Biological treatment of refinery spent caustics under halo-alkaline conditions

► The biological treatment of refinery spent caustics in a continuous system was studied. ► Soda lake bacteria that enable operating under halo-alkaline condition were used. ► Thioalkalivibrio species completely oxidized sulfide into sulfate. ► Benzene removal efficiencies of 93% were obtained. ► Several bacteria were identified which might have played a role in benzene removal.