A comparative study of azo dye decolorization by electro‐Fenton in two common electrolytes

BACKGROUND: This study compared the decolorization behaviors of a model azo dye of methyl red in Na₂SO₄ and NaCl media by electro‐Fenton process, in which FeSO₄ was added into the solution, while H₂O₂ was efficiently generated on a graphite–polytetrafluoroethylene cathode. Parameters such as pH, cathodic potential, electrolyte concentration, and initial dye concentration as well as the treatment time were investigated to disclose different decolorization behaviour. RESULTS: Decolorization in NaCl medium had an advantage over that in Na₂SO₄ medium not only in performance but also in its suitability for application, which seemed less sensitive to variations in parameters and thus broadened the optimal performance range. In NaCl medium, indirect oxidation by active chlorine contributed greatly to the decolorization, and the removal of methyl red obeyed pseudo‐first‐order kinetics. CONCLUSION: Electro‐Fenton oxidation in the present system in the presence of NaCl would is a promising procedure for azo dye waste‐water treatment. Copyright © 2009 Society of Chemical Industry     

The mechanism and application of the electro‐Fenton process for azo dye Acid Red 14 degradation using an activated carbon fibre felt cathode

BACKGROUND: The discharge of azo dyes into the environment poses concerns due to their limited biodegradability. The electro‐Fenton process (EF) is a good method to effectively degrade these dyes. The aim of this work was to study the mechanism and the feasibility of the EF reaction using an activated carbon fibre (ACF) cathode. In this study, two methods were used to measure the reactive species generated in anodic oxidation (AO), anodic oxidation with electrogenerated H₂O₂ (AO‐H₂O₂) and the EF process. Acid Red 14 (AR14) was chosen as a model pollutant. The effects of the operational parameters, pH and initial concentrations were investigated. A short‐term biodegradability test was also carried out to evaluate the EF process from a biological point of view. RESULTS: After 2 h EF reaction 118.7 µmol L^?1?OH were produced, which was much higher than that of the AO‐H₂O₂ (63.2 µmol L^?1) process. H₂O₂ is largely generated and Fe³⁺ efficiently reduced on the high surface area of the ACF cathode. The EF process provides more effective degradation of AR14 than the conventional Fenton process, and its current efficiency is significantly affected by the initial pH and the initial AR14 concentration. Following EF treatment, the biodegradability of AR14 is significantly increased. CONCLUSION: The higher formation of ^?OH in the EF process suggests it is an effective method for pollutant removal. This process also leads to increased biodegradability, which is expected to facilitate subsequent biological treatment. Copyright © 2010 Society of Chemical Industry     

Effects of ultrasonics on the properties of continuous nickel foam

Environmental pollution and high cost are two typical problems when vacuum gas deposition or electroless nickel conductive technology is applied to the production of continuous nickel foam. To solve these problems, conductive colloid coating technology is usually used. But the continuous nickel foam obtained via this method has drawbacks, such as low tensile strength and elongation, high deposit thickness ratios (DTRs), inhomogeneous surface density distribution and inhomogeneous morphology. In this work, ultrasonic treatment was applied to certain production stages to investigate the effects on the properties of continuous nickel foam mentioned above. It was found through the comparison of the results obtained that using ultrasonic waves can significantly improve the structures and performances of continuous nickel foam.     

Cellulose–chitosan interpenetrating polymer network for electro‐active paper actuator

In this article, the cellulose‐chitosan interpenetrating polymer network (IPN) films were prepared and fabricated as the electro‐active paper actuator. The characteristics of the cellulose–chitosan IPN films were examined by SEM, FT‐IR, XRD, DSC, and tensile test. The performance of the IPNs based actuator was evaluated in terms of bending displacement with respect to the actuation frequency, voltages, humidity levels, chitosan content, and time variation. It was observed that with chitosan content increasing in the IPNs, the crystallinity decreased and the network became denser, which caused the Young's modulus to increase. Chitosan content in IPNs also significantly affected the bending performance. The optimum IPN weight ratio of cellulose and chitosan was 60 : 40. The maximum bending displacement of 7.2 mm was found at 80% relative humidity level. In terms of durability, the bending lifetime at 70% humidity level was about 10 h with 17% performance degradation. More issues on the actuator performance and durability are addressed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Dry and durable electro‐active paper actuator based on natural biodegradable polymer

This article describes a dry and durable electro‐active paper (EAPap) actuator based on natural biodegradable polymer: cellulose and chitosan. To fabricate this actuator, cellulose and chitosan were dissolved in trifluoroacetic acid. The solution was cast to form a film followed by depositing thin gold electrode on both sides of the film. The actuator was actuated under AC voltage at an ambient condition by changing the actuation voltage, frequency, and time. The actuator revealed a large bending displacement under low voltage, electrical power consumption at low humidity condition. This cellulose–chitosan blended EAPap actuator is suitable for dry and durable actuator. Details about the fabrication, durability, electrical power consumption, and characteristics as well as morphology of the actuator are explained. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Oxygen reduction electrode in advanced chlor‐alkali with ruthenium as electro‐catalyst

The platinum (Pt) diffusion gas electrodes are frequently used in chlor‐alkali process industry. The platinum (Pt) diffusion gas electrodes used in advanced chlor‐alkali process has encountered many disadvantages such as flooding, which is the result of peroxide production phenomenon. The flooding reduces the process efficiency. In this article new electrodes are used to overcome some of the above‐mentioned disadvantages to increase efficiency. The effects of seven process parameters are also individually studied. The results show the brine concentration increase CCE by increasing, anolyte, oxygen temperatures, and flow rates. The brine concentration decreases as the current density increases. The Ru/C catalyst performance is higher than Pt/C catalyst. Besides, Ru effectively prevents the aggregation and growth of platinum nano‐particles in the thermal heating process. The higher activity, good stability, and the better caustic current efficiency of the Ru/C catalyst make it more suitable cathode in advanced chlor‐alkali process.     

Structure for electro‐spun silk fibroin nanofibers

Electro‐spinning was made using silk fibroin and it was found that silk fibroin nanofibers of partially oriented amorphous structure are producible using HFIP(1,1,1,3,3,3 hexafluoro‐2‐propanol) as a solvent for fibroin via the electro‐spinning setup equipped with parallel electrodes as a collector. Transformation from amorphous to silk I of a highly contracted beta‐turn form or amorphous to silk II of a regular array of antiparallel beta‐sheets occurred preferentially via the treatment with water vapor or ethanol, respectively. In addition the c‐axis of crystallites was oriented parallel to the fiber axis. When the electro‐spinning was made using a dish‐type collector filled with ethanol, a peculiar web texture was obtained. Such a web texture seems to be brought about by the shrinkage of fiber due to the crystallization of fibroin and/or surface tension of ethanol droplets formed between the fibers. In this spinning setup, the c‐axis of crystallites was also oriented parallel to the fiber axis. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

A practical parametrical characterization of the Fenton and the photo‐Fenton sulfamethazine treatment using semi‐empirical modeling

BACKGROUND: Sulfamethazine (SMT) has received little attention in the water treatment literature. Yet, SMT is among the non‐biodegradable substances increasingly found in aqueous media and affecting both public health and wastewater treatments. For a long time, advanced oxidation processes (AOPs) were studied via pure empirical modeling, although the surface response models resulting from lumped information (TOC, COD, etc.) present limitations regarding extrapolation and optimization. Conversely, detailed first‐principles modeling may not be affordable due to the computational burden and the chemical analysis needs. Thus, a balanced approach may be practical in many cases. RESULTS: Experiments on SMT solutions (500 mL, 50 mg L^?1) were performed under conditions set by an experimental design. A set of replicated degradation time‐profiles (TOC and SMT concentrations) was obtained and a semi‐empirical kinetic model was fitted to these data to determine maximum conversion and kinetic rate. CONCLUSIONS: SMT can be completely degraded from water via photo‐Fenton treatment. Conditions for this treatment were investigated and its outcomes were systematically characterized by a simple kinetic model and two lumped parameters, conversion and kinetic rate. Both, the model and the corresponding parametrical characterization are introduced as a means to discriminate the most efficient treatment conditions in a practical and efficient way. Copyright © 2011 Society of Chemical Industry     

Removal of tannins and polyhydroxy phenols by electro‐chemical techniques

The removal of tannins and their basic molecules such as catechol, pyrogallol, phloroglucinol and resorcinol was studied by electro‐flotation and electro‐oxidation techniques. Iron rods and triple oxide (TaO₂/RuO₂/IrO₂) coated titanium rods were used as electrodes for electro‐flotation and electro‐oxidation respectively. Interaction of tannins and polyhydroxy phenols with iron oxy‐hydroxide formed by anodic dissolution of iron was studied by UV‐Visible, FT‐IR and zeta‐potential measurements. GC–MS was used to identify the intermediate compounds formed during electro‐oxidation. Catechol, pyrogallol, phloroglucinol and resorcinol were found to be mineralized in the presence of triple oxide (TaO₂/RuO₂/IrO₂) coated titanium electrodes. Catechol and pyrogallol were found to form insoluble organo‐metal complexes while resorcinol and phloroglucinol were found to adsorb on iron oxy‐hydroxide. The sludge thus formed was simultaneously separated from the aqueous phase by hydrogen bubbles. It was observed that the power consumption is relatively high for electro‐oxidation compared with electro‐flotation. The effects of pH and reaction time on their removal were also studied and the results are discussed. Copyright © 2005 Society of Chemical Industry     

Batch and Fed‐Batch Degradation of Enrofloxacin by the Fenton Process

Enrofloxacin is a synthetic second‐generation fluoroquinolone used as an antimicrobial agent exclusively in veterinary medicine. To simulate the treatment of wastewater contaminated by enrofloxacin, four‐day long fed‐batch runs were carried out according to the Fenton process with an enrofloxacin solution as model, to which hydrogen peroxide and ferrous ion were added twice a day. The residual enrofloxacin concentration was practically coincident to that detected at the end of the batch tests. Hydrogen peroxide was almost completely consumed after each feeding period, while the total organic carbon (TOC) concentration decreased gradually within three days, corresponding to a reduction > 58 %. From the third day on, the TOC falling rate was quite low. A yellow sludge settled due to the precipitation of both Fe(OH)₃ and a complex formed by ferric ion with adsorbed enrofloxacin and/or its oxidation products.     

Effects of current density and electrode material on the dewaterability of the thickened activated sludge by electro‐flotation

BACKGROUND: Electro‐flotation (EF) could improve thickening and subsequent dewatering characteristics of activated sludge although the settling characteristics of the sludge were very poor. The objectives of this study were to evaluate the performance of EF in the thickening and dewatering of activated sludge and the effects of current density and electrode material on the dewaterability of the sludge. RESULTS: The specific resistance to filtration (SRF) of the sludges thickened by EF was much lower than that by gravity sedimentation. The SRF of the thickened sludge decreased exponentially with increase of gas generation rate of the EF system. Gas generation rate could be controlled by varying the current density of the electrode. Degassing of the microbubbles by moderate mixing of the thickened sludge layer deteriorated the dewaterability of the sludge. Therefore, it is obvious that the gas bubbles entrapped in the thickened sludge play a key role in the observed dewaterability improvement. The effect of electrode material on the thickening and dewatering efficiency was trivial compared with the effect of current density of the electrode. CONCLUSION: The EF system was quite promising as an alternative to gravity sedimentation for thickening of activated sludge and the dewaterability was also improved by microbubbles generated in the system. Copyright © 2009 Society of Chemical Industry     

Multi‐phase electro‐chemical catalytic oxidation of wastewater

The removal of organic pollutants from synthetic wash wastewater by a combined multi‐phase electro‐catalytic oxidation method was evaluated using porous graphite as anode and cathode, and CuO–Co₂O₃–PO₄^3? modified kaolin as catalyst. The synergic effect on COD removal was studied when integrating the electro‐chemical reactor with the effective modified kaolin in a single undivided cell; the results showed that higher COD removal efficiency was obtained than those obtained using the individual processes. Under optimal conditions of pH 3, 30 mA cm^?2 current density, very effective reduction of organic pollutants was achieved with this combined electro‐chemical method. High removal efficiency (90%) of the chemical oxygen demand (COD) was obtained in 60 min in the treatment of simulated wash wastewater (anionic surfactant, sodium dodecyl benzene sulfonate [DBS]). This method was also applied to treat wastewater form paper‐making and resulted in a COD reduction of 84%. Based on the investigation, a possible mechanism of this combined electro‐chemical process was proposed. The pollutants in wastewater could be decreased by the high reactive OH? that were produced via the decomposition of electro‐generated H₂O₂ activated by the synergic effect of electro‐field and catalyst. The results indicate that the multi‐phase catalytic electro‐chemical oxidation process is a promising technique for wastewater treatment. Copyright © 2006 Society of Chemical Industry     

A microbial fuel cell–electro‐oxidation system for coking wastewater treatment and bioelectricity generation

BACKGROUND: Coking wastewater is generated from coal coking, coal gas purification, and by‐product recovery processes. Increased interest is being focused on finding more sustainably effective and energy‐efficient methods for treating this wastewater. In this work, a system termed microbial fuel cell‐electro‐oxidation (MFC‐EO) was developed for simultaneous coking wastewater treatment and bioelectricity generation. RESULTS: Raw coking wastewater was first treated using MFCs. Power production, removal of total chemical oxygen demand (TCOD) and total nitrogen (TN) reached 538 ± 9 mW m^?2, 52 ± 1% and 50 ± 1%, respectively. Wastewater strength and phosphate addition were evaluated for the enhancement of power production and treatment efficiency. At the EO stage, the effect of current density and chloride concentration on pollutant abatement, current efficiency (CE_EO) and energy consumption (EC_EO) were investigated. The overall removal of TCOD and TN was 82 ± 1% and 68 ± 1%, respectively using the MFC‐EO process. CONCLUSIONS: A MFC‐EO process was developed for the first time for simultaneous bioelectricity generation and coking wastewater treatment. This study attempted to combine MFCs with a conventional EO process for coking wastewater treatment. Further strategies need to be investigated to optimize reactor configuration using low‐cost and highly efficient electrode materials. Copyright © 2009 Society of Chemical Industry