Energy Procedia 50 ( 2014 ) 702 – 710

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1876-6102 © 2014 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).Selection and peer-review under responsibility of the Euro-Mediterranean Institute for Sustainable Development (EUMISD) doi: 10.1016/j.egypro.2014.06.086

The International Conference on Technologies and Materials for Renewable Energy, Environment and Sustainability, TMREES14

Production of Hydrogen and Methane from Banana Peel by Two Phase Anaerobic Fermentation

Chananchida Nathoaa, Ubonrat Sirisukpocab, Nipon Pisutpaisala,c,* aDepartment of Agro-Industrial, Food and Environmental Technology, Faculty of Applied Science,

King Mongkut’s University of Technology North Bangkok, Bangkok, 10800, Thailand bProgram of Computer, Faculty of Science and Technology, Nakhon Pathom Rajabhat University,

Nakhon Pathom, 73000, Thailand c The Biosensor and Bioelectronics Technology Centre, King Mongkut’s University of Technology

Northn Bangkok 10800, Thailand

Abstract

A two phase anaerobic digestion of banana peel is an attractive process for producing hydrogen and methane. Comparative performance and total energy recovery between two phase process (sequential hydrogen and methane fermentation) and one phase process (methane fermentation) in were evaluated in batch reactor under mesophilic incubation at varying ratios of feedstock to microbial inoculum (F/M) ranging from 2.5 – 10. F/M ratios influence biogas yield, production rate, and potential. Best performance of one phase methane fermentation was observed at F/M of 5.0. At this condition, methane yield, production rate, and potential were 251.3 mL g-1 VS, 2.05 mL h-1, and 352.9 mL, respectively. Hydrogen and methane yields of 209.9 and 284.1 mL g-1 VS mL g-1 VS were achieved at F/M of 5.0 in two stage process. Acetic acid is the main volatile fatty acids (VFAs) produced in the hydrogen fermentation stage. Little amount of VFAs were accumulated in methane fermentation in both stage processes. Total energy recovery in two stage process is higher than that in one stage by 81%. This work demonstrated two phase achieved a better performance than one phase fermentation of banana peel. © 2014 The Authors. Published by Elsevier Ltd. Selection and peer-review under responsibility of the Euro-Mediterranean Institute for Sustainable Development (EUMISD).

Keywords: Hydorogen; methane; banana peel; fermentation; two phase process

* Corresponding author. Nipon Pisutpaisal Tel.: +662-587-8257; fax: +662-587-8257. E-mail address: ubonrat76@hotmail.com, npp@kmutnb.ac.th

© 2014 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).Selection and peer-review under responsibility of the Euro-Mediterranean Institute for Sustainable Development (EUMISD)

Chananchida Nathoa et al. / Energy Procedia 50 ( 2014 ) 702 – 710 703

1. Introduction

Hydrogen is one of the most promising alterative to fossil fuels due to its clean, renewable, and high energy yield (122 kJ g-1). It could be either directly combusted or used to produce electricity through fuel cells. Many processes, thermochemical, electrochemical, and biological can be used to generate hydrogen [1]. Thermochemical and electrochemical processes are not renewable due to their dependence on fossil fuels. Biological hydrogen production more environmentally friendly since it is less energy intensive than non-biological processes. Biohydrogen can be generated from different metabolic pathways including direct water biophotolysis by green algae, indirect water bio-photolysis by cyanobacteria, photofermentation by photosynthetic purple non-sulfur bacteria, hydrogen synthesis via water-gas shift reaction by microalgae in Rhodospirillaceae family, and dark fermentation by heterotrophic anaerobic bacteria. Higher production rate, wider spectrum of substrates, and lower energy requirement make dark fermentation more advantageous than other processes [2-4]. Broad types of organic feedstocks such as glucose, starch, municipal waste, livestock manure, crop residues, food waste, and wastewater have been utilized as substrates in the dark fermentation [5-8]. Banana is one of the most popular tropical fruits consumed worldwide. In Thailand, banana peel of 200 tons is daily generated, and its generating trend becomes continuously increased [9]. A small fraction of the peel is used for animal feed and the remaining becomes rotted garbage. The peel is carbohydrate rich (Table 1) and is potentially converted into hydrogen and methane in the fermentation process.

Table 1. Organic content in ripped banana peel

The present study compared the performance of one and two stage mesophilic fermentation of the banana peel based on biogas yield and production rate, and overall energy recovery. 2. Materials and methods

2.1 Inoculum Microbial seed used throughout the study was obtained from a full-scale up ow anaerobic sludge blanket

(UASB) reactor treating cassava wastewater (Eiamburapa Co., Ltd., Thailand). Coarse matter >0.5 mm diameter was removed by sieving and the granules were washed twice with tap water. The fine granules, used in the hydrogen fermentation were boiled at 100oC for 30 min to deactivate methanogens [10], while those without heat treatment were used in methane production stage.

2.2 Banana peel

Ripped banana peel was obtained from local banana processing store. It was rinsed with tap water and ground in a blender to particles of diameter approx. 0.5 mm. The food waste was adjusted to the desire concentration (g VS L-1) with distilled water.

Parameter % Wet weight Moisture 83.5 Organic carbon 41.3

Starch 1.2

Protein 1.8

Cellulose 8.4 Himecellulos 5.3 Glucose 2.4 Total sugar 29

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2.3 Batch fermentation The two stage batch fermentation system including H2 fermentation in the first stage and CH4 fermentation in the

second stage was set up in 500 mL screw-cap bottles with a working volume of 500 mL (375 mL of feed stock and 125 mL of inoculum). The inoculum in all conditions was fixed at 4.75 g total volatile solids (VS) per batch. The banana peel was added at varying concentrations between 23.75-95.0 g VS L-1, corresponding to F/M ratios of 2.5-10. The initial pH in the H2 fermentation was adjusted to 6.0 with 6 N NaOH or 6 N HCl. The system was flushed with nitrogen gas to generate anaerobic conditions. H2 fermentation was conducted at 37°C with rotary shaking at 150 rpm. After H2 fermentation was exhausted, the non-heat pretreated seed of 4.75 g VS per batch was added, the initial pH was adjusted to 7.0, and the system was reflused with nitrogen gas, and the CH4 fermentation was conducted at 37°C. All experiments were setup in duplicate. During the fermentation experiment, total gas volume and composition were periodically monitored by gas counters and gas chromatography, respectively. The liquid samples were analyzed for pH and volatile fatty acids (VFA) every 4-6 h.

2.4 Analytical methods Total solids (TS), total volatile solids (VS), and chemical oxygen demand (COD) were measured according to

Standard Methods 2540 G and 5220 B, respectively [11]. The amount of generated biogas was recorded using liquid displacement gasometers. Biogas content (H2, CH4, and CO2) was measured periodically every 5 h using a gas chromatograph (Shimadzu GC-8A, Kyoto, Japan) equipped with a thermal conductivity detector (TCD) with a Unibeads C 60/80 column (GL Sciences, Inc., Tokyo, Japan). Helium was used as a carrier gas. The temperatures of the injection port and the detector were 150 and 80 C, respectively. VFAs were analyzed by gas chromatography (Shimadzu GC-7A system equipped with a flame ionization detector and a Stabilwax DA capillary column (Restek Corporation, PA, USA)). The temperatures of the injection port and detector were maintained at 240 C [12].

2.5 Kinetics of gas production

The modified Gompertz equation (eqn. 1) was used to fit cumulative hydrogen/methane production data obtained from each batch experiment. This model has long been used for describing hydrogen, methane, or biogas production in batch fermentation experiments.

1)(expexp)( tP

eRPtH m (1)

where H(t) is cumulative hydrogen production (mL) during the incubation time, t (h), P is the biogas production potential (mL), Rm is the maximum production rate (mL h-1), is the lag phase duration (h), and e is the exp(1) = 2.718. Biogas yield (Y) is calculated by dividing the biogas production potential by the amount of VS removed. 3. Results and Discussions

3.1 One stage fermentation pH in the reactor during one stage banana peel fermentation at varying F/M ratio in the range of 2.5 – 10 was stable in the range of 6.72 – 7.30 (Fig. 1). The results implied that the banana peel might be composed of buffer compounds that can maintain the fermentation pH to suit the methanogenic activity. Methane was produced after 12 h incubation for all F/M ratios with the methane content approximately 48–54 % and the accumulative methane reached the plateau region after 240 h fermentation (Fig. 2). The cumulative methane profile data was fitted to the modified Gompertz equation (R2 > 0.99). The methane evolution had the S-shape trend and the kinetics data from the equation was statistically significant. Methane production rate and yield were increased as the increased F/M ratios and maximized at F/M of 5.0 (Fig. 3). The kinetics parameters were decreased when the F/M ratio above 5.0 (Table 2). Methane yield obtained from the present study was comparable to those in the previous studies (Table 3). Little amount of VFA (< 5 mM) accumulated in the reactor content suggested that no inhibitory effect of VFA on the microorganisms.

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5.0

5.5

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Fig. 1. pH during one stage fermentation under varying F/M ratio of 2.5 ( ), 5 ( ), 7.5 ( ), 10 ( ). Symbols represent mean values of triplicate experiments, error bars represent one standard deviation.

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Fig. 2. Cumulative methane production from F/M ratios of 2.5 ( ), 5 ( ), 7.5 ( ), 10 ( ). Symbols represent mean values of triplicate

experiments, error bars represent one standard deviation.

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Table 2. Summary of kinetics parameters in one stage methane production.

Fig. 3. Methane production rate (A) and yield (B) under varying F/M ratios. Histograms represent mean values of triplicate experiments, error bars represent one standard deviation.

F/M ratio

Hm Rm Y % pH [VFA] (mL) (mL h-1 ) (mL g-1VS) mmol L-1 (h)

2.5 277.3 ± 29 1.54± 0.3 250.1±29 54 7.2±0.1 0.27±0.05 7.6 5.0 352.8 ± 31 2.0 ± 0.7 251.3 ±10 47 7.1±0.1 0.24±0.04 7.6 7.5 223.4 ± 15 1.4± 0.1 134.5 ±3 33 7.3±0.1 0.38±0.10 10.9 10.0 85.1 ± 17 1.2 ±0.1 38.1 ± 8 31 7.3±0.1 2.88±0.09 12.1

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Table 3. Methane yield reported by previous studies

3.2 Two stage fermentation pH in the hydrogen fermentation (first stage) slightly decreased and stabilized at 5.4 until the end of fermentation, while that in the methane fermentation (second stage) was stabilized at the narrow range of 7.11 – 7.22 (Fig. 5). Those stabilized pH ranges are optimum for hydrogen- and methane-producing bacteria. Since no buffer was added into the reactor, the results suggested that the stabilized pH in both stages was due to the buffer capacity from the banana peel.

4

5

6

7

8

0 50 100 150 200 250 300

Time (h)

pH

MethaneHydrogen

Fig. 5. pH profile during two stage fermentation of F/M 5. Symbols represent mean values of quadruplicate experiments,

error bars represent one standard deviation.

The cumulative H2 and CH4 fermentation profile data were fitted to the modified Gompertz equation (R2 > 0.99). The hydrogen evolution had the S-shape trend and the kinetics data from the equation was statistically significant. Lag phase approximately 12 h prior to the evolution of H2 was observed in the first stage fermentation (Fig. 6). No methane was detected in this stage.

Waste Reactor Yield Reference mL CH4 g-1 VS

Banana peel Batch 210 [13] Banana peel Batch 266 [14] Banana peel Batch 231 [15] Banana peel Batch 251 This study

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Hydrogen

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Gas

con

tent

(%)

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gas

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)

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Fig. 6. Profile of gas content ( ) and cumulative gas volume ( ) during two stage fermentation of F/M 5. Symbols represent mean values of

quadruplicate experiments, error bars represent one standard deviation. The hydrogen yield and content of 209.9 mL g- 1 VS and 35% were achieved after 12 h fermentation (Fig. 6, Fig. 7A). The results showed that the F/M ratios have strong effect on the H2 production. The methane yield and content in the second stage were 284.12 mL g-1 VS and 61% (Fig. 7B). The analysis of VFA after 50 h fermentation showed that acetate was the major fermentation by-product with 65 mM. The acetate dominant by-product suggested the desirable condition for the hydrogen fermentation. Theoretically, maximum hydrogen yield achieved when acetate-related pathways are the main routes for H2 production that yielded 4 mol H2/ mol glucose. Minimal ethanol and propionate generated from the hydrogen consuming pathway were detected. Negligible amount of VFA detected in the methane fermentation stage after 336 h fermentation indicated that VFA produced in the hydrogen stage was efficiently converted to methane in the second stage. The overall energy recovery from two stages is equivalent to 6.9 x 10-3 kW-h, which increased by 81% compared to that recovered from one stage fermentation 3.8 x 10-3 kW-h). The finding suggested that the first stage of hydrogen fermentation plays significant role in the overall improvement of degradation efficiency and biogas recovery. Separation of combined hydrolysis, acidogenesis, and acetogenesis in the first stage from the second stage fermentation allows more flexibility in controlling of fermentation conditions and could be more beneficial for simultaneous treating and extracting complex organic feedstocks or recalcritant organic matters.

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Fig. 7. Hydrogen (A) and methane (B) production potential, rate, and yield during two stage fermentation of F/M 5. Histograms represent mean

values of quadruplicate experiments, error bars represent one standard deviation.

Table 4. Summary of kinetics parameters in two stage fermentation at F/M 5.

Hydrogen stage Hm Rm Y % pH [VFA]

(mL) (mL h-1 ) (mL g-1VS) mmol L-1 (h) 93.5 ± 19 5.04± 1.3 209.9 ± 28 35 5.43±0.4 65.8±0.5 1.5

Methane stage Mmax Rmax Yield % pH VFA (mL) (mL h-1 ) (mL g-1VS) mmol L-1 (h)

617.6 ± 21 4.4 ± 0.5 284.1 ± 34 67 7.1±0.1 6.5±0.1 1.2

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4. Conclusion

The current study successfully illustrated more efficient performance in two stage than one stage fermentation of banana peel regarding the energy recovery. The total energy recovery from sequential hydrogen and methane fermentation was improved by 81% compared to the one stage fermentation. Two stage process is feasible to simultaneously treat and extract hydrogen and methane from agricultural waste containing high complex organic molecules.

Acknowledgements

The authors would like to express their gratitude to the Electricity Generation Authority of Thailand (grant no. 52-2115-031-JOB NO. 518-KMUTNB) for the financial support.

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