Microbial lead(II) precipitation : the influence of growth substrate

Abstract

The objective of the study was to explore the influence of various growth substrates on the removal of aqueous lead from solution. The fermentation media tested consisted of glucose- and xylose-supplemented LB-broth, with and without CaCO3 as pH buffer. In addition, combinations of the various constituents of LB-broth, i.e. yeast extract, tryptone, and NaCl, were tested. Results from the sugar-supplement runs showed that significant removal of lead, without observable precipitation, was measured both with and without pH buffering (75–90% in 48–72 hours). Significant gas build-up in all runs, and a drop in pH in the unbufferred runs, indicate an anaerobic digestion mechanism with either internal or external sequestration of lead. The LB-broth constituent experiments indicate that even though the commercial growth medium LB-broth exhibited the best performance in terms of lead(II) removal (89%), yeast extract-NaCl complex medium performed nearly as well (80%). Results show that substituting the tryptone with corn steep liquor provided minimal gains in lead removal performance, compared to the yeast extract-NaCl medium. The aqueous lead removed by the yeast extract-only medium was limited to 56% in 144 hours. Dark grey precipitates and pH values greater than 5 indicate that the lead(II) were reduced to elemental lead. The observations also suggest that the growth factors in the LB broth, required by the consortium, can be largely replaced by the yeast extract-NaCl medium.