In this study, the hydrogen yield obtained by dark fermentation
was 5.74 mmol H2/g COD consumed. The maximum
hydrogen yield of photo fermentation (0.68 mmol H2/g COD
consumed) was obtained from 5 times dilution of DFE without supplement of yeast extract þ NaHCO3, and 2 mM glutamate.
Combined the two-stage processes obtained the hydrogen
yield of 6.42 mmol H2/g COD consumed which was 10.4% of
the theoretical yield. Many studies have reported on biohydrogen
production by two-stage processes with the difference
in various types of wastewater, photosynthetic bacterial
strains, and operating conditions. Therefore, it is rather difficult
to make a comparison. The total hydrogen yield obtained
in this study (6.42 mmol H2/g COD consumed) was slightly
lower than those from the previous reports using wastes such
as ground wheat waste (6.9 mmol H2/g COD) [30], corncob
(28.1 mmol H2/g COD) [13], and cheese whey wastewater
(26.2 mmol H2/g COD) [12]. Possible cause for low hydrogen
yield obtained in this study may be due to the interference of
some organic matter such as potassium, phosphorus and
sulfur in crude glycerol that might affect the hydrogen production
[18].