Kinetic modeling of electrochemical oxidation of phenol on boron-doped diamond anode in the presence of some inorganic species

Abstract

Phenolic wastewater from many industries contains inorganic species such as cyanide, sulfide, ammonium, thiocyanate, etc. Presence of these inorganic pollutants in phenolic wastewater could hinder the proper understanding of phenol oxidation kinetics when chemical oxygen demand (COD) decay data are used in the kinetic modeling, because these inorganic species exert oxygen demand as phenol. Unlike COD decay data, total organic carbon (TOC) decay data does not have any correlation with such inorganic species, and also available TOC measurements techniques are currently better in terms of automation, accuracy, and reliability compared with COD measurement techniques. In the present study, the kinetics of electrochemical oxidation of phenol on boron-doped diamond anodes in synthetic wastewater containing sulfide, cyanide, and ammonia species in single, binary, tertiary, and quaternary mix matrixes were modeled via employing current limiting modeling (CLM) using TOC in addition to traditional COD decay data. For all the different mix matrixes investigated, comparable trends describing the kinetics of electrochemical oxidation process were obtained for both the COD and the TOC decay models. Statistical diagnostics of the developed COD and TOC decay models parameters revealed that the operating regimes of the oxidation processes were accurately predicted to be limited by mass transfer. These results establish the suitability of using TOC decay for the CLM of phenol oxidation kinetics both in the presence and absence of the inorganic species. Based on these results in relation to the disparity between COD and TOC as parameters for evaluating phenol oxidation kinetics, it was concluded that TOC decay data are more appropriate compared with COD decay data for the CLM of kinetics of electrochemical oxidation of phenol in wastewater containing inorganic species that exert oxygen demand.