key: cord-0737908-b6t2qn8y
authors: da Luz, Vilson Conrado; Bazoti, Suzana Fátina; Behling, Laura; Dalla Rosa, Clarissa; Pasquali, Gean Delise Leal
title: Enhanced UV Direct Photolysis and UV/H(2)O(2) for Oxidation of Triclosan and Ibuprofen in Synthetic Effluent: an Experimental Study
date: 2022-04-02
journal: Water Air Soil Pollut
DOI: 10.1007/s11270-022-05583-z
sha: 0806d31a5279b8e0ceba8571e05a6cb91ec43ddb
doc_id: 737908
cord_uid: b6t2qn8y

This study aimed to evaluate the implementation of an advanced oxidation system based on UV radiation and UV/H(2)O(2) for degradation of TCS and IBU in synthetic effluent. The assays occurred in a 2-L reactor, protected from external light and equipped with a UV lamp (λ = 254 nm). The effect of contaminant concentration, fractions of chemical species present, and mineralization were evaluated. In the UV/ H(2)O(2) system, different concentrations of H(2)O(2) were studied for oxidation of the contaminants. The kinetic experiments took place between 75 and 270 min of UV irradiation. The results showed > 99% oxidation of TCS in the direct photolysis system at pH 9.4 after 12 min. The degradation of IBU in the UV/H(2)O(2) system, when 10 mg L(−1) of H(2)O(2) was used, was 97.39% oxidation. We obtained k′ values of 0.189 min(−1) for TCS when its highest oxidation occurred and k′ values of 0.0219 min(−1) for IBU. The system was not able to completely mineralize the contaminants, presenting high values of TOC and COD after treatment, thus suggesting the occurrence of phototransformation. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11270-022-05583-z.

wastewater treatment plants (Bandala et al., 2021; Espejo et al., 2020; Guidony et al., 2021) . These contaminants can be non-prescription drugs that combat common symptoms such as fever, in the case of ibuprofen (Jamerson & Haryadi, 2020) , and antimicrobial agents widely present in hand sanitizers such as triclosan (Guidony et al., 2021) .

Ibuprofen (IBU, (RS)-2-(4-(2 methylpropyl)phenyl) propanoic acid) is a weak organic acid, highly bound to plasma albumin and extensively metabolized and excreted in the form of metabolites and their conjugates, having an elimination half-life of approximately 2 h (Hersh & Dionne, 2017) . After administration, about 15% of the compound is excreted in the parental form and 26% and 43% in the form of hydroxyl-IBU and carboxy-IBU metabolites, respectively (Farré et al., 2008) . In the natural environment, IBU poses several risks, such as oxidative stress in fish (Stancova et al., 2017) and negative effects of rotifer survival and reproduction (González-Pérez 2016) .

Triclosan (TCS, 5-chloro-2-(2.4-dichlorophenoxy) phenol) is a broad-spectrum antimicrobial agent and, due to its great efficiency, it has been increasingly used in the formulations of soaps, toothpastes, and various skin and oral cosmetic products (Gopalakrishnan et al., 2021; Iovino et al., 2019) . TCS is introduced into the natural environment mainly through the discharge of domestic effluents. Already in the environment, triclosan represents a potential risk because of its ability to inhibit algal growth (Mohan & Balakrishnan, 2019) , toxic effects on invertebrates (Khatikarn et al., 2018) , and increased microbial resistance (Drury et al., 2013) , among other effects.

Ingested pharmaceuticals are excreted into the environment through animal and human urine and feces (Fang et al., 2012) . About 10-90% of administered doses of pharmaceutical and personal care products (PPCPs) are excreted from the human body in parent forms and the remainder as metabolites and/or conjugated forms (Balakrishna et al., 2017) .

Due to the wide use of TCS and IBU, these emerging contaminants are detected in natural environments, such as rivers, at concentrations of 3-68 ng L −1 (Yang et al., 2015) and 0.59-1.4 µL −1 (Amos Sibeko et al., 2019) , also being found in wastewater treatment plants 443-1757 ng L −1 (Mohan & Balakrishnan, 2019 ) and 8612.9-1607.8 ng L −1 (Kermia et al., 2016) . A few of the physicochemical properties of TCS and IBU are presented in Table 1 .

Advanced oxidation processes (AOPs) is a concept initially proposed by Glaze in 1987 . They consist of methods that can be applied to the treatment of various compounds that are difficult to remove, as they chemically destroy numerous contaminants by generating strong oxidizing agents, such as hydroxyl radicals (HO • ), which can attack and mineralize organic contaminants (Coha et al., 2021; Glaze et al., 1987) .

AOPs are considered powerful engineering solutions for processes that usually need to be integrated for the removal of different contaminants, since they reach numerous compounds of different concentrations in the same treatment system (Coha et al., 2021) . Among the main AOPs used for degradation of organic substances are Fenton processes, ozonation, electrochemical oxidation, and photochemical processes (Domingues et al., 2021) .

Photochemical processes have low secondary pollution rates and low operating costs Tan et al., 2021) . Such processes are based on the supply of energy through radiation (Eλ = hv) to a molecule, where the substance absorbs the energy photons and reaches specific levels of excited states, levels sufficient for the excitation of electrons, and formation of free radicals that will act on the organic contaminant (Cuerda-Correa et al., 2020) . In this work, the photochemical processes UV/H 2 O 2 and direct UV photolysis were evaluated as final polishing technology for multicomponent oxidation of TCS and IBU, as well as the mineralization effectiveness and the energy consumption.

Triclosan (≥ 97.0%) and ibuprofen (≥ 99.0%), used for chromatographic curves, were purchased from Sigma-Aldrich. LC-MS grade MeOH, formic acid (analytical grade), and ultrapure water (> 18 MΩ cm, Milli-Q-POD) were used for HPLC analyses. Triclosan (≥ 97%, Êxodo científica, Brazil), commercial ibuprofen powder (Artesani, Brazil), NaOH, and H 2 O 2 (35%, Êxodo científica, Brazil) were used for the synthetic effluent. Na 2 HPO 4 , KH 2 PO 4 , Na 2 CO 3 , NaHCO 3 , CH 3 COOH, and C 2 H 3 NaO 2 (analytical grades) were used for buffer solutions. 

Quantitative analyses were performed using highperformance liquid chromatography (LC-MS, Shimadzu) with an SPD-M20A photodiode array detector. Separation took place on a C18 column (250 × 4.6 mm; 5 µm) operated at 30 °C, using mobile phase in isocratic mode (80:20 MeOH and ultrapure water mixture, acidified with 0.001% formic acid) with flow rate of 0.8 mL min −1 , injection volume of 20 µL and 25 min of analysis time. The wavelength was maintained at 200 and 280 nm for detection of IBU and TCS, respectively. Quantification was done through chromatographic curves updated periodically with standard solutions of TCS and IBU. The chromatographic detection limit was 0.05 and 0.1 mg L −1 for TCS and IBU, respectively. TOC concentration was determined by the difference of total carbon and inorganic carbon using a total organic carbon analyzer (TOC-L CPN, Shimadzu), with values reported as the average of three successive readings. The H 2 O 2 residual was determined using a MQuant 0.5-25 mg L −1 colorimetric test (Merck).

The stock solution of triclosan uses a methodology adapted from Lu et al. (Lu et al., 2009) , being the mass of triclosan dissolved in 20 mL of NaOH 0.01 Mol L −1 , previously cooled. The volume was gauged with buffer solution. The stock solution of ibuprofen was adapted from Wang et al., 2019) , formulated by dissolving the mass of IBU in 0.5 mL of MeOH, due to the low solubility of the compound in water.

The synthetic effluent was made up from the solutions of triclosan and ibuprofen and the pH was controlled by 10 mM buffer solutions. Carbonate-bicarbonate buffer was used for pH = 9.4, phosphate buffer for pH = 6.0, and acetate buffer for pH = 3.6.

The reactor was made of glass with dimensions of 15 cm × 45 cm × 15 cm, with the base established on two magnetic stirrers kept at 120 rpm. At the top, a UV-C lamp (OSRAM Puritec HNS L, Italy) of 38 cm in length and 36 W of power, average wavelength of 254 nm, and average light intensity of 7800 cd ( Fig. 1) , was used because of the large absorption at this wavelength by the phenol group present in the TCS molecule. The reactor was installed in a dark room with no light entering from the external environment, and 2L of solution was added.

The reactor operating conditions on the photo-oxidation of IBU and TCS were evaluated as a function of irradiation time (0-270 min). The direct photolysis experiments occurred by varying the parameters, initial concentration (TCS 0 = 8.89-17.79 mg L −1 ; IBU 0 = 9.90-34.24 mg L −1 ), and pH of the solution (pH = 3.6; 6.0; 9.4). The UV/H 2 O 2 system was studied by adding H 2 O 2 (0-15 mg L −1 ) at the beginning of the irradiation, keeping the concentrations of IBU and TCS constant (TCS 0 = 15.46 mg L −1 ; IBU 0 = 34.5 mg Vol.: (0123456789) L −1 ) and pH = 6.0. For all experiments, the temperature was kept constant at 25 ± 2 °C. The UV lamp was turned on 30 min before the effluent was submitted to irradiation in order to reduce the variation of photon incidence due to the previous heating of the equipment.

The presence of different concentrations of IBU and TCS in liquid effluents justifies the need to understand the effect of this parameter on the degradation process.

The effect of the initial concentration of triclosan (TCS 0 ) and ibuprofen (IBU 0 ) on the photo-oxidation system is presented by Fig. 2 , as a function of irradiation time. The experiments were developed using 2L of synthetic effluent at pH = 6.0, a value adopted respecting the limits for discharge of effluents into water bodies according to Brazilian federal regulations (Conama, 2005) .

For ibuprofen (Fig. 2a) , when in initial concentration (IBU 0 = 34.24 ± 1.24 mg L −1 ), the system showed a removal rate of 83.28% in 270 min with a remaining concentration of 5.73 ± 0.16 mg L −1 . The reduction of the initial concentration led to a reduction of the remaining concentration. In terms of degradation efficiency, the highest value was achieved by the system with IBU 0 = 24.77 ± 0.51, about 88.10%. Overall, the average efficiency was 82.63% among all experiments. Wang et al. (2019) in 90 min of irradiation using a UV-LED system reported 51.58% degradation using an initial concentration of 41.25 mg L −1 in 8 mL, a value lower than that obtained by this study.

The system was not greatly affected by the concentration of IBU for values lower than 34.24 ± 1.24 mg L −1 , where the difference between tests was 0.88 ± 0.43 mg L −1 , which was lower than the final difference of 3.63 ± 0.21 mg L −1 obtained between the experiment with higher and lower concentration, thus revealing some effect on removal efficiency when high concentrations are used. Peng et al. (2017) attributed such behavior to the high presence of intermediates, which hinder the oxidation reactions of IBU. Wang et al. (2019) , employing concentrations of 41.26-103.14 mg L −1 , showed that the photo-oxidation rate of IBU is directly proportional to IBU 0 , going against the results suggested by the present study, where concentrations ≥ 34.24 mg L −1 affect the removal efficiency of the direct UV photo-oxidation system.

TCS degradation ( to affect the degradation system, similar to the behavior exhibited by IBU. In the experiment with TCS 0 = 17.79 ± 0.44 mg L −1 , the degradation efficiency was 87.12% in 60 min, showing a remaining concentration of 2.29 ± 0.01 mg L −1 . Iovino et al. (2019) , using a direct photolysis system at pH 6.0 and concentrations of 4.48-17.89 mg L −1 in 100 mL, concluded that 80% of the initial concentration was degraded in the first 5 min. Iovino et al. (2019) also reported a remaining concentration of 0.049 mg L −1 when TCS 0 = 7.78 mg L −1 in a direct photolysis system after 60 min of irradiation in 100 mL of solution. This value is lower than the one presented in this study, because when TCS 0 = 8.89 ± 0.83 mg L −1 was used, values below the detection limit were obtained after 40 min of irradiation.

The chemical speciation was evaluated by dissolving the contaminants in different pH ranges, respecting the pKa of each target pollutant. In general, the molecular species is favored when pH < pKa, as is the anionic species when pH > pKa.

The pKa = 4.9 (Pemberton & Hart, 1999) and pKa = 7.9 (Luo et al., 2018) values were used for TCS and IBU, respectively. The fractions of anionic (α − ) and neutral (α) species of the target contaminants were determined according to Eq. (1) and Eq. (2), as proposed by Luo et al. (2018) .

The behavior of IBU and TCS chemical fractions as a function of pH is shown in Fig. 3 .

For IBU, the experiments were performed at pH = 6.0 and 3.2, and 92.64% of the anionic species (IBU − ) and 95.2% of the neutral species prevailed, respectively. For TCS, the experiments were performed at pH = 9.4 and 6.0 and 96.93% of the anionic form (TCS − ) and 98.76% of the neutral form prevailed, respectively.

The obtained data show a higher efficiency of IBU − degradation than IBU (Fig. 4a) , with the contaminant being reduced by 83.2% in 270 min (Fig. 3a) . Such results are in agreement with the values reported by Iovino et al. (2016) , who observed the decrease of oxidation efficiency with decreasing pH, obtaining the lowest oxidation values near pH 3.

When compared to TCS, it is remarkable the greater difficulty of oxidation of the IBU molecule by the UV system. Such behavior can be justified by the difference between the chemical structures (1) = 10 −pH 10 −pKa + 10 −pH of the contaminants. The presence of certain functional groups such as phenol (Ar-OH), weak C-H bonds, and aryl chloride (Ar-Cl) in the TCS molecule can facilitate photochemical reactions stimulated by the direct absorption of ultraviolet radiation (Ahmad et al., 2016; Bartolomeu et al., 2018) , while the IBU molecule presents only weak C-H bonds.

The oxidation of TCS using the direct photolysis system at pH 9.4 proved to be much more efficient (Fig. 4b) , obtaining pH 98.73% oxidation in 10 min, and in 12 min the TCS concentration was already below the detection level of the chromatograph. When the experiments took place at pH 6.0, said result was only obtained between 60 and 100 min. The deprotonated form of TCS was shown to be more susceptible to degradation by direct photolysis than its molecular form. The quick oxidation of TCS at pH > 9, as reported by this study, is in line with data obtained by Iovino et al. (2019) , using a direct photolysis system in a 100 mL reactor at pH 10, achieving nearly 99% removal in less than 30 min.

When compared to pH 6, the anionic form of the TCS molecule was shown to be more efficient for degradation (Fig. 4b) . It is suggestive to state that this process occurred due to the percentage of deprotonated anions of the phenol group present in the synthetic effluent, which is affected with increasing pH, thus increasing the molar absorption coefficient (Huang et al., 2018) .

Photo-assisted peroxidation was evaluated using different concentrations of H 2 O 2 in synthetic effluent containing IBU and TCS at pH = 6.0 and room temperature (25 ± 2 °C). Concentrations of 15, 10, and 5 mg L −1 of H 2 O 2 were used. The use of H 2 O 2 aims to increase the speed of degradation of the target contaminants through oxidation by • OH radicals arising from photolytic cleavage of the H 2 O 2 molecule (Eq. 3).

The hydroxyl radical is a strong, non-selective oxidizing agent that acts on the oxidation of organic and organometallic pollutants present in the solution, thus leading to their mineralization in the forms of inorganic ions, H 2 O or CO 2 (Cuerda-Correa et al., 2020).

The low oxidation rate of IBU by the direct photolysis system justifies the use of H 2 O 2 as an oxidizing agent, acting in tandem with UV radiation in the UV/H 2 O 2 system. The results show a reduction in the irradiation time needed for the oxidation of the contaminant when compared to the direct UV system at pH 6.0, presented in Fig. 4 a. The irradiation time was reduced in 195 min when using the lowest concentration of H 2 O 2 (5 mg L −1 ) and 225 min when using the highest concentration of H 2 O 2 (15 mg L −1 ).

(3) The highest efficiency for IBU oxidation was obtained when 10 mg L −1 of H 2 O 2 was used, resulting in 97.39% oxidation of the contaminant after 75 min (Fig. 5a) . The use of 15 and 5 mg L −1 of H 2 O 2 resulted in 95.38% and 82.32% oxidation, respectively. Peng et al. (2017) reported 82.4% removals of IBU in 30 min UV/H 2 O 2 system when using 20 mg L −1 and 15 mg L −1 of IBU in 200 mL and 75 W lamp. In the present study, 30 min of irradiation and 34.5 mg L −1 of IBU obtained 72.03% oxidation of the target contaminant in the system with 15 mg L −1 of H 2 O 2 .

Unlike IBU, when compared to the direct photolysis system at pH 9.4, the oxidation of TCS by UV/ H 2 O 2 did not prove to be the superior reactor among those used in this study. The results obtained for degradation of TCS by UV/H 2 O 2 showed that the efficiency is inversely related to the concentration of H 2 O 2 used, with lower concentrations being the source of higher oxidation rates. Using 5 mg L −1 of H 2 O 2 degraded 97.69% of TCS in the synthetic effluent in 15 min and found below the detection limit between 15 and 30 min of irradiation. By increasing oxidant concentration, using 10 and 15 mg L −1 of H 2 O 2 , TCS was below the detection limit only between 30 and 60 min and between 60 and 75 min, respectively.

H 2 O 2 was not shown to be fully decomposed by the system and its residual was found in all treatments. For the experiments using 15, 10, and 5 mg L −1 of H 2 O 2 , after 60 min, a residual of 10, 5, and 5 mg L −1 of H 2 O 2 in the synthetic effluent was still present. Liu et al. also reported a delay in H 2 O 2 consumption in the UV/H 2 O 2 system, being consumed by 20% after 10 h using 17 mg L −1 of H 2 O 2 (Liu et al., 2016) .

The degradation kinetics were fitted to the pseudofirst order model. The pseudo-first order rate (k′, min −1 ) is obtained from Eq. (4) and can also be observed from the slope of the curve of ln(C t /C 0 ) by t.

where t is the photochemical oxidation time (min); C t is the concentration at any instant t (mg L −1 ); C 0 is the initial concentration (mg L −1 ); and k′ is the pseudo-first order rate (min −1 ).

The photochemical degradation half-life was obtained from Eq. (5) according to Luo et al. (2018) .

where t 1/2 is the degradation half-life (min) and k′ is the pseudo-first order rate. Figure 5 presents the degradation kinetic models of IBU and TCS fitted to the pseudo-first-order model at different pH values (pH = 3.6; 6.0; 9.4) and H 2 O 2 concentrations (5, 10, and 15 mg L −1 ; pH = 6.0) presenting as a fixed parameter the initial concentration of the target contaminants. Table 3 lists the constants and degradation half-lives of TCS and IBU. The degradation constant k′ TCS − was higher than k′ TCS . It was observed that the target contaminant was degraded faster when the pH values increased from 3.6 to 9.4 (Fig. 6b) . For IBU, the same behavior was observed (Fig. 6a) , where the degradation constant k′ IBU − was higher than that obtained when the contaminant was in its neutral molecular form. As the pH is increased, the neutral form deprotonates in solution, occurring the increase of k′ for IBU, as can be observed the values of the constants at pH 3.6, 6.0, and 9.4 (Table 2 ). This same behavior was observed by Luo et al. (2018) , in which the constant at pH 7.55 was higher than that at pH 3.0 in the degradation of IBU by direct photolysis.

For TCS, the chemical speciation showed that the direct UV photolysis system at pH 9.4 is more efficient in the photo-oxidation of the contaminant, which is confirmed by the obtained values of k′ and t 1/2 (Table 2) . Azarpira et al. (2019) reported degradation constants of 0.131 and 0.0687 for TCS at concentrations of 7.5 and 10.0 mg L −1 in a UV/Iodide/ ZnO (UIZ) degradation system with 11 W lamps in 150 mL of solution. Sanchez-Prado et al. (2006) , in a study on the photodegradation of TCS in domestic wastewater using UV and solar radiation, found that the t 1/2 for degradation of the contaminant was 4.8 min at pH around 7, with the pollutant being mostly in its molecular form. Such a result points to the reverse of that reported in this study, in which the contaminant in its molecular form (pH 6.0 and 3.6) showed longer degradation half-lives both in the absence of H 2 O 2 and in the presence of it (Table 2) . This difference in results presented by Sanchez-Prado et al. (2006) can be explained by the use of a real matrix, where it is possible to occur the interference of different substances present in solution and even the acceleration of degradation through organic matter, as reported by Iovino et al. (2019) using humic acids as a model compound of natural organic matter in the degradation of TCS by UV radiation.

The system used for IBU oxidation showed large degradation half-lives in the absence of H 2 O 2 ( Table 2 ). This may be related to the high concentration of IBU used. According to Peng et al. (2017) , in an experiment using concentrations of 5-25 mg L −1 of IBU, increasing the concentration hindered the oxidation process, since the high concentration of IBU in solution also means the existence of high concentrations of intermediates. These intermediates act as scavengers for OH radicals, reducing the reaction of the oxidant with IBU. Peng et al. further concluded similar results to those presented by the present study, such as the difficulty of oxidation of IBU by UV radiation alone (Peng et al., 2017) .

The comparison between the pseudo-first order rates reported by the scientific literature is presented by Table 3 for both TCS and IBU under different operating conditions.

Despite the high oxidation rates of TCS and IBU obtained in this study, the results for TOC and COD showed that the contaminants were not entirely mineralized by the direct photolysis and UV/H 2 O 2 systems. For the multicomponent direct photolysis system, the highest mineralization rate obtained was 47.27% at pH 9.4 after 270 min of irradiation time for TOC removal. In the UV/H 2 O 2 system, 10.97% TOC removal was obtained using 15 mg L −1 of H 2 O 2 in multicomponent solution after 75 min. The substantial difference in oxidation may be directly related to the irradiation time and the pH of the solution. In more alkaline ranges, the presence of anionic species facilitates the oxidation of IBU and TCS, and thus may enhance the mineralization of the contaminants. The higher mineralization of contaminants by the direct UV system was also proven by the COD (Supplementary File). The experiments in UV/H 2 O 2 system occurred at pH = 6.0, where even though the IBU was mostly in anionic form, the system showed low removals of TOC, due to the very difficult oxidation of IBU, the competition for • OH by the contaminants and the formation of intermediates. In pH 6.0 system TCS obtained 40.63% of TOC removal after 75 min, while for IBU about 10.26% was obtained. Trousil et al. (2018) also obtained low TOC removal values for IBU degradation, about 20.37% in direct photolysis system and 30.09% in UV/TiO 2 system after 1-h irradiation. The removal of TOC in the oxidation of IBU may be related to the continuous formation of small carboxylic acids during the process (Szabó et al., 2011) .

The low mineralization data point to byproduct formation from the oxidation of TCS and IBU by both the direct photolysis system and the UV/H 2 O 2 system. TCS has been known for its high rate of byproduct formation by phototransformation (Apell et al., 2020) . Huang et al. (2018) draw attention to nonremoval of byproduct cytotoxins by the UV and UV/ (Apell et al., 2020; Kliegman et al., 2013) , where due to the use of MeOH as a cosolvent, the formation of 2-phenoxyphenol (PP) is facilitated (Apell et al., 2020) . For IBU, it has been widely reported that decarboxylation occurs (Luo et al., 2018; Szabó et al., 2011) . Also, hydroxylation to the benzene ring under high energy absorptions is possible (Luo et al., 2018; Wang et al., 2021) . Some byproducts are 1-ethyl-4-(2-methylpropyl)-benzene, 1-(4-isobutylphenyl) ethanol and 4-isobutylacetophenone (Szabó et al., 2011; Wang et al., 2021) . (Apell et al., 2020; Kliegman et al., 2013) and b IBU (Szabó et al., 2011; Wang et al., 2021) 

The E EO is a parameter used to evaluate the amount of energy required for the decay of the target contaminant concentration by order of magnitude a 90% reduction in 1 m 3 of water (Keen et al., 2018) . The figure of merit was calculated according to Bolton et al. (2001) and is represented using Eq. (6) and fitted to pseudo-first order kinetic behavior (Eq. 7).

where E EO is the electrical energy per order (kWh m −3 order −1 ), P is the lamp power (kW), t is the time required for degradation (h), V is the solution volume (L), C 0 and C f are the initial and final contaminant concentrations (mg L −1 ), and k′ is the pseudo-first order rate (min −1 ). Table 4 shows the E EO values obtained under different operating conditions of the photochemical reactors employed for the degradation of IBU and TCS in synthetic effluent at different pH values and H 2 O 2 concentrations. The low energy required for TCS degradation compared to IBU is remarkable. The lower E EO values for TCS were already expected, since this contaminant proved to be more photosensitive than IBU.

The low E EO value found in the direct photolysis system at pH 9.4 for TCS may be related to the wide presence of the TCS − species in the solution. As discussed earlier, photochemical transformations

occur more easily on the deprotonated anionic form of this contaminant. Due to the high interaction of TCS with ultraviolet radiation, the chemical bonds are more susceptible to direct exposure and thus all of them can be broken (Azarpira et al., 2019) . The presence of H 2 O 2 in the reactor did not significantly reduce the energy required for oxidation of TCS, with the chemical speciation of the contaminant being much more significant. The chemical speciation showed that the greater presence of deprotonated species reduced the amount of energy required by 51.77%, when compared to pH 3.6 where there is a majority of the molecular form of the target substance. Azarpira et al. (2019) , using a UV/iodide/ZnObased advanced oxidation system (UIZ) in a 150-mL tubular photochemical reactor and an 11 W power UV lamp achieved E EO values in range of 2.48-12.29 kWh m −3 order −1 for TCS degradation between 1 and 10 mg L −1 . These values reported by Azarpira et al. (2019) are lower than those developed by the present study, where in a larger volume of effluent it was possible to reach lower amounts of energy required for TCS degradation, thus implying cost reduction for oxidation of such contaminants through a simpler system of operation, when compared to a tubular reactor and without the need to use chemical catalysts.

For IBU degradation, the photochemical system showed the need of H 2 O 2 for E EO reduction. IBU proved to be difficult to remove using the direct photolysis system, becoming more expensive when compared to TCS oxidation, requiring longer irradiation times and thus greater use of electricity. The use of 15 mg L −1 of H 2 O 2 reduced the energy required for IBU degradation by 82.29%. Although the use of H 2 O 2 means implementing yet another cost to the system, the high reduction in energy use for degradation and the low concentration of H 2 O 2 makes the cost of the oxidant less significant.

Trousil et al. reported E EO of 136.2 kWh dm −3 using 11 W power UV lamp in a volume of 20 dm −3 and a concentration of 20 mg dm −3 of IBU in a recirculating reactor. When using the UV/H 2 O 2 system with concentration of 0.5 g dm −3 of oxidant, the energy required for degradation of 90% of the contaminant went to order of 61.2 kWh dm −3 , a 55.1% reduction in energy consumption (Trousil et al., 2018) . 

In this study, the degradation of TCS and IBU was evaluated using two photochemical oxidation systems. The processes in direct photolysis and UV/ H 2 O 2 obtained favorable results for implementation as final polishing technology, indicating the use of direct photolysis at pH = 9.4 for TCS oxidation and the increment of H 2 O 2 for IBU. The direct photolysis system at pH 9.4 obtained values below the detection level of the chromatograph after 10 min, the lowest E EO , and the highest k′ value, which was the best result obtained for TCS degradation. The UV/H 2 O 2 system for oxidation of IBU reduced the E EO values and the time required for concentration decay. About 97.39% of the contaminant was oxidized when 10 mg L −1 of H 2 O 2 was used in 75 min of irradiation. The results point to incomplete mineralization of the target contaminants after both UV and UV/H 2 O 2 treatments. About 10.75% was mineralized in the reactor with 10 mg L −1 of H 2 O 2 and 47.27% in direct UV photolysis reactor pH 9.4, thus proving the formation of degradation byproducts, which can lead to toxic substances.

Author Contribution All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Vilson Conrado da Luz, Suzana Fátima Bazoti, Laura Behling, Clarissa Dalla Rosa, and Gean Delise Leal Pasquali. The first draft of the manuscript was written by Vilson Conrado da Luz, and Gean Delise Leal Pasquali and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Funding The authors received financial support from the Rio Grande do Sul State Research Support Foundation for the (grant n°368/UFFS/2020). The authors received financial support from the Rio Grande do Sul State Research Support Foundation (FAPERGS) [scientific initiation scholarship grant n°270/UFFS/2020] and the Federal University of Fronteira Sul which was responsible for the laboratory area and the acquisition of reagents and equipment, (n ° 270/ UFFS /2020).

Data Availability All data generated or analyzed during this study are included in this published article [and its supplementary information files].

Ethics Approval and Consent to Participate Not applicable.

Not applicable.

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The chemistry of water treatment processes involving ozone, hydrogen peroxide and ultraviolet radiation

Effects of selected pharmaceuticals (ibuprofen and amoxicillin) on the demography of Brachionus calyciflorus and Brachionus havanaensis (Rotifera)

Sensitive and selective determination of triclosan using visual spectroscopy

ABC proteins activity and cytotoxicity in zebrafish hepatocytes exposed to triclosan. Environmental Pollution

Nonopioid Analgesics

Efficient degradation of cytotoxic contaminants of emerging concern by UV/H2O2

Ibuprofen photodegradation in aqueous solutions

Triclosan photolysis: Operating condition study and photo-oxidation pathway

The use of ibuprofen to treat fever in COVID-19: A possible indirect association with worse outcome? Medical Hypotheses

Standard reporting of electrical energy per order (E EO ) for UV/H 2 O 2 reactors

Occurrence, fate and removal efficiencies of pharmaceuticals in wastewater treatment plants (WWTPs) discharging in the coastal environment of Algiers

Effects of triclosan on aquatic invertebrates in tropics and the influence of pH on its toxicity on microalgae. Environmental Science and Pollution Research

Experimental and theoretical insights into the involvement of radicals in triclosan phototransformation

Degradation kinetics and mechanism of oxytetracycline by hydroxyl radical-based advanced oxidation processes

UV-driven hydroxyl radical oxidation of tris(2-chloroethyl) phosphate: Intermediate products and residual toxicity

Spectrophotometric determination of triclosan in personal care products

UV direct photolysis of sulfamethoxazole and ibuprofen: An experimental and modelling study

Triclosan in treated wastewater from a city wastewater treatment plant and its environmental risk assessment. Water, Air, and Soil Pollution

Electrochemical behaviour of triclosan at a screen-printed carbon electrode and its voltammetric determination in toothpaste and mouthrinse products

Photo-degradation ibuprofen by UV/H2O2 process: Response surface analysis and degradation mechanism

Faster photodegradation rate and higher dioxin yield of triclosan induced by cationic surfactant CTAB

Individual and mixture toxicity evaluation of three pharmaceuticals to the germination and growth of Lactuca sativa seeds

Monitoring the photochemical degradation of triclosan in wastewater by UV light and sunlight using solid-phase microextraction

Effects of the pharmaceutical contaminants ibuprofen, diclofenac, and carbamazepine alone, and in combination, on oxidative stress parameters in early life stages of tench (Tinca tinca). Veterinární medicína

Phototransformation of ibuprofen and ketoprofen in aqueous solutions

Kinetic removal of acetaminophen and phenacetin during LED-UV365 photolysis of persulfate system: Reactive oxygen species generation

Paracetamol and ibuprofen removal from aqueous solutions by ozonation and photochemical processes

Mechanistic insight into the degradation of ibuprofen in UV/H2O2 process via a combined experimental and DFT study

A preliminary assessment of the impact of COVID-19 on environment -A case study of China

Degradation of ibuprofen by UV-LED/catalytic advanced oxidation process

Occurrence of triclosan in the tropical rivers receiving the effluents from the hospital wastewater treatment plant. Environmental Monitoring and Assessment

COVID-19 and surface water quality: Improved lake water quality during the lockdown

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