Inhibiting 1,3-dinitrobenzene formation in Fenton oxidation of nitrobenzene through a controllable reductive pretreatment with zero-valent iron

Abstract

Nitrobenzene (NB) oxidation through conventional Fenton process produces a considerable amount of highly toxic 1,3-dinitrobenzene (1,3-DNB) as a byproduct. Aiming at significantly decreasing 1,3-DNB production in Fenton process, we developed a novel system integrating a reductive pretreatment via zero-valent iron (ZVI) with Fenton process to degrade NB in aqueous solution and industrial wastewater. The NB reduction efficiency of ZVI pretreatment could be controlled by adjusting the initial ZVI concentration and/or the initial pH of NB solution in a completely stirred ZVI reactor. After partial NB reduction by ZVI pretreatment, the residual NB was oxidized by a subsequent Fenton process. Aniline and ferrous irons were generated in ZVI pretreatment, producing an inhibitory effect on the formation of 1,3-DNB in Fenton process. While conventional Fenton process attained the NB removal efficiency of 95.0% and brought the relative 1,3-DNB yield (the molar concentration of 1,3-DNB in relation to that of converted NB) of 5.0%, the integrated system with the NB reduction efficiency of 48.1% achieved a similarly high NB removal efficiency (93.0%), but its relative 1,3-DNB yield was only 0.4%. Applied to the full-scale treatment of NB-rich industrial wastewater, the ZVI-Fenton integrated system with the NB reduction efficiency of 50.0% and conventional Fenton process produced dinitrobenzene isomers at the total concentrations of 0.005 mM and 0.060 mM, respectively. Accordingly, the integrated system increased the biodegradability and decreased the acute toxicity of the wastewater significantly more than conventional Fenton process. Therefore, the novel ZVI-Fenton integrated process is effective in the degradation of NB wastewater.