초록
<P><B>Abstract</B></P> <P>Our previous studies have demonstrated the positive impacts of low-strength (LS)-ultrasonication on biological methane production via anaerobic digestion. In this study, the effects of LS-ultrasonication and effluent recirculation on dark fermentative hydrogen production using upflow anaerobic sludge blanket reactor were investigated. Significant increase in hydrogen (H<SUB>2</SUB>) yield (up to 0.89 mol H<SUB>2</SUB>/mol hexose) was observed under LS-ultrasonication conditions. This enhanced H<SUB>2</SUB> yield seems to be associated with the decrease in dissolved H<SUB>2</SUB> concentration via a degassing effect, as evident from increased H<SUB>2</SUB> content (up to 20%). Effluent recirculation alone led to positive effects. However, applying both LS-ultrasonication and effluent recirculation decreased H<SUB>2</SUB> yield compared to the trial with only LS-ultrasonication (0.89–0.72 mol H<SUB>2</SUB>/mol hexose), possibly due to the cumulative shear stress and sludge bed expansion above the ultrasonication zone. Microbial community analysis revealed that the presence/absence of LS-ultrasonication and/or effluent recirculation significantly affected the microbial communities. <I>Ethanoligenes cloacae</I>, <I>Aeromonas hydrophila</I> and <I>Clostridium pasteurianum</I> were identified as principal H<SUB>2</SUB> producers under the LS-ultrasonic conditions, while <I>C. butyricum</I>, the most commonly reported H<SUB>2</SUB> producer, was more abundant in the controls. The energy balance of the LS-ultrasonication system was evaluated and future research directions were suggested.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Low-strength ultrasonication enhanced bio-hydrogen production by dark fermentation. </LI> <LI> Effluent recirculation also affected hydrogen production performance. </LI> <LI> <I>Ethanoligenes</I>, <I>Aeromonas</I> and <I>Clostridium</I> were assumed as key H<SUB>2</SUB> producers. </LI> <LI> Some <I>Clostridium</I> spp. responded differently upon ultrasonication treatment. </LI> </UL> </P>