Sequential use of a continuous-flow electrocoagulation reactor and a (photo)electro-Fenton recirculation system for the treatment of Acid Brown 14 diazo dye.

The decolorization and TOC removal of solutions of Acid Brown 14 (AB14) diazo dye containing 50 mg L-1 of total organic carbon (TOC) have been first studied in a continuous-flow electrocoagulation (EC) reactor of 3 L capacity with Fe electrodes of ∼110 cm2 area each. Total loss of color with poor TOC removal was found in chloride, sulfate, and/or hydrogen carbonate matrices after 18 min of this treatment. The best performance was found using 5 anodes and 4 cathodes of Fe at 13.70 A and low liquid flow rate of 10 L h-1, in aerated 39.6 mM NaCl medium within a pH range of 4.0-10.0. The effluent obtained from EC was further treated by electro-Fenton (EF) using a 2.5 L pre-pilot flow plant, which was equipped with a filter-press cell comprising a Pt anode and an air-diffusion cathode for H2O2 electrogeneration. Operating with 0.10-1.0 mM Fe2+ as catalyst at pH 3.0 and 50 mA cm-2, a similar TOC removal of 68 % was found as maximal in chloride and sulfate media using the sequential EC-EF process. The EC-treated solutions were also treated by photoelectro-Fenton (PEF) employing a photoreactor with a 125 W UVA lamp. The sequential EC-PEF process yielded a much higher TOC reduction, close to 90 % and 97 % in chloride and sulfate media, respectively, due to the rapid photolysis of the final Fe(III)-carboxylate complexes. The formation of recalcitrant chloroderivatives from generated active chlorine limited the mineralization in the chloride matrix. For practical applications of this two-step technology, the high energy consumption of the UVA lamp in PEF could be reduced by using free sunlight.

Tetracycline removal from aqueous solution by electrooxidation using ruthenium-coated graphite anode.

This paper reports the electrochemical oxidation treatment of 80 mL of acidic aqueous solutions with 0.2 mM of the drug tetracycline in 25 mM Na2SO4 using a lab-scale electrochemical cell. The performance of tetracycline removal with Ru-coated graphite by the chemical bath deposition (CBD) and raw graphite anode has been demonstrated. The effects of operating parameters were tested such as pH, applied current, supporting electrolyte concentration, and initial tetracycline concentration. The best tetracycline degradation was obtained with Ru-coated graphite anode due to its higher oxidation power, which allowed the complete degradation of refractory compounds. The modified surface structure of the Ru-coated graphite anode was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy-dispersive X-ray (EDX). The EO process with Ru-coated graphite anode allowed 93.8% tetracycline abatement after 100 min of electrolysis at an applied current of 100 mA. In all cases, tetracycline decay obeyed pseudo-first-order kinetics. The tetracycline removal performance of graphite electrodes with nano coating on graphite has offered a performing alternative. A Comparative study revealed that electrolysis with Ru-coated graphite acted as a better electrode material than raw graphite for the catalytic reaction.

A comprehensive review on green perspectives of electrocoagulation integrated with advanced processes for effective pollutants removal from water environment.

The rapidly expanding global energy demand is forcing a release of regulated pollutants into water that is threatening human health. Among various wastewater remediating processes, electrocoagulation (EC) has scored a monumental success over conventional processes because it combines coagulation, sedimentation, floatation and electrochemical oxidation processes that can effectively decimate numerous stubborn pollutants. The EC processes have gained some attention through various academic and industrial publications, however critical evaluation of EC processes, choices of EC processes for various pollutants, process parameters, mechanisms, commercial EC technologies and performance enhancement via other degradation processes (DPs) integration have not been comprehensively covered to date. Therefore, the major objective of this paper is to provide a comprehensive review of 20 years of literature covering EC fundamentals, key process factors for a reactor design, process implementation, current challenges and performance enhancement by coupling EC with pivotal pollutant DPs including, electro/photo-Fenton (E/P-F), photocatalysis, sono-chemical treatment, ozonation, indirect electrochemical/advanced oxidation (AO), and biosorption that have substantially reduced metals, pathogens, toxic compound BOD, COD, colors in wastewater. The results suggest that the optimum treatment time, current density, pulse frequency, shaking speed and spaced electrode improve the pollutants removal efficiency. An elegant process design can prevent electrode passivation which is a critical limitation of EC technology. EC coupling (up or downstream) with other DPs has resulted in the removal of organic pollutants and heavy metals with a 20% improved efficiency by EC-EF, removal of 85.5% suspended solid, 76.2% turbidity, 88.9% BOD, 79.7% COD and 93% color by EC-electroflotation, 100% decolorization by EC-electrochemical-AO, reduction of 78% COD, 81% BOD, 97% color by EC-ozonation and removal of 94% ammonia, 94% BOD, 95% turbidity, >98% phosphorus by aerated EC and peroxicoagulation. The major wastewater purification achievements, future potential and challenges are described to model the future EC integrated systems.

Removal of salicylic acid by electrochemical processes using stainless steel and platinum anodes.

Salicylic acid is an important pharmaceutic and widely used in plant hormones and personal care products. Peroxicoagulation (PC) method has recently been employed in treatment of various pollutants. In general, carbon-based cathode materials such as graphite and carbon fiber are used for in situ H2O2 production and stainless steel (SS316-L) anode for low iron production in PC studies as an efficient system modification. This study was conducted to investigate salicylic acid removal efficiency of electrochemical processes. Stainless steel was used as anode in this study. It was believed that the oxidation effect of stainless steel could be responsible for partial removal of salicylic acid. In this study, stainless steel anode and graphite or carbon fiber cathodes were employed in PC treatments for removing salicylic acid from aqueous solution, and some model trials were also made to investigate the in-situ Fe2+ and H2O2 production performance. Present findings revealed a total organic carbon (TOC) removal of 30.5% and salicylic acid removal of 69.5% at optimized conditions. The EF system modification used in the study can be proposed as an easy, low-cost and effective treatment alternative for treatment of pharmaceutical industry wastes such as salicylic acid.

Agricultural waste materials for adsorptive removal of phenols, chromium (VI) and cadmium (II) from wastewater: A review.

Management of basic natural resources and the spent industrial and domestic streams to provide a sustainable safe environment for healthy living is a magnum challenge to scientists and environmentalists. The present remedial approach to the wastewater focuses on recovering pure water for reuse and converting the contaminants into a solid matrix for permanent land disposal. However, the ground water aquifers, over a long period slowly leach the contaminants consequently polluting the ground water. Synthetic adsorbents, mainly consisting of polymeric resins, chelating agents, etc. are efficient and have high specificity, but ultimate disposal is a challenge as most of these materials are non-biodegradable. In this context, it is felt appropriate to review the utility of adsorbents based on natural green materials such as agricultural waste and restricted to few model contaminants: phenols, and heavy metals chromium(VI), and cadmium(II) in view of the vast amount of literature available. The article discusses the features of the agricultural waste material-based adsorbents including the mechanism. It is inferred that agricultural waste materials are some of the common renewable sources available across the globe and can be used as sustainable adsorbents. A discussion on challenges for industrial scale implementation and integration with advanced technologies like magnetic-based approaches and nanotechnology to improve the removal efficiency is included for future prospects.

Removal of disperse and reactive dyes from aqueous solutions using ultrasound-assisted electrocoagulation.

This study investigates the effectivenesses of electrocoagulation, ultrasound, and ultrasound-assisted electrocoagulation processes for the removal of color and chemical oxygen demand (COD) from aqueous dye solutions. The coupling of electrocoagulation processes with ultrasound has been found useful for water and wastewater treatment in recent years. These experimental results demonstrate that ultrasound-assisted electrocoagulation processes provide greater color and COD removal than ultrasound or electrocoagulation processes alone. The optimum conditions for the combined process were found to be Fe-Fe-SS-SS/Al-Al-SS-SS (electrode connection type) in the monopolar electrode connection mode; 75 and 50 A m-2 (current density) for RR241 and DB 60, respectively, at a fixed frequency of 40 kHz; and an ultrasound power of 180 W in a 1 L aqueous solution. Under these optimum conditions, the color and COD removal efficiencies for an aqueous solution of 100 mg L-1 reached 99-99.9% and 100 - 100% for RR241 and DB 60, respectively. Complete removal was achieved for both COD and color by employing a combination of ultrasound-assisted electrocoagulation (US + EC) with only 4 min of electrolysis, while the traditional EC treatment achieved removal of approximately 87% of COD and 92% color for both dyes using the MP-P connection mode for 5 min. Conversely, ultrasound power alone removed approximately 34-60% of color and 30-36% of COD for RR241 and DB 60, respectively. Compared with the traditional EC treatment, the combination of ultrasound irradiation and electrocoagulation treatment significantly reduced electrode passivation and increased the removal of pollutants in shorter operation times.