Rapid development and application of nanotechnology have introduced various nanopaticles,
such as single-walled carbon nanotubes (SWCNTs), whose negative effects on
aquatic organisms and cultured cells have been reported, into anaerobic wastewater
treatment systems. In this study, the response of methanogenic sludge exposed to
SWCNTs in anaerobic digestion process was investigated. Results show that SWCNTs, at a
concentration up to 1000 mg/L, had no significant impact on the maximum methane yield.
In contrast, they induced much faster substrate utilization and methane production rates.
Scanning electron microscopy examination shows that more extracellular polymeric
substances (EPS) were excreted from the anaerobic sludge and closely interacted with
SWCNTs. Such an interaction prevented nanoparticles from piercing into cells, and thus
reduced their cytotoxicity. In the compact anaerobic granule structure, SWCNTs exposure
enhanced the electrical conductance of the sludge, which might promote direct interspecies
electron transfer among anaerobic fermentative bacteria and methanogens in the
anaerobic digestion process. Our results provide useful information to understand the
response of anaerobic microorganisms to CNTs in complex environmental matrix.