., Kurisaki, T., Prieto-Mahaney, O.O., Ohtani, B., Wakita, H., 2013. Moreira, N.F.F., Narciso-da-Rocha, C., Polo-Lo pez, M.I., Pastrana-Martínez, L.M.,
Visible-light photocatalysis with phosphorus-doped titanium(IV) oxide parti- Faria, J.L., Manaia, C.M., Ferna ndez-Ib an~ ez, P., Nunes, O.C., Silva, A.M.T., 2018.
cles prepared using a phosphide compound. Appl. Catal. B Environ. 39e44. Solar treatment (H2O2, TiO2-P25 and GO-TiO2 photocatalysis, photo-Fenton) of
Jallouli, N., Pastrana-Martínez, L.M., Ribeiro, A.R., Moreira, N.F.F., Faria, J.L., organic micropollutants, human pathogen indicators, antibiotic resistant bac-
Hentati, O., Silva, A.M.T., Ksibi, M., 2018. Heterogeneous photocatalytic degra- teria and related genes in urban wastewater. Water Res. 195e206.
dation of ibuprofen in ultrapure water, municipal and pharmaceutical industry Moreira, N.F.F., Sampaio, M.J., Ribeiro, A.R., Silva, C.G., Faria, J.L., Silva, A.M.T., 2019.
wastewaters using a TiO2/UV-LED system. Chem. Eng. J. 976e984. Metal-free g-C3N4 photocatalysis of organic micropollutants in urban waste-
Kabra, K., Chaudhary, R., Sawhney, R.L., 2004. Treatment of hazardous organic and water under visible light. Appl. Catal. B Environ. 184e192.
inorganic compounds through aqueous-phase photocatalysis: a review. Ind. Nogueira, V., Lopes, I., Rocha-Santos, T., Gonçalves, F., Pereira, R., 2017. Treatment of
Eng. Chem. Res. 24, 7683e7696. real industrial wastewaters through nano-TiO2 and nano-Fe2O3 photocatalysis:
Kagaya, S., Shimizu, K., Arai, R., Hasegawa, K., 1999. Separation of titanium dioxide case study of mining and kraft pulp mill effluents. Environ. Technol. 1e11.
photocatalyst in its aqueous suspensions by coagulation with basic aluminium Nogueira, V., Lopes, I., Rocha-Santos, T., Gonçalves, F., Pereira, R., 2015. Toxicity of
chloride. Water Res. 7, 1753e1755. solid residues resulting from wastewater treatment with nanomaterials. Aquat.
Kahru, A., Dubourguier, H., 2010. From ecotoxicology to nanoecotoxicology. Toxi- Toxicol. 172e178.
cology 2, 105e119. Ohtani, B., 2011. Photocatalysis by inorganic solid materials: revisiting its definition,
Ka€kinen, A., Kahru, A., Nurmsoo, H., Kubo, A., Bondarenko, O.M., 2016. Solubility- concepts, and experimental procedures. Adv. Inorg. Chem. 395e430.
driven toxicity of CuO nanoparticles to Caco2 cells and Escherichia coli: effect of Ohtani, B., 2013. Titania photocatalysis beyond recombination: a critical review.
sonication energy and test environment. Toxicol. Vitro 172e179. Catalysts 4, 942e953.
Karaolia, P., Michael-Kordatou, I., Hapeshi, E., Drosou, C., Bertakis, Y., Christofilos, D., Ohtani, B., 2010. Photocatalysis A to Zdwhat we know and what we do not know in
Armatas, G.S., Sygellou, L., Schwartz, T., Xekoukoulotakis, N.P., Fatta- a scientific sense. J. Photochem. Photobiol. C Photochem. Rev. 4, 157e178.
Kassinos, D., 2018. Removal of antibiotics, antibiotic-resistant bacteria and their Oller, I., Malato, S., Sanchez-Pe rez, J.A., 2011. Combination of Advanced Oxidation
associated genes by graphene-based TiO2 composite photocatalysts under solar Processes and biological treatments for wastewater decontaminationda re-
radiation in urban wastewaters. Appl. Catal. B Environ. 810e824. view. Sci. Total Environ. 20, 4141e4166.
Klitzke, S., Metreveli, G., Peters, A., Schaumann, G.E., Lang, F., 2015. The fate of silver Ollis, D.F., 2000. Photocatalytic purification and remediation of contaminated air
nanoparticles in soil solutiondsorption of solutes and aggregation. Sci. Total and water. Comptes Rendus Acad. Sci. - Ser. IIC Chem. 6, 405e411.
Environ. 54e60. Pan, X., Zhang, N., Fu, X., Xu, Y., 2013. Selective oxidation of benzyl alcohol over TiO2
Kudo, A., Miseki, Y., 2009. Heterogeneous photocatalyst materials for water split- nanosheets with exposed {001} facets: catalyst deactivation and regeneration.
ting. Chem. Soc. Rev. 1, 253e278. Appl. Catal. Gen. 181e187.
Lara-Martín, P.A., Gonz alez-Mazo, E., Petrovic, M., Barcelo , D., Brownawell, B.J., 2014. Patchaiyappan, A., Saran, S., Devipriya, S.P., 2016. Recovery and reuse of TiO2 pho-
Occurrence, distribution and partitioning of nonionic surfactants and phar- tocatalyst from aqueous suspension using plant based coagulant - a green
maceuticals in the urbanized Long Island Sound Estuary (NY). Mar. Pollut. Bull. approach. Kor. J. Chem. Eng. 7, 2107e2113.
2, 710e719. Pintado-Herrera, M.G., Gonza lez-Mazo, E., Lara-Martín, P.A., 2014. Atmospheric
Lee, S., Kim, S., Choi, J., 2009. Genotoxicity and ecotoxicity assays using the fresh- pressure gas chromatographyetime-of-flight-mass spectrometry (APGCeToF-
water crustacean Daphnia magna and the larva of the aquatic midge Chirono- MS) for the determination of regulated and emerging contaminants in aqueous
mus riparius to screen the ecological risks of nanoparticle exposure. Environ. samples after stir bar sorptive extraction (SBSE). Anal. Chim. Acta 1e13.
Toxicol. Pharmacol. 1, 86e91. Qi, K., Cheng, B., Yu, J., Ho, W., 2017. Review on the improvement of the photo-
Levchuk, I., Rueda-M arquez, J.J., Suihkonen, S., Manzano, M.A., Sillanp€ aa€, M., 2015. catalytic and antibacterial activities of ZnO. J. Alloys Compd. 792e820.
Application of UVA-LED based photocatalysis for plywood mill wastewater Quinn, B., Gagne , F., Blaise, C., 2009. Evaluation of the acute, chronic and teratogenic
treatment. Separ. Purif. Technol. 1e5. effects of a mixture of eleven pharmaceuticals on the cnidarian, Hydra
Levchuk, I., Guillard, C., Dappozze, F., Parola, S., Leonard, D., Sillanp€ a€a, M., 2016a. attenuata. Sci. Total Environ. 3, 1072e1079.
Photocatalytic activity of TiO2 films immobilized on aluminum foam by atomic Quinn, B., Schmidt, W., O’Rourke, K., Hernan, R., 2011. Effects of the pharmaceuticals
layer deposition technique. J. Photochem. Photobiol. Chem. 16e23. gemfibrozil and diclofenac on biomarker expression in the zebra mussel
Levchuk, I., Sillanpa €a
€, M., Guillard, C., Gregori, D., Chateau, D., Chaput, F., Lerouge, F., (Dreissena polymorpha) and their comparison with standardised toxicity tests.
Parola, S., 2016b. Enhanced photocatalytic activity through insertion of plas- Chemosphere 5, 657e663.
monic nanostructures into porous TiO2/SiO2 hybrid composite films. J. Catal. Rao, T.N., Tryk, D.A., Fujishima, A., 2003. Applications of TiO2 Photocatalysis.
117e124. Encyclopedia of Electrochemistry.
Li, Y., Jiao, Z., Yang, N., Gao, H., 2009. Regeneration of nano-ZnO photocatalyst by the Ratova, M., Tosheva, L., Kelly, P.J., Ohtani, B., 2019. Characterisation and properties of
means of soft-mechanochemical ion exchange method. J. Environ. Sci. S69eS72. visible light-active bismuth oxide-titania composite photocatalysts. Sus-
Li, X., He, J., 2013. Synthesis of raspberry-like SiO2eTiO2 nanoparticles toward tain.Mater. Technol., e00112
antireflective and self-cleaning coatings. ACS Appl. Mater. Interfaces 11, Rosman, N., Salleh, W.N.W., Ismail, A.F., Jaafar, J., Harun, Z., Aziz, F., Mohamed, M.A.,
5282e5290. Ohtani, B., Takashima, M., 2018. Photocatalytic degradation of phenol over
visible light active ZnO/Ag2CO3/Ag2O nanocomposites heterojunction. industry wastewater. Environ. Technol. 1e8.
J. Photochem. Photobiol. Chem. 602e612. Tso, C., Zhung, C., Shih, Y., Tseng, Y., Wu, S., Doong, R., 2010. Stability of metal oxide
Rueda-M arquez, J.J., Pintado-Herrera, M.G., Martín-Díaz, M.L., Acevedo-Merino, A., nanoparticles in aqueous solutions. Water Sci. Technol. 1, 127e133.
Manzano, M.A., 2015. Combined AOPs for potential wastewater reuse or safe Tsoumachidou, S., Velegraki, T., Antoniadis, A., Poulios, I., 2017. Greywater as a
discharge based on multi-barrier treatment (microfiltration-H2O2/UV-catalytic sustainable water source: a photocatalytic treatment technology under artificial
wet peroxide oxidation). Chem. Eng. J. 80e90, 0. and solar illumination. J. Environ. Manag. 232e241.
Sano, T., Puzenat, E., Guillard, C., Geantet, C., Matsuzawa, S., 2008. Degradation of Turan, N.B., Erkan, H.S., Engin, G.O., Bilgili, M.S., 2019. Nanoparticles in the aquatic
C2H2 with modified-TiO2 photocatalysts under visible light irradiation. J. Mol. environment: usage, properties, transformation and toxicityda review. Process
Catal. Chem. 1, 127e133. Saf. Environ. Protect. 238e249.
Santiago-Morales, J., Go mez, M.J., Herrera, S., Fern
andez-Alba, A.R., García-Calvo, E., United Nations, 2018. Minamata Convention on Mercury.
Rosal, R., 2012. Oxidative and photochemical processes for the removal of Vaiano, V., Iervolino, G., 2018. Facile method to immobilize ZnO particles on glass
galaxolide and tonalide from wastewater. Water Res. 14, 4435e4447. spheres for the photocatalytic treatment of tannery wastewater. J. Colloid
Sauer, M.L., Ollis, D.F., 1996. Catalyst deactivation in gasesolid photocatalysis. Interface Sci. 192e199.
J. Catal. 1, 215e217. Vela, N., Calín, M., Y ~ez-Gasco
an n, M.J., Garrido, I., Pe rez-Lucas, G., Fenoll, J.,
Saverini, M., Catanzaro, I., Sciandrello, G., Avellone, G., Indelicato, S., Marcì, G., Navarro, S., 2018a. Photocatalytic oxidation of six endocrine disruptor chemicals
Palmisano, L., 2012. Genotoxicity of citrus wastewater in prokaryotic and in wastewater using ZnO at pilot plant scale under natural sunlight. Environ.
eukaryotic cells and efficiency of heterogeneous photocatalysis by TiO2. Sci. Pollut. Control Ser. 35 (25), 34995e35007.
J. Photochem. Photobiol. B Biol. 8e15. Vela, N., Calín, M., Y ~ez-Gasco
an n, M.J., Garrido, I., Pe rez-Lucas, G., Fenoll, J.,
Shan, A.Y., Ghazi, T.I.M., Rashid, S.A., 2010. Immobilisation of titanium dioxide onto Navarro, S., 2018b. Photocatalytic oxidation of six pesticides listed as endocrine
supporting materials in heterogeneous photocatalysis: a review. Appl. Catal. disruptor chemicals from wastewater using two different TiO2 samples at pilot
Gen. 1e2, 1e8. plant scale under sunlight irradiation. J. Photochem. Photobiol. Chem. 271e278.
Sordo, C., Van Grieken, R., Marugan, J., Fern andez-Iban~ ez, P., 2010. Solar photo- Vevers, W.F., Jha, A.N., 2008. Genotoxic and cytotoxic potential of titanium dioxide
catalytic disinfection with immobilised TiO2 at pilot-plant scale. Water Sci. (TiO2) nanoparticles on fish cells in vitro. Ecotoxicology 5, 410e420.
Technol. 2, 507e512. Vilhunen, S., Puton, J., Virkutyte, J., Sillanpa€a
€, M., 2011. Efficiency of hydroxyl radical
Souza, R.P., Freitas, T.K.F.S., Domingues, F.S., Pezoti, O., Ambrosio, E., Ferrari- formation and phenol decomposition using UV light emitting diodes and H2O2.
Lima, A.M., Garcia, J.C., 2016. Photocatalytic activity of TiO2, ZnO and Nb2O5 Environ. Technol. 865e872.
applied to degradation of textile wastewater. J. Photochem. Photobiol. Chem. Wang, H., Wick, R.L., Xing, B., 2009. Toxicity of nanoparticulate and bulk ZnO, Al2O3
9e17. and TiO2 to the nematode Caenorhabditis elegans. Environ. Pollut. 4, 1171e1177.
Spasiano, D., Marotta, R., Malato, S., Fernandez-Iban ~ ez, P., Di Somma, I., 2015. Solar Wang, Y., Zhang, X., Liu, J., Wang, Y., Duan, D., Fan, C., 2015. Facile regeneration and
photocatalysis: materials, reactors, some commercial, and pre-industrialized photocatalytic activity of CuO-modified silver bromide photocatalyst. Mater. Sci.
applications. A comprehensive approach. Appl. Catal. B Environ. 90e123. Semicond. Process. 613e620.
Sun, R., Nakajima, A., Watanabe, T., Hashimoto, K., 2003. Decomposition of gas- Wu, J., Ma, L., Chen, Y., Cheng, Y., Liu, Y., Zha, X., 2016. Catalytic ozonation of organic
phase octamethyltrisiloxane on TiO2 thin film photocatalystsdcatalytic activ- pollutants from bio-treated dyeing and finishing wastewater using recycled
ity, deactivation, and regeneration. J. Photochem. Photobiol., A 2, 203e209. waste iron shavings as a catalyst: removal and pathways. Water Res. 140e148.
Talwar, S., Sangal, V.K., Verma, A., 2018. Feasibility of using combined TiO2 photo- Zhao, Y., Zhong, J., Li, H., Xu, N., Shi, J., 2002. Fouling and regeneration of ceramic
catalysis and RBC process for the treatment of real pharmaceutical wastewater. microfiltration membranes in processing acid wastewater containing fine TiO2
J. Photochem. Photobiol. Chem. 263e270. particles. J. Membr. Sci. 1, 331e341.
Threrujirapapong, T., Khanitchaidecha, W., Nakaruk, A., 2017. Treatment of high Zhuang, H., Han, H., Hou, B., Jia, S., Zhao, Q., 2014. Heterogeneous catalytic ozona-
organic carbon industrial wastewater using photocatalysis process. Environ.- tion of biologically pretreated Lurgi coal gasification wastewater using sewage
Nanotechnol. Monit.Manag. 163e168. sludge based activated carbon supported manganese and ferric oxides as cat-
Tichonovas, M., Krugly, E., Grybauskas, A., Janku naite,
_ D., Racys, V., alysts. Bioresour. Technol. 178e186.
Martuzevi cius, D., 2017. Advanced oxidation-based treatment of furniture

A Critical Review

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Journal of Cleaner Production 258 (2020) 120694

Contents lists available at ScienceDirect

Journal of Cleaner Production

A critical review on application of photocatalysis for toxicity reduction

1. Introduction compounds, pesticides, polycyclic aromatic hydrocarbons (PAHs),

L. Concentration of oxygen 8 inhibition of Vibrio ﬁscheri

3. Photocatalysis of oxidation and reduction reactions on the surface of photo-

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