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As a support material,zeolite can be used to promote the granulation process due to its high settable property and the ability to retain biomass on its surface.The present paper reports on the influence of zeolite addition on the hydrodynamic behavior of an expanded granular sludge bed reactor (EGSB).Different models were applied to fit the flow patt and to compare EGSB hydrodynamic performance with and without the addition of zeolite.The experimental data fit the tanks in a series model for zeolite bed height of 5 cm and upflow velocity of 6 m/hr.Higher axial dispersion degree (D/uL) was obtained at lower heights of zeolite.The real hydraulic retention time (HRTr) was increased with both increased zeolite bed height and increased upflow velocity.The short-circuit results for 5 cm of zeolite bed and 6,8 and 10 m/hr upflow velocity were 0.3,0.24 and 0.19 respectively,demonstrating the feasibility of using zeolite for a proper hydrodynamic environment to operate the EGSB reactor.The presence of zeolite resulted in the higher percentage values of dead zones,ranging from 12％ to 24％.Zeolite addition exerted a positive effect on the hydrodynamics patt for this technology being advantageous for the anaerobic process because of its possible contribution to better biofilm agglomeration,granule formation and substrate-microorganism contact.