Reducing toxicity and antimicrobial activity of a pesticide mixture via photo-Fenton in different aqueous matrices using iron complexes

Enhancing disinfection and microcontaminant removal by coupling LED driven UVC and UVA/photo-Fenton processes in continuous flow reactors

For the first time, the sequential combination of UVC-LED (276 nm) and photo-Fenton/UVA-LED (376 nm) process has been assessed in continuous flow mode for wastewater reclamation according to the new European Regulation for reuse in agricultural irrigation (EU 2020/741). The results show that it is possible to obtain water quality class B (Escherichia coli ≤ 100 CFU/100 mL) by UVC-LED irradiation alone, operating the system with a hydraulic residence time (HRT) of 6.5 min and liquid depth of 5 cm in the case of secondary effluents with low Escherichia coli load (8.102-3.1.103 CFU/100 mL). As for high bacteria concentrations (1.2-4.2.104 CFU/100 mL), HRTs longer than 30 min are required. The bacterial load has not influenced decontamination, removing 18 ± 4 % of microcontaminants. Coupling the UVC (30-min HRT and 5.0 cm liquid depth) and the UVA/photo-Fenton (60-min and 15-cm liquid depth) systems allows 58 ± 4 % of real organic microcontaminants to be removed, in addition to achieving water quality class B.

Efficient destruction of basic organo-nitrogenous compounds in liquid hydrocarbon fuel using ascorbic acid/H2O2 system under ambient condition

Due to the limitations of the conventional refinery methods, development of a new method such as oxidative denitrogenation (ODN) is highly desirable. This study described a novel ODN to remove organo-nitrogenous compounds (ONCs) in liquid fuel by ascorbic acid (AscH2) and H2O2 redox system under ambient conditions. Seven ONCs including pyridine, quinoline, acridine, 7,8-benzoquinoline, indole, N-methylpyrrolidone (NMP), and N,N-dimethylformamide (DMF) were chosen to assess the fuel-denitrified ability of the AscH2/H2O2 system. The results showed that the basic group of ONCs (pyridine, quinoline, and acridine) can be effectively removed (removal ratio > 95 %) while the removal efficiency of water-soluble compounds (7,8-benzoquinoline, NMP, and DMF) was moderate (61-68 %) under a mild temperature (30 °C) and atmospheric pressure. Free radical quenching and electron paramagnetic resonance experiments confirmed that hydroxyl and AscH2 radicals played a major role in the degradation of ONCs. The degraded products of quinoline were analyzed by gas chromatography-mass spectroscopy and ion chromatography. Based on the identified intermediate products, a putative reaction pathway majorly involving three steps of N-onium formation, transfer hydrogenation, and free radical oxidative ring-opening was suggested for the quinoline degradation. The presented approach can be performed at a normal temperature and pressure and will live up to expectations in the pre-denitrogenation and selective removal of basic ONCs in fuel oils.

Influence of water matrix components and peroxide sources on the transformation products and toxicity of tebuthiuron under UVC-based advanced oxidation processes

Coupling of UV-C irradiation to different peroxides (H₂O₂, S₂O₈^2- and HSO₅^-) has great potential to degrade persistent organic compounds due to the formation of HO^• or SO₄^•- species. However, an in-depth comparison between the performance of different UV-C/peroxide processes as a function of (i) target compound degradation, (ii) generated transformation products and (iii) lethal/sub lethal toxicity effects has not yet been performed. To this end a comparison study was carried out to evaluate the effectiveness of different UV-C/peroxide processes using the herbicide tebuthiuron (100 or 500 μg L^-1) as a model pollutant. TBH degradation experiments were performed at lab-scale in real municipal wastewater treatment plant effluent and distilled water. Faster degradation occurred by increasing peroxide concentration from 735 to 2206 μmol L^-1 in the municipal wastewater treatment plant effluent, mainly for S₂O₈^2-. Experiments performed in the presence of peroxide trapping agents - HO^• and SO₄^•- (methoxibenzene) or HO^• (2-propanol) - revealed that oxidation in the UV-C/S₂O₈^2- system occurs mainly through SO₄^•-. Lower toxicity for the MWWTP effluent was obtained after oxidative treatments using hydrogen peroxide or monopersulfate as oxidants which react mainly through HO^• radicals. Two mechanistic pathways were proposed for tebuthiuron degradation: (i) hydrogen abstraction by HO^• (H₂O₂ and HSO₅^-) and (ii) electron transfer by SO₄^•- (S₂O₈^2-). In addition, one unprecedented transformation product was identified. In conclusion, results emphasize the relevance of comparing the degradation of toxic compounds in the presence of different peroxide sources and matrices and simultaneouly evaluating responses chemical and biological endpoints.

Photo-Fenton oxidation of cylindrospermopsin at neutral pH with LEDs

Cylindrospermopsin (CYN) is a potent cyanobacterial toxin found in freshwaters worldwide. In this work, the feasibility of the photo-Fenton process under neutral pH using light emitting diodes as irradiation source for the removal of this hazardous cyanotoxin from freshwater was investigated. The impact of the kind of iron chelating agent (ethylenediamine-N, N'-disuccinic acid vs. ethylenedinitrilotetraacetic acid) as well as the effect of the main operating conditions viz. H₂O₂ dose, Fe(III) load, initial CYN concentration, and Fe(III):EDDS molar ratio on the performance of the process was systematically evaluated. EDDS was selected as the most appropriate iron chelating agent considering the kinetics of the process and the environmental impact (Vibrio fischeri and Artemia salina). Under optimized conditions ([H₂O₂] = 30 mg L^-1; [Fe(III)] = 5 mg L^-1; Fe(III):ligand = 1:0.5 (molar ratio)), complete removal of CYN was achieved in 15-min reaction time. Furthermore, the catalytic system showed to be effective in real water matrices (river and reservoir waters) spiked with CYN. Although the presence of inorganic ions (mainly HCO₃^-/CO₃^2-) and dissolved organic carbon decreased the oxidation rate of CYN due to scavenging reactions and iron coordination, respectively, complete elimination of the cyanotoxin was achieved in all cases. The fate of EDDS along the process was also evaluated to demonstrate that the catalytic system investigated, apart from its effectiveness, warrants the complete absence of residues after reaction. Therefore, the proposed system constitutes a promising method for cyanotoxin treatment either as a drinking water treatment step in conventional plants or as a potential remediation strategy in the natural environment.

Challenges on solar oxidation as post-treatment of municipal wastewater from UASB systems: Treatment efficiency, disinfection and toxicity

The application of solar photo-Fenton as post-treatment of municipal secondary effluents (MSE) in developing tropical countries is the main topic of this review. Alternative technologies such as stabilization ponds and upflow anaerobic sludge blanket (UASB) are vastly applied in these countries. However, data related to the application of solar photo-Fenton to improve the quality of effluents from UASB systems are scarce. This review gathered main achievements and limitations associated to the application of solar photo-Fenton at neutral pH and at pilot scale to analyze possible challenges associated to its application as post-treatment of MSE generated by alternative treatments. To this end, the literature review considered studies published in the last decade focusing on CECs removal, toxicity reduction and disinfection via solar photo-Fenton. Physicochemical characteristics of effluents originated after UASB systems alone and followed by a biological post-treatment show significant difference when compared with effluents from conventional activated sludge (CAS) systems. Results obtained for solar photo-Fenton as post-treatment of MSE in developed countries indicate that remaining organic matter and alkalinity present in UASB effluents may pose challenges to the performance of solar advanced oxidation processes (AOPs). This drawback could result in a more toxic effluent. The use of chelating agents such as Fe³⁺-EDDS to perform solar photo-Fenton at neutral pH was compared to the application of intermittent additions of Fe²⁺ and both of these strategies were reported as effective to remove CECs from MSE. The latter strategy may be of greater interest in developing countries due to costs associated to complexing agents. In addition, more studies are needed to confirm the efficiency of solar photo-Fenton on the disinfection of effluent from UASB systems to verify reuse possibilities. Finally, future research urges to evaluate the efficiency of solar photo-Fenton at natural pH for the treatment of effluents from UASB systems.

Efficacy of a large-scale integrated constructed wetland for pesticide removal in tail water from a sewage treatment plant

The higher and higher detection frequencies of micro-pollutants such as pesticides in water are nowadays intensifying the investigation for strategies to provide effective engineering methods that could mitigate such substances. Traditional sewage treatment plants (STP) do not design specific processes for micro-pollutants removal in water. As an environmentally-friendly measure, some laboratory-scale wetlands have been proved to be effective in the removal of pesticides in water, but such studies are rarely carried out in large-scale wetlands, especially when they are adopted as a polishing step of STPs. Therefore, the further removals of micro-pollutants in tail water of STPs through the large-scale wetlands and the relevant removal mechanism are still knowledge gaps. In this study, 44 target pesticides were detected in the water of a large-scale integrated constructed wetland (ICW) for four seasons. The ICW was established to further process the tail water from a STP, whose drainage was from domestic sewage of local residents. There were 19, 16, 17, and 19 pesticides detected in spring, summer, autumn, and winter, respectively. The removal values for Σ₁₉ pesticides ranged from 49.99% to 84.96% during the study period, and the removal of these pesticides followed significant seasonal trends, which was likely because the microorganisms responsible for biotic degradation were markedly influenced by seasonal temperature fluctuations. Proteobacteria, Chloroflexi, Acidobacteria, Planctomycetes, and Bacteroidetes were the dominant phyla, and might be associated with the biodegradation of organic pollutants in the ICW. Removal of pesticides by the ICW resulted in overall toxicity reductions in water, but butachlor and chlorpyrifos were still at non-ignorable ecological risks. This study highlights the potential of constructed wetlands for micro-pollutants removal in water as a polishing step in STPs.

Use of organic fertilizers in solar photo-Fenton process as potential technology to remove pineapple processing wastewater in Costa Rica

Background: This work studied the use of the organic fertilizers DTPA-Fe and EDDS-Fe as iron chelates for solar driven photo-Fenton process at natural pH. This process was proposed to investigate its performance on removing a mixture of agrochemicals (propiconazole, imidacloprid and diuron) from pineapple processing wastewater to obtain a suitable effluent to be reused in the agricultural sector. Methods: Experiments were carried out in a solar simulator with a stirred cylindric photoreactor, with a volume of 150 mL and controlled temperature (20°C). The first set of experiments was carried out with ultrapure water to determine optimal iron and H 2O 2 concentrations. The second was performed with simulated wastewater of pineapple processing. Results: The optimized operational conditions for both iron complexes were 10 mg L -1 of Fe (III) and 25 mg L -1 of H 2O 2, since more than 80% of micropollutants (MP) (at an initial concentration of 1 mg L -1 of each compound) were removed in only 20 min with both DTPA-Fe and EDDS-Fe. The effect of organic matter and inorganic salts on radicals scavenging and chelates stability was also investigated in the experiments performed with synthetic pineapple processing wastewater. The results disclosed differences depending on the iron complex. Nitrites were the principal component influencing the tests carried out with EDDS-Fe. While carbonates at low concentration only significantly affected the experiments performed with DTPA-Fe, they were the major influence on the MPs removal efficiency decrease. In contrast, the presence of Ca 2+ and Mg 2+ only influence on this last one. Finally, the results of phytotoxicity disclosed the suitability of treated effluent to be reused in the agricultural sector.  Conclusions: This work demonstrated that solar powered photo-Fenton catalysed by iron fertilizer EDDS is a suitable technology for depolluting water streams coming from pineapple processing plants at circumneutral pH, and its subsequent reuse for crop irrigation.

Effect of Iron Complex Source on MWWTP Effluent Treatment by Solar Photo-Fenton: Micropollutant Degradation, Toxicity Removal and Operating Costs

Benzophenone-3, fipronil and propylparaben are micropollutants that are potential threats to ecosystems and have been detected in aquatic environments. However, studies involving the investigation of new technologies aiming at their elimination from these matrices, such as advanced oxidation processes, remain scarce. In this study, different iron complexes (FeCit, FeEDTA, FeEDDS and FeNTA) were evaluated for the degradation of a mixture of these micropollutants (100 µg L−1 each) spiked in municipal wastewater treatment plant (MWWTP) effluent at pH 6.9 by solar photo-Fenton. Operational parameters (iron and H2O2 concentration and Fe/L molar ratio) were optimized for each complex. Degradation efficiencies improved significantly by increasing the concentration of iron complexes (1:1 Fe/L) from 12.5 to 100 µmol L−1 for FeEDDS, FeEDTA and FeNTA. The maximum degradation reached with FeCit for all iron concentrations was limited to 30%. Different Fe/L molar ratios were required to maximize the degradation efficiency for each ligand: 1:1 for FeNTA and FeEDTA, 1:3 for FeEDDS and 1:5 for FeCit. Considering the best Fe/L molar ratios, higher degradation rates were reached using 5.9 mmol L−1 H2O2 for FeNTA and FeEDTA compared to 1.5 and 2.9 mmol L−1 H2O2 for FeEDDS and FeCit, respectively. Acute toxicity to Canton S. strain D. melanogaster flies reduced significantly after treatment for all iron complexes, indicating the formation of low-toxicity by-products. FeNTA was considered the best iron complex source in terms of the kinetic constant (0.10 > 0.063 > 0.051 > 0.036 min−1 for FeCit, FeNTA, FeEDTA and FeEDDS, respectively), organic carbon input and cost-benefit (USD 327 m−3 > USD 20 m−3 > USD 16 m−3 > USD 13 m−3 for FeEDDS, FeCit, FeEDTA and FeNTA, respectively) when compared to the other tested complexes.

A review toward contaminants of emerging concern in Brazil: Occurrence, impact and their degradation by advanced oxidation process in aquatic matrices

This work presents data regarding the occurrence and treatment of Contaminants of Emerging Concern (CECs) in Brazil in the past decade. The literature review (2011-2021) revealed the detection of 87 pharmaceutical drugs and personal care products, 58 pesticides, 8 hormones, 2 illicit drugs, caffeine and bisphenol A in distinct matrices (i.e.: wastewater, groundwater, sea water, rainwater, surface water, drinking water and hospital effluent). Concentrations of CECs varied from ng-μg L^-1 depending on the location, compound and matrix. The inefficiency of conventional wastewater treatment methods on the removal of CECs and lack of basic sanitation in some regions in the country aggravates contamination of Brazilian aquatic environments and poses potential environmental and health risks. Advanced oxidation processes (AOPs) are pointed out as viable and efficient alternatives to degrade CECs and prevent environmental contamination. A total of 375 studies involving the use of AOPs in Brazilian aqueous matrices were published in the last decade. Fenton and photo-Fenton processes, photo-peroxidation, ozonation, electrochemical advanced oxidation and heterogeneous photocatalysis are some of the AOPs applied by Brazilian research groups. Although many works discuss the importance of applying these technologies for CECs removal in real treatment plants, most of these studies assess the treatment of distilled water or simulated effluent. Therefore, the conduction of studies applying AOPs in real matrices are critical to drive the implementation of these processes coupled to conventional water and wastewater treatment in real plants in order to prevent the contamination of environmental matrices by CECs in Brazil.

Valorization of UWWTP effluents for ammonium recovery and MC elimination by advanced AOPs

The main objective of this study was to generate ready-to-use revalorized irrigation water for fertilization from urban wastewater treatment plant (UWWTP) effluents. The focus was on controlled retention of NH₄⁺ and microcontaminants (MC), using nanofiltration. Retentates generated were treated by solar photo-Fenton at circumneutral pH using Ethylenediamine-N, N'-disuccinic acid (EDDS) iron complexing agent. Solar photo-Fenton degradation efficacy was compared with electrooxidation processes as anodic oxidation, solar-assisted anodic oxidation, electro-Fenton and solar photoelectro Fenton. Finally, phytotoxicity and acute toxicity tests were performed to demonstrate the potentially safe reuse of treated wastewater for crop irrigation. Nanofiltration was able to produce a ready-to-use permeate stream containing recovered NH₄⁺. (valuable nutrient). Solar photo-Fenton treatment at circumneutral pH would only be of interest for rapid degradation of contaminants at less than 1 mg/L in nanofiltration retentates. Other alternative tertiary treatments, such as electrooxidation processes, are a promising alternative when a high concentration of MC requires longer process times. Anodic oxidation was demonstrated to be able to eliminate >80% of microcontaminants and solar-assisted anodic oxidation significantly reduced the electricity consumption. Electro-Fenton processes were the least efficient of the processes tested. Phytotoxicity results showed that irrigation with the permeates reduced germination, root development was mainly promoted and shoot development was positive only at low retention rate (concentration factor = 2). Acute and chronic Daphnia magna toxicity studies demonstrated that the permeate volumes should be diluted at least 50% before direct reuse for crop irrigation.

Assessment of a Novel Photocatalytic TiO2-Zirconia Ultrafiltration Membrane and Combination with Solar Photo-Fenton Tertiary Treatment of Urban Wastewater

The objective of this study was to assess the combination of a photocatalytic TiO2-coated ZrO2 UF membrane with solar photo-Fenton treatment at circumneutral pH for the filtration and treatment of urban wastewater treatment plant (UWWTP) effluents. Photocatalytic self-cleaning properties were tested with a UWWTP effluent under irradiation in a solar simulator. Then, both the permeates and retentates from the membrane process were treated using the solar photo-Fenton treatment. The UWWTP effluent was spiked with caffeine (CAF), imidacloprid (IMI), thiacloprid (THI), carbamazepine (CBZ) and diclofenac (DCF) at an initial concentration of 100 µg/L each. Retention on the membrane of Pseudomonas Aeruginosa (P. Aeruginosa), a Gram-negative bacterial strain, was tested with and without irradiation. It was demonstrated that filtration of a certain volume of UWWTP effluent in the dark is possible, and the original conditions can then be recovered after illumination. The photocatalytic membrane significantly reduces the turbidity of the UWWTP effluent, significantly increasing the degradation efficiency of the subsequent solar photo-Fenton treatment. The results showed that the membrane allowed consistent retention of P. Aeruginosa at an order of magnitude of 1 × 103–1 × 104 CFU/mL.

An insight into the bioelectrochemical photoreduction of CO2 to value-added chemicals

Goal of sustainable carbon neutral economy can be achieved by designing an efficient CO₂ reduction system to generate biofuels, in particular, by mimicking the mechanism of natural photosynthesis using semiconducting nanomaterials interfaced with electroactive bacteria (EAB) in a photosynthetic microbial electrosynthesis (PMES) system. This review paper presents an overview of the recent advancements in the biohybrid photoanode and photocathode materials. We discuss the reaction mechanism observed at photoanode and photocathode to enhance our understanding on the solar driven MES. We extend the discussion by showcasing the potential activity of EABs toward high selectivity and production rates for desirable products by manipulating their genomic sequence. Additionally, the critical challenges associated in scaling up the PMES system including the strategies for diminution of reactive oxygen species, low solubility of CO₂ in the typical electrolytes, low selectivity of product species are presented along with the suggestions of alternative strategies to achieve economically viable generation of (bio)commodities.

Effect of salinity on preconcentration of contaminants of emerging concern by nanofiltration: Application of solar photo-Fenton as a tertiary treatment

This study focused on the effect of salinity on the performance of a pilot-scale nanofiltration (NF) for preconcentration of microcontaminants (MCs) in combination with solar photo-Fenton or photo-Fenton-like treatment for their elimination from NF permeate and concentrate streams. Photo-Fenton was carried out in a solar simulator at pH of 3 and at natural pH using Ethylenediamine-N, N'-disuccinic acid (EDDS) as an iron complexing agent. Degradation efficacy was tested with MCs commonly found in urban wastewater treatment plant effluents (caffeine, imidacloprid, thiacloprid, carbamazepine and diclofenac). Hydrogen peroxide and persulfate were compared in solar processes. Increase in salinity and pressure had a negligible influence on MC permeability order and NF selectivity. Solar photo-Fenton was able to degrade MCs present in the concentrated stream, and rapidly eliminate any residual MCs that might finally be present in permeate streams. Persulfate used instead of hydrogen peroxide was shown to be inefficient for the selected MCs. Fe(III):EDDS at circumneutral pH was able to remove MCs as quickly as classical photo-Fenton at acid pH, or even faster. This effect supports use of Fe(III):EDDS at natural pH for treating NF concentrates or polishing NF permeates when NF membranes are operated under extreme conditions of salinity.