Under darkness incubation, the results in Figure 3.11A showed that addition of extra carbon sources could not stimulate cells to produce biohydrogen at a higher rate. Then, the experiment was re-designed to add the carbon sources at the beginning of the growth phase. The C-sources were added to the culture with the same final concentration and the culture was grown at the same condition. The hydrogen production of each condition was measured as shown in Figure 3.11B. The hydrogen production was not significantly stimulated when carbon sources were added during growth phase, whereas glucose caused a significant decrease on the hydrogen production.