Abstract: Shewanella oneidensis MR-1 has been proved to be a potential bacterium to decolorize methyl orange (MO). Nevertheless, longer reaction time was needed to achieve higher decolorization efficiency. Thus, it's necessary to further improve the decolorization efficiency of azo dyes using S. oneidensis MR-1. The embedding of S. oneidensis MR-1 and nano-Fe₃O₄ with sodium alginate (SA) is an ideal mode for efficient decolorization of MO. Morphology, rheology and mechanical strength were studied to better understand the decolorization capacity and recycle of the beads. The MO decolorization efficiency with SA, SA/Fe₃O₄, SA/S. oneidensis MR-1 and SA/S. oneidensis MR-1/Fe₃O₄ beads was studied. Compared with the beads of SA/S. oneidensis MR-1, the decolorization efficiency with SA/S. oneidensis MR-1/Fe₃O₄ was improved. After three cycles, 77.83％ of decolorization capability could be recovered with beads of SA/S. oneidensis MR-1/Fe₃O₄ while only 53.19％ recovered with SA/S. oneidensis MR-1 at 1.75 h in cycle 4 under transverse condition, respectively. The addition of Fe₃O₄ not only improved the decolorization capacity of beads of SA/S. oneidensis MR-1/Fe₃O₄ but also increased the mechanical strength. This research would provide the feasibility for recycling of immobilized microbial with higher efficiency and longer lifetime during wastewater treatment.

Key words: nano-Fe₃O₄, embedding with sodium alginate, Shewanella oneidensis MR-1, azo dyes methyl orange