Statistical optimization of arsenic removal from synthetic water by electrocoagulation system and its application with real arsenic-polluted groundwater.

Arsenic presence in the water has become one of the most concerning environmental problems. Electrocoagulation is a technology that offers several advantages over conventional treatments such as chemical coagulation. In the present work, an electrocoagulation system was optimized for arsenic removal at initial concentrations of 100 µg/L using response surface methodology. The effects of studied parameters were determined by a 23 factorial design, whereas treatment time had a positive effect and current intensity had a negative effect on arsenic removal efficiency. With a p-value of 0.1629 and a confidence of level 99%, the type of electrode material did not have a significant effect on arsenic removal. Efficiency over 90% was reached at optimal operating conditions of 0.2 A of current intensity, and 7 min of treatment time using iron as the electrode material. However, the time necessary to accomplish with OMS arsenic guideline of 10 µg/L increased from 7 to 30 min when real arsenic-contaminated groundwater with an initial concentration of 80.2 ± 3.24 µg/L was used. The design of a pilot-scale electrocoagulation reactor was determined with the capacity to meet the water requirement of a 6417 population community in Sonora, Mexico. To provide the 1.0 L/s required, an electrocoagulation reactor with a working volume of 1.79 m3, a total electrode effective surface of 701 m2, operating at a current intensity of 180 A and an operating cost of 0.0208 US$/day was proposed. Based on these results, electrocoagulation can be considered an efficient technology to treat arsenic-contaminated water and meet the drinking water quality standards.

Kinetics and mechanism of Paraquat's degradation: UV-C photolysis vs UV-C photocatalysis with TiO2/SiC foams.

In this study, the photolytic and photocatalytic removal of the herbicide paraquat is investigated under UV-C (254 nm). For photocatalytic experiments, SiC foams were used with P25-TiO2 nanoparticles deposited by dip-coating. The foams were characterized by scanning electron microscopy and paraquat's degradation under UV-C photolysis or photocatalysis, followed by UV-vis spectroscopy, total organic carbon analyzer, LC-MS and ion chromatography. After 3 h of reactions by photolysis and photocatalysis, 4% and 91% of TOC removal were observed. An analysis of degradation by-products showed a similar degradation pathway with pyridinium ions observed by LC/MS and carboxylic acids (succinate, acetate, oxalate and formate) detected by ion chromatography. In conclusion, these two different photo-degradation processes are able to remove paraquat and produce similar by-products. However, the kinetics of degradation is rather slow during photolysis and it is recommended to combine the UV-C lightning with a TiO2 photocatalyst to improve the mineralization rate.

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

Atrazine (ATZ) is one of the most common pesticides detected in surface water in Quebec (Canada). The present study was mainly focused on the degradation of ATZ and its by-products using electrochemical advanced oxidation processes such as photo-electro-Fenton (PEF), electro-Fenton (EF) and anodic-oxidation with simultaneous H2O2 formation (AO - H2O2). The comparison of these processes showed that PEF process was found to be the most effective process in removing ATZ and its by-products from both synthetic solution (ATZ0 = 100 µg L-1) and real agricultural surface water enriched with ATZ (ATZ0 = 10 µg L-1). Different operating parameters, including wavelength of the light, pH, current density and the presence of natural organic matter (humic acids) were investigated for PEF process using boron-doped diamond (BDD) anode and graphite cathode. The current density and the wavelength of the light were the most important parameters in the ATZ degradation efficiency. The best operating conditions were recorded for the synthetic samples at a current density of 18.2 mA cm-2, a pH of 3.0 and treatment time of 45 min. Results showed that atrazine-desethyl-desisopropyl (DEDIA) was the most important by-product recorded. More than 99% of ATZ oxidation was recorded after 15 min of treatment and all the concentrations of major by-products were less than the limit of detection after 45 min of treatment. The PEF process was also tested for real surface water contaminated by ATZ: i) with and without addition of iron; ii) without pH adjustment (pH âˆ¼ 6.7) and with pH adjustment (pH âˆ¼ 3.1). In spite of the presence of radical scavenger and iron complexation the PEF process was more effective to remove ATZ from real surface water when the pH value was adjusted near to 3.0. The ATZ removal was 96.0% with 0.01 mM of iron (kapp = 0.13 min-1) and 100% with 0.1 mM of iron (kapp = 0.17 min-1).

Degradation of atrazine in aqueous solution with electrophotocatalytic process using TiO2-x photoanode.

The present study investigates the efficiency of a sustainable treatment technology, the electrophotocatalytic (EPC) process using innovative photoanode TiO2-x prepared by a magnetron sputter deposition process to remove the herbicide atrazine (ATZ) from water. The coexistence of anatase and rutile were identified by X-ray diffraction (XRD) and the presence of oxygen vacancies reduce the value of the observed bandgap to 3.0 eV compared to the typical 3.2 eV TiO2, this reduction is concomitant with a partial phase transition which is probably responsible for the increase in photoactivity. The experimental results with an initial concentration of ATZ (100 µg L(-1)) show that more than 99% of ATZ oxidation was obtained after 30 min of treatment and reaction kinetic constant was about 0.146 min(-1). This good efficiency indicates that EPC process is an efficient, simple and green technique for degradation of pesticides such as ATZ in water. The analysis with liquid chromatography technique permits to identify, quantify and see the evolution of ATZ by-products which are generated by dechlorination, dealkylation and alkylic-oxidation mechanisms. Finally, the possible pathways of ATZ degradation by hydroxyl radicals were proposed.

Performance of electrochemical oxidation process for removal of di (2-ethylhexyl) phthalate.

Di (2-ethylhexyl) phthalate (DEHP) is the most detected and concentrated plasticizer in environment and wastewaters, worldwide. In this study, different operating parameters such as current intensity, treatment time, type of anodes, and supporting electrolytes were tested to optimized the electro-oxidation process (EOP) for the removal of DEHP in the presence of methanol as a dissolved organic matter. Among the anodes, the Nb/BDD showed the best degradation rate of DEHP, at low current intensity of 0.2 A after 90 min of treatment time with a percentage of degradation recorded of 81 %, compared to 70 % obtained with the Ti/IrO2-RuO2. Furthermore, due to the combination of direct and indirect oxidation, the removal of DEHP in the presence of 1 g/L Na2SO4 was higher than NaBr, even though the oxidant production of NaBr was 11.7 mmol/L against 3.5 mmol/L recorded in the presence of sulfate at 0.5 A and after 60 min of electrolysis time. Under optimal condition (current intensity = 0.5 A, time = 120 min, using Nb/BDD anode and Na2SO4 as supporting electrolyte), the removal of 87.2 % of DEHP was achieved. The total cost of 0.106 US$/m(3) of treated water was achieved based on economical optimization of reactor with current intensity of 0.2 A and 1 g/L Na2SO4.

Removal of carbamazepine from spiked municipal wastewater using electro-Fenton process.

The electrochemical degradation of carbamazepine (CBZ) in both synthetic solutions (CBZo = 12 mg/L) and enriched municipal effluents (CBZo = 60-70 µg/L) was investigated using an electro-Fenton (EF) process. Different operating parameters were investigated, including current intensity, pH, reaction time, ferrous ion concentration, and the type of anode material. The current intensity, the type of anode material, and the concentration of ferrous ions played an important role in the CBZ degradation efficiency. The degradation was mainly attributed to direct anodic oxidation. The best operating conditions for the synthetic sample were obtained at a current density of 0.2 A, a pH of 3.0, and 120 min of treatment using a boron-doped diamond (BDD) anode in the presence of 0.25 mM of Fe(2+). Under these conditions, 52% of total organic carbon (TOC) and 73% of CBZ were removed. The process was also tested as tertiary treatment for a municipal wastewater treatment plant effluent, and CBZ was completely removed.

Electrochemical degradation of the antibiotic sulfachloropyridazine by hydroxyl radicals generated at a BDD anode.

The treatment of aqueous solutions of the antibiotic sulfachloropyridazine (SCP) was carried out at the natural pH of the solution (pH 4.5) with hydroxyl radicals (OH) generated at a BDD anode surface by electro-oxidation using an undivided electrochemical cell equipped with a three-dimensional carbon-felt cathode. Hydroxyl radicals are powerful oxidants and react with the antibiotic leading to its overall mineralization. The kinetic study showed that oxidative degradation of SCP follows pseudo first-order reaction kinetics, with a relatively short degradation time. The degree of mineralization of SCP solutions increased with the applied current, being higher than 95% after 8 h of electrolysis at 350 mA or higher current. To determine the degradation pathway upon the action of hydroxyl radicals, the cyclic and aliphatic by-products, as well as the released inorganic ions, were identified and quantified over electrolysis time. The values of the rate constants of reactions between OH and the SCP and its intermediates were determined by the competition kinetics method using p-hydroxybenzoic acid. The absolute rate constant for the OH-mediated degradation of SCP was found to be 1.92 × 10(9)M(-1)s(-1). Toxicity assessment by the Microtox method during the electro-oxidation of SCP solutions revealed the formation of compounds that can be more toxic than the parent molecule, but the overall results confirm the effectiveness of this electrochemical process for the removal of the antibiotic SCP and its by-products from aqueous media.

Electrochemical treatment of the antibiotic sulfachloropyridazine: kinetics, reaction pathways, and toxicity evolution.

The electro-Fenton treatment of sulfachloropyridazine (SCP), a model for sulfonamide antibiotics that are widespread in waters, was performed using cells with a carbon-felt cathode and Pt or boron-doped diamond (BDD) anode, aiming to present an integral assessment of the kinetics, electrodegradation byproducts, and toxicity evolution. H(2)O(2) electrogeneration in the presence of Fe(2+) yielded (•)OH in the solution bulk, which acted concomitantly with (•)OH adsorbed at the anode (BDD((•)OH)) to promote the oxidative degradation of SCP (k(abs,SCP) = (1.58 ± 0.02) × 10(9) M(-1) s(-1)) and its byproducts. A detailed scheme for the complete mineralization was elucidated. On the basis of the action of (•)OH onto four different SCP sites, the pathways leading to total decontamination includes fifteen cyclic byproducts identified by HPLC and GC-MS, five aliphatic carboxylic acids, and a mixture of Cl(-), SO(4)(2-), NH(4)(+), and NO(3)(-) that accounted for 90-100% of initial Cl, S, and N. The time course of byproducts was satisfactorily correlated with the toxicity profiles determined from inhibition of Vibrio fischeri luminescence. 3-Amino-6-chloropyridazine and p-benzoquinone were responsible for the increased toxicity during the first stages. Independent electrolyses revealed that their toxicity trends were close to those of SCP. The formation of the carboxylic acids involved a sharp toxicity decrease, thus ensuring overall detoxification.

Degradation and mineralization of sulcotrione and mesotrione in aqueous medium by the electro-Fenton process: a kinetic study.

INTRODUCTION: The degradation and mineralization of two triketone (TRK) herbicides, including sulcotrione and mesotrione, by the electro-Fenton process (electro-Fenton using Pt anode (EF-Pt), electro-Fenton with BDD anode (EF-BDD) and anodic oxidation with BDD anode) were investigated in acidic aqueous medium. METHODS: The reactivity of both herbicides toward hydroxyl radicals was found to depend on the electron-withdrawing effect of the aromatic chlorine or nitro substituents. The degradation of sulcotrione and mesotrione obeyed apparent first-order reaction kinetics, and their absolute rate constants with hydroxyl radicals at pH 3.0 were determined by the competitive kinetics method. RESULTS AND DISCUSSION: The hydroxylation absolute rate constant (k(abs)) values of both TRK herbicides ranged from 8.20 × 10(8) (sulcotrione) to 1.01 × 10(9) (mesotrione) L mol(-1) s(-1), whereas those of the TRK main cyclic or aromatic by-products, namely cyclohexane 1,3-dione, (2-chloro-4-methylsulphonyl) benzoic acid and 4-(methylsulphonyl)-2-nitrobenzoic acid, comprised between 5.90 × 10(8) and 3.29 × 10(9) L mol(-1) s(-1). The efficiency of mineralization of aqueous solutions of both TRK herbicides was evaluated in terms of total organic carbon removal. Mineralization yields of about 97-98% were reached in optimal conditions for a 6-h electro-Fenton treatment time. CONCLUSIONS: The mineralization process steps involved the oxidative opening of the aromatic or cyclic TRK by-products, leading to the formation of short-chain carboxylic acids, and, then, of carbon dioxide and inorganic ions.

Electrochemical abatement of the antibiotic sulfamethoxazole from water.

The electrochemical abatement of the antibiotic sulfamethoxazole (SMX) from aqueous solutions at pH 3.0 has been carried out by anodic oxidation and electro-Fenton (EF) processes with H(2)O(2) electrogeneration. The electrolyses have been performed using a small, undivided cell equipped with a Pt or thin film boron-doped diamond (BDD) anode and a carbon-felt cathode. The higher performance of the EF process with 0.2mM Fe(2+) in a BDD/carbon felt cell is demonstrated. This is due to the higher production of ()OH radicals, as well as to the simultaneous degradation at the anode surface and in the bulk solution. At low current, the oxidation at the anode was predominant; at high current, SMX was pre-eminently degraded in the bulk. SMX was quickly destroyed under all the conditions tested, following pseudo first-order kinetics; however, the almost total removal of the total organic carbon was only achieved in the BDD/carbon felt cell. The reaction by-products were quantified by chromatographic techniques and thus, the reaction pathway for the mineralization of SMX by EF has been elucidated. Hydroxylation of SMX on the sulfanilic ring is suggested as the first step, followed by the formation of p-benzoquinone and 3-amino-5-methylisoxazole. Their oxidative cleavage led to the formation of five carboxylic acids that were finally mineralized to CO(2); the release of NH(4)(+), NO(3)(-), and SO(4)(2-) accounted for almost 100% of the initial nitrogen and sulfur content. The absolute rate constants for the oxidative degradation of SMX and the detected aromatic by-products have also been determined.