Application of low-cost adsorbents for dye removal – A review

As the environment preservation gradually becomes a matter of major social concern and more strict legislation is being imposed on effluent discharge, more effective processes are required to deal with non-readily biodegradable and toxic pollutants. Synthetic organic dyes in industrial effluents cannot be destroyed in conventional wastewater treatment and consequently, an urgent challenge is the development of new environmentally benign technologies able to mineralize completely these non-biodegradable compounds. This review aims to increase the knowledge on the electrochemical methods used at lab and pilot plant scale to decontaminate synthetic and real effluents containing dyes, considering the period from 2009 to 2013, as an update of our previous review up to 2008. Fundamentals and main applications of electrochemical advanced oxidation processes and the other electrochemical approaches are described. Typical methods such as electrocoagulation, electrochemical reduction, electrochemical oxidation and indirect electro-oxidation with active chlorine species are discussed. Recent advances on electrocatalysis related to the nature of anode material to generate strong heterogeneous OH as mediated oxidant of dyes in electrochemical oxidation are extensively examined. The fast destruction of dyestuffs mediated with electrogenerated active chlorine is analyzed. Electro-Fenton and photo-assisted electrochemical methods like photoelectrocatalysis and photoelectro-Fenton, which destroy dyes by heterogeneous OH and/or homogeneous OH produced in the solution bulk, are described. Current advantages of the exposition of effluents to sunlight in the emerging photo-assisted procedures of solar photoelectrocatalysis and solar photoelectro-Fenton are detailed. The characteristics of novel combined methods involving photocatalysis, adsorption, nanofiltration, microwaves and ultrasounds among others and the use of microbial fuel cells are finally discussed.

Decontamination of wastewaters containing synthetic organic dyes by electrochemical methods. An updated review

The problem of textile dye pollution has been addressed by various methods, mainly physical, chemical, biological, and acoustical. These methods mainly separate and/or remove the dye present in water. Recently, advanced oxidation processes (AOP) have been focused for removal of dye from waste water due to their advantages such as ecofriendly, economic and capable to degrade many dyes or organic pollutant present in water. Photocatalysis is one of the advance oxidation processes, mainly carried out under irradiation of light and suitable photocatalytic materials. The photocatalytic activity of the photocatalytic materials mainly depends on the band gap, surface area, and generation of electron–hole pair for degradation dyes present in water. It has been observed that the surface area plays a major role in photocatalytic degradation of dyes, by providing higher surface area, which leads to the higher adsorption of dye molecule on the surface of photocatalyst and enhances the photocatalytic activity. This present review discusses the synergic effect of adsorption of dyes on the photocatalytic efficiency of various nanostructured high surface area photocatalysts. In addition, it also provides the properties of the water polluting dyes, their mechanism and various photocatalytic materials; and their morphology used for the dye degradation under irradiation of light along with the future prospects of highly adsorptive photocatalytic material and their application in photocatalytic removal of dye from waste water.

Recent advances based on the synergetic effect of adsorption for removal of dyes from waste water using photocatalytic process

The electrocatalytic properties of Ti–Ru–Sn ternary oxide, platinum, lead dioxide and boron-doped diamond anodes for the oxidation of methyl red have been compared by potentiodynamic measurements and bulk electrolysis. The results of the cyclic voltammetries have shown that in the potential region of supporting electrolyte stability polymeric materials, which result in electrode deactivation, are formed on the electrode surfaces. While Ti–Ru–Sn ternary oxide and platinum cannot restore their initial activity by polarization, lead dioxide and boron-doped diamond anodes can be reactivated by electrolysis in the potential region of electrolyte decomposition due to the electrogeneration of hydroxyl radicals. The bulk electrolysis showed that the complete COD and colour removal were only achieved using lead dioxide and boron-doped diamond while Ti–Ru–Sn ternary oxide and platinum only permitted a partial oxidation of methyl red.

Electrocatalytic materials for the electrochemical oxidation of synthetic dyes

Ultrasound as a basic and auxiliary process for dye remediation: A review

Electrochemical methods are being used increasingly as an alternative treatment process for the remediation of textile wastewaters. This study focused mainly on the colour removal and chemical oxygen demand (COD) reduction of vat textile dye (CI Vat Blue 1: indigo) from its aqueous solution by electrochemical oxidation. The process was carried out in a batch-type divided electrolytic cell under constant potential using a Pt cage as anode and Pt foil as cathode. Operating variables such as supporting electrolyte, pH, ultrasonification and treatment time were investigated to probe their effects on the efficiency of the electrochemical treatment. Colour removal was estimated by monitoring the disappearance of the absorbance peak at 681.5 nm. It was found that in acidic conditions the electrolysis was more efficient. At pH 1, an NaCl concentration of 0.24 mol dm−3, a dyeing solution concentration of 0.1% (w/v) and a period of 90 min of electrolysis, there was almost 100% colour removal and 60% reduction in COD. Voltammetric and IR investigations demonstrated that partial degradation of dye was achieved. The experimental results indicate that this electrochemical method could effectively be used as a pretreatment stage before conventional treatment. Copyright © 2005 Society of Chemical Industry

Electrochemical oxidation of textile dye indigo

Electrochemical methods are being used increasingly as an alternative treatment process for the remediation of textile wastewaters. This study focused mainly on the color removal and chemical oxygen demand (COD) reduction of a vat textile dye (CI Vat Blue 1: indigo) from its most polluted actual effluent by electrochemical oxidation. The process was carried out in a batch-type divided electrolytic cell under constant potential using a Pt cage as anode and Pt foil as cathode. It was shown that complete colour removal was achieved in a very short time (16 mins) at pH 2 by applying a constant electrolysis voltage between the platinum electrodes. The repeated experiments indicated that extending the treatment to 40 minutes caused a considerable percentage of COD reduction (46%), occurring mainly due to indigo oxidation. It is concluded that this electrochemical method can be used effectively as a pre-treatment alternative for reducing COD and colour in industrial textile effluents before conventional treatment.

Dogan Dogan

Papers

Electrochemical oxidation of textile dye indigo

Electrochemical Treatment of Actual Textile Indigo Dye Effluent