Selective cathodic microbial biofilm retention allows a high current-to-sulfide efficiency in sulfate-reducing microbial electrolysis cells

• Published in: Bioelectrochemistry (Amsterdam, Netherlands) Vol. 118; pp. 62 - 69
• Main Authors: Pozo, Guillermo, Lu, Yang, Pongy, Sebastien, Keller, Jürg, Ledezma, Pablo, Freguia, Stefano
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.12.2017; Elsevier BV
• Subjects: Antimicrobial agents; Bacteria; Bacteria - metabolism; Biofilms; Carbon; Desulfovibrio; Electric Conductivity; Electrode materials; Electrodes; Electrolysis; Electrolysis - instrumentation; Electrolytes; Electrolytic cells; Experimentation; Growth rate; Hydrogen-Ion Concentration; Microorganisms; Multi wall carbon nanotubes; Nanotechnology; Nanotubes; Nanotubes, Carbon - chemistry; Power consumption; Relative abundance; Retention; rRNA 16S; Sulfate reduction; Sulfate-reducing bacteria; Sulfates; Sulfates - chemistry; Sulfates - metabolism; Sulfide; Sulfides; Sulfides - chemistry; Sulfides - metabolism
• ISSN: 1567-5394; 1878-562X
• DOI: 10.1016/j.bioelechem.2017.07.001

Selective microbial retention is of paramount importance for the long-term performance of cathodic sulfate reduction in microbial electrolysis cells (MECs) due to the slow growth rate of autotrophic sulfate-reducing bacteria. In this work, we investigate the biofilm retention and current-to-sulfide conversion efficiency using carbon granules (CG) or multi-wall carbon nanotubes deposited on reticulated vitreous carbon (MWCNT-RVC) as electrode materials. For ~2months, the MECs were operated at sulfate loading rates of 21 to 309gSO4 -S/m2/d. Although MWCNT-RVC achieved a current density of 57±11A/m2, greater than the 32±9A/m2 observed using CG, both materials exhibited similar sulfate reduction rates (SRR), with MWCNT-RVC reaching 104±16gSO4 -S/m2/d while 110±13gSO4 -S/m2/d were achieved with CG. Pyrosequencing analysis of the 16S rRNA at the end of experimentation revealed a core community dominated by Desulfovibrio (28%), Methanobacterium (19%) and Desulfomicrobium (14%), on the MWCNT-RVC electrodes. While a similar Desulfovibrio relative abundance of 29% was found in CG-biofilms, Desulfomicrobium was found to be significantly less abundant (4%) and Methanobacterium practically absent (0.2%) on CG electrodes. Surprisingly, our results show that CG can achieve higher current-to-sulfide efficiencies at lower power consumption than the nano-modified three-dimensional MWCNT-RVC. •MWCNT-RVC electrodes achieved higher current densities than CG.•Both electrode materials yielded similar sulfate reduction rates.•Desulfovibrio abundance well explained the similar sulfate reducing performance.•CG can achieve higher current-to-sulfide efficiency at lower power consumption.•The biofilm on MWCNT-RVC is more active in producing H2 than in consuming it.