Removal of atrazine and its by-products from water using electrochemical advanced oxidation processes

Electrochemical oxidation of surfactants as an essential step to enable greywater reuse

The practical application of electrochemical oxidation technology for the removal of surfactants from greywater was evaluated using sodium dodecyl sulfate (SDS) as a model surfactant. Careful selection of electrocatalysts and optimization of operational parameters demonstrated effective SDS removal in treating a complex greywater matrix with energy consumption below 1 kWh g-1 COD (Chemical Oxygen Demand), paving the way for a more sustainable approach to achieving surfactant removal in greywater treatment when aiming for decentralized water reuse. Chromatographic techniques identified carboxylic acids as key byproducts prior to complete mineralization. These innovative approaches represent a novel pathway for harnessing electrochemical technologies within decentralized compact devices, offering a promising avenue for further advancements in this field.

Hydrogen peroxide electrogeneration from O2 electroreduction: A review focusing on carbon electrocatalysts and environmental applications

Hydrogen peroxide (H2O2) stands as one of the foremost utilized oxidizing agents in modern times. The established method for its production involves the intricate and costly anthraquinone process. However, a promising alternative pathway is the electrochemical hydrogen peroxide production, accomplished through the oxygen reduction reaction via a 2-electron pathway. This method not only simplifies the production process but also upholds environmental sustainability, especially when compared to the conventional anthraquinone method. In this review paper, recent works from the literature focusing on the 2-electron oxygen reduction reaction promoted by carbon electrocatalysts are summarized. The practical applications of these materials in the treatment of effluents contaminated with different pollutants (drugs, dyes, pesticides, and herbicides) are presented. Water treatment aiming to address these issues can be achieved through advanced oxidation electrochemical processes such as electro-Fenton, solar-electro-Fenton, and photo-electro-Fenton. These processes are discussed in detail in this work and the possible radicals that degrade the pollutants in each case are highlighted. The review broadens its scope to encompass contemporary computational simulations focused on the 2-electron oxygen reduction reaction, employing different models to describe carbon-based electrocatalysts. Finally, perspectives and future challenges in the area of carbon-based electrocatalysts for H2O2 electrogeneration are discussed. This review paper presents a forward-oriented viewpoint of present innovations and pragmatic implementations, delineating forthcoming challenges and prospects of this ever-evolving field.

Insights into the efficient mineralization of antibiotic trimethoprim in aqueous media by Fe2+ catalytically enhanced vacuum-UV irradiation: Kinetics, mechanisms, and toxicity evaluation

The widespread existence of antibiotics in the environment has attracted growing concerns regarding the potential adverse effects on aquatic organisms, ecosystems, and human health even at low concentrations. Extensive efforts have been devoted to developing new methods for effective elimination of antibiotics from wastewater. Herein, a novel process of Fe2+ catalytically enhanced vacuum ultraviolet (VUV) irradiation was proposed as a promising approach for the removal of antibiotic trimethoprim (TMP) in water. Compared with UVC photolysis, VUV photolysis, and UVC/Fe2+, VUV/Fe2+ could increase the pseudo-first-order reaction rate constant of TMP removal by 6.6-38.4 times and the mineralization rate by 36.5%-59.9%. The excellent performance might originate from the synergistic effect of VUV and Fe2+, i.e., VUV irradiation could effectively split water and largely accelerate the Fe3+/Fe2+ cycle to generate more reactive oxygen species (ROS). EPR results indicated that •OH and O2•- were identified as the main ROS in the UVC/Fe2+ and VUV/Fe2+ processes, while •OH, O2•-, and 1O2 were involved in the VUV process. The operating parameters, such as Fe2+ dosage and initial TMP contents, were evaluated and optimized. Up to 8 aromatic intermediates derived from hydroxylation, demethylation, carbonylation, and methylene group cleavage were identified by UPLC-QTOF-MS/MS technique, the possible pathways of TMP degradation were proposed. Finally, the acute and chronic toxicity of intermediates formed during TMP degradation in the VUV/Fe2+ process were also evaluated.

Degradation pathways of atrazine by electrochemical oxidation at different current densities: Identifications from compound-specific isotope analysis and DFT calculation

Current density was the key factor that impacted pollutant degradation by electrochemical oxidation, and reaction contributions at various current densities were non-negligible for the cost-effective treatments of organic pollutants. This research introduced compound specific isotope analysis (CSIA) into atrazine (ATZ) degradation by boron doped diamond (BDD) with current density of 2.5-20 mA/cm², in order to provide "in-situ" and "fingerprint" analysis of reaction contributions with changed current densities. As results, the increased current density displayed a positive impact on ATZ removal. The Ʌ_C/H values (correlations of Δδ¹³C and Δδ²H) were 24.58, 9.18 and 8.74 when current densities were 20, 4, and 2.5 mA/cm², with ·OH contribution of 93.5%, 77.2% and 80.35%, respectively. While DET process favored lower current density with contribution rates up to ∼20%. What's more interesting, though the carbon and hydrogen isotope enrichment factors (ε_C and ε_H) were fluctuate, the Ʌ_C/H linearly increased accompanied with applied current densities. Therefore, increasing current density was effective due to the larger ·OH contribution even though side reactions may occur. DFT calculations proved the increase of C-Cl bond length and the delocalization of Cl atom, confirming dechlorination reaction mainly occurred in the direct electron transfer process. While ·OH radical mainly attack the C-N bond on the side chain, which was more benefit to the fast decomposition of ATZ molecule and intermediates. It was forceful to discuss pollutant degradation mechanism by combining CSIA and DFT calculations. Target bond cleavage (i.e., dehalogenation reaction) can be conducted by changing reaction conditions like current density due to the significantly different isotope fractionation and bond cleavage.

Global distribution of pesticides in freshwater resources and their remediation approaches

The role of pesticides in enhancing global agricultural production is magnificent. However, their unmanaged use threatens water resources and individual health. A significant pesticide concentration leaches to groundwater or reaches surface waters through runoff. Water contaminated with pesticides may cause acute or chronic toxicity to impacted populations and exert adverse environmental effects. It necessitates the monitoring and removing pesticides from water resources as prime global concerns. This work reviewed the global occurrences of pesticides in potable water and discussed the conventional and advanced technologies for the removal of pesticides. The concentration of pesticides highly varies in freshwater resources across the globe. The highest concentration of α-HCH (6.538 μg/L, at Yucatan, Mexico), lindane (6.08 μg/L at Chilka lake, Odisha, India), 2,4, DDT (0.90 μg/L, at Akkar, Lebanon), chlorpyrifos (9.1 μg/L, at Kota, Rajasthan, India), malathion (5.3 μg/L, at Kota, Rajasthan, India), atrazine (28.0 μg/L, at Venado Tuerto City, Argentina), endosulfan (0.78 μg/L, at Yavtmal, Maharashtra, India), parathion (4.17 μg/L, at Akkar, Lebanon), endrin (3.48 μg/L, at KwaZuln-Natl Province, South Africa) and imidacloprid (1.53 μg/L, at Son-La province, Vietnam) are reported. Pesticides can be significantly removed through physical, chemical, and biological treatment. Mycoremediation technology has the potential for up to 90% pesticide removal from water resources. Complete removal of the pesticides through a single biological treatment approach such as mycoremediation, phytoremediation, bioremediation, and microbial fuel cells is still a challenging task, however, the integration of two or more biological treatment approaches can attain complete removal of pesticides from water resources. Physical methods along with oxidation methods can be employed for complete removal of pesticides from drinking water.

Atrazine induces phagocytotic dysfunction of microglia depends on nucleocytoplasmic translocation of acetylated HMGB1

Atrazine (ATR) is a widely applied herbicide which was named an environmental endocrine disrupting chemical (EDC). Increasing evidence indicates ATR causes neurotoxic effects resulting in central nervous system (CNS) disease. As the primary immunocytes in the CNS, microglia cells carry out their phagocytosis to maintain the CNS microenvironment by preventing damage from healthy cells. However, the mechanism in which ATR affects the phagocytic function of microglia remains unclear. The present study was designed to investigate the effect of ATR on the phagocytosis of microglia. BV-2 cells and primary microglia selected as microglial models in which BV-2 cells were administrated by ATR at different concentrations (0, 4, 8, 16 μM) for 24 h. Results demonstrated ATR dose-dependently increased the expression of ionized calcium binding adapter molecule 1 (Iba-1), indicating that microglia were activated. Microglial phagocytotic activity induced by ATR fluctuated at the different time points, accompanied by fluctuations in membrane receptor MERTK and cytoplasmic lysosomal marker LAMP1 (two markers related to cell phagocytosis). In this period, the expression of iNOS gradually increased. A mechanistic study further demonstrated that the translocation of High Mobility Group Protein-B1 (HMGB1) from nucleus to cytoplasm in the BV-2 and primary microglial cells induced by ATR, and the process showed a positive correlation with phagocytosis activity of BV-2 cells induced by ATR (r = 0.8030, P = 0.05; α = 0.1). ATR was also shown to spur the acetylation of HMGB1 by breaking the balance between acetylase P300 and deacetylase SIRT1. Unexpectedly, the inhibition of acetylating HMGB1 by resveratrol (Res) was effectively retained by HMGB1 in the nucleus, reversed the SIRT1 and MERTK expression, and enhanced the phagocytosis activity in BV-2 cells. Our results suggested that ATR exposure influenced microglial phagocytosis by acetylating HMGB1 further translocated it in the nucleoplasm.

Citric acid modified ultrasmall copper peroxide nanozyme for in situ remediation of environmental sulfonylurea herbicide contamination

Herbicide residues in the environment threaten high-quality agriculture and human health. Consequently, in situ remediation of herbicide contamination is vital. We synthesized a novel self-catalyzed nanozyme, ultrasmall (2-3 nm) copper peroxide nanodots modified by citric acid (CP@CA) for this purpose, which can break down into H₂O₂ and Cu²⁺ in water or soil. Ubiquitous glutathione reduces Cu²⁺ into Cu⁺, which promotes the decomposition of H₂O₂ into •OH through a Fenton-like reaction under mild acid conditions created by the presence of citric acid. The generated •OH efficiently degrade nicosulfuron in water and soil, and the maximum degradation efficiency could be achieved at 97.58% in water at 56 min. The possible degradation mechanisms of nicosulfuron were proposed through the 25 intermediates detected. The overall ecotoxicity of the nicosulfuron system was significantly reduced after CP@CA treatment. Furthermore, CP@CA had little impact on active components of soil bacterial community. Moreover, CP@CA nanozyme could effectively remove seven other sulfonylurea herbicides from the water. In this paper, a high-efficiency method for herbicide degradation was proposed, which provides a new reference for the in situ remediation of herbicide pollution.

Insight into atrazine removal by fallen leaf biochar prepared at different pyrolysis temperatures: Batch experiments, column adsorption and DFT calculations

The environmental pollution caused by atrazine in the agricultural production cannot be ignored. In this study, the fallen leaf biochar (LBC) was prepared at three different temperatures (500 °C, 600 °C, and 700 °C) using a simple pyrolysis method (500 LBC, 600 LBC, and 700 LBC) for atrazine adsorption. Batch experiments showed that the performance of LBC in atrazine adsorption improved with rising pyrolysis temperature, and the highest adsorption amount of 700 LBC reached 84.32 mg g^-1. Kinetic and isotherm models showed that the adsorption behaviors were both monolayer and multilayer chemisorption. The findings of the characterizations (Elemental analysis, BET, XRD, Raman, FT-IR, and XPS) confirmed that the degree of aromatization determined the adsorption capacity of LBC to atrazine, and π-π electron donor-acceptor interaction was the main adsorption mechanism. Density functional theory (DFT) calculations showed that the highly aromatized biochar was more effective for atrazine adsorption, manifested as smaller molecular distances, higher adsorption energies, more stable complex structures, and stronger π-electron conjugation. In the column adsorption experiments, reducing the inlet flow rate or increasing the bed height extended the breakthrough time and exhaustion time of the breakthrough curves, and 700 LBC still showed good adsorption performance after five cycles. Overall, fallen leaf biochar as a reuse product of resource showed good potential for application in atrazine adsorption, which can be used for atrazine-contaminated water remediation.

The effect of interlayer water of metal-modified montmorillonite for catalytic ozonation

The catalytic ozonation-based advanced oxidation process (AOP) is applied to remove nondegradable chemical oxygen demand (COD), while the application in industry is limited by the economics and activity of catalysts. In this study, we demonstrate that by taking atrazine (ATZ) as a model pollutant, the removal rates of catalytic ozonation were negatively correlated with the interlayer water content of metal-modified montmorillonite (M_x@MMT), instead of the loadings metals. Among the modified MMT, Zn_0.1@MMT achieved 83.2% degradation of ATZ within 15 min, and corresponding removal rates of COD and total organic carbon (TOC) reached 40.3% and 46.5%, respectively. Detailed EPR and quenching experiments identified that hydroxyl radicals (HO•) were the main reactive oxygen species and QTOF/MS/MS analysis helped to propose a possible degradation pathway of ATZ. Moreover, the catalytic performance of Zn_0.1@MMT under different conditions was also systematically evaluated.

Visible-light photoelectrocatalysis/H2O2 synergistic degradation of organic pollutants by a magnetic Fe3O4@SiO2@mesoporous TiO2 catalyst-loaded photoelectrode

In this paper, we describe a method for photoelectrocatalysis (PEC)/H₂O₂ synergistic degradation of organic pollutants with a magnetic Fe₃O₄@SiO₂@mesoporous TiO₂ (FST) photocatalyst-loaded electrode. At optimal conditions of pH 3.0, 2.25% H₂O₂, working electrode (fixed FST 30 mg) potential +0.6 V (vs. SCE), and 10 mg L^-1 of all experimental pollutants, the FST PEC/H₂O₂ synergistic system exhibited high activity and stability for the removal of various organic pollutants under visible light with comparable degradation efficiencies, including MB (98.8%), rhodamine B (Rh B, 96.7%), methyl orange (MO, 97.7%), amoxicillin (AMX, 83.9%). Moreover, this system obtained TOC removal ratios of 83.5% (MB), 77.9% (Rh B), 80.2% (MO), 65.5% (AMX) within 8 min. The kinetic rate constants of the PEC/H₂O₂ synergistic system were nearly 53 and 1436 times higher than that of the PEC process and H₂O₂ photolysis under visible light, respectively. Furthermore, the main reactive oxidant species (˙OH, ˙O₂ ^-) were studied and enhanced mechanisms of the photocatalytic-electro-H₂O₂ coupling system were proposed. This work brings new insights to efficiently purify organic pollutants by PEC coupled with peroxide under solar light illumination.

Kinetics and mechanism of the reaction of hydrogen peroxide with hypochlorous acid: Implication on electrochemical water treatment

Reduction of HOCl to Cl^- by in-situ electrochemical synthesis or ex-situ addition of H₂O₂ is a feasible method to minimize Cl-DBPs and ClO_x^- (x = 2, 3, and 4) formation in electrochemical oxidative water treatment systems. This work has investigated the kinetics and mechanism of the reaction between H₂O₂ and HOCl. The kinetics study showed the species-specific second order rate constants for HOCl with H₂O₂ (k₁), HOCl with HO₂^- (k₂) and OCl^- with H₂O₂ (k₃) are 195.5 ± 3.3 M^-1s^-1, 4.0 × 10⁷ M^-1s^-1 and 3.5 × 10³ M^-1s^-1, respectively. The density functional theory calculation showed k₂ is the most advantageous thermodynamically pathway because it does not need to overcome a high energy barrier. The yields of ¹O₂ generation from the reaction of H₂O₂ with HOCl were reinvestigated by using furfuryl alcohol (FFA) as a probe, and an average of 92.3% of ¹O₂ yields was obtained at pH 7-12. The second order rate constants of the reaction of ¹O₂ with 13 phenolates were determined by using the H₂O₂/HOCl system as a quantitative ¹O₂ production source. To establish a quantitative structure activity relationship, quantum chemical descriptors were more satisfactory than empirical Hammett constants. The potential implications in electrochemical oxidative water treatment were discussed at the end.

Scaled-up multi-anode shared cathode microbial fuel cell for simultaneous treatment of multiple real wastewaters and power generation

Microbial fuel cell (MFC) is lauded for its capacity to valorize organic substrates in wastes, providing a solution to environmental pollution and energy crisis. While different types of organic substrates affect removal efficiency and current output, most MFCs are designed to only be able to utilize one type of wastewater. However, many real wastewater treatment sites generate more than one type of wastewater which hinders the installation of most MFCs. This study aimed to investigate the performance of the novel-designed multi-anode shared cathode MFC (MASC-MFC) compared with a standard single anode/cathode MFC (SAC-MFC) and the simultaneous treatment of different types of real wastewaters (sewage, slaughterhouse, and hospital) in one MFC unit. The MASC-MFC (9025 mW/m² at 23.332 mA/m²) produced 1.7 times and 1.6 times higher in power density and current density and 2.2 times lower in internal resistance than the standard single anode/cathode MFC (SAC-MFC). A maximum COD removal efficiency of 62.7% was achieved with synthetic wastewater. Feeding the MASC-MFC with multiple real wastewaters decreased maximum power density 3.5 (2599 mW/m²) times and increased internal resistance 2.7 times. Stable current generation 1.575 mA was achieved over 300 h despite the different and complex wastewater physio-chemical compositions. The MASC-MFC achieved over 40% and approximately 30% coulombic efficiency independently in all the anode chambers irrespective of the type of real wastewater used, demonstrating the MASC-MFC's capacity to treat different real wastewaters with the added benefit of electricity production.

Toward efficient electrocatalytic degradation of iohexol using active anodes: A laser-made versus commercial anodes

The X-ray iodinated contrast medium iohexol is frequently detected in aquatic environments due to its high persistence and the inefficiency of its degradation by conventional wastewater treatments. Hence, the challenge faced in this study is the development of an alternative electrochemical treatment using active anodes. We investigate the oxidation of iohexol (16.42 mg L^-1) using different operating conditions, focusing on the role of different mixed metal oxide anodes in the treatment efficiency. The electrocatalytic efficiency of the Ti/RuO₂-TiO₂ anode prepared using a CO₂ laser heating and an ionic liquid is compared with Ti/RuO₂-TiO₂-IrO₂ and Ti/IrO₂-Ta₂O₅ commercial anodes. The hypochlorite ions generated by the anodes are also analyzed. The effect of the electrolyte composition (NaCl, Na₂SO₄, and NaClO₄) and current density (15, 30, and 50 mA cm^-2) on the iohexol degradation is also studied. The Ti/RuO₂-TiO₂ laser-made anode is more efficient than the commercial anodes. After optimizing experimental parameters, this anode removes 95.5% of iohexol in 60 min and displays the highest kinetic rate (0.059 min^-1) with the lowest energy consumption per order (0.21 kWh m^-3order^-1), using NaCl solution as the electrolyte and applying 15 mA cm^-2. Additionally, iohexol-intensified groundwater was used to compare the efficiency of anodes. The Ti/RuO₂-TiO₂ is also more efficient in removing the organic charge from the real water matrix (21.7% TOC) than the commercial anodes. Notably, the iohexol removal achieved is higher than all electrochemical treatments already reported using state-of-the-art non-active anodes in lower electrolysis time. Therefore, data from this study indicate that the electrochemical degradation of iohexol using the Ti/RuO₂-TiO₂ anode is efficient and has excellent cost-effectiveness; thus, it is a promising approach in the degradation of iohexol from wastewater. Furthermore, the Ti/RuO₂-TiO₂ active anode is competitive and can be an excellent option for treating effluents contaminated with recalcitrant organic compounds such as iohexol.

Atomically-thin Schottky-like photo-electrocatalytic cross-flow membrane reactors for ultrafast remediation of persistent organic pollutants

The remediation of persistent organic pollutants in surface and ground water represents a major environmental challenge worldwide. Conventional physico-chemical techniques do not efficiently remove such persistent organic pollutants and new remediation techniques are therefore required. Photo-electro catalytic membranes represent an emerging solution that can combine photocatalytic and electrocatalytic degradation of contaminants along with molecular sieving. Herein, macro-porous photo-electro catalytic membranes were prepared using conductive and porous stainless steel metal membranes decorated with nano coatings of semiconductor photocatalytic metal oxides (TiO₂ and ZnO) via atomic layer deposition, producing highly conformal and stable coatings. The metal - semiconductor junction between the stainless steel membranes and photocatalysts provides Schottky - like characteristics to the coated membranes. The PEC membranes showed induced hydrophilicity from the nano-coatings and enhanced electro-chemical properties due to the Schottky junction. A high electron transfer rate was also induced in the coated membranes as the photocurrent efficiency increased by 4 times. The photo-electrocatalytic efficiency of the TiO₂ and ZnO coated membranes were demonstrated in batch and cross flow filtration reactors for the degradation of persistent organic pollutant solution, offering increased degradation kinetic factors by 2.9 and 2.3 compared to photocatalysis and electrocatalysis, respectively. The recombination of photo-induced electron and hole pairs is mitigated during the photo-electrocatalytic process, resulting in an enhanced catalytic performance. The strategy offers outstanding perspectives to design stimuli-responsive membrane materials able to sieve and degrade simultaneously toxic contaminants towards greater process integration and self-cleaning operations.

On the behaviour of Atrazine removal from water using fabrics as anodes and cathodes

This study examines the degradation of atrazine (ATZ) with Pt-modified textile electrodes using an electrochemical method that is comparatively studied in two electrochemical cell configurations: cells with separated anodic and cathodic compartments (divided configuration); and without any separation (undivided configuration). The influence of the presence of chloride ions was studied. The best results were obtained when an undivided cell was used. The morphology and composition of the dispersed Pt coatings were analyzed using field emission scanning electron microscopy (FESEM) and Energy Dispersive X-Ray Analysis. The FESEM analyses confirmed that the textile surface was effectively modified by the electrocatalytic material. High performance liquid chromatography, gas chromatography mass spectrometry, and spectroscopic methods were used to follow the evolution of major oxidation products. Total organic carbon, chemical oxygen demand, and total nitrogen were used to evaluate the degradation efficiency of treated aqueous solutions. The experimental results obtained indicate that the efficiency of the electrochemical treatment was high with a low energy consumption when using electrodes based on textile materials, such as anodes or as cathodes (in particular, in electrolysis without compartment separation). All these can be produced at very competitive prices.

Emerging Pollutants in Moroccan Wastewater: Occurrence, Impact, and Removal Technologies

The rapid growth of anthropogenic activities in recent decades has resulted in the appearance of numerous new chemical compounds in the environment, known as “emerging pollutants” (EPs) or “contaminants of emerging concern” (CECs). Although partially or not yet regulated or monitored, there is growing research interest in these EPs among the scientific community because of their bioaccumulation, persistence, and adverse effects. Among these, endocrine disruptors, pesticides, and pharmaceuticals can have harmful impacts on human health and the ecosystem. Conventional wastewater treatment technologies are not effective in removing these contaminants, allowing them to be released into the receiving environment. In order to improve the understanding of emerging pollutants, this review discusses the source, occurrence, and impacts of bisphenol A, atrazine, amoxicillin, and paracetamol as model molecules of emerging environmental pollutants, an issue that remains underrepresented in Morocco. Then, treatment methods for EPs are reviewed, including adsorption, advanced oxidation processes, biodegradation, and hybrid treatment. It is proposed that adsorption and photocatalysis can be used as simple, effective, and environmentally friendly technologies for their removal. Thus, we summarize some of the adsorbent and photocatalyst materials applied in recent work to control these pollutants. Towards the end of this paper, the development of inexpensive and locally available (Morocco) materials to remove these compounds from wastewater is considered.

Monitoring of pesticides in surface water, pesticides removal efficiency in drinking water treatment plant and potential health risk to consumers using Monte Carlo simulation in Behbahan City, Iran

Excessive application of pesticides to control pests and weeds leads to contaminating bodies of water and health problems for consumers. The present study was designed to investigate the concentration of pesticides in raw water originated from the Marun River as well as the treated water of the drinking water treatment plant in Behbahan City. The efficiency of each treatment process was evaluated. Moreover, the health risks caused by detectable pesticides for consumers of treated water were assessed. The target pollutants were extracted using droplet liquid-liquid microextraction and detected by a gas chromatograph-mass spectrophotometer. The results showed relatively high mean concentrations of organophosphate pesticides ranging from 0.87 to 3.229 μg/L in the river water and low concentrations of organochlorine pesticides, except for 1,3-dichloropropene with the concentration of 3.58 μg/L. Alachlor had a rather high concentration (2.44 μg/L) in the river water. The concentration of pesticides in the drinking water had been reduced to an acceptable amount. The major part of pesticides removal occurred in coagulation-flocculation and rapid sand filtration units (87 %) due to the hydrophobic nature of pesticides and the use of GAC in the filtration unit. Based on the risk assessment estimates, the total hazard quotient (THQ) for all the pesticides was much less than one. The value of THQ was higher in younger individuals and children for all the given pesticides. The highest value of THQ in children was 0.2 which was attributed to aldrin. Similarly, the carcinogenic risk (CR) of aldrin for children and teenagers was in the unsafe range (more than 10^-4) while the CR for other target compounds in all the age groups was negligible (10^-4-10^-6 or less). The high concentration of pesticides in the river water might be concerning and therefore selling and using pesticides, especially the banned ones, should be more regulated.

Enhancing degradation of atrazine by Fe-phenol modified biochar/ferrate(VI) under alkaline conditions: Analysis of the mechanism and intermediate products

In this study, Fe-phenol modified biochar was prepared to enhance atrazine (AT) degradation by ferrate (Fe(VI)) under alkaline conditions, and the properties, mechanism and transformation pathways were extensively investigated. Degradation experiments showed that Fe-phenol modified biochar was more beneficial for improving the oxidation capacity of Fe(VI) than unmodified biochar, and the biochar with a molar ratio of Fe³⁺ to phenol of 0.1:5 (BC-2) showed the best promoting effect, and more than 94% of AT was removed at pH = 8 within 30 min. Moreover, the rate of oxidation (k_app) of AT by Fe(VI) increased 1.86 to 4.11 times by the addition of BC-2 in the studied pH range. Fe(Ⅴ)/Fe(Ⅳ) and ·OH were the main active oxidizing species for AT degradation in the Fe(VI)/BC-2 group and contributed to 70% and 24%, respectively, of degradation. The formation of ·OH and Fe(Ⅴ)/Fe(Ⅳ) was mainly due to the persistent free radicals and reducing groups on the surface of BC-2. AT was oxidized to 12 intermediate products in the Fe(VI)/BC-2 group through 5 pathways: alkyl hydroxylation, dealkylation, dichlorination, hydroxylation, alkyl dehydrogenation and dichlorination. Compared with those of the initial solution, the total organic carbon content and toxicity after the reaction decreased by 32.8% and 19.02%, respectively. Therefore, the combination of Fe-phenol modified biochar and Fe(VI) could be a promising method for AT removal.

Pesticide residues in drinking water, their potential risk to human health and removal options

The application of pesticides in agricultural and public health sectors has resulted in substantially contaminated water resources with residues in many countries. Almost no reviews have addressed pesticide residues in drinking water globally; calculated hazard indices for adults, children, and infants; or discussed the potential health risk of pesticides to the human population. The objectives of this article were to summarize advances in research related to pesticide residues in drinking water; conduct health risk assessments by estimating the daily intake of pesticide residues consumed only from drinking water by adults, children, and infants; and summarize options for pesticide removal from water systems. Approximately 113 pesticide residues were found in drinking water samples from 31 countries worldwide. There were 61, 31, and 21 insecticide, herbicide, and fungicide residues, respectively. Four residues were in toxicity class IA, 14 residues were in toxicity class IB, 55 residues were in toxicity class II, 17 residues were in toxicity class III, and 23 residues were in toxicity class IV. The calculated hazard indices (HIs) exceeded the value of one in many cases. The lowest HI value (0.0001) for children was found in Canada, and the highest HI value (30.97) was found in Egypt, suggesting a high potential health risk to adults, children, and infants. The application of advanced oxidation processes (AOPs) showed efficient removal of many pesticide classes. The combination of adsorption followed by biodegradation was shown to be an effective and efficient purification option. In conclusion, the consumption of water contaminated with pesticide residues may pose risks to human health in exposed populations.

Modeling pesticides in global surface soils: Evaluating spatiotemporal patterns for USEtox-based steady-state concentrations

To better manage pesticide pollution in surface soils, we introduced a first-order-kinetics-based screening model to evaluate the steady-state concentrations of pesticides in surface soils while considering degradation, volatilization, plant uptake, and precipitation processes. For each process, we developed a spatiotemporal-pattern-based model using spatiotemporal variables, including air temperature (T_A), relative humidity (RH_A), and rainfall intensity (I_R^A), to characterize the overall dissipation rates (k_T) of pesticides in the soil. These dissipation rates were converted to fate factors (FFs), which are commonly used in life cycle analyses. The results indicate that, in general, the k_T values increase with increasing T_A and I_R^A and decrease with increasing RH_A. This is because increased T_A boosts the degradation, volatilization, and plant uptake processes, whereas increased RH_A lowers the plant transpiration rate. Also, the simulation for over 700 pesticides indicated that the degradation process dominates the overall dissipation of most pesticides in the soil, and the volatilization process contributes the least. In addition, we simulated chlorpyrifos FFs for Brazil, China, the US, and the European Union (EU) using the annual average T_A, RH_A, and I_R^A values. The results indicate that, in general, Brazilian federal units have the smallest FFs and the narrowest simulated FF range because of their humid tropical climates. Meanwhile, the EU member states have the largest FFs and the widest FF range because of their range in locations. In addition, our simulated results show that the surface soils in the high-latitude regions could accumulate more chlorpyrifos than those in low-latitude regions because of the larger simulated FFs. Furthermore, we parameterized our model using 737 pesticides with the USEtox, thereby providing an alternative approach to simulate the steady-state concentration of pesticides in surface soils from the USEtox available data. The model developed herein is a useful screening tool for predicting pesticide concentrations in surface soil worldwide to improve soil and ecological health risk management.

Enhanced in-situ electro-generation of H2O2 using PTFE and NH4HCO3 modified C/PTFE electrode for treatment of landfill leachate

In this study, the carbon black/polytetrafluoroethylene (C/PTFE) electrode was prepared under the best conditions, and then it was modified by PTFE and NH₄HCO₃ to make a PTFE-C/PTFE electrode. PTFE-C/PTFE electrode was used to enhance H₂O₂ in-situ electro-generation and the electro-peroxone process (EPP) treatment of leachate. Various analytical methods results were applied to prove that the PTFE-C/PTFE electrode greatly improved the performance of H₂O₂ generation and electrode stability. The effects of initial pH, current intensity, ozone flow and Cl^- concentration on the removal of NH₄⁺ and chemical oxygen demand (COD) from landfill leachate were studied in the EPP with PTFE-C/PTFE as cathode (MEPP) by one factor at a time (OFAT) method. The initial pH value 7.5, current intensity 300 mA, ozone flow 875 mg/h and Cl^- concentration value 4198 mg/L were selected as the best operating parameters. A response surface methodology based on box-behnken design (BBD) was employed to optimize running conditions of the MEPP of leachate. After optimization, Mineralization efficiency of the NH₄⁺ and COD was obtained to be 79.83% and 52.14%, and biochemical oxygen demand (BOD₅)/COD ratio increased to 0.38 after 4 h. The removal curves of NH₄⁺ and COD in the MEPP conforms to the zero-order and first-order reaction kinetics, respectively. Three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM) analysis shows that MEPP has a good removal effect on organics in leachate. Energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis were carried out for the cathode sediment, which was mainly magnesium ion silicate precipitation and NaCl.

A comparison of visible-light photocatalysts for solar photoelectrocatalysis coupled to solar photoelectro-Fenton: Application to the degradation of the pesticide simazine

Three different visible-light photocatalysts (hematite (α-Fe₂O₃), bismuth vanadate (BiVO₄) and Mo-doped bismuth vanadate (BiMoVO₄)) deposited on transparent fluorine-doped SnO₂ (FTO) were evaluated for the solar-driven photoelectrocatalytic treatment of emerging pollutants. BiMoVO₄ was found to be the most effective photoanode, yielding the fastest degradation rate constant and highest mineralization efficiency using phenol as the oxidation probe. The BiMoVO₄ photoanode was then used to degrade the herbicide simazine in a photoelectrolytic cell combining photoelectrocatalysis (PEC) with photoelectron-Fenton (PEF) under solar light (SPEC-SPEC). Total simazine removal was achieved within 1 min of treatment (k_app = 4.21 min^-1) at the optimum electrode potential of 2.5 V vs Ag/AgCl, with complete TOC removal in 2 h. The analysis of anionic species in solution during treatment showed that most of the nitrogen heteroatoms in the simazine structure were converted into NO₃^- following ^•OH addition to organic N. This innovative process combining BiMoVO₄-PEC with PEF using solar light as a sustainable source of energy (SPEC-SPEF) achieved the highest degradation/mineralization efficiency ever reported for simazine treatment. Besides, this is the first work reporting the photo(electrochemical) degradation of this toxic herbicide.

Electrochemical degradation of DCF by boron-doped diamond anode: degradation mechanism, pathways and influencing factors

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been widely detected in wastewater and surface water, indicating that the removal of NSAIDs by wastewater treatment plants was not efficient. Electrochemical advanced oxidation technology is considered to be an effective process. This study presents an investigation of the kinetics, mechanism, and influencing factors of diclofenac (DCF) degradation by an electrochemical process with boron-doped diamond anodes. Relative operating parameters and water quality parameters are examined. It appears that the degradation follows the pseudo-first-order degradation kinetics. DCF degradation was accelerated with the increase of pH from 6 to 10. The degradation was promoted by the addition of electrolyte concentrations and current density. Humic acid and bicarbonate significantly inhibited the degradation, whereas chloride accelerated it. According to the quenching tests, hydroxyl radicals (•OH) and sulfate radicals contributed 76.5% and 6.5%, respectively, to the degradation. Sodium sulfate remains a more effective electrolyte, compared to sodium nitrate and sodium phosphate, suggesting the quenching effect of nitrate and phosphate on •OH. Major DCF transformation products were identified. According to the degradation products detected by liquid chromatography-mass spectrometry, hydroxylation and decarboxylation are the main pathways of DCF degradation; while dechlorination, chlorination, and nitro substitution are also included in this electrochemical degradation process.

Simultaneous electrochemical oxidation and ferrate generation for the treatment of atrazine: A novel process for water treatment applications

A novel process involving the simultaneous electrochemical-oxidation (EO) and electrosynthesis of ferrate has been investigated for the treatment of the commonly detected and recalcitrant pesticide, atrazine. The present study considered the electrosynthesis of ferrate, in neutral pH, using low concentration iron (Fe²⁺) representative of raw water levels and its subsequent effect on atrazine degradation. Ferrate synthesis was unaffected by current density (10-80 mA cm^-2), indicating mass transport limitations. Synthesis was affected by the initial iron concentration, whereby 0.051, 0.108 and 0.332 mg L^-1 was generated with an Fe²⁺ concentration of 0.5, 1.0 and 3.0 mg L^-1, respectively. When operating under simultaneous EO and ferrate oxidation, atrazine degradation exceeded that of a solely EO process. From an initial concentration of 2.00 mg L^-1, atrazine was degraded to 1.34, 1.05 and 0.51 mg L^-1 during 10, 40 and 80 mA cm^-2, characterised by pseudo-first-order kinetics. Degradation with electrochemically-generated ferrate could be described by second-order kinetics, and yielded a degradation rate constant of 23.5 M^-1 s^-1. The effect of natural organic matter (NOM) on atrazine degradation was also investigated. Ferrate was observed to be mostly scavenged by resorcinol, a representative NOM compound, having a second-order reaction rate constant of 9.71 × 102 M^-1 s^-1.

Electrochemical degradation of atrazine by BDD anode: Evidence from compound-specific stable isotope analysis and DFT simulations

Direct charge transfer (DCT) and •OH attack played important roles in contaminant degradation by BDD electrochemical oxidation. Their separate contributions and potential bond-cleavage processes were required but lacking. Here, we carried out promising compound-specific isotope fractionation analysis (CSIA) to explore ¹³C and ²H isotope fractionation of atrazine (ATZ), followed by assessing the reaction pathway by BDD anode. The correlation of ²H and ¹³C fractionation allows to remarkably differentiate DCT process and •OH attack, with Λ values of 18.99 and 53.60, respectively. Radical quenching identified that •OH accounted for 79.0%-88.5% in the whole reaction. While CSIA methods provided biased results, which suggested that ATZ degradation exhibited two stages with •OH contributions of 24.6% and 84.3% respectively, confirming CSIA was more sensitive and provided more possibilities to estimate degradation processes. Combined with Fukui index and intermediate products identification, we deduced that dechlorination-hydroxylation mainly occurred in the first 30 min by DCT reaction. While lateral chain oxidation with C-N broken was the governing route once •OH was largely generated, with the production of DEA (m/z 188), DIA (m/z 174), DEIA (m/z 146) and DEIHA (m/z 128). Our results demonstrated that isotope fractionation can offer "isotopic footprints" for identifying the rate-limiting steps and bond breakage process, and opens new avenues for degradation pathways of contaminants.

Chronic ciprofloxacin and atrazine co-exposure aggravates locomotor and exploratory deficits in non-target detritivore speckled cockroach (Nauphoeta cinerea)

The global detection of ciprofloxacin and atrazine in soil is linked to intensive anthropogenic activities in agriculture and inadvertent discharge of industrial wastes to the environment. Nauphoeta cinerea is a terrestrial insect with cosmopolitan distribution and great environmental function. The current study probed the neurobehavioral and cellular responses of N. cinerea singly and jointly exposed to atrazine (1.0 and 0.5 μg g^-1 feed) and ciprofloxacin (0.5 and 0.25 μg g^-1 feed) for 63 days. Results demonstrated that the reductions in the body rotation, maximum speed, turn angle, path efficiency, distance traveled, episodes, and time of mobility induced by atrazine or ciprofloxacin per se was exacerbated in the co-exposure group. The altered exploratory and locomotor in insects singly and jointly exposed to ciprofloxacin and atrazine were verified by track plots and heat maps. Furthermore, we observed a decrease in acetylcholinesterase and anti-oxidative enzyme activities with concomitant elevation in the levels of lipid peroxidation, nitric oxide, and reactive oxygen and nitrogen species were significantly intensified in the midgut, hemolymph, and head of insects co-exposed to ciprofloxacin and atrazine. In conclusion, exposure to binary mixtures of ciprofloxacin and atrazine elicited greater locomotor and exploratory deficits than upon exposure to the individual compound by inhibiting acetylcholinesterase activity and induction of oxido-inflammatory stress responses in the insects. N. cinerea may be a usable model insect for checking contaminants of ecological risks.

Co/Sm-modified Ti/PbO2 anode for atrazine degradation: Effective electrocatalytic performance and degradation mechanism

In this work, Ti/PbO₂-Co-Sm electrode has been successfully prepared using electrodeposition and further applied for the electrocatalysis of atrazine (ATZ) herbicide wastewater. As expected, Ti/PbO₂-Co-Sm electrode displays highest oxygen evolution potential, lowest charge transfer resistance, longest service lifetime and most effective electrocatalytic activity compared with Ti/PbO₂, Ti/PbO₂-Sm and Ti/PbO₂-Co electrodes. Orthogonal and single factor experiments are designed to optimize the condition of ATZ degradation. The maximum degradation efficiency of 92.6% and COD removal efficiency of 84.5% are achieved in electrolysis time 3 h under the optimum condition (current density 20 mA cm^-2, Na₂SO₄ concentration 8.0 g L^-1, pH 5 and temperature 35 °C). In addition, Ti/PbO₂-Co-Sm electrode exhibits admirable recyclability in degradation progress. The degradation of ATZ is accomplished by indirect electrochemical oxidation and ∙OH is tested as the main active substance in ATZ oxidation. The possible degradation mechanism of ATZ has been proposed according to the degradation intermediates detected by LC-MS. This research suggests that Ti/PbO₂-Co-Sm is a promising electrode for ATZ degradation.

Aquaculture-derived distribution, partitioning, migration, and transformation of atrazine and its metabolites in seawater, sediment, and organisms from a typical semi-closed mariculture bay

Atrazine (ATR) is one of the most commonly used herbicides that could directly impair the growth and health of organisms in mariculture areas and adversely affect human health through the food chain. This study investigated the contaminant occurrence, migration, and transformation of ATR and three of its chlorinated metabolites, namely deethylatrazine (DEA), deisopropylatrazine (DIA), and didealkylatrazine (DDA), in surface seawater, sediment, and aquatic organisms from the Xiangshan Harbor. ATR was detected in all samples, while DIA and DDA were only respectively detected in aquatic and seawater samples. The distribution of ATR and its metabolites presented different patterns depending on the geographic location and showed a higher level in the aquaculture area than that in the non-aquaculture area. The bioaccumulation of ATR in aquaculture organisms showed that benthic organisms, such as Ditrema, and Sinonovacula constricta (Sin), had increased levels. The ecological risks indicated that ATR posed medium or high risks to algae in the water phase of the study area. The microcosm experiment showed that the main fate of ATR in the simulated microenvironment was sedimentation, which followed the first-order kinetic equation. The ATR in the sediment could be enriched 3-5 times in Sin, and its major metabolites were DEA and DIA.

Rapid uptake of atrazine from aqueous phase by thermally activated MCM-41

This study was designed to prepare an adsorbent without any complex modification process for the removal of atrazine (AZN) from aqueous phase. Thus, Mobil composition of matter No. 41 (MCM-41) was synthesized and modified by physical activation at high temperature (650 °C). The synthesized adsorbent was tested by XRD, SEM, EDX, FT-IR and BET to confirm the successful synthesis as well as effectiveness for the adsorption of AZN. The average particle size of prepared material was found to be about 500 nm, while the BET calculations showed that adsorbent was porous with a specific surface area of 25.9 m²/g. Later, it was used in batch removal studies of AZN for which, it showed a high adsorption capacity of 89.99 (mg/g). The pH of 6, temperature of 313 K was found to be the optimized conditions for the maximum removal of AZN. Of the four kinetic models studied, the pseudo-first-order yielded a superior fit in comparison with the other three models. The results indicated that the five linearized adsorption equilibrium isotherm models (Langmuir, Freundlich, Dubinin-Radushkevich, Temkin and Harkins-Jura models) closely correlate the AZN adsorption removal process with Pearson correlation coefficient (R²) values of 0.9955, 0.8551, 0.8736, 0.8913 and 0.7253, respectively. The energy functions obtained by thermodynamic analysis suggested that the AZN sorption follows a non-spontaneous and endothermic path.

Occurrence, statutory guideline values and removal of contaminants of emerging concern by Electrochemical Advanced Oxidation Processes: A review

A wide variety of chemical compounds are used in human activities; however, part of these compounds reach surface water, groundwater and even water considered for potable uses. Due to the limited efficiency of water treatment by the Water and Wastewater Treatment Plants, the presence of these compounds in natural and human consumption waters can be very harmful due to their high persistence and adverse effects; these characteristics define the contaminants of emerging concern (CECs). Water treatment by Electrochemical Advanced Oxidation Processes (EAOPs) has been evaluated as a promising process for the removal of persistent and recalcitrant organic contaminants. With this background, the present review aims to gather studies and information published between 2015 and 2020 regarding the occurrence of CECs in surface, potable and groundwater, its treatment by EAOPs, the main operating conditions and by-product generation of EAOPs, contaminant toxicity assessments and international statutory guideline values concerning CEC standards and allowable concentrations in the environment and treated drinking water. Therefore, in this review it was found that the compounds bisphenol A (BPA), diethyltoluamide (DEET), 17α-ethinyl estradiol (EE2), perfluorobutanoic acid (PFBA), carbamazepine, caffeine and atrazine were the most frequently detected in water sources, with concentrations ranging from 35.54-4800, 1.21-98, 0.005-38.5, 5-742.904, 0.0071-586, 0.89-1040, and 100-323 (ng L-1), respectively. Among the operational conditions of EAOPs, current density, pH and oxidant concentration are the main operational parameters that have an influence on these treatment technologies, besides the by-products generated, which might be removed by the integration of EAOPs with biological digestion treatments. Regarding the values of water quality standards, many CECs do not have established standard allowable concentration values, which represents a concern toward the possible toxic effects of these compounds on non-target organisms.

Effective treatment of levofloxacin wastewater by an electro-Fenton process with hydrothermal-activated graphite felt as cathode

The performance of the cathode significantly affects the ability of the electro-Fenton (EF) process to degrade chemicals. In this study, a simple method to modify the graphite felt (GF) cathode was proposed, i.e. oxidizing GF by hydrothermal treatment in nitric acid. The surface physical and electrochemical properties of modified graphite felt were characterized by several techniques: scanning electron microscope (SEM), water contact angle, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and linear scanning voltammetry (LSV). Compared with an unmodified GF (GF-0), the oxygen reduction reaction (ORR) activity of a modified GF was significantly improved due to the introduction of more oxygen-containing functional groups (OGs). Furthermore, the results showed that GF was optimally modified after 9 h (GF-9) of treatment. As an example, the H₂O₂ generation by GF-9 was 2.26 times higher than that of GF-0. After optimizing the process parameters, which include the initial Fe²⁺ concentration and current density, the apparent degradation rate constant of levofloxacin (LEV) could reach as high as 0.40 min^-1. Moreover, the total organic carbon (TOC) removal rate and mineralization current efficiency (MCE) of the modified cathode were much higher than that of the GF-0. Conclusively, GF-9 is a promising cathode for the future development in organic pollutant removal via EF.

Tuning the Atrazine Binding Sites in an Indium-Based Flexible Metal-Organic Framework

Constructing flexible metal-organic frameworks (MOFs) with targeted properties is of high interest given their demonstrated potential as smart materials that undergo structural transformations in response to external stimuli. Herein, we report a flexible and interpenetrated indium-based MOF, NU-50, comprising four-connected [In(CO₂)₄]^- nodes and tetracarboxylate pyrene-based ligands assembled in the pts topology. The flexible framework of NU-50 exhibits intricate structural transformations upon exposure to external stimuli, namely, guest solvent molecules and elevated temperatures. The high density of pyrene moieties throughout the interpenetrated framework offers numerous sites for the adsorption of highly conjugated guest molecules such as atrazine via π-π interactions. As a result, NU-50 efficiently removes atrazine from water, achieving a maximum atrazine uptake capacity of 74 mg of atrazine per gram of NU-50. Molecular simulations reveal that the dynamic behavior of NU-50 involves the distortion of metal-ligand bonds, resulting in a narrow pore structure that affords effective adsorption of atrazine molecules in a sandwich-like geometry. Moreover, washing in acetone quickly regenerates the sorbent.

Study on the efficacy and mechanism of Fe-TiO2 visible heterogeneous Fenton catalytic degradation of atrazine

In order to improve the catalytic activity and recycling performance of heterogeneous Fenton catalyst, a heterogeneous Fenton catalyst Fe/TiO₂ based on TiO₂ supported visible light response was prepared by a simple method using TiO₂ synthesized by sol-gel method as carrier and ferric nitrate as Fe source. It was characterized by SEM, EDX, XRD, UV-vis instruments. The influencing factors of catalytic degradation of atrazine by visible light heterogeneous Fenton of Fe/TiO₂ were studied and the reaction kinetics were fitted. The mineralization degree of atrazine was reflected by the removal rate of TOC. The intermediate products by the degradation of the catalytic system was analyzed and the reaction mechanism of Fe/TiO₂-H₂O₂ visible light system was discussed. The XRD results showed that Fe was highly dispersed on the surface of TiO₂ in the form of α-Fe₂O₃. The Fe/TiO₂ catalyst with heterogeneous Fenton and visible light photocatalytic activity was successfully optimized, forbidden bandwidth of Fe/TiO₂ after Fe supported was narrower, the scope of light absorption red-shifted, the electron-hole pairs were more generated, and there was a significant synergistic effect between the carrier TiO₂ and the supported Fe, which exhibited good oxidation capacity for degradation of 10 mg L^-1 atrazine in pH of 3, the concentration of H₂O₂ was 1.6 mM, and the catalyst was added at 1 g L^-1, achieving over 95% removal efficiency within 30 min, and, in the range of pH 3-7, the degradation rate of the reaction for 30 min can be maintained above 75%, which greatly broadened the range of pH application and had good recycling performance. The degradation process conformed to the quasi-first-order kinetic model. Through LC-MS analyzed, 12 intermediate products were formed during the degradation of atrazine, the final products were all cyanuric acid, and then the triazine ring was mineralized into inorganic substances such as CO₂, H₂O and NO₃^- by oxidation of ·OH, and the possible degradation pathways were inferred.

Enhanced anodic oxidation and energy saving for dye removal by integrating O2-reducing biocathode into electrocatalytic reactor

Simultaneous enhancement of dye removal and reduction of energy consumption is critical for electrochemical oxidation in treating dyeing wastewater. To address this issue, this work presented a novel process termed biocathode-electrocatalytic reactor (BECR). The dual-chamber BECR employed O₂-reducing biocathode instead of normal stainless steel (SS) cathode and MnO_x/Ti anode to reduce O₂ in the cathode chamber and treat methylene blue (MB) in the anode chamber, respectively. BECR successfully started up at 0.7 and 1 V and substantially improved MB and total organic carbon (TOC) removal compared with the electrocatalytic reactor with SS cathode (ECR-SS), e.g., removal of MB (150 mg L^-1) increased from 27.0 ± 0.2% to 78.1 ± 0.4% at 1 V. To achieve the same TOC removal, BECR reduced the energy consumption by approximately 45.7% compared with ECR-SS (19.5 and 35.9 kWh (kg TOC) ^-1 for BECR and ECR, respectively). To explain the above merits of BECR, M(·OH) (·OH adsorbed on the anode surface) generation, potential of MnO_x/Ti anode (E_a), and their correlation were investigated. When coupled with O₂-reducing biocathode, MnO_x/Ti anode considerably accelerated M(·OH) generation because E_a increased. The increased E_a in BECR was due to the fact that its cathodic reaction was converted to the four-electron O₂ reduction, which exhibited a higher cathodic potential than hydrogen evolution reaction on SS cathode in ECR-SS. Thereby, BECR simultaneously promoted dye removal and reduced energy consumption, showing promise in treating dyeing wastewater.

A review on the photoelectro-Fenton process as efficient electrochemical advanced oxidation for wastewater remediation. Treatment with UV light, sunlight, and coupling with conventional and other photo-assisted advanced technologies

Wastewaters containing recalcitrant and toxic organic pollutants are scarcely decontaminated in conventional wastewater facilities. Then, there is an urgent challenge the development of powerful oxidation processes to ensure their organic removal in order to preserve the water quality in the environment. This review presents the recent development of an electrochemical advanced oxidation process (EAOP) like the photoelectro-Fenton (PEF) process, covering the period 2010-2019, as an effective treatment for wastewater remediation. The high oxidation ability of this photo-assisted Fenton-based EAOP is due to the combination of in situ generated hydroxyl radicals and the photolytic action of UV or sunlight irradiation over the treated wastewater. Firstly, the fundamentals and characteristics of the PEF process are described to understand the role of oxidizing agents. Further, the properties of the homogeneous PEF process with iron catalyst and UV irradiation and the benefit of sunlight in the homogeneous solar PEF one (SPEF) are discussed, supported with examples over their application to the degradation and mineralization of synthetic solutions of industrial chemicals, herbicides, dyes and pharmaceuticals, as well as real wastewaters. Novel heterogeneous PEF processes involving solid iron catalysts or iron-modified cathodes are subsequently detailed. Finally, the oxidation power of hybrid processes including photocatalysis/PEF, solar photocatalysis/SPEF, photoelectrocatalysis/PEF and solar photoelectrocatalysis/SPEF, followed by that of sequential processes like electrocoagulation/PEF and biological oxidation coupled to SPEF, are analyzed.

Effects of the long-term application of atrazine on soil enzyme activity and bacterial community structure in farmlands in China

Atrazine has been used on Chinese farmlands for a long time and over a wide range. The concentration of atrazine (1.86-1100 mg kg^-1) has exceeded the allowable limit in the soil (1.0 mg kg^-1), and concern is increasing about the potential harm to farmland soil. Four treatments (AT₀, AT₆, AT₁₀, AT₁₆) were established to reveal the effects of the long-term application of atrazine on soil health. The results showed a nonlinear regulation of the atrazine residue concentrations in the four treatments. The highest concentration of atrazine residue was in AT₆, at 167 mg kg^-1, and the lowest concentration of atrazine residue was in AT₁₆, at 102 mg kg^-1, but there was no significant difference between AT₁₀ and AT₁₆. The soil urease activity decreased significantly with the increase in the years of atrazine application, the saccharase and cellulase activities in the AT₆ were significantly higher than those observed in the other three treatments, the catalase activity gradually decreased with the increase in atrazine application years, and the activity in AT₆ was significantly higher than that in AT₁₆. A total of 238 genera were identified by Illumina MiSeq sequencing, and 28 dominant genera were screened. Atrazine significantly increased the relative abundance of Actinobacteria and contributed to the relative abundance of Rubrobacter, Blastococcus, Promicromonospora, Jiangella, Psychroglaciecola and Acetobacteraceae_uncultured, which exhibited significantly higher abundance in AT₁₆ than in AT₀. Although there were atrazine-degrading bacteria in the soil, and the atrazine residue decreased with the increase in application years, the concentration of the atrazine residue was still nearly 100 times higher than the allowable limit in the soil, which is a great threat to the soil health.

Susceptibility of atrazine photo-degradation in the presence of nitrate: Impact of wavelengths and significant role of reactive nitrogen species

The role of reactive nitrogen species (RNS) formed from nitrate photolysis has aroused interests in transformation of contaminants of emerging concern. This study investigated the influence of UV wavelengths (255, 285 and 365 nm) on photolysis of nitrate for degradation of atrazine (ATZ). The UV₂₈₅/nitrate system showed the fastest rate constant for degradation of ATZ with k_obs of 0.0022 cm² mJ^-1. UV photolysis, RNS, and hydroxyl radical (HO) were identified as main contributors to ATZ degradation in UV/nitrate system. Among the contributors, RNS made the major contribution to degradation of ATZ in UV₂₈₅/nitrate system, while HO is the predominant specie in UV₂₅₅/nitrate system. Variance decomposition analysis showed that degradation of ATZ was slightly impacted by natural organic matter and carbonate/bicarbonate in UV₂₈₅/nitrate system but was dramatically affected in UV₂₅₅/nitrate system. Main transformation products of ATZ in UV₂₈₅/nitrate system were identified and possible pathways were proposed. RNS were confirmed to be favorable for acceleration of ATZ photolysis through further reaction of RNS with hydroxyatrazine (with electron-rich moieties). Our study provides deep insights on the influence of UV wavelength on nitrate photolysis and ATZ degradation, and provides a novel method for remediation of water co-contaminated by nitrate and organic contaminants.

Expanding the application of photoelectro-Fenton treatment to urban wastewater using the Fe(III)-EDDS complex

This work reports the first investigation on the use of EDDS as chelating agent in photoelectro-Fenton (PEF) treatment of water at near-neutral pH. As a case study, the removal of the antidepressant fluoxetine was optimized, using an electrochemical cell composed of an IrO₂-based anode an air-diffusion cathode for in-situ H₂O₂ production. Electrolytic trials at constant current were made in ultrapure water with different electrolytes, as well as in urban wastewater (secondary effluent) at pH 7.2. PEF with Fe(III)-EDDS (1:1) complex as catalyst outperformed electro-Fenton and PEF processes with uncomplexed Fe(II) or Fe(III). This can be explained by: (i) the larger solubilization of iron ions during the trials, favoring the production of ^•OH from Fenton-like reactions between H₂O₂ and Fe(II)-EDDS or Fe(III)-EDDS, and (ii) the occurrence of Fe(II) regeneration from Fe(III)-EDDS photoreduction, which was more efficient than conventional photo-Fenton reaction with uncomplexed Fe(III). The greatest drug concentration decays were achieved at low pH, using only 0.10 mM Fe(III)-EDDS, although complete removal in wastewater was feasible only with 0.20 mM Fe(III)-EDDS due to the greater formation of ^•OH. The effect of the applied current and anode nature was rather insignificant. A progressive destruction of the catalytic complex was unveiled, whereupon the mineralization mainly progressed thanks to the action of ^•OH adsorbed on the anode surface. Despite the incomplete mineralization using BDD as the anode, a remarkable toxicity decrease was determined. Fluoxetine degradation yielded F^- and NO₃^- ions, along with several aromatic intermediates. These included two chloro-organics, as a result of the anodic oxidation of Cl^- to active chlorine. A detailed mechanism for the Fe(III)-EDDS-catalyzed PEF treatment of fluoxetine in urban wastewater is finally proposed.

A highly efficient cathode based on modified graphite felt for aniline degradation by electro-Fenton

The graphite felt (GF) was modified through the concentrated sulfuric acid, potassium permanganate and ammonia activation with the aim of improving the specific surface area, hydrophilicity and the electrocatalytic activity for the electrogeneration of hydrogen peroxide and its application in the electro-Fenton (EF). The modified graphite felt (M-GF) was characterized by contact angle, scanning electron microscope, X-ray photoelectron spectroscopy, Raman spectrum, cyclic voltammetry and electrochemical impedance spectroscopy. The surface physic-chemical characteristics and morphology of the M-GF were considerably changed after the modification. The current efficiency for H₂O₂ generation was explored at an optimized current density of 10 mA cm^-2 and the value of H₂O₂ generation for the M-GF was 478.6 mg L^-1, while the GF was 276.5 mg L^-1 after 360 min of electrolysis. Finally, the M-GF was used for the mineralization of aniline (100 mg L^-1), reaching a mineralization percentage of 97% with EF process. The M-GF demonstrated good stability as the aniline mineralization percentage was above 90% after 10 cycles' degradation, indicating that the M-GF is a promising cathode material for improving the degradation and mineralization of others organic pollutants by the EF process.