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Anaerobic Fermentative Co-productionof Hydrogen and Methane from anOrganic Fraction of Municipal Solid WasteL. Dong a b c , Y. Zhenhong a , S. Yongming a & M. Longlong aa Guangzhou Institute of Energy Conversion, Chinese Academy ofSciences, Guangzhou, Chinab Key Laboratory of Renewable Energy and Gas Hydrate, ChineseAcademy of Sciences, Guangzhou, Chinac Graduate University of Chinese Academy of Sciences, Beijing,ChinaPublished online: 15 Dec 2010.

To cite this article: L. Dong , Y. Zhenhong , S. Yongming & M. Longlong (2011) Anaerobic FermentativeCo-production of Hydrogen and Methane from an Organic Fraction of Municipal Solid Waste,Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 33:6, 575-585, DOI:10.1080/15567030903117653

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Energy Sources, Part A, 33:575–585, 2011

Copyright © Taylor & Francis Group, LLC

ISSN: 1556-7036 print/1556-7230 online

DOI: 10.1080/15567030903117653

Anaerobic Fermentative Co-production of

Hydrogen and Methane from an Organic Fraction

of Municipal Solid Waste

L. DONG,1;2;3 Y. ZHENHONG,1 S. YONGMING,1 and

M. LONGLONG1

1Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences,

Guangzhou, China2Key Laboratory of Renewable Energy and Gas Hydrate, Chinese Academy of

Sciences, Guangzhou, China3Graduate University of Chinese Academy of Sciences, Beijing, China

Abstract In order to improve energy recovery efficiency, the fermentative hydrogenproduction from organic fraction of municipal solid waste was followed by methane

production using the residual of hydrogen production as a substrate. Six individualcomponents of organic fraction of municipal solid waste, including rice, potato,

lettuce, lean meat, peanut oil, and banyan leaves, were selected as experimentalmaterials. The results showed that at the hydrogen production stage, the hydrogen

yields were 125, 103, 35, 0, 5, and 0 mL/gVS for rice, potato, lettuce, lean meat,peanut oil, and banyan leaves, respectively. During the methane production stage, the

methane yields were 232, 237, 148, 278, 866, and 50 mL/gVS. For example, for ricethe co-production of hydrogen and methane increased the energy efficiency from 7.9

to 56.3% compared with single hydrogen production.

Keywords anaerobic fermentation, co-production, hydrogen, methane, municipalsolid waste

Introduction

The methane production by anaerobic digestion has been applied for energy production

and waste treatment for years. Today, the anaerobic process is mainly utilized in four

sectors of waste treatments: (1) the primary and secondary sludge produced during

aerobic treatment of municipal sewage; (2) industrial wastewaters produced from biomass

treatment, food processing and fermentation industries; (3) agricultural and livestock

wastes; and (4) a relatively new sector for treatment of the organic fraction of municipal

solid waste (OFMSW) (Angelidaki et al., 2003). So far, a lot of researches have been

done by many scientists (Bolzonella et al., 2006; Sosnowski et al., 2003) and more than

120 large-scale biogas plants are now operating to treat organic fraction of municipal

solid waste (OFMSW) all over the world (De Baere, 2006). As a major burden to

the environment, the generation of municipal solid waste (MSW) amounted to 170

million tons in 2006 in China, and this number is growing by 6% per year (Ministry

Address correspondence to Dr. Li Dong, Guangzhou Institute of Energy Conversion, ChineseAcademy of Sciences, Guangzhou 510640, China. E-mail: lidong@ms.giec.ac.cn

575

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576 L. Dong et al.

of Environmental Protection of China, 2007). Nearly 60% of MSW is organic wastes,

such as kitchen waste, waste paper and urban greening waste. To treat the OFMSW by

anaerobic digestion for recovering energy, not only alleviates the conflict between energy

supply and demand to a certain extent, but also improves economic feasibility for MSW

treatment.

Recently, hydrogen has been widely recognized as an ideal alternative energy source

to substitute fossil fuels since it is a clean and environmentally friendly fuel, which

produces water instead of greenhouse gases when combusted. Furthermore, it could be

directly used to produce electricity through fuel cells (Ramachandran and Menon, 1998).

Among the hydrogen production methods, the most promoting and environmentally

friendly method seems to be dark fermentation of organic wastes (Benemann, 1996).

Previous studies on fermentative production of hydrogen were developed using pure

carbohydrates (Kraemer and Bagley, 2005), agricultural waste (Collet et al., 2004),

organic wastewaters (Ren et al., 2006), wastewater sludge (Wang et al., 2003), and

municipal organic wastes (Okamoto et al., 2000) as substrates. Nevertheless, the low

energy efficiency is the main bottleneck for fermentative production of hydrogen, which

greatly limits its development and industrial application. It is considered a key and

difficult problem to increase the energy conversion efficiency of the hydrogen production

process.

Hallenbeck (2005) described the fundamentals of biological hydrogen production by

dark fermentations. For example of fermentative hydrogen production of glucose, hydro-

gen production accompanies productions of intermediate metabolites (such as acetate and

butyrate ethanol). These intermediate metabolites can be utilized to produce methane by

methanogens. Theoretically, the maximum hydrogen yield is 4 mol/mol glucose when

acetate is the sole intermediate metabolite, which is shown in Eq. (1). This maximum

value is also called “Thauer limit” (Thauer et al., 1997). However, the results of several

studies indicated that actual hydrogen yield was lower than 4 mol, typically ranging

between 0.5–2.5 mol/mol hexose. In fact, the intermediate metabolites are usually a

mixture of acetate and butyrate, which is shown in Eq. (2). When the residual of hydrogen

production can be utilized by methanogens, the total fermentation reaction is shown in

Eq. (4). Table 1 shows the energy efficiency for various fermentation reactions. The

energy efficiency of the new combined reaction for hydrogen and methane production is

higher than either hydrogen or methane production reaction shown in Eq. (3). Therefore,

the combined production of hydrogen and methane is considered to be an ideal way to

utilize OFMSW.

Table 1

Energy efficiency of various fermentation reactions using glucose as substrate

Eq. Fermentation reaction

Energy

efficiencya

(1) C6H12O6 C 2H2O ! 2CH3COOH C 2CO2 C 4H2 33.5%

(2) 4C6H12O6 ! 2CH3COOH C 3CH3CH2CH2COOH C 8CO2 C 8H2 16.8%

(3) C6H12O6 ! 3CH4 C 3CO2 83.2%

(4) C6H12O6 C 2H2O ! 2CH4 C 4CO2 C 4H2 89.0%

aEnergy efficiency is calculated based on the heating value of C6H12O6 (2,888 kJ/mol), H2 (242kJ/mol), and CH4 (801 kJ/mol).

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Anaerobic Fermentative Co-production 577

In this study, a sequential anaerobic fermentative production of hydrogen and methane

was investigated. At the first stage (hydrogen production stage, HPS), hydrogen was

produced by hydrogen producing bacteria under low pH conditions. At the second stage

(methane production stage, MPS), the residual of the HPS was utilized to produce

traditional fuel methane by methanogens under neutral conditions. For this purpose, six

kinds of organic wastes were selected as substrates, including rice, potato, lettuce, lean

meat, peanut oil, and banyan leaves, which wildly exist in the OFMSW.

Material and Methods

Seed Microorganisms

The sludge was originally obtained from a swine manure anaerobic digester and accli-

matized with kitchen waste for 2 months at 37ıC. First, the sludge was introduced into

anaerobic reactor, then the kitchen waste was added once a week and the adding amount

was increased step by step. Prior to use, the sludge was sieved to remove bone, sand

and other coarse matters. The sieved sludge was used as a seed for methane production.

The pH, ammonia nitrogen, alkalinity, volatile fatty acids (VFAs) and volatile suspended

solid (VSS) were 7.3, 480, 1,800, 210, and 4,000 mg/L, respectively.

The hydrogen producing seed used in this study was heat-treated anaerobic sludge

and used at low pH. The sieved sludge was boiled for 15 min to inactivate the hydro-

gentrophic methanogens. After boiling, the pH, ammonia nitrogen, alkalinity, VFAs, and

VSS were 9.5, 310, 900, 150, and 3,700 mg/L, respectively.

Experimental Substrate

The materials used in this study are given in Table 2. All the feeding amounts of the

substrates were 8.0 g (calculated by volatile solid [VS]), except 5.0 g for meat in order

to avoid ammonia inhibition (Salerno et al., 2006).

Experimental Setup and Procedure

The experimental setup is shown in Figure 1. A 500 mL serum bottle used as a reactor

was placed in the water bath at .37 ˙ 1/ıC. The headspace of reactor was filled with

pure N2 to assure its anaerobic condition. Mixing was conducted twice a day manually.

The anaerobic digestion was finished until no gas produced. Experimental design is

given in Table 3. The anaerobic digestion of each substrate was carried out as duplicate

experiments.

Table 2

Characteristics of substrates

Substrate TS, g

Heat value,

J/gTS VS/TS, % VS, g [C]/TS, % [H]/TS, % [O]/TS, % [N]/TS, % [C]/[N]

Rice 8.0 17,053 99.5 8.0 42.63 5.74 50.06 0.89 47.7

Potato 8.0 16,324 99.5 8.0 41.36 5.59 51.16 1.17 35.4

Lettuce 9.5 16,669 84.6 8.0 42.12 4.84 33.66 3.26 12.9

Lean meat 5.3 24,077 94.9 5.0 50.97 6.10 23.04 13.11 3.9

Peanut oil 8.0 38,196 100.0 8.0 76.40 7.90 12.90 0.01 6,967.0

Banyan leaves 9.3 17,563 85.9 8.0 45.34 4.98 34.48 0.36 125.7

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578 L. Dong et al.

Figure 1. Schematic diagram of experimental setup.

Analytical Methods

Total solid (TS), VS, ammonia nitrogen, and alkalinity were determined using standard

techniques (APHA, 1995). Heat values were determined by a WGR-1 heat value analyzer

(Changsha Bente Instrument Corporation, Changsha, China). Elementary analysis was

done by a Vario EL element analyzer. The pH was determined by a pHS-3C pH meter

(Shanghai Precision & Scientific Instrument Co. LTD, Shanghai, China).

Biogas production was measured by the displacement of saturated brine solutions.

The gas volumes were corrected to a standard temperature (0ıC) and pressure (1 atm)

(STP). The compositions of biogas (H2, CH4, and CO2) were analyzed by a gas

chromatograph (Agilent 6890) equipped with a thermal conductivity detector and a 2 m

stainless column packed with Porapak Q (50/80 mesh). The operational temperatures at

the injection port, column oven, and detector were 100, 70, and 150ıC, respectively.

Argon was used as carrier gas at a flow rate of 30 mL/min.

Liquid samples were centrifuged with 8,000 r/min at 0–4ıC and filtrated with

0.45 �m filter. The concentrations of VFAs and alcohols were determined using a

gas chromatograph (Agilent 6820) equipped with a flame ionization detector (FID) and

Table 3

Experimental design

HPS MPS

Substrate

Feed,

gVS

Inoculum,a

mL

Initial,

pHb

Period,

d

Inoculum,c

mL

Initial,

pHd

Period,

d

Rice 8 150 5.5 0–7 100 6.5 7-finishe

Potato 8 150 5.5 0–7 100 6.5 7-finish

Lettuce 8 150 5.5 0–7 100 6.5 7-finish

Lean meat 5 150 5.5 0–7 100 6.5f 7-finish

Peanut oil 8 150 5.5 0–7 100 6.5 7-finish

Banyan leaves 8 150 5.5 0–7 100 6.5 7-finish

aThe inoculum was methane production seed.bThe pH was adjusted by adding 2 mol/L HCl.cThe inoculum was methane production seed.d The pH was adjusted by adding 2.5 mol/L NH4HCO3.eThe fermentation finished until no gas produced.f The pH was adjusted by adding 5 mol/L KOH in order to avoid ammonia inhibition.

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Anaerobic Fermentative Co-production 579

a 30 m � 0.25 mm � 0.25 �m fused-silica capillary column (DB-FFAP). Nitrogen

was used as a carrier gas at a flow rate of 30 mL/min and split ratio was 1:50. The

operational temperatures of the injection port and detector were 250 and 300ıC. The

initial temperature of oven was 40ıC for 5 min, then increased to 140ıC at a rate of

10ıC/min and maintained for 1 min, and again increased to 250ıC at a rate of 5ıC/min

and maintained for 3 min. The analyzed VFAs and alcohols included acetate, propionate,

butyrate, isobutyrate, valerate, isovalerate, methanol, ethanol, propanol, and butanol.

The modified Gompertz equation was used to describe the progress of cumulative

hydrogen production obtained from the batch experiments (Lee et al., 2001). Using the

cumulative hydrogen production data to fit the modified Gompertz equation, the maximum

hydrogen production rates were estimated:

H.t/ D P � exp

�

� exp

�

Rm � e

P.� � t/ C 1

��

; (5)

where H.t/ is cumulative hydrogen production (mL), P is hydrogen production potential

(mL), Rm is maximum hydrogen production rate (mL/d), e D 2:71828, and � is lag-phase

time (d) and t time (d).

Results and Discussion

Hydrogen Production

Figure 2 shows the cumulative hydrogen production and hydrogen contents for those

substrates. In contrast to the 1 day lag-time reported by Xie (2008a) using potato as

hydrogen production substrate, this study found negligible lag-phase time for hydrogen

production, perhaps because the inoculum was acclimatized with kitchen waste for

2 months. For the rice, potato, and lettuce, more than 95% of hydrogen production

accomplished at the end of day 3 and the hydrogen compositions in the biogas were about

34–59, 41–56, and 37–70%, respectively. The methane was not found during HPS. Their

hydrogen yields were 125, 103, and 35 mL/gVS. The maximum hydrogen production

rates with one gram of VS were 119, 94, and 43 mL/(gVS � d). It can be concluded

that among the organic waste components, carbohydrate is the most optimal substrate

for fermentative production of hydrogen compared with protein, lipid and lignocellulose.

This conclusion is in agreement with the result from Okamoto et al. (2000).

Figure 2. Hydrogen production: (a) Cumulative hydrogen productions and (b) hydrogen contents.

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Methane Production

The MPS started on day 7 by adding methane production inoculum. The cumulative

methane productions and methane contents for various substrates were shown in Figure 3.

During the MPS, the biogas was free from hydrogen content for all substrates. Compared

with other substrates, there was a lag-time of 13 days for MPS of rice. This lag-

time could be associated with the inhibition of high concentration of VFAs, which

was accompanied with the hydrogen production. Although there was no obvious lag-

time for lettuce, the increasing of cumulative methane production was less than that of

potato and lean meat. The complex components and structure of banyan leaves limited

the rate and extent of hydrolysis (Lynd et al., 2002). Therefore, it is very difficult to

produce hydrogen and methane from lignocellulose substrate unless suitable pretreatment

is adopted.

Figure 3. Methane production: (a) Cumulative methane productions and (b) methane contents.

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Anaerobic Fermentative Co-production 581

The methane yields with rice, potato, lettuce, lean meat, peanut oil, and banyan

leaves were 232, 237, 148, 278, 866, and 50 mL/gVS, respectively. Due to the low

hydrolysis rate, the fermentation period of peanut oil was longer than those of rice,

potato, lettuce, and lean meat. The hydrolysis constants of carbohydrates, proteins and

lipids were 0.025–0.200, 0.015–0.075, and 0.005–0.010 1/d, respectively (Christ et al.,

2000). However, the peanut oil’s high ratio of carbon and hydrogen contents to oxygen

content (([C] C [H])/[O]) produced more methane than that of other substrates. During

the stable MPS, the methane content were 42–70, 57–71, 73–77, 59–73, 68–80, and

54–74% for rice, potato, lettuce, lean meat, peanut oil, and banyan leaves.

Intermediate Metabolites Production

The pH and intermediate metabolites were determined during the process of hydrogen

and methane production. The results are shown in Figure 4. They were determined four

times at different stages of fermentations for rice, potato, lettuce, lean meat and banyan

leaves. The first time was carried out at the end of HPS; the second was at the start-up

of MPS after methane production inoculum was added; the third was at the stable MPS,

and the last was at the end of MPS. However, for the peanut oil, the pH and intermediate

metabolites were determined twice during the stable MPS due to the long period of

fermentation.

The hydrogen productions changed the pH from 5.50 to 4.68, 4.99, 5.2, 5.91, 5.43,

and 5.24 for rice, potato, lettuce, lean meat, peanut oil, and banyan leaves, respectively.

The total intermediate products concentrations (including VFAs and alcohols) at the end

of HPS were strongly associated with the cumulative hydrogen production, similar to

the conclusions made by Xie et al. (2008b). The amounts of total intermediate products

followed the order: rice > potato > lettuce > lean meat > peanut oil > banyan leaves.

This order was the same as that of hydrogen production.

For the carbohydrates (such as rice, potato, and lettuce), acetate and butyrate were

the main intermediate products from the hydrogen production with a little propionate,

ethanol, and valerate. The start-up of methane production fermentation sharply reduced

the concentrations of total intermediate products and increased pH values. During the

stable MPS, the total intermediate products were 2,260, 1,300, and 2,200 mg/L. Acetate

and butyrate also were the main intermediate products with no alcohols detected during

the MPS.

For the lean meat, the start-up of methane production fermentation increased the

concentrations of total intermediate products. This unexpected result may be because

the methane production fermentation relieved the inhibition of protein and/or amino

degradation. For example, there was an amino acid degradation reaction under anaerobic

condition (Thauer et al., 1977):

Oxidative deamination from leucine:

Leucine C 3H2O ! Iso-valerate C HCO�

3 C NHC

4 C 2H2 �G00

D C4:2 kJ/mol (6)

It is a thermodynamically unfavorable reaction unless the hydrogen partial pressure is

maintained at an extremely low level. The methane production fermentation happened to

consume the hydrogen which was helpful to produce VFAs, especially iso-valerate. This

conclusion can be substantially proved by the increasing of iso-valerate concentration

which is shown in Figure 4. Even though total VFAs increased, pH did not decrease.

This resulted from the production of ammonia for amino degradation.

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582 L. Dong et al.

Figure 4. Intermediate metabolites and pH during the fermentation process. (Butyrate includes

n-butyrate and iso-butyrate; valerate includes n-valerate and iso-valerate; and alcohols include

methanol, ethanol, propanol, and butanol.)

For the peanut oil, the main intermediate product was butyrate with little acetate.

This was seemingly conflict with the result of the degradations of LCFA (ˇ-oxidation):

n-LCFA ! .n � 2/-LCFA C 2acetate C 2H2 �G00

D C48 kJ/mol (7)

This reaction was also thermodynamically unfavorable unless the hydrogen partial pres-

sure is maintained at an extremely low level. Nevertheless, there was a metabolizing

pathway of pyruvate (coming from degradation of glycerol) under anaerobic condition

(Thauer et al., 1977) as below:

Pyruvate C acetate C 2H2 ! Butyrate C CO2 C H2O �G00

D �95:4 kJ/mol (8)

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Anaerobic Fermentative Co-production 583

It is a thermodynamically favorable reaction. This reaction clearly explains that the

butyrate yielded more than 70% but the acetate lower than 10% at the end of HPS which

is shown in Figure 4. When the methane producing inoculum was added, the hydrogen

in reactor was consumed by hydrogenotrophic methanogens. The low hydrogen partial

pressure was favorable of ˇ-oxidation. Therefore, the concentration of acetate was greater

than that of butyrate during the MPS.

For the banyan leaves, acetate was the main intermediate product during the HPS

and MPS. However, the start-up of methane production fermentation increased the con-

centrations of intermediate products. This could be because the methane production

fermentation relieved the inhibition to some extent or some new microorganisms (coming

from reinoculating) enhanced the production of intermediate products. However, they are

required to be verified.

COD Balance Analysis

The chemical oxygen demand (COD) balance is given in Table 4. During the HPS,

99.36, 56.92, 23.20, 24.32, 8.21, and 7.58% of the added COD were degraded for rice,

potato, lettuce, lean meat, peanut oil, and banyan leaves, respectively. This result was

positively correlated with the hydrogen production. The degraded CODs were mainly

converted to intermediate metabolites (such as acetate, butyrate and propionate). The

hydrogen production based on COD was achieved in an order: rice > potato > lettuce >

peanut oil > lean meat D banyan leaves. During the MPS, the intermediate metabolites

and the undegraded from HPS were converted into methane and biomass. The methane

Table 4

COD balance for hydrogen and methane production with the six substrates

COD Rice Potato Lettuce Lean meat Peanut oil

Banyan

leaves

Addeda (mg) 8,770.00 8,310.00 11,160.00 8,580.00 20,340.00 11,760.00

Added (%) 100.00 100.00 100.00 100.00 100.00 100.00

HPS

Undegradedb (%) 0.64 43.08 76.80 75.68 91.79 92.42

Intermediate (%) 89.72 49.84 21.41 24.32 8.07 7.58

Acetate (%) 33.27 20.36 12.10 5.74 0.18 4.83

Propionate (%) 19.15 3.77 1.18 3.47 0.63 0.76

Butyrate (%) 32.46 19.32 6.33 10.01 6.55 1.14

Valerate (%) 4.67 0.30 0 3.93 0.16 0

Alcohols (%) 1.67 6.09 1.80 1.17 0.54 0.85

Hydrogen (%) 8.14 7.08 1.79 0 0.14 0

MPS

Final intermediate (%) 3.69 9.43 0.53 1.28 0 1.57

Methane (%) 60.47 65.19 30.31 46.31 97.32 9.72

Residuec (%) 27.70 18.30 67.37 52.41 2.54 88.71

aThe added COD was calculated as: TSadded � [C] � 2:67 C TSadded � [H] � 8 � TSadded � [O].bThe undegraded COD was calculated as: Added–intermediate–hydrogen.cThe residue includes the undegraded COD and the COD converted into biomass, calculated as:

Added–end intermediate–hydrogen–methane.

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Table 5

Energy efficiency of the co-production of hydrogen and methane

H2 production CH4 production

Energy recovery

efficiency

Substrate

Input,

kJ/gVSa mL/gVS kJ/gVSb mL/gVS kJ/gVSc H2, % H2 C CH4, %

Rice 17.14 125 1.35 232 8.30 7.9 56.3

Potato 16.41 103 1.11 237 8.47 6.8 58.4

Lettuce 19.70 35 0.38 148 5.29 1.9 28.8

Lean meat 25.37 0 0 278 9.94 0 39.2

Peanut oil 38.20 5 0.05 866 30.97 0.1 81.2

Banyan leaves 20.45 0 0 50 1.79 0 8.8

aHeat value directly determined.bHeat value calculated based on 242 kJ/mol.cHeat value calculated based on 801 kJ/mol.

production based on COD was found as: peanut oil > potato > rice > lean meat >

lettuce > banyan leaves. The total COD removal rate of the whole process of hydrogen

and methane production was also abided by this order.

Energy Recovery Efficiency

The energy efficiencies of hydrogen production and co-production of hydrogen and

methane are given in Table 5. The energy efficiency of hydrogen production is cal-

culated by dividing the heat value of hydrogen yield by the heat value of substrate

which was directly determined. The energy efficiency of the co-production process is

calculated by dividing the heat value of hydrogen and methane yield by the heat value

of substrate. Compared with that of the hydrogen production, the energy efficiency

of the co-production could be improved from 7.9, 6.8, 1.9, 0, 0.1% and 0 to 56.3,

58.4, 28.8, 39.2, 81.2, and 8.8% for rice, potato, lettuce, lean meat, peanut oil, and

banyan leaves, respectively. Although the energy efficiencies were improved, there are

still some problems to work on. For example, the energy stored in residue should be

further recovered especially for lettuce, lean meat, and banyan leaves.

Conclusion

Compared with the fermentative production of hydrogen from OFMSW, the energy recov-

ery efficiency of the co-production of hydrogen and methane was improved remarkably.

At the hydrogen production stage, the hydrogen yields were 125, 103, 35, 0, 5, and 0

mL/gVS, and at the methane production stage, the methane yields were 232, 237, 148,

278, 866, and 50 mL/gVS for rice, potato, lettuce, lean meat, peanut oil, and banyan

leaves, respectively. The energy efficiencies were improved from 7.9, 6.8, 1.9, 0, 0.1,

and 0 to 56.3, 58.4, 28.8, 39.2, 81.2, and 8.8%, and the total COD removal rate for the

whole process of hydrogen and methane production were 72.30, 81.70, 32.63, 47.59,

97.46, and 11.29%, for rice, potato, lettuce, lean meat, peanut oil, and banyan leaves,

respectively.

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Anaerobic Fermentative Co-production 585

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