Enhanced methane production from anaerobic wastewater treatment by carbon nanotubes: Surface defect mediated interfacial electron transfer

Abstract

Interfacial electron transfer, a crucial process in direct interspecies electron transfer (DIET) between exo-electrogenic microorganisms and conductive materials, has played a vital role in enhancing methane production in anaerobic wastewater treatment. To improve interfacial electron transfer, the construction of surface defect has been identified as an effective approach. In this study, a range of metals and non-metals were used to dope carbon nanotubes (CNTs), which were served as the conductive materials and added into anaerobic wastewater treatment systems. The effect of surface defect of CNTs on methane production were investigated. The results demonstrated that all the doped CNTs can significantly increase methane production rate in anaerobic systems. Among them, boron and iron doped CNTs (B-CNTs and Fe-CNTs) exhibited the most promising performance as non-metal and metal doped CNTs. The addition of B-CNTs and Fe-CNTs led to impressive increase of 101.6% and 149.8% in the methane production rate of the anaerobic systems. Furthermore, this study elucidated the underlying mechanisms responsible for the enhanced methane production in the anaerobic wastewater treatment with doped CNTs. The introduction of doped CNTs enriched exo-electrogenic bacteria and archaea, thereby promoting the DIET process. Additionally, the CNTs also acted as the capacitor, storing and discharging electrons, which contributed to the maintenance of a stable methane production in anaerobic wastewater treatment.