Cd(II) removal from aqueous solution by immobilised waste brewery yeast in fixed-bed and airlift reactors

A fixed-bed reactor (FBR) and an airlift reactor (AR) were compared as to their effectiveness for the bioremoval of cadmium from dilute aqueous solutions (1 mM in Cd(II)), using, as biosorbent, a strain of Saccharomyces cerevisiae collected from the waste of a brewing industry and immobilised by entrapment in polyurethane foam. A liquid recirculation flow rate of 0.027 dm3.dm−3.min−1, in the FBR, and an injection of air at a flow rate of 0.1 v.v.m., in the AR, both to promote turbulent flow around the biosorbent, were required to maximize Cd(II) removal yields. A pH increase associated with a release of intracellular compounds to the aqueous solution were apparently involved in this effect. The Cd(II) bioremoval capacity attained values of 7.06 mmol Cd.gbiomass−1 and 1.29 mmol Cd.dm−3reactor, in the AR and 1.90 mmol Cd.gbiomass−1 and 6.08 mmol Cd.dm−3reactor in the recirculated FBR.