Fe3O4 poly (styrene-glycidyl methacrylate) magnetic porous microspheres (MPPMs) were introduced to immobilize Klebsiella sp. FD-3, an iron-reducing bacterium applied to reduce Fe(III) EDTA. The effects of potential inhibitors (S2-, SO32- NO3- NO2- and Fe(II) EDTA-NO) on Fe(III) EDTA reduction were investigated. S2- reacted with Fe(III) EDTA as an electron-shuttling compound and enhanced the reduction. But Fe(III) EDTA reduction was inhibited by SO32- and Fe(II) EDTA-NO due to their toxic to microorganisms. Low concentrations of NO3- and NO2- accelerated Fe(III) EDTA reduction, but high concentrations inhibited the reduction, whether by free or immobilized FD-3. The immobilized FD-3 performed better than freely-suspended style. The substrate mass transfer and diffusion kinetics in the porous microspheres were calculated. The value of Thiele modulus and effectiveness factors showed that the intraparticle diffusion was fairly small and neglected in this carrier. Fe(III) EDTA reduction fitted first-order model at low Fe(III) EDTA concentration, and changed to zero-order model at high concentrations. (C) 2014 Elsevier Ltd. All rights reserved.