초록
<P><B>Abstract</B></P> <P>The present study compared the mesophilic and thermophilic alkaline fermentation of waste activated sludge (WAS) for hydrogen production with focus on homoacetogenesis, which mediated the consumption of H<SUB>2</SUB> and CO<SUB>2</SUB> for acetate production. Batch experiments showed that hydrogen yield of WAS increased from 19.2 mL H<SUB>2</SUB>/gVSS at 37 °C and pH 10–80.1 mL H<SUB>2</SUB>/gVSS at 55 °C and pH 10. However, the production of volatile fatty acids (mainly acetate) was higher at 37 °C and pH 10 by comparison with 55 °C and pH 10. Hydrogen consumption due to homoacetogenesis was observed at 37 °C and pH 10 but not 55 °C and pH 10. Higher expression levels of genes relating with homoacetogenesis and lower expression levels of genes relating with hydrogen production were found at 37 °C and pH 10 compared to 55 °C and pH 10. The continuous experiment demonstrated the steady-state hydrogen yield of WAS was comparable to that obtained from batch experiments at 55 °C and pH 10, and homoacetogenesis was still inhibited. However, the steady-state hydrogen yield of WAS (6.5 mL H<SUB>2</SUB>/gVSS) was much lower than that (19.2 mL H<SUB>2</SUB>/gVSS) obtained from batch experiments at 37 °C and pH 10 due to the gradual enrichment of homoacetogens as demonstrated by qPCR analysis. The high-throughput sequencing analysis of 16S rRNA genes showed that the abundance of genus <I>Clostridium</I>, containing several homoacetogens, was 5 times higher at 37 °C and pH 10 than 55 °C and pH 10.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Higher hydrogen yield was obtained at 55 °C and pH 10 compared to 37 °C and pH 10. </LI> <LI> Higher production of VFAs was obtained at 37 °C and pH 10 compared to 55 °C and pH 10. </LI> <LI> Long-term inhibition of homoacetogenesis was achieved at 55 °C and pH 10. </LI> <LI> Homoacetogenesis occurred and homoacetogens were enriched at 37 °C and pH 10. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>