Biochar conductivity and electron donating capability control Cr(VI) bioreduction.

Area of Science:

• Environmental Science
• Microbiology
• Materials Science

Background:

• Biochar can enhance the bioreduction of chromium(VI) (Cr(VI)), a toxic heavy metal.
• The specific biochar properties governing this process, particularly the kinetics, remain unclear.

Purpose of the Study:

• To investigate the kinetics and efficiency of biochar in promoting Cr(VI) reduction by Shewanella oneidensis MR-1.
• To analyze the influence of biochar properties (concentration, conductivity, particle size) on fast and slow bioreduction processes.

Main Methods:

• Utilized a "dual-process model" to differentiate between fast and slow Cr(VI) bioreduction rates.
• Performed correlation analysis between biochar properties and the identified bioreduction rate constants.
• Investigated bioreduction in neutral solutions using S. oneidensis MR-1 and various biochar types.

Main Results:

• Cr(VI) bioreduction by S. oneidensis MR-1 occurred in fast (r_f0) and slow (r_s0) processes, with r_f0 being 2-15 times higher.
• Fast bioreduction rates correlated positively with biochar conductivity and negatively with particle size, indicating enhanced direct electron transfer.
• Slow bioreduction rates were primarily determined by biochar's electron donating capability, independent of microbial cell concentration.

Conclusions:

• Cr(VI) bioreduction is mediated by both the electron conductivity and redox potential of biochar.
• Tailoring biochar properties like conductivity and particle size can optimize Cr(VI) removal and detoxification in contaminated environments.
• Findings provide guidance for producing biochar with specific characteristics for effective environmental remediation.