Assessment of the functionality of a pilot-scale reactor and its potential for electrochemical degradation of calmagite, a sulfonated azo-dye

• Published in: Chemosphere (Oxford) Vol. 73; no. 5; pp. 837 - 843
• Main Authors: Agarwal, Shirish, Cluxton, Phillip, Kemper, Mark, Dionysiou, Dionysios D., Al-Abed, Souhail R.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-10-2008; Elsevier
• Subjects: Applied sciences; Azo Compounds - chemistry; Bioreactors; Coloring Agents - chemistry; Decolorization; Degradation pathway; Electrochemistry; Environmental Restoration and Remediation; ESI–MS; Exact sciences and technology; Granular graphite; Industrial wastewaters; Kinetics; Pollution; Spectrometry, Mass, Electrospray Ionization; UV spectra; Waste Disposal, Fluid - methods; Wastewaters; Water Purification - methods; Water treatment and pollution; Decolorization; Granular graphite; Degradation pathway; ESI–MS; UV spectra; Reaction intermediate; Organic dye; ESI-MS; Operating conditions; Sulfonate; Electrolysis; Industrial waste water; Azo dye; Model compound; Reaction mechanism; Physicochemical purification; Waste water purification; Performance; Electrochemical reaction; Degradation product; Organic compounds
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2008.06.050

Electrochemical degradation (ECD) is a promising technology for
in situ remediation of diversely contaminated environmental matrices by application of a low level electric potential gradient. This investigation, prompted by successful bench-scale ECD of trichloroethylene, involved development, parametric characterization and evaluation of a pilot-scale electrochemical reactor for degradation of calmagite, a sulfonated
azo-dye used as a model contaminant. The reactor has two chambers filled with granulated graphite for electrodes. The system has electrical potential, current, conductivity, pH, temperature, water-level and flow sensors for automated monitoring. The reactor supports outdoor and fail-safe venting, argon purging, temperature regulation and auto-shutdown for safety. Treatment involves recirculating the contaminated solution through the electrode beds at small flow velocities mimicking low fluid-flux in groundwater and submarine sediments. The first phase of the investigation involved testing of the reactor components, its parametric probes and the automated data acquisition system for performance as designed. The results showed hydraulic stability, consistent pH behavior, marginal temperature rise (<5
°C) and overall safe and predictable performance under diverse conditions. Near complete removal of calmagite was seen at 3–10
V of applied voltage in 8–10
h. The effects of voltage and strength of electrolyte on degradation kinetics have been presented. Further, it was observed from the absorption spectra that as calmagite degrades over time, new peaks appear. These peaks were associated with degradation products identified using electrospray ionization mass spectrometry. A reaction mechanism for ECD of calmagite has also been proposed.