An internal circulation iron–carbon micro-electrolysis reactor for aniline wastewater treatment: Parameter optimization, degradation pathways and mechanism

Aniline is a vital industrial raw material. However, highly–toxic aniline wastewater usually deteriorated effluent quality, posed a threat to human health and ecosystem safety. Therefore, this study reported a novel internal circulation iron–carbon micro-electrolysis (ICE) reactor to treat aniline wastewater. The effects of reaction time, pH, aeration rate and iron–carbon (Fe/C) ratio on the removal rate of aniline and the chemical oxygen demand were investigated using single-factor experiments. This process exhibited high aniline degradation performance of approximately 99.86% under optimal operating conditions (reaction time = 20 min, pH = 3, aeration rate = 0.5 m3·h−1, and Fe/C = 1:2). Based on the experimental results, the response surface method was applied to optimize the aniline removal rate. The Box–Behnken method was used to obtain the interaction effects of three main factors. The result showed that the reaction time had a dominant effect on the removal rate of aniline. The highest aniline removal rate was obtained at pH of 2, aeration rate of 0.5 m3·h−1 and reaction time of 30 min. Under optional experimental conditions, the aniline content of effluent was reduced to 3 mg·L–1 and the removal rate was as high as 98.24%, within the 95% confidence interval (97.84%–99.32%) of the predicted values. The solution was treated and the reaction intermediates were identified by high–performance liquid chromatography, ultraviolet–visible spectroscopy, Fourier–transform infrared spectroscopy, gas chromatography–mass spectrometry, and ion chromatography. The main intermediates were phenol, benzoquinone, and carboxylic acid. These were used to propose the potential mechanism of aniline degradation in the ICE reactor. The results obtained in this study provide optimized conditions for the treatment of industrial wastewater containing aniline and can strengthen the understanding of the degradation mechanism of iron–carbon micro-electrolysis.