Degradation of O-toluidine by fenton processes

Abstract

o-toluidine (OT) is an important aromatic amines that used in the dyestuffs industry and more recently in the rubber industry. OT can be found in several wastewaters and is associated with an increased incidence of bladder cancer. This study investigated the degradation and detoxification of OT by several Fenton processes. In the Design-Expert software, factorial design (24) approach was used for the selection of significant parameters after that the Box-Benhken response surface function was used for optimization of degradation conditions for OT and COD removals by electro-Fenton process. The amount of Fe2+ (0.2-1.0 mM) and H2O2 (1-5 mM), pH (2-4), and current (1-4 A) were selected as independent variables while OT and COD removal efficiency were considered as the response functions. The pH, Fe2+ and H2O2 concentrations were found to be the key parameters and; hence were used to find the optimum condition with constant current of 1 A. The model suggestion for the selected condition for OT oxidation, at pH 2, 1 mM of Fe2+, 4.85 mM of H2O2 and 1 A of constant current, would provide 91% and 41% removal for OT and COD, respectively. Experimental results revealed that 1 mM of OT could be removed completely within 90 and 60 minutes by electro-Fenton and photoelectro-Fenton processes, respectively. COD abatement by ordinary, electro- and photoelectro-Fenton processes were 36%, 50% and 52%, respectively. The OT oxidation was a two-step process; hence, characterized separately by using zero-order kinetics for the initial stage and first-order kinetics for the second stage. The initial rate constants for OT oxidation were 0.369, 0.384 and 0.389 mMmin-1 where as the second-stage, first-order rate constants were 0.0124, 0.0356 and 0.0572 min-1 for ordinary, electro- and photoelectro-Fenton processes, respectively. Electro- and photoelectro-Fenton processes could effectively detoxify the OT better than the ordinary Fenton, i.e., the BOD5:COD ratio increased from 0.125 of the ordinary Fenton to 0.289 and 0.357 for electro- and photoelectro-Fenton processes, respectively. Maleic and oxalic acids were identified as the intermediates of OT oxidation by hydroxyl radicals.