Exoelectrogenic anaerobic granular sludge for simultaneous electricity generation and wastewater treatment

Thick and electroactive biofilm is the key for successful development of microbial electrochemical technologies and systems (METs). In this study, intact anaerobic granular sludge (AGS), which are spherical and dense microbial associations, was successfully demonstrated as novel and efficient biocatalysts in METs such as microbial fuel cell (MFC). Three different strategies were explored to shift the microbial composition of AGS from methanogenic into exoelectrogenic microbes, including varying external resistance, organic loading, and manipulating anode potential. Among other strategies, only with positive anode potential, AGS was successfully shifted from methanogenic to exoelectrogenic conditions, as indicated by the significantly high current response (10.32 A/m2) and 100% removal of organic carbon from wastewater. Moreover, AGS bioanode showed no significant decrease in current generation and organic removal at pH 5, indicating good tolerance of AGS to acidic conditions. Finally, 16S rRNA sequencing revealed the enrichment of exoelectrogens and inhibition of methanogens in the microbial community of AGS after anode potential control. This study provides a proof-in-concept of extracting electrical energy from organic wastes by exoelectrogenic AGS along with simultaneous wastewater treatment, and meanwhile opens up a new paradigm to create efficient and cost-effective exoelectrogenic biocatalyst for boosting the industrial application of METs.