Toxic dye removal by thermally modified lignocellulosic waste in a threephase air-lift reactor: Kinetic insights

Abstract

This paper investigates the influence of the air flow rate in a three-phase air-lift reactor on the sorption of toxic dye, Brilliant green, onto a promising and efficient sorbent, sour cherry stone biochar. In order to gain a comprehensive insight into the sorbent/sorption behaviour, sour cherry stone biochar was characterized by Fourier transform infrared spectroscopy with attenuated total reflection, pH of the suspension, point of zero charge, scanning electron microscopy with energy-dispersive X-ray spectroscopy and X-ray diffraction. The experiments were performed in an air-lift reactor using airflows of 2.50 and 5.55 dm3 h-1. The experimental data of sorption kinetics experiments were fitted by non-linear form of pseudo-first and, pseudo-second models as well as the Weber-Morris model based on intraparticle diffusion. The overall sorption rate was found to be limited by the Brilliant Green mass transport rate to the sorbent at a lower airflow and thus mixing intensity, while it was kinetically controlled at a higher rate following the pseudo-second order kinetic model. Furthermore, sorption at lower air flow was delayed by mass transfer resistance through the liquid boundary layer surrounding sorbent particles. Presented results clearly indicate that airflow intensity plays a significant role in the overall sorption kinetics and support possible application of the applied biochar for efficient Brilliant Green sorption.