Effective Advanced Oxidation Process Research Articles

Effect of pH on degradation and mineralization of catechol in calcium-aid ozonation: Performance, mechanism and products analysis

Catechol, common in industrial wastewater, is very toxic and non-biodegradable, and its desirable removal is still a challenge. Catalytic ozonation as an effective advanced oxidation process, however was limited by the application of intricately fabricated catalysts. Herein, catalytic ozonation by OH– (generated by common sodium hydroxide) with the aid of calcium was developed for catechol degradation and mineralization in this study. The removal performance, mechanism and products were investigated. The results showed that ozonation at pH 12.5 could achieve complete catechol removal and excellent mineralization (maximum of 75 % COD removal efficiency) within 15 min. The adorable effect of calcium for enhanced organics removal was observed at pH 12.5, with the formation of precipitates as well. Catechol and COD removal were fitted to the pseudo-first-order kinetic model, while the reaction constant was increased by higher pH and calcium concentration. The results of quenching experiment and EPR affirmed •OH and •O2– radicals were pivotal for the enhanced organics removal. In addition, DFT calculation revealed the O atoms were reactive sites for electrophilic and radical attack via molecular electrostatic potential, highest occupied molecular orbital, lowest unoccupied molecular orbital and Fukui index. UPLC-Q-TOF-MS analysis revealed the intermediate products and verified the brilliant performance of catalytic ozonation. According to reactive sites and intermediates identification, the degradation pathway of catechol was proposed. As tawny precipitate appeared after reaction, the characteristics of insoluble product was analyzed using FTIR, XRD and XPS. The component of the precipitate was recognized as calcium oxalate and calcium carbonate, accompanied by the decreased Ca2+ concentration at high pH, which declared the enhanced removal was linked to the precipitation of Ca2+. Finally, toxicity assessment stated the lower acute toxicity, bioconcentration factor, developmental toxicity and mutagenicity of intermediates, indicating that calcium-aid ozonation catalyzed by high pH was useful for both catechol degradation and toxicity reduction. This study provides a reference for understanding the performance and mechanism of catechol degradation. More importantly, as an environmentally friendly process, catalytic ozonation possesses a great application potential for treatment of wastewater containing metal ions in terms of simultaneous removal of organics and metal ions.

Piezo-Fenton catalysis in Fe3O4-BaTiO3 nanocomposites: A low-cost and highly efficient degradation method without the additive of H2O2 or Fe(II) ions

The Fenton reaction, an effective advanced oxidation process (AOP) for degrading organic pollutants, requires the addition of H2O2 that is expensive and not environmentally friendly to some extent. It has been reported that piezocatalysis can generate H2O2 under mechanical excitation. Therefore, it is promising to carry out the Fenton catalysis utilizing in situ H2O2 generated by piezocatalysis. However, the current piezocatalysis-assisted Fenton (Piezo-Fenton) reaction was realized by adding piezoelectric nanoparticles and Fe(II) ions to pollutant solutions, which would induce more iron-based chemicals that are not easy to recycle. Herein, Fe3O4-BaTiO3 nanocomposites were prepared to demonstrate the feasibility of piezo-Fenton catalysis without the addition of H2O2 or Fe(II) ions. The organic dye degradation efficiency of 98.2% is obtained using Fe3O4-BaTiO3 nanocomposites in the acidic solution, one-third and two-thrid greater than that of pure piezocatalysis and that of iron-based Fenton reaction, respectively. Moreover, since the piezocatalysis process is the rate-determining step of the whole piezo-Fenton reaction, all the H2O2 generated can be consumed. Considering that the solid nanocomposites can be magnetically recycled, piezo-Fenton catalysis leaves no additional chemicals in clean water and thus provides an environmentally friendly and low-cost approach for organic dye degradation.

Mechanism of anodic activation of chloride to generate singlet oxygen for fast organic removal using an innovative anode

Electrochemical persulfate activation (E-PS) has recently emerged as a highly effective advanced oxidation process in water decontamination. However, the presence of chloride ions (Cl−) in waters can accelerate anodic corrosion as well as lead to the formation of toxic chlorinated byproducts (i.e., ClO4−), limiting its practical application. In this study, we introduce a novel Nd/Bi@SnO2 anode to construct E-PS, which exhibits high stability in chloride-containing water with a long-expected service lifetime of 13.7 years. The Nd/Bi@SnO2 electrode can effectively convert Cl− to reactive chlorine with the assistance of PMS, triggering singlet oxygen (1O2) generation for superior organic removal while avoiding toxic chlorinated byproducts (i.e., ClO4−) generation as well as greatly reducing the energy consumption. Comprehensive structural and electrochemical characterization results demonstrate Nd/Bi co-doping introduces oxygen vacancy on Nd/Bi@SnO2, enabling the anode with high oxygen evolution potential, excellent conductivity and superior stability. Scavenging experiments and electron paramagnetic resonance illustrate the generation of various reactive species in the system, among which 1O2 predominantly contributes to organic removal and results in harmless intermediates. This innovative approach transforms Cl− into ROSs for eco-friendly, energy-efficient water decontamination.

Efficient activation of peroxydisulfate by 3D flower spherical-like Fe–NC for organic contaminant removal: Fe(IV)=O as a dominant species

The high-valent iron-oxo species (Fe(IV)O) exhibit great prospects for the removal of organic contaminants in iron-mediated persulfate activation. Nevertheless, an adequate research of the mechanisms involved in Fe(IV)-based activation processes and organic degradation remains elusive. Here, an Fe encapsulated in N-doped carbons catalyst (2Fe–NC) with three-dimensional flower shape and mesoporous structure was developed, which can 100 % remove various organic pollutants such as chloramphenicol (CAP), sulfamethoxazole, amoxicillin, benzoic acid, and bisphenol A within 30 min by peroxydisulfate (PDS) activation. In the oxidation system, 2Fe–NC as an electron transfer medium was critical to mediate electron transfer from organic compound to PDS, accompanied by the redox cycle of Fe(IV)/Fe(II) and Fe(IV)/Fe(III). Multiple experiments reveal that the oxidation mechanism of 2Fe–NC@PDS system is similar to the dioxygen activation mechanism of binuclear active sites, which activates PDS to form surface-active Fe(IV)O species without producing radicals. The two pathways of CAP degradation simulated by density functional theory calculations release 6.92 and 4.23 eV, respectively, which is thermodynamically favorable. Overall, the new insights gained in this work offer a significant route to design more effective advanced oxidation processes for refractory contaminant treatment.

The overlooked role of electrostatic repulsion between nanoparticle catalysts in ligand-enhanced heterogeneous Fenton-like reactions

Chelating agents are now frequently used to facilitate Fenton and Fenton-like reactions by building complexes with iron. A series of advantages can be exemplified, such as fast circulation of Fe(Ⅲ)/Fe(Ⅱ), enhanced catalytic performance of Fe-ligand, and iron precipitation inhibition, etc. However, few studies explored whether electrostatic repulsion between nanoparticle catalysts had an influence on catalytic performance in ligand-enhanced Fenton-like reactions. In this study, we discovered that the coexistence of 0.1 mM EDTA and 10 mM phosphate dramatically accelerated diclofenac (DCF) degradation by Fe3O4/Air (∼95% within 20 h). In-depth explorations demonstrated the enhanced electrostatic repulsion between Fe3O4 caused by the addition of EDTA and phosphate played a key role in the promoted DCF degradation. The enhanced electrostatic repulsion between Fe3O4 led to a notable increase in the percentage of Fe-EDTA, which benefited O2 activation and DCF degradation. Reactive oxygen species (ROS) were mainly generated through one-electron activation mechanism of O2 and •OH were confirmed to be predominant active species responsible for DCF degradation. Fe(Ⅱ)-EDTA on Fe3O4 surface was evidenced to be served as main sites for O2 and H2O2 activation. During the degradation reaction, sufficient surface Fe(Ⅱ) on Fe3O4 was maintained with the assistance of EDTA. Toxicity analysis showed that DCF was transformed into less toxic intermediates, demonstrating the feasibility of this technology in practical applications. This work for the first time reveals the importance of electrostatic repulsion between nanoparticle catalysts in ligand-enhanced Fenton-like reactions, providing a low-cost and effective advanced oxidation process for contaminants degradation.

Density Functional Theory and Machine Learning-Based Quantitative Structure-Activity Relationship Models Enabling Prediction of Contaminant Degradation Performance with Heterogeneous Peroxymonosulfate Treatments.

Heterogeneous peroxymonosulfate (PMS) treatment is recognized as an effective advanced oxidation process (AOP) for the treatment of organic contaminants. Quantitative structure-activity relationship (QSAR) models have been applied to predict the oxidation reaction rates of contaminants in homogeneous PMS treatment systems but are seldom applied in heterogeneous treatment systems. Herein, we established QSAR models updated with density functional theory (DFT) and machine learning approaches to predict the degradation performance for a series of contaminants in heterogeneous PMS systems. We imported the characteristics of organic molecules calculated using constrained DFT as input descriptors and predicted the apparent degradation rate constants of contaminants as the output. The genetic algorithm and deep neural networks were used to improve the predictive accuracy. The qualitative and quantitative results from the QSAR model for the degradation of contaminants can be used to select the most appropriate treatment system. A strategy for selection of the optimum catalyst for PMS treatment of specific contaminants was also established according to the QSAR models. This work not only increases our understanding of contaminant degradation in PMS treatment systems but also highlights a novel QSAR model to predict the degradation performance in complicated heterogeneous AOPs.

Review of Bi-based catalysts in piezocatalytic, photocatalytic and piezo-photocatalytic degradation of organic pollutants.

Photocatalysis, as an effective advanced oxidation process, has been widely carried out in water waste treatment, especially in the degradation of organic pollutants. However, the photocatalytic process is limited by the high recombination rate of photo-generated carriers. To improve photocatalytic efficiency, piezocatalysis has attracted increasing attention, especially that using lead-free piezoelectric materials, which avoids the secondary pollution of lead toxicity in the environment. Bi-based materials have both photocatalytic activity and piezocatalytic activity, which can perfectly combine the advantages of these two catalytic processes to promote the degradation of organic pollutants. Under an external mechanical action, the Bi-based catalyst produces a polarized electric field due to the piezoelectric effect, and the photo-generated carriers can be effectively separated under electrostatic attraction, thus obtaining more efficient photocatalytic performance. However, there are still many gaps in the design, reaction mechanism, and development prospects of Bi-based piezo-photocatalysts. Therefore, to acquire a deeper understanding of the research status of Bi-based piezo-photocatalysts, we summarize the existing literature to provide effective ways to improve piezo-photocatalytic performance. Moreover, this paper points out the developmental direction of piezo-photocatalysis in the future. Last but not least, we also look forward to the prospect of piezo-photocatalysis in the degradation of organic pollutants.

Oxidative degradation of micropollutants by a pilot-scale UV/H<sub>2</sub>O<sub>2</sub> process: Translating experimental results into multiphysics simulations

The UV/H<sub>2</sub>O<sub>2</sub> system is an effective advanced oxidation process (AOP) widely used for micropollutant abatement in drinking water and wastewater treatment plants. Recently, multiphysics simulations based on computational fluid dynamics (CFD) and chemical kinetics have shown promise by accurately depicting water treatment processes. This study demonstrates the feasibility of incorporating experimental results from a pilot-scale UV/H<sub>2</sub>O<sub>2</sub> system into a multiphysics model. Various factors affecting contaminant degradation and oxidant production such as H<sub>2</sub>O<sub>2</sub> dose, H<sub>2</sub>O<sub>2</sub> injection methods, and reactor size were investigated. The obtained data became the basic building blocks when developing the numerical model. The model predictions exhibited a good correlation with the experimental results. 3-D visualizations using the model allow further in-depth analysis of the distribution of oxidants and target pollutant in the UV photoreactor, providing insights into the possibilities of reactor optimization.

Degradation of sulfamethoxazole by a new modified Fenton-like process using Cu(II)-nitrilotriacetic acid complex as catalyst at neutral pH in aqueous medium

Fenton process is among the most effective advanced oxidation process in wastewater treatment, but the necessity to work at acidic pH, in order to avoid metal precipitation, limits its large-scale application. In this work, a new Fenton-like process using copper(II)-nitrilotriacetic acid (CuII -NTA) complex as catalyst, was used for the activation of hydrogen peroxide (H2O2) to degrade sulfamethoxazole (SMX) in aqueous medium under neutral pH conditions. The results showed that the CuII -NTA/H2O2 process was not efficient in the degradation of SMX. The reason being that the generation of HO radicals is still limited by the extremely slow CuII -NTA/CuI -NTA redox cycle. Therefore, the combination of hydroxylamine (HA) accelerate the CuI recovery to induce the continuous production of HO radicals by the decomposition of H2O2. It was evident that the steady-state CuI concentration in CuII-NTA/HA/H2O2 process was much elevated than the CuII -NTA/H2O2 process due to the quick regeneration of CuI -NTA complex by HA. Kinetic profiles were evaluated under a wide range of experimental conditions in order to assess the effects of the initial concentrations, working pH, Cu(II):NTA molar ratio and reaction temperature. The results showed that the degradation rates were enhanced with the increase of H2O2 and CuII -NTA concentration during SMX oxidation. SMX was fully (83.64 %) degraded for an initial SMX concentration of 0.01 mM and an optimal Cu(II):NTA molar ratio of 1:1. Solution pH influenced SMX degradation and the highest degradation rate constant was achieved at pH 7.2. The radical scavenging experiments indicates that hydroxyl radical (HO) has major role for SMX degradation. The presence of metal ions such as MgII, CaII and MnII had no impacts or little inhibitory effect on the CuII -NTA complex catalyzed Fenton-like reaction, however, a complete degradation of SMX was achieved in the presence of FeIII ions. Also, the effects of various inorganic anions such as Cl−, SO42−, NO3− and HCO3− on the oxidation efficiency of SMX were studied. The efficiency of mineralization of aqueous solution of SMX was evaluated by measuring total organic carbon (TOC). These results demonstrate that CuII -NTA catalyzed Fenton-like oxidation may be an efficient approach for remediation of wastewater containing antibiotics.

Doping of TiO2 Using Metal Waste (Door Key) to Improve Its Photocatalytic Efficiency in the Mineralization of an Emerging Contaminant in an Aqueous Environment

Photocatalysis is an effective advanced oxidation process to mineralize recalcitrant contaminants in aqueous media. TiO2 is the most used photocatalyst in this type of process. To improve the deficiencies of this material, one of the most used strategies has been to dope TiO2 with metallic ions. Chemical reagents are often used as dopant precursors. However, due to the depletion of natural resources, in this work it was proposed to substitute chemical reagents and instead use a metallic residue (door key) as a doping precursor. The materials were synthesized using the sol–gel method and calcined at 400 °C to obtain the crystal structure of anatase. The characterization of the materials was carried out using X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), scanning electron microscopy–energy-dispersive X-ray analysis (SEM-EDX) methods X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectroscopy (ICP-OES). The results obtained indicate that Cu+/Cu2+ and Zn2+ ions coexist in the support, which modifies the physicochemical properties of TiO2 and improves its photocatalytic efficiency. The synergistic effect of the dopants in TiO2 allowed the mineralization of diclofenac in an aqueous medium when T-DK (1.0) was used as photocatalyst and simulated solar radiation as an activation source.

Sorption Potential of Different Forms of TiO2 for the Removal of Two Anticancer Drugs from Water

Anticancer drugs pose a potential risk to the environment due to their significant consumption and biological effect even at low concentrations. They can leach into soils and sediments, wastewater, and eventually into drinking water supplies. Many conventional technologies with more effective advanced oxidation processes such as photocatalysis are being extensively studied to find an economical and environmentally friendly solution for the removal of impurities from wastewater as the main source of these pharmaceuticals. Since it is impossible to treat water by photocatalysis if there is no sorption of a contaminant on the photocatalyst, this work investigated the amount of imatinib and crizotinib sorbed from an aqueous medium to different forms of photocatalyst. In addition, based on the sorption affinity studied, the applicability of sorption as a simpler and less costly process was tested in general as a potential route to remove imatinib and crizotinib from water. Their sorption possibility was investigated determining the maximum of sorption, influence of pH, ionic strength, temperature, and sorbent dosage in form of the suspension and immobilized on the fiberglass mesh with only TiO2 and in combination with TiO2/carbon nanotubes. The sorption isotherm data fitted well the linear, Freundlich, and Langmuir model for both pharmaceuticals. An increasing trend of sorption coefficients Kd was observed in the pH range of 5–9 with CRZ, showing higher sorption affinity to all TiO2 forms, which was supported by KF values higher than 116 (μg/g)(mL/μg)1/n. The results also show a positive correlation between Kd and temperature as well as sorbent dosage for both pharmaceuticals, while CRZ sorbed less at higher salt concentration. The kinetic data were best described with a pseudo-second-order model (R2 > 0.995).

Complete mineralization of phenolic compounds in visible-light-driven photocatalytic ozonation with single-crystal WO3 nanosheets: Performance and mechanism investigation

Complete mineralization of phenolic compounds into CO2 and H2O is desirable for removing them in wastewater, but it is challenging due to the generated recalcitrant intermediates, which requires highly effective advanced oxidation process with proper catalysts. Herein, we found that single-crystal WO3 nanosheets (NSs)-based photocatalytic ozonation (PCO) can realize complete mineralization of phenols (phenol and 2-chlorophenol) under visible light irradiation. Almost 100% mineralization ratio of phenols was achieved through WO3 NSs-based PCO system within short time. By comparing their performances with those of polycrystalline WO3 nanoparticles, detecting and analyzing the intermediates, identifying the dominant radicals and conducting some electrochemical characterizations, the origin of superior catalytic activity of WO3 NSs was uncovered, the mineralization pathways and the overall mechanism were proposed. The excellent PCO performance of WO3 NSs was contributed to their nanosheet morphology with single-crystal microstructure and good dispersion, which can provide continuous interior channels for the photogenerated charge transport from the bulk to surface of WO3 NSs and enough active sites for the surface reactions triggered by these charges. This work puts forwards new ideas to design highly active photocatalysts for PCO and helps deepen understanding of the catalytic mechanism of PCO.

UV/chlorinated cyanurates as an emerging advanced oxidation process for drinking water and potable reuse treatments

Chlorinated cyanurates, prepared by application of hypochlorite to cyanuric acid at different ratios, have been commonly employed for disinfection. Combining UV with chlorinated cyanurates (UV/Cl-cyanurates) can be a novel and effective advanced oxidation process (AOP) because (1) Cl-cyanurates structurally resemble chlorinated amides that feature low reactivity with radicals, and (2) Cl-cyanurates, which bear multiple –Cl, may exhibit high molar absorptivity at 254 nm due to red-shifting absorption. Those chemiphysical properties of Cl-cyanurates may facilitate oxidant photolysis rate and lower radical scavenging rates in an AOP, thereby increasing steady-state concentrations of radicals. In this study, UV spectra measured for Cl-cyanurates highlighted molar absorptivities at 254 nm (∼200 M−1cm−1) much higher than free chlorine or H2O2, while k•OH determined using competition kinetics suggests low •OH reactivity (<1.95 × 107 M−1s−1) for Cl-cyanurates. Photolysis of Cl-cyanurates forms •Cl (i.e., Cl–N cleavage), and •Cl converts to •OH; formation of •OH during a UV/Cl-cyanurates AOP was evaluated using terephthalate as a probe compound. Experiments systematically investigated the effects of pH, Cl2 dosage, and cyanuric concentration (three key factors affecting the equilibrium concentrations of chlorinated-cynaurate species) on the efficacy of removing three indicator contaminants by UV/Cl-cyanurates AOP. UV/Cl-cyanurates AOP conducted in phosphate buffers or authentic surface waters highlighted efficiencies up to 170% higher than UV/Cl2 AOP at neutral pH when the same dosage of oxidants was employed, and the presence of certain levels of background ammonia or chloramines further enhanced its performance. Transformation of cyanuric acid or Cl-cyanurates by reacting with radicals during a UV/Cl-cyanurates AOP treatment was minimum. Toxicity assay indicated that UV/Cl-cyanurates AOP treated water was comparable or less toxicity than UV/H2O2 or UV/Cl2 AOP treated water, and the initial cost estimate indicates UV/Cl-cyanurates AOP is potentially a cost-effective alternative AOP.

Decomposition of perfluorooctanic acid by carbon aerogel with persulfate

Thermally-activated persulfate (PS) has been recognized as one of the most effective Advanced oxidation processes (AOPs) to oxidize Persistent perfluorooctanoic acid (PFOA). Applications of Carbon aerogel (CA)-activated PS for PFOA decomposition at 25, 40, 50 and 60 °C were evaluated. With the presence of CA in PS oxidation, 85.7% of PFOA was decomposed to fluoride ions and intermediates of short-chain perfluorinated carboxylic acids (PFCAs) with a 34.5% defluorination efficiency at 60 °C after 8 h. PFOA was decomposed and mineralized to fluoride ions in the CA + PS system following a stepwise degradation process of C6F13COOH → C5F11COOH → C4F9COOH → C3F7COOH → C2F5COOH → CF3COOH at 60 °C. The decomposition and defluorination rates of the combined CA + PS system at 60 °C were approximately 1.83 and 1.61 times faster than those of the PS-only system, respectively. With CA in the PS system, activation energies of PFOA removal and defluorination were significantly reduced from 66.8 to 37.2 and 97.3 to 49.2 kJ/mol, respectively. It implies that applying CA could effectively promote the PFOA degradation that leads to significant savings in energy consumption and reductions in process time. Characteristics of CA used were evaluated by using N2 adsorption, zeta potential, Raman, SEM, XRD, XPS and FT-IR techniques. A quenching test was conducted by using methanol as an inhibitor and Electron spin resonance (ESR) spectra of free radicals were analyzed for development of proposed reaction mechanisms.

Determination of optimum operational conditions for the removal of 2-MIB from drinking water by peroxone process: a pilot-scale study

Abstract Taste and odor in drinking water are one of the main problems of the water supply and treatment sector. Peroxone is an effective advanced oxidation process, which combines ozone with hydrogen peroxide to create hydroxyl radicals that decompose organic compounds. 2-Methylisoborneol (2-MIB) is one of the significant taste and odor causing compounds, which can be removed with the peroxone process. In this study, removal of a 2-MIB compound by peroxone process was investigated in a pilot-scale treatment plant and optimum operational conditions were determined. For safety reasons, it is important that residual O3 and H2O2 concentrations in the water leaving the reactor should not exceed 0.1 and 0.5 mg/L, respectively. Results indicate that while dissolved ozone concentration was below the indicated limit for all experiments, concentrations over 0.5 mg/L residual H2O2 were observed during the experiments with an H2O2:O3 ratio of 0.5. This limit exceedance affected the decision on the ideal peroxone ratio along with the 2-MIB removal results. Therefore; optimum H2O2:O3 ratio was determined as 0.3. 2-MIB removal efficiency of 81% was achieved at the optimum H2O2:O3 ratio with a contact time of 15 min. According to the results, 2-MIB removal rate had a linear correlation with the contact time.

Natural iron ligands promote a metal-based oxidation mechanism for the Fenton reaction in water environments

The Fenton reaction is an effective advanced oxidation process occurring in nature and applied in engineering processes toward the degradation of harmful substances, including contaminants of emerging concern. The traditional Fenton application can be remarkably improved by using iron complexes with organic ligands, which allow for the degradation of contaminants at near-neutral pH and for the reduction of sludge production. This work discusses the mechanisms involved both in the classic Fenton process and in the presence of ligands that coordinate iron. Cyclohexane was selected as mechanistic probe, by following the formation of the relevant products, namely, cyclohexanol (A) and cyclohexanone (K). As expected, the classic Fenton process was associated with an A/K ratio of approximately 1, evidence of a dominant free radical behavior. Significantly, the presence of widely common natural and synthetic carboxyl ligands selectively produced mostly the alcoholic species in the first oxidation step. A ferryl-based mechanism was thus preferred when iron complexes were formed. Common iron ligands are here proven to direct the reaction pathway towards a selective metal-based catalysis. Such a system may be more easily engineered than a free radical-based one to safely remove hazardous contaminants from water and minimize the production of harmful intermediates.

Remediation of aristolochic acid-contaminated soil by an effective advanced oxidation process

Aristolochic acids (AAs) are persistent soil pollutants in the agricultural fields of the Balkan Peninsula that are endemic for Aristolochia clematitis L. This class of carcinogenic and nephrotoxic phytotoxins is taken up by crops through root absorption and contaminates staple foods across the peninsula. Human exposure to AAs via dietary intake has recently been recognized as a cause of Balkan endemic nephropathy. For the sake of public health, human exposure to AAs from all sources should be minimized in a timely manner. However, currently, there is no available remediation method to remove AAs from soil. In this study, we developed the first soil remediation method for AAs using Fenton's reagent (FR), a combination of ferrous ion and hydrogen peroxide, and optimized factors, including pH, temperature, time, and dose of FR, to achieve the best degradation performance. The maximum AA degradation efficiency was found to be >97% in soil with 500 μg kg-1 of AAs. We anticipate that this developed method, mediated via Fenton reaction, will be useful to effectively eliminate AAs from the Balkan farmlands.

Fe (II)-activated persulfate oxidation effectively degrades iodoform in water: Influential factors and kinetics analysis

Iodoform (CHI3) is one of the disinfection by-products (DBPs) that is formed in the pre-oxidation and disinfection processes of drinking water treatment. In this study, Fe(II)-activated persulfate oxidation (Fe2+/PS) was employed to degrade iodoform, the effects of initial reactants concentration, reaction parameters, kinetics model were investigated, and the underlying mechanisms of CHI3 degradation in Fe2+/PS oxidation process was unveiled. The results showed that the mole ratio Fe2+/PS of 1:5, initial PS concentration of 15 μmmol/L, and pH of 3.0 were identified as the optimum operating parameters. In addition, a relatively higher temperature could enhance CHI3 removal and deiodination. The kinetic model has two different reaction steps: a fast one during the first ten minutes of reaction; then followed by a much slower one. Suppression of the reaction by TBA and MeOH showed that the combined effects of SO4−· and ·OH contributed to the degradation of CHI3, but ·OH played a dominant role. The degradation pathways and the products of total liberated iodine species demonstrate that the applicability of the Fe2+/PS oxidation process for CHI3 degradation. These results indicated that the Fe2+/PS oxidation process is an effective advanced oxidation process for CHI3 removal in water treatment.

Photo-assisted electroperoxone of 2,4-dichlorophenoxy acetic acid herbicide: Kinetic, synergistic and optimization by response surface methodology

In this study, the potential of UV-assisted electroperoxone process (UV-EPP) was assessed into oxidative degradation of 2,4-Dichlorophenoxy acetic (2,4-D) herbicide in a batch system. The influence of several experimental factors like pH of aqueous media, applied current, ozone concentration, reaction time and initial 2,4-D concentration on the UV-EPP performance was evaluated using response surface methodology (RSM). Coupling of UV with ozonation and electrolysis showed the better performance into 2,4-D removal compared to their implementation in individual and binary systems. The process possesses a good efficiency in a wide range of solution pH. Under optimal conditions (pH 5.6, 1.8 mg/L. min ozone, 0.9 A applied current and 112 min reaction), over 91% removal of 58 mg/L 2,4-D was achieved. In addition, the complete removal of 2,4-D and 85% COD and 76% TOC were obtained by UV-EPP over 160 min reaction. Trapping tests verified the presence of both O2− and HO species in the degradation of 2,4-D during UV-EPP, while superoxide radicals have contributed as dominant species. The obtained results were fitted to pseudo-first-order kinetic model with a high correlation coefficient. In conclusion, UV-EPP integrated system can be utilized as an effective advanced oxidation process into excellent degradation/mineralization of herbicides and refractory or toxic organic compounds.

DBP alteration from NOM and model compounds after UV/persulfate treatment with post chlorination

The UV/persulfate process is an effective advanced oxidation process (AOP) for the abatement of a variety of micropollutants via producing sulfate radicals (SO4•-). However, when this technology is used to reduce target pollutants, the precursors of disinfection byproducts (DBPs), such as natural organic matter (NOM) and organic nitrogen compounds, can be altered. This study systematically investigated the DBP formation from NOM and five model compounds after UV/H2O2 and UV/persulfate treatments followed with 24 h chlorination. Compared to chlorination alone, the yields of trichloromethane (TCM) and dichloroacetonitrile (DCAN) from NOM decreased by 50% and 54%, respectively, after UV/persulfate treatment followed with chlorination, whereas those of chloral hydrate (CH), 1,1,1-trichloropropanone (1,1,1-TCP) and trichloronitromethane (TCNM) increased by 217%, 136%, and 153%, respectively. The effect of UV/H2O2 treatment on DBP formation shared a similar trend to that of UV/persulfate treatment, but the DBP formation was higher from the former. As the UV/persulfate treatment time prolonged or the persulfate dosage increased, the formation of TCM and DCAN continuously decreased, while that of CH, 1,1,1-TCP and TCNM presented an increasing and then decreasing pattern. SO4•- activated benzoic acid (BA) to form phenolic compounds that enhanced the formation of TCM and CH, while it deactivated resorcinol to decrease the formation of TCM. SO4•- reacted with aliphatic amines such as methylamine (MA) and dimethylamine (DMA) to form nitro groups, which significantly increased the formation of TCNM in post chlorination, and the rate was determined to be higher than that of HO•. This study illuminated the diverse impacts of the structures of the precursors on DBP formation after UV/persulfate treatment, and DBP alteration depended on the reactivity between SO4•- and specific precursor.