2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 23 -
Abstract
-- Continuous bio-hydrogen production
from xylose was investigated comparatively in the up-
flow anaerobic sludge blanket (UASB) reactor and the
anaerobic filter (AF) reactor by using mixed culture
at thermophilic temperatures (55 ºC).
The highest
hydrogen yield of 251.2±11.3 ml
–
H
2
/g-xylose,
corresponding to hydrogen production rate of 15073.8
± 675.5 mL
–
H
2
/d/L was obtained from UASB reactor
operated at the organic loading rate (OLR) of 60 g-
xylose/d/l (4 hr HRT and 10 g/L xylose concentration).
Meanwhile the highest hydrogen production rate of
19383.5± 693.9 ml-H
2
/d/L, corresponding to hydrogen
yield of 161.5 ± 5.8 mL
–
H
2
/g
–
xylose was able to
achieve from the AF reactor fed at the OLR of 120 g-
xylose/d/L (2 hr HRT and 10 g/L xylose
concentration). Additional, Hydrogen producing
bacterial strains metabolized dominantly to butyrate
and acetate pathways. These results demonstrate that
continuous xylose fermentation with OLR for
hydrogen production is potentially feasible in both
UASB reactor and AF reacto
r.
Index Terms
—
Dark Fermentation, Biohydrogen, Xylose,
Thermophilic mixed culture
I.
I
NTRODUCTION
Xylose is the dominant monomeric sugars present the
hemicellulosic part of lignocelluloses. However,
hemicelluloses, which consists mainly with xylose
approx. 74.1 % of total sugar contained in its, has not
been utilized for fermentative ethanol by wild
S.
cerevisiae
as effectively as cellulosic part of
lignocelluloses [1]. Alternatively, xylose based substrate
like hemicellulosic hydrolysate generated simultaneously
with cellulose fraction from the hydrothermal
pretreatment of wheat straw has potential for fermentative
hydrogen production [2]. Furthermore, this hydrogen
production option could lead to have full energy
recovered from lignocelluloses beyond bio-refinery
concept, in which fermentative ethanol and H
2
are
produced from cellulose and hemicelluloses respectively,
meanwhile CH
4
can be sequentially produced from H
2
and ethanol process effluent by anaerobic digestion [3].
However, xylose is still more difficult than glucose to be
fermented by hydrogen producing bacteria [4], thus, more
understanding the microbial physiology and reactor
performance of hydrogen production from pure xylose is
necessary to develop the platform technology of
fermentative hydrogen production from xylose rich
substrates.
The microbial dark fermentation gives higher
hydrogen yield and less variety of the fermentation end
products at thermophilic conditions than mesophilic
conditions due to favorable thermodynamic conditions.
Furthermore, thermophilic bacteria are able to degrade a
wide range of substrate in particular with complex
carbohydrates [5-7]. Due to low cell densities of
thermophiles achieved in the liquid culture, leading to
have low hydrogen production rate [8], immobilized cell
systems of UASB and AF reactor are successfully
employed for improving cell mass concentration with
high hydrogen production rate during thermophilic mixed
culture fermentation [5,9-10]. Apart from those
mentioned influences, organic loading rate (OLR) is
another major factor affecting on hydrogen production
because high OLR usually obtained by either high
influent concentration or short hydraulic retention time
(HRT) results high hydrogen partial pressure and VFAs
concentration which can inhibit hydrogen producing
microorganisms directly. Additionally, low pH as a result
from high VFAs generation could also inhibit acidogens
[11].
In this study, xylose was therefore used as the
substrate for continuous hydrogen production using
enriched mixed culture, which were immobilized on
granules and plastic carriers contained in UASB and AF
reactors respectively. The performance of both reactors
was investigated comparatively by varying organic
loading rate (OLR) under thermophilic temperature
(55ºC).
II. M
ATERIAL AND METHOD
A. Experimental set-up and operation
Continuous hydrogen production was carried out in
UASB and AF with a working volume of 220 mL each.
The reactors were maintained at 55 ºC for both UASB
and AF reactors by circulating hot water inside a water
jacket surrounding each reactor. Those reactors was fed
with 10 g/L and xylose and supplemented with BA
medium at a 16-hr HRT in our previous investigation,
corresponding to an organic loading rate (OLR) of 15
g-
xylose/d/L[12]. BA medium containing nutrients and
bicarbonate buffer was the same composition as
previously used by Angelidaki et al, (1990) [13] and was
amended with 1 g/l of yeast extract. The reactor OLR was
kept OLR at 15 g-xylose/d L by decreasing the HRT and
Thermophilic Bio-Hydrogen Production From
Xylose using the Up-Flow Anaerobic Reactors
P. Kongjan
*
and S. O-Thong
**
*Department of Science, Faculty of Science and Technology, Prince of Songkla University, Pattani 94000,
(
Thailand
)
**
Department of Biology, Faculty of Science, Thaksin University, (
Thailand
)
