Biosorption of azo dyes by raspberry-like Fe3O4@yeast magnetic microspheres and their efficient regeneration using heterogeneous Fenton-like catalytic processes over an up-flow packed reactor

Raspberry-like Fe3O4@yeast composite microspheres, whose properties integrate the biosorption features of yeast cells with the excellent magnetic and catalytic properties of Fe3O4 nanoparticles were synthesized by a simple electrostatic-interaction-driven self-assembly heterocoagulation. They were successfully applied in an up-flow packed column for the removal of the model water contaminant methylene blue dye (MB) by consecutive bioadsorption-heterogeneous Fenton oxidation cycles. The as-synthesized Fe3O4@yeast composites were characterized by field emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS), powder X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. The adsorption process was controlled by the electrostatic interactions between the adsorbent and contaminant. The adsorbent is suitable for the adsorption of positively charged compounds at mildly acidic pH, neutral and alkaline pH, with the highest performance observed at alkaline pH. The experimental breakthrough curves measured at different influent MB concentration, flow rate, bed height and pH were modeled by the Yoon-Nelson model. The in-situ regeneration of the contaminant-loaded Fe3O4@yeast microspheres and their reuse in multiple cycles was demonstrated by triggering the heterogeneous Fenton-like reaction catalyzed by the supported magnetite. The raspberry-like Fe3O4@yeast magnetic microsphere should be a promising and practical adsorbent for removal and destruction of positively charged organic compounds in wastewater.