Electrochemical reactivation of granular activated carbon.

Abstract

The main objectives of this dissertation were to refine electrochemical GAC reactivation technology, a promising alternative technology, and to investigate its technical feasibility. The specific objectives of the study were: (1) to evaluate alternative reactor designs; (2) to assess the effect of contaminant and GAC types on the regeneration efficiency; (3) to study the electrolyte post-treatment; and (4) to investigate reactivation mechanisms and model them. To achieve these objectives many interrelated topics were investigated using phenol, 2-nitrophenol (2NP) and naturally occurring background organic matter (NOM) as adsorbates and Filtrasorb 400 (F-400), Westvaco Carbon (WV-B), Darco Norit, and Filtrasorb 300 (F-300) as adsorbents. The impact of reactor operation conditions (reactivation time, current density, pH) on the reactivation efficiency showed that the reactivation efficiency (RE%) could be increased to a maximum by increasing the current and/or time. It was concluded that electrochemical reactivation of GAC is contaminant-type dependent. The reactivation efficiencies of F-400 loaded with 2NP and phenol at different reactivation currents and times showed similar patterns. A comparison of the percent reactivation of GACs showed that F-400 and WV-B performed essentially the same for the tested conditions. Total destruction of desorbed contaminants and their by-products were possible. Desorbed phenol and 2NP from loaded GAC react to form a number of reaction by-products that are eventually oxidized to CO2 and H 2O. The main mechanism responsible for electrochemical reactivation is high-pH induced desorption at the cathode. It accounts for approximately 50--60% of the total reactivation of a single layer of GAC. It is recommended that the GAC electrochemical reactivation should be a three step process. First, the GAC is reactivated with a relatively low current to minimize potential alterations of the GAC surface. Second, the GAC is drained and rinsed with a buffered solution. Finally, the electrolyte is treated electrochemically for an extended time at a much higher current (and possibly a different electrode) to reduce the electrolyte's TOC so that it may be reused or discharged. (Abstract shortened by UMI.)