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Oil palm empty fruit bunch (OPEFB) was subjected to acid hydrolysis (6% v/v sulfuric acid;8 mL acid per g dry OPEFB;120 C, 15-min) to release the fermentable sugars.The hydrolysate contained xylose, acetic acid and glucose as the major carbon components.This hydrolysate was used as the sole carbon source for photofermentative production of hydrogen using a newly identified photosynthetic bacterium Rhodobacter sphaeroides S 10.Batch and repeated-batch photofermentations were carried out under an incident light level of 10 klux, at temperature of 35 C.The best results for hydrogen production on batch experiments were found in the culture medium composed of(per L) mixed carbon in oil palm empty fruit bunch (30 mM), K2HPO4 (0.9 g), KH2PO4 (0.6 g), CaCl22H2O (75 mg), L-glutamic acid (795.6 mg), FeSO47H2O (11 mg), Na2MoO22H2O (1.45 mg), MgSO47H2O (2.46 g), EDTA (0.02 g) and yeast extract (0.3 g).With this medium, the cumulative hydrogen was 2,019 mL H2/L medium;the lag period of hydrogen production was 7.65 h;the volumetric production rate was 22.4 mL H2/L medium per hour and the specific hydrogen production rate was 7.0 mL H2/g (xylose + glucose + acetic acid) after 90h of fermentation.Among the 3 carbons being investigated in the hydrolysate, the bacterium preferred to consume acetic acid > glucose > xylose.Acetic acid acted as carbon catabolite repression for xylose.Of these carbons, glucose and xylose were conversed to hydrogen.Best results for the repeated-batch were obtained when 90% of the broth volume was replaced with the fresh medium after 84 h of a batch operation.With these conditions fixed, four repeated-batch photofermentation cycles were monitored.The duration of each cycle was 60 h.For the five cycles (including the first batch phase), the average conversion efficiency, the average substrate specific hydrogen production rate and the average maximum hydrogen production rate were quite comparable, indicating an excellent reproducibility.