The role of a metabolically independent lead removal mechanism in an industrially obtained lead-precipitating consortium was investigated. Cultures were prepared under anaerobic conditions for 24 hours in batch reactors starting with 20 g L-1 tryptone, 10 g L-1 yeast extract, 1.0 g L-1 NaCl and 0.43 g L-1 NaNO3. Bacteria were suspended in 50 mM of sodium azide (NaN3) solution for 3 h to successfully inhibit the microbial respiratory chain, thereby preventing bacteria growth and activity. Fourier-transform infrared spectroscopy (FTIR) was used to inspect whether NaN3 deformed the structure of bacteria cell walls and changed material characteristics.
Reactors containing 100 mL of 80 mg L-1 Pb(II) and 1.0 g/L NaCl were spiked with 1 mL of NaN3-sterilized bacteria culture and sampled over a 3 h period. Bulk Pb(II) concentration and metabolic activity were measured.
Results showed that NaN3 was an effective means to cease metabolic activity of the consortium without altering the surface properties. Pb(II) is still removed from solution (61.7 %) by dead bacteria after NaN3 sterilization, indicating that the initial removal of Pb(II) from solution by the lead-precipitating consortium is an abiotic process. FTIR analysis revealed functional groups such as carboxyl, amine, and phosphate playing a role in Pb(II) biosorption.
Conclusions drawn from this study allow for future experimentation, modelling, and optimization of the biosorption mechanism in an industrially obtained lead-precipitating consortium.