Although chromium ions exist in several oxidation states, Cr(III) and Cr(VI) predominate in the ambient environment. Chromium(III) is essential to humans and other animals due to its role in glucose and cholesterol metabolism, whereas Cr(VI) has many industrial applications and is very toxic. 1,2 Occupational exposure to chromium occurs from chromate processing, stainless-steel production, chrome plating and tanning industries. 3 Due to the severe toxicity of Cr(VI), a total chromium measurement cannot be used to determine the actual environmental impact. 4,5 Thus, the chemical speciation of chromium in environmental samples is necessary for accurate assessments of pollution levels.The methods cited in the literature for the determination of both Cr(VI) and Cr(III) include spectrophotometry, [6][7][8] fluorometry, 9,10 inductively coupled plasma, 11 atomic emission spectrometry, 12 atomic absorption spectrometry, 13,14 X-ray fluorescence spectrometry, 15 differential pulse polarography, 16 adsorptive stripping voltammetry, 17,18 and high-pressure liquid chromatography. 19 Many of these methods, however, involve several time-consuming manipulation and extraction steps, derivatization reactions and are liable to various interference, not applicable to colored and turbid solutions and require sophisticated instruments.Potentiometric sensors for the determination of Cr(VI) have been suggested as an alternative simple technique. These are based on the use of chromate complexes with bathophenanthroline, 20 quaternary ammonium ions, 21-25 quaternary phosphonium ions, 26,27 and crystal violet 28 as electroactive materials dispersed in polymeric membranes. Some of these sensors, are not applicable for determining chromium at concentration levels < 10 -3 or 10 -4 mol l -1 , display a non-Nernstian response, suffer from the interference by many cations and anions and require a long time for stable response. 20,21,27 The present paper describes the preparation and characterization of a novel potentiometric sensor for Cr(VI). This is based on the use of an ion-associate complex of rhodamine-B cation with the chromate anion in a poly(vinyl chloride) matrix membrane plasticized with o-nitrophenyloctyl ether. The proposed sensor has some significant advantages over many previously reported chromium sensors, 20,21 since it offers a lower detection limit (1 × 10 -6 mol l -1 ), covers a wider working concentration range (1 × 10 -1 -5 × 10 -6 mol l -1 ), displays a faster response time (10 -20 s) and exhibits a higher selectively in the presence of many common interfering ions. The sensor is satisfactory used for the accurate determination of Cr(III) and Cr(VI) ions in industrial wastewater, either singly or sequentially. Experimental ApparatusPotentiometric measurements were carried out at 25 ± 1˚C with an Orion pH/mV meter microprocessor Ionalyzer (Model 720). The developed rhodamine-B chromate PVC membrane The construction and performance characteristics of a novel chromate ion-selective membrane sensor are described and used fo...

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Electrocoagulation (EC) is one of the attractive methods for textile wastewater treatment because it is simple, economic and less sludge production technology. The performance of a batch EC process was studied for decolorization of synthetic colored water containing different concentrations of dye using iron electrodes. The effect of various operational conditions such as applied voltage, initial pH and processing time on color removal efficiency and energy consumption was studied in order to identify the optimum operational conditions. It was noticed that the removal efficiency of dye stabilized after 20 to 25 min. of operation using applied voltage between 10 to 20 V. The results indicate that the dye was removed with high efficiency using applied voltage of 10 V and initial pH ranged from 6 to 9 for a solution with initial dye concentration of 250 mg/l. Color removal efficiency is inversely related to solution initial dye concentration. However, the energy