초록
<P><B>Abstract</B></P> <P>In the present work, various carbon sources, xylose, glucose, galactose, sucrose, cellobiose, and starch were tested for thermophilic (60 °C) fermentative hydrogen production (FHP) by using the anaerobic mixed culture. An inoculum was obtained from a continuously-stirred tank reactor (CSTR) operated at pH 5.5 and HRT 12 h, and fed with tofu processing waste. The dominant species in the CSTR were found to be <I>Thermoanaerobacterium thermosaccharolyticum</I> and <I>Clostridium thermosaccharolyticum</I>, which are well known thermophilic H<SUB>2</SUB>-producers in anaerobic-state, and have the ability to utilize a wide range of carbohydrates. When initial pH was adjusted to 6.8 ± 0.1 but not controlled during fermentation, vigorous pH drop began within 5 h, and finally reached 4.0–4.5 in all carbon sources. Although over 90% of substrate removal was achieved for all carbon sources except cellobiose (71.7%), the fermentation performances were profoundly different with each other. Glucose, galactose, and sucrose exhibited relatively higher H<SUB>2</SUB> yields whereas lower H<SUB>2</SUB> yields were observed for xylose, cellobiose, and starch. On the other hand, when pH was controlled (pH ≥ 5.5), the fermentation performance was enhanced in all carbon sources but to a different extent. A substantial increase in H<SUB>2</SUB> production was observed for cellobiose, a 1.9-fold increase of H<SUB>2</SUB> yield along with a substrate removal increase to 93.8%, but a negligible increase for xylose. H<SUB>2</SUB> production capabilities of all carbon sources tested were as follows: sucrose > galactose > glucose > cellobiose > starch > xylose. The maximum H<SUB>2</SUB> yield of 3.17 mol H<SUB>2</SUB>/mol hexose<SUB>added</SUB> achieved from sucrose is equivalent to a 26.5% conversion of energy content in sucrose to H<SUB>2</SUB>. Acetic and butyric acids were the main liquid-state metabolites of all carbon sources while lactic acid was detected only in cellobiose, starch and xylose exhibiting relatively lower H<SUB>2</SUB> yields.</P> <P><B>Highlights</B></P> <P>► Various carbon sources were tested for thermophilic fermentative H<SUB>2</SUB> production. ► When pH was not controlled, glucose, galactose, and sucrose showed high performance. ► By pH control, the fermentation performance was enhanced but to a different extent. ► H<SUB>2</SUB> yield was: sucrose > galactose > glucose > cellobiose > starch > xylose. ► Acetate and butyrate were the main liquid-state metabolites of all carbon sources.</P>