2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
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The theoretical maximum yield of hydrogen
fermentation is reported to be four moles of hydrogen
per mole of glucose [12] or eight moles of hydrogen per
mole of sucrose [1], if all of the substrate were to be
converted to acetic acid. These values correspond to a
theoretical maximum yield of 0.467 L-H
2
/g-COD. If all
the substrate were to be converted to butyric acid, these
values are two and four moles of hydrogen per mole of
glucose and sucrose, respectively. In practice, a
fraction of the substrate is used for biomass production
and other metabolic products are also produced,
resulting in a lower hydrogen yield.
The SHPR (ml H
2
/gcells-hr) was determined by
dividing the maximum rate of H
2
production (ml/hr)
obtained from the slope of the graph (during the first 24
hours) to the initial amount of the cell concentration.
For the study of Batch set 1, slopes of 1.20, 1.13, 1.25,
and 1.50 ml at STP/hr (at initial pH 5.5, 6, 6.5 and 7,
respectively), were found and the initial cell
concentration was 1.950 g (in 100 ml of serum bottle).
Hence, estimates of SHPR were 0.61, 0.58, 0.64 and
0.77
ml at STP/g cells-hr
(at initial pH 5.5, 6, 6.5 and 7,
respectively) (Fig. 4). For the study of Batch set 2,
slopes of 0.07, 0.06, 1.45, and 3.59 ml at STP/hr (at
initial pH 5.5, 6, 6.5 and 7, respectively), were found
and the initial cell concentration was 0.4860 g (in 100
ml). Hence, estimates of SHPR were 0.14, 0.13, 2.99,
and 7.38
ml at STP/g cells-hr
, (at initial pH 5.5, 6, 6.5 and
7, respectively) (Fig. 4). The SHPR obtained from
Batch set 1 (Cell:COD = 4 g cell/g COD) was
compared with that of Batch set 2 (Cell :COD = 0.26 g
cell/g COD) at different initial pH’s of wastewater and
shown in Fig. 4.
Fig. 4. Comparison of SHPR from bioreactors operated with the
Cell : COD at 4 to that of Cell : COD at 0.26 (results shown at initial
pH 5.5 -7).
For starch wastewater with a strength 25000
mgCOD/l treated by dark fermentation with a heat
treated mixed bacterial culture originated from the
digested sludge of its plants, the transformation of
starch wastewater to H
2
was highly efficient when the
system contained a low ratio of Cell:COD. The highest
cumulative H
2
production, H
2
yield and SHPR for these
tests were obtained when the system contained a
Cell:COD ratio at 0.26 g cell/gCOD. When operating
at the Cell:COD ratio 0.26 g cell/gCOD and at initial
pH of starch wastewater of 7, the highest H
2
yield
obtained was 63 ml at STP/g COD degraded and the
SPHR was 7.38 ml at STP/g cells-hr. Argun et al. [8]
studied the effects of the substrate and cell
concentration on bio-hydrogen production from ground
wheat by combined dark and photo-fermentation. They
found that the highest cumulative hydrogen and yield
were obtained at the optimal biomass: substrate ratio of
0.22 g cell/g wheat powder.
IV. C
ONCLUSION
Starch wastewater is a good substrate for biological
production of hydrogen. Mixed bacteria originating
from the digested sludge obtained from plants with
starch-containing waste water showed great potential to
transform wastewater to hydrogen by dark
fermentation, after pretreatment of the bacterial mixture
by heat to inactivate methanogens. It is more
advantageous to operate the system with the optimum
Cell:COD ratio for effective and fast degradation of
wastewater. High cell concentrations tended to lower
the hydrogen yield and specific rate of hydrogen
production. For the Cell:COD ratios tested in this
study, hydrogen was produced more effectively at
initial wastewater pH of 7.
A
CKNOWLEDGMENT
This research was supported by Kasetsart University
Research and Development Institute (KURDI),
Kasetsart University, Bangkok, Thailand.
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EFERENCES
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0.61
0.58
0.64
0.77
0.14
0.13
2.99
7.38
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
5.5
6
6.5
7
InitialpH
SHPR (ml at STP/g-hr)
Cell:COD = 4
Cell:COD = 0.26
