Influence
of organic loading rates on continuous
H2
production by a membrane bioreactor from food waste
Influence of organic loading rate[JH1] on
continuous H2 production from food
waste in membrane bioreactor
Abstract
The possibility of [JH2] long-term
stability
of stability of H2
fermentation in an
MBR (HF-MBR) with
food waste by membrane bioreactor
(HF-MBR) from food waste was investigated. An
HF-MBR was started up using a heat-pretreated anaerobic mixed
sludge to inactive activate H2-consuming
bacteria, and acclimated with 4.5% total solids (TS) food waste slurry. The HF-MBR
was operated at the under various[JH3] organic
loading rates (OLRs) of 70.2, 89.4 and 125.4 kg-COD/m3/day, corresponding to
the
hydraulic retention times (HRTs) of 18.7, 14.0 and 10.5 hrs, respectively.
The biogas production at for the H2 content
range of 44 ~ 48% H2 content range increased from
22.38 to 32.82 and 62.49 l/day when with the OLRs increasesd.
The maximum H2 yield and H2 production rate were 111.1
ml-H2/g-VS added and 10.7 l-H2/l/day at an OLR of 125.4kg-COD/m3/day.
The major volatile fatty acids (VFAs) produced from the degradation of organic
fractions were acetate and butyrate. The Ttotal
carbohydrate degradation was beyond better than 96%
throughout the experimental
runs. Continuous H2 production by
HF-MBR from food waste of TS 4.5% TS food waste absent CH4
production at 5.5±0.1 pH was
successfully achieved sustained in the HF-MBR for 90
days. without
CH4 production at pH control of 5.5±0.1 in the
bioreactor. The copy number of acidogens 16S rRNA gene was around 3.25
´ 107 copies/ml, and whereas that
of archaea was not detected. The microbial community is was predominated
by[JH4] Clostridium sp. strain Z6. The H2
production was significantly improved by shortening the HRTs and increasing the OLRs. The HF-MBR had showed a
higher degradation potential and H2 production capacity at the high
OLRs due to its higher cell- retention. in the
bioreactor.[JH5]
Keywords: Membrane bioreactor; hydrogen production; organic
loading rate; food
waste
1. Introduction
H2 has enormous potentials as
a future clean
fuel of the future, which will create benefits for the economy promising significant
economic and as well as make
contribution to the protection of the global warming environmental benefits,
has enormous potential. World H2 production
is around 500 billion Nm3/year. Most of world H2
this is mostly
recovered from fossil fuels, such as typically[JH6] by steam reforming[JH7] of
natural gas and gasification of coal (Hart D 1997). The Water
electrolysis of water is has been
proposed as a alternative greener recovery methods alternative[JH8] , to
recovery H2 but the process is costly. to run.[JH9] Therefore Consequently, both H2
production approaches
that are both environmentally friendly and cost effective approaches
for its production have been more important coveted and pursued.
Anaerobic digestion of organic wastes will be a the best
option to produce for production of biogas
and reduce reduction of
environmental pollutions, during the gasification,
especially COx, CnHm and SOx, respectively during gasification.
In industrial wastes were
produced about 298 million tons of industrial wastes are produced every
year, 6.7% of which, i.e. or 20 million tons, were
from are food wastes. Most parts
of food wastes are generated by food manufacturers, and
restaurants, and hotels, including and include unsold
food and lunch boxes at supermarkets and convenience stores, all of which
are incinerated or go to landfills (BJCS, 2004). On the other hand, it is
noticed that tThe high water content of food
wastes, however, will be make them good
choice suitable for
bio-gasification, which is accomplished by by
means of fermentation technology.
In
the anaerobic fermentative pathway, H2 is an intermediate metabolite
converted from the complex organic materials for bi-products of the biochemical
degradation process under oxygen-free conditions in the liquid
phase. Theoretical H2
yields can be obtained with the maximal
4 moles together with 2 moles of acetic acid as the carbohydrate
fermentation end products from the fermentation
process of carbohydrate (Hawkes et a., 2007). Fang
et al. (2006) reported that the achievement of H2 production
from soluble wastewater including rice slurry has been achieved
in a continuous stirred tank reactor (CSTR) using anaerobic mixed microflora. The Ppotentials
of fermentative H2 production from organic wastes such as bean curd
manufacturing waste, rice bran and wheat bran was were investigated
using by batch
experiments (Noike et al., 2000). Generally, H2 production by
anaerobic microflora can be influenced by environmental conditions such as the organic loading rate
(OLR), HRT, pH,
mixing intensity, nutrients and temperature. It is has been pointed out determined that low H2 production in
continuous cultures was is due to the cell
wash-out and the unstable cell levels
in
the operational condition such as under shorten HRT and solids retention time (SRT) [JH10] conditions.[JH11]
TheCell
retention techniques of cells has been
focused on have
been topics of research interest for their application to the continuous
H2 fermentation process, which provides high H2
production in the acidogenic phase from the hydrolysis of the complex
organic materials, compared with the
continuous-flow
systems like such as CSTRs.
Various Ccells
retention of various types techniques has have been
applied to the wastewater treatment in
fermentation processes such as granular sludge bed,
the attached anaerobic reactor and MBR (Akutsu et al., 2009; Rachman et al.,
1998; Lee et al., 2006; Gavala et al., 2006,; Kim et
al., 2008). Among
cell retentions,[JH12] The membrane MBR
process is an extremely useful technique[JH13] which for
selectively separates separation
of the requested materials via membrane pores, and is widely
used in various fields including waste treatment, purification, and enrichment
(Nomura et al., 2002). In the fermentation process, the membrane
provides for excellent
organic acid/bacterial
cell separation efficiency, between
organic acids and bacterial cells, reflecting the MBR’s higher
biogas recovery efficiency compared with the
conventional continuous
stirred tank reactors (CSTRs)[JH14] (Keith et al., 1995). Our previous study
investigated the characteristics of fermentative H2 production at
various solids retention time (SRTs)
at under the
mesophilic condition using in a submerged membrane
bioreactor MBR (Lee et al., 2010b).
Sustainable CH4-free H2
production with CH4-free was
observed at for long SRTs with the
control of pH (5.5) in the a mixed
culture.
However, fermentative H2
fermentation in an MBR (HF-MBR) from with high-solids-content food
waste with high-solids content has not been yet to be
reported. yet.
As such, currently there
is no information available
on the feasibility of
long-term continuous HF-MBR operation with food
waste. The drop of the
pPermeate
flux drop by
membrane clogging and the change of bacterial community alteration by
solids retention [JH15] will be are
serious obstacles for to
continuous operation (Hawkes et al., 2007; Lee et al., 2008). No
information is available on the possibility of long-term operation in a
continuous H2 fermentation in MBR from food waste.[JH16] Therefore,
iIt is
necessary,
therefore, to find that the important[JH17] key to achieve[JH18] sustainable H2 production
in a HF-MBR be found. To that end, Tthe
objective of this the present study
was, first, to confirm
the possibility of
long-term stability stability of continuous HF-MBR
from TS 4.5% TS using fermentative anaerobic
bacteria and,
second, to investigate the pertinent H2
production capacity at various organic loading rates (OLRs).
2. Methods
2.1 Inocula and feedstock
Seed sludge was taken at from a digester
storage tank in in the a CH4
fermentation plant for the combination combined
treatment of food waste and sewage sludge. Anaerobic sludge was acclimated with
food
waste slurry of TS 4.1% TS food waste slurry (FWS) in a
CSTR which that was operated had been in operation[JH19] beyond for more than two
years. The pH, VS, and alkalinity of sludge
the acclimated
sludge were
5.5, 38,100 mg/l and 1,650 mg CaCO3/l,
respectively. The microbial community is was
dominated by Clostridium sp. strain Z6.
Food wastes were collected from a cafeteria at the National
Institute of Environmental Studies, which consisted consisting of a
great of variety of grains, vegetables, meats and fishes.
As shown in Fig. 1, the food wastes were inputted loaded into the bioreactor
after only once-per-week mechanical pretreatment
using a circulation pump with and a
cutting apparatus. once a week. TS
concentration in 4.5% TS food
waste slurry ranged from 4.5% was prepared by the
dilution of tap-water and crushed crushing with the a
cutting pump at a vacuum liquid circulation of
100 L/min and
dilution with tap water to maintain a particle
size of 5mm (Zenoah, Model: KD50MS). The pH in the FWS was in range of maintained at 4.3 ± 0.1. The characteristics of the FWS used in
this study[JH20] are represented listed in
Table 1. The VS/TS ratio was 0.96 ± 0.019.
2.2 Operation of HF-MRB
The laboratory-scale submerged
MBR of a laboratory-scale is shown in Fig.
1. The 5 L volume rectangular
bioreactor, which was made from an acrylic resin, with a
total volume of 5 L, has been employed for install was designed for two membrane
modules. Each module (module size: 240 ´ 340 ´ 10 ㎜) consists of The a membrane was a
plate-flame-type membrane and the situated in a membrane cartridge was produced
by Kubota.. The membrane Each membrane
had
has[JH21] a pore size of 0.45mm and an effective surface area of 0.1㎡.
per
membrane module (module size : 240 ´ 340 ´ 10 ㎜).
Two
membrane The modules were submerged in the bioreactor at intervals of
10 mm apart between membrane modules into bioreactor
to effectively brush away solidss fractions attached
on the membrane surfaces. [JH22]
As shown in Table 1, a
semi-continuous operation was employed conducted for the
reduction of organic factions under the thermophilic temperature of 55± 0.5℃, which temperature was maintained constant by means of circulating
water using within a water
jacket surrounding surrounding the
bioreactor. to keep
a constant temperature desired. The MBR was operated at various
OLRs of 70.2, 89.4 and 125.4 kg-COD/m3/day, corresponding to HRTs of
18.7, 14.0 and 10.5 hrs, respectively. The HRT-reducing Ffeeding
periods for reducing HRTs were increased stepwise incrementally from
24 and and 48 to 96
cycles per day, corresponding to fed and non-fed periods;: the
1 min-On and 59 min-Off, 2 min-On and 28 min-Off, and finally 3 min-On and 12
min-OFF, respectively. To minimize cake formation on the membrane, firstly, coarse
bubbles using a biogas re[JH23] circulation pump (T.G.K:
FP-15N) in the headspace
of the bioreactor
were
supplied coarse
bubbles under to the underside of each membrane
module at the flow rate of 3.5 L/min; using a biogas
circulation pump (T.G.K: FP-15N), and
secondly, permeates were intermittently
extracted by a vacuum pump controlled by a programmed timer
(TERAOKA, timely-S). TThe Food
waste slurry FWS, additionally, was also
semi-continuously fed into the bioreactor in parallel
with the extraction of the permeates at the
regulated time using peristaltic pumps.
In
order Tto avoid prevent the
excessive biomass
accumulation, of biomass in the
bioreactor[JH24] , the HRT/SRT
ratios were maintained to at an equal equivalent value
of 0.25 for each experimental condition, and the wasting of suspended surfeit sludge
was carried out eliminated by as
overflowing when new feed
was fed into the bioreactor.
The suction pressure of the membranes was monitored
using a vacuum gauge, and flux obtained through the permeate
line was continuously measured in order to
maintain stable HRTs for the different experimental
runs. The pH in the mixed culture was controlled by by
means of a pH controller (Mettler Toledo,
pH 2050e) using incorporating 2.0 N
NaOH to maintain the pH[JH25] value in range of at[JH26] 5.5±0.1.
2.3 Microbial community analysis
The predominant bacterial type was investigated determined by the
16S rDNA sequence analysis. The DNA was extracted from the mixed liquid in the
HF-MBR and purified using extrap solid DNA kit plus by the QProbe-PCR (polymerase chain reaction)
method (J-Bio 21, Japan) using an extrap[JH27] solid
DNA kit plus. The concentration in the extracted DNA solution was
measured by using a Picogreen dsDNA assay kit
(Invitrogen). The volume of the purified
DNA solution was 50 mL, and
the concentration of that[JH28] was 32.1g ng/mL. The PCR
amplification of 16S rDNA sequences was carried out using the primer
sets of 27f (5’-AGAGTTTGATCMTGGCTCAG-3’) (Marchesi et al.,
1998) and Bac1392R
(5’-ACGGGCGGTGTGTAC-3’) primer sets[JH29] (Kirsti
et al., 2006). The cycles of PCR cycles, performed with an
automatic thermal cycler iCyclerTM (Applied Biosystems), were determined according to results obtained from the monitor of a QPrimer-PCR: . PCR was performed with an automatic thermal cycler
iCyclerTM (Applied Biosystems) using the
following thermal program: an
initial denaturation at 95 oC for 30 sec, 20 cycles of
denaturation at 95 oC for 15 sec, annealing at 50 oC
for 20 sec, and extension at 72 oC
for 50 sec, with a final hold at 40 oC
for 30 sec.
The
amplified-PCR products of 16S rDNA were cloned using a TOPO TA PCR cloning kit (Invitrogen),
according to the manufacturer’s
instructions. A total of 32 clones were isolated and
classified. The PCR products were purified and sequenced using a BigDye Terminator v3.1 Cycle
Sequencing Kit (Applied Biosystems) and a model ABI3730xl sequencer (Applied
Biosystems). Comparative analyses of the full-length sequences were carried out
by the
BLAST search. The sequences
of the[JH30]
closest sequences were retrieved from GenBank.
2.32.4 Quantitative analysis by real-time
PCR
The DNA for the quantitative analysis of
acidogens and methanogenic archaea was extracted by the same procedure as
described in sSection 2.2[JH31] . The copies copying of 16S
rRNA gene originated originating from the acidogens
and methanogens was performed with the
LightCycler 1.0 (Roche Diagnostics). The primer sets for the dominated dominant
acidogens were Bac105YF and Bac1392R (Ritalahti et al., 2006). The PCR program process[JH32] for the quantification of acidogens consisted of a DNA
denaturation step at 95 oC for the initial
120 sec, 50 cycles of repeated denaturation at 95oC for 15 sec, annealing
at 61oC for 20 sec, and extension at 72oC
for 25 sec. The primer sets for the dominated dominant
archaea were ARC787F and ARC1059R (Yu et al., 2005). The PCR condition process was as
follows: initial denaturing step for 120 sec at
95oC, followed by 60 cycles of denaturation at 95 oC for
10sec, and annealing
30sec
at 60oC for 30 sec. The
standard curves for
the acidogens and archaea was were determined from the PCR product amplification
of
PCR products using the genomic DNA of the Escherichia coli K12 (ATCC 10798) and Methanobacterium bryantii M.o.H. (ATCC
33272), respectively, as the standard DNA (R2
= 0.9992).
2.42.5 Analytical
methods
The biogas contents, including H2, CH4,
CO2 and N2, were analyzed using a gas
chromatograph equipped with a thermal conductivity detector (GC-8A, Shimadzu)
and a φ 3㎜ ´ 2 m
stainless column packed with ShinCarbon ST 50/80 mesh (Shimadzu GLC Ltd., A The flow
rate of argon, as
the carrier gas, was 50ml/min. Lactate
assay kit (BioVision, volatile fatty acids (VFAs)
and the alcohol were analyzed using a gas chromatograph (GC-14B, Shimadzu Co.,)
equipped with a flame ionization detector (FID) and a Stabilwax-DA capillary column
(30m ´ 0.53 mm ID, method of phenol
sulfuric acid method (Dubois
et al., 1956). The protein was analyzed using the Lowery method (Protein assay
kit, C,). The
total nitrogen (TN), total phosphate (TP), NH4-N and PO4-P
were determined by using an auto-analyzer TrAACs 8000 using equipped with[JH35] a colorimeter (Bran + Luebbe K.K., Japan).
The TS, VS
and alkalinity were analyzed according to standard methods (APHA, 1995).
3.
Results and discussion
3.1 Behavior Characteristics[JH36] of H2
productions
The OLRs
gradually increased in three stages at under each
experimental condition when the fermentation parameters,
including biogas production, VFAs concentration and VS concentration,
reached at the steady-state conditions.
It was observed that, as the OLRs increased, there was continuous excessive
foaming continuously occurred through the biogas
diffuser under the membrane module, resulting from
the physiological changes of the anaerobic
microbial consortium. when OLRs increased.
Biogas flow rate was temporarily regulated[JH37] between 2 and 3 l/min to prevent the
damage of to the biogas recirculation
pump without the when there was no
addition of anti-foam reagent.
Figure.
2 shows the variation of the biogas production and
biogas contents. The fluctuation in
biogas production was somewhat observed only slight, due to little change in permeate
flux[JH38] . The margins of
error in the permeate flux was were[JH39] less than 1.3%. Biogas production was
gradually increased incrementally with the increase of increasing OLRs, in
steps, which was and stably continued during
the given operational periods. At variable
OLRs As the OLRs were increased
from 70.2 to 125.42 kg COD/m3/day, the biogas productions, s
at various specific OLRs,
were 22.4 ± 1.5, 32.8 ± 1.8 and 62.5 ± 3.7 l/day,
corresponding to 9.9 ± 0.6, 15.6 ± 0.9 and 31.1 ± 2.7 l-H2/day. when OLRs increased from 70.2 to 125.42 kg COD/m3/day. At the OLR of
70.2 kg-COD/m3/day, the content of[JH40] biogas produced was mainly composed mainly of H2 of
(at 44.1% ± 1.3%) and CO2
of
(at 46.1% ± 1.3%),. respectively.
At OLRs between 89.37 and 125.42 kg-COD/m3/day, the H2
content slightly increased from its level at the 70.2 kg-COD/m3/day
OLR, H2 content slightly increased in from the
range of 47.5% - to 48.5%. as
compared with that in the
OLR of 70.2 kg-COD/m3/day.
This
result showed that H2
production with MBRs was is favorable for high OLRs and
shortens HRTs.
Sustainable H2
productions with in the MBR
under thermophilic
conditions [JH41] was achieved at considerably higher
OLRs and under lower HRTs
compared to with
previous studies reported reporting from on
food wastes (e.g.[JH42] Kim et
al., 2008). The CSTR, indeed, has
been widely applied at under various operating
conditions due to its simple design to control system[JH43] . However, the cell retention in the
CSTR is the CSTR’s limiting factor because is cell retention, in
that HRTs are equal to SRTs. The washout of cells in
the bioreactor is frequently occurred occurs at low
HRTs, and the
the result being the
failure of the H2 production process. is
resultingly fail. Particularly Specifically, H2
fermentation from organic solids is very poor in the
CSTR, is very
poor due to low degradation of organic fractions and the aforementioned washout
of cells. Kim et al. (2008) suggested that continuous H2
fermentation using an anaerobic sequencing batch
reactor (ASBR) provides for cells retention
in the bioreactor by means of the
control of the SRT, independent
from that of the HRT.
From the point of biotechnology-based
viewpoint, MBRs will be new
challenge to represent the future of develop the
fermentation technology development for bio-energy recovery[JH44] . MBRs lead to allow for the enhancement
of the
completed retention in organic solid fractions and microorganisms, which could
result in can increasing increase the
H2 production from the hydrolysis of organic fractions. in the
bioreactor[JH45] . The HRT/SRT
in the MBR will be are one of the important
factors to
improve for improvement of the
membrane permeability
of
membrane and reduce the reduction of membrane biofouling. of
membrane.
In the
present study, the
permeate Fflux
was increased from 0.6 and 0.8 to 1.0 l/㎡/day in order to maintain[JH46] the HRT within range
of the 18.67-10.5 hr range. The permeate
flux was monitored to security the margin of error (±1%) in HRT several times a per day.[JH47] A relatively flux was
stably[JH48] maintained at OLRs
between 70.2 and
89.37 kg-COD/㎥/day; where an
unstable flux was
evident at at the OLR of 125.42 kg-COD/㎥/day, was observed
due to the drop of the permeate flux by resulting from
membrane bio-fouling. After 91 days of operation[JH49] , the permeate flux was rapidly
decreased from 1.0 to 0.2 l/m2/hr (figure not shown) and, due to
the pressure difference across the membrane surface resulting from the
formation of a cake layer, the a biogas
bubble in the permeate line was observed formed. due to
the pressure difference across membrane surface by the formation of cake layer.
From this result Nonetheless, the feasibility of long-term
(90 days) HF-MBR operation
of
90 days using the HF-MBR was confirmed, which fact can
bolsters the
possibility on a of sustainable H2
production from organic fractions of municipal solid waste. The permeate
extracted from MBRs could be further application applied in to
bioenergy recovery processes, for the to photo-H2 production
by photosynthetic bacteria, or for to CH4 production (using via wet-
or dry fermentation) by methanogenic bacteria.
3.2
Organic matter removal
Tables 2[JH50] shows the changes of the COD,
carbohydrate and protein concentrations in the permeate, for reflecting the
HF-MBR’s
performance from for food waste of TS
4.5% TS food waste. The Aaverage
CODcr, carbohydrate, and protein concentrations in the
influent was were 52.7 ± 2.8, 17.7 ± 0.4
and 11.35 ± 0.5 g/L, respectively.
The carbohydrate removal
efficiencies of carbohydrate in permeate[JH51] were beyond 97%, ranging from 0.56 ± 0.08 to 0.66 ±
0.03g/l, for all of the different[JH52] OLRs. The Pprotein
concentrations in the permeate
ranged from 0.48 ~ to 0.83g/L, representing nearly the maximal
95.7% of removal efficiency, throughout the experimental
runs. The VS concentration
of
VS in the bioreactor was stably kept maintained at 5.96 ± 0.28%, which
corresponding to a nearly 1.38 times increase over
that in the influent. A The solids
fraction in the feed was completely separated by with the
membrane pore size of 0.4 mm.
However, organic fractions derived from biofilm formation of a
biofilm was were observed in the
permeate line for the operational
periods, as a
result of owing to the
long retention of soluble substances filtered inside the membrane
module,, when an itself caused by an
increase in pore size caused by resulting from the predominance of the thermodynamic
effect. is
predominant. Membrane permeability for operation has gotten better at shorten
HRT of 10 hr without the discharge from any ones.[JH53] Notably, it was observed that the a swell in a flat sheet of the membrane
module was unavoidable for the during idle time of membrane operation,[JH54]
ranging from 29 (R 2) to 59 (R 1) min, to minimize membrane clogging by the
attachment of solids fraction of membrane performance and membrane module for
the idle time of 15min (R 3) was relatively stable.[JH55] It can
be thought considered, then, that it needs to develop
a suitable membrane material and its together with its module
configuration needs
to be developed for the thermophilic fermentation process. The membrane module should be also provided offer high-permeability and high-temperature durability in order so as to maintain long-term process stability. in the
process. The VS/TS ratios in the feed were within range of the 0.94 ~ 0.96 range, which indicated indicating that the food waste occupied had a high degradable degradability content. The VS/TS ratio in the HF-MBR was
reduced from 8.6 to 9.2%
as compared with that in the feed[JH56] . This result shows
that the reduction of the VS was achieved at over long
solids
retention SRTs[JH57] in the
membrane bioreactor and
could be more better converted into biogas
via hydrolysis at under a the
thermophilic condition of 55℃. Under
thermophilic conditions, the hydrolysis rate is higher
than that that in under
mesophilic conditions. Therefore, the
HF-MBR could tolerate a larger loading of organic solids. In general,
hydrolysis of particulate organics in the fermentation process depends
upon is a function of
operational
parameters including temperature, pH, HRT and substrate concentration. If the hydrolysis
rate is the a first-order reaction about for biodegradable organic matters[JH58] , it could can be
expressed as equation (1). in the HF-MBR[JH59] . Under steady-state conditions, the change of MLSS (P) is[JH60] almost zero. Accordingly,[JH61] Hhydrolysis
constants (k) were observed at 0.9, 1.2 and 1.6 (1/d), respectively, when the OLRs were increased.
(1)
(2)
where k is the reaction rate
constant., P is the VS
concentration in the
bioreactor., and Pi is the VS concentration in the
influent.
In the present study, the MBR
could easily improve the retention of biomass in the bioreactor[JH62] independently of HRTs for over
long-term operations,. which are This is the
suggested as a means to of obtaining the efficient H2
production, by that
is, via the degradation of
organic solids fractions and the fermentative pathways
of bacteria. from the
degradation of organic solids fractions.
3.3 Metabolites products
In the anaerobic fermentation, H2
is the intermediate product which that is positively correlated with the pathway
of liquid-phase byproduct butyric acid and acetic acid metabolic[JH63] pathways. as byproducts in the
liquid phase[JH64] . The Ttotal
metabolites observed in the present experimentation were
increased from 15,399 mg/l and 19,268 mg/l to 20,933 mg/l with the increase of the OLRs, as
shown in tTable 3. The major metabolites
produced from by the degradation of the organic
fractions in the food waste were, in fact, acetic
acid and butyric acid., Aacetic
acid ranged ranging from 11.8 to 15.1% and
butyric acids accounted for from 24.4 ~
27.9% range of the total metabolites, based on
CODcr[JH65] . Propionic acid accounted for around 1.8 ~
2.1% range when the OLRs were between
70.2 and 89.4 kg-COD/m3/day, and was decreased to 0.8% when
the OLR was increased
to 125.4 kg-COD/m3/day. Among the soluble metabolites, Llactic
acid occupied fell in the range
of 24.2 ~ 25% range among the soluble
metabolites for each all of the OLRs; and
its concentration was little increased with increase of increments in the OLR. The H2 fermentation pathway was
dominantly,
regardless of being in the form of lactic acid at high OLR levels. of OLR. [JH66] Lee et al., (2010b)
reported that their low H2 yield[JH67] was due to the metabolic pathway shift to
lactic acid under
SRT[JH68] . In the present study, the Iincrease
in H2 production was accomplished by the cell
retention under effected by the
regulation of the SRT.
The deficiency of the iron concentration in
food wastes will be is a
significant factor determining the formation of lactic acid. From
these According to the experimental
results, the increased in
H2 production was resulted in less lesser
production of propionic acid as well as more greater
production of acetic acid and butyric acid., It
indicates indicating that optimized the OLR in
a MBR needs to be optimized in order to improve
H2 production and avoid producing the
butyrate-propionate via the fermentation pathway.
The effect of H2 production on the metabolic
pathway has been studied in previously. other
studies. Many researchers have been used employed the
butyric acid/acetic acid (B/A) ratio as the quantitative indicator for
inspecting of the H2
production pathway of the anaerobic bacteria. In the present
study, the B/A ratio, based[JH69] on the molar basis, was in the range
of 1.65 ~ 1.7 range, which was
observed almost the and showed similar[JH70] values at all each of the OLRs.
The molar B/A ratios
were relatively high compared with the values[JH71] reported of for
thermophilic H2 fermentation from food waste of TS 10%
TS food waste in our
previous study (Lee et al., 2010a). It These results
indicated that the optimal B/A ratio in the H2
fermentation is different differs depending
on according to the cultivation
conditions including culture, temperature and substrate conditions of cultivation. Chen
et al. (2001) demonstrated the relationship between the
B/A ratio and rH2 on in H2 production from a sucrose substrate. as
substrate[JH72] . Kim et al.
(2006) reported that the B/A ratio was beyond over 4.0
when the sucrose
concentration was beyond more than
20g-COD/l, which conditions provides for favorable H2-producing
metabolism in a CSTR[JH73] . Han and Shin (2004) reported that H2
production deteriorated when the B/A ratio was low (1.3)[JH74] . In this the present study,
the B/A ratio from food waste of TS 4.5% TS food waste was mainly
observed mainly at in the stable
range at under all of the experimental
conditions. This result indicates Therefore it could be
concluded that that the
metabolic pathway from the carbohydrate-rich food waste in the thermophilic
HF-MBR kept maintained the the optimal B/A ratio[JH75] for effective H2 formation due
to the security effectiveness of the active
cell retention in the
bioreactor[JH76] at at high OLRss
and shortens short HRTss.
3.4 H2
yield
The A good correlation between the H2
yield and the OLRs
was found with the H2
conversion in range of in the 10.4 ~
18.4% H2 conversion range, and
the efficiency of H2 production which was a the result
of the a change
in the metabolic
pathway during the biodegradation of food waste, as shown in tTable 3.
OLR
of The 125.4 kg-COD/m3/day
OLR allowed
for the large
amount
of high H2 production
and as well as for a the high
quality of the permeate.
The H2
yields, with rising OLRs, increased
from 1.24 to 2.2 mol-H2/mol-hexose added, with
increase of OLRs, which is a higher value compared
with than achieved in our
previous studies study[JH77] (Lee et al., 2010a). As mentioned in sSection
3.2, the increase
in H2 increase was resulted
from the result of the
degradation of organic waste via hydrolysis, which was effected by
maintaining a higher
microbial cells count. The incubation
temperature of 55oC could also could enhance
the substrate utilization
rate of substrate and the decrease of the
dissolved H2 concentration in the liquid phase (Duran and Speece
1997; Mu et al., 2006). In tTable 5, shows that the H2
yield using an ASBR was in ranging of around 80.9
ml-H2/g-VS at the HRT of 33 hr using food waste of VS
4.4% VS food waste (Kim et
al., 2008). The Ccarbohydrate-rich
biomass, via nitrogen or protein
replenishment in sewage sludge, could successfully increased
the H2 yield by the replenishment of sewage
sludge as nitrogen or protein source[JH78] (Kim et al., 2004; Kim and Lee.
2010a). Therefore, cContinuous
H2 and CH4 fermentation in a two-stage
process using including recirculation
of digestion sludge, was significant therefore, meaning for
improving can effectively improve H2
yields. Zhu
et al. (2008) also demonstrated that an enhanced H2
yield, 112ml-H2/g-VS, was
enhanced by the co-digestion of food waste,
primary sludge and waste-activated sludge, which
gave the H2 yield of 112ml-H2/g-VS based on specifically a combination of feed and 250 ml-H2/g-VS
based on food,. respectively.[JH79] This result indicates that the feed stocks
replenished contained nitrogen, metals and
carbonate alkalinity, which is have important roles in improving
H2 yields. It is interesting to note that, H2 yield
in the HF-MBR was similar value of 111.1 ml-H2/g-VS but high H2
production rate was achieved at 10.7 l-H2/l/d compared with the
previous other study using CSTR.[JH80] This result[JH81] inflected is an important
illustration of the fact that H2
yields using from MBRs can be significantly
can
increased at the
high OLRs and short HRTs without the addition of adding waste-activated
sludge, sewage sludge or primary sludge. HF-MBRs have the high
recovery potentials on in H2 formation via
enriched bacteria at
the higher loading capacity from the complex organic waste[JH82] . The retention of bacterial cells will be a crucial
key factor for improving H2 production from the high-organic
solids.
3.5 Microbial community analysis
The clones developed
from the sample were classified into three operational taxonomic units (OTUs).
Table 3 shows that the three OTUs were closely related with to
Clostridium, Thermoanaerobacterium, and Lactobacillus, respectively. The
microbial community under the thermophilic condition of 55oC was
less diverse, even though a food waste as complex substrate food waste was fed., It
reflects evidencing that acidogenic bacteria demand
high maintenance energy as well as nitrogen and phosphorus
sources at high cultivation temperatures (Ziner
et al., 1986).
The microbial community is was predominated
by Clostridium sp. strain Z6, that which was affiliated related to to 93.8 %
among of the 32
clones, which that, together
with acetic acid and butyrate as intermediate products, play
an important role for in the production of H2. together
with acetic acid and butyrate as intermediate product. 3.13%
of total clones were affiliated to the
Thermoanaerobacterium
thermosaccharolyticum, which is known as an H2-producing
bacteria in the thermophilic acidogenic
fermentation, was related
to 3.13% of the clones. The
genus Thermoanaerobacterium, as a gram-type positive[JH83] , is are thermophilic
anaerobes. T.
thermosaccharolyticum can produce large amounts of H2
via the acetate-butyrate
fermentation pathway at pH range of in the 5 - 6 pH range and at the
cultivation temperatures of between 55 - and 60oC
(Ueno et al., 2001;
Akutsu et al., 2008). It has been reported that the H2 yield by T.
thermosaccharolyticum is almost equal that by Clostridium butyricum (Shin et al., 2005). The rest remaining 3.13% of the
clones was were related to Lactobacillus
helveticus, which is well known as the bacteria for lactic acid
production. L. helveticus can
attain a high
conversion efficiency into for lactic acid at a temperature
of 42oC and a pH of 5.7 (Roy et al., 1986;
Chiriani et al., 1992). It might be concluded, then, that Lactobacillus is not going to cannot
contribute to increasing higher H2
production rates (Jo et al., 2007). In fact, H2
production via the formation of lactic acid may could be as difficult
as that
given indicated in
equation (3). On the other hand However, Yang
et al. (2007) reported that high H2 production from cheese-processing
wastewater was observed
at
the presence of when the genus Lactobacillus was predominant over over Clostridia in the bacterial
community.
Glucose à 2Lactic acid (3)
In
general, the bacterial population depends on the is a
function of cultural culture conditions such as
temperature, pH, substrate and reactor type. Shin and Youn (2005) reported that
T.
thermosaccharolyticum dominated, as in fact was the only species
at pH
the 5.5±0.1 pH and temperature of
a 55±1oC temperature in a CSTR.
Kim et al. (2006) demonstrated that microbial communities under sparging
of CO2 sparging were simplified as three species of C. tyrobutyricum, C. proteolyiticum and C.
acidisoli[JH84] ., And but the did not observe any change
in the bacterial population by N2 and internal biogas sparging. was not
observed. Akutsu et al. (2008) reported that an H2
yield of 2.32 mol-H2/mol-glucose was obtained in thermophilic H2
fermentation from starch using a batch feeding reactor and that the
Thermoanaerobacterium was predominant
over Clostridium from for
different seed sludges including waste-activated
sludge, cattle manure and acidified potato. The Clostridium was
dominated from in seed sludge in the of co-digested of the night
soil[JH85] and municipal organic waste. In the
present study, the thermophilic HF-MBR was
commonly mostly was dominated
by the genus Clostridium, compared
with similarly to
the result reported in for the mesophilic condition (Oh et
al. 2004), due to the fact that the cultivation conditions were
operated at similar pH in the range of
pH likewise was controlled within
the 5.4 ~
5.6 range[JH86] . (Oh et al. 2004). Both Clostridium and Thermoanaerobacterium, as the H2
producers,
contributed largely to improving the improvement of the H2
productivity from by the degradation of food
wastes.
The concentrations of the 16S
rRNA genes of acidogenic bacteria and methanogenic archaea, at the OLR of 125.4
kg-COD/m3/day, was were quantified by
real-time PCR as shown in table 6.
It was and are expressed by in
Table 6 as the Nno. of copies per 16S
rRNA and per sample of ml, respectively. Acidogenic bacteria accounted for around
1.09 ´ 108 copies/mg-VS (3.25 ´ 107
copies/ml-DNA), and whereas methanogenic
archaea was below the detection limit (1.03 ´ 101
copies/ml-DNA). This result indicated showed that the
population level growth of methanogenic archaea
was completely inhibited by the control of a the pH range
of at 5.5±0.1, regardless of the organic
solid accumulation and retention in the bioreactor. In conclusion, the
microbial community in the thermophilic HF-MBR was favorable effectual to for sustainable H2
production despite microbial[JH87] contamination from the complex organic waste.
4. Conclusions
Continuous H2 production by MBR from food
waste of TS 4.5% TS food waste was
successfully achieved for 90 days with CH4-free biogas at a pH control
of 5.5±0.1. in the
bioreactor.[JH88] The maximal H2 yield and H2
production rate were 111.1 ml-H2/g-VS added[JH89] and 10.7 l-H2/l/day, respectively, at an OLR of
125.4 kg-COD/m3/day. The aAcetate
and butyrate, as the major
metabolites, were produced
from the degradation of the food waste. The Ttotal
carbohydrate degradation efficiency was beyond 96% throughout the experimental
runs. The copy number of acidogens 16S rRNA genes at the OLR of 125.4
kg-COD/m3/day was 3.25 ´ 107
copies/ml-DNA, and
whereas[JH90] that of archaea was below the detection
limit. The
microbial community is was predominated by Clostridium sp. strain Z6, which, together
with acetic acid and butyrate as intermediate products, plays an
important role for in the production of H2. together
with acetic acid and butyrate as intermediate product. The The H2
production using
MBR from food waste as organic solids[JH91] was significantly improved by shortening the HRTs and increasing the OLRs. It This
indicated that the MBR, due to
its higher cell retention, had a
higher degradation potential and a better H2
production capacity at high OLRs. due to its higher
cell-retention in
the bioreactor[JH92] .
Akutsu,
Y., Lee, D.-Y., Chi, Y.-Z., Li, Y.-Y., Darada, H., Yu, H.-Q., 2009.
Thermophilic fermentative hydrogen production from starch-wastewater with
bio-granules. Int J Hydrogen Energy 34, 5061-5071.
Akutsu,
Y., Li, Y.-Y., Tandukar, M., Kubota, K., Harada, H., 2008. Effects of seed
sludge on fermentative characteristics and microbial community structures in
thermophilic hydrogen fermentation of starch. Int J Hydrogen Energy 33,
6541-6548.
Biomass
Japan comprehensive strategy (BJCS), 2004. 29 (in Japanese).
Chiriani,
L., Mara, L., Tabacchioni, S., 1992. Influence of growth supplements on lactic
acid production in whey ultrafiltrate by Lactobacillus
helveticus. Applied Microbiology and Biotechnology 36, 461-464.
Duran,
M., Speece, R.E. 1997. Temperature-stage anaerobic process. Environ Technol 18,
747-754.
Fang,
H.H.P., Li, C., Zhang, T., 2006. Acidophilic biohydrogen production from rice
slurry, Int J. Hydrogen energy 31, 683-692.
Gavala,
H.N., Skiadas, I.V., Ahring, B.K,. 2006. Biological hydrogen production in
suspended and attached growth anaerobic reactor systems. Int J Hydrogen Energy
31, 1164-1175.
Han,
S.-K., Shin, H.-S., 2004. Biohydrogen production by anaerobic fermentation of
food waste. Int J. Hydrogen Energy 29, 569-577.
Hart, D.,
1997. Hydrogen power: the commercial future of the “ultimate fuel”. Financial
times energy publishing, Lodon.
Hawkes, F.R., Hussy,
Jo, J.H., Jeon, C.O., Lee,
D.S., Park, J.M., 2007. Process stability and microbial community structure in
anaerobic hydrogen producing microflora from food waste containing kimchi. J
Biotechnol 131, 300-308.
Keith, B., Tom, S., 1995. The
application of membrane biological reactors for the treatment of wastewaters.
Biotech Bioengin 49, 601-610.
Kim, D.-H., Han, S.-K., Kim,
S.-H., Shin, H.-S., 2006. Effect of gas sparging on continuous fermentative
hydrogen production. Int J. Hydrogen Energy 31, 2158-2169.
Kim, M.-S., Lee, D.-Y., 2010.
Fermentative hydrogen production from tofu-processing waste and anaerobic
digester sludge using microbial consortium. Biores Technol 101, S48-S52.
Kim, S.-H., Han, S.-K., Shin,
H.-S., 2004. Feasibillity of biohydrogen production by anaerobic co-digestion
of food waste and sewage sludge. Int J Hydrogen Energy 29, 1607-1616.
Kim, S.-H., Han, S.-K., Shin,
H.-S., 2008. Optimization of continuous hydrogen fermentation of food waste as
a function of solids retention time independent of hydraulic retention time.
Process Biochemistry 43, 213-218.
Kim, S.-H., Hang, S.-K., Shin,
H.-S., 2006. Effect of substrate concentration on hydrogen production and 16S
rDNA-based analysis of the microbial community in a continuous fermenter.
Process Biochem 41,199-207.
Lee, D.-Y., Ebie, Y., Xu,
K.-Q., Li, Y.-Y., Inamori, Y., 2010a. Continuous H2 and CH4
production from high-solid food waste in the two-stage thermophilic
fermentation process with the recirculation of digester sludge. Biores Technol
101, S42-S47.
Lee, D.-Y., Li, Y.-Y., Noike,
T., 2009. Continuous H2 production by anaerobic mixed microflora in
membrane bioreactor. Biores Technol 100 (2): 690-695.
Lee, D.-Y., Li, Y.-Y., Noike, T.,
2010b. Influence of solids retention time on continuous H2
production using membrane bioreactor. Int J Hydrogen Energy 35,
52-60.
Lee, D.-Y., Li,
Y.-Y., Noike, T., Cha, G.-C., 2008. Behavior of extracellular polymers and bio-fouling during hydrogen fermentation with a
membrane bioreactor. J. Membr. Sci 32,
13-18.
Lee, K.S., Lo, Y.C., Lin, P.J.,
Chang, J.S., 2006. Improving biohydrogen production in a carrier-induced
granular sludge bed by altering physical configuration and agitation pattern of
the bioreactor. Int J Hydrogen Energy 31 (12), 1648-1657.
Marchesi,
J.R., Sato, T., Seightman, A.J., Martin, T.A., Fry, J.C., Hiom, S.J., 1998.
Design and evaluation of useful bactriu-specific PCR primers that amlilfy genes
coding for bacterial 16s rRNA. Appl. Environ. Microbiol 64: 795-799, Published
erratum 1998. Appl. Environ. Microbiol 64, 2333.
Mu. Y.,
Zheng, X.-J., Yu, H.-Q., Zhu, R.-F., 2006. Biological hydrogen production by
anaerobic sludge at various temeratres. Int J Hydrogen Energy 31, 780-785.
Noike, T., Mizuno, O., 2000. Hydrogen fermentation
of organic municipal wastes, Wat Sci Technol 42(12), 155-162.
Nomura,
M., Bin, Tang., Nakao. SI., 2002. Selective ethanol extraction from
fermentation broth using a silicalite membrane. Sep Puri Technol 27(1), 59-66.
Oh,
S.-E., Lyer, P., Bruns, M.A.,
Rachman, M.A., Nakashimada, Y., Kakizono, T.,
Nishio, N., 1998. Hydrogen production with high yield and high evolution rate
by self-flocculated cells of Enterobacter aerogenes in a packed-bed reactor.
App Micro Biotech 49, 450-454.
Ritalahti,
K.M., Amos, B.K., Sung, Y., Wu, Q., Koenigsberg, S.S., Löffler, F.E., 2006.
Quantitative PCR targeting 16Sr RNA and reductive dehalogenase genes
simultaneously monitors multiple Dehalococcoides
strains. Appl. Environ. Mcrobiol 72 (4), 2765-2774.
Roy, D., Goulet, J., LeDuy, A.,
1986. Batch fermentation of whey ultrafiltrate by Lactobacillus helveticus for lactic acid production. Applied and
Microbiology Biotechnology 24, 206-13.
Shin,
H.-S., Youn, J.-H., 2005. Conversion of food waste into hydrogen by
thermophilic acidogenesis. Biodegradation 16, 33-44.
Ueno, Y., Otsuka, S., Morimoto,
M., 1996. Hydrogen production from industrial wastewater by anaerobic
microflora in chemostat culture. J Ferment Bioeng 82 (2), 194-197.
Yang, P., Zhang, R., McGarvey,
J.A., Benemann, J.R., 2007. Biohydrogen production from cheese processing
wastewater by anaerobic fermentation using mixed microbial communities. Int J
Hydrogen Energy 32 (18), 4761-4771.
Yu,
Y.S., Lee C.S., Kim J.A., Hwang S.H., 2005.
Group-specific primer and probe sets to detect methanogenic communities using
quantitative real-time polymerase chain reaction. Biotechnol Bioeng 89. 670 - 679.
Zhu, H., Parker, W., Basnar,
R., Proracki, A., Falletta, P., BéLand, M., Seto, P., 2008. Biohydrogen
production by anaerobic co-digestion of municipal food waste and sewage sludge.
Int J Hydrogen Energy 33, 3651-3659.
Zinder, S.H., 1986.
Thermophilic waste treatment systems. In: Brock TD, editor. Thermopiles:
general, Molecular and applied biology.
Figure
legends
Figure 1 Schematic diagram of
experimental apparatus for submerged HF-MBR
Figure 2 Profiles of (a) biogas
production (a) and (b) biogas composition (b)
in HF-MBR
Figure 3 The cChange
of CODcr, carbohydrate and protein concentrations in the permeate
Fig.
1
Fig.
2
A
B
Fig.
3
Table
legends
Table 1 Characteristics of food waste slurry
Table 2 The oOperational conditions of the HF-MBR
Table 3 H2
production yields and metabolites at under different operational conditions
Table 4 The
cClosest relatives of 16S rDNA sequences retrieved from the
thermophilic HF-MBR
Table 5 Summary of comparable H2
yields from food wastes in different continuous systems
Table 6 The
qQuantitation [JH94] of acidogenic
bacteria and methanogenic archaea
Table 1
|
Characteristics |
Unit |
Average |
|
Total
solids |
% |
4.5 ± 0.3 |
|
Volatile
solids |
% |
4.3 ± 0.2 |
|
Total COD |
g/l |
52.7 ± 2.8 |
|
Total
carbohydrate |
g/l |
17.7 ± 0.4 |
|
Total
protein |
g/l |
11.4 ± 0.5 |
|
Total
nitrogen |
g/l |
2.22 ± 0.25 |
|
Total
phosphorus |
mg/l |
176 ± 16 |
|
NO3-N |
mg/l |
14 ± 4.8 |
|
NH4-N |
mg/l |
28 ± 7.4 |
|
PO4-P |
mg/l |
37 ± 8.3 |
|
pH |
- |
4.3 ± 0.1 |
Table 2
|
|
Parameter |
R 1 |
R 2 |
R 3 |
|
Membrane |
Type |
Plate & flame |
||
|
Material |
Polyethylene |
|||
|
Pore size |
0.45mm |
|||
|
Bioreactor |
Total volume (l) |
5 |
||
|
Temperature (oC) |
55 ± 0.5 |
|||
|
pH |
5.5 ±0.1 |
|||
|
HRT/SRT (-) |
0.25 |
|||
|
OLR (kg-COD/m3/d) |
70.2 |
89.4 |
125.4 |
|
|
HRT (h) |
18.67 |
14.0 |
10.5 |
|
|
Biogas bubbling rate (l/min) |
3.5 |
|||