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In this paper, reaction kinetics, degradation mechanisms and associated toxicity have been assessed in detail concerning the abatement of neonicotinoid insecticide clothianidin (CLO) by ozone-based oxidation in water. The second-order rate constants for the reaction of CLO with molecular ozone (O3) and hydroxyl radical ([rad]OH) were determined by the direct and competition kinetics (with UV/H2O2 system as the radical source) methods, respectively, and estimated to be 103 M−1 s−1 and 3.7·109 M−1 s−1. This suggested a (potential) higher contribution of the indirect mechanism rather than the direct degradative pathway in the CLO ozonation process. Additionally, CLO oxidation was studied through an O3 and O3/H2O2 system for three complex real water matrices with distinct characteristics. DOC content was found to be the main parameter responsible for making difficult the achievement of high CLO degradations, whereas carbonate alkalinity did not exert a great impact on the process efficiency. Results indicated that typical ozone doses (up to 1 mg O3/mg DOC) were not enough for the complete removal of this micropollutant, ranging only from 50 to 80%. The study concerning the transformation products (TPs), performed by means of high-resolution mass spectrometry, allowed to suggest potential degradation routes based on the five major CLO-TPs identified. It was inferred that [rad]OH was involved in the formation of all TPs, whereas O3 was only involved in the formation of two of them. A preliminary toxicity assessment concerning CLO and its TPs during ozonation was conducted at three different trophic levels via the ECOSAR software. Results showed that none of the compounds was classified as very toxic for aquatic organisms, and all TPs exhibited minor toxicity than the parent compound. Changes in molecular structure, such as chlorothiazole ring breakdown, could be the main reason for this considerable decrease in toxicity. Overall, the present study demonstrates that ozonation can be considered a suitable technology alternative for CLO (and associated toxicity) abatement from aqueous matrices., This work was financially supported by MCIN/AEI/10.13039/501100011033, with the project PID2020-112674RB-I00, as well as by the Agency for Management of University and Research Grants of the Government of Catalonia (project 2017SGR131).

In this work, the effect of solar light as a “reducing agent” in Fe(VI)/PMS process for disinfection and decontamination of water was investigated. Single, double and triple-factor disinfection processes were systematically studied against Escherichia coli and validated on sulfamethoxazole. The experiments performed with PMS or Fe(VI) in dark conditions only achieved 1-log reduction in 2 h, while no significant enhancement was found in the Fe(VI)/PMS system. The introduction of solar light in either PMS or Fe(VI) process enhanced the E. coli inactivation, and complete inactivation (6-log) was reached at 90 min. However, the best improvement was achieved with the triple-factor disinfection process (Fe(VI)/PMS/solar light) which presented 6-log reduction at only 40 min. In the case of sulfamethoxazole, more than 70% removal was achieved under the Fe(VI)/PMS/solar light system, while only about 20% was observed with single and double-factor processes. Our study revealed the light spectrum distribution effects and the iron speciation implications. A main role for HO. and the participation of SO4.- was found, without overlooking the direct effects of solar light and PMS itself, as well as the possible involvement of other transient species. Overall, the efficacy of the Fe(VI)/PMS/solar light process against a series of microorganisms combined with the effectiveness at near-neutral pH, suggest its suitability for further assessment in disinfection and/or decontamination of water., Stefanos Giannakis would like to acknowledge the Spanish Ministry of Science, Innovation and Universities (MICIU) for the Ramón y Cajal Fellowship (RYC2018-024033-I) and the ‘NAVIA’ Project (PID2019-110441RB-C32). Núria López is grateful to the Spanish Ministry of Science and Innovation (aids for mobility for short-term research stays of FPU predoctoral staff, grant N° FPU-16/02101) which provided the economic support required to carry out the research stay at UPM.

The catalytic activity of membranes produced with commercial unmodified reduced graphene oxide (rGO) was demonstrated for the first time in persulfate (PS) activation through experiments performed in continuous mode. Phenol (Ph; C-0 = 5 mg L-1) and venlafaxine (VFX; C-0 = 250 mu g L-1) were employed as model compounds. The influence of the main operation parameters was first investigated considering an operation period of 24 h. For a rGO membrane with an effective area of 2.1 cm(2) , contaminant removal is favored at lower flow rates (0.1 mL min(-1)) and higher catalyst loads (15 mg). Assays carried out under these conditions yielded average removals of 90 and 94% for Ph and VFX, respectively, corresponding to normalized removal rates in the range of 1.71-1.79 L m(-2) h(-1) mg(cat)(-1). Membrane stability tests were conducted in continuous mode for 1 week, allowing to observe a significant catalyst deactivation after 2-3 d of operation, although the catalytic activity could be recovered through simple thermal regeneration procedures. Batch mode oxidation tests employing powder rGO treated at different temperatures (500, 850 and 1000 degrees C) and materials characterization data allowed to conclude that a shift of the surface chemistry character from acidic to basic enhances the catalytic performance. Moreover, scavenging tests indicated that singlet oxygen (O-1(2)), apparently generated by nucleophilic attack of PS to C = O in pyrone-like functionalities, is the main oxidizing species in the rGO-PS system.

Nowadays, reaction mechanisms of photo-Fenton process with chelated iron are not yet clearly defined. In this study, five organic fertilizers were used as iron complexes to investigate the role of sunlight and oxygen in photo-Fenton at near neutral pH. UV absorbance and stability constant of each selected iron chelate is different, and this work demonstrates that these parameters affect the reaction mechanisms in SMX degradation. Irradiation experiments without H2O2 revealed that only EDDS-Fe and DTPA-Fe achieved SMX degradation, but different iron release. These results, together with soluble oxygen free experiments, allowed the proposal of complementary reaction mechanisms to those of the classical photo-Fenton. The proposed mechanisms start through the potential photoexcitation of the iron complex, followed by subsequent oxygen-mediated hydroxyl radical generation reactions that are different for EDDS-Fe and DTPA-Fe. Moreover, irradiation experiments using EDTA-Fe and HEDTA-Fe had negligible SMX degradation despite iron release was observed, evidencing the differences between iron chelates., The authors are grateful with the Ministry of Economy and Competitiveness (project CTQ2017-86466-R, MINECO/FEDER, UE), AGAUR-Generalitat de Catalunya (project 2017SGR-131) and Nuria López FPU research fellowship (FPU-16/02101) financed by Ministry of Science, Innovation and Universities.

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic has challenged societies around the globe. Technologies based on ozone, a powerful oxidant, have been evaluated to inactivate this virus in aerosols and fomites. However, the high data diversity hinders the possibility of establishing a common ground for determining best practices for the use of these technologies. Furthermore, there is a lack of consensus regarding which are the main mechanisms of ozone virus inactivation. This critical review examined the most relevant information available regarding ozone application in gas-phase for different viruses inactivation (including recent publications dealing with SARS-CoV-2), and pointed towards envelope alteration as the main reaction pathway for enveloped viruses, such as is the case of SARS-CoV-2. It could also be concluded that gaseous ozone can be indeed an effective disinfectant, successfully inactivating viruses such us influenza A H1N1, MERS-CoV, SARS-CoV-1 or even SARS-CoV-2 in aerosols or fomites. In reviewed works, low ozone exposures, just around 0.1–0.4 mg L-1 min, achieve about 4 log10 of inactivation in aerosols, while exposures between 1 and 4 mg L-1 min may be needed to guarantee an inactivation of 3–4 log10 in different fomites. Although further studies are required, ozone is an effective candidate to be used against SARS-CoV-2 or other viruses in surfaces and indoor locations., Graphical Abstract ga1

Five organic fertilizers (DTPA, EDDHA, HEDTA, EDTA and EDDS) were studied as iron sources for photo-Fenton process at natural pH to remove micropollutants (MPs) from wastewater for its reuse in irrigation. The results demonstrated that the stability constant of iron chelates is a key parameter for optimal micropollutants removal and it is linked to the structure of chelator. Mixtures of organic fertilizers were also tested to overcome excessive iron loose and to optimize MPs abatement kinetics. An improvement of photo-Fenton process occurred when using chelating mixtures. For instance, with 50 %EDDS + 50 %EDTA total removal of propranolol (PROP) was achieved at 30 min while EDTA needed up to 90 min of reaction and with EDDS total degradation was not achieved. In addition, the availability of dissolved iron of the mixture at the end of the treatment was 5.5 times higher than EDDS, increasing its suitability as reuse water for irrigation.

Nowadays photoactivation mechanism of titanium dioxide nanoparticles (TiO

In a water scarcity scenario, the reused wastewater could be an essential source for agricultural irrigation considering that 60% of fresh water is destined to this area. In this study, an organic fertilizer (Diethylene triamine pentaacetic acid, DTPA) was used as a new chelating agent of iron for photo-Fenton's application at neutral pH using LEDs. Secondary effluents with different characteristics were tested for propranolol removal and bacterial inactivation. With DTPA, the best results were achieved with MBR matrix: 94.0% of propranolol removal and total bacterial inactivation after 120 min. IFAS matrix showed the worst results: 63.2% of propranolol removal and only 2-log reduction for Total Coliforms. The performance of DTPA as chelating agent was compared with EDTA and EDDS with two matrices. In MBR matrix, propranolol removal with EDTA was 100% in 15 minutes, while DTPA and EDDS reached similar results at 120 minutes (94.0 and 91.3%), respectively. The iron precipitation was evaluated, and DTPA showed high stability with Fe2+ (only 10.4% of iron reduction instead 97.3% for EDDS). In addition, it looks like that the stability of iron chelates plays an important role in bacterial inactivation. Thus, the experiments with DTPA showed the lowest bacterial growth-on-the-plate after 72 hours of the end of the experiment. Biodegradability and phytotoxicity were also evaluated and the experiments with DTPA had the lowest toxicity. The results of the experiments performed with DTPA were compared with the values in Proposal for agricultural water reuse suggesting that treated effluent accomplish the requirements for agriculture.

Nowadays photoactivation mechanism of titanium dioxide nanoparticles (TiO2 NPs) and reactive species involved in saline waters is not sufficiently established. In this study, TiO2 photocatalytic process under simulated solar irradiation was evaluated in synthetic seawater and compared with deionized water, using sulfamethoxazole (SMX) as model organic compound. For a TiO2 concentration of 100 mg L−1, SMX degradation resulted two times slower in seawater than in deionized water by the determination of their pseudo-first order rate constants of 0.020 min−1 and 0.041 min−1, respectively. Selected scavenging experiments revealed no significant contribution of hydroxyl radicals ( OH) on the degradation process in seawater, while these radicals contributed to circa 60% on the SMX depletion in deionized water. Instead, the involvement of reactive halogen species (RHS) as main contributors for the SMX degradation in seawater could be established. A mechanism for the RHS generation was proposed, whose initiation reactions involve halides with the TiO2 photogenerated holes, yielding chlorine and bromine radicals (Cl and Br ) that may later generate other RHS. Production of RHS was further confirmed by the identification of SMX transformation products (TPs) and their evolution over time, carried out by liquid chromatography-mass spectrometry (LC-MS). SMX transformation was conducted through halogenation, dimerization and oxidation pathways, involving mainly RHS. Most of the detected transformation products accumulated over time (up to 360 min of irradiation). These findings bring concerns about the viability of photocatalytic water treatments using TiO2 NPs in saline waters, as RHS could be yielded resulting in the generation and accumulation of halogenated organic byproducts.

Three organic fertilizers (EDTA (Ethylenedinitrilotetraacetic acid), EDDS (Ethylenediamine-N, N'-disuccinic acid) and DTPA (Diethylene triamine pentaacetic acid)) were tested as Fe-complexes in photo-Fenton process at natural pH for micropollutants (MPs) abatement and simultaneous E.coli inactivation. Less stable Fe-complexes show high iron precipitation, stopping MPs degradation. On the contrary, stable Fe-complexes imply low kinetic rates for MPs removal. To solve these inconveniences, three mixtures of organic fertilizers were also tested, trying to improve the kinetic rates of micropollutants oxidation and overcome iron precipitation. Three different pollutants (propranolol (PROP), acetamiprid (ACMP) and sulfamethoxazole (SMX)) were used as the target compounds. As the iron release is, in part, linked to the hardness of water, two water matrices from two different secondary wastewaters (Membrane Bioreactor (MBR) and Conventional Activated Sludge (CAS)) were tested. The best performance in micropollutant degradation and E.coli inactivation was achieved with the combination of EDDS + EDTA, accomplishing a good equilibrium between iron precipitation and rate of MPs removal. For instance, total removal of propranolol was achieved at 45 min in MBR, while it was only 85.7% in CAS, being an improvement of the process comparing with that obtained using single organic fertilizers. At the end of the treatment, 2.1 log-inactivation for E.coli was reached in CAS. The differences observed between both wastewaters were related to CAS' higher DOC, turbidity, and hardness. Finally, from the physicochemical characterization conducted, including Biochemical Oxygen Demand at 5 days and phytotoxicity, it is possible to highlight the suitability of these treated effluents for its reuse in irrigation, as long as in CAS matrix the final values of E. coli are within the legal limit., The authors wish to thank the Ministry of Economy and Competitiveness of Spain (project CTQ2017-86466-R, MINECO/FEDER, UE), AGAUR-Generalitat de Catalunya (project 2017SGR-131) and Nuria López FPU research fellowship (FPU-16/02101) financed by Ministry of Science, Innovation and Universities of Spain.

Combined sewer overflows (CSO), generated during the wet weather flow from the combination of the inflow and stormwater runoff in sewer system, result in an overflow of untreated wastewater from sewer system, which might ultimately contain different micropollutants (MPs). In this study, a coagulation-flocculation-sedimentation (CFS) pretreated CSO spiked with MPs was treated by catalytic ozonation using carbon, iron, and peroxide-based catalysts. The catalysts were characterized and their activity on MPs removal was studied at two different ozone (O3) doses (5 and 10 mg L−1). The effect of the treatment on the spiked CSO effluent was also assessed from the acute toxicity of the effluent using Microtox®, Yeast, and Macrophage cell-line toxicity assay tests. All the carbon-based catalysts showed large surface area, which was strongly influenced by the activation technique in the preparation of the catalysts. The CFS treatment strongly reduced the turbidity (≥60%) but had marginal effect on the UV254, dissolved organic carbon (DOC), and pH. Sludge Based Carbon (SBC) showed strong adsorption capacity (≥60% removal efficiency) for all MPs studied compared to other carbon and iron-based catalysts. Ozonation alone was effective for the degradation of easily oxidizable MPs (sulfamethoxazole, mecoprop, and 2,4-dichlorophenoxyl acetic acid), achieving more than 80% degradation efficiency at 10 mg L−1 of ozone, but not effective for atrazine (≤60% degradation efficiency) at similar O3 dose. Catalytic ozonation (at 10 mg L−1 O3 dose) improved the degradation of the MPs at low catalyst dosage but higher dosage strongly inhibited their degradation. In all cases, the effluents showed negligible acute toxicity, indicating the suitability of the process for the treatment of CSO.

The photo-Fenton process, with UV-A LED (λ = 380–390, 390–400 and 380–400 nm) has demonstrated to be effective in the abatement of a target micropollutant, such as diphenhydramine hydrochloride (DPH). Different concentrations of iron (Fe2+) and H2O2 were tested and monitored, and the best results in DPH removal were obtained for the highest concentrations of both iron (II) and H2O2 (10 mg Fe2+/L - 150 mg H2O2/L). The evolution of iron and peroxide concentration was also monitored. Kinetic studies showed that dark Fenton process prevails at the beginning of the experiment, when Fe2+ concentration is higher. However, after these initial moments, the prevailing process is photo-Fenton and, in addition, wavelength radiation plays an important role. Concerning the effect of radiation, four LEDs (4.2 W total power) were used, emitting radiation in the wavelength range between 380–390 or 390–400 nm. Similar results were obtained in both cases in DPH removal by photo-Fenton (30 min for total elimination). However, a synergistic effect was observed when two LEDs of 380–390 nm and two LEDs of 390–400 nm were used. Total power was the same (4.2 W) in each experimental condition, but the increase in the wavelength range to 20 nm (380–400 nm) produces an increase in the rate of DPH removal, achieving its total elimination at 15 min. This fact, with the use of a simple radiation model, reveals the important role that radiation plays in the photo-Fenton process. Finally, the formed intermediates were determined and some reaction pathways were proposed.

In this study, photo-Fenton treatment was performed to remove a target compound (propranolol, PROP) from wastewaters of secondary effluents coming from WWTP. Two different radiation sources were tested: BLB and UV-A LEDs, which implies low electrical power and no mercury content. The differences observed in the PROP removal with both lamps may be due to the different radiation distribution, absorption inside the reactor, emission angle and wavelength emission, which are key parameters in the radiation field of the photoreactor. Four wastewaters (IFAS, MBR, CAS and CAS-NE) and ultrapure water were tested to determine the influence of water matrix. Instead the propranolol degradation using UV-A LEDs was smaller than using BLB lamps, in ultrapure water the degradation was very similar. The matrices with more organic matter and turbidity achieved low propranolol removals due to the competition for hydroxyl radicals and the effect of the light scattering. In addition, photo-Fenton at neutral pH (to avoid the acidification/basification) was also carried out using two chelating agents (EDDS and EDTA). Two molar ratios ligand-Fe(II) were tested (1:1 and 1.5:1). EDDS with L:Fe(II) molar ratio 1:1 was selected based on studies of MP degradation, biodegradability and toxicity. Comparisons between conventional photo-Fenton and photo-Fenton with EDDS-Fe(II) were performed with UV-A LEDs. For Milli-Q and IFAS best results were achieved in conventional photo-Fenton (32.9% for IFAS instead of 14.3% in EDDS-Fe(II)). Contrary, for the MBR, CAS and CAS-NE the best results were shown for EDDS-Fe(II) photo-Fenton. In IFAS, biopolymers and humic substances were the responsible of the different behavior of IFAS than other WW. Finally, for conventional photo-Fenton, dark Fenton plays an important role during the first 30 s, then, photo-Fenton controls the process. For circumneutral photo-Fenton, dark Fenton is not so important during the initial time. These observations have been corroborated by different kinetic fittings for different reaction times.

Several works in literature demonstrated that catalytic ozonation using metal ions promotes the decomposition of ozone and generation of hydroxyl radicals (HO•). The purpose of this study was to assess the effects of different metal ions (Fe2+, Co2+ and Al3+) in disinfection of urban wastewater through E.coli and Pseudomonas spp inactivation along with cellular adenosine triphosphate (ATP) depletion. Simultaneously, the effect of catalytic ozonation of secondary effluent on the selected micropollutants removal with different ozone kinetics (acetamiprid, dichlorvos and atrazine) was evaluated in semi-continuous operation. Results demonstrated that E.coli and Pseudomonas spp inactivation increased almost 20% with 1 mg L−1 Fe2+, Co2+, Al3+ and 40% with 10 mg L−1 Fe2+ compared with single ozonation. Fe2+ was the most effective metal ion on inhibiting regrowth after the treatments. The cellular ATP followed the same trend as the indicators microorganisms inactivation, with significant reduction of ATP over the treatment to single ozonation comparison. The ROH,O3 was applied for the treatments to quantify and compare the micropollutants removal by the radical pathway. The improvement of metal ions on ROH,O3 values occurred significantly for both stages of ozonation (before and after initial ozone demand) for all tested metals. Thus, metal ions addition to ozonation process provided an increase in simultaneous disinfection and pesticides removal as well as in the inhibition of bacterial reactivation, which resulted in savings between 30–50% of ozone dose needs compared with the same attainment in single ozonation.