A three-phase fluidized reactor with biocatalyst particles (immobilized bacteria Pseudomomas putida on polyvinyl alcohol matrix) has been employed for mercury removal from aqueous solution. The effective diffusivity D-eff of HgCl2 in PVA hydrogel biocatalyst particle and the volumetric mass transfer coefficients for liquid-solid film k(s)a(s) as well as for gas-liquid film k(L)a(L) have been determined. Transport resistance evaluation revealed that in spite of significant intraparticle diffusion limitation (effectiveness factor in the range of 0.01), the both resistances of mass transfer around the catalyst particle and inside the catalyst pores should be taken into account.