Laboratory Scale Hydrogen Production from Brewer s Grains

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1 Laboratory Scale Hydrogen Production from Brewer s Grains Lucie Houdková, Ferdinand Ožana Institute of Process and Environmental Engineering (UPEI VUT), Faculty of Mechanical Engineering, Brno University of Technology Technická 2896/2, Brno, Czech Republic, houdkova.lucie@fme.vutbr.cz The paper is focused on the evaluation of the experiments of the hydrogen production from brewer s grains by the method of dark fermentation. The brewer s grains were chosen for the experiments based on the literature review and also because of its good availability. The experiments were carried out in a stirred reactor with a volume of 25 L operated under semi-continuous mode. Mixing, heating and keeping constant ph are automatic. There were carried two experiments, where the hydraulic retention time showed to be very important. Under higher hydraulic retention time H 2 were not produced, because methanogenic bacteria were grown. 1. Introduction Hydrogen is considered one of the fuels of the future. Its combustion has one important advantage no carbon dioxide is produced (water is the end product of its reaction with oxygen). A direct combustion of H 2 in engines or its utilization in fuel cells is possible. The use of fuel cells is very large from a drive of car to an energy source of houses. Currently, almost all of the hydrogen production (5 MNm 3 /y as mentioned by Perera et al, 2010) is produced from fossil sources. It is either natural gas or oil or coal. Guo et al (2010) states that it is 88 %, Perera et al (2010) argue that it is even 96% of world production. In recent years, the importance of water electrolysis has been increased and nowadays it represents up to 4% of hydrogen production (Guo et al, 2010). It must be noted that the production of 1 Nm 3 consumes of 4.5 to 5 kwh (Peixoto et al, 2010), which is produced mainly from fossil sources. To be considered as a renewable source of energy with minimal CO 2 footprint hydrogen should be produced using such methods, which do not need fossil fuels as an energy source or a raw material. The possibility of H 2 production from biomass offers some potential in this regard. Biomass can be processed in two basic ways, when high temperature processes like pyrolysis are not considered. The first is a photofermentation and the second is a dark fermentation. In photo-fermentation, anoxygenic photoheterotrophic bacteria degrade organic substrate in the presence of light according to the equation: C 6 H 12 O H 2 O 12 H CO 2 ΔG = kj (1)

2 Dark fermentation takes place without the presence of light under anaerobic conditions where anaerobic heterotrophic bacteria decompose organic substrate according to the equation: C 6 H 12 O H 2 O 2 CH 3 COOH + 4 H CO 2 ΔG = -184 kj (2) Unlike photo fermentation, dark fermentation is spontaneous as is obviously from free enthalpy of above mentioned reactions. It has also a higher degree of conversion theoretically, but the yield is relatively low. The H 2 yield during dark fermentation is strongly influenced by the type of substrate and operating conditions and pretreatment of substrate and inoculum. Pretreatment of the substrate provides a better degradation of cellulose and hemicelluloses. The effect of substrate pretreatment and fermentation temperature on the yield of H 2 from certain substrates is shown in the Table 1, as stated by Guo (2010). Pretreatment of the substrate such as grass silage is also recommended Pakarinen et al (2008), who came to the conclusion that energy yield of dark fermentation without pretreatment of the substrate is much lower than yields of energy produced by conventional methane digestion. Table 1: Estimated hydrogen yields of dark fermentation (Guo, 2010) Substrate Maximum assessed production yield (ml H 2 /g VS) Pretreatment Temperature ( C) Reactor operation mode Corn straw 9-35 Batch Corn straw 68 * 220 C, 3 min 35 Batch Corn straw 49 * 1.2% HCl C, 1 min 35 Batch Cow feces 18 * - 75 Batch Cow feces 29 * - 60 Batch Cow feces 0.7 * - 37 Batch VS = volatile solids. - No pretreatment of a substrate. * Calculation from literature data. Digested sewage sludge or cattle manure is often used as inoculum. These materials contain the mixed cultures including methanogenic bacteria. Pure cultures are also used for laboratory tests (Wang and Wan, 2009), but in terms of practical application their price is disadvantage compared to the sludge or manure. The inhibition of methanogenic bacteria present in sludge or manure is recommended using pretreatment by high temperature (above 100 C for 1 2 h) or by extreme ph (ph 3 for 24 h or ph 10 for 24 h), as mentioned by Koskinen (2008). Pretreatment of inoculum is suitable for suppression of methanogenesis, in which hydrogen is consumed by hydrogentrophic methanogens to produce methane according to the Equation (3) 4 H 2 + CO 2 CH H 2 O (3)

3 Hydrogen can be also used by sulfate-reducing bacteria to produce H 2 S or by homoacetogenic bacteria to produce acetic acid according to the equation: 4 H CO 2 CH 3 COOH + 2 H 2 O (4) In terms of operating conditions, temperature is the most important parameter. Hydrogen producing bacteria are capable of living in low temperatures (4 C psycrophilic bacteria) to extremely high (106 C hyperthermophilic bacteria) as described Karlsson et al (2008). In laboratory experiments, temperatures around 35; 55 and 70 C resp. are frequently used. The effect of temperature on the H 2 yield is shown in Table 1. ph is another important parameter in the production of H 2 by dark fermentation. As it turns out the optimum ph of 5 6 for the grass silage (Pakarinen, 2008), but some authors reported an optimum ph of 4.2 for synthetic wastewater rich in sucrose (Mu et al, 2006) or, conversely, at ph 7 for sewage sludge as a substrate (Zhao and Yu, 2008). As is evident, the optimum ph must be found with respect to the substrate and inoculum. Some authors also studied the influence of hydraulic retention time (Karlsson et al, 2008, Fan et al, 2006). Overall, the hydraulic retention time is much shorter than with methane production by conventional digestion. There the hydraulic retention time is around days, while in the dark fermentation it is around several days. The aim of the research presented in this paper is to find the best operating conditions for production of H 2 from brewer's grains. As seen from the above searches, it is necessary to focus mainly on temperature, ph and hydraulic retention time. The next phase of research will be focused on experiments that will lead to obtain data for calculation of energy and material balances, both of dark fermentation and conventional digestion with production of methane. Then it will be possible to compare that two methods and evaluate their energy efficiency and economic intensity. 2. Materials and methods 2.1 Substrate and inoculum The initial search was introduced several possible materials, other possible materials suitable for the experiment include food waste, molasses, rice slurry, dairy wastewater etc. Finally, for H 2 production brewer s grains were selected for good availability. Grains were collected from the brewery Starobrno, where they are the waste of beer production. Currently grains are mainly used as feed for livestock. The parameters of grains are published in Table 2. Brewer s grains were stored in refrigerator and were not pretreated. It was only diluted 1:1 with water for better mixing. Table 2: Characteristics of brewer s grains Parameter Value Unit Parameter Value Unit Total solids (TS) 15.2 % Total nitrogen 4.6 % of TS Volatile solids (VS) 69.2 % of TS C:N Total organic carbon (TOC) 47.6 % of TS

4 Digested sludge from wastewater treatment plant in Brno was used as inoculum. Sludge is stabilized under mesophilic anaerobic conditions. High temperature was selected for sludge pretreatment. Pretreatment of sludge was carried out at the temperature of 120 C for 1 h. Pretreated digested sludge contains 3.7 % of TS and 54.2 % of VS. It was dosed only at the beginning of experiments in the amount of 1 kg of pretreated sludge per 4.5 kg of wet brewer s grains in average. Sodium hydroxide (4 % solution) was used to regulate the ph of the mixture during the fermentation. Dosing of NaOH was automatic when ph decreased below 5.5. The acid regulator of ph was not necessary to be used, because ph did not increase over the selected level of 6 during the experiments. 2.2 Reactor Most laboratory experiments presented in the literature were carried out in very small reactors (batch or continuous). The volume of these reactors ranging from 100 ml to 2 L mostly (Canul-Chan et al, 2010; Pakarinen et al, 2008, Karlsson et al, 2008, Fan et al, 2006, Peixoto et al, 2010). Experiments described here were carried out in a stirred reactor of the useful capacity of 25 L which can be operated batch or semi-continuous. For purposes of these experiments, semi-continuous mode was chosen. It was manually fed fresh substrate instead of a part of filling. Heating was ensured by external thermostat and temperature was chosen 37 C (mesophilic area). The overpressure in the reactor was maintained at 1 2 kpa. Mixing of reactor was automatic. It took place in a time interval of 10 minutes for about 2 minutes or when dosed NaOH. 2.3 Experiment description In the first phase of the research two experiments were carried out, in which a suitable hydraulic retention time was searched for. The initial filling was consisted of 10 kg of wet brewer s grains and diluting water in ration of 5:3 and 2 kg of pretreated sludge and 4 kg of wet brewer s grains and diluting water in ration of 1:1 and 1 kg of pretreated sludge, respectively. Other doses of grains and water (already without the addition of sludge) during the experiment are shown in Table 3. Table 3: Material dosage Material First test Second test Dosage (kg) Day of test Dosage (kg) Day of test Grains 10 4 Water Sludge 2 1 Grains ; 16; 17; 18 Water ;4;6;7 Grains Water Grains 2.1 Water

5 3. Results and discussion As demonstrated in the first experiment, the hydraulic retetion time has a significant influence on both the total gas production, as well as the hydrogen content in it. There was not added any fresh substrate for the first seven days of the first experiment. This eventually led to the growth of methanogenic bacteria in the reactor because the gas contained only methane and no hydrogen (see Table 4). Therefore, dosing of fresh substrate was initiated in the third day in the second experiment, which is positively reflected in both the quantity (see Figure 2) and the quality of gas. The samples contained 6 to 17 % of H 2, and methane was negligible. Table 4: Gas composition Sample First test Second test number H 2 (%) CH 4 (%) H 2 (%) CH 4 (%) Daily gas production (L/kg TS and day) Day of dosage - 1st test Day of dosage - 2nd test 1st test 2nd test Day of experiment Figure 1: Daily gas production (in L/kg of TS and day) 4. Conclusions Two experiments were carried out to confirm the material and reactor is suitable to produce hydrogen by dark fermentation. Brewer s grains contained about 15 % of total solids and had to be diluted with water for better mixing. Thermally pretreated digested sludge was used as inoculum. Based on the literature search fermentation temperature 37 C and ph 5.5 was selected. The first experiment lasted for 20 days, during which 4 samples of gas were taken and analyzed. The second experiment took place only 8 days

6 and 3 samples of gas were taken to analyze. In the first experiment failed to produce hydrogen, while the second was successful. It can be said that the reason is to shorten the hydraulic retention time. Acknowledgements We gratefully acknowledge financial support of the Ministry of Education, Youth and Sports of the Czech Republic within the framework of research plan No. 2B08048 "Waste as raw material and energy source". References Canul-Chan, M., Salgado-Manjarrez, E., Aranda-Barradas, J. and Garcia-Pena, E.I., 2010, Hydrogen and electricity production from the organic fraction of solid waste, Proceeding Venice 2010, Third International Symposium of Energy from Biomass and Waste, Italy. Fan, K.S., Kan, N.R. and Lay, J.J., 2006, Effect of hydraulic retention time on anaerobic hydrogenesis in CSTR, Bioresource Technology 97, Guo X.M., Trably E., Latrille E., Carrère H. and Steyer J.P., 2010, Hydrogen production from agricultural waste by dark fermentation: A review, Int. J. Hydrogen Energy 35, Karlsson, A., Vallin, L. and Ejlertsson, J., 2008, Efects of temperature, hydraulic retention time and hydrogen extraction rate on hydrogen production from the fermentation of food industry residues and manure, Int. J. Hydrogen Energy 33, Koskinen, P., 2008, The development and microbiology of bioprocesses for production of hydrogen and ethanol by dark fermentation, Tampere University of Technology, Tampere, Finland Mu, Y., Yu, H.Q. and Wang, Y., 2006, The role of ph in the fermentative H 2 production from an acidogenic granule-based reactor, Chemosphere 64, Pakarinen, O., Lehtomaki, A. and Rintala, J., 2008, Batch dark fermentative hydrogen production from grass silage: The effect of inoculum, ph, temperature and VS ratio, Int. J. Hydrogen Energy 33, Peixoto, G., Agnelli, J.A.B., Pantoja Filho, J.L.R., Pasotto, M.B., Innocentini, M.D.M. and Zaiat, M., 2010, Hydrogen and methane production from domestic ad industrial wastewaters, In: Proceeding Venice 2010, Third International Symposium of Energy from Biomass and Waste, Italy. Perera K.R.J., Ketheesan B., Gadhamshetty V. and Nirmalakhandan N., 2010, Fermentative biohydrogen production: Evaluation of net energy gain, Int. J. Hydrogen Energy 35, Wang, J.L. and Wan, W., 2009, Factors influencing fermentative hydrogen production: A review, Int. J. Hydrogen Energy 34, Zhao, Q.B. and Yu, H.Q., 2008, Fermentative H 2 production in an upflow anaerobic sludge blanket reactor at various ph values, Bioresource Technol. 99,