Paired electrooxidative degradation of phenol with in situ electrogenerated hydrogen peroxide and hypochlorite

Degradation of antibiotics by advanced oxidation processes: An overview

Antibiotics are becoming emerging contaminants due to their extensive production and consumption, which have caused hazards to the ecological environment and human health. Various techniques have been studied to remove antibiotics from water and wastewater, including biological, physical and chemical methods. Among them, advanced oxidation processes (AOPs) have received increasing attention due to their fast reaction rate and strong oxidation capability, which are effective for the degradation of antibiotics in aquatic environments. In this review paper, a variety of AOPs, such as Fenton or Fenton-like reaction, ozonation or catalytic ozonation, photocatalytic oxidation, electrochemical oxidation, and ionizing radiation were briefly introduced, including their principles, characteristics, main influencing factors and applications. The current applications of AOPs for the degradation of antibiotics in water and wastewater were analyzed and summarized, the concluding remarks were given and their future perspectives and challenges were discussed.

Electro Fenton removal of clopyralid in soil washing effluents

The removal of a commercial herbicide, based on clopyralid, by means of Electro-Fenton (EF) was studied using a soil washing effluent obtained using synthetic ground water as washing fluid. From the results, it was observed that the degradation and mineralization yields of clopyralid were high, even without the addition of supporting electrolyte. The groundwater could be then used as a sustainable supporting electrolyte. The influence of the minerals constituents, the current and the ferrous ions regeneration was evaluated. The highest hydrogen peroxide production was achieved working at 200 mA but regeneration of ferrous ions was not efficient at this current. Iodide ions were one of the main responsible in the EF efficiency decrease due to their reaction with the produced hydrogen peroxide. Electrochemical study proved that clopyralid was not electroactive and that its degradation was mainly due to radical oxidation. Long duration electrolysis carried out at 200 mA in groundwater provided an improvement of the solution biodegradability after 480 min that can be linked to a significant increase in the carboxylic acids production. These results support the feasibility of applying an EF process in order to carry out a subsequent biological mineralization.

Electrochemical oxidation of ampicillin antibiotic at boron-doped diamond electrodes and process optimization using response surface methodology

Electrochemical oxidation and process optimization of ampicillin antibiotic at boron-doped diamond electrodes (BDD) were investigated in a batch electrochemical reactor. The influence of operating parameters, such as ampicillin concentration, electrolyte concentration, current density, and reaction temperature, on ampicillin removal, COD removal, and energy consumption was analyzed in order to optimize the electrochemical oxidation process under specified cost-driven constraints using response surface methodology. Quadratic models for the responses satisfied the assumptions of the analysis of variance well according to normal probability, studentized residuals, and outlier t residual plots. Residual plots followed a normal distribution, and outlier t values indicated that the approximations of the fitted models to the quadratic response surfaces were very good. Optimum operating conditions were determined at 618 mg/L ampicillin concentration, 3.6 g/L electrolyte concentration, 13.4 mA/cm(2) current density, and 36 °C reaction temperature. Under response surface optimized conditions, ampicillin removal, COD removal, and energy consumption were obtained as 97.1 %, 92.5 %, and 71.7 kWh/kg CODr, respectively.

Decomposition of nitrotoluenes in wastewater by sonoelectrochemical and sonoelectro-Fenton oxidation

Oxidative degradation of dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT) in wastewater was conducted using electrochemical and electro-Fenton processes respectively, combined with ultrasonic irradiation, wherein a synergistic effect is observed. Experiments were carried out to elucidate the influence of various operating variables on the sonoelectrolytic behavior, such as electrode potential, sonoelectrolytic temperature, acidity of wastewater, oxygen dosage, and dosage of ferrous ions. It deserves to note that the nitrotoluene contaminants could be completely decomposed by sonoelectro-Fenton method, wherein hydrogen peroxide was in situ generated from cathodic reduction of oxygen, supplied partially by anodic oxidation of water. During the sonoelectrolytic process, in spite of existence of degassing phenomenon, the high yield of hydrogen peroxide was produced due to the significantly enhanced mass transfer rate of oxygen toward the cathode, caused by ultrasonic irradiation. Because higher removal efficiency of DNTs and TNT obtained at ambient conditions, it is believed that the sonoelectrolytic method is potentially applied to dispose wastewater from toluene nitration processes.

Recycle of electrolytically dissolved struvite as an alternative to enhance phosphate and nitrogen recovery from swine wastewater

Operational parameters such as electric voltage, NaCl, reaction time (RT) and initial struvite amount were optimized for struvite dissolution with a designed electrolysis reactor, and the effect of recycling the dissolved solution on the performance of struvite crystallization was also assessed. The electrolytic reactor was made of plexiglas having titanium plate coated with iridium oxide as anode (surface area: 400 cm(2)) and stainless steel plates as cathodes. For reutilization of dissolved struvite, four runs were conducted with different recycle ratio of the solution. Optimum conditions for the electric voltage, NaCl, RT and initial struvite amount were 7 V, 0.06%, 1.5h and 1.25 g/L, respectively. At the above optimized conditions, 49.17 mg/L phosphate (PO(4)(3-)-P) was dissolved and ammonium-nitrogen (NH(4)-N) got completely removed from the solution. When 0.0, 0.5, 1.0 and 2.0 moles of the dissolved struvite with respect to PO(4)(3-)-P in swine wastewater were recycled along with 0.5M magnesium chloride (MgCl(2)), the PO(4)(3-)-P removal was 63, 69, 71 and 79%, and NH(4)-N was 9, 31, 40 and 53%, respectively. Hence, the performance of struvite formation process was proportionally increased. It is concluded that struvite can be re-dissolved by electrolysis and reused as a source of P and Mg.

Paired removal of color and COD from textile dyeing wastewater by simultaneous anodic and indirect cathodic oxidation

The anodic and indirect cathodic removals of color and COD from real dyeing wastewater were investigated simultaneously using a stacked Pt/Ti screen anode and a graphite packed-bed cathode in a divided flow-by electrochemical reactor. The anodically generated hypochlorite and cathodically generated hydrogen peroxide were the main species used to remove color and COD in the wastewater. Various experimental operating factors that can affect the removal efficiency were investigated, including the applied current density, the amount of NaCl added, the solution pH in alkaline ranges and the temperature. The color and COD removal efficiencies in the anodic chamber were much higher than those in the cathodic chamber. The overall (anodic plus cathodic) removal efficiencies increased with the applied current density, the amount of NaCl added and the temperature. In contrast, increasing the solution pH decreased the overall removal efficiency. The anodic and cathodic current efficiencies at 20 mA/cm(2) were 63.50% and 19.57%, respectively. In this work the total treatment cost for removing 1g COD was US $0.643 when an air cylinder was used.

Destruction of nitrotoluenes in wastewater by Electro-Fenton oxidation

Electrolytic degradation of dinitrotoluenes (DNTs) and 2,4,6-trinitrotoluene (TNT) in wastewater was conducted by Electro-Fenton's reagents. The batch-wise experiments were carried out to elucidate the influence of various operating variables on the electrolytic behavior, including electrode potential, oxygen dosage, electrolytic temperature, acidity of wastewater and dosage of ferrous ions. It deserves to note that the nitrotoluenes contained could be completely decomposed by Electro-Fenton's reagents, wherein hydrogen peroxide was in situ generated from cathodic reduction of oxygen, supplied mainly by anodic oxidation of water. During the electrochemical process, the influence of electrolytic temperature on the degradation of nitrotoluenes is the most significant, followed by electrode potential, acidity of wastewater and oxygen dosage. Based on the spectra analyzed by gas chromatograph/mass spectrometer (GC/MS), it is proposed that initial denitration of 2,4-DNT and/or 2,6-DNT gives rise to formation of o-mononitrotoluene, which undergoes the cleavage of nitro group into toluene, followed by oxidation of methyl group to benzoic acid and subsequent decarboxylation. It is believed that the electrolytic method established is potentially applied to dispose wastewater from toluene nitration processes in practice.

Electrochemical degradation of phenol using electrodes of Ti/RuO(2)-Pt and Ti/IrO(2)-Pt

Electrochemical degradation of phenol was evaluated at two typical anodes, Ti/RuO(2)-Pt and Ti/IrO(2)-Pt, for being a treatment method in toxic aromatic compounds. The influences of current density, dosage of NaCl, initial phenol concentration on electrochemical phenol degradation were investigated. It was found that Ti/RuO(2)-Pt anode had a higher oxygen evolution potential than Ti/IrO(2)-Pt anode, which will increase the current efficiency for electrochemical degradation, and the instantaneous current efficiency (ICE) was relatively higher at the initial time during phenol electrolysis. HOCl formed during electrolysis would play an important role on the oxidation of phenol. For the Ti/RuO(2)-Pt anode, phenol concentration decreased from around 8mg/L to zero after 30min of electrolysis with 0.3g/L NaCl as supporting electrolyte at the current density of 10mA/cm(2). Although phenol could be completely electrochemical degraded at both Ti/RuO(2)-Pt and Ti/IrO(2)-Pt anodes, phenol degradation was slower at the Ti/IrO(2)-Pt anode than at the Ti/RuO(2)-Pt anode due to the fact that passivation was to be found at the Ti/IrO(2)-Pt anode.

Electrochemical destruction of dinitrotoluene isomers and 2,4,6-trinitrotoluene in spent acid from toluene nitration process

Mineralization of dinitrotoluene (DNT) isomers and 2,4,6-trinitrotoluene (TNT) in spent acid was conducted by in situ electrogenerated hydrogen peroxide. The electrolytic experiments were carried out to elucidate the influence of various operating parameters on the performance of mineralization of total organic compounds (TOC) in spent acid, including electrode potential, reaction temperature, oxygen dosage and concentration of sulfuric acid. It is worth noting that organic compounds could be completely mineralized by hydrogen peroxide obtained from cathodic reduction of oxygen, which was mainly supplied by anodic oxidation of water. Based on the spectra identified by gas chromatograph/mass spectrometer (GC/MS), it is proposed that oxidative degradation of 2,4-DNT and/or 2,6-DNT, 2,4,6-TNT results in o-mononitrotoluene (MNT) and 1,3,5-trinitrobenzene, respectively. Due to the removal of TOC and some amount of water, the electrolytic method established is promising for industrial application to regeneration of spent acid from toluene nitration process.

Electrochemical treatment of simulated textile wastewater with industrial components and Levafix Blue CA reactive dye: optimization through response surface methodology

The electrochemical oxidation of simulated textile wastewater was studied on iron electrodes in the presence of NaCl electrolyte in a batch electrochemical reactor. The simulated textile wastewater was prepared from industrial components based on the real mercerized and non-mercerized cotton and viscon process, being first in literature. The highest COD, color and turbidity removals were achieved as 93.9%, 99.5%, and 82.9%, respectively, at 40% pollution load, 8 V applied potential, 37.5 g/L electrolyte concentration and 30 degrees C reaction temperature. The electrochemical treatment of industrial textile wastewater was optimized using response surface methodology (RSM), where applied potential and electrolyte concentration were to be minimized while COD, color and turbidity removal percents were maximized at 100% pollution load. In a specific batch run under the optimum conditions of 30 degrees C reaction temperature, 25 g/L electrolyte concentration and 8 V applied potential applied with 35.5 mA/cm2 current density at 100% pollution load, COD, color and turbidity removals were realized as 61.6%, 99.6% and 66.4%, respectively.

Removal of o-nitrophenol from water by electrochemical degradation using a lead oxide/titanium modified electrode

This study examined o-nitrophenol removal from aqueous solutions by electrochemical oxidation employing a modified electrode. The modified electrode was produced by electrodepositing lead oxide onto a titanium substrate. Following electrochemical oxidation of o-nitrophenol-containing solutions, the remaining o-nitrophenol concentration and chemical oxygen demand (COD) values were determined. The optimum parameters were current density of 40 mA cm(-2), pH of 2.47, 60 min of electrolysis time, 4 g L(-1) NaCl electrolyte solution and temperature of 30 degrees C. Under these optimum conditions of electrochemical degradation using a lead oxide/titanium modified electrode complete removal of o-nitrophenol and COD was achieved.

Study on superoxide and hydroxyl radicals generated in indirect electrochemical oxidation by chemiluminescence and UV-Visible spectra

The generation and transformation of radicals on the cathode of indirect electrochemical oxidation were studied by chemiluminescence (CL) and UV-Visible spectra in the reactor with a salt bridge that connected the separated chambers. The CL intensity of 4 x 10(-9) mol/L luminol on the cathode with bubbling oxygen was about seven times that of the intensity without it, which was because of the generation of reactive oxygen species (ROS). The existence of ROS, especially the generation of the superoxide radical, could be affirmed by the fact that the CL intensity of 4 x 10(-9) mol/L 2-methyl-6-(4-methoxyphenyl)-3,7-dihydroimidazo[1,2-a]pyrazin-3-one with bubbling oxygen was about four times that of the intensity without it. However, there was no chemiluminescence on the anode under the same condition. The change in the UV-Visible spectra of nitro blue tetrazolium and N,N-dimethyl-4-nitrosoaniline at the cathode chamber affirmed the transformation from oxygen to superoxide and hydroxyl radicals. The mechanism of the superoxide and hydroxyl radical generation and transformation on the cathode was discussed with the help of the experimental results and relative references.

Optimization of electrochemical treatment of industrial paint wastewater with response surface methodology

The electrochemical oxidation of water-based paint wastewater was investigated batch-wise in the presence of NaCl electrolyte with carbon electrodes for the first time in literature. The electrochemical treatment conditions were optimized using response surface methodology where potential difference, reaction temperature and electrolyte concentration were to be minimized while chemical oxygen demand (COD), color and turbidity removal percents and initial COD removal rate were maximized at 100% pollution load. The optimum conditions were satisfied at 35 g/L external electrolyte concentration, 30 degrees C reaction temperature and 8 V potential difference (64.37 mA/cm(2) current density) realizing 51.8% COD and complete color and turbidity removals, and 3010.74 mg/Lh initial COD removal rate. According to these results, the electrochemical method could be a strong alterative to conventional physicochemical methods for the treatment of water-based paint wastewater.

Response surface optimization of electrochemical treatment of textile dye wastewater

The electrochemical treatment of textile dye wastewater containing Levafix Blue CA, Levafix Red CA and Levafix Yellow CA reactive dyes was studied on iron electrodes in the presence of NaCl electrolyte in a batch electrochemical reactor. The wastewater was synthetically prepared in relatively high dye concentrations between 400mg/L and 2000mg/L. The electrochemical treatment of textile dye wastewater was optimized using response surface methodology (RSM), where current density and electrolyte concentration were to be minimized while dye removal and turbidity removal were maximized at 28 degrees C reaction temperature. Optimized conditions under specified cost driven constraints were obtained for the highest desirability at 6.7mA/cm(2), 5.9mA/cm(2) and 5.4mA/cm(2) current density and 3.1g/L, 2.5g/L and 2.8g/L NaCl concentration for Levafix Blue CA, Levafix Red CA and Levafix Yellow CA reactive textile dyes, respectively.

Electrochemical degradation of Acid Blue and Basic Brown dyes on Pb/PbO2 electrode in the presence of different conductive electrolyte and effect of various operating factors

Electrocatalytic degradation of Acid Blue and Basic Brown dyes from simulated wastewater on lead dioxide anode was investigated in different conductive electrolytes. It was shown that complete degradation of these dyes is dependent primarily on type and concentration of the conductive electrolyte. The highest electrocatalytic activity was achieved in the presence of NaCl (2g/l) and could be attributed to indirect oxidation of the investigated dyes by the electrogenerated hypochlorite ions formed from the chloride oxidation. In addition, contribution from direct oxidation could also be possible via reaction of these organic compounds with the electrogenerated hydroxyl radicals adsorbed on the lead dioxide surface. In the presence of NaOH, the electrocatalytic activity of the employed anode was not comparable to that in NaCl due primarily to the absence of chloride. This indicates that dyes degradation in NaOH occurs exclusively via direct electrochemical process. However, in H2SO4, the electrode performance was poor due partially to the absence of chloride from the conductive solution. The possibility of electrode poisoning as a result of growth of adherent film on the anode surface or production of stable intermediates not easily further oxidized by direct electrolysis in H2SO4 might also be accountable for the poor performance observed in this conductive electrolyte. Optimizing the conditions that ensure effective electrochemical degradation of Acid Blue and Basic Brown dyes on lead dioxide electrode necessitates the control of all the operating factors.

Influence of anode material on electrochemical oxidation for the treatment of tannery wastewater

The treatment of tannery wastewater by electrochemical oxidation, mediated by an electro-generated species was carried out under galvanostatic conditions in an electrochemical reactor equipped with anodes based on noble metals and metal oxides (Ti/Pt-Ir, Ti/PbO2, Ti/PdO-Co3O4 and Ti/RhO(x)-TiO2). The decrease in time of chemical oxygen demand, nitrogen (TKN and ammonia), Cr and sulphides was monitored. The study showed that the rate of pollutant removal was significantly influenced by the type of anode material and electrochemical parameters. Different mechanisms contributed to the removal of pollutants when the reactor operated under conditions close to the limiting current for chlorine evolution and under much higher current density, with the reactor performing better at a high current/voltage. The kinetic pseudo-first order model applied for the interpretation of the results showed that the Ti/Pt-Ir and Ti/PdO-Co3O4 anodes performed better than the other two electrodes under the majority of tested conditions, with the highest rate of removal obtained for ammonia (kinetic rate constant k=0.75 min(-1)). Electrochemical oxidation can be applied as a post-treatment after the conventional biological process in order to remove the residual ammonia with low energy consumption (0.4 kWh m(-3)).

Continuous electrochemical treatment of phenolic wastewater in a tubular reactor

The electrochemical treatment of phenolic wastewater in a continuous tubular reactor, constructed from a stainless steel tube with a cylindrical carbon anode at the centre, was investigated in this study, being first in literature. The effects of residence time on phenol removal was studied at 25 degrees C, 120 g l(-1) electrolyte concentration for 450 and 3100 mg l(-1) phenol feed concentrations with 61.4 and 54.7 mA cm(-2) current densities, respectively. The change in phenol concentration and pH of the reaction medium was monitored in every run and GC/MS analyses were performed to determine the fate of intermediate products formed during the electrochemical reaction in a specified batch run. During the electrolysis mono, di- and tri-substituted chlorinated phenol products were initially formed and consumed along with phenol thereafter mainly by polymerization mechanism. For 10 and 20 min of residence time phenol removal was 56% and 78%, respectively, with 450 mg l(-1) phenol feed concentration and above 40 min of residence time all phenol was consumed within the column. For 1, 1.5, 2 and 3h of residence time, phenol removal achieved was 42%, 71%, 81% and 98%, respectively, at 3100 mg l(-1) phenol feed concentration. It is noteworthy that more than 95% of the initial phenol was converted into a non-passivating polymer without hazardous end products in a comparatively fast and energy-efficient process, being a safe treatment.

Synergetic effects of anodic-cathodic electrocatalysis for phenol degradation in the presence of iron(II)

A novel electrocatalysis method for phenol degradation was described using a beta-PbO2 anode modified with fluorine resin and a Ni-Cr-Ti alloy cathode. In case of air sparging at the cathodic zone, the techniques of anodic-cathodic electrocatalysis (ACEC) and ferrous ion catalyzed anodic-cathodic electrocatalysis (FACEC) in the presence of iron(II) were developed. Both of ACEC and FACEC were more effective than anodic electrocatalysis (AEC). The percentage of phenol eliminated by FACEC could increase by nearly 30% compared with that of AEC, and the current efficiency could reach to 70%. Important operating factors such as ferrous ion concentration, air-sparging rate and applied current were investigated and it was found that such beneficial effects could be achieved at a suitable current and ratio of the concentration of ferrous ion to the air sparged. The mechanism of phenol degradation is proposed to be the generation of hydroxyl radicals concerned with the two electrodes. Results also indicated that the process provided an efficient way to regenerate ferrous ion compared with the conventional Fenton's system.

Coupling of anodic and cathodic reactions for phenol electro-oxidation using three-dimensional electrodes

We studied the electrochemical oxidation of phenol by the coupling of anodic and cathodic reactions. The experiments were done in an electrochemical filter press cell equipped with an Sb-doped SnO2-coated titanium foam and a RVC cathode. The oxidation occurs by a direct oxidation on the anodic side, while on the cathodic side oxidation occurs via an electro-Fenton mechanism. We studied the influence of the working parameters. The electrical yield increases when pH decreases and is strongly dependent on an optimum between current density, iron and dissolved oxygen concentration. This method may be applicable to refractory compounds.

Removal of organic pollutants from industrial wastewater by electrogenerated Fenton's reagent

This study was performed to investigate the treatment of an industrial wastewater mainly containing naphthalene- and anthraquinone-sulphonic acids, by electrogenerated Fenton's reagent. The hydrogen peroxide was produced in situ by electrochemical reduction of oxygen on graphite-felt cathodes and the Fe2+ ions were also regenerated by cathodic reduction of Fe3+. The influence of cathode potential, Fe2+ concentration and electrode surface pre-treatment on chemical oxygen demand (COD) removal and colour fading were studied. Results indicated that the higher COD removal was obtained in the presence of 3 mM of ferrous ions working at a constant potential of -1 V vs. SCE. Moreover, it was shown that both chemical and electrochemical pre-treatments of the cathode surface resulted in a decrease of COD depletion.

Approach to a two-step process of dye wastewater containing acid red B

The treatment of simulated wastewater containing Acid Scarlet BS was tested with a two-step process that the pretreatment of Fe(II)-mediated decolorization was followed by the electrochemical oxidation with a three-phase three-dimensional electrodes. The experimental results showed that the decolorization mechanism was reductive destruction for the azo group of the dye molecular rather than flocculation or absorption and that the three-phase three-dimensional electrode can effectively reduce COD in the decolorized wastewater simultaneously by several mechanisms such as absorption, air-oxidation, anodic oxidation, cathodic electrogenerated H2O2 and so on. It was also observed that COD for the decolorized wastewater was easier removed as compared with the original dye wastewater, implying that the first and second stage act synergistically to destroy the organic pollutants.