Combination Of Electro-oxidation Research Articles

Apparent and true mineralization during combined electro‐oxidation and electro‐coagulation on stainless steel anode

AbstractPresent study is a novel attempt to experimentally verify that electrochemical treatment of organic pollutants on stainless steel (SS) anode is a combination of electro‐oxidation (EO) and electro‐coagulation (EC) with quantitative estimation of individual contributions of the two mechanisms. Target organic pollutants, metformin HCl (MET‐HCl) and lamotrigine (LAM), were electrochemically treated with SS anode for this purpose. Experiments were designed using central composite rotatable design (CCRD) to assess the effect of current density (CD) and supporting electrolyte concentration (SEC) as independent process parameters. Under all conditions, the process was experimentally verified to be a combination of EO and EC. For MET‐HCl, true mineralization (TM) as a result of EO contribution varied between 50.13% and 66.64%. EO contribution and resulting TM for LAM ranged from 37.5% to 61.83%. EC contributed 30.6%–31.84% towards MET‐HCl remediation causing the TOC to be transferred from the liquid to the sludge produced (SP). EC contribution was 23.68%–35.89% for LAM remediation. Thus, apparent mineralization (AM), the sum of EO and EC contributions, ranged from 80.63% to 97.79% for MET‐HCl and 61.18% to 96.82% for LAM.Process parameters were statistically optimized using response surface methodology (RSM) to simultaneously maximize TM and AM with minimal energy consumption and maximal current efficiency. The optimized conditions were 0.83 mA/cm2 CD and 86.66 ppm SEC for MET‐HCl. The corresponding values were 1.31 mA/cm2 CD and 79.51 ppm SEC for LAM.

C(sp3)–H Aerobic Alkenylation of Tetrahydroisoquinolines via Organic Electrosynthesis

A method for the C(sp3)-H alkenylation of N-aryl-tetrahydroisoquinoline (THIQ) has been developed by the combination of electrooxidation and a copper catalyst. The corresponding products were obtained with good to excellent yields under mild conditions. Besides, the addition of TEMPO as an electron mediator is crucial to this transformation, since the oxidative reaction could proceed under a low electrode potential. In addition, the catalytic asymmetric variant has also been demonstrated with good enantioselectivity.

Improved mineralization and total nitrogen reduction by combination of electro-reduction and electro-oxidation for nitrophenol removal

In this work, p-Nitrophenol (p-NP) was electro-chemically removed by using a prepared Co3O4/Ti cathode and a BDD anode to achieve the simultaneous reduction of total organic carbon (TOC), total nitrogen (TN) and toxicity. The prepared Co3O4/Ti cathode showed higher electro-activity than the Ti cathode towards p-NP reduction with the removal rate higher than 90.6% but without mineralization. The electro-oxidation removed 84.3% of TOC but none of TN. To develop an optimized process for mineralization and TN removal during p-NP electrolysis, the combination of electro-oxidation and electro-reduction were evaluated by using a dual-chamber cell and a single-chamber cell, respectively. As a result of the re-oxidation and re-reduction in the single-chamber cell, the typically used mode of the simultaneous redox, showed a lower removal of TOC and TN than the combination processes as well as an increased toxicity. The TN removal for both combined modes (21.0%–32.9%) was all higher than that of the mode of reduction because the produced inorganic nitrogen such as ammonia and nitrate could be partially oxidized or reduced to nitrogen gas. The results suggested that the combination process could significantly improve the mineralization and TN reduction for p-NP removal, accompanied with 60.3% decrease of acute toxicity for the reduction after oxidation mode.

Ciprofloxacin removal via sequential electro-oxidation and enzymatic oxidation

The combination of electro-oxidation and enzymatic oxidation was tested to evaluate the potency of this system to remove ciprofloxacin (CIP), a fluoroquinolone antibiotic, from water. For the electro-oxidation boron-doped diamond (BDD) and mixed metal oxides anodes were tested, at three current densities (4.42, 17.7 and 35.4 A/cm2). BDD anode at 35.4 A/cm2 exhibited the highest removal efficiency in the shortest time (>90 % removal in 6 min). For the enzymatic oxidation, laccase from Trametes versicolor was chosen. Laccase alone was not able to remove CIP; hence the influence of redox mediators was investigated. The addition of syringaldehyde (SA) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) resulted in enhanced CIP transformation. About 48.9±4.0 % of CIP remained after 4 h of treatment when SA-mediated laccase was applied and 87.8±6.6 % in the case of ABTS-mediated laccase. The coupling of enzymatic oxidation followed by electro-oxidation led to 73 % removal of the antibiotic. Additionally, the antimicrobial activity increased up to its original efficiency after the treatment. The combination of electro-oxidation followed by enzymatic oxidation led to 97–99 % removal of CIP. There was no antimicrobial activity of the solution after the treatment. The tests with wastewater confirmed the efficacy of the system to remove CIP from the complex matrix.

Spectrum evolution of dissolved aromatic organic matters (DAOMs) during electro-peroxi-coagulation pretreatment of coking wastewater

Enormous existence of dissolved aromatic organic matters (DAOMs) is considered to be a major cause that coking wastewater is hardly degraded. In this study, an advanced electro-chemical process i.e., electro-peroxi-coagulation (EPC) was developed as a pretreatment for efficiently degrading DAOMs and improving the biodegradability of the raw coking wastewater. Gas chromatography-mass spectrometry (GC-MS) also confirmed that most of DAOMs (phenolics, heterocycles, polycyclic aromatic hydrocarbons, benzenes, organic nitriles and anilines) could be effectively decomposed by EPC pretreatment. Ultraviolet visible (UV–Vis), Fourier transform infrared spectroscopy (FTIR) and excitation-emission matrix (EEM) consistently found remarkable spectrum variations of DAOMs in the first 15 min, while spectrum changes became gentle until 2 h. The spectrum evolution of DAOMs suggests the strong attacks on the benzene rings and unsaturated bonds of DAOMs occurs initially and then low molecule intermediates are further degraded. Therefore, EPC should be a feasible option for coking wastewater pretreatment based on the combination of electro-oxidation and electro-precipitation.

Electro-oxidation by graphite anode for naphthenic acids degradation, biodegradability enhancement and toxicity reduction

Electro-oxidation (EO) by using graphite anode and at relatively low current densities was successfully applied for the degradation of commercial naphthenic acids (NAs) mixture in water samples. At current densities of 0.5, 2.5, and 5 mA/cm2, acid extractable fraction (AEF) was removed by 42.2%, 57.0% and 67.9%, respectively, while classical NAs were degraded by 76.9%, 77.6% and 82.4%, respectively. EO reactivity towards NAs increased with increasing the carbon number (n) and was higher for cyclic NAs compared to the acyclic component. Oxidized NAs containing O3 and O4 were also degraded effectively during EO. The biodegradability of organics in the NA mixture was clearly improved by 1.7, 2.5 and 2.7 folds when the samples were pre-treated with EO at current densities of 0.5, 2.5, and 5 mA/cm2, respectively. The aromatic fraction in the commercial NA mixture consisted mainly of single-ring aromatics and was degraded effectively by EO. Biodegradation alone was able to reduce the toxicity of the commercial NA mixture towards Vibrio fischeri; however, the combination of EO with biodegradation resulted in a complete removal of the toxicity, showing a synergistic effect of combining these two processes. Coupling EO with aerobic biodegradation can result in an effective and energy-efficient treatment option for NA-bearing waters such as oil sands process water (OSPW) and refinery effluents.

Coupling electrooxidation and Oxone for degradation of 2,4-Dichlorophenoxyacetic acid (2,4-D) from aqueous solutions

2,4-Dichlorophenoxyacetic acid (2,4-D) is one of the most applicable of herbicides in the world. The presence of 2,4-D in aquatic environment threatens the human health and ecosystem. In current study, a hybrid process was conducted based on the combination of electrooxidation (EO) and Oxone for integration of hydroxyl and sulfate radicals. The operational parameters were investigated and 91% of 2,4-D was removed under the best condition (pH = 4.0, Oxone = 3 mM and 30 mA/cm2). The combination of Oxone and EO indicated a synergistic effect on 2,4-D removal. NaCl and Na2SO4 as supporting electrolyte demonstrated similar results while NaNO3 reduced the removal efficiency. The presence of Co2+ and Fe2+ enhanced 2,4-D removal through Oxone activation. EO/Oxone/Co2+ could completely degrade 2,4-D during 90 min reaction time while 68.9% of total organic carbon was eliminated within 3 h. Scavenging experiments showed that the contribution of sulfate and hydroxyl radicals was nearly the same in 2,4-D degradation in EO/Oxone while sulfate radical was prevailing species in EO/Oxone/Co2+. The performance of EO/Oxone was also examined on a real matrix.

Enhanced membrane fouling mitigation by modulating cake layer porosity and hydrophilicity in an electro-coagulation/oxidation membrane reactor (ECOMR)

A novel electro-coagulation/oxidation membrane reactor (ECOMR), in which electrocoagulation (EC) and electrooxidation (EO) were integrated into one reactor with the membrane module placed in the electric field zone between the electrodes, was designed to create synergistic coagulation and oxidation effects for mitigation of ultrafiltration membrane fouling. The results showed that EO modulated the morphology of the cake layer by breaking up humic acid (HA) molecules (i.e., carboxylic functional groups and aromatic structures), giving a more porous cake layer, while EC increased the hydrophilicity of the formed cake layer, leading to the alleviation of membrane fouling. The cake layer formed in the ECOMR by combination of EC and EO under electric fields was more hydrophilic and more porous, resulting in a normalized water flux about 9.57% and 13.2% higher than the EC membrane reactor (ECMR) and EO membrane reactor (EOMR), respectively. Moreover, the cake layers formed in the ECOMR exhibited lower affinity for the membrane surface, which meant they were easier to clean off. These findings demonstrate that the ECOMR is a promising water treatment technology to alleviate membrane fouling as well as improve water quality.

Treatment of highly toxic cardboard plant wastewater by a combination of electrocoagulation and electrooxidation processes

The objective of this study was to investigate the removal efficiencies of the electrochemical treatment systems as an alternative for the treatment of cardboard plant wastewater (CPW). In accordance with this purpose, CPW was treated by electrocoagulation (EC) with Al electrodes and the effects of current density (CD), operating time (t), and initial pH (pHi) were investigated. The results showed that EC at optimum treatment conditions (CD: 7.5mA/cm2, pHi: 7.0 and t: 60min) have limited removal efficiencies for total organic carbon (TOC; 17.1%) and chemical oxygen demand (COD, 14.2%), on the contrary of turbidity (98.7%). Due to the low TOC and COD removal efficiencies, a secondary treatment was needed and the electrocoagulated effluent was subjected to electrooxidation (EO) by using a boron doped diamond (BDD) electrode for investigating the effect of CD, t, pHi and electrolyte concentration (Ce). Higher TOC (83.7%) and COD (82.9%) removal efficiencies were obtained by EO under the optimum treatment conditions (CD: 100mA/cm2, pHi: 7.2, Ce: 5.0g/L Na2SO4 and t: 180min). In addition, a toxicity test was carried out to the raw and treated wastewater under the optimum operating conditions. This study demonstrated that the combination of EC and EO have a satisfactory potential for real industrial wastewater with a high organic content, suspended solids and toxicity.

A COMBINED ELECTROCOAGULATION-ELECTROOXIDATION TREATMENT FOR DAIRY WASTEWATER

Abstract - Dairy industry effluent is characterized by high chemical oxygen demand (COD) and other pollution load. This study addresses the elimination of organic compounds in dairy wastewater using electrocoagulation (EC), electrooxidation (EO) and a synergistic combination of EC and EO. The removal of COD, color and turbidity was investigated at various current intensities by using different electrodes and at various electrolysis times. Results show that EC is a relatively quick process (6 min), which is very effective in removing colloidal and suspended particles, as seen in changes in turbidity and color, but it is effective to eliminate only half of the COD. However, EO reduces 40% of COD in a practical time of about 30 min. To improve the removal of COD we proceeded to combine the two processes. Thus, the coupled process eliminates 60% of COD in a practical amount of time (21 min), removes the colloidal and suspended particles and eliminates color, turbidity, phosphorus, K + and NTK. The use of the seed toxicity test allows evaluating the quality and effectiveness of the studied effluent treatment system. Seed irrigated with raw waste or treated dairy effluent show no phytotoxicity.

Controlling Synergistic Oxidation Processes for Efficient and Stable Blue Thermally Activated Delayed Fluorescence Devices.

Efficient sky-blue organic light-emitting diodes (OLEDs) employing thermally activated delayed fluorescence (TADF) display a three orders of magnitude increase in lifetime, which is superior to those of controlled phosphorescent OLEDs used in this study. The combination of electro-oxidation and photo-oxidation of the TADF emitters in their triplet excited-states is suppressed through molecule design and device engineering.

Synthesis of optically active 1,3-dienes from alkenylstannanes by a combination of electro-oxidation and copper-mediated homocoupling reaction

A combination of electro-oxidation and copper(II) chloride mediated homocoupling of γ-acyloxyvinylstannanes afforded 1,3-dienes. The stereoselectivity strongly depended on the solvent system and no isomerization occurred when the reactions were carried out in DMF (0.01 M). The facile synthesis of (6 R, 11 R)-(7E, 9E)-6,11-hexadeca-7,9-dienyl dibenzoate was thus accomplished from ( R)-(E)-1-tributyl-stannyl-1-octene-3-ol, which was prepared through the lipase-catalyzed reaction in an optically pure form.