Selective electrochemical degradation of 4-chlorophenol at a Ti/RuO2-IrO2 anode in chloride rich wastewater

Abstract

The electrochemical degradation of 4-chlorophenol (4-CP) in the presence of chlorides by the use of a Ti/RuO2-IrO2 anode was investigated under different operational parameters such as applied current density (J) and chloride concentration ([NaCl]). By performing a design of experiments, a model for the removal of 4-chlorophenol under these circumstances was obtained. To investigate matrix effects for this oxidation process, the influence of various biodegradable substrates (such as glucose, a complex synthetic wastewater and a pilot-scale UASB effluent) on the degradation profile of 4-chlorophenol was investigated. The 4-CP degradation was hardly affected by the presence of glucose, which was itself only limitedly degraded (max. 5%). This indicates a selective degradation for the phenolic compound, independent of the values of the operational parameters. The presence of a more complex synthetic wastewater, however, resulted in a decrease in 4-CP degradation rate up to a factor 7. The biodegradable substrates are in this case also degraded by the electrochemical treatment. In the case where 4-CP was added to a pilot-scale UASB effluent and this wastewater was afterwards treated, the degradation rate of 4-CP only decreased by a factor 2. After 2 h of treatment, a full mineralization was obtained in this experiment. The latter observation suggests the suitability of the technique as an effluent polishing step after a biological treatment or as a treatment in recycle over a biological reactor.