Hydrogen generation by Rhodobacter sphaeroides O.U.001 using pretreated waste barley

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In the present study, valorization of waste barley by producing hydrogen (H2) and 5-aminolevulinic acid (5-ALA) using Rhodobacter sphaeroides O.U.001 was aimed. Firstly, 3 % (w/v) waste barley hydrolysate was prepared by treating 3 g of powdered waste barley with H2SO4 in a total volume of 100 mL mixture and then autoclaving this mixture at 121 ºC for 30 min. Upon generation of fermentable simple sugars by pretreatment and analytical examination of the hydrolysate in terms of ammonium content, element composition and light transmittance, various types of growth media containing various concentrations of sugar (5 - 6 - 7 - 8 g/L) were prepared. The cells were cultivated in these media under photo-heterotrophic conditions which favor H2 and 5-ALA generations. pH changes, growth, H2 production and 5-ALA generation were monitored in the media. The results showed that all the media prepared from 3 % (w/v) waste barley hydrolysate sustained the cell growth appreciably. The highest OD value (OD660: 1.71) was attained when using 8 g/L sugar. Furthermore, biological H2 evolution was seen in each bioreactor. In particular, the highest hydrogen accumulation (0.29 L H2/L) was achieved in 6 g/L sugar-containing medium. However, 5-ALA was not detected in any of the media. To conclude, considerable cell growth and biological hydrogen production was achieved using 3 % (w/v) waste barley hydrolysate under the conditions tested but there was no detectable 5-ALA generation.