Time Varying Toxicity of Effluents from the Electrochemical Oxidation of Phenol

The Microtox® test was used to quantify the impact of holding time on toxicity of compounds formed in the electrochemical treatment of phenol. Phenol was treated in the presence of a sodium chloride (NaCl) or sodium sulfate (Na2SO4) electrolyte using either a boron-doped diamond anode/stainless steel cathode, or graphite anode/SS cathode. The intermediates from both oxidative and chlorine-substitution pathways were measured concurrently using HPLC immediately after the application of constant current was stopped and at time intervals up to 18 days. The toxicity of the samples were measured using the Microtox® basic test protocol at each of these time points as well. Chlorine-substitution pathway effluents, consisting mainly of chlorinated phenols, exhibited little toxicity change over the 18 day storage period considered in the study. Oxidative pathway effluents, however, consisting of quinone products, most notably the highly toxic benzoquinone, exhibited significant toxicity loss over the time period of the study. Over a period of 18 days, a 0.092 mM solution of benzoquinone alone lost over 92% of its initial toxicity. Over a 13 day period, an electrochemical effluent from conditions conducive to the oxidative pathway and benzoquinone formation also lost over 96% of its initial toxicity.