PLEASE E-MAIL THIS FORM TO 2013 CHALLENGE COMMITTEE CHAIRS: JOSE CUETO (JCUETO@HAZENANDSAWYER.COM) OR CRISTINA ORTEGA (CRISTINA.ORTEGA@CH2M.COM) BY FRIDAY DECEMBER 7TH, 2012.

CUBA INFRASTRUCTURE CHALLENGE 2013 Student Participation Form

Team Name:

ENERGÍA

University:

University of Miami

Faculty Advisor:

Dr. Helena Solo‐Gabriele

Does the team need an Industry Advisor to be assigned by the Challenge Committee? Yes No x If the team already has an Industry Advisor, please enter his/her name in the box below:

Dr. Negat Veziroglu, a world leading expert in hydrogen energy, has served as our industrial advisor. We are in the process of contacting Dr. Jeffry Padin, an expert in the production of hydrogen from solar energy, and Dr. Debrata Das, an expert in biohydrogen systems, to obtain additional advice.

Team Members:

# First Name Last Name Degree/Major Expected

Graduation Date E‐mail address

1 Maggie Giraldo Environmental Engineering May 2014 m.giraldo4@umiami.edu954‐235‐3028

2 Melissa Barona Environmental Engineering and Chemistry

May 2014 m.barona@umiami.edu561‐207‐1355

3 Seth Marini Environmental Engineering May 2013 s.marini@umiami.edu305‐761‐5701

Team Leader Contact Information:

Name Melissa Barona

Phone (561) 207 1355

Address 4651 Mimosa Terrace Unit 1207 Coconut Creek, FL 33073

E‐mail m.barona@umaimi.edu

Project Title:

Biohydrogen as an Alternative Energy Source for Cuba

Project Abstract (150 words max):

The deteriorated energy infrastructure of Cuba provides an opportunity to explore completely new forms of energy production. This report evaluates the potential of biohydrogen, the biological production of hydrogen fuel. Biohydrogen is chosen because it is a sustainable, renewable, and a clean energy source characterized by relatively low capital costs. We specifically explore the potential for sugarcane bagasse to serve as the primary substrate for the growth of the bacteria and compare the amounts needed to the available capacity for sugarcane production in Cuba. Biohydrogen processes evaluated include dark fermentation, biophotolysis, and the most recent technology, microbial electrolysis cells (MECs). The chosen design is based upon a coupled system that combines dark fermentation and MECs. Based upon literature values, the chosen process was sized for the production of a 1 kW fuel cell, which is enough to power a modest home. Recommendations and limitations of the technology are described.

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Summary of Project Team

The team consists of 3 engineering students from the University of Miami. Each member’s role is outlined below.

Melissa Barona: Melissa Barona worked on the use of Microbial Electrolysis Cells to produce hydrogen. The process requires a combination of bacteria and small amounts of voltage applied to an electrolysis cells to produce hydrogen. Along with the MEC cells, Melissa analyzed the possibilities of using a dual MEC-MFC system. The calculations for the efficiency, capacity of the reactors, and the total hydrogen production of a fermentation-MEC coupled system were also researched by her. She also was responsible for the computation method for sizing the bioreactors.

Margarita Giraldo: Margarita Giraldo evaluated the use of hydrogen gas and the benefits of using this new technology instead of the fossil fuels. She analyzed the dark-fermentation processes and the use of the bacteria producing hydrogen under anaerobic conditions in reactors with the use of sugar cane bagasse as the substrate for the biological reactions.

Seth Marini: Seth Marini worked on the biophotolysis section and gathered information about Cuba’s historical sugarcane production. He also compiled the data that describes the amount of hydrogen generated per unit sugar for the various processes. He developed a spreadsheet to convert this data into reactor sizes and a GIS map of sugar mill locations in Cuba.

Acknowledgement: We acknowledge the assistance received from Dr. Helena Solo-Gabriele our faculty advisor for this project. We also acknowledge the information received from Dr. Nejat Veziroglu about the benefits of hydrogen energy. Between the submission of this project and the presentation we will continue to seek input from experts in the area.

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Table of Contents

Page No.

STUDENT PARTICIPATION FORM (Including the Abstract) 1

PROJECT TEAM AND ACKNOWLEDGMENTS 2

DISCUSSION OF PROJECT

1. Introduction 4

1.1 Why Biohydrogen? 4

1.2 Why Cuba? 5

2. Biohydrogen Processes 7

2.1 Biophotolysis 7

2.2 Fermentation 9

2.3 Bioelectrochemical Systems 11

2.3.1 BES Reactor Design 12

2.3.2 Energy Losses 13

2.3.3 Electrode Material 14

2.3.4 MFC-MEC Coupled System 15

3. Design 16

4. Conclusion and Recommendations 20

END OF DISCUSSION SECTION

5. Bibliography 21

6. Appendices

Appendix A: Illustrations (Figures and Drawings) 24

Appendix B: Tables 29

Appendix C: Calculations 30

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1. Introduction

In this section we address the questions of “Why biohydrogen?,” by emphasizing the

environmental advantages of biohydrogen over the use of fossil fuels and other forms of

alternative energy. We also address “Why Cuba?” as an ideal location for a biohydrogen

economy because of the need to completely revamp the country’s power systems and the ability

to produce the substrate, sugar cane, needed for the biological process.

1.1. Why Biohydrogen?

One of the biggest challenges facing society today is climate change. The constant

discharge of greenhouse gases, such as carbon dioxide, methane, and nitrous oxide, into the

atmosphere has resulted in temperature increases of the Earth’s atmosphere (Garrison, 2005).

The burning of fossil fuels is responsible for the discharge of greenhouse gases, with CO₂

accounting for 80% of these emissions. The CO₂ concentrations in our atmosphere have

increased dramatically since the industrial revolution. As of 2005, there was an estimated

concentration of CO₂ in the atmosphere of 380ppm, which is the highest concentration measured

in a 600,000 year record (Gore, 2006). Fossil fuels are burned primarily to generate electricity at

power plants and for automobiles and other forms of transportation. In addition to the

environmental implications, fossil fuel reservoirs are limited and their costs are high (Kalia and

Purohit, 2008). There is thus a need and an opportunity to generate cleaner energy (Kalia and

Purohit, 2008).

Various technologies of cleaner energy production have been implemented in many

places around the world, but their cost is generally high, and developing countries would not be

able to invest in the infrastructure needed to build these. Some of them are thermonuclear, solar,

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wind energy, and tidal. Also, another setback of some forms of alternative energy is that their

production fluctuates and so they require a conversion to a form of storable fuel in order to meet

energy demands, increasing the cost of running them even more (Kalia and Purohit, 2008).

Bio-fuels; methanol, ethanol, natural gas, hydrogen, amongst others have been proposed

as a cleaner alternative to fossil fuels. These do not need the conversion to stored fuel that the

other green technologies require. They tend to be cheaper than other renewable alternative

energies as they can be generated from biological wastes and water (Kalia and Purohit, 2008).

Out of the multiple bio-fuels, hydrogen seems to be the most promising. It has the highest energy

content of 120 MJ/kg versus 44 MJ/kg of gasoline (Lalaurette et al, 2009). That is 2.75 times

greater than hydrocarbon fuel, which means it has the highest economic value per unit weight

(Pattra et al, 2008). Hydrogen is easier and safer to handle than other fuels used to produce

energy or transportation, it is easily collected, stored, and transported, and it produces water upon

combustion (Kalia and Purohit, 2008). Hydrogen fuel when burned does not radiate heat and is

not poisonous (Veziroglu, personal communication). There are multiple methods to biologically

produce hydrogen, which include the use of fermentative hydrogen-producing bacteria, microbial

electrolysis cells, biophotolysis, etc. These methods, aside from being less costly than other

energy producing techniques, are non-polluting and can be used in developing nations, taking

advantage of their already existing bio-wastes.

1.2. Why Cuba?

The Republic of Cuba encompasses over one hundred thousand square miles of land of

which over 50% of the land is arable. It is located approximately 90 miles away from the United

States and lies at the entrance of the Yucatan Peninsula making this country of great

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geographical importance from a trade perspective. Cuba’s major commodities include sugar,

nickel, tobacco, fish, medical products, and coffee. At one point in history, Cuba was the one of

the world’s leading producers of sugar. Figure 1.2 illustrates the locations of the most recent

known sugar mills in Cuba. However, economic decline and deteriorating infrastructure have

impacted greatly sugar cane production (Peters, 2003).

In Cuba, there is an evident need for a reliable, economical, and sustainable system to

produce energy. The power plants in Cuba are old and poorly maintained resulting in an

inefficient and unpredictable power capacity. Cuba’s energy grid is in need of significant

upgrades with cost estimates in the billions of dollars. Modernization of Cuba’s power

infrastructure should consider both the development of a smart grid and smart generation

(Cereijo & Solo-Gabriele, 2011). Future power generation will rely heavily upon the decision to

utilize fuel oil versus natural gas and to supplement power production with alternative

technologies that rely on wind, biomass, solar, nuclear power (Cereijo 2010), and possibly

biohydrogen.

Biohydrogen technology could be an alternative solution to Cuba’s energy deficiency and

the answer to end dependency on fossil fuels, which are not available on the island, are costly,

are imported from foreign nations, and contaminate the environment. Hydrogen can be produced

in the island using the natural resources already there. Some of the already available resources

are the waste from sugar cane production, called bagasse, which can be used by bacteria to

produce hydrogen, via fermentation our with the aid of microbial electrolysis cells (MEC). In

addition to bacteria, there are processes in development that utilize algae and sunlight to produce

hydrogen. Thus biohydrogen appears to be a promising energy alternative for Cuba given the

countries natural resources and the possibility of an independent source of fuel energy.

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2. Biohydrogen Processes

Hydrogen can be generated through the action of microbes through several different

processes. These include biophotolysis (both direct and indirect), fermentation (both light and

dark), microbial electrolysis cells (MEC), and through various combinations of these processes

including the use of microbial fuel cells to generate the electricity needed for MECs.

2.1. Biophotolysis (Direct and Indirect)

Photosynthesis is the only process on Earth that can convert light energy into chemical

energy. This process occurs in plants, algae, and many bacteria. Algae are typically autotrophic

organisms which utilize photosynthesis like plants, but are much more simplistic due to their

lack of distinct cells and organ types found in typical land plants. There is extensive amount of

research being done on certain single-celled green algae that are capable of producing hydrogen:

Ankistrodesmus, Chlamydomonas, Chlorella, Chrondrus, Codium, Corallina, Kirchneriella

Porphyridium, Scenedesmus are among the many species investigated.

In 1939 the University of Chicago was conducting research on a specific species of algae,

Chalmydomonas reinhartii. The lead scientist, Hans Gaffron, observed that during

photosynthesis this particular species of algae would sometimes switch from the production of

oxygen to the production of hydrogen (Gaffron, 1940). It wasn’t until the late 1990s that a

researcher by the name of Anastasios Melis discovered the cause of this occurrence. Melis found

that if an algae culture medium is deprived of the nutrient sulfur, it would disrupt the oxygen

flow creating anaerobic conditions causing the inactivation of the enzyme hydrogenase,

ultimately leading to the production of hydrogen gas.

The hydrogen production occurs in a two stage process consisting of light reactions and

dark reactions. The light reaction captures light energy and converts it into biochemical energy.

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The dark reaction uses the biochemical energy and CO2 in order to produce organic compounds,

such as sugars. During light reaction, photons of light are absorbed by pigments inside specific

organelles, causing a loss of an electron for every photon that is absorbed. In order to gain the

lost electron, an accessory protein must split a H2O molecule into hydrogen ions and oxygen gas.

The process of splitting the H2O molecule is called photolysis. Studies have shown that few

groups of algae and bacteria contain enzymes such as: Fe-hydrogenase, nitrogenase, and NiFe-

hydrogenase. Under certain conditions, instead of reducing CO2, these enzymes use the

biochemical energy to produce molecular hydrogen in a process called biophotolysis. The cells

generate hydrogen as part of an alternate biochemical pathway to produce needed adenosine

triphosphate (ATP). This so-called direct biophotolysis of water occurs in the chloroplasts of

algae and in the thylakoids of photosynthetic bacteria.

Biophotolysis can be separated into two categories: direct and indirect. The direct

biophotolysis process consists of electrons flowing from water by means of photosystem II to

photosystem I (Huesemann et al. 2010). This causes a reduction of the iron-sulfur protein that

mediates electron transfer called ferredoxin, which in turn causes a reduction in the hydrogenase

enzyme. The reduction of hydrogenase allows the transfer of electrons to protons, resulting in the

production of hydrogen gas. This simple and seemingly attractive process still faces critical

issues: the hydrogenase enzyme is inactivated in the presence of oxygen, thereby reducing the

amount of H2 formed. Also, the resulting H2 and O2 mixtures are highly explosive. Because of

the sensitivity of the hydrogenage enzyme to oxygen, studies show that the hydrogen production

rates are very low, of the order of 0.07 mmol/h per liter (Manish and Banerjee, 2007).

Solutions to these oxygen sensitive issues are currently the subject of intense study

through a process called indirect biophotolysis. Indirect biophotolysis involves a separate two-

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stage light driven process. The first stage involves the accumulation of cellular substances during

CO2 fixation and O2 production. These reduced substrates are then used in the second stage in

order for hydrogen production to take place under anaerobic conditions. The separation of the

photosynthetic O2 production eliminates the hydrogenase enzymes sensitivity to oxygen, as well

as the generation of the potentially highly explosive H2 and O2 mixture. Recent studies have

shown that the hydrogen production rates are of the order of 0.355 mmol/h per liter, which is five

times more than the hydrogen production from direct biophotolysis (Manish and Banerjee,

2007).

2.2. Microbial Fermentation

Fermentation is one of the less expensive techniques for the biological production of

hydrogen gas (Kalia and Purohit, 2008). The dark-fermentation process is preferred because it

does not rely on the availability of light and can occur continuously in a reactor (Manikkandan et

al, 2009). The fermentation process uses anaerobic digestion and complex biochemical reactions

for the microbial growth to produce energy. Growth and the subsequent production of hydrogen

is dependent upon many factors including pH, temperature, time of reaction, and most

importantly the substrate used by the microorganisms. There are many different substrates that

can be used in the fermentation process. The classic substrate is glucose. Glucose is found in

sugarcane bagasse, corn pulp, and raw starch of corn among many others. Figure 2.2.2 shows

that glucose is a very effective substrate for biohydrogen generation.

The anaerobic metabolism of glucose is a process known as glycolysis. This process

yields pyruvate, which is broken down into compounds and becomes an energy source for the

organisms. These energy source compounds are adenosine triphosphate (ATP) and reduced

nicotinamide adenine dinucleotide (NADH). (Kalia and Purohit, 2008).

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Because the substrate is so important to maximize the yield of hydrogen, it is key to find

a bio-waste that has great potential. The sugarcane bagasse is the waste left after the sugarcane

extraction process. It accounts for up to 25% of the sugarcane mass, and given Cuba’s average

annual sugarcane production of 50 tons, 12.2 tons of bagasse can be turn into bacteria substrate

for hydrogen production. The sugarcane bio-waste is made up of three different fractions;

Cellulose, hemicelluloce, and lignin (Pattra et al, 2008). For the organisms to use bagasse as a

substrate during anaerobic fermentation, it must first be hydrolyzed, which is usually done with

small amounts of sulfuric acid (Manikkandan et al, 2009). It is the hemicelluloce in the bagasse

that reacts with the acid and yields glucose and xylose. The other two components, cellulose and

lignin form a solid waste. The amount of substrate produced from sugarcane waste can then be

calculated as approximately 30-35% of the bagasse which is the portion composed of

hemicelluloce (Pattra et al, 2008).

To convert the raw bagasse to the substrate the bacteria will ferment, it must first be

treated with adequate amounts of sulfuric acid. Too much acid may inhibit bacterial growth and

shortens the life use of equipment by corrosion. Manikkandan et al, 2008 found that small

amounts of the acid with extended hydrolysis times yield higher glucose concentrations. The

production of Hydrogen relies greatly on the initial pH of the production. As noted in Table 2.2.1

shown in the appendix, the optimum initial pH of different bacteria strains varies. The pH also

influences the rate yielding. Really low pH may increase formation of weak acids, which

destabilizes the cell’s ability to maintain internal pH, damages the cell membrane, proteins and

DNA, slowing down or completely inhibiting cell production. Numerous research indicates that

for fermentation, the pH at which this may occur is 5.0 and below (Pattra et al, 2008).

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The production of hydrogen increases as the initial bagasse extract concentration also

increases. However, continuous increase in concentration of bagasse extract affects the

organisms growth rate, dropping drastically the production of hydrogen (Manikkandan et al,

2009). Temperature is yet another factor that must be monitored in microbial hydrogen

production. The optimum temperature that several authors have reported is 32°C. Manikkandan

et al, 2009 found that for Bacillus sp. the production rate at 40°C dropped significantly due to

protein deactivation. However, the use of acclimated pure or mixed cultures have had high

conversion efficiencies at 37°C (Logan et al, 2002).

The time for reaction as well as the other factors affecting production depends on the

specific bacteria. For example, while Bacillus sp. has a maximum hydrogen production of 0.23

mol of H₂ per mol of substrate under optimized conditions at 48hr (Manikkandan et al, 2009), C.

butyricum achieved maximum yield of 1.73 mol of H₂ per mol of substrate , under optimized

condition in just 40 hours.

2.3. Bioelectrochemical Systems

The microbial electrolysis cell (MEC) is the newest innovation in biohydrogen

production. Its discovery originates from the modified microbial fuel cell (MFC) design. Both

devices are referred to as bioelectrochemical systems (BES), where microorganisms serve as

catalysts for the electrochemical reactions that occur in the bioanode of the cell. As opposed to

MFCs, which generate current, MECs require electricity for the production of hydrogen gas.

Figure 2.3.1 in the appendix illustrates the two processes. MFCs (Figure 2.3.1a) consist of the

biocatalyzed electron transfer from the anode to the cathode of the cell. Bacteria in the anode

compartment oxidize organic matter and release carbon dioxide and protons to the solution, and

12

electrons to the anode. The protons are transferred to the cathode chamber through a cation

specific membrane, while the electrons are transferred to the cathode chamber through an

external electric circuit. Under aerobic conditions, the protons and the electrons are consumed in

the cathode chamber by combining with oxygen to form water. In order to generate a current

through the MFC process, a continuous supply of substrate must be replenished at the anode.

The MEC process is nonspontaneous and it requires an external source of energy to drive

the electrochemical reactions. Under anaerobic conditions, applying a small amount of voltage (>

0.2 V) between the anode and the cathode drives the production of hydrogen gas. This process is

now known as electrohydrogenesis or microbial electrolysis. The device used in the microbial

electrolysis process is called a MEC (Logan et al., 2008).

2.3.1. BES Reactor Design

Early experiments utilized a traditional and inexpensive design to demonstrate the

concept of BESs. Characterized by its H shape, the design consists of two bottles that are

connected by a tube and a cation/proton exchange membrane (e.g., Nafion or Ultrex) or a salt

bridge that assists the movement of protons from the anode to the cathode of the cell, but isolates

the substrate (Figure 2.3.2). In the case of a MEC, a gas collection and release system

accompanies the cathode. However, low power density or hydrogen production is obtained due

to the high internal resistance. This is influenced by the relative surface area and distance of the

cathode to that of the anode, and the small size of the cation exchange membrane (Logan et al,

2006, Logan et al, 2008). Thus, BES efficiency was successfully improved by increasing the size

of the membrane and the surface area of the anode with the addition of graphite granules.

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As previously mentioned, the presence of oxygen in the cathode creates the necessary

potential to create a spontaneous current. Therefore, the cathode of a MFC can be placed in

direct contact with air, regardless of the presence of a membrane. A membrane is employed to

prevent water from leaking to the cathode and oxygen from reaching the anode, as oxygen

consumption by bacteria results in a lower Coulombic efficiency and lower hydrostatic pressure.

Further modifications have led to continuous flow designs including the upflow fixed-bed

biofilm reactor, in which fluid flows through porous anodes toward a membrane that separates

the two opposing chambers (Logan et al, 2006).

The MEC reactor volume can be reduced by integrating the membrane with the cathode

and placing a platinum catalyst layer that faces the gas collection system, eliminating the

surrounding liquid in the cathode chamber. In MECs, however, the membrane is not essential

because of the absence of oxygen. Thus, single-chambered MECs that lack a membrane simplify

reactor design and reduce costs.

2.3.2. Energy Losses

The electrochemical reactions that take place in a MFC are spontaneous. In other words,

the process is thermodynamically favored. The maximum work that can be extracted from such

system is determined by the potential difference between the cathode and the anode. Although

the theoretical cathode potential can range between 0.361 V to 0.805 V, the observation of a

potential of 0.2 V in several studies indicates the occurrence of ohmic losses within the system..

Because the electrochemical reactions that take place in MECs are nonspontaneous, an

external source of energy is required to drive the process. As in the MFC, the theoretical

potential difference between the electrode compartments is dependent on the substrate. Using

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acetate as a substrate results in a theoretical voltage of 0.14 V that must be supplied to the cell

for the process to occur under standard biological conditions. In addition, electrode potentials are

influenced by the pH gradient that arises from the presence of a membrane. Thus, the addition of

0.2 V or higher is necessary due to energy losses including activation losses, bacterial metabolic

losses, and mass transport or concentration losses, which can be reduced by decreasing the

distance between electrodes and using a membrane and solution with higher conductivity.

2.3.3.Electrode Material

Bioanode

Several studies have evaluated BES performance by operating the bioanode with mixed

or pure cultures of microbes. Laboratory-scale BES open systems are commonly enriched with

pure cultures while large-scale experimental designs utilize mixed cultures. The microbial

diversity of the cultures may vary as they are enriched using inocula from natural resources such

as soil, anaerobic sediment sludge, and wastewater treatment sludge (Pham et al, 2009).

Bioanode community is usually contains the taxonomic class of Proteobacteria, but no particular

microbial community composition has been found to date.

Anodic material that efficiently interacts with the microorganisms and the substrate

should be biocompatible, cost-effective, non-corrosive, and conductive. Anodes commonly

consist of carbon in the form of compact graphite plates, rods, granules, graphite brush, fibrous

materials, or glassy carbon due to their defined surface area and simple use. Studies have

observed that current increases in the order carbon felt > carbon foam > graphite (Logan et al,

2006). The three-dimensional structure of graphite granule, graphite felt, and graphite brush

anodes completely fills the anode compartment and decreases electrode spacing and contact

15

losses. Thus, resulting in a larger effective surface area and higher power output (Pham et al,

2009).

Cathode

Electrons are consumed in the cathode chamber, where oxygen is reduced to water in a

MFC and hydrogen gas evolves in a MEC. The catalytic base material of the cathode

significantly influences the efficiency of the cell and, as the anode, must be non-corrosive,

conductive, and possess an efficient surface area. It may be graphite, titanium or other

conductive metal. Hydrogen evolution on plain carbon is slow and a conductive metal, such as

platinum, is usually the preferred catalyst. Due to the high cost of platinum, researchers suggest

noble-metal free catalysts that use pyrolyzed iron(II) phthalocyanine or CoTMPP (Logan et al,

2006) or stainless steel, MoS2, and nickel foam (Kundu et al, 2012).

2.3.4 MFC-MEC Coupled System

Hydrogen production by employing a MEC is not entirely sustainable because the cell

requires an external energy source in the form of electricity. Therefore, a MFC can provide the

power required by a MEC, resulting in a MEC-MFC coupled system. Sun et al. (2009) evaluated

the performance of such system by varying the loading resistors and using several MFCs

connected in series or in parallel. In both the MEC and MFC, the cathode was composed of

carbon paper and platinum and the anode was plain carbon paper. The biofilms were cultivated

with anaerobic sludge as inoculums and acetate as substrate. It was observed that a higher

resistance resulted in lower hydrogen production rate and hydrogen yield. At the loading

resistance of 10 Ω, hydrogen was produced at a rate of 2.9±0.2mLL−1 d−1, and the maximum

output power density of the MFC reached 28.6±4.5mWm−2. When two MFCs were connected in

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series, hydrogen production rates of 10.95±0.64 or 14.54±0.12mLL−1 d−1 were obtained.

However, a significant amount of energy in the substrate was lost in the circuit or consumed by

other processes.

A recent study conducted by Hatzell et al. (2013) employed capacitors to prevent voltage

reversal. The MFCs charged the capacitors in parallel, and the capacitors were discharged in

series to power the MEC. The system consisted of cube-shaped, single-chambered MFC and

MEC reactors, a glass tube to collect the hydrogen gas, and brush anodes from graphite fibers

and a titanium wire core. The MFC cathode was made from wet-proofed carbon cloth with a

platinum catalyst, and the MEC cathode was made from type 304 stainless steel with a platinum

layer. Adding the capacitors improved the performance of the system in terms of hydrogen

production rate and yield by 38% and 60%, and energy recovery by 77%. Up to 95% of the

energy produced by the MFCs was transferred to the MEC.

3. Design

As previously mentioned, hydrogen gas is generated in the presence of bacteria, whose

catalysts aid in the electrochemical reaction between protons and electrons during fermentation.

However, bacteria use additional metabolic paths that lead to the production of various end-

products such as acetate, butyrate, and ethanol that reduce hydrogen yield. Further breakdown of

this organic matter is nonspontaneous and requires an external source of energy. An alternative

approach considers the combination of two or more biological processes to attain greater

hydrogen production rates and yields.

In this section, a coupled system that combines dark fermentation and a microbial

electrolysis cell to produce biohydrogen from sugarcane waste is proposed. Methods (i.e.,

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calculations for reactor volume) and data (i.e.,hydrogen production rates) were obtained from the

literature to design the system. The substrate, sugarcane bagasse, initially undergoes hydrolysis,

followed by fermentation and electrohydrogenesis. Lastly, the necessary hydrogen gas produced

by both processes is collected in a storage tank and transferred to 1kW fuel cell for electricity

production. To further extract hydrogen gas from organic matter that can’t be broken down

during fermentation, various studies have examined the performance of this two stage process, in

which the fermentation effluent is fed into a MEC.

In a study performed by Lu et al. (2009), a membraneless, single-chamber MEC was fed

with the effluent from an ethanol-type dark-fermentation reactor. The continuous stirred-tank

reactor was fed with molasses wastewater and produced hydrogen gas at a maximum rate of

0.70m3 H2/m3/d. The effluent contained ethanol, acetic acid, propionic acid, butyric acid, and

valeric acid.To prepare the MECs, MFCs were inoculated with domestic wastewater and the

cathodes were aerated. The new MECs were fed with buffered effluent from the fermentation

process after changing the polarity of the MFCs. The application of 0.6 V resulted in a maximum

hydrogen production rate of 1.41±0.08m3 H2/m3/d. The absence of a membrane allowed for a

higher current density, which resulted in higher hydrogen production rate.

A separate study conducted by Lalaurette et al. (2009) examines the conversion of

lignocellulose and cellobiose into hydrogen gas through a two-stage process, in which

electrohydrogenesis in a MEC is followed by fermentation. A pure culture of Clostridium

thermocellum was utilized for the fermentation process, and the MEC was inoculated with

wastewater and fed with the fermentation effluent. The MEC consisted of graphite-fiber-brush

anodes pretreated using an ammonia gas process, and flat carbon-cloth cathodes containing a

platinum catalyst that faced the anode. During the fermentation, pre-treated lignocellulosic

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biomass was converted into hydrogen, carbon dioxide, acetic, formic, succinic, and lactic acids,

and ethanol. The organic end-products constitute the effluent that was decomposed in the MEC

to generate biohydrogen. The two-stage process attained an overall hydrogen production yield of

9.95 mol H2/mol glucose from cellobiose, where 1.64 mol-H2/mol glucose was attained in the

fermentation stage, and 8.31 mol H2/mol glucose was produced in the second MEC stage.

Volumes of the reactors were calculated using the method devised by Levin et al. and are

shown in the last “calculations” appendix. According to Pattra and workers, 25% of sugar

production that results in waste consists of 30-35% of hemicellulose, and the rest of cellulose and

lignin. Hemicellulose is obtained from the hydrolysis of sugarcane bagasse and can be

fermented, while lignin and cellulose remain as solids. A settling tank following hydrolysis

separates the solids, and the solution containing hemicellulose is fed into a fermentation batch

reactor, as done by Pattra et al. (2008). The effluent from the fermentation reactor and

precipitate from the settling tank are fed into the MEC. A hydrogen production rate of 1611 mL

L-1 hr-1 obtained by Pattra et al. during the fermentation of sugarcane bagasse, and that obtained

by Lalaurette et al. (2009) during the electrohydrogenesis of lignocellulose were used to

determine the volumes of the respective reactors (Appendix C). A total hydrogen production rate

of 4.4 mmol L-1 hr-1 resulted in fermentation and MEC reactor volumes of approximately 3360 L

and 2090 L respectively. Figure 4.1. illustrates the coupled fermentation-MEC system that

utilizes sugarcane bagasse as the substrate.

In an attempt to design a system that is independent of an external energy source, Wang et al.

(2011) studied the performance of a two-stage process powered by MFCs. The inoculum for the

fermentation process was prepared by enriching a mixed culture with rotted wood crumbs.

Cellulose was continuously fed to the fermentation reactor, and the effluent of this process was

19

fed to the MEC. The MFCs were single-chamber reactors with brush anodes and an air cathode.

The same design was used for the MECs, except that the cathode was not aerated and had a

larger anode. The MECs and MFCs were placed in different combinations to test the efficiency

of the entire system. While it was found that the use of a combined MEC–MFC system can

increase hydrogen yields by 41%, the applied voltage was limited and dependent on the

efficiency of the MFCs. Thus, further research into this area is necessary to fully assess the

utilization of a MFC that provides the required 0.6 V of a MEC. Nevertheless, integrating the

two bioelectrochemical technologies and fermentation in a two stage process is an innovative

idea of creating a system that sustains the conversion of biomass into hydrogen without an

external source of energy.

In order to generate 1 kW of energy, which is the amount needed for a modest home, we

estimate that 2 acres would be needed to provide the substrate for the process (see computations

appendix). The 2 acres corresponds to the utilization of the sugarcane bagasse waste. If the

actual sugarcane were to be utilized, the area needed could be decreased by a factor of 4 to ½ of

an acre, given that bagasse represents 25% of the glucose yield of whole sugarcane. During the

late 1980’s, the area harvested for sugarcane in Cuba was on-the-order of 3.2 million acres

(Echevarria year). Assuming that only the bagasse waste is utilized for biohydrogen production,

this area represents about 1,600 MW of electricity given the technology available today. This is

enough energy to provide power to 1.6 million modest sized homes. Assuming that 4 people live

per home, this represents the provision of power for 6.4 million residents which is about half the

population of Cuba. If the entire sugarcane crop, as opposed to only the bagasse waste, were

utilized for the production of energy, Cuba’s sugarcane agriculture would be capable of

theoretically providing 6,400 MW of electricity which could serve the country’s energy needs.

20

With improvements in the technology, there is a potential for sugarcane and the bagasse waste to

provide a greater amount of hydrogen energy per acre of harvested land.

4. Conclusion and Recommendations

Our theoretical design shows encouraging results and demonstrates the possibility of

producing biohydrogen from readily available resources, such as sugarcane bagasse. It is

important to note that our design is based on experimental results obtained through laboratory

scale methods. Therefore, assumptions were made in order to scale up the processes. Further

research into bioelectrochemical and biophotolysis processes is necessary to enhance the process

efficiency and performance. A full-scale prototype is recommended to further analyze hydrogen

gas production. Ultimately, the utilization of this technology can potentially provide a promising

alternative for power generation in Cuba.

21

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APPENDIX A: Illustrations (Figures and Drawings)

Figure 1.2 GIS map of known locations of current sugar mills in Cuba.

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Figure 2.2.2. Hydrogen production from fermentation processes that utilize different

substrates (from Logan et al. 2002).

26

Figure 2.3.1. Illustration of the microbial fuel cell (MFC) shown to the left (a) and the microbial electrolysis cell (MEC) shown to the right (b). The MFC generates electricity. The MEC

generates hydrogen through the addition of an external voltage (from Dominguez-Benetton et al., 2012).

Figure 22.3.2. “H” sh

27

haped microbbial electrolyysis cell.

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Figure 4.1 Fermentation-MEC conceptual design for hydrogen fuel cell from the production of sugarcane bagasse.

29

APPENDIX B: Tables

Bacteria Substrate pH Temperature Time H₂ Yield (mol H₂ / mol

substrate)

Bacillus sp. Glucose 7.0 32°C 48 hrs 0.23

Clostridium butyricum

Glucose 5.5 37°C 40 hrs 1.73

Table 2.2.1. Comparison of dark fermentation bacteria (From Manikkandan et al., 2009 and Pattra et al., 2008)

30

Appendix C: Calculations

Step 1: Data collection and Assumptions

• Sugarcane production in Cuba is approximately 50 tons/ha-yr. • 25% of sugar production that results in waste consists of 30-35% (about 33%) of

hemicellulose, and the rest of cellulose and lignin (Pattra et al., 2008) • The fermentation process conducted by Pattra et al. (2008) had 51% efficiency when the

maximum hydrogen production rate was 1611ml H2/L-d. • In the coupled system that extracts hydrogen gas from lignocellulose by Lalaurette et al.

(2009), an average hydrogen production rate of 1000 ml H2/L*d was obtained from the MEC.

• The hydrogen flow rate required by a 1kW fuel cell is 23.9 mol H2 / L (Levin et al., 2004).

Sugarcane (ton/ha*yr) 50 Percent Mass Sugarcane Bagasse (%) 0.25

FermentationIN (%) 0.33

FermentationOUT (%) 0.51

MECIN 1 (%) 0.77

MECIN 2 (%) 0.51

Fermentation (ml H2/L*d) 1611

MEC (ml H2/L*d) 1000

mol H2 / L 23.9 Step 2: Calculate the volume of reactors following the methods devised by Levin et al. (2004).

Convert the rates to (mol H2/L*h):

Hydrogen flow rate/ VREACTOR

mL H2/L-d mol H2/L-h Fermentation 1611 0.0027 MEC 1000 0.0017

The volume of a reactor that supplies hydrogen to a fuel cell can be calculated by

dividing the required hydrogen flow rate of 23.9 mol H2 / L by the total hydrogen production rate of 0.0044 mol H2/L-h

Volume (L) = 5450 However, our system involves both a fermentation batch reactor and an MEC reactor. Setting the ratio of the calculated rates equal to the ratio of volumes of the reactors will provide the volume of the fermentation batch reactor alone:

VFerm/VMEC = VFerm/V-VFerm = 1.61

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VolumeFerm (L) = 3362 The difference of the volumes will provide the proportional volumes required for 1 kW of power generation:

V-VFerm = 2086.64 L Thus,

VOLUME OF REACTORS Ferm(L) MEC(L)

3362 2087 Step 3: Calculate the rate of sugar going into the system Separate and convert the composition of sugarcane bagasse:

Ferm. (g/mol) Rate_Ferm (mol H2/L-h) (g sugar/h) Glucose 180 0.0027 842Xylose 150Arabinose 150Average: 160

MEC (g/mol) Rate_MEC(mol H2/L-h) (g sugar/h) Cellulose 162 0.0017 347Lignin 180Average: 171

Sum the total rates of sugarcane bagasse consumption:

SUM(g sugar/h) 1189 Step 4: Calculate the area of sugarcane fields required to produce 1 kW Using the given data and the total rate of sugar input into the system:

RSF = rate of sugarcane field usage (g sugar/h) Fermentation input + MEC input = Total rate of sugarcane bagasse consumption

RSF(0.25)(0.33) + RSF(0.25)(0.77) + (842.23)(0.25)(0.33)(0.5141) = 1189 RSF = 4194 g sugar/h

Convert to area of sugarcane field:

Field Sugar (ha) Field Sugar

(ac) Field Sugar

(m2) Field Sugar

(ft2) 0.81 2.00 8,100 87,180