The study using SRBs showed that SRB cells could achieve up to 68% removal of strontium from the medium (Ngwenya and Chirwa, 2011). Most of the solid phase Sr2+ species were easily desorbed from biomass using MgCl2 (Fig. 15.8). Metal species in the desorbed fraction gave an indication of the amount of Sr2+ that is bound on the biomass surface by relatively weak electrostatic interactions which are easily released by the ion-exchange process (Dahl et al., 2008). The elevated concentrations of Sr2+ in the desorbed fraction may be due to the release from the complexing agents on the microbial cell surface.

These experiments showed that the SRB cells were excellent cation exchangers. The significance of these findings was that Sr2+ and other diva­lent cationic fission products could be extracted from water using bacteria under natural biological conditions. Separation of bacteria from water is relatively easy and cost effective. The bacteria could then be treated with an eluant to reverse the process thereby recovering the metals. The bacteria could then be returned into the biosorption reactors.