Growth of naturally occurring microbial isolates in metal-citrate medium and bioremediation of metal-citrate wastes

The use of citrate as a chelating agent in decontamination operations is of environmental concern as it can mobilize toxic heavy metals if discharged into the environment. Many heavy metal‐citrate complexes are recalcitrant to biodegradation. Citrate‐utilizing strains of Pseudomonas aeruginosa and Pseudomonas putida were isolated from a mixed culture which had been maintained with EDTA as the carbon source for 2 years. Citrate (5 mM) was used as the sole carbon source in medium supplemented with 5 mM Cd, Zn, Cu, Fe, Co, or Ni. Removal of the metals from the medium was promoted by the incorporation of inorganic phosphate as a precipitant, with formation of nickel and cobalt phosphates confirmed by X‐ray powder diffraction analysis. The potential of P putida to biodegrade citrate in a nickel–citrate secondary waste was illustrated using a fill‐and‐draw reactor supplied with effluent from a bioinorganic ion exchange column that had been used previously to concentrate nickel from aqueous solution. © 2000 Society of Chemical Industry