Simultaneous formation of nanoscale zero-valent iron and degradation of nitrobenzene in wastewater in an impinging stream-rotating packed bed reactor

A novel process based on an impinging stream-rotating packed bed (IS-RPB) was proposed for preparing nanoscale zero-valent iron (NZVI) and degrading nitrobenzene (NB) simultaneously. The obtained NZVI particles were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy experiments (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The experimental results showed that the NB removal efficiency increased with the augment of liquid flow rate and initial reactant concentrations. The NZVI prepared with Fe²⁺ as an iron source had high reactive activity and its removal efficiency of NB could be maintained at a high level in acidic or a weakly basic condition (pH < 8). Compared with the traditionally mixing method, the IS-RPB could reduce the iron dosing amounts by 49.6% and the prepared NZVI could achieve 100% efficiency of the NB removal. Considering the operational cost and treatment efficiency, the optimal ratio between NaBH₄ and iron concentration could be in the range of 2.0–3.0. Through the strong micro-mixing intensification performance of IS-RPB, the reported approach has compensated for the shortcomings of the traditional nanoparticles production such as complicated procedures and the potential oxidation of Fe⁰. This study encourages further optimization and development of the high gravity system towards industrial production of NZVI and large-scale NB-containing wastewater treatment.