TECHNICAL PAPER
ISSN 1047-3289 J. Air & Waste Manage. Assoc. 54:242–249
Copyright 2004 Air & Waste Management Association
Performance of an Innovative Two-Stage Process Converting
Food Waste to Hydrogen and Methane
Sun-Kee Han and Hang-Sik Shin
Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and
Technology, Daejeon, South Korea
ABSTRACT
This study was conducted to evaluate the performance of
an innovative two-stage process, BIOCELL, that was developed to produce hydrogen (H2) and methane (CH4)
from food waste on the basis of phase separation, reactor
rotation mode, and sequential batch technique. The
BIOCELL process consisted of four leaching-bed reactors
for H2 recovery and post-treatment and a UASB reactor for
CH4 recovery. The leaching-bed reactors were operated in
a rotation mode with a 2-day interval between degradation stages. The sequential batch technique was useful to
optimize environmental conditions during H2 fermentation. The BIOCELL process demonstrated that, at the high
volatile solids (VS) loading rate of 11.9 kg/m3䡠day, it could
remove 72.5% of VS and convert VSremoved to H2 (28.2%)
and CH4 (69.9%) on a chemical oxygen demand (COD)
basis in 8 days. H2 gas production rate was 3.63 m3/m3䡠day,
while CH4 gas production rate was 1.75 m3/m3䡠day. The
yield values of H2 and CH4 were 0.31 and 0.21 m3/kg
VSadded, respectively. Moreover, the output from the posttreatment could be used as a soil amendment. The
BIOCELL process proved to be stable, reliable, and effective in resource recovery as well as waste stabilization.
INTRODUCTION
The generation of food waste reaches 11,237 t/day in
Korea, accounting for 23.2% of municipal solid waste.1
Because of its high volatile solids (85–95%) and moisture
content (75– 85%), food waste causes decay, odor, and
leachate in collection and transportation. Most food
IMPLICATIONS
Because food waste is a major burden to the environment,
the landfill of food waste will be prohibited in 2005. Thus,
research on the recycling technology of this waste is a
major field of waste management in Korea. The innovative
two-stage process, BIOCELL, is an ideal method for treating food waste. The BIOCELL process was developed to
convert food waste to H2 and CH4 because H2 recovery
could improve the economic feasibility of waste treatment.
waste is consolidated with other wastes, resulting in various problems such as odor emanation, vermin attraction,
toxic gas emission, and groundwater contamination.
However, because food waste has a high energy content, it
seems ideal to achieve dual benefits of energy production
and waste stabilization. Anaerobic digestion is a preferred
method for resource recovery from food waste, because it
has several advantages, including volume reduction,
waste stabilization, and biogas recovery. In particular,
biohydrogen production from food waste has considerable potential to enhance the economic feasibility of
waste treatment.
Concerns about global warming have increased interest in hydrogen (H2) as a fuel. H2 is a promising alternative to fossil fuels because it has a high energy yield (122
kJ/g) and produces water instead of greenhouse gases
when combusted. In addition, H2 can be directly used to
produce electricity through fuel cells.2,3 H2 can be generated in a number of ways, such as electrochemical processes, thermochemical processes, photochemical processes, photocatalytic processes, or photoelectrochemical
processes.4,5 However, these processes require electricity
derived from fossil-fuel combustion; thus, they are energy-intensive and expensive. Biohydrogen production is
potentially attractive, especially if organic waste could be
used as the raw material.6,7 Microorganisms are capable of
producing H2 via either photosynthesis or fermentation.8,9 Fermentation is generally preferred because it is
technically simpler than photosynthesis and it generates
H2 from carbohydrate materials obtained as refuse or
waste products.10
Anaerobic bacteria use organic substances as the sole
source of electrons and energy, converting them into H2.
The reactions involved in H2 production (eqs 1 and 2) are
rapid and these processes do not require solar radiation,
making them useful for treating large quantities of wastewater by using a large fermenter.
Glucose ⫹ 2H2O 3 2 Acetate ⫹ 2CO2 ⫹ 4H2
⌬G ⫽ ⫺184.2 kJ
242 Journal of the Air & Waste Management Association
(1)
Volume 54 February 2004
Han and Shin
Glucose 3 Butyrate ⫹ 2CO2 ⫹ 2H2
⌬G ⫽ ⫺257.1 kJ
(2)
Because organic substrates cannot utilize light energy,
their decomposition is incomplete, and organic acids remain. Nevertheless, these reactions are still suitable as an
initial step of H2 production from waste, which is followed by methanogenesis. A two-stage process is, therefore, a rational configuration because it provides the preferred environments for acidogenic hydrogenesis and
methanogenesis in two separate spaces.
Figure 1 shows the innovative two-stage process,
BIOCELL. The BIOCELL process comprises two main
parts: four leaching-bed reactors for H2 recovery and posttreatment and an upflow anaerobic sludge blanket (UASB)
reactor for CH4 recovery. H2 fermentation in a batch
reactor is highly feasible because the process operation
is simple and the treatment cost is low.11 Thus, four
leaching-bed reactors are employed as H2 fermenters. The
leaching-bed reactors are operated in a rotation mode
with a 2-day interval between degradation stages. A UASB
reactor continuously converts chemical oxygen demand
(COD) materials from the leaching-bed reactors to CH4.
Effluent from the UASB reactor recirculates through the
leaching-bed reactors as dilution water. A portion of the
effluent is replaced periodically with fresh water so as to
reduce the concentration of inhibitory materials in dilution water. Meanwhile, residues are treated in the same
leaching-bed reactor without moving to another posttreatment facility. Residues are dewatered by gravity in
the reactor for 3 hr, and then 15 L/min of air is introduced
through the bottom of the reactor for 45 hr.
The primary factor in treating food waste is the physicochemical characteristics of substrate, including particle
size and composition. The reduction of particle size to
improve hydrolysis and liquefaction is costly, and its effect in the leaching-bed reactor is open to discussion.12
Degradation of each component of food waste is affected
by environmental conditions. Carbohydrate, cellulose,
and protein have their own optimum pHs and retention
times for degradation. This means that the degradation of
food waste could be enhanced by adjusting the environmental conditions depending on the state of degradation.
A leaching-bed reactor is, therefore, operated in a sequential batch mode to improve environmental conditions
during H2 fermentation. Seed sludge [10% volume/volume (v/v)] is boiled for 15 min and then inoculated into
the reactor. A heat-shock treatment is conducted to inhibit hydrogenotrophic bacteria and to harvest anaerobic
Figure 1. The BIOCELL process.
Volume 54 February 2004
Journal of the Air & Waste Management Association 243
Han and Shin
spore-forming bacteria (i.e., Clostridium sp.).2,13 After 6 hr
of acclimation, dilution water is delivered to a leachingbed reactor. Dilution rate (D; day⫺1) is equal to volumetric flow rate of dilution water (L/day) divided by working
reactor volume (L). Proper D control could make the environmental conditions favorable to microbial growth
during H2 fermentation. In the initial stage, rapidly
degradable matters (e.g., carbohydrates) are likely to
cause pH drop and product inhibition.14 Initial D
(4.5 days⫺1) is, therefore, maintained relatively highly
to move produced volatile fatty acids (VFA) to the
UASB reactor quickly. However, after 2 days, D is lowered from 4.5 to 2.3 days⫺1 for the enhanced degradation of slowly degradable matters such as cellulose
and protein.15 It was reported that cellulose degradation
increased at high retention time16 and protein degradation increased at both high retention time and neutral
pH.17 H2 fermentation of 6 days is reasonable considering
operation time and efficiency,15 which is followed by
post-treatment. Fifteen L/min of air is injected through
the bottom of the reactor for 45 hr after dewatering in the
same reactor for 3 hr.
The objective of this work was to evaluate the performance of an innovative two-stage process, BIOCELL. The
BIOCELL process was operated for 110 days to produce H2
and CH4 from food waste. The process configuration and
the operating method were suggested to enhance the ease
of operation, to supply optimal environments for anaerobes, and to maximize resource recovery and volume
reduction, as well as waste stabilization.
EXPERIMENTAL METHODS
Seed Sludge
The seed sludge was taken from an anaerobic digester in a
sewage treatment plant and boiled for 15 min to inactivate hydrogenotrophic bacteria and to harvest anaerobic
spore-forming bacteria such as Clostridium sp. The digester
was operated at a temperature of 35 °C and a hydraulic
retention time (HRT) of 25 days by feeding a mixture
(1.5–2% VS) of primary sludge and waste-activated sludge.
The pH, alkalinity, and volatile suspended solids (VSS)
concentration of the sludge were 7.5, 1350 mg/L as calcium carbonate (CaCO3), and 14,600 mg/L, respectively.
Feedstock
Food waste, collected from a dining hall, was fed into the
reactor after separating out bones and shells. Table 1
shows the characteristics of food waste as feedstock. The
bulk density, moisture content, VS/total solids (TS), sodium (Na⫹), and carbon/nitrogen (C/N) of the waste were
519.5 kg/m3, 80.2%, 0.95, 0.8 g/L and 15.4, respectively.
Food waste contained grains, vegetables, and meats,
244 Journal of the Air & Waste Management Association
Table 1. Characteristics of food waste as feedstock.
Item
Unit
Value
Bulk density
Moisture content
VS/TS
Na⫹
C/N
Composition
Grains (⬍10)a
Vegetables (⬍00)a
Meats (⬍50)a
kg/m3
%
519.5 ⫾ 27.4
80.2 ⫾ 2.9
0.95 ⫾ 0.01
0.8 ⫾ 0.2
15.4 ⫾ 3.7
a
g/L
% TS
% TS
% TS
61.1 ⫾ 10.3
29.7 ⫾ 15.8
9.2 ⫾ 3.4
Indicates the particle size in mm.
whose composition was 61.1, 29.7, and 9.2% on a TS
basis.
Experimental Setup
Four leaching-bed reactors were operated for H2 recovery.
Each leaching-bed reactor was 3.9 L in working volume
with an internal diameter of 0.15 m and a height of
0.22 m. Acidified products from four leaching-bed reactors were converted to CH4 in a UASB reactor with a
working volume of 20.1 L (lower part: 0.6 m high by
0.15 m i.d.; upper part: 0.21 m high by 0.24 m i.d.). The
biogas production was measured using a wet gas meter.
Operating Conditions
The BIOCELL process was operated at a temperature of 37
°C. The organic loading rates of the leaching-bed reactors
and the UASB reactor were 11.9 kg VS/m3䡠day and 5.4 kg
COD/m3䡠day, respectively, as shown in Table 2. Residues
were dewatered for 3 hr and then treated by blowing air at
15 L/min through the bottom of the reactor for 45 hr.
Analytical Methods
Samples of the leaching-bed reactors and the UASB reactor were collected daily during the experiment. Biogas
composition was analyzed by a gas chromatograph (GC,
GowMac series 580) equipped with a thermal conductivity detector (TCD) and two columns. The contents of
CH4 and carbon dioxide (CO2) were determined using
a 1.83 m ⫻ 3.18 mm i.d. stainless-steel column packed
with Porapak Q (80/100 mesh). H2 content was measured
with a 1.83 m ⫻ 3.18 mm i.d. stainless-steel column packed
with molecular sieve 5A. The operational temperatures of
injector, detector, and column were kept at 80, 90, and 50
°C, respectively. Helium (He) was used as a carrier gas at a
flow rate of 40 mL/min. The concentrations of individual
VFAs were analyzed by a high-performance liquid chromatograph (HPLC, SpectraSYSTEM P2000) equipped
Volume 54 February 2004
Han and Shin
where CODo is the theoretical COD of substrate (g COD);
Table 2. Operating conditions of the BIOCELL process.
Item
Hydrogen fermentation
Temperature
Organic loading rate
SRT
Dilution rate (D)
Methane fermentation
Temperature
Organic loading rate
HRT
Post-treatment
Temperature
SRT
Airflow rate
CODp is the actual COD produced in H2 fermentation of
substrate at a time (g COD); and t is the time elapsed
during H2 fermentation (days).
Unit
Value
°C
kg VS/m3 䡠 day
day
day⫺1
37 ⫾ 1
11.9 ⫾ 1.2
6
4.3 ⫾ 0.1 3 2.1 ⫾ 0.1
°C
kg COD/m3 䡠 day
day
37 ⫾ 1
5.4 ⫾ 0.3
0.6 ⫾ 0.1
°C
day
L/min
20 ⫾ 5
2
15 ⫾ 4
RESULTS
Hydrogen Fermentation Performance
Figure 2 illustrates the variation of VFA, pH, and H2 evolution during H2 fermentation of food waste (error bars
indicate the standard deviation of samples during repeat
runs). Because of the various components of food waste,
it is important to adjust the fermentation conditions
with a UV (210 nm) detector and a 300 m ⫻ 7.8 mm
Aminex HPX-97 Hr column after pretreatment with a
0.45-␮m membrane filter. H2SO4 of 0.005 M was used as
a mobile phase at a flow rate of 0.6 mL/min. Alcohols
were determined by an HPLC (DX-600 Bio-LC system)
equipped with an ED50A electrochemical detector and a
250 m ⫻ 4 mm CarboPac PA10 column after pretreatment
with a 0.45-␮m membrane filter. Deionized water was
used as the mobile phase at a flow rate of 0.6 mL/min.
Na⫹ and ammonia (NH3)-N were measured by atomic
absorption spectrophotometer (Shimadzu AA-6701F) and
ion chromatograph (Dionex DX-120), respectively. Parameters such as pH, alkalinity, COD, VSS, VS, and TS
of the samples were measured according to standard
methods.18
Data Analysis
The efficiency of H2 fermentation was calculated using
the following equation.
efficiency of hydrogen fermentation 共%兲 ⫽
CODp
⫻ 100
CODo
(3)
where CODo is the theoretical COD of substrate (g COD);
and CODp is the actual COD (e.g., VFA, H2, and ethanol)
produced in H2 fermentation of substrate at a time (g
COD).
When the availability of substrate, not the microbial
growth, limits the microbial degradation of substrate, the
degradation process can be described by the first-order
kinetic law. Thus, the kinetic constant (k) of H2 fermentation was obtained from eq 4.19
COD o ⫺ CODp
⫽ exp(⫺kt)
CODo
Volume 54 February 2004
(4)
Figure 2.
fermentation.
Variation of VFA, pH, and H2 evolution during H2
Journal of the Air & Waste Management Association 245
Han and Shin
properly depending on the state of degradation. In the
early stage, carbohydrate materials are converted to VFA
rapidly. The accumulated VFA is likely to decrease the
fermentation efficiency because of pH drop and product
inhibition.14 Thus, initial D became relatively high to
transfer produced VFA to a UASB reactor quickly.15 VFA,
pH, and H2 evolution ranged 2226 –3202 mg COD/L, 5.4 –
5.5, and 14.4 –34.1 L/day, respectively, at initial D of 4.5
days⫺1 in the first 2 days. The pH values were optimal for
Clostridium sp. producing H2 from carbohydrates.2,20,21 It
was found that the initial D was appropriate to avoid the
accumulation of excess VFA and the washout of H2producing bacteria in early stage. After 2 days, the reduction of carbohydrate matters could cause a decline in VFA
production and H2 evolution.15 D was, therefore, reduced
to improve the degradation of slowly degradable matters.
It was reported that cellulose degradation increased at
high retention time16 and protein degradation increased
at both high retention time and neutral pH.17 The production of VFA and H2 was dramatically enhanced by
reducing D from 4.5 to 2.3 days⫺1. The pH increased
gradually to neutral values and the second VFA peak
(2990 mg COD/L) and H2 peak (27.4 L/day) appeared on
day 3. These peaks meant that the environmental conditions became favorable to microbial growth by D shift.
Meanwhile, throughout the operation period, the biogas
generated consisted of H2 (10 –55%) and CO2 (90 – 45%).
There was no H2S produced.
Table 3 lists the variation of individual VFAs, butyrate/acetate (B/A) ratio, and ethanol during H2 fermentation of food waste. The distribution of metabolites
formed during H2 fermentation is often a crucial signal in
assessing the efficiency of H2-producing cultures.22–24 At
initial D of 4.5 days⫺1 (days 1–2), VFA concentration was
higher than ethanol. Butyrate (45.2– 49.7%) and acetate
(12.9 –15.4%) were the two major components of VFAs in
the first two days, though lactate composition was high
on day 1. The B/A ratios were maintained at more than
3.4. The B/A ratio frequently has been used as an indicator
for evaluating the effectiveness of H2 production.25,26 A
high B/A ratio is favorable to frequent production. After
day 2, D was lowered from 4.5 to 2.3 days-1 to prevent a
decline in B/A ratio for enhanced H2 production. Compared with 0.5–2.2 with no D control,15 the B/A ratios
were kept high (2–2.7) on days 3– 6, accompanied by the
second H2 peak. It meant that D shift resulted in the
improved degradation of slowly degradable matter. On
the other hand, ethanol concentration became higher
than VFA on day 6, indicating that D control could delay
the shift of predominant metabolic flow from the H2- and
acid-forming pathway to the alcohol-forming pathway.
Figure 3 shows the efficiency of H2 fermentation by
eq 3. The theoretical COD of food waste (CODt) was 408.4
g COD (i.e., 371.3 g VS ⫻ 1.1 g COD/g VS), and the actual
COD (the sum of VFA, ethanol, and H2) produced during
H2 fermentation until day 6 (CODp) was 287.2 g COD.
Thus, the efficiency of H2 fermentation was 70.3%, which
was higher than that (59.1%) of the fermentation with no
D control.15 It indicated that H2 fermentation of food
waste could be improved by adjusting D properly.
Figure 4 illustrates that the first-order rate constant,
obtained by eq 4, was 0.2067 days-1, which was also
higher than that (0.1342 days-1) of the fermentation with
no D control.15
Post-Treatment Performance
The residues after H2 fermentation were post-treated in
the same leaching-bed reactors without transferring because the ease of operation was as important as the characteristics of the output produced. Table 4 shows the
post-treatment performance data. Moisture content decreased to 55.8% and VS reduction increased to 72.5%.
The remaining acids in the residues were volatilized so
that the pH increased to 7. The characteristics of the
output after post-treatment met the Korean regulation on
the compost as shown in Table 5.27 Therefore, the output
could be used as a soil amendment, which improved the
economics and the environmental benefits of the process.
Table 3. Variation of individual VFAs, butyrate/acetate (B/A) ratio, and ethanol during H2 fermentation.
Time (days)
1
2
3
4
5
6
VFA(mg COD/L)
nHBua (%)
iHBua (%)
HAca (%)
HLaa (%)
HPra (%)
nHVaa (%)
iHVaa (%)
HFoa (%)
B/Ab
EtOHa (mg COD/L)
3202
2226
2990
1976
1323
901
45.2
49.7
47.3
42.5
40.1
40.1
2.5
2.4
2.1
2.3
2.8
2.8
12.9
15.4
18.3
21.5
21.9
21.9
31.2
1.5
0
0
0
0
0.6
2.9
8.9
14.2
11.8
11.8
4.2
21.2
5.1
0
0
0
0.5
5.3
16.1
19.2
23.2
23.2
2.9
1.6
2.2
0.3
0.2
0.2
3.7
3.4
2.7
2.1
2
2
397
701
1097
1237
1303
1924
nHBu ⫽ normal butyric acid; iHBu ⫽ iso butyric acid; HAc ⫽ acetic acid; HLa ⫽ lactic acid; HPr ⫽ propionic acid; nHVa ⫽ normal valeric acid; iHVa ⫽ isovaleric acid; HFo ⫽ formic
acid; EtOH ⫽ ethanol; bB/A ⫽ (nHBu ⫹ iHBu)/HAc.
a
246 Journal of the Air & Waste Management Association
Volume 54 February 2004
Han and Shin
Table 5. Characteristics of the output and the Korean regulation on the compost.
Item
Standard
Valueb
a
Figure 3. Efficiency of H2 fermentation.
Heavy Metal (mg/kg)
OMa
(%)
OM/N
As
Cd
Hg
Pb
⬎25
40.1
⬍50
9.2
⬍50
ND
⬍5
ND
⬍2
ND
⬍150
ND
Cr
Cu
⬍300 ⬍500
ND
8.1
Organic matter; bND ⫽ not detected.
respectively. The COD materials included VFA and alcohol, whose composition was 71 and 29% on COD basis.
At the COD loading rate of 5.4 kg/m3䡠day, which
corresponded to 0.57 days of HRT, the COD removal
efficiency was kept over 95%. The pH in the effluent
ranged between 7.3 and 7.7. The CH4 gas production rate
was 1.75 m3/m3䡠day and CH4 yield was 0.21 m3/kg VS.
Thus, the BIOCELL process was efficient to recover CH4 as
well as H2.
Accumulation of Inhibitory Materials
Some inhibitory materials accumulated in the process
because of the recycle of the process effluent as dilution
water. The concentrations of NH3-N and Na⫹ were, therefore, monitored regularly. There are conflicting reports on
the effect of NH3-N concentrations. It was reported that
NH3 concentrations between 1500 and 3000 mg/L were
inhibitory at pH levels above 7.4 and those in excess of
3000 mg/L were toxic regardless of pH.28 On the other
hand, Parkin and Miller29 reported that with acclimation,
Figure 4. Kinetic analysis of H2 fermentation.
⬃8000 –9000 mg/L of NH3-N could be tolerated with no
significant decrease in CH4 production. Many researchers
Methane Fermentation Performance
consider that the toxicity is associated with free NH3
The performance data of the UASB reactor is summarized
depending on pH and that concentrations in excess of
in Table 6. The leachate from three leaching-bed reactors
⬃100 mg/L may cause severe toxicity.28 The increase of
was collected in the reservoir and then fed into the UASB
salt is also inhibitory because it results in dehydration of
reactor. The pH, alkalinity, and COD of the mixed
cells. Na⫹ is more toxic than any other salt on a molar
leachate were 5.7, 2.5 g/L (as CaCO3), and 3.1 g COD/L,
basis. Kugelman and McCarty30 reported that Na⫹
showed moderate inhibition at
Table 4. Performance data of the post-treatment.
3500 –5500 mg/L and strong inhibition at 8000 mg/L. Microorganisms
Value
can, however, acclimate to Na⫹ conResidue after Hydrogen
Output after
centrations as high as 8000 mg/L,
Item
Unit
Food Waste
Fermentation
Post-Treatment
though considerable acclimation time
is required.28
Wet weight
g
1974.1 ⫾ 29.1
785.7 ⫾ 14.2
308.0 ⫾ 11.6
The process effluent was, thereMoisture content
%
80.2 ⫾ 2.9
82.7 ⫾ 4.7
55.8 ⫾ 6.1
fore, exchanged once every 25 days
TS
%
19.8 ⫾ 2.9
17.3 ⫾ 4.7
44.2 ⫾ 6.1
with prepared dilution water by 40%
VS/TS
0.95 ⫾ 0.01
0.81 ⫾ 0.03
0.75 ⫾ 0.03
since day 50. This was intended to
VS
g
371.3 ⫾ 63.8
110.1 ⫾ 36
102.1 ⫾ 22
prevent the occurrence of inhibition
VS reduction
%
—
70.3 ⫾ 9.6
72.5 ⫾ 5.9
and to minimize the generation of
pH
6.3 ⫾ 0.3
6.5 ⫾ 0.2
7 ⫾ 0.1
the effluent that required further
C/N
15.4 ⫾ 3.7
11.3 ⫾ 1.3
9.2 ⫾ 1.2
treatment. As shown in Figure 5, the
Volume 54 February 2004
Journal of the Air & Waste Management Association 247
Han and Shin
Table 6. Performance data of the UASB reactor.
Item
Influent (mixed leachate)
pH
Alkalinity
COD
COD composition
VFA
Alcohol
Effluent
pH
Alkalinity
COD removal efficiency
CH4 percentage
CH4 yield
CH4 gas production rate
Unit
Value
g/L as CaCO3
g/L
5.7 ⫾ 0.2
2.5 ⫾ 0.3
3.1 ⫾ 0.3
%
%
71 ⫾ 0.1
29 ⫾ 0.1
g/L as CaCO3
%
%
m3/kg VSadded
m3/m3 䡠 day
7.5 ⫾ 0.2
2.6 ⫾ 0.2
97.3 ⫾ 1.8
76.4 ⫾ 3.2
0.21 ⫾ 0.01
1.75 ⫾ 0.13
concentrations of total NH3, free NH3, and Na⫹ in
this study were kept in the range of 500 – 850, 35– 60,
and below 1650 mg/L, respectively. Because those
concentrations were below the reported inhibitory levels,
the BIOCELL process resulted in stable and efficient
performance.
Overall Process Performance
Table 7 lists the overall process performance data. Using
food waste as the feedstock over 110 days, the BIOCELL
process resulted in large VS reduction (72.5%) at high
organic loading rates (11.9 kg VS/m3䡠 day) in a short solids
retention time (8 days). The recovery efficiencies of H2
and CH4 from VSremoved were 28.2 and 69.9% on a COD
basis, respectively. The H2 gas production rate was 3.63
m3/m3䡠day, while CH4 gas production rate was 1.75 m3/
m3䡠day. The yield values of H2 and CH4 were 0.31 and
0.21 m3/kg VSadded, respectively. It was found that the
BIOCELL process was stable and relatively easy to operate.
CONCLUSIONS
An innovative two-stage process, BIOCELL, demonstrated
excellent performance for the production of H2 and CH4
from food waste. At the high VS loading rate of 11.9
Figure 5. Variation of total NH3-N, free NH3-N, and Na⫹ in the process effluent.
248 Journal of the Air & Waste Management Association
Volume 54 February 2004
Han and Shin
Table 7. Summary of the BIOCELL process performance.
Item
Operating conditions
Temperature
Organic loading rate
SRT
Operating results
VS reduction
H2 recovery (from VSremoved)
CH4 recovery (from VSremoved)
H2 gas production rate
H2 yield
CH4 gas production rate
CH4 yield
Unit
Value
°C
kg VS/m3 䡠 day
day
37 ⫾ 1
11.9 ⫾ 1.2
8
%
% COD
% COD
72.5 ⫾ 5.9
28.2 ⫾ 3.3
69.9 ⫾ 4.2
3.63 ⫾ 0.58
m3/m3 䡠 day
m3/kg VSadded
m3/m3 䡠 day
m3/kg VSadded
0.31 ⫾ 0.04
1.75 ⫾ 0.19
0.21 ⫾ 0.02
kg/m3䡠day, the BIOCELL process removed 72.5% of VS
and converted VSremoved to H2 (28.2%) and CH4 (69.9%)
on a COD basis in 8 days. Furthermore, the output from
the post-treatment could be used as a soil amendment,
which was produced at the same leaching-bed reactors
without troublesome moving. The principal advantages
of this process are (1) the recovery of H2 as well as CH4
that can be used as a fuel for the production of energy, (2)
the production of compost that can be used as a soil
amendment, (3) the stability of performance by supplying
preferred environments for acidogenic hydrogenesis and
methanogenesis in two separate spaces, (4) the ease of
operation by employing reactor rotation mode and sequential batch technique, (5) no need of agitation by
using leaching-bed reactors, and (6) the convenience of
post-treatment by treating residues in the same reactor
without troublesome moving. In summary, the BIOCELL
process proved stable, reliable, and effective in treating
food waste.
ACKNOWLEDGMENTS
This research was supported by a grant (M1-0203-000063) from the Korean Ministry of Science and Technology, through the National Research Laboratory Program.
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About the Authors
Sun-Kee Han is a research professor and Hang-Sik Shin is
a professor in the Department of Civil and Environmental
Engineering, Korea Advanced Institute of Science and
Technology, Daejeon, South Korea. Address correspondence to: Sun-Kee Han, Department of Civil and Environmental Engineering, Korea Advanced Institute of Science
and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, South Korea; fax: 82-42-869-3610; e-mail:
skhan003@kaist.ac.kr.
Journal of the Air & Waste Management Association 249