Ind. Eng. Chem. Res. 2009, 48, 2493–2498
2493
Bioconversion of Aging Corn to Biohydrogen by Dairy Manure Compost Yaoting Fan,*,† Yiping Guo,† Chunmei Pan,†,‡ and Hongwei Hou† Department of Chemistry, Zhengzhou UniVersity, Zhengzhou, Henan 450052, P. R. China, and Department of Biotechnology, Zhengzhou College of Animal Husbandry Engineering, Zhengzhou, Henan 450011, P. R. China
Biohydrogen production by anaerobic culture using aging corn as the feedstock is reported for the first time. The biopretreatment of aging corn with solid microbe additives was essential for adequate conversion of the substrate into biohydrogen. The maximum H2 yield (Ps) and H2 production rate (R) utilizing aging corn were 346 (mL of H2)/(g of TVS) and 11.8 mL/h, respectively, at a fixed substrate concentration of 10 g/L and an initial pH of 6.0 by dairy manure compost in a batch validation test. The H2 yield was approximately 2.5 times that obtained from raw aging corn. During the optimal hydrogen-producing period, the oxidation-reduction potential ranged from -521 to -458 mV. Both butyrate (49.4-55.7%) and acetate (23.7-28.5%) as the two main byproducts were left in the reactor in the process of hydrogen fermentation during the conversion of aging corn into hydrogen. 1. Introduction Considering global environmental impacts, such as the greenhouse effect and resource recovery, increasingly stringent requirements for the control of pollution from the use of fossil fuels are challenging the scientific community to develop nonpolluting and renewable energy source strategies. Effective biohydrogen production from biomass wastes is an attractive paradigm that could not only produce clean biologic energy but also clean up the environment.1 Moreover, hydrogen as an excellent alternative energy candidate is attracting increasing interest because of its environmentally friendly and energysaving process,1,2 as well as its production of only water instead of greenhouse gases upon combustion. 3–5 Meanwhile, hydrogen can provide a high calorific value of 142.35 kJ/g, which is about 2.75 times that of fossil fuel.2 In addition, hydrogen is also a high-value industrial commodity with a wide range of applications.1,3–6 For example, it can be used for the syntheses of ammonia, alcohols, and aldehydes, as well as for the hydrogenations of edible oils, petroleum, coal, and shale oil.3 A hydrogenbased economy could impose no risk of global warming and will significantly improve the environmental quality of the community atmosphere.1 Many people believe that hydrogen will substitute fossil fuels as the next generation of clean energy sources. Traditionally, hydrogen has mainly been generated by fossil fuels or the electrolysis of water;7,8 however, fossil fuels are limited and nonrenewable resources. From environment and sustainable-energy points of view, microbial hydrogen production from renewable organic wastes can reduce dependence on fossil fuel, decrease carbon dioxide emissions, and recover bioenergy.5,6,8,9 At present, most biohydrogen-production studies have focused on using mixed cultures because of lower costs, ease of control, and the possible use of organic wastes as substrates.5,6,10–14 Recently, Fang and Li reported acidophilic biohydrogen production from a rice slurry in batch experiments, in which the maximum hydrogen yield of 346 mL/(g of carbohydrate) was obtained at pH 4.5.1 * To whom correspondence should be addressed. Tel./Fax: +86(0)371-67766017. E-mail:
[email protected], yt.fan@zzu. edu.cn. † Zhengzhou University. ‡ Zhengzhou College of Animal Husbandry Engineering.
Aging corn, as a common starch-rich substrate, is a valuable and vast renewable biomass resource. The Chinese National Grain and Oils Information Center (CNGOIC) reported that the Chinese annual yield of corn exceed 1.46 hundred million tons in 2006, of which 73% was used for feed, 13% for food, 11% for industry, 1% for seed, and 2% was left as aging corn (about 3 million tons).2,15 The aging corn, however, needs to be converted into a high-value-added product. An alternative approach is to convert aging corn to biohydrogen as a highvalue-added clean energy source. Although producing bioalcohol from aging corn by anaerobic hydrogen fermentation has been successfully achieved in China, so far, little information is known about biohydrogen production by mixed culture using aging corn as the feedstock. For the above reasons, the focus of this study was investigating the performance and optimal operating conditions of biohydrogen production from aging corn as the feedstock by dairy manure compost and evaluating its feasibility for biohydrogen production. 2. Materials and Methods 2.1. Seed Hydrogen-Producing Microflora. The seed microorganism, dairy manure compost, was taken from the suburb of Zhengzhou city in batch tests. Before it was used, the compost (20 g) was placed onto a 30-cm stainless steel pizza pan to a depth of 1 cm and baked in an infrared oven for 2 h in order to inhibit the bioactivity of hydrogen consumers and to harvest hydrogen-producing spore-forming anaerobes. The baked compost was employed as hydrogen-producing microflora based on the high activity of the microbial community. 2.2. Biopretreatment Methods of Substrate. As an abundant biomass resource, aging corn, which is corn that has been stored in excess of two years after it was harvested and usually cannot be used as a food grain in China, was chosen as the model for a hydrogen-producing feedstock based on its high starch content of 73%. Aging corn was obtained from the suburb of Zhengzhou city. The aging corn was first ground with a vegetation disintegrator (FZ102) to pass 40-mesh screens. Then, a mixture of ground aging corn, water, and solid microbe additives (consisting mainly of protease, amylase, xylanase, and pectase; provided by Gaojiawang Inc.) in a ratio of 167:77:1
10.1021/ie801125g CCC: $40.75 2009 American Chemical Society Published on Web 02/02/2009
2494 Ind. Eng. Chem. Res., Vol. 48, No. 5, 2009 Table 1. Central Composite Design Matrix of Two Variables in Coded and Natural Units along with Observed Responses
c
no.
X1
X2
substrate (g/L)
1 2 3 4 5 6 7 8 9 10
-1 1 -1 1 0 -2 2 0 0 0
-1 -1 1 1 0 0 0 -2 2 0
15 25 15 25 20 10 30 20 20 20
a Hydrogen production Correlation coefficient.
pH
Psa [mL/(g of TVS)]
Rb (mL/h)
R2 c
6 6 7 7 6.5 6.5 6.5 5.5 7.5 6.5
299 235 257 269 283 319 246 239 265 279
9.2 7.9 8.2 8 8.3 11.4 7.4 8.5 8.5 8.2
0.996 0.9972 0.998 0.9984 0.9985 0.9974 0.9984 0.9978 0.9991 0.998
potential.
b
Hydrogen
production
rate.
(g/g/g) was sealed in serum bottles16 and afterward was biopretreated under anaerobic conditions at 45 ( 1 °C. The total volatile solids (TVS) content in the cornmeal was determined as Wcornmeal-Wash TVS ) × 100% Wcornmeal
(1)
where W represents the quality of the cornmeal. 2.3. Experimental Design and Procedure. To optimize and quantitatively describe the hydrogen production process, the statistical experimental method of central composite design was employed as an effective tool in batch tests.17,18 Furthermore, a modified Gompertz equation was used to fit the experimental data to determine the hydrogen production potential [Ps, (mL of H2)/(g of TVS)] and the hydrogen production rate (R, (mL of H2)/h). The cumulative volume of hydrogen produced in the batch experiments followed the modified Gompertz equation
{ [
H ) P exp -exp
]}
Rme (λ - t) + 1 P
(2)
where H represents the cumulative hydrogen production (mL), λ represents the lag time (h), P represents the hydrogen production potential (mL), Rm represents the maximum hydrogen production rate (mL/h), and e is 2.718281828. In this study, the values of P, Rm, and λ for each batch were estimated using the solver function in Excel with a Newtonian algorithm. Herein, Ps [in units of (mL of H2)/(g of TVS)] was calculated by dividing P by the initial TVS (total volatile solids) content in the reactor.19–21 The results are summarized in Table 1. The batch experiments were performed with 250-mL serum vials as batch reactors filled to 150 mL with a mixture of the seed microorganism (80 g/L), varying amounts of biopretreated cornmeal, and 3 mL of nutrient stock solution.3,5 Each liter of nutrient stock solution contained 80 g of NH4HCO3, 12.4 g of KH2PO4, 0.1 g of MgSO4 · 7H2O, 0.01 g of NaCl, 0.01 g of Na2MoO4 · 2H2O, 0.01 g of CaCl2 · 2H2O, 0.015 g of MnSO4 · 7H2O, and 0.0278 g of FeCl2, which was slightly modified from the composition used by Lay et al.3,7 Both dilute sodium hydroxide (NaOH) and dilute hydrochloric acid (HCl) were used to adjust the pH values of the reaction mixtures. Then, these vials were gassed with nitrogen gas to remove oxygen and maintain an anaerobic environment in the headspace of the reactors. The bottles were incubated at 36 ( 1 °C and shaken in an orbital shaker at a rotation speed of 90 rpm to provide better contact among substrates. At each time interval, the biogas volume was measured by releasing the pressure in the bottles using glass syringes of 5-100 mL. All experiments were carried out independently in triplicate.
Figure 1. Changes in the cumulative H2 yield with initial pH at different biopretreatment times using biopretreated aging corn at a concentration of 20 g/L.
2.4. Analytical Methods. The hydrogen gas production was calculated by measurements of the gas composition in the headspace plus the total volume of biogas production at each time interval using the mass equation22 VH,i)VH,i-1 + CH,i(VG,i - VG,i-1) + VH(CH,i - CH,i-1)
(3)
where VH,i and VH,i-1 are the cumulative hydrogen volumes at the current (i) and previous (i - 1) time intervals, VG,i and VG,i-1 are the total biogas volumes in the current and previous time intervals, CH,i and CH,i-1 are the fractions of hydrogen gas in the headspace in the current and previous time intervals, and VH is the volume of headspace of vials (90 mL). The hydrogen gas percentage was calculated by comparing the sample biogas with a standard of pure hydrogen using a gas chromatograph (GC, Agilent 4890D) equipped with a thermal conductivity detector (TCD) and a 6-ft stainless column packed with Porpak Q (80/100 mesh).The operating temperatures of the injection port, oven, and detector were 100, 80, and 150 °C, respectively. Nitrogen was used as the carrier gas at a flow rate of 20 mL/min. The concentrations of volatile fatty acids (VFAs) and alcohols were detected using a second GC of the same model with a flame ionization detector (FID) and an 8-ft stainless column packed with 10% PEG-20 M and 2% H3PO4 (80/100 mesh). The temperatures of the injection port, FID detector, and oven were 220 °C, 140 °C, and a programmed column temperature of 115-170 °C, respectively. Nitrogen was used as the carrier gas at a flow rate of 20 mL/min. The pH values inside the reactors were determined using a microcomputer pH-vision 6071 instrument. 3. Results and Discussion 3.1. Effect of Biopretreatment of Substrate on Hydrogen Yield. In our previous tests, we found that direct hydrogen fermentation with raw wheat bran, beer lees, wheat straw, and corn stalk wastes gives maximum hydrogen yields of only 50.6, 6.8, 0.5, and 3.16 (mL of H2)/(g of TVS), respectively.5,11 To obtain better exploitation of the raw material for hydrogen production, the effectiveness of biopretreatment of substrate on hydrogen production was further investigated. The processes of hydrogen fermentation were performed at a fixed substrate concentration 20 g/L and a solid microbe addition of 6.0 g/kg. Figure 1 illustrates the changes in cumulative H2 yield with initial pH ranging from 4.0 to 9.0 and biopretreatment time ranging from 45 to 105 h. As shown in Figure 1, the cumulative H2 yield increased gradually with increasing initial pH value in
Ind. Eng. Chem. Res., Vol. 48, No. 5, 2009 2495 Table 2. Changes in Cumulative H2 Yield (Ps) with Biopretreatment Time at Different Substrate Concentrations and Initial pH Levels time (h) [S I]a
0b
8
14.5
22.5
41
52
65.5
89.5
R2
[15 6.0]
0E 0.04M 0E 0M 0E 0.03M 0E 0.21M 0E 0.36M 0E 0.07M 0E 0.03M 0E 0.35M 0E 0M
14.16 2.69 12.96 0.83 18.35 2.74 15.12 6.29 15.58 7.4 22.43 6.11 14.23 2.61 19.93 11.9 6.94 0.67
24.27 17.92 24.73 10.4 27.79 18.85 20.23 29.19 25.21 30.45 30.56 37.14 20.8 17.57 38.78 48.35 15.68 8.96
60.14 67.36 61.21 52.39 72.67 68.34 86.96 84.05 79.63 84.17 119.15 115.49 67.43 63.24 115.28 114.34 55.58 49.21
211.6 213.71 177.8 178.17 199.05 194.29 207.75 207.25 210.34 212.91 277.26 266.6 171.03 180.32 215.62 210.73 189.58 189.26
282.73 261.71 225.17 212.35 240.19 229.26 246.99 241.66 259.26 253.26 316.03 299.22 214.34 213.3 233.61 228.25 238.72 232.47
295.28 288.09 234.82 228.16 254.47 246.56 263.53 259.49 280.43 276.07 318.41 313.29 229.05 229.81 236.03 235.33 263.95 253.86
295.28 300.71 234.82 234.23 254.47 253.89 268.89 267.61 280.43 287.65 318.41 318.39 233.26 236.9 238.33 237.74 263.95 262.7
0.996
[25 6.0] [15 7.0] [25 7.0] [20 6.5] [10 6.5] [30 6.5] [20 5.5] [20 7.5] a
0.9972 0.998 0.9984 0.9985 0.9974 0.9984 0.9978 0.9991
S, substrate concentration (g/L); I, initial pH. b E, actual experimental values; M, values modified according to the modified Gompertz equation.
the range of 4.0-8.0 for a biopretreatment of 45 h, in the range of 4.0-7.0 for a biopretreatment of 60 h, and in the range of 4.0-6.0 for a biopretreatment of 105 h. In addition, the cumulative H2 yield declined gradually with increasing initial pH value from 256.6 (mL of H2)/(g of TVS) at pH 8.0 to 211 (mL of H2)/(g of TVS) at pH 8.5 for a biopretreatment of 45 h; from 270.5 (mL of H2)/(g of TVS) at pH 7.0 to 190.3 (mL of H2)/(g of TVS) at pH 8.5 for a biopretreatment of 60 h; and from 242.4 (mL of H2)/(g of TVS) at pH 6.0 to 23.2 (mL of H2)/(g of TVS) at pH 9.0 for a biopretreatment of 105 h. The maximum cumulative H2 yields of 256.6,, 270.5, and 242.4 mL/ H2/(g of TVS) occurred at initial pH 8.0 and biopretreatment of 45 h, pH 7.0 and biopretreatment of 60 h, as well as pH 6.0 and biopretreatment of 105 h, respectively. The maximal cumulative H2 yield of 256.6, 270.5, and 242.4 (mL of H2)/(g of TVS) occurred at an initial pH of 8.0 for a biopretreatment of 45 h, an initial pH of 7.0 for a biopretreatment of 60 h, and an initial pH of 6.0 for a biopretreatment of 105 h, respectively. Thus, it can be seen that a biopretreatment of 60 h at a pH of 7.0 was the best condition for maximum hydrogen production from aging corn. In this instance, the cumulative H2 yield of 270.5 mL/(g of TVS) was approximately twice that from raw aging corn. However, for the raw aging corn, the cumulative H2 yield increased slightly with increasing initial pH value in the range of 4.0-12.0 all the time upon direct hydrogen fermentation, so the maximum H2 yield of 142.8 (mL of H2)/(g of TVS) was observed only at an initial pH of 12.0 in the batch tests. The above results clearly show that both the biopretreatment of the substrate and the initial pH strongly affect the hydrogen productivity because the biopretreatment can significantly improve the saccharification hydrolysis efficiency of the substrate and result in an increase in the H2 yield by hydrogen fermentation.16 Similarly, the change in initial pH directly affects the hydrogenase activity and the metabolism pathway, leading to a change in the H2 yield during the hydrogen fermentation.3,23 3.2. Optimization of Key Process Parameters for Biohydrogen Production. Statistically based central composite experimental designs were applied to optimize the key process parameters for hydrogen production from aging corn by dairy manure compost. Table 1 shows the central composite design matrix of two independent variables in coded and natural units along with the parameters Ps and R. R2 for all parameters was larger than 0.996, indicating that the parameters were statistically
significant. According to the experimental results, the changes in the cumulative hydrogen yield with biopretreatment time, the response surface plots, and the corresponding contour charts based on two independent variables, the biopretreated aging corn concentration (X1) and the initial pH (X2), are presented in Table 2 and Figure 2. As can be seen from Table 2, the H2 production potential (Ps) based on the modified Gompertz equation (eq 2) fit the cumulative hydrogen yield well as the substrate concentration and initial pH varied from 10 to 30 (g of feedstock)/L and from 5.5 to 7.5, respectively. Herein, eq 2 correlates the H2 production data well, with R2 > 0.996 in Table 2. To facilitate a straightforward examination of the dependence of Ps and R on the biopretreated aging corn concentration and initial pH, response surface plots and corresponding contour charts were constructed (Figure 2). In light of Figure 2, it should be noted that the aging corn concentration and initial pH level had a significant effect on Ps and R. The angle of inclination of the principal axis is not evidently toward either the aging corn concentration (X1) or the initial pH (X2), which indicates that Ps is nearly equally dependent on these two variables. As can be seen from Figure 2, Ps presented a clear “saddle”. Ps increased from 280.0 to 340.0 mL/(g of TVS) as the substrate concentration and initial pH level decreased from 16.5 to 10 g/L and from 6.9 to 6.0, respectively. The R value increased from 10.0 11.5 mL/h as the substrate concentration and initial pH decreased from ∼15.5 to ∼12 g/L and from 7.50 to 6.00, respectively. According to the results of the statistically designed experiments, we can obtain the optimized fermentation condition, which is a substrate concentration of 10 g/L and an initial pH of 6.0. The maximum predicted Ps and R values could be higher than 340 (mL of H2)/(g of TVS) and 11.5 mL/h, respectively. From the above results, it can be seen that a superior hydrogen yield was observed at an approximately chemically neutral initial pH level and a lower substrate concentration in the tests. This finding is in close agreement with earlier reports, in which the optimum initial pH value and substrate concentration for hydrogen-producing systems occurred in the ranges of 6.0-8.0 and 10-20 g/L substrate, respectively.21,24,25 This can be explained because the substrate inhibition becomes predominant and results in modified metabolic pathways at higher substrate concentrations.21,25 On the other hand, the pH control could stimulate the microorganisms to produce hydrogen, thereby achieving a system with maximum hydrogen production po-
2496 Ind. Eng. Chem. Res., Vol. 48, No. 5, 2009
Figure 2. Effects of substrate concentration and initial pH level on specific hydrogen-producing yield [Ps, mL/(g of TVS)] and hydrogen production rate (R, mL/h) based on the response surface plot and corresponding contour plot. Table 3. Maximum H2 Yield and Main Soluble Byproducts for Hydrogen Fermentation of Some Feedstocks main soluble byproducts substrate food waste rice sludge starch food residues pineapple waste aging corn a
seeda ADS ADS ADS ADS ADS DMC
pH
temperature (°C)
maximum H2 yield
butyrate (%)
acetate (%)
ref
5.3 4.5c 6.0b 4.40-5.00c 7.5b 6.0b
35 37 55 36 37 37
80.9 mL/(g of VS) 346 mL/(g of carbohydrate) 92 mL/(g of carbohydrate) 186.23 mL/g 145.2 mL/(g of COD) 340 mL/(g of TVS)
30.6-48.3 51.4-70.10 40.2-53.5 s s 49.4-55.7
19.5-28.3 28.3-43.0 26.0-40.9 s s 23.7-28.5
28 1 19 29 30 this study
b
ADS, anaerobic digest sludge; DMC, dairy manure compost. b Initial pH. c Reaction pH.
tential. This is because the activity of hydrogenase is inhibited by low pH in overall hydrogen fermentation.9,23 However, the contours of similar trends in Ps and R led us to reason that the optimal condition for the aging corn concentration and pH level for compost generating hydrogen could be found by considering the Ps and R contours simultaneously. To validate the test results of Table 2 and Figure 2, repeated experiments under optimal conditions were carried out. The maximum H2 yield (Ps) of 346 ( 6.3 (mL of H2)/(g of TVS) (N ) 5), and a H2 production rate (R) of 11.8 ( 0.3 (mL of H2)/h were obtained. The experimental values were found to be in agreement with the predictions. 3.3. Biodegradation Characteristics of the Substrate. The characteristics of hydrogen fermentation from the biopretreated aging corn were further investigated in a 5-L continuously stirred bioreactor. Figure 3 illustrates the development of the cumulative H2 yield, operating pH, and ORP (oxidation-reduction potential, Figure 3a); the VFA (volatile fatty acid) content (Figure 3b), and the alcohol content (Figure 3c) with the culture time at a substrate concentration of 10 g/L and an operating pH of 6.0. As shown in Figure 3a, hydrogen production began immediately after a lag phase of 2 h, and the hydrogen production rate
maintained a high level at 8-20 h. The pH of the culture dropped significantly from 6.0 to 4.79 in the first 27 h and then remained steady at about 4.6 during hydrogen fermentation. The cumulative H2 yield of 46.5 mL/(g of TVS) at 4.5 h reached a maximum value of 340 mL/(g of TVS) at 88.5 h; meanwhile, the H2 percentage in the biogas was 34.3-50.2% (v/v), and no significant accumulation of methane was observed in the 5-L bioreactor. The maximum H2 production rate of 11.3 (mL of H2)/h was observed during the optimal H2 production period. During the optimum hydrogen-producing period, the operating pH value varied from 5.12 to 4.79. This pH level was slightly higher than the previous report by Fang et al. in 2006, in which hydrogen production from rice slurry was found to be most effective at pH 4.5 and 37 °C treating a slurry containing 5.5 (g of carbohydrate)/L,1 but it was lower than in another work, in which the optimum operational pH range was about 5.5-5.7 using sucrose and starch as organic substrates.26 So far in the literature, an operating pH of 5.0-5.5 is regarded as the optimal value, and little information is reported about the hydrogen production under a more acidophilic environment. Meanwhile, the ORP value dropped rapidly with increasing culture time from -200 to -521 mV in the first 4.5 h and then
Ind. Eng. Chem. Res., Vol. 48, No. 5, 2009 2497 13
substrate. The difference between these studies might be due to the diverse pretreatment methods and the distinct pH values in the course of hydrogen production. Moreover, the control of ORP values is important in the overall hydrogen fermentation. To the best of our knowledge, hydrogen production is usually accompanied with the key VFAs (expressed as volatile fatty acids) and alcohols produced. Therefore, both were selected as main byproducts of the compost consuming aging corn in the batch tests. As can be seen from Figure 3b,c, butyrate (49.4-55.7%) and acetate (23.7-28.5%, expressed as a quality percentage in total soluble byproducts) were two main byproducts in the batch, and they accounted for 73-84% of the total VFAs, followed by small amounts of butanol (8.6-10.2%), propionate (5.4-7.1%), and ethanol (3.6-7.4%). The biodegradation characteristics of the biopretreated aging corn were in close agreement with previous reports based on the studies of fermentation producing hydrogen from rice slurry, wheat straw wastes, and starch, in which the VFAs mainly consisted of acetate and butyrate.1,5,19 In addition, these phenomena could be expected because the acetate and butyrate producers were active in contrast to the propionate producer during the hydrogen production process.3,5 To effectively convert the substrate into biohydrogen using the microorganisms, the activity of the propionate producer should be suppressed. Finally, a table is provided to compare the hydrogenproducing potential utilizing some feedstocks (Table 3). Although the hydrogen yield units are not exactly the same, we still can reach the conclusion that aging corn can be a promising feedstock for biohydrogen production. 4. Conclusions
Figure 3. Developments of (a) cumulative H2 yield, pH, and ORP; (b) VFAs; and (c) alcohols in the course of hydrogen production from aging corn biopretreated by dairy manure compost at a fixed substrate concentration of 10 g/L and an initial pH value of 6.0.
decreased rapidly to -540.6 mV in the following 7.5 h. This shows that the reactor was shifted from facultative anaerobic running conditions to strict anaerobic running conditions with the depletion of trace oxygen; the ORP value stayed in the range from -521 to -458 mV during the optimum hydrogenproducing period and then rose gradually to around -320 mV as the hydrogen yield decreased. The results can be easily understood because the ORP value usually exhibited a gradual increasing trend with the accumulation of VFAs and declining pH in the running reactor.13 Generally, the ORP value reflects the amounts and types of oxidative-reductive substrates in the reactor. The hydrogen-producing bacteria obtained from dairy manure compost, which belong to a species of strict anaerobes (e.g., Clostridium sp.), exhibited a relative low ORP level in our tests. This result is lower than the previous reports. For example, Lay and Sung et al. reported ORP values of -311 to -368 mV and -320 to -340 mV using sucrose as the substrate,4,14 and Wang and Ren et al. found that the ORP level of -350 to -420 mV by the ethanol type of fermentation (ETF) was optimal for the maximal hydrogen production using molasses wastewater as the feedstock by mixed culture.27 In another work, however, the ORP values dropped to a very low level of -600 to -730 mV during the optimum hydrogenproducing period and then rose and stayed stable at around -500 mV for sewage sludge with alkaline pretreatment as the
This work demonstrated the feasibility of using a renewable resource (aging corn) as the feedstock for dairy manure compost to produce hydrogen. The statistical optimization method was applied to optimize process parameters for hydrogen production from aging corn by dairy manure compost. The biopretreatment of aging corn was found to be most effective at a biopretreatment time of 60 h and a temperature of 45 ( 1 °C using solid microbe addition of 6.0 g/kg. The experimental results indicate that the biopretreatment of aging corn, substrate concentration, pH value, and ORP level all have individual significant influences on the compost generating hydrogen. Meanwhile, the biopretreatment of substrate with solid microbe additive played a crucial role in the effective conversion of the aging corn into biohydrogen by mixed culture. Acknowledgment This work was supported by the National Natural Science Foundation of China (Nos. 90610001 and 20871106), the China National Key Basic Research Special Funds (Nos. 2009CB220001 and 2006CB708407), the Specialized Research Fund for the Doctoral Program of Higher Education (SRFDP, 20070459007), and the Energy and Technology Program from Zhengzhou University. Literature Cited (1) Fang, H. H. P.; Li, C. L. Acidophilic biohydrogen production from rice slurry. Int. J. Hydrogen Energy 2006, 31, 683. (2) Das, D.; Venzuriglu, T. N. Hydrogen production by biological processes: A survey of literature. Int. J. Hydrogen Energy 2001, 26, 13. (3) Fan, Y. T.; Li, C. L.; Lay, J. J.; Hou, H. W.; Zhang, G. S. Optimization of initial substrate and pH levels for germination of sporing hydrogen-producing anaerobes in cow dung compost. Bioresour. Technol. 2004, 91, 189.
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ReceiVed for reView July 22, 2008 ReVised manuscript receiVed January 2, 2009 Accepted January 8, 2009 IE801125G
