초록
<P><B>Abstract</B></P> <P>The addition of conductive materials or metal oxide nanoparticles (NPs) to anaerobic systems is an attractive strategy to enhance the anaerobic digestion and the production of CH<SUB>4</SUB>. This study proposed a strategy to boost the CH<SUB>4</SUB> production by adding granular activated carbon (GAC)-MnO<SUB>2</SUB> nanocomposites into an anaerobic methanogenic system. The associated mechanisms and the microbial community structure during anaerobic digestion were investigated systematically. Compared with a control with GAC only, after adding GAC-MnO<SUB>2</SUB> composite the chemical oxygen demand (COD) removal efficiency and CH<SUB>4</SUB> yield were increased by 77% and 36%, respectively. The addition of GAC-MnO<SUB>2</SUB> stimulated the secretion of extracellular polymeric substance (EPS), while the secretion of humic substances was inhibited. The spatial distribution of EPS in the anaerobic sludge affects the extracellular electron transfer efficiency as well. Manganese ions concentrated in the EPS layer facilitated the electron flow and, thus, accelerated the extracellular electron transfer. The enhancement of anaerobic methanogenesis can be mainly attributed to the reduction/oxidation cycle of Mn<SUP>4+</SUP>/Mn<SUP>2+</SUP>. Electron transfer system activity and Cytochrome <I>C</I> content reached up to 341 and 38 nmol/L, respectively, under optimal conditions. 16S rRNA gene sequencing analysis indicated that <I>Spirochaetaceae, Cloacibacterium</I>, and <I>Treponema</I> were the dominant bacteria. The abundance of the methanogenic archaea <I>Methanobacterium</I> and <I>Methanosaeta</I> were increased with the addition of GAC-MnO<SUB>2</SUB>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> GAC-MnO<SUB>2</SUB> notably accelerates CH<SUB>4</SUB> production in anaerobic digestion. </LI> <LI> MnO<SUB>2</SUB> acts as a catalyst to improve interspecies electron transfer. </LI> <LI> The secretion of humic substances was inhibited by GAC-MnO<SUB>2</SUB>. </LI> <LI> <I>Spirochaetae</I> and <I>Methanobacterium</I> response to the increase of CH<SUB>4</SUB> production. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>