The structural modification of external surface of NaY was investigated in order to enhance efficient biosorption systems
consisting of a bacterial biofilm, Arthrobacter viscosus, supported on that zeolite, for removing hexavalent chromium from
aqueous solutions. The supported bacterial biofilm reduces Cr(VI) to Cr(III) and this cation is then retained in the zeolite by ion
exchange. NaY zeolite was modified by alkali-treatments using NaOH 2.0 M, with two different contact periods of time between
the zeolite and the alkaline solutions, resulting in NaYA and in NaYB. The biosorbents supported on the modified NaY zeolite
were tested in solutions with low concentration of chromium. The results showed that the modification of external surface of NaY
zeolite allows an efficient Cr removal, and the maximum removal efficiency was observed for NaYA sample that was submitted to
a smoother chemical treatment.The authors acknowledge to Dr. A.S. Azevedo for collecting the powder diffraction data and Dr. C Ribeiro, from Departamento de Ciencias da Terra of Universidade do Minho, for chemical analyses. This work was supported by Fundacao para a Ciencia e Tecnologia (FCT-Portugal), under program POCTI-SFA-3-686. H.F. and B.S. gratefully acknowledge FCT-Portugal for the PhD grants
