Sweet sorghum cultivation was carried out in South-west Greece. The fresh biomass yield was about 126 t/ha. Stalks weight accounts for 82% of total crop weight while leaves and panicle account for 17% and 1%, respectively. The major components in variety 'Keller' stalks were, based on dry weight, sugars (45%), (hemi)cellulose (35%), lignin (9%) and ash (3%). This means that per hectare, 14.5 ton sugars is produced for hydrogen fermentation. Hydrogen fermentations by the extreme thermophilic bacterium, Caldicellulosiruptor saccharolyticus, using sweet sorghum juice as carbon and energy substrate showed that it is an excellent substrate with a H2 yield of 58% of the theoretical maximum at a maximal production rate of 21 mmol/L.h. Besides the sugary juice, 15 ton/ha bagasse (dry weight) is obtained from the sweet sorghum crop. The pre-treatment of bagasse for increasing biomass fermentability was optimised. After hydrolysis with commercial enzymes, 37 g glucose and 26 g xylose from 100 g bagasse could be obtained which corresponded to conversion efficiencies of 60% for cellulose and 100% for xylan. Defined media with glucose, xylose or a mixture corresponding to the sugars in the sweet sorghum bagasse hydrolysate supported growth and hydrogen production by Caldicellulosiruptor saccharolyticus. The theoretical production in the complete bioprocess under consideration from the 14.5 t sugars/ha could amount to 1.3 ton hydrogen/ha and to 2.1 ton when the bagasse is also converted to hydrogen.
|Publication status||Published - 2004|