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Fermentative biohydrogen production from starch-containing textile wastewater
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 2 0 5 0 e2 0 5 7
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Fermentative biohydrogen production from starch-containing textile wastewater Chyi-How Lay a,b, Szu-Yu Kuo c, Biswarup Sen d, Chin-Chao Chen e, Jo-Shu Chang f, Chiu-Yue Lin a,b,g,* a
Department of Environmental Engineering and Science, Feng Chia University, Taiwan Green Energy Development Center, Feng Chia University, Taiwan c Master Program of Green Energy Science and Technology, Feng Chia University, Taiwan d Microbial Sciences Division, Agharkar Research Institute, Pune 411004, India e Department of Landscape Architecture, Chungchou Institute of Technology, Taiwan f Department of Chemical Engineering, National Cheng Kung University, Taiwan g Department of Water Resources Engineering, Feng Chia University, Taiwan b
article info
abstract
Article history:
The present study deals with the biohydrogen production from starch-containing waste-
Received 28 April 2011
water collected from the textile industry in Taiwan. The effects of inoculums collected
Received in revised form
from different sources (sewage sludge, soil and cow dung), substrate concentrations
2 August 2011
(5e25 g COD/L) and pH (4.0e8.0) on hydrogen production from wastewater were investigated.
Accepted 2 August 2011 Available online 1 September 2011
The cow dung seed had the highest hydrogen production of 101 mL with hydrogen content in biogas of 32.2%. It corresponds to a hydrogen yield (HY) of 1.56 mol H2/mol hexose and hydrogen production rate (HPR) of 0.93 L/L/d. Response surface methodology
Keywords:
was used to evaluate the effects of initial cultivation pH (4.0e8.0) and substrate concen-
Biohydrogen
tration (5e25 g COD/L) on the hydrogen production at 35 C. At pH 7.0 with a wastewater
Hydrogen yield
concentration of 20 g COD/L, a maximum hydrogen production of 66 mL with 31.9% H2 and
Hydrogen production rate
corresponding to an HY of 0.97 mol H2/mol hexose and an HPR of 1.14 L/L/d were obtained.
Response surface methodology
According to the response surface analysis, the optimal conditions for high HPR were
Textile wastewater
a wastewater concentration of 13 g COD/L at an initial cultivation pH of 7.0. The main
Volatile fatty acid
soluble metabolic products were acetate and butyrate for hydrogen fermentation from textile wastewater. Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
1.
Introduction
Global fossil fuel energy reserves are going to be exhausted in near future and the environmental pollution problems associated due to their usage compel scientists to search for alternate energy sources that can substitute the
conventional ones. One of the most promising energy sources is hydrogen which is a clean energy source with high calorific value. Hydrogen production using wastewater is a promising technology. It not only helps in the treatment of the waste but also in generation of the eco-friendly energy source.
* Corresponding author. Department of Environmental Engineering and Science, Feng Chia University, Taiwan. Tel.: þ886 4 2451 7250x6200; fax: þ886 4 35072114. E-mail address: [email protected] (C.-Y. Lin). 0360-3199/$ e see front matter Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2011.08.003
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i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 2 0 5 0 e2 0 5 7
2.3.
Organic wastewater is a potential bioenergy source by anaerobic fermentation technology. Hydrogen generation from wastewater costs less and can be carried out using local feedstock [1]. Cotton textile industries are characterized by high water consumption during the pre-treatment (desizingescouringebleaching) and dyeing processes. Thus, the wastewater contains a variety of polluting compounds the sources of which are the natural impurities extracted from the cotton fiber, the processing chemicals and the dyes. The discharge of textile wastewater to the environment causes environment pollution [2]. The present study deals with the fermentative biohydrogen production from starch-containing wastewater collected from the textile industry in Taiwan. The effects of inoculums collected from different sources (sewage sludge, soil and cow dung), substrate concentrations (5e25 g COD/L) and pH (4.0e8.0) on hydrogen production from the wastewater were investigated.
Experimental procedures
Batch hydrogen production experiments were performed using serum bottles (125 mL) with anaerobic head space. In the vials there were 25 mL of seed inoculum, 10 mL of nutrient solution, 5 mL of pH adjustment solution (1 N HCl or 1 N NaOH) and 20 mL of substrate. The vials were initially gassed with argon to remove oxygen from the head space for maintaining anaerobic environment and then incubated in a reciprocal airbath shaker. Each experimental condition was carried out in triplicate. The volume and composition of gas and the concentrations of volatile fatty acids (VFAs) produced in 120 h or 212.5 h cultivation were determined.
2.3.1.
Effect of various seed inoculums
The vials were cultivated with substrate concentration 20 g COD/L at 35 C and initial cultivation pH 7.0.
2.3.2. Effect of initial cultivation pH and substrate concentration
2.
Materials and methods
2.1.
Seed inoculums
RSM was used to assess the relationship between the response functions and variables [3e5]. The variables studied were substrate concentrations (5, 10, 15, 20 and 25 g COD/L) and initial cultivation pH (4, 5, 6, 7 and 8). The full-factorial centralcomposite-design matrix of two variables in coded is listed in Table 2a. The vials were cultivated at 35 C using cow dung as the seed.
The seed inoculums were collected from different sources (sewage sludges from different municipal wastewater treatment plants, soil and cow dung) located in central Taiwan. All the inoculums were pretreated at 95 C for 40 min to enrich the fermentative microbial flora whereas for the control no pre-treatment was done. The characteristics of the seed inoculums are shown in Table 1.
2.2.
2.3.3.
Effect of temperature
The vials were cultivated at initial cultivation pH 7.0 and substrate concentration 13 g COD/L using cow dung seed with cultivation temperatures of 35 and 55 C.
Bioreactors and substrate
Batch hydrogen production experiments were conducted using bioreactors of 125 mL capacity. The starch-containing wastewater was collected from a textile factory as the substrate. The collected wastewater was stored in a refrigerator at 4 C before use. The characteristics of the textile wastewater were: chemical oxygen demand (COD) 29.8 g/L, total carbohydrate 20.0e23.5 g/L and pH 7.2. The substrate concentrations of 5e25 g COD/L were supplemented with sufficient inorganic nutrients necessary for microorganisms (mg/L): NH4HCO3 5240, K2HPO4 125, MgCl26H2O 15, FeSO4 7H2O 25, CuSO45H2O 5, CoCl25H2O 0.125, NaHCO3 6720 [6].
2.4.
Monitoring and analysis
2.4.1.
Monitoring
During fermentation, the monitoring parameters were pH, ORP (oxidation-reduction potential), alkalinity, ethanol concentration, VFAs distribution and biogas production. The gas volume was determined by a gas-tight syringe at room temperature (20 C) and pressure (760 mm Hg). The optimal initial cultivation pH was defined as the pH giving peak hydrogen yield (HY) values. For the batch tests, peak HY and hydrogen production rate (HPR) values were determined based on the hydrogen production potential and maximum HPR data obtained from the modified Gompertz equation (Eq. (1)) [7].
Table 1 e Characteristics of the seed inoculums. Sludge type
pH
Alkalinity (g/L as CaCO3)
VSSa (g/L)
TCODa (mg/L)
Total carbohydrate (g/L)
Sewage sludge I Sewage sludge II Sewage sludge III Humus soil Cow dung
7.2 7.1 7.4 7.2 6.6
1.38 1.29 1.31 1.27 0.71
5.2 70.1 21.1 47.2 25.7
4720 2624 4566 3149 19760
775 410 1204 1770 1661
a VSS, volatile suspended solids; TCOD, total chemical oxygen demand.
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0.047 0.068 0.096 0.081 0.163
l (h) Rmax (mL/h) Pmax (mL)
0.985 0.991 0.995 0.999 0.985 16.4 26.5 26.6 22.6 32.2 37.9 76.0 65.1 54.8 100.6
Final Initial
7400 8800 8700 8500 10,500 191 343 295 244 371
*n ¼ 2; initial pH, 7.0; temperature, 35 C; SS, sewage sludge; HS, humus soil; CD, cow dung.
Modified Gompertz equation parameter values
r2
Table 2b summarizes the results of hydrogen production from the textile wastewater (20 g COD/L) at 35 C and initial cultivation pH 7.0 using various seed inoculums. The results indicate that the final pH and ORP were 5.58e6.32 and -191e371 mV, respectively, after 212.5 h fermentation. These five seed inoculums could convert the wastewater carbohydrate into hydrogen (Fig. 1). The peak cumulative hydrogen production of 101 mL with hydrogen content of 32.2% was obtained by using cow dung seed. The maximum HPR, specific HPR (SHPR) and HY were evaluated by modified Gompertz equation. The cow dung had peak hydrogen production efficiencies of HPRmax 0.93 L/L/d, SHPRmax 0.163 L/g VSS/d and
Final
Effect of various seed inoculums
Initial
3.1.
Final
Results and discussion
Final
3.
0.22 0.34 0.51 0.39 0.93
HPRmax (L/L/d)
Analysis
The analytical procedures of Standard Methods [8] were used to determine pH, ORP, alkalinity and VSS (volatile suspended solid) concentration of liquid content. Ethanol and VFA were analyzed with a gas chromatograph having a flame ionization detector (Shimadzu GC-14, Japan). Biogas composition was analyzed with a gas chromatograph having a thermal conductivity detector (China Chromatograph 8700T, Taiwan). Other analytical details for the VFA, ethanol and biogas assays were the same as those indicated in our previous studies [8,9]. Anthrone-sulphuric acid method was used to measure total carbohydrate concentration [10].
H2 (%)
2.4.2.
H2 (mL)
H(t) is the cumulative hydrogen production (mL); P is the hydrogen production potential (mL); Rm is the maximum hydrogen production rate (mL/h); e is 2.71828; l is the lag phase time (h) and t is the cultivation time (h). STATISTIC Software (version 6.0, Statsoft Inc., USA) and Sigmaplot Software (trial version 9.0, Systat Software Inc., USA) were used for regression and graphical analyses of the data obtained, respectively.
T-Carbohydrate (mg/L as glucose)
(1)
Alkalinity (mg/L as CaCO3)
Rm $e ðl tÞ þ 1 P
ORP (mV)
exp
pH
HðtÞ ¼ P$exp
58.7 0.4 4.5 0.2 0.6
10 10 20 20 15 15 15 15 5 25
0.5 0.8 1.3 1.0 2.3
5 7 5 7 6 6 4 8 6 6
39.0 73.4 52.3 64.7 99.8
1 1 1 1 0 0 0 0 2 2
3962 4575 3715 5403 5336
1 1 1 1 0 0 2 2 0 0
13,237 11,420 12,020 12,637 13,145
x2 (substrate concentration, g/L)
958 1675 1025 1500 1275
x1 (pH)
5.58 6.32 6.15 5.90 6.18
x2
SHPRmax (L/g VSS/d)
x1
SS 1 SS 2 SS 3 HS CD
Real Values
Seed
1 2 3 4 5 6 7 8 9 10
Code Values
Table 2b e Experimental results of hydrogen production from textile wastewater (20 g COD/L) using various seed inoculums.
No.
HYmax (mol H2/mol hexose)
Table 2a e Full-factorial central-composite-design matrix of two variables in coded.
0.51 1.31 0.88 0.95 1.56
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350
10000
300 8000
250
Products (mg COD/L)
Cumulative total biogas production (mL)
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200 150 SS 1 SS 2 SS 3 HS CD
100 50
6000
EtOH HAc HPr HBu HVa SMP
4000
2000
120 0
100
SS 1
SS 2
SS 3
Humus soil
Cow dung
Seed inoculums
80
Fig. 2 e Soluble metabolic product concentrations for hydrogen fermentation from the textile wastewater (SS, Sewage sludge; HS, Humus soil, CD, Cow dung).
60
40
20
0 0
50
100
150
200
250
Time (h)
Fig. 1 e Hourly variations of total biogas and hydrogen production from textile wastewater using various seed inoculums (SS, Sewage sludge; HS, Humus soil, CD, Cow dung).
HYmax 1.56 mol H2/mol hexose. The HPRmax and SHPRmax values were 70e323% higher than those of other seeds. Our previous studies had shown that cow dung has high hydrogen production efficiency from glucose, xylose and cellulose [11]. The soluble metabolic products (SMPs) concentrations for hydrogen fermentation from the textile wastewater at 35 C and initial cultivation pH 7.0 using various seed inoculums after 212.5 h fermentation are illustrated in Fig. 2a and b. The main metabolic product using sludge 1, sludge 2, sludge 3 and humus soil was acetate (48e69% of SMP). However, butyrate concentration of 7441 mg COD/L (87% of SMP) was higher than those of using other seed inoculums. Ethanol was the other main SMP with 254e1217 mg COD/L.
3.2. Effects of initial cultivation pH and substrate concentration The optimization of H2 production can be analyzed by means of the relationship existing between the response functions and process variables. HPRmax (L/L/d), HYmax (mol H2/mol hexose), hydrogen content (%) and cumulative hydrogen production (mL) were used as the response variables. The experimental design, hydrogen production performance and the modified Gompertz equation parameter values for optimizing the initial pH and substrate concentration at 35 C using cow dung seed inoculum are summarized in Table 2b. The hydrogen quantity varied from 0 to 66 mL and the hydrogen content in the biogas ranged from 0 to 32.2%. The
peak cumulative hydrogen production (66 mL) and hydrogen content of 32% were obtained at pH 7 and substrate concentration of 20 g COD/L (Run 4) and pH 6 and substrate concentration of 10 g COD/L (Run 2), respectively. The fermentation of cow dung only (Run 11) and textile wastewater only (Run 12) produced no biogas. The peak HPRmax 1.14 L/L/d, SHPRmax 0.3 L/g VSS/d and HYmax 0.97 mol H2/mol glucose were obtained at pH 7 and substrate concentration of 20 g COD/L (Run 4). A comparative study was carried out by Khanal et al. [12] on hydrogen production at initial pH 4.5 and 35 C from starch. According to the response surface analysis results (Fig. 3), the optimal substrate concentration for HPRmax, HYmax, cumulative hydrogen production and hydrogen content was 13 g COD/L. However, the optimal pHs for these hydrogen production indexes was 6.5e7.0. Fig. 3 reveals that the highest contour level corresponded to approximately 0.7 L/L/d at pH 7.0 and substrate concentration of 13 g COD/L. The main SMPs in an anaerobic hydrogen fermentation process are ethanol, acetate, butyrate and propionate. Table 3 shows that acetate and butyrate concentrations were obviously higher (28e64% and 17e60% of SMP, respectively) than those of other conditions for textile wastewater fermentation. However, low butanol concentrations (18e49 mg COD/L) were detected at pH 6e7 and low substrate concentration of 5e10 g COD/L (Runs 2, 4 and 9) with high butyrate concentration (1907e4790 mg COD/L).
3.3.
Effect of temperature
The cultivation conditions of initial pH 7.0 and substrate concentration of 13 g COD/L were used to investigate the optimal cultivation temperature for anaerobic hydrogen production from textile wastewater. The results indicate that the thermophilic fermentation could enhance the hydrogen production (Table 4). The cumulative hydrogen production 28.2 mL and hydrogen gas 22.6% at 55 C were higher than those of at 35 C with cumulative hydrogen production
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Fig. 3 e Contour plots of (a) hydrogen production rate (L/L/d), (b) hydrogen yield (mol H2/mol hexose), (c) hydrogen content (%), and (d) cumulative hydrogen production (mL).
Table 3 e Experimental design, hydrogen production performance and the modified Gompertz equation parameter values for optimizing the initial pH and substrate concentration at 35 C using cow dung seed inoculum. Run
1 2 3 4 5 6 7 8 9 10 11a 12a
pH
5 7 5 7 6 6 4 8 6 6 6.7 6.7
Substrate conc. (g COD/L)
H2 (mL)
CH2 (%)
10 10 20 20 15 15 15 15 5 25 0 20
NA 34.1 9.5 65.9 23.8 30.1 NA 11.7 13.2 0.6 2.1 NA
ND 32.2 15.6 31.9 30.5 30.9 ND 10.3 25.7 1.8 16.4 ND
NA, not available; ND, not detected. a Run 11, no substrate; Run 12, no seed.
Modified Gompertz equation parameter values 2
Pmax (mL)
Rmax (mL/h)
l (h)
r
NA 34.1 9.7 65.7 24.4 29.7 NA 11.8 13.2 0.2 NA NA
NA 2.7 0.4 2.9 0.8 1.9 NA 0.5 1.2 0.4 NA NA
NA 19.9 55.0 36.7 39.2 34.9 NA 48.3 13.4 0.4 NA NA
NA 0.999 0.985 0.999 0.992 0.999 NA 0.998 0.999 0.060 NA NA
HPRmax (L/L/d)
SHPRmax (L/g VSS/d)
HYmax (mol H2/mol hexose)
NA 1.08 0.16 1.14 0.31 0.76 NA 0.21 0.48 0.14 NA NA
NA 0.28 0.04 0.30 0.08 0.20 NA 0.06 0.12 0.04 NA NA
NA 0.62 0.38 0.97 0.41 0.66 NA 0.18 0.65 0.01 NA NA
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Table 4 e Soluble metabolic products for hydrogen production at various initial pHs and substrate concentrations at 35 C using cow dung as the seed inoculum. No
pH
Substrate conc. (gCOD/L)
Ethanol
Butanol
HAc
HPr
HBu
HVa
TVFA
SMP
ND 5 6 6 6 6 5 5 6 2 ND ND
572 3927 1365 4790 2342 2179 598 3216 1907 739 ND 206
619 4264 1394 5364 2382 2276 622 3919 2058 828 ND 266
(mg COD/L) 1 2 3 4 5 6 7 8 9 10 11a 12a
5 7 5 7 6 6 4 8 6 6 6.7 6.7
10 10 20 20 15 15 15 15 5 25 0 20
47 291 30 525 41 97 23 703 132 89 ND 60
ND 47 ND 49 ND ND ND ND 18 ND ND ND
396 2234 598 1833 758 741 374 2025 574 523 ND 156
88 179 84 130 86 83 75 167 94 74 ND 9
89 1509 677 2821 1492 1350 145 1020 1233 140 ND 41
ND, not detected. a Run 11, no substrate; Run 12, no seed.
Cumulative total biogas production (mL)
14.0 mL and hydrogen content 13.1% (Fig. 4). The HPR of 0.55 L/L/d, SHPR of 0.11 L/g VSS/d and HY of 0.375 mol H2/mol hexose at thermophilc fermentation (55 C) were 2 times higher than those of mesophilic fermentation (35 C). This HPR value was lower than the estimated value (higher than 0.7 L/L/
140
120
100 35 C 55 C
80
3.4.
60
40
20
30 0
Cumulative H production (mL)
d) by the RSM analysis. The reason could be the change in carbohydrate concentration which was used in this experiment (from 23.9 g/L to 20 g/L) after storage in the refrigerator at 4 C for 15 days. However, the total carbohydrate concentration was suggested as the index for hydrogen production from wastewaters (Table 5). The SMP concentration was comparable to those of thermophilc and mesophilic fermentations (Fig. 5). The ethanol concentration at 55 C was slightly higher than that of 35 C. In contrast higher propionate concentration was detected at 35 C. The propionate accumulation in an anaerobic process might inhibit biohydrogen production [12].
25
20
15
10
5
0 0
20
40
60
80
100
120
140
Time (h) Fig. 4 e Hourly variations of total biogas and hydrogen production from textile wastewater (13 g COD/L) using cow dung seed inoculums at 35 and 55 C.
Significances of the experimental results
The textile wastewater now-a-days constitutes an important environmental problem. The colour and toxic chemicals in textile wastewater, and the possible problems associated with the discharge of dyes and dye degradation products are of environmental concern [13]. Currently, biological and/or combination treatment systems can efficiency remove dyes [14]. This study carried out the biohydrogen production potential using anaerobic mixed microflora. The results indicated that the optimal textile wastewater concentration for peak hydrogen production efficiency is low (8e17 g COD/L). The reason might be due to the presence of toxic chemicals that represent major fraction of the COD and are inhibitory to the hydrogen production. High substrate concentration (about 40 g COD/L) of food wastewater [15] is mainly attributed to high carbohydrate content and that usually enhances the hydrogen production efficiency. Therefore, mixing of the textile wastewater and other carbohydrate-rich wastewater is suggested which could solve the disposal problem of textile wastewater and simultaneously generate bioenergy in form of hydrogen. It can also reduce the nutrient addition in the process, because some wastewaters contain nutrients, such as condensed molasses fermentation soluble [15] which is
2056
0.174 0.375
4000
Products (mg COD/L)
3000
0.05 0.11
SHPRmax (L/g VSS/d)
HYmax (mol H2/mol hexose)
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2000
SMP EtOH BuOH HAc HPr HBu HVa
0.25 0.55
HPRmax (L/L/d)
1000
0.981 0.990 6.7 11.8
Fig. 5 e Soluble metabolic products for hydrogen fermentation from textile wastewater (13 g COD/L) using cow dung seed inoculums at 35 and 55 C.
0.6 1.4
necessary for hydrogen producer. Moreover, the effluent from hydrogen production process can also be converted to methane and thus overall improve the energy production efficiency from textile wastewater.
14.1 28.6
r2 l (h) Rmax (mL/h)
3092 2612 9938 9337
14.0 28.2
Acknowledgments
*n ¼ 2; initial cultivation pH, 7.0.
2517 2250 3050 3100 451 444 7.11 6.94 35 55
Conclusions
The textile wastewater containing starch is a potential energy resource for anaerobic hydrogen fermentation. The hydrogen production efficiency depends on seed inoculums, initial cultivation pH, substrate concentration and operating temperature. At pH 7.0 and with a wastewater concentration of 20 g COD/L, a maximum hydrogen production of 66 mL with 32% H2 in the total biogas and corresponding to an HY of 0.97 mol H2/mol hexose and an HPR of 1.14 L/L/d was obtained. According to the response surface analysis, the optimal conditions for high HPR would be obtained at a wastewater concentration of 13 g COD/L at an initial pH of 7.0. The main soluble metabolic products were acetate and butyrate for hydrogen fermentation from textile wastewater.
13.1 22.6
Pmax (mL) Final Initial Initial Final Final
Final
Alkalinity (mg/L as CaCO3) pH
55
Temperature (oC)
4.
ORP (mV)
T-Carbohydrate (mg/L as glucose)
H2 (mL)
H2 (%)
Modified Gompertz equation parameter values
35
Temp. ( C)
Table 5 e Experimental results of hydrogen production from textile wastewater (13 g COD/L) at various cultivation temperatures.
0
The authors gratefully acknowledge the financial support by Taiwan’s Bureau of Energy (grant no. 99-D0204-3), Taiwan’s National Science Council (NSC-99-2221-E-035 -024 -MY3, NSC99-2221-E-035 -025 -MY3, NSC-99-2632-E-035 -001 -MY3), Feng Chia University (FCU-10G27101) and APEC Research Center for Advanced Biohydrogen Technology.
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[1] del Aguila NKS, Zaiat M. Potential to produce biohydrogen from various wastewaters. Energy for Sustainable Dev 2010; 14(2):143e8.
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[2] Georgiou D, Hatiras J, Aivasidis A. Microbial immobilization in a two-stage fixed-bed-reactor pilot plant for on-site anaerobic decolorization of textile wastewater. Enzyme Microb Technol 2005;37(6):597e605. [3] Box GEP, Hunter WG, Hunter JS. Statistics for experimenters. New York, USA: John Wiley & Sons; 1978. [4] Lay JJ. Modeling and optimization of anaerobic digested sludge converting starch to hydrogen. Biotechnol Bioeng 2000;68(3):269e78. [5] Wang J, Wan W. Experimental design methods for fermentative hydrogen production: a review. Int J Hydrogen Energy 2009;34(1):235e44. [6] Endo G, Noike T, Matsumoto J. Characteristics of cellulose and glucose decomposition in acidogenic phase of anaerobic digestion. Proc Soc Civ Engrs 1982; 325:61e8. [7] Lin CY, Lay CH. A nutrient formulation for fermentative hydrogen production using anaerobic sewage sludge microflora. Int J Hydrogen Energy 2005; 30(3):285e92. [8] APHA. Standard methods for the examination of water and wastewater. 19th ed. New York, USA: American Public Health Association; 1995.
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[9] Lin CY, Chang RC. Hydrogen production during the anaerobic acidogenic conversion of glucose. J Chem Technol Biotechnol 1999;74(6):498e500. [10] Khanal SK, Chen WH, Li L, Sung S. Biological hydrogen production: effects of pH and intermediate products. Int J Hydrogen Energy 2004;29(11):1123e31. [11] Lin CY, Hung WC. Enhancement of fermentative hydrogen/ ethanol production from cellulose using mixed culture. Int J Hydrogen Energy 2008;33(1):3660e7. [12] Wang L, Zhou Q, Li FT. Avoiding propionic acid accumulation in the anaerobic process for biohydrogen production. Biomass Bioenergy 2006;30(2):177e82. [13] Senthilkumar M, Gnanapragasam G, Arutchelvan V, Nagarajan S. Treatment of textile dyeing wastewater using two-phase pilot plant UASB reactor with sago wastewater as co-substrate. Chem Eng J 2011;166(1):10e4. [14] Pearce CI, Lloyd JR, Guthrie JT. The removal of colour from textile wastewater using whole bacterial cell: a review. Dyes Pigm 2003;58:179e96. [15] Lay CH, Wu JH, Hsiao CL, Chang JJ, Chen CC, Lin CY. Biohydrogen production from soluble condensed molasses fermentation using anaerobic fermentation. Int J Hydrogen Energy 2010;35(4):13445e51.
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journal homepage: www.elsevier.com/locate/he
Fermentative biohydrogen production from starch-containing textile wastewater Chyi-How Lay a,b, Szu-Yu Kuo c, Biswarup Sen d, Chin-Chao Chen e, Jo-Shu Chang f, Chiu-Yue Lin a,b,g,* a
Department of Environmental Engineering and Science, Feng Chia University, Taiwan Green Energy Development Center, Feng Chia University, Taiwan c Master Program of Green Energy Science and Technology, Feng Chia University, Taiwan d Microbial Sciences Division, Agharkar Research Institute, Pune 411004, India e Department of Landscape Architecture, Chungchou Institute of Technology, Taiwan f Department of Chemical Engineering, National Cheng Kung University, Taiwan g Department of Water Resources Engineering, Feng Chia University, Taiwan b
article info
abstract
Article history:
The present study deals with the biohydrogen production from starch-containing waste-
Received 28 April 2011
water collected from the textile industry in Taiwan. The effects of inoculums collected
Received in revised form
from different sources (sewage sludge, soil and cow dung), substrate concentrations
2 August 2011
(5e25 g COD/L) and pH (4.0e8.0) on hydrogen production from wastewater were investigated.
Accepted 2 August 2011 Available online 1 September 2011
The cow dung seed had the highest hydrogen production of 101 mL with hydrogen content in biogas of 32.2%. It corresponds to a hydrogen yield (HY) of 1.56 mol H2/mol hexose and hydrogen production rate (HPR) of 0.93 L/L/d. Response surface methodology
Keywords:
was used to evaluate the effects of initial cultivation pH (4.0e8.0) and substrate concen-
Biohydrogen
tration (5e25 g COD/L) on the hydrogen production at 35 C. At pH 7.0 with a wastewater
Hydrogen yield
concentration of 20 g COD/L, a maximum hydrogen production of 66 mL with 31.9% H2 and
Hydrogen production rate
corresponding to an HY of 0.97 mol H2/mol hexose and an HPR of 1.14 L/L/d were obtained.
Response surface methodology
According to the response surface analysis, the optimal conditions for high HPR were
Textile wastewater
a wastewater concentration of 13 g COD/L at an initial cultivation pH of 7.0. The main
Volatile fatty acid
soluble metabolic products were acetate and butyrate for hydrogen fermentation from textile wastewater. Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
1.
Introduction
Global fossil fuel energy reserves are going to be exhausted in near future and the environmental pollution problems associated due to their usage compel scientists to search for alternate energy sources that can substitute the
conventional ones. One of the most promising energy sources is hydrogen which is a clean energy source with high calorific value. Hydrogen production using wastewater is a promising technology. It not only helps in the treatment of the waste but also in generation of the eco-friendly energy source.
* Corresponding author. Department of Environmental Engineering and Science, Feng Chia University, Taiwan. Tel.: þ886 4 2451 7250x6200; fax: þ886 4 35072114. E-mail address: [email protected] (C.-Y. Lin). 0360-3199/$ e see front matter Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2011.08.003
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2.3.
Organic wastewater is a potential bioenergy source by anaerobic fermentation technology. Hydrogen generation from wastewater costs less and can be carried out using local feedstock [1]. Cotton textile industries are characterized by high water consumption during the pre-treatment (desizingescouringebleaching) and dyeing processes. Thus, the wastewater contains a variety of polluting compounds the sources of which are the natural impurities extracted from the cotton fiber, the processing chemicals and the dyes. The discharge of textile wastewater to the environment causes environment pollution [2]. The present study deals with the fermentative biohydrogen production from starch-containing wastewater collected from the textile industry in Taiwan. The effects of inoculums collected from different sources (sewage sludge, soil and cow dung), substrate concentrations (5e25 g COD/L) and pH (4.0e8.0) on hydrogen production from the wastewater were investigated.
Experimental procedures
Batch hydrogen production experiments were performed using serum bottles (125 mL) with anaerobic head space. In the vials there were 25 mL of seed inoculum, 10 mL of nutrient solution, 5 mL of pH adjustment solution (1 N HCl or 1 N NaOH) and 20 mL of substrate. The vials were initially gassed with argon to remove oxygen from the head space for maintaining anaerobic environment and then incubated in a reciprocal airbath shaker. Each experimental condition was carried out in triplicate. The volume and composition of gas and the concentrations of volatile fatty acids (VFAs) produced in 120 h or 212.5 h cultivation were determined.
2.3.1.
Effect of various seed inoculums
The vials were cultivated with substrate concentration 20 g COD/L at 35 C and initial cultivation pH 7.0.
2.3.2. Effect of initial cultivation pH and substrate concentration
2.
Materials and methods
2.1.
Seed inoculums
RSM was used to assess the relationship between the response functions and variables [3e5]. The variables studied were substrate concentrations (5, 10, 15, 20 and 25 g COD/L) and initial cultivation pH (4, 5, 6, 7 and 8). The full-factorial centralcomposite-design matrix of two variables in coded is listed in Table 2a. The vials were cultivated at 35 C using cow dung as the seed.
The seed inoculums were collected from different sources (sewage sludges from different municipal wastewater treatment plants, soil and cow dung) located in central Taiwan. All the inoculums were pretreated at 95 C for 40 min to enrich the fermentative microbial flora whereas for the control no pre-treatment was done. The characteristics of the seed inoculums are shown in Table 1.
2.2.
2.3.3.
Effect of temperature
The vials were cultivated at initial cultivation pH 7.0 and substrate concentration 13 g COD/L using cow dung seed with cultivation temperatures of 35 and 55 C.
Bioreactors and substrate
Batch hydrogen production experiments were conducted using bioreactors of 125 mL capacity. The starch-containing wastewater was collected from a textile factory as the substrate. The collected wastewater was stored in a refrigerator at 4 C before use. The characteristics of the textile wastewater were: chemical oxygen demand (COD) 29.8 g/L, total carbohydrate 20.0e23.5 g/L and pH 7.2. The substrate concentrations of 5e25 g COD/L were supplemented with sufficient inorganic nutrients necessary for microorganisms (mg/L): NH4HCO3 5240, K2HPO4 125, MgCl26H2O 15, FeSO4 7H2O 25, CuSO45H2O 5, CoCl25H2O 0.125, NaHCO3 6720 [6].
2.4.
Monitoring and analysis
2.4.1.
Monitoring
During fermentation, the monitoring parameters were pH, ORP (oxidation-reduction potential), alkalinity, ethanol concentration, VFAs distribution and biogas production. The gas volume was determined by a gas-tight syringe at room temperature (20 C) and pressure (760 mm Hg). The optimal initial cultivation pH was defined as the pH giving peak hydrogen yield (HY) values. For the batch tests, peak HY and hydrogen production rate (HPR) values were determined based on the hydrogen production potential and maximum HPR data obtained from the modified Gompertz equation (Eq. (1)) [7].
Table 1 e Characteristics of the seed inoculums. Sludge type
pH
Alkalinity (g/L as CaCO3)
VSSa (g/L)
TCODa (mg/L)
Total carbohydrate (g/L)
Sewage sludge I Sewage sludge II Sewage sludge III Humus soil Cow dung
7.2 7.1 7.4 7.2 6.6
1.38 1.29 1.31 1.27 0.71
5.2 70.1 21.1 47.2 25.7
4720 2624 4566 3149 19760
775 410 1204 1770 1661
a VSS, volatile suspended solids; TCOD, total chemical oxygen demand.
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0.047 0.068 0.096 0.081 0.163
l (h) Rmax (mL/h) Pmax (mL)
0.985 0.991 0.995 0.999 0.985 16.4 26.5 26.6 22.6 32.2 37.9 76.0 65.1 54.8 100.6
Final Initial
7400 8800 8700 8500 10,500 191 343 295 244 371
*n ¼ 2; initial pH, 7.0; temperature, 35 C; SS, sewage sludge; HS, humus soil; CD, cow dung.
Modified Gompertz equation parameter values
r2
Table 2b summarizes the results of hydrogen production from the textile wastewater (20 g COD/L) at 35 C and initial cultivation pH 7.0 using various seed inoculums. The results indicate that the final pH and ORP were 5.58e6.32 and -191e371 mV, respectively, after 212.5 h fermentation. These five seed inoculums could convert the wastewater carbohydrate into hydrogen (Fig. 1). The peak cumulative hydrogen production of 101 mL with hydrogen content of 32.2% was obtained by using cow dung seed. The maximum HPR, specific HPR (SHPR) and HY were evaluated by modified Gompertz equation. The cow dung had peak hydrogen production efficiencies of HPRmax 0.93 L/L/d, SHPRmax 0.163 L/g VSS/d and
Final
Effect of various seed inoculums
Initial
3.1.
Final
Results and discussion
Final
3.
0.22 0.34 0.51 0.39 0.93
HPRmax (L/L/d)
Analysis
The analytical procedures of Standard Methods [8] were used to determine pH, ORP, alkalinity and VSS (volatile suspended solid) concentration of liquid content. Ethanol and VFA were analyzed with a gas chromatograph having a flame ionization detector (Shimadzu GC-14, Japan). Biogas composition was analyzed with a gas chromatograph having a thermal conductivity detector (China Chromatograph 8700T, Taiwan). Other analytical details for the VFA, ethanol and biogas assays were the same as those indicated in our previous studies [8,9]. Anthrone-sulphuric acid method was used to measure total carbohydrate concentration [10].
H2 (%)
2.4.2.
H2 (mL)
H(t) is the cumulative hydrogen production (mL); P is the hydrogen production potential (mL); Rm is the maximum hydrogen production rate (mL/h); e is 2.71828; l is the lag phase time (h) and t is the cultivation time (h). STATISTIC Software (version 6.0, Statsoft Inc., USA) and Sigmaplot Software (trial version 9.0, Systat Software Inc., USA) were used for regression and graphical analyses of the data obtained, respectively.
T-Carbohydrate (mg/L as glucose)
(1)
Alkalinity (mg/L as CaCO3)
Rm $e ðl tÞ þ 1 P
ORP (mV)
exp
pH
HðtÞ ¼ P$exp
58.7 0.4 4.5 0.2 0.6
10 10 20 20 15 15 15 15 5 25
0.5 0.8 1.3 1.0 2.3
5 7 5 7 6 6 4 8 6 6
39.0 73.4 52.3 64.7 99.8
1 1 1 1 0 0 0 0 2 2
3962 4575 3715 5403 5336
1 1 1 1 0 0 2 2 0 0
13,237 11,420 12,020 12,637 13,145
x2 (substrate concentration, g/L)
958 1675 1025 1500 1275
x1 (pH)
5.58 6.32 6.15 5.90 6.18
x2
SHPRmax (L/g VSS/d)
x1
SS 1 SS 2 SS 3 HS CD
Real Values
Seed
1 2 3 4 5 6 7 8 9 10
Code Values
Table 2b e Experimental results of hydrogen production from textile wastewater (20 g COD/L) using various seed inoculums.
No.
HYmax (mol H2/mol hexose)
Table 2a e Full-factorial central-composite-design matrix of two variables in coded.
0.51 1.31 0.88 0.95 1.56
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350
10000
300 8000
250
Products (mg COD/L)
Cumulative total biogas production (mL)
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200 150 SS 1 SS 2 SS 3 HS CD
100 50
6000
EtOH HAc HPr HBu HVa SMP
4000
2000
120 0
100
SS 1
SS 2
SS 3
Humus soil
Cow dung
Seed inoculums
80
Fig. 2 e Soluble metabolic product concentrations for hydrogen fermentation from the textile wastewater (SS, Sewage sludge; HS, Humus soil, CD, Cow dung).
60
40
20
0 0
50
100
150
200
250
Time (h)
Fig. 1 e Hourly variations of total biogas and hydrogen production from textile wastewater using various seed inoculums (SS, Sewage sludge; HS, Humus soil, CD, Cow dung).
HYmax 1.56 mol H2/mol hexose. The HPRmax and SHPRmax values were 70e323% higher than those of other seeds. Our previous studies had shown that cow dung has high hydrogen production efficiency from glucose, xylose and cellulose [11]. The soluble metabolic products (SMPs) concentrations for hydrogen fermentation from the textile wastewater at 35 C and initial cultivation pH 7.0 using various seed inoculums after 212.5 h fermentation are illustrated in Fig. 2a and b. The main metabolic product using sludge 1, sludge 2, sludge 3 and humus soil was acetate (48e69% of SMP). However, butyrate concentration of 7441 mg COD/L (87% of SMP) was higher than those of using other seed inoculums. Ethanol was the other main SMP with 254e1217 mg COD/L.
3.2. Effects of initial cultivation pH and substrate concentration The optimization of H2 production can be analyzed by means of the relationship existing between the response functions and process variables. HPRmax (L/L/d), HYmax (mol H2/mol hexose), hydrogen content (%) and cumulative hydrogen production (mL) were used as the response variables. The experimental design, hydrogen production performance and the modified Gompertz equation parameter values for optimizing the initial pH and substrate concentration at 35 C using cow dung seed inoculum are summarized in Table 2b. The hydrogen quantity varied from 0 to 66 mL and the hydrogen content in the biogas ranged from 0 to 32.2%. The
peak cumulative hydrogen production (66 mL) and hydrogen content of 32% were obtained at pH 7 and substrate concentration of 20 g COD/L (Run 4) and pH 6 and substrate concentration of 10 g COD/L (Run 2), respectively. The fermentation of cow dung only (Run 11) and textile wastewater only (Run 12) produced no biogas. The peak HPRmax 1.14 L/L/d, SHPRmax 0.3 L/g VSS/d and HYmax 0.97 mol H2/mol glucose were obtained at pH 7 and substrate concentration of 20 g COD/L (Run 4). A comparative study was carried out by Khanal et al. [12] on hydrogen production at initial pH 4.5 and 35 C from starch. According to the response surface analysis results (Fig. 3), the optimal substrate concentration for HPRmax, HYmax, cumulative hydrogen production and hydrogen content was 13 g COD/L. However, the optimal pHs for these hydrogen production indexes was 6.5e7.0. Fig. 3 reveals that the highest contour level corresponded to approximately 0.7 L/L/d at pH 7.0 and substrate concentration of 13 g COD/L. The main SMPs in an anaerobic hydrogen fermentation process are ethanol, acetate, butyrate and propionate. Table 3 shows that acetate and butyrate concentrations were obviously higher (28e64% and 17e60% of SMP, respectively) than those of other conditions for textile wastewater fermentation. However, low butanol concentrations (18e49 mg COD/L) were detected at pH 6e7 and low substrate concentration of 5e10 g COD/L (Runs 2, 4 and 9) with high butyrate concentration (1907e4790 mg COD/L).
3.3.
Effect of temperature
The cultivation conditions of initial pH 7.0 and substrate concentration of 13 g COD/L were used to investigate the optimal cultivation temperature for anaerobic hydrogen production from textile wastewater. The results indicate that the thermophilic fermentation could enhance the hydrogen production (Table 4). The cumulative hydrogen production 28.2 mL and hydrogen gas 22.6% at 55 C were higher than those of at 35 C with cumulative hydrogen production
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Fig. 3 e Contour plots of (a) hydrogen production rate (L/L/d), (b) hydrogen yield (mol H2/mol hexose), (c) hydrogen content (%), and (d) cumulative hydrogen production (mL).
Table 3 e Experimental design, hydrogen production performance and the modified Gompertz equation parameter values for optimizing the initial pH and substrate concentration at 35 C using cow dung seed inoculum. Run
1 2 3 4 5 6 7 8 9 10 11a 12a
pH
5 7 5 7 6 6 4 8 6 6 6.7 6.7
Substrate conc. (g COD/L)
H2 (mL)
CH2 (%)
10 10 20 20 15 15 15 15 5 25 0 20
NA 34.1 9.5 65.9 23.8 30.1 NA 11.7 13.2 0.6 2.1 NA
ND 32.2 15.6 31.9 30.5 30.9 ND 10.3 25.7 1.8 16.4 ND
NA, not available; ND, not detected. a Run 11, no substrate; Run 12, no seed.
Modified Gompertz equation parameter values 2
Pmax (mL)
Rmax (mL/h)
l (h)
r
NA 34.1 9.7 65.7 24.4 29.7 NA 11.8 13.2 0.2 NA NA
NA 2.7 0.4 2.9 0.8 1.9 NA 0.5 1.2 0.4 NA NA
NA 19.9 55.0 36.7 39.2 34.9 NA 48.3 13.4 0.4 NA NA
NA 0.999 0.985 0.999 0.992 0.999 NA 0.998 0.999 0.060 NA NA
HPRmax (L/L/d)
SHPRmax (L/g VSS/d)
HYmax (mol H2/mol hexose)
NA 1.08 0.16 1.14 0.31 0.76 NA 0.21 0.48 0.14 NA NA
NA 0.28 0.04 0.30 0.08 0.20 NA 0.06 0.12 0.04 NA NA
NA 0.62 0.38 0.97 0.41 0.66 NA 0.18 0.65 0.01 NA NA
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Table 4 e Soluble metabolic products for hydrogen production at various initial pHs and substrate concentrations at 35 C using cow dung as the seed inoculum. No
pH
Substrate conc. (gCOD/L)
Ethanol
Butanol
HAc
HPr
HBu
HVa
TVFA
SMP
ND 5 6 6 6 6 5 5 6 2 ND ND
572 3927 1365 4790 2342 2179 598 3216 1907 739 ND 206
619 4264 1394 5364 2382 2276 622 3919 2058 828 ND 266
(mg COD/L) 1 2 3 4 5 6 7 8 9 10 11a 12a
5 7 5 7 6 6 4 8 6 6 6.7 6.7
10 10 20 20 15 15 15 15 5 25 0 20
47 291 30 525 41 97 23 703 132 89 ND 60
ND 47 ND 49 ND ND ND ND 18 ND ND ND
396 2234 598 1833 758 741 374 2025 574 523 ND 156
88 179 84 130 86 83 75 167 94 74 ND 9
89 1509 677 2821 1492 1350 145 1020 1233 140 ND 41
ND, not detected. a Run 11, no substrate; Run 12, no seed.
Cumulative total biogas production (mL)
14.0 mL and hydrogen content 13.1% (Fig. 4). The HPR of 0.55 L/L/d, SHPR of 0.11 L/g VSS/d and HY of 0.375 mol H2/mol hexose at thermophilc fermentation (55 C) were 2 times higher than those of mesophilic fermentation (35 C). This HPR value was lower than the estimated value (higher than 0.7 L/L/
140
120
100 35 C 55 C
80
3.4.
60
40
20
30 0
Cumulative H production (mL)
d) by the RSM analysis. The reason could be the change in carbohydrate concentration which was used in this experiment (from 23.9 g/L to 20 g/L) after storage in the refrigerator at 4 C for 15 days. However, the total carbohydrate concentration was suggested as the index for hydrogen production from wastewaters (Table 5). The SMP concentration was comparable to those of thermophilc and mesophilic fermentations (Fig. 5). The ethanol concentration at 55 C was slightly higher than that of 35 C. In contrast higher propionate concentration was detected at 35 C. The propionate accumulation in an anaerobic process might inhibit biohydrogen production [12].
25
20
15
10
5
0 0
20
40
60
80
100
120
140
Time (h) Fig. 4 e Hourly variations of total biogas and hydrogen production from textile wastewater (13 g COD/L) using cow dung seed inoculums at 35 and 55 C.
Significances of the experimental results
The textile wastewater now-a-days constitutes an important environmental problem. The colour and toxic chemicals in textile wastewater, and the possible problems associated with the discharge of dyes and dye degradation products are of environmental concern [13]. Currently, biological and/or combination treatment systems can efficiency remove dyes [14]. This study carried out the biohydrogen production potential using anaerobic mixed microflora. The results indicated that the optimal textile wastewater concentration for peak hydrogen production efficiency is low (8e17 g COD/L). The reason might be due to the presence of toxic chemicals that represent major fraction of the COD and are inhibitory to the hydrogen production. High substrate concentration (about 40 g COD/L) of food wastewater [15] is mainly attributed to high carbohydrate content and that usually enhances the hydrogen production efficiency. Therefore, mixing of the textile wastewater and other carbohydrate-rich wastewater is suggested which could solve the disposal problem of textile wastewater and simultaneously generate bioenergy in form of hydrogen. It can also reduce the nutrient addition in the process, because some wastewaters contain nutrients, such as condensed molasses fermentation soluble [15] which is
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0.174 0.375
4000
Products (mg COD/L)
3000
0.05 0.11
SHPRmax (L/g VSS/d)
HYmax (mol H2/mol hexose)
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2000
SMP EtOH BuOH HAc HPr HBu HVa
0.25 0.55
HPRmax (L/L/d)
1000
0.981 0.990 6.7 11.8
Fig. 5 e Soluble metabolic products for hydrogen fermentation from textile wastewater (13 g COD/L) using cow dung seed inoculums at 35 and 55 C.
0.6 1.4
necessary for hydrogen producer. Moreover, the effluent from hydrogen production process can also be converted to methane and thus overall improve the energy production efficiency from textile wastewater.
14.1 28.6
r2 l (h) Rmax (mL/h)
3092 2612 9938 9337
14.0 28.2
Acknowledgments
*n ¼ 2; initial cultivation pH, 7.0.
2517 2250 3050 3100 451 444 7.11 6.94 35 55
Conclusions
The textile wastewater containing starch is a potential energy resource for anaerobic hydrogen fermentation. The hydrogen production efficiency depends on seed inoculums, initial cultivation pH, substrate concentration and operating temperature. At pH 7.0 and with a wastewater concentration of 20 g COD/L, a maximum hydrogen production of 66 mL with 32% H2 in the total biogas and corresponding to an HY of 0.97 mol H2/mol hexose and an HPR of 1.14 L/L/d was obtained. According to the response surface analysis, the optimal conditions for high HPR would be obtained at a wastewater concentration of 13 g COD/L at an initial pH of 7.0. The main soluble metabolic products were acetate and butyrate for hydrogen fermentation from textile wastewater.
13.1 22.6
Pmax (mL) Final Initial Initial Final Final
Final
Alkalinity (mg/L as CaCO3) pH
55
Temperature (oC)
4.
ORP (mV)
T-Carbohydrate (mg/L as glucose)
H2 (mL)
H2 (%)
Modified Gompertz equation parameter values
35
Temp. ( C)
Table 5 e Experimental results of hydrogen production from textile wastewater (13 g COD/L) at various cultivation temperatures.
0
The authors gratefully acknowledge the financial support by Taiwan’s Bureau of Energy (grant no. 99-D0204-3), Taiwan’s National Science Council (NSC-99-2221-E-035 -024 -MY3, NSC99-2221-E-035 -025 -MY3, NSC-99-2632-E-035 -001 -MY3), Feng Chia University (FCU-10G27101) and APEC Research Center for Advanced Biohydrogen Technology.
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