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Hydrogen production from waste activated sludge by using separation membrane acid fermentation reactor and photosynthetic reactor
International Journal of Hydrogen Energy 32 (2007) 525 – 530 www.elsevier.com/locate/ijhydene
Hydrogen production from waste activated sludge by using separation membrane acid fermentation reactor and photosynthetic reactor Tae-Young Jeong a , Gi-Cheol Cha a,∗ , Ik-Keun Yoo b , Dong-Jin Kim c aYIEST, Division of Environmental Engineering, Yonsei University, Wonju, 220-710 Korea, South Korea b School of Chemical Engineering and Bioengineering, Ulsan University, Ulsan, 680-749 Korea, South Korea c Department of Environmental Science, Hallym University, Chuncheon, 220-702 Korea, South Korea
Available online 7 November 2006
Abstract The possibility and characteristics of hydrogen production from waste activated sludge were investigated using separation membrane acid fermentation reactor (AR) and photosynthetic reactor (PR). The AR used submerged and external separation membranes and it was followed by the PR. The COD removal efficiencies in the AR with submerged and external separation membrane were about 65% and 40%, respectively. More VFA was produced in the AR with external separation membrane than AR with submerged separation membrane. Hydrogen was produced in the PR but not in the AR and hydrogen productions in the PR connected with submerged membrane AR and external membrane AR were about 50.1 and 160.5 ml H2 /g T-VFA, respectively. 䉷 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. Keywords: Hydrogen production; Waste activated sludge; Acid fermentation reactor; Photosynthetic reactor; Separation membrane
1. Introduction Waste activated sludge (WAS) production from wastewater treatment plants increases every year and its disposal has been a central issue in Korea for many years. Ocean dumping, landfill, and incineration have been the most widely used methods, but the needs for new and environment friendly methods are growing rapidly due to the pollutions of ocean and air. As an alternative method, researches on the production and utilization of methane from WAS have been intensively carried out considering the potential of WAS as an alternative energy source. Recently, environmental issues have come to the forefront, with global warming, regional air pollution and economic/ecological sustainability all being major driving forces behind the renewed interest in alternative energy sources. Therefore, hydrogen gas as a potential clean energy source of the future could be a possible alternative energy to fossil fuels [1–3]. The types of microorganism that can be utilized for hydrogen production are divided into three groups: cyanobacteria,
∗ Corresponding author.
E-mail address: [email protected] (G.-C. Cha).
anaerobic bacteria and photosynthetic bacteria [4]. The cyanobacteria split water into hydrogen and oxygen gas by photosynthesis. Anaerobic bacteria use organic substrates as the sole source of electrons and energy, and convert them into hydrogen. The reaction is rapid and the process requires no solar radiation, making it useful for treating large quantities of wastewater. Finally, the photosynthetic bacteria fall somewhere between the other two systems, as although they also convert organic substances to hydrogen at fairly high rates, they also require light energy to assist, or promote, the reactions involved in hydrogen production. Some non-photosynthetic bacteria can produce hydrogen from different organic substrates, such as Enterobacter aerogenes from glucose [5] or a Clostridium beijerinckii strain from glucose and starch [6]. Non-photosynthetic bacteria, like Clostridium butyricum, evolve hydrogen from carbohydrates at a high rate, but the yield is limited because they also produce organic acids. Photosynthetic bacteria, such as Rhodobacter sphaeroides RV, are powerful hydrogen producer, showing 7% energy conversion efficiency in the presence of lactate and glutamate [7,8]. The high rate of hydrogen production makes them suitable for photo-bioreactor applications [9,10].
0360-3199/$ - see front matter 䉷 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2006.09.028
526
T.-Y. Jeong et al. / International Journal of Hydrogen Energy 32 (2007) 525 – 530
Therefore, the objectives of this study is to investigate the possibility and the characteristics of hydrogen production from WAS in acid fermentation reactor (AR) and photosynthetic reactor (PR), and to suggest on the feasibility of using a separation membrane bioreactor for the treatment of WAS.
2. Materials and methods The production of hydrogen in this study used the AR and PR. The AR and the membrane reactor were separated in this study to make it easy to clean and change the membranes. The AR used submerged and external separation membranes and it was followed by the PR, and the broths of the AR and the submerged membrane reactor were maintained same condition by recirculation (Fig. 1(A)). In the case of external membrane reactor, the reactor broths were not circulated between the AR and the membrane reactor. The effluent of the AR enters into the external membrane reactor (Fig. 1(B)). The VFA (volatile fatty acid) and hydrogen were produced in the submerged membrane AR and external membrane AR. The VFA produced in the AR is converted to hydrogen in the PR. The AR and PR were operated at 35±1 ◦ C. The bacteria used in this study are C. beijerinckii and R. sphaeroides. The experimental conditions and compositions of influent WAS were described in Tables 1 and 2. The membrane module used in this study is the hollow fiber type. The specification of membrane was shown in Table 3. The WAS was obtained from a municipal sewage treatment plant in Wonju-city, Korea. The CODcr was measured using standard methods [11], the carbohydrate was measured by the anthrone-H2 SO4 method [11] and the protein by the Lowry method [12]. The gas
Table 1 Experimental conditions Membrane position Acid reactor (AR) Run HRT (day) pH Flux (l/m2 /h) Temperature (◦ C) Illumination (Lux)
I-1a
Run
II-1b
3 5.5 0.1852 35 ± 1 ◦ C —
Photosynthetic reactor (PR) Run I-2c
Run II-2d
5 7 — 30 ± 1 ◦ C 6000
a The
AR with the submerged membrane. AR with the external membrane. c The PR is connected with Run I-1. d The PR is connected with Run II-1. b The
Table 2 Influent waste activated sludge composition Concentration (mg/l) (average value) COD Total Soluble Protein Total Soluble Carbohydrate Total Soluble
10,100 2500 5500 1500 750 150
Table 3 Specification of membrane Parameters
Specification
Type Pore size (tm) Diameter (mm) Internal External Material Effective area (m2 )
Hollow fiber (MF) 0.1 0.7 1 PS (poly sulfone) 6.25 × 10−2
Fig. 1. Schematic diagrams for the continuous experiment: (A) submerged membrane AR and PR; (B) external membrane AR and PR. a; influent reactor (WAS), b; feed pump, c; suction pump, d; acid reactor (AR), e; membrane reactor, f; permeate reactor, g; photosynthetic reactor (PR), h; effluent reactor, i; air pump.
T.-Y. Jeong et al. / International Journal of Hydrogen Energy 32 (2007) 525 – 530
composition and VFA were analyzed by gas chromatography utilizing thermal conductivity detector (TCD) and flame ionization detector (FID).
3. Results and discussion 3.1. Acid fermentation reactor (AR)
permeate from submerged and external membrane reactor averaged 950 and 300 mg/l, respectively. The T-VFA production rates per COD removal of permeate averaged 0.05% and 0.15%, respectively. The reason for this was considered to be due to the interception effect of the membrane. With submerged membrane, the concentration of T-VFA in the AR and permeate slowly decreased after 17 days. The reason for this was considered to be as a result of the acid fermentation bacteria taking part in the biomass growth as a substrate for producing T-VFA due to the interception effect of the membrane in the reactor. However, the concentration of T-VFA in the AR and permeate, with the external membrane showed much higher permeate efficiency than with submerged membrane. 3.2. Photosynthetic reactor (PR) Generally, photosynthetic bacteria have been reported to use various organic matters, such as sugars, organic acids and VFA, for their hydrogen production. Also, the hydrogen production reactions using VFA by the photosynthetic bacteria are as follows: Acetate + 2H2 O → 2CO2 + 8H+ + 8e− → 2CO2 + 4H2 , G = 75.2 kJ, Butyrate + 6H2 O → 4CO2 + 20H+ + 20e− → 4CO2 + 10H2 , G = 223.3 kJ, Lactate + 3H2 O → 3CO2 + 12H+ + 12e− → 3CO2 + 6H2 , G = 51.2 kJ. This study observed the hydrogen production using R. Sphaeroides from the T-VFA produced in the AR. Fig. 5 shows the variation of hydrogen production. As shown Fig. 5, the hydrogen gas content in the PR started after 15 days, and the hydrogen gas production per T-VFA produced from a submerged and external membrane was 15 and 100 ml/l/d,
40
40
30
30 Gas composition (%)
Gas composition (%)
Fig. 2 shows the components of the gas composition in the AR. With submerged membrane (Fig. 2(a)), the methane gas content was increased over time because the SRT (sludge retention time) was longer due to the interception effect of membrane. Hence, the growth of the methane bacteria was inhibited due to the additional BESA (2-Bromoethane sulfonic acid). Whereas, with external membrane, the methane gas content (Fig. 2(b)) showed a little variation. Generally, the C. beijerinckii bacteria in the acid fermentation reactor used in the study are known to produce hydrogen by degrading carbohydrates. However, the WAS used in this study was not able to produce the expected hydrogen because carbohydrates concentration was very low. Fig. 3 shows the COD removal in the AR. The COD removal in the AR and permeate with submerged membrane reactor were 65% and 75%, respectively. With external membrane reactor, these were 40% and 55%, respectively. Therefore, the submerged membrane AR showed higher COD removals than external membrane AR. The reason for this was considered to be due to the C. beijerinckii bacteria accumulated in reactor caused by the interception effect of the membrane. Fig. 4 shows the variation in the total volatile fatty acid (T-VFA). The T-VFA concentration in the influent WAS was about 250 mg/l and those produced in submerged and external membrane AR averaged 550 and 1100 mg/l, respectively. Also, T-VFA production rates per COD removal averaged 0.11% and 0.18%, respectively. The T-VFA concentration of
H2 CH4
20
CO2
H2
20
CH4 CO2
10
10
0
0 0
(a)
527
20
40
60
Time (days)
80
0
100
20
(b)
Fig. 2. Gas compositions in the AR: (a) Run I-1; (b) Run II-1.
40
60
Time (days)
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T.-Y. Jeong et al. / International Journal of Hydrogen Energy 32 (2007) 525 – 530
100
100 Run I-1
90
Run I-1
90
Run II-1
80
80
70
70
COD removal (%)
COD removal (%)
Run II-1
60 50 40 30
60 50 40 30
20
20
10
10
0
0 0
20
(a)
40 60 Time (days)
80
0
100
20
40 60 Time (days)
(b)
80
100
1400
1400
1200
1200
1000
1000
Total VFA (mg/l)
Total VFA (mg /L)
Fig. 3. COD removal rates in the AR: (a) supernatant; (b) permeate.
Run I-1
800
Run II-1 600
800 Run I-1 600
400
400
200
200
0
Run II-1
0 0
20
40
60
80
100
Time (days)
(a)
0
20
40
60
80
100
Time (days)
(b)
Fig. 4. Variation of total VFA productions in the AR: (a) supernatant; (b) permeate.
influent 18
12
600
10 8
400
6 4
200
H2 gas 1000 T-VFA (mg/L)
T-VFA (mg/L)
14
H2 gas production (ml /L/day)
16
H2 gas
0
(a)
20
40
60
Time (days)
80
180 160 140 120
800
100 600
80
400
60 40
200
2 0
effluent
1200
effluent
0 100
20
0 0
(b)
20
40
60
Time (days)
Fig. 5. Variations of hydrogen gas production and T-VFA in the PR: (a) Run I-2; (b) Run II-2.
80
0 100
H2 gas production (ml/L/day)
influent 800
200
1400
20
1000
T.-Y. Jeong et al. / International Journal of Hydrogen Energy 32 (2007) 525 – 530
respectively. All the T-VFA removal rates were 60% and above. The observed hydrogen production efficiency in the PR with a submerged membrane AR was lower than that with the external membrane AR. The reason for this was considered to be the T-VFA concentration of the permeate caused by the accumulation of acid production bacteria, and the longer SRT showed a lower value for the activation of the photosynthetic bacteria, and with the additional BESA inhibiting the growth of the methane bacteria. Whereas, the PR is connected with the external membrane AR showed approximately 9 times increase in the hydrogen production. Fig. 6 shows the hydrogen production per T-VFA removed. As shown Fig. 6, the hydrogen productions in the PR, with submerged and external membranes AR were 50.1 and 160.5 ml H2 /g T-VFA, respectively. In conclusion, if it is possible to acquire more organic acid from the AR using the WAS; it should
H2 gas production (ml/g T-VFA/day)
240 Submerged membrane AR + PR External membrane AR + PR
220 200 180 160 140 120
529
be possible to increase the production of hydrogen utilizing the photosynthetic bacteria. Also, it is expected that hydrogen gas could be useful substitute energy, from waste materials if the separation membrane in the hydrogen producing process is used properly. 3.3. Variation of MLVSS Fig. 7 shows the MLVSS of the AR and the PR. C. beijerinckii was accumulated in the reactors with submerged and external membranes due to membrane separation effect. Acid fermentation bacteria are accumulated in the AR due to the recirculation of the MLVSS with the submerged membranes. In the case of external membrane reactor, the reactor broths were not circulated between the AR and the membrane reactor. The AR with external membrane system does not expect accumulation of bacteria but keep the SS concentration constant. Therefore, the AR with submerged membrane has higher bacteria concentration than the AR with external membrane, and it caused higher COD removal rates in the AR with submerged membrane. The growth rate of photosynthetic bacteria was faster in the PR with submerged membrane AR (Run I-2) than the PR with external membrane AR (Run II-2). In case of Run I-2, bacterial concentration was maintained at 2100 mg/l of MLVSS in 70 days while, in case of Run II-2, the same concentration was achieved in 50 days.
100
4. Conclusion and summary
80 60 40 20 0 0
20
40 60 Time (days)
80
100
Fig. 6. Variation of H2 gas production per removal of T-VFA.
The WAS influenced from the AR showed no direct production of hydrogen gas when using hydrogen producing bacteria (C. beijerinckii) with low concentration of carbohydrates. The COD removal rates from submerged and external membrane AR were 65% and 40%, respectively. The COD removals with submerged membrane were higher than those with external membrane. The T-VFA concentration produced in submerged
2600 9000
2400
8000
2200
Run II - 1
MLVSS Concentration (mg/L)
MLVSS Concentration (mg/ L)
Run I - 1
7000 6000 5000 4000 3000
1800 1600 1400 1200 Run I - 2
1000
Run II - 2
800 600 400
2000
200
1000
0 0
(a)
2000
20
40
60
Time (days)
80
0
100
20
(b)
Fig. 7. Variation of MLVSS concentration: (a) AR; (b) PR.
40
60
Time (days)
80
100
530
T.-Y. Jeong et al. / International Journal of Hydrogen Energy 32 (2007) 525 – 530
and external membrane AR averaged 550 and 1100 mg/l, respectively. Also, the T-VFA production rates per COD removed averaged 0.11% and 0.18%, respectively. The hydrogen gas production per T-VFA produced from submerged and external membrane was 15 and 100 ml/l/d, respectively. The hydrogen productions in the PR, with submerged and external membranes AR were 50.1 and 160.5 ml H2 /g T-VFA, respectively. These results indicate that an acid fermentation reactor with membrane separation system will operate as bioreactor in which VFA produce from WAS effectively and the PR is connected with membrane separation AR shows a synergic effect of hydrogen production. Acknowledgments This work was supported by the Brain Korea 21 project. References [1] Bockris JOM. Hydrogen economy. Science 1972;176:1323. [2] Maugh TH. Hydrogen: synthetic fuel of the future. Science 1972; 178:849.
[3] Gregory DP. The hydrogen economy. Sci Am 1972;223:13–21. [4] Oskar RZ. Biohydrogen. New York: Plenum Press; 1998. [5] Perego P, Fabiano B, Ponzano GP, Palazzi E. Experimental study of hydrogen kinetics from agro industrial by-product: optimal conditions for production and fuel cell feeding. Bioproc Eng 1998;19(2):205–11. [6] Taguchi F, Chang JD, Takiguchi S, Morimoto M. Efficient hydrogen production from starch by a bacterium isolated from termites. J Ferment Bioeng 1992;73(3):244–5. [7] Miyake J, Kawamura S. Efficiency of light energy conversion to hydrogen by the photosynthetic bacterium Rhodobacter sphaeroides. Int J Hydrogen Energy 1987;12(2):147–9. [8] Miyake J, Asada T, Kawamura S. In: Hall CW, Kitani O, editors. Nitrogenase, biomass handbook. New York: Gordon and Breach Scientific Publishers; 1989. p. 362–70. [9] Tsygankov AA, Hirata Y, Miyake M, Asada Y, Miyake J. Photobioreactor with photosynthetic bacteria immobilized on porous glass for hydrogen photoproduction. J Ferment Bioeng 1994;77(4):575–8. [10] Nakada E, Nishikata S, Asada Y, Miyake J. Hydrogen production by gel-immobilized cells of Rhodobacter sphaeroides—distribution of cells, pigments, and hydrogen evolution. J Mar Biotechnol 1996;4:38–42. [11] APHA, AWWA, WPCF: standard methods for the examination of water and wastewater. 17th ed. Washington DC, USA; 1989. [12] Lowry OH. Protein measurement with folic phenol reagent. J Biol Chem 1951;193:265–75.
Hydrogen production from waste activated sludge by using separation membrane acid fermentation reactor and photosynthetic reactor Tae-Young Jeong a , Gi-Cheol Cha a,∗ , Ik-Keun Yoo b , Dong-Jin Kim c aYIEST, Division of Environmental Engineering, Yonsei University, Wonju, 220-710 Korea, South Korea b School of Chemical Engineering and Bioengineering, Ulsan University, Ulsan, 680-749 Korea, South Korea c Department of Environmental Science, Hallym University, Chuncheon, 220-702 Korea, South Korea
Available online 7 November 2006
Abstract The possibility and characteristics of hydrogen production from waste activated sludge were investigated using separation membrane acid fermentation reactor (AR) and photosynthetic reactor (PR). The AR used submerged and external separation membranes and it was followed by the PR. The COD removal efficiencies in the AR with submerged and external separation membrane were about 65% and 40%, respectively. More VFA was produced in the AR with external separation membrane than AR with submerged separation membrane. Hydrogen was produced in the PR but not in the AR and hydrogen productions in the PR connected with submerged membrane AR and external membrane AR were about 50.1 and 160.5 ml H2 /g T-VFA, respectively. 䉷 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. Keywords: Hydrogen production; Waste activated sludge; Acid fermentation reactor; Photosynthetic reactor; Separation membrane
1. Introduction Waste activated sludge (WAS) production from wastewater treatment plants increases every year and its disposal has been a central issue in Korea for many years. Ocean dumping, landfill, and incineration have been the most widely used methods, but the needs for new and environment friendly methods are growing rapidly due to the pollutions of ocean and air. As an alternative method, researches on the production and utilization of methane from WAS have been intensively carried out considering the potential of WAS as an alternative energy source. Recently, environmental issues have come to the forefront, with global warming, regional air pollution and economic/ecological sustainability all being major driving forces behind the renewed interest in alternative energy sources. Therefore, hydrogen gas as a potential clean energy source of the future could be a possible alternative energy to fossil fuels [1–3]. The types of microorganism that can be utilized for hydrogen production are divided into three groups: cyanobacteria,
∗ Corresponding author.
E-mail address: [email protected] (G.-C. Cha).
anaerobic bacteria and photosynthetic bacteria [4]. The cyanobacteria split water into hydrogen and oxygen gas by photosynthesis. Anaerobic bacteria use organic substrates as the sole source of electrons and energy, and convert them into hydrogen. The reaction is rapid and the process requires no solar radiation, making it useful for treating large quantities of wastewater. Finally, the photosynthetic bacteria fall somewhere between the other two systems, as although they also convert organic substances to hydrogen at fairly high rates, they also require light energy to assist, or promote, the reactions involved in hydrogen production. Some non-photosynthetic bacteria can produce hydrogen from different organic substrates, such as Enterobacter aerogenes from glucose [5] or a Clostridium beijerinckii strain from glucose and starch [6]. Non-photosynthetic bacteria, like Clostridium butyricum, evolve hydrogen from carbohydrates at a high rate, but the yield is limited because they also produce organic acids. Photosynthetic bacteria, such as Rhodobacter sphaeroides RV, are powerful hydrogen producer, showing 7% energy conversion efficiency in the presence of lactate and glutamate [7,8]. The high rate of hydrogen production makes them suitable for photo-bioreactor applications [9,10].
0360-3199/$ - see front matter 䉷 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2006.09.028
526
T.-Y. Jeong et al. / International Journal of Hydrogen Energy 32 (2007) 525 – 530
Therefore, the objectives of this study is to investigate the possibility and the characteristics of hydrogen production from WAS in acid fermentation reactor (AR) and photosynthetic reactor (PR), and to suggest on the feasibility of using a separation membrane bioreactor for the treatment of WAS.
2. Materials and methods The production of hydrogen in this study used the AR and PR. The AR and the membrane reactor were separated in this study to make it easy to clean and change the membranes. The AR used submerged and external separation membranes and it was followed by the PR, and the broths of the AR and the submerged membrane reactor were maintained same condition by recirculation (Fig. 1(A)). In the case of external membrane reactor, the reactor broths were not circulated between the AR and the membrane reactor. The effluent of the AR enters into the external membrane reactor (Fig. 1(B)). The VFA (volatile fatty acid) and hydrogen were produced in the submerged membrane AR and external membrane AR. The VFA produced in the AR is converted to hydrogen in the PR. The AR and PR were operated at 35±1 ◦ C. The bacteria used in this study are C. beijerinckii and R. sphaeroides. The experimental conditions and compositions of influent WAS were described in Tables 1 and 2. The membrane module used in this study is the hollow fiber type. The specification of membrane was shown in Table 3. The WAS was obtained from a municipal sewage treatment plant in Wonju-city, Korea. The CODcr was measured using standard methods [11], the carbohydrate was measured by the anthrone-H2 SO4 method [11] and the protein by the Lowry method [12]. The gas
Table 1 Experimental conditions Membrane position Acid reactor (AR) Run HRT (day) pH Flux (l/m2 /h) Temperature (◦ C) Illumination (Lux)
I-1a
Run
II-1b
3 5.5 0.1852 35 ± 1 ◦ C —
Photosynthetic reactor (PR) Run I-2c
Run II-2d
5 7 — 30 ± 1 ◦ C 6000
a The
AR with the submerged membrane. AR with the external membrane. c The PR is connected with Run I-1. d The PR is connected with Run II-1. b The
Table 2 Influent waste activated sludge composition Concentration (mg/l) (average value) COD Total Soluble Protein Total Soluble Carbohydrate Total Soluble
10,100 2500 5500 1500 750 150
Table 3 Specification of membrane Parameters
Specification
Type Pore size (tm) Diameter (mm) Internal External Material Effective area (m2 )
Hollow fiber (MF) 0.1 0.7 1 PS (poly sulfone) 6.25 × 10−2
Fig. 1. Schematic diagrams for the continuous experiment: (A) submerged membrane AR and PR; (B) external membrane AR and PR. a; influent reactor (WAS), b; feed pump, c; suction pump, d; acid reactor (AR), e; membrane reactor, f; permeate reactor, g; photosynthetic reactor (PR), h; effluent reactor, i; air pump.
T.-Y. Jeong et al. / International Journal of Hydrogen Energy 32 (2007) 525 – 530
composition and VFA were analyzed by gas chromatography utilizing thermal conductivity detector (TCD) and flame ionization detector (FID).
3. Results and discussion 3.1. Acid fermentation reactor (AR)
permeate from submerged and external membrane reactor averaged 950 and 300 mg/l, respectively. The T-VFA production rates per COD removal of permeate averaged 0.05% and 0.15%, respectively. The reason for this was considered to be due to the interception effect of the membrane. With submerged membrane, the concentration of T-VFA in the AR and permeate slowly decreased after 17 days. The reason for this was considered to be as a result of the acid fermentation bacteria taking part in the biomass growth as a substrate for producing T-VFA due to the interception effect of the membrane in the reactor. However, the concentration of T-VFA in the AR and permeate, with the external membrane showed much higher permeate efficiency than with submerged membrane. 3.2. Photosynthetic reactor (PR) Generally, photosynthetic bacteria have been reported to use various organic matters, such as sugars, organic acids and VFA, for their hydrogen production. Also, the hydrogen production reactions using VFA by the photosynthetic bacteria are as follows: Acetate + 2H2 O → 2CO2 + 8H+ + 8e− → 2CO2 + 4H2 , G = 75.2 kJ, Butyrate + 6H2 O → 4CO2 + 20H+ + 20e− → 4CO2 + 10H2 , G = 223.3 kJ, Lactate + 3H2 O → 3CO2 + 12H+ + 12e− → 3CO2 + 6H2 , G = 51.2 kJ. This study observed the hydrogen production using R. Sphaeroides from the T-VFA produced in the AR. Fig. 5 shows the variation of hydrogen production. As shown Fig. 5, the hydrogen gas content in the PR started after 15 days, and the hydrogen gas production per T-VFA produced from a submerged and external membrane was 15 and 100 ml/l/d,
40
40
30
30 Gas composition (%)
Gas composition (%)
Fig. 2 shows the components of the gas composition in the AR. With submerged membrane (Fig. 2(a)), the methane gas content was increased over time because the SRT (sludge retention time) was longer due to the interception effect of membrane. Hence, the growth of the methane bacteria was inhibited due to the additional BESA (2-Bromoethane sulfonic acid). Whereas, with external membrane, the methane gas content (Fig. 2(b)) showed a little variation. Generally, the C. beijerinckii bacteria in the acid fermentation reactor used in the study are known to produce hydrogen by degrading carbohydrates. However, the WAS used in this study was not able to produce the expected hydrogen because carbohydrates concentration was very low. Fig. 3 shows the COD removal in the AR. The COD removal in the AR and permeate with submerged membrane reactor were 65% and 75%, respectively. With external membrane reactor, these were 40% and 55%, respectively. Therefore, the submerged membrane AR showed higher COD removals than external membrane AR. The reason for this was considered to be due to the C. beijerinckii bacteria accumulated in reactor caused by the interception effect of the membrane. Fig. 4 shows the variation in the total volatile fatty acid (T-VFA). The T-VFA concentration in the influent WAS was about 250 mg/l and those produced in submerged and external membrane AR averaged 550 and 1100 mg/l, respectively. Also, T-VFA production rates per COD removal averaged 0.11% and 0.18%, respectively. The T-VFA concentration of
H2 CH4
20
CO2
H2
20
CH4 CO2
10
10
0
0 0
(a)
527
20
40
60
Time (days)
80
0
100
20
(b)
Fig. 2. Gas compositions in the AR: (a) Run I-1; (b) Run II-1.
40
60
Time (days)
80
100
528
T.-Y. Jeong et al. / International Journal of Hydrogen Energy 32 (2007) 525 – 530
100
100 Run I-1
90
Run I-1
90
Run II-1
80
80
70
70
COD removal (%)
COD removal (%)
Run II-1
60 50 40 30
60 50 40 30
20
20
10
10
0
0 0
20
(a)
40 60 Time (days)
80
0
100
20
40 60 Time (days)
(b)
80
100
1400
1400
1200
1200
1000
1000
Total VFA (mg/l)
Total VFA (mg /L)
Fig. 3. COD removal rates in the AR: (a) supernatant; (b) permeate.
Run I-1
800
Run II-1 600
800 Run I-1 600
400
400
200
200
0
Run II-1
0 0
20
40
60
80
100
Time (days)
(a)
0
20
40
60
80
100
Time (days)
(b)
Fig. 4. Variation of total VFA productions in the AR: (a) supernatant; (b) permeate.
influent 18
12
600
10 8
400
6 4
200
H2 gas 1000 T-VFA (mg/L)
T-VFA (mg/L)
14
H2 gas production (ml /L/day)
16
H2 gas
0
(a)
20
40
60
Time (days)
80
180 160 140 120
800
100 600
80
400
60 40
200
2 0
effluent
1200
effluent
0 100
20
0 0
(b)
20
40
60
Time (days)
Fig. 5. Variations of hydrogen gas production and T-VFA in the PR: (a) Run I-2; (b) Run II-2.
80
0 100
H2 gas production (ml/L/day)
influent 800
200
1400
20
1000
T.-Y. Jeong et al. / International Journal of Hydrogen Energy 32 (2007) 525 – 530
respectively. All the T-VFA removal rates were 60% and above. The observed hydrogen production efficiency in the PR with a submerged membrane AR was lower than that with the external membrane AR. The reason for this was considered to be the T-VFA concentration of the permeate caused by the accumulation of acid production bacteria, and the longer SRT showed a lower value for the activation of the photosynthetic bacteria, and with the additional BESA inhibiting the growth of the methane bacteria. Whereas, the PR is connected with the external membrane AR showed approximately 9 times increase in the hydrogen production. Fig. 6 shows the hydrogen production per T-VFA removed. As shown Fig. 6, the hydrogen productions in the PR, with submerged and external membranes AR were 50.1 and 160.5 ml H2 /g T-VFA, respectively. In conclusion, if it is possible to acquire more organic acid from the AR using the WAS; it should
H2 gas production (ml/g T-VFA/day)
240 Submerged membrane AR + PR External membrane AR + PR
220 200 180 160 140 120
529
be possible to increase the production of hydrogen utilizing the photosynthetic bacteria. Also, it is expected that hydrogen gas could be useful substitute energy, from waste materials if the separation membrane in the hydrogen producing process is used properly. 3.3. Variation of MLVSS Fig. 7 shows the MLVSS of the AR and the PR. C. beijerinckii was accumulated in the reactors with submerged and external membranes due to membrane separation effect. Acid fermentation bacteria are accumulated in the AR due to the recirculation of the MLVSS with the submerged membranes. In the case of external membrane reactor, the reactor broths were not circulated between the AR and the membrane reactor. The AR with external membrane system does not expect accumulation of bacteria but keep the SS concentration constant. Therefore, the AR with submerged membrane has higher bacteria concentration than the AR with external membrane, and it caused higher COD removal rates in the AR with submerged membrane. The growth rate of photosynthetic bacteria was faster in the PR with submerged membrane AR (Run I-2) than the PR with external membrane AR (Run II-2). In case of Run I-2, bacterial concentration was maintained at 2100 mg/l of MLVSS in 70 days while, in case of Run II-2, the same concentration was achieved in 50 days.
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4. Conclusion and summary
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The WAS influenced from the AR showed no direct production of hydrogen gas when using hydrogen producing bacteria (C. beijerinckii) with low concentration of carbohydrates. The COD removal rates from submerged and external membrane AR were 65% and 40%, respectively. The COD removals with submerged membrane were higher than those with external membrane. The T-VFA concentration produced in submerged
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and external membrane AR averaged 550 and 1100 mg/l, respectively. Also, the T-VFA production rates per COD removed averaged 0.11% and 0.18%, respectively. The hydrogen gas production per T-VFA produced from submerged and external membrane was 15 and 100 ml/l/d, respectively. The hydrogen productions in the PR, with submerged and external membranes AR were 50.1 and 160.5 ml H2 /g T-VFA, respectively. These results indicate that an acid fermentation reactor with membrane separation system will operate as bioreactor in which VFA produce from WAS effectively and the PR is connected with membrane separation AR shows a synergic effect of hydrogen production. Acknowledgments This work was supported by the Brain Korea 21 project. References [1] Bockris JOM. Hydrogen economy. Science 1972;176:1323. [2] Maugh TH. Hydrogen: synthetic fuel of the future. Science 1972; 178:849.
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