The presence of chloride ions can facilitate the COD removal efficiency due to the involvement of active chlorine species in the electro-oxidation process, but few attentions have been paid to the negative effect of the electro-generated oxychlorides on electro-oxidation performance. In this study, the effects of oxychlorides were investigated as functions of current density and phenol concentration using DSA anodes in terms of the evaluation of the COD removal performance and the biological toxicity. The results show that oxychlorides formed in the electro-oxidation system could result in the over-evaluation of the COD removal performance. Increasing current density (15-50 mA cm-2) aggravated the over-evaluation of COD removal (4%-18%), owing to the enhancement in the electrochemical generation of oxychlorides. The increase of phenol concentration inhibited the production of oxychlorides, but the effect of oxychlorides on COD values at phenol concentration of 200 mg L-1 (82 mg L-1) was higher than that at 100 mg L-1 (51 mg L-1). The ClO3- was predominantly responsible for over-evaluation of the COD removal. In addition, bioassays with chlorella indicated that the electro-generated oxychlorides significantly increased the biological toxicity of the treated Cl--containing wastewater. This work provides new guidance for the correct evaluation of COD treatment performance and highlight the importance of minimizing toxic inorganic chlorinated byproducts during electro-oxidation of Cl--containing wastewater.
Keywords: Biological toxicity; COD removal Performance; Cl(−)-containing wastewater; DSA anodes; Electro-oxidation; Oxychlorides.
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