Bacterial Precipitation of Lead

Example 6

This Example illustrates the involvement of alkalinity of culture medium in mediating Pb′ precipitation.

The pH of culture broth after the recovery of bioprecipitated Pb′ by B. licheniformis strain ECOBIO_2 was found to be 12. However, the pH of the control broth remained at 7. With this background, experiments were conducted to assess the involvement of alkalinity of the culture medium in mediating lead precipitation. Both the chelated and non-chelated forms of Pb(C₂H₃O₂)₂) and Pb(NO₃)₂ were added in culture broth and the initial pH was recorded as 7.4. Further, after the three days of incubation, individual flasks were tested for change in the pH. Results are shown in FIG. 6. To rule out the involvement of pH alone in precipitation, ammonium chloride was added to the broth amended with Pb(NO₃)₂+EDTA till the pH of the medium reached 12 and the broth was observed for signs of precipitation. No precipitation was observed even after increasing the pH of medium to 12 and 14. Thus the investigation confirmed that pH alone without the bacteria cannot bring forth the precipitation of lead, and that the lead precipitation is due to the bacteria and not due to the pH change.