초록
<P><B>Highlights</B></P><P>► Semi-continuous photo-fermentative H<SUB>2</SUB> production was attempted. ► The effect of decanting volume ratio (DVR) on H<SUB>2</SUB> production was investigated. ► H<SUB>2</SUB> production was not efficient at 30% and 40% DVR. ► The highest H<SUB>2</SUB> yield of 3.7molH<SUB>2</SUB>/mol succinate<SUB>added</SUB> was achieved at 60% DVR. ► Soluble microbial products accounted for 3–15% of substrate electrons.</P> <P><B>Abstract</B></P><P>In this study, a semi-continuous operation of photo-fermentative H<SUB>2</SUB>-producing reactor was attempted at various decanting volume ratios (DVR, decanting volume per day/total working volume, %), ranging 30–70%, using <I>Rhodobacter sphaeroides</I> KD131. H<SUB>2</SUB> production was not efficient with showing low H<SUB>2</SUB> yields of 0.2 and 0.5molH<SUB>2</SUB>/mol succinate<SUB>added</SUB> at 30% and 40% DVR, respectively. The low performance ascribed to the fact that over 70% of substrate electrons were diverted towards cell growth under these conditions. Meanwhile, cell growth was limited at DVR⩾50%; therefore, higher H<SUB>2</SUB> yields (>2.0molH<SUB>2</SUB>/mol succinate<SUB>added</SUB>) were observed. Both the highest H<SUB>2</SUB> yield of 3.7molH<SUB>2</SUB>/mol succinate<SUB>added</SUB> and production rate of 1494mL H<SUB>2</SUB>/L-reactor/d were achieved at 60% DVR. The content of soluble microbial products (SMPs) was measured, which accounted for 3–15% of substrate electrons. It was found that the largest (65–75%) portion of SMPs comprised low molecular-weight (<3kDa).</P>