Synergic effect of ozonation and electrochemical methods on oxidation and toxicity reduction: Phenol degradation

The degradation of phenol was studied under three chemical environments, ozonation (O-3), electrooxidation (EO) and ozonation-electro-oxidation (O-3-EO) coupled process. The parent compound concentration was established by UV-Vis spectrophotometry while the by-products were identified by HPLC. This allowed proposing a mechanism of phenol oxidation during the coupled process. This coupled process was found to practically mineralize all phenol (TOC removal = 99.8%) under pH 7.0 +/- 0.5 and at a current density of 60 mA cm (2), 0.05 L min (1) flowrate, ozone concentration of 5 +/- 0.5 mg L (1). Furthermore, it was found that the coupled process is practically twice faster than the EO process alone to achieve a high degree of mineralization. In this sense, it was concluded that ozone alone only partially mineralizes the phenol molecule and mainly leads to the formation of aliphatic compounds. In addition, the toxicities of phenol and its degradation products were established by using a bioassay with lettuce seeds. It was concluded that, unlike ozonation, the coupled oxidation process not only mineralizes the organic molecule but also completely eliminates the toxicity of the treated phenolic solution. (C) 2016 Elsevier Ltd. All rights reserved.