Abstract

Oil palm empty fruit bunch (OPEFB) was hydrolyzed with dilute sulfuric acid (6% v/v; 8 mL acid per g dry OPEFB) at 120°C for 15-min to release the fermentable sugars. The hydrolysate contained xylose (23.51 g/L), acetic acid (2.44 g/L) and glucose (1.80 g/L) as the major carbon components. This hydrolysate was used as the sole carbon source for photofermentive production of hydrogen using a newly identified photosynthetic bacterium Rhodobacter sphaeroides S10. A Plackett-Burman experimental design was used to examine the influence of the following on hydrogen production: yeast extract concentration, molybdenum concentration, magnesium concentration, EDTA concentration and iron concentration. These factors influenced hydrogen production in the following decreasing order: yeast extract concentration > molybdenum concentration > magnesium concentration > EDTA concentration > iron concentration. Under the conditions used (35°C, 14.6 W/m² illumination, initial pH of 7.0), the optimal composition of the culture medium was (per L): mixed carbon in OPEFB hydrolysate 3.87 g, K<inf>2</inf>HPO<inf>4</inf> 0.9 g, KH <inf>2</inf>PO<inf>4</inf> 0.6 g, CaCl<inf>2</inf>2H<inf>2</inf>O 75 mg, l-glutamic acid 795.6 mg, FeSO<inf>4</inf>7H<inf>2</inf>O 11 mg, Na <inf>2</inf>MoO<inf>2</inf>2H<inf>2</inf>O 1.45 mg, MgSO<inf>4</inf>7H <inf>2</inf>O 2.46 g, EDTA 0.02 g, yeast extract 0.3 g). With this medium, the lag period of hydrogen production was 7.65 h, the volumetric production rate was 22.4 mL H<inf>2</inf>/L medium per hour and the specific hydrogen production rate was 7.0 mL H<inf>2</inf>/g (xylose + glucose + acetic acid) per hour during a 90 h batch culture of the bacterium. Under optimal conditions the conversion efficiency of the mixed carbon substrate to hydrogen was nearly 29%. Copyright © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.