Batch and continuous flow anodic oxidation of 2,4-dinitrophenol: Modeling, degradation pathway and toxicity

•Electrochemical oxidation of 2,4-DNP was performed using a novel MS-PbO2 anode.•Application of RSM for the first time in electrochemical degradation of 2,4-DNP•High current efficiency and low energy consumption for the degradation in flow reactor•Identification of degradation intermediates using HPLC, MS and ion chromatography•Toxicity study of 2,4-DNP and intermediates at different stages of degradation

Being a priority pollutant, complete degradation of 2,4-dinitrophenol (2,4-DNP) is recommended. This study attempts the electrochemical oxidation of 2,4-DNP using a novel PbO2 electrode. Multiparameter optimization is studied to elucidate the interactive role of parameters on the degradation. The critical operational parameters and its range of operation were identified using uniparameter studies in a batch reactor as NaCl concentration (0.5–1.5 g L− 1), current density (0.96–1.91 mA cm− 2) and pH (4–8). The operational range was further optimized using response surface methodology as NaCl concentration of 0.08–1.4 g L− 1 at pH of 4.5 to 8 and a current density of 1.2 to 1.79 mA cm− 2. Maximum COD removal efficiency was predicted as 94.2% at a pH of 6.59, NaCl concentration of 1.12 g L− 1 and current density of 1.44 mA cm− 2, which upon experimentation was obtained as 93.9%. Complete degradation of the contaminant was obtained within 150 min in a continuous flow reactor at a flow rate of 500 mL h− 1 with NaCl concentration of 0.5 g L− 1 and current density of 1.44 mA cm− 2. Intermediates of the reaction were identified as benzoquinone, hydroquinone, catechol, 4-nitrocatechol and 2-nitrobenzoquinone using high performance liquid chromatography (HPLC) and mass spectroscopy (MS) analysis. Ion chromatography analysis showed nitrate removal to be one of the foremost steps in the degradation. Cytotoxicity of the intermediates was found to be lesser than that of 2,4-DNP. The results show feasibility for field application of the tested method for the degradation of 2,4-DNP.

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