Oxidation of phenol and the adsorption of breakdown products using a graphite adsorbent with electrochemical regeneration

The process of adsorption using an unexpanded graphite intercalation compound (GIC) adsorbent with electrochemical regeneration has been investigated for the removal and oxidation of phenol in wastewater. During electrochemical regeneration of the adsorbent, the formation of intermediate oxidation products is critical because these could affect the toxicity of the treated effluent. The present study is concerned with the formation of breakdown products released in the treated water during electrochemical regeneration of GIC adsorbents, using phenol as a model pollutant. Batch studies were carried out on a small laboratory scale electrochemical cell and flow-through treatment studies were carried out in a pilot scale circulating fluidised bed reactor. In batch studies, the main breakdown products formed were benzoquinone and catechol, with small amounts of hydroquinone. It was found that hydroquinone was oxidized to benzoquinone in the presence of the GIC adsorbent. In the continuous process, studied in a batch recycle mode, benzoquinone and maleic acid were the main breakdown products detected. This investigation has revealed that there are similarities in the breakdown products formed during electrochemical regeneration of GIC adsorbents with those observed during the indirect electrochemical oxidation of phenol in an electrochemical cell. However much lower concentrations of breakdown products can be achieved with the process of adsorption/electrochemical regeneration than with indirect oxidation.