Shifts of the Rate-Limiting Step in Airlift Microbial Electrolysis Cells for Gaseous Propanethiol Degradation

The hydrophobicity and biotoxicity of volatile organicsulfur compoundshinder them from being efficiently biodegraded. Herein, combiningthe advantages of the airlift (AL) bioreactor and microbial electrolysiscell (MEC) on mass transfer and bioreaction enhancement, we proposedAL-MEC systems for gaseous propanethiol (PT) degradation for the firsttime, in which the electrodes were modified by polypyrrole (PPy) andpolypyrrole/carbon nanotubes (PPy/CNTs) to further strengthen thebiodegradation process. The resulting PPy-AL-MEC and PPy/CNTs-AL-MECpossessed the best PT removal efficiencies of 84.0 and 94.4%, respectively(PT, 50 mg m(-3); empty bed residence time (EBRT),90 s; anode potential, 0.5 V vs. SHE), which were much higher than68.8% in a control system with an unmodified graphite electrode (GS-AL-MEC).Moreover, the kinetics analysis reveals that the rate-limiting stepshifted from biodegradation in GS-AL-MEC to mass transfer in PPy/CNTs-AL-MEC,while that in PPy-AL-MEC also shifted to mass transfer at an EBRT >= 45 s.

Automated summary

In this study, AL-MEC systems were proposed for the degradation of gaseous propanethiol, utilizing the advantages of the airlift bioreactor and microbial electrolysis cell. The modified electrodes, PPy and PPy/CNTs, enhanced the biodegradation process and achieved higher removal efficiencies compared to the control system with an unmodified graphite electrode.