OPTIMIZATION OF BIOHYDROGEN PRODUCTION FROM FOOD PROCESSING WASTEWATER

  • : Ms Word Format
  • : 100 Pages
  • : ₦3000
  • : 1-5 Chapters
  •  
  • Click to DOWNLOAD Materials

OPTIMIZATION OF BIOHYDROGEN PRODUCTION FROM FOOD PROCESSING WASTEWATER

Abstract

The ideas of dwindling fossil fuel reserves, global warming, and the need for energy efficiency in our nation’s infrastructure inspired this thesis.  One area vital to our nation’s well being is wastewater treatment.  The production of hydrogen gas from wastewater using anaerobic treatment processes makes wastewater treatment more economical.  Although hydrogen gas can be produced from any organic wastestream, the production of hydrogen from high strength food processing wastewater makes the most economic sense. The objectives of this thesis were to convert food processing wastewaters to hydrogen and to maximize hydrogen yields from glucose at concentrations typically found in the food processing industry.

Batch and continuous reactor experiments were conducted to determine conditions for maximum biological H2 production yields and rates.  A method used to increase H2 production yields involved decreasing the H2 concentration in the reactor vessel to reduce H2 partial pressure inhibition.   This method was accomplished in two different ways using both batch and continuous reactor tests.  In batch tests, H2 gas produced was released either continuously using a respirometer or intermittently using a glass syringe.  H2 yields increased 43% when the continuous release system was used reaching a maximum of 0.92 mol-H2/mol-glucose.  In continuous reactor tests, low glucose concentrations were used to reduce the H2 production rate and reduce H2 partial pressure inhibition.  Continuous reactors were operated at glucose concentrations of 2.5 to 10 g COD/L at hydraulic retention times of 1 to 10 hours (2L reactor volume).  H2 yields increased with decreasing glucose loading rate reaching a high of 2.6±2 mol H2 / mol glucose at the lowest glucose loading rates (0.5 – 1.9 g glucose/hr).  High yields of hydrogen were consistent with a high molar acetate:butyrate ratio of 1.08:1 as more hydrogen is produced with acetate as a product (4 mol-H2/mol-acetate) than with butyrate (2 mol-H2/mol-

 

butyrate).  Flocculation was also an important factor in the performance of the reactors.  The flocculant nature of the biomass allowed reactor operation at low HRTs with steady H2 production and > 90% glucose removal.

In addition to inhibition due to hydrogen gas, undissociated acids also cause inhibition. In continuous reactor tests, the effect of the undissociated form of acetic and butyric acids on H2 production yields was tested by varying the pH, by operating reactors at high glucose concentrations, and by adding these acids directly to the influent of the reactors.  Overall, total undissociated acid (p-value = 0.02) and undissociated butyric acid concentrations (p-value = 0.06) in the reactor (pH 5.5) were observed to decrease H2 yields while acetic acid had a lesser effect on H2 yields (p-value = 0.89).  At influent glucose concentrations of 10 to 30 g/L, H2 yields were fairly constant at 50±2%.  At a glucose concentration of 40 g/L, H2 yields were the lowest of all conditions tested at 1.6±0.1 mol-H2 / mol-glucose where a switch to solventogenesis occurred.  It was concluded that a self-produced total undissociated acid concentration of >19 mM is the threshold concentration that significantly decreased H2 yields and initiated solventogenesis under the conditions tested.

In more applied tests, domestic and five different food processing wastewaters (apple, two potato wastewaters, and two confectioner wastewaters) were used as the substrate in batch tests.  Gas produced from the domestic wastewater sample (concentrated 25×) contained only 23±8% hydrogen, resulting in an estimated maximum production of only 0.01 L/L for the original, non-diluted wastewater.  COD removals from the food processing wastewaters as a result of hydrogen gas production were generally in the range of 5-11%.  Overall hydrogen gas conversions were 0.7-0.9 L-H2/L-wastewater for the apple wastewater, 0.1 to 2.0 L/L for the confectioner wastewaters, and 2.1-2.8 L/L for the potato wastewater.

TABLE OF CONTENTS

PAGE

List of Tables ……………………………………………………………………………………………………………        x

List of Figures…………………………………………………………………………………………………………..        xi

Acknowledgements……………………………………………………………………………………………………      xii

Chapter 1: Introduction………………………………………………………………………………………………         1

1.1  Oil and the World……………………………………………………………………………………..        1

1.1.1 Effects of using Oil and other Fossil Fuels………………………………………        2

1.2 Developing Countries are suffering the most from the use of

non-renewable fossil fuels ………………………………………………………………………….        3

1.2.1  Eliminating Poverty through the use of Renewable Energy………………        4

1.3 Renewable Energy…………………………………………………………………………………….        5

1.3.1 Wind Energy has the Greatest Potential to Satisfy

the World’s Energy Needs……………………………………………………………        5

1.3.2 Other Forms of Renewable Energy can also Satisfy our Energy Needs.        7

1.4  The Transition to the Renewable Energy Economy………………………………………        8

1.4.1 When will the World make the Transition to a

Renewable Energy Economy?………………………………………………………        8

1.4.2  The Transition to the Renewable Energy Economy

– Getting it Right the First Time……………………………………………………        9

1.4.3  Energy Efficiency will Speed Up the Transition to a

Renewable Energy Economy………………………………………………………..      10

1.5 Taking Care of the Infrastructure that Sustains Us…………………………………………     11

1.5.1 Energy Efficient Wastewater Treatment through

Anaerobic Treatment Technologies………………………………………………..      11

1.5.2 Anaerobic Treatment and Domestic Wastewater ……………………………..      11

1.6 Hydrogen Production from Food Processing Wastewater –

The Main Subject of this Thesis ………………………………………………………………….      14

1.6.1  Hydrogen Energy’s Role in Improving Food Processing

Wastewater Treatment ………………………………………………………………….      14

1.6.2  Improving H2 Yields from Food Processing Wastewater………………….      15

1.6.2.1  Inhibition due to H2………………………………………………………..      15

1.6.2.2  Inhibition due to acetic and butyric acid……………………………      17

1.7 Chapters in Brief……………………………………………………………………………………….     18

1.8 Literature Cited…………………………………………………………………………………………     21

Chapter 2: Biological Hydrogen Production Measured in Batch Anaerobic

Respirometers …………………………………………………………………………………………..      26

Abstract…………………………………………………………………………………………………………      26

2.1 Introduction………………………………………………………………………………………………      27

2.2 Methods……………………………………………………………………………………………………      29

2.2.1 Culture Conditions……………………………………………………………………….      29

 

2.2.2 Reactors………………………………………………………………………………………      30

2.2.3 Analytical……………………………………………………………………………………      30

2.3 Results……………………………………………………………………………………………………..      31

2.3.1 Hydrogen Production Using Different Substrates …………………………….      33

2.4 Discussion………………………………………………………………………………………………..      34

2.4.1 Implications for Hydrogen Production During

Wastewater Treatment ………………………………………………………………….      38

2.5 Acknowledgements……………………………………………………………………………………      39

2.6 Literature Cited…………………………………………………………………………………………      39

2.7 Figure Captions…………………………………………………………………………………………      43

Chapter 3: Increased biological hydrogen production with reduced organic loading………….       50

Abstract…………………………………………………………………………………………………………      50

3.1 Introduction………………………………………………………………………………………………      51

3.2 Methods……………………………………………………………………………………………………      53

3.2.1 Startup and feeding………………………………………………………………………      53

3.2.2 Reactor Operation………………………………………………………………………..      54

3.2.3 Gas production…………………………………………………………………………….      55

3.2.4 Analytical……………………………………………………………………………………      55

3.3 Results……………………………………………………………………………………………………..      56

3.3.1 H2 yield and production as a function of the glucose loading rate ………      57

3.3.2 Biomass concentrations in the reactor …………………………………………….      58

3.3.3 Soluble products produced by glucose fermentation…………………………      59

3.3.4 COD Mass Balance………………………………………………………………………      59

3.4 Discussion………………………………………………………………………………………………..      60

3.4.1 Implications of increased hydrogen production with low

organic loading rates…………………………………………………………………….      62

3.5 Conclusions………………………………………………………………………………………………      62

3.6 Acknowledgements……………………………………………………………………………………      63

3.7 Literature Cited…………………………………………………………………………………………      63

3.8 Figure Captions…………………………………………………………………………………………      67

Chapter 4: The Inhibition of Biohydrogen Production caused by Undissociated Acid

Concentrations at High Glucose Concentrations……………………………………………      75

Abstract…………………………………………………………………………………………………………      75

4.1 Introduction………………………………………………………………………………………………      76

4.2 Methods……………………………………………………………………………………………………      78

4.2.1 Startup and feeding………………………………………………………………………      78

4.2.2 Reactor Operation………………………………………………………………………..      78

4.2.3 Analytical……………………………………………………………………………………      79

4.3 Results……………………………………………………………………………………………………..      81

4.3.1 H2 Yields as a function of pH ………………………………………………………..      81

4.3.2 H2 Yields as a function of added acetic and butyric acids at pH 5.5……      81

4.3.3 H2 Yields as a function of added acetic and butyric acids at pH 5.0……      83

4.3.4 H2 Production as a function of glucose concentration……………………….      83

4.3.5 Differences in bacterial floc morphology………………………………………..      84

 

4.4 Discussion………………………………………………………………………………………………..      85

4.6 Acknowledgements……………………………………………………………………………………      88

4.7 Literature Cited…………………………………………………………………………………………      89

4.8 Figure Captions…………………………………………………………………………………………      94

Chapter 5: Biohydrogen Gas Production from Food Processing

and Domestic Wastewaters…………………………………………………………………………    103

Abstract…………………………………………………………………………………………………………    103

5.1 Introduction………………………………………………………………………………………………    104

5.2 Methods……………………………………………………………………………………………………    105

5.2.1 Wastewater tests…………………………………………………………………………..    105

5.2.2 Data analysis……………………………………………………………………………….    108

5.2.3 Analytical Methods………………………………………………………………………    109

5.3 Results……………………………………………………………………………………………………..    110

5.3.1 Food processing wastewater tests…………………………………………………..    110

5.3.2 Additional tests on potato processing wastewaters……………………………    111

5.3.3 Domestic wastewater ……………………………………………………………………    112

5.4. Discussion……………………………………………………………………………………………….    113

5.4.1 Hydrogen Production from wastewater …………………………………………..    113

5.4.2 Economic value of hydrogen …………………………………………………………    115

5.5 Acknowledgements……………………………………………………………………………………    116

5.6 Literature Cited…………………………………………………………………………………………    116

5.6 Literature Cited…………………………………………………………………………………………    123

Chapter 6: Conclusions………………………………………………………………………………………………     127

Chapter 1 Introduction

1.1  Oil and the World

The United States and a few other countries have literally fueled themselves into greatness using cheap and readily useable energy forms, especially oil.  The world’s oil is limited in quantity.  An insufficient amount may be remaining to bring developing nations to the American standard of living if the United States and others continue to consume remaining oil reserves.

The United States is by far the largest user of oil.  With just 5% of the world’s population, we consume 26% of the world’s oil, yet we hold only 2% of the world’s oil reserves (EIA, 2001).  It is estimated that an additional 1% of the world’s oil reserves lay in the Artic

National Wildlife Refuge in Alaska which may open up for exploration in the first few months of 2005 (Cleveland and Kaufman, 2001).  Of the 1800 to 2200 billion barrels of oil ultimately recoverable worldwide, 875 billion barrels have been consumed (Youngquist, 1997; EIA, 2001).

The most important estimate is not how much oil the world has but when will the supply of oil not meet our demand for oil.  Current estimates suggest that non-OPEC (Organization of Petroleum Exporting Countries) oil-producing nations will peak in oil production in 2010 while OPEC oil-producing nations will peak in oil production by 2015 (Youngquist, 1997).  In other words, within this time frame the world would have produced half of its recoverable oil reserves. Worldwide, per capita consumption peaked in 1979 and has decreased ever since due to exponential population growth (Rifkin, 2002).  Campbell and Laherrere (1998) suggest world oil production could peak before 2010.  After the peak, most of the remaining oil will lie in Middle East countries.  Most of these countries are ruled by autocracies and could use oil as a weapon and demand a high price for this oil (Rifkin, 2002).  In effect, these high oil prices will weaken the United States’ economy.  Almost every segment of our economy relies on oil.  Considering that food production currently uses 17% of the nation’s energy, mainly from oil for fertilizers and pesticides and to operate heavy machinery, any lack in oil supply or a high price for oil would severely weaken our ability to produce food economically (Gever, 1991).

Jeremy Rifkin, in his book, The Hydrogen Economy, stated that it would be illusory to expect other countries to have the same standard of living we enjoy here in the U.S. given the current world production rates (2001).  For example, if China were to have the same consumption rates as the U.S., it would require 81 million barrels per day or 10 million more barrels than the entire world’s production in 1997 (Youngquist, 1997).

1.1.1  Effects of using Oil and other Fossil Fuels

America’s use of oil and other fossil fuels may be causing global warming through CO2 emissions which could affect the entire world through extreme changes in the weather (IPCC, 2001).  At home, the use of oil and other fossil fuels is also degrading our air and water supplies (Kennedy, 2002).  Approximately 75% of the increase in CO2 concentrations in the atmosphere in the last twenty years has been due to the combustion of fossil fuels.  Americans produce 30% of the CO2 emissions (Rifkin, 2002).   According to the Millennium Assessment Report launched by the U.N. Secretary-General Kofi Annan in June 2001, 60% of the ecosystem services that support life on Earth are being degraded or used unsustainably.  The degradation of ecosystems services could grow significantly worse during the first half of this century and is a barrier to achieving the UN Millennium Developments Goals.  In a report commissioned by the Pentagon, it was stated that millions of lives could be lost over the next 20 years as abrupt climate changes due to global warming forces people to secure food, water, and energy supplies (Schwartz and Randall, 2003).   Any catastrophic weather events (droughts, floods) indirectly caused by global warming would injure developing countries the most since these countries are already disadvantaged.  It seems the use of oil or the lack of oil in the future will cause major lifestyle changes or will prohibit developing countries to adapt to climate change in the future.

1.2  Developing Countries are suffering the most from the use of non-

renewable fossil fuels

It can also be argued that poverty in developing nations is also a major cause of the destruction of ecosystem services since people who are starving are less concerned about conserving their environment than getting their next meal.  Mass poverty is often at the root of environmental degradation (United Nations, 1987).  In the United States, the poor often bear more of the burden of environmental pollution than the wealthy (Inyang, 2004).

If the U.S. continues to consume oil at the same rate it does currently, the situation in the developing world will get worse for a number of reasons.  First, the price of oil will remain high since the demand for oil will be high.  Since the two spikes in OPEC oil prices in 1973 and 1979, the developing world had to seek financial assistance to pay for the increased costs of oil imports (IEA, 2000).  By the end of 1999, about 1.1 billion people in forty seven countries in the developing world owe $422 million for their oil imports (Annan, 2000).  Collectively, the developing world debt has exceeded $1 trillion.  Considering that the average per capita debt of $380 in the developing world is nearly equal to the average per-capita gross national product, the developing world may never get out of debt (Roodman, 2001).  Second, since the developing world (about 2.5 billion people) has low per capita energy consumption and still relies on wood, animal manure, and crop residues for their fuel, these people spend each day just trying to survive rather than being able to advance their basic quality of life (Star, 1997; Ponting, 1991). As of the year 2004, approximately 40% of the world’ population is without electricity while most of the world’s population does not have enough energy per capita to break free from a life where basic survival is the goal rather than the goal of living life abundantly (Inyang, 2004; Rifkin, 2005).

The inability of the U.S. to implement energy production systems with zero greenhouse gas emission could be considered to be ‘poor’ as well.  Renewable energy production technologies exists today that would enable everyone in the world to live their life abundantly. Yet, Nelson Mandela’s request for the developed nations to eliminate poverty still remains despite the existence of renewable energy production technologies (CNN, 2005).

1.2.1  Eliminating Poverty through the use of Renewable Energy

A remedy for eliminating poverty and mitigating global warming while sustaining the U.S.’s standard of living could be the implementation of a hydrogen economy where the hydrogen gas is produced by renewable energy.  The speed of this implementation of energy is the difference between life and death in developing nations.  Energy sources that could maintain our standard of living without causing adverse affects to the environment include wind, solar, and biomass, among others, but these three will arguably be the best sources in the future. Collectively, renewable energy supplies 6-8% of our energy demand (EIA, 2001; Rifkin, 2002). Hydropower provides about half of the U.S.’s renewable energy today but nearly all sites have been utilized.  Energy produced from biomass provides the bulk of the rest of our renewable energy through biomass/coal co-combustion in power plants or through the use of biomassproduced ethanol in automobiles.

1.3  Renewable Energy

1.3.1  Wind Energy has the Greatest Potential to Satisfy the World’s Energy Needs.

Currently, wind energy supplies 1% of the U.S. energy demand and the wind industry is one of the fastest growing market segments in the world economy especially in Europe (Rifkin, 2002).  The American Wind Energy Association (AWEA) projects wind energy will supply 10% of our energy demand by 2020.  According to Lloyd and Hassan (2000), the wind generating potential along the coastal regions of the Baltic and North Seas could supply enough wind to produce electricity for the entire European Continent.  In the U.S., the wind energy potential is 10,777 billion kWh annually—three times the electricity generated in the U.S. today (AWEA, 2005).

Currently, there are few new wind energy installations in development as companies wait for the renewal of the federal Production Tax Credit, which provides key incentives to greenpower developers.  If renewed by the U.S. Congress this Fall 2005, 2000 MW of wind energy are planned to be built with a 310-megawatt installation planned for two sites in northern Iowa.  This installation will be the biggest land-based wind farm in the world (Tompkins, 2005).  The State of Pennsylvania plans to install 170 MW over the next two years and provide 10% of its energy demand by 2010 using wind energy (AWEA, 2005).

Harry Braun (2005), the creator of the Phoenix Project, promotes an aggressive plan to rid fossil fuels from our economy by the installation of 10 million one mega-watt (MW) wind turbines or one million 10 MW ‘wind ships’ off the California coast well out of viewing distance.  He estimates that a $3 trillion investment would generate $1 trillion annually in energy sales.  The electricity would cost one cent per kWh.  The ten million wind turbines are mentioned to be just as easy to produce as the six million automobiles produced per year in the U.S.  We could be energy independent by 2010 and the production of wind turbines would be a significant boost to the U.S. economy.

At sea, wind speeds are the greatest.  Every continent on the planet can utilize wind energy off their coastlines to satisfy their energy needs and eliminate their dependence on fossil fuels.  In the wind ship idea presented by Harry Braun, seawater would be converted to hydrogen gas by electrolysis using electricity provided by the wind ships and piped to the California coast (personal communication, April 13th, 2005).  All ground and air transportation would be fueled using liquid hydrogen using slightly modified internal combustion engines operating at high efficiencies.  Mr. Braun states that liquid hydrogen has a proven track record of safety noting NASA and BMW studies while he also mentions that fuel cells would cost too much and would take too much time to implement stating that the mitigation of global warming has to occur immediately.  Since the wind ships would have a crew of ten, approximately ten million highquality private sector jobs will be created in the process.  The wind ships would be an oasis for marine life since unregulated destructive fishing and trawling practices have already destroyed over 90 percent of the ocean ecosystems.

According to Braun, the production of hydrogen from wind would eliminate the two problems limiting the penetration of wind energy into the market.  The first problem is that wind energy is intermittent while electricity is consumed continuously.  If electricity is produced from wind energy in a greater supply than what the electrical grid demands, excess wind energy can be stored as hydrogen and then converted to electricity via fuel cells to satisfy electrical demand when the wind energy output is low.  Second, Braun mentioned that there is currently a lack of space on the existing electrical grid.  Fossil fuel power plants would have to produce less electricity to allow electricity from renewable sources to come onto the electrical grid.   The storage of wind energy as hydrogen and the conversion of hydrogen to electricity during times of peak usage would allow power plants to reduce electricity production.  According to Rifkin (2002), thirty states in the U.S require electrical utilities to buy back electricity produced using renewable energy sources.

1.3.2  Other Forms of Renewable Energy can also Satisfy our Energy Needs.

In regard to solar energy, the amount of solar energy that hits the Earth in forty minutes is equal to the amount of energy the world uses in an entire year (Houghton, 1997).  Currently, photovoltaic cells (PVC) are too inexpensive to compete with electricity production using fossil fuels, but the price for PVCs has come down significantly in the last few decades (Rifkin, 2002). In regard to geothermal energy, the resources in the U.S. alone are estimated to exceed 70,000,000 quads which is enough energy to supply our energy needs for hundreds of thousands of years (Rifkin, 2002).  It is also estimated that in the U.S., the use of biomass to produce hydrogen (primarily through pyrolysis) could fuel 150 million fuel cell vehicles (NREL, 2004). However, greater than half of this biomass would come from agricultural residues and energy crops which would further deplete our nation’s soil as well as compete with food production for available land.

1.4  The Transition to the Renewable Energy Economy

1.4.1  When will the World make the Transition to a Renewable Energy Economy?

From the facts presented previously, it is easy to see that there is enough renewable energy in the world to satisfy our needs.  Many technologies are available and some of these technologies cost more than others.  It seems the only question that remains is when we will make the transition to a new renewable energy economy.  The current political powers in the United States seem to prefer to stay with the fossil fuel energy infrastructure.  In the last few decades, many natural gas fired power plants have come on line while there are plans to construct hundreds of coal fired power plants to start the new H2 economy based on coal (Rifkin, 2002; Braun, 2005).  However, natural gas production is estimated to peak a few years after the peak in oil production (Rifkin, 2002).  The U.S. has a 250-year supply of coal which would seem to dissipate any energy worries for at least the current and next several generations.  However, at current rates of energy consumption, if we were to produce hydrogen on a scale to displace oil and natural gas in the transportation and energy sectors, the 250-year supply of coal would be used up in about 40 years.  Furthermore, the environmental impact from the strip mining alone would disturb large tracts of land and lead to acid mine drainage.  Dr. Inyang (2004) has stated that by 2020, 1300 new power plants will be needed because our demand for electricity is expected to grow by 1.8% per year.  Lee Raymond, the CEO of ExxonMobil, has stated that it is impossible to make the U.S. energy independent with oil and other fossil fuels.  It is no wonder why Shell and other large energy firms are investing billions into renewable ways to produce hydrogen (Rifkin, 2002).  But, how much time must pass before we arrive with our new renewable energy infrastructure?  How many more years of increasing greenhouse gas emissions and rising energy prices can the world sustain?  Should we transition to a renewable energy economy before the climate or our economies suffer too much?  Would it be better if we transition now rather than after a few decades of more abuse from the utilization of fossil fuels?

Should we save the remaining oil for chemical uses rather than burning it?

1.4.2  The Transition to the Renewable Energy Economy – Getting it Right the First Time.

The transition from a fossil fuel based energy economy to a renewable energy / H2 based economy will be an enormous undertaking that will cost trillions of dollars, but this expenditure is no more than the trillions already spent on the implementation of the fossil fuel based economy.  The transition will be easiest if the transmission of energy is efficient.  The distance between the energy producer and the end user should be short.  Such is the case with distributed generation (DG).  In DG systems, each region of the world is fueled by its own inherent renewable energy source.  Energy could be produced anywhere at any scale.  Distributed generation is said to be more efficient, secure, democratic, and reliable than the current energy infrastructure (Rifkin, 2002).   Furthermore, because of the way energy would be produced in a distributed generation system, communities would be more distributed and therefore more in tune and integrated with nature.  It would be a sharp contrast from the large urban centers supplied electricity from nuclear and coal power plants many miles away or oil that has been transported through hundreds of miles of pipelines.  In the developing world, community digestors are one example of distributed generation systems and are currently planned in Jamaica and El Salvador (Alexander, 2001; Sinclair, 2002).

1.4.3  Energy Efficiency will Speed Up the Transition to a Renewable Energy Economy.

The transition to a renewable energy economy would be made easier if people simply consumed less energy since less energy would have to be provided to meet our demand.   Robert Kennedy (2003), the leading attorney of the Natural Resources Defense Council, has mentioned that requiring cars to average 40 miles per gallon would rid all of our oil demand from Saudia Arabia saving nearly 2 million barrels of oil per day.   If we were to raise the fuel efficiency to 55 miles per gallon, we would save 5 million barrels of oil per day which is nearly twice our current Persian Gulf imports.  In effect, we could also save a considerable amount of the $1 billion dollars per day the Pentagon spends since our military presence to protect Persian Gulf oil would be eliminated (Caruba, 2003).  Similar in thought to Harry Braun, Kennedy also prefers not to use H2 fuel cells stating their implementation would take 10 to 20 years and that we should starting saving oil now.

Other energy efficiency measures could have similar gains.  For example, urban sprawl, at least in the outskirts of Des Moines, Iowa, results in hundreds of large 2” by 4” stick built houses that are built quickly but are very expensive to heat (Shafer, 2004).  Compare stick built homes with the passively heated concrete home built by the Iowa State University ‘Energy and the Environment’ professor, Dr. Laurent Hodges, who pays $90/winter in heating costs.  Dr. Hodges states that incorporating passive solar design into homes adds just 15% to the initial capital costs.  Passively heated solar homes can save heating bills by as much as 50% (U.S.

DOE, 2005).

1.5  Taking Care of the Infrastructure that Sustains Us.

1.5.1 Energy Efficient Wastewater Treatment through Anaerobic Treatment Technologies

Another way we could save energy is in regard to wastewater treatment.  Hydrogen as well as methane gases can be produced from wastewater through anaerobic treatment of the wastewater.  These two gases can be combusted onsite for electricity production or be used to produce electricity via fuel cells.  The practical history of applying anaerobic treatment in the West began in the 1890’s when biogas was recovered from sewage treatment facilities and used to fuel street lamps in England.  Current interest in the use of anaerobic treatment at sewage treatment facilities is increasing, because anaerobic treatment reduces the ultimate volume of biosolids needing disposal by 50-80 percent.  Methane is produced which has energy value, and the residual biosolids can be safely used as a humus-rich compost if it is low in heavy metal content.  Within the world of anaerobic treatment technology, farm-based facilities are the most common.  Six to eight million low-technology digesters are used in the East to provide biogas for cooking and lighting fuels with varying degrees of success. In China and India, there is a trend toward employing larger, more sophisticated farm-based systems with better process control that generate electricity (Lusk, 1996).  In Minnesota, the Haubenchild’s farm dairy manure digestor produces enough electricity to operate the entire farm (750 cows) and also generate $85,000 in annual revenues.

1.5.2  Anaerobic Treatment and Domestic Wastewater

Traditionally, in the U.S., and in most parts of the developed world, domestic wastewater treatment occurs via aerobic treatment processes.  Aerobic treatment processes have proven to be reliable and have truly helped to clean up our nation’s waterways.  However, these systems are energy intensive since they require oxygen to be pumped into the wastewater.  The supply of oxygen to these systems can represent approximately half of the treatment costs (Van Ginkel, 2002).  In addition, since aerobic bacteria have much higher cell yield values (~0.5 g biomass/gCOD) than anaerobic bacteria (~0.15 g biomass/g-COD), the waste is not actually degraded but converted in form to new bacteria cells which still represents a disposal problem (Grady et al., 1998, Speece, 1996).  It is no wonder why most of the aerobic wastewater treatment systems in the U.S. include several large anaerobic digestors to degrade this excess biomass.

The conversion of domestic wastewater to hydrogen and methane gases may not be economically feasible since domestic wastewater is too dilute in chemical energy.  Furthermore, a significant amount of the waste is probably fermented in the sewer line leading to the centralized wastewater treatment facility.  But if new distributed energy generation systems were coupled to decentralized wastewater treatment systems, domestic wastewater could be combined with other waste streams in a codigestion process to produce energy.  These other wastes could be animal wastes, yard wastes, or municipal solid waste.  Furthermore, the use of toilets that conserve water would increase the concentration of domestic wastewater making it more amenable to anaerobic treatment processes.  A decentralized treatment system would also lead to water reuse for irrigation and agriculture purposes particularly in regions suffering from a lack of water.  The digested sludge could provide fertilizers and soil conditioners to surrounding areas (van Lier and Lettinga, 1999).

In lieu of the potential advantages of decentralized wastewater treatment coupled to distributed energy systems, it appears that our nation’s domestic wastewater treatment infrastructure is near collapse anyway (Rifkin, 2002).  Some of our sewer systems are over 100 years old and there is currently a $12 billion annual shortfall in funding our nation’s wastewater treatment infrastructure (ASCE, 2001).  A new distributed wastewater treatment and energy production system with anaerobic treatment at its core could be more environmentally compatible, cost effective, and less of an economic burden to communities than expanding the current centralized treatment systems to meet new wastewater treatment needs (Freshwater Institute, 2005; CIDWT, 2005).  In the developing world, decentralized wastewater treatment is in great need.  Currently, 1.7 billion people do not have treatment systems for their sewage and water borne diseases kill as many as 25 million people annually (Inyang, 2004).

In the past, anaerobic treatment has been considered an unstable and unreliable technology compared to aerobic systems.  Anaerobic bacteria, in general, have higher Ks values defined as the wastewater concentration where bacteria are growing at half their maximum rate. In practical terms, conventional anaerobic treatment works well only when the wastewater concentration is high.  As stated earlier, since domestic wastewater is dilute or low in concentration, it is thought that domestic wastewater treatment could not be economically treated anaerobically.  Furthermore, domestic wastewater is usually at ambient temperatures which further decrease the growth rates or substrate utilization rates of anaerobic bacteria.   However, according to the Lettinga Associates Foundation in the Netherlands, anaerobic treatment should be considered a ‘proven’ technology and can be used for domestic wastewater treatment at low temperatures (Lettinga et al. 2001, Bogte et al., 1993).  Lettinga’s group is responsible for >1500 full scale applications of high rate anaerobic treatment.  These systems have an upflow configuration that causes the anaerobic bacteria present to condense into granules.  Granulation of the bacteria allows high bacterial concentrations to develop which allows effective wastewater treatment over a variety of conditions of wastewater strength and temperature (Lettinga et al.

2001).

Anaerobic treatment should be considered as a pre-treatment step since the effluent of their systems is still high in concentration.  However, COD (chemical oxygen demand) removals are still high at >80%, so any aerobic system required downstream to meet discharge requirements would require much less oxygen and be much smaller in size.  However, relatively few high rate anaerobic treatment installations exist in the U.S.  According to a representative of Paques which is an outgrowth of LEAF and a distributor of high rate anaerobic treatment systems, ‘energy is too cheap and land is too plentiful for anaerobic treatment to be competitive in the U.S.’ (Mareka, 2005).

1.6 Hydrogen Production from Food Processing Wastewater –

       The Main Subject of this Thesis

In contrast to the domestic wastewater treatment market of high rate anaerobic treatment, the food processing wastewater treatment market is fairly saturated with high rate anaerobic treatment (van Lier, 2005).  Food processing wastewater is high in sugar and starch concentrations and enough methane is produced to be utilized.  However, we can make it better by producing hydrogen gas while still recovering up to 2/3 of the methane gas if methane were the only gas recovered.

1.6.1  Hydrogen Energy’s Role in Improving Food Processing Wastewater Treatment

Chapter 5 presents an economic analysis of implementing a H2/CH4 producing anaerobic treatment system at a potato chip manufacturing facility in Pennsylvania which currently has an aerobic treatment system.  The proposed system would have a payback time of 2.3 years (typical of LEAF’s systems) and it will save the company $1.2 million dollars over the next 10 years.

The analysis assumes hydrogen could be sold as a pure chemical at market price which is $6 / kg.  Furthermore, no gas conditioning or handling costs were included in the analysis.  The analysis also assumes a yield value of two moles of H2 and two moles of CH4 per mole glucose. The theoretical yield is four moles of H2 and two moles of CH4 per mole glucose.  The yield value of two mol-H2/mol-glucose was used since this is the average yield observed in continuous systems using glucose as the substrate (Van Ginkel and Logan, 2005; Nandi and Sengupta, 1998).  However, in batch tests using this wastewater, a yield of only one mol-H2/mol-glucose was observed (see Chapter 5 of this thesis).  Furthermore, the potato processing wastewater composition is not simply glucose, but mostly starch.  Observed yields using starch as the substrate in continuous reactors were even lower at 1.6 mol-H2/mol-glucose.  Even lower yields were obtained when using the actual wastewater in a continuous system.

1.6.2  Improving H2 Yields from Food Processing Wastewater

After observing the low yields from actual potato processing wastewater, a more scientific study was conducted using glucose as the sole substrate.  In an attempt to improve H2 yields, this research focused on two inhibitory mechanisms that reduce H2 yields.  These two mechanisms are competitive inhibitions due to H2 and acetic and butyric acids and are the subjects of most of this thesis.

1.6.2.1  Inhibition due to H2

According to model developed by Ruzicka (1996), the main limitation for producing the highest yields of H2 is the inhibitory affect of H2 partial pressure on hydrogen production.  In this model, as the concentration of dissolved H2 increases in the liquid phase, it increasingly re-enters the cell and binds to NAD+ creating NADH2.   When all of the NAD+ is in the form of NADH2, the flux of glucose through the glycolytic pathway and through the phosphoroclastic reaction stops.  In order to increase this flux for maximum ATP production, some bacteria (for example, Clostridium pasteurianum) divert the electrons in NADH2 to the production of butyrate, resulting in only three moles of ATP instead of the four moles produced with acetate production.  The production of butyrate rather than acetate allows for NAD+ regeneration and a greater flux of glucose through the bacterial glycolytic pathway, and greater overall ATP production than what acetate production alone could sustain (Crabbenbaum et al., 1985).  In order to increase the production of H2 (and acetate) while maintaining a high flux of glucose through glycolysis, NAD+ must be regenerated with the production of H2.  This may be favorable only when the amount of H2 in the liquid phase is low.

Several studies have shown that hydrogen yields can be increased in continuous culture by decreasing hydrogen partial pressure in the reactor.  One approach to achieve this is to strip hydrogen from the liquid using N2 sparging (Hussy et al., 2003, Crabbenbaum et al., 1985, Mizuno et al. 2000).  A second method has been to apply a vacuum to the headspace, lowering the overall partial pressure in the system (Kataoka et al., 1997).  Conversely, chemostat reactors have even been pressurized to decrease H2 yields to promote butanol production (Doremus et al., 1985).  These methods to reduce H2 in the liquid phase pose an added cost and may not be economically viable.  An alternative method to lowering the dissolved H2 concentrations would be to reduce the rate of hydrogen production, allowing more efficient stripping of the hydrogen from the liquid phase by stirring.  Thus, as explained in Chapter 3, an experimental matrix was designed to systematically test a combination of four different glucose concentrations and four hydraulic loading rates in order to systematically test the effect of glucose loading rate, and therefore H2 production rate, on hydrogen yields from glucose.

1.6.2.2  Inhibition due to acetic and butyric acid

Many authors have studied the affect of acetic and butyric acids to produce solvents in the traditional acetone-butanol-ethanol (ABE) fermentation.  In their research, ‘normal’ hydrogen fermentations were carried out using a variety of substrates from jerusaleum artichokes to molasses using pure cultures of Clostridium acetobutylicum.  The hydrogen fermentation changed to a solvent forming reaction once the undissociated acid concentration got too high resulting in two inhibitory mechanisms:  (1) uncoupling of the proton motive force and (2) a decrease in the glucose flux through glycolysis by the tying up of the CoA and PO4 pools by the uptake of acids (Gottwald and Gottschalk, 1985).  A detailed description of the mechanisms of acid inhibition can be found in Jones and Woods (1986).

The major difference between hydrogen and solvent fermentations is pH.  The optimum pH for H2 production is 5.5 while the optimum pH for solvent production is ~ 4.5 (Van Ginkel et al. 2001; Liu and Fang, 2003; Jones and Woods, 1986).  The undissociated form of acetic acid is ten times greater at a pH of 4.5 than at pH 5.5 and since this form is nonpolar, it is able to pass through or partition in the nonpolar bacterial cell membrane and cause the inhibitory mechanisms described earlier.  If the pH is maintained at its optimum (5.5) for H2 production, the only other way undissociated acid concentrations can be increased is by increasing the substrate concentration from which the acids would be produced.  This poses an upper limit on how high the glucose concentration can be for biohydrogen production.  Of course, for economic purposes, we would want to treat wastewaters ‘as is’ and at substrate concentrations as high as possible, but if H2 yields decrease substantially due to inhibition caused by high undissociated acid concentrations, it would be economically advantageous to operate H2 fermentations at lower substrate concentrations that still generate high H2 yields.

A range of undissociated acid concentrations (2 – 30 mM) that cause inhibition or a switch to solventogenesis has been proposed but this range varies widely (Zeng et al. 1994, Soni and Jain 1997, Terracciano and Kashket 1986, Monot et al. 1984, Grupe and Gottschalk 1992). The inhibitory effect of undissociated acid concentrations on H2 production has not been well documented.  In this study, we determined the acid concentration that causes a significant decrease in H2 production yields in a continuous system by adding acetic and butyric acids directly to the feed and by increasing the glucose concentration from which these acids are produced

1.7  Chapters in brief

Chapter 2 is the paper, Biological Hydrogen Production Measured in Batch Anaerobic Respirometers, published in the journal, Environmental Science and Technology (Logan et al. 2002).  This paper discusses the inhibition of biohydrogen production by the hydrogen gas produced.  Dr. Oh and I conducted batch tests using two different methods of gas production quantification.  The first method, the Owen Method, intermittently measured biogas production using a Perfektum gas syringe.  I used this method during my M.S. degree at Iowa State University.  The second method allowed a continuous release of H2.  We observed a 43% increase in hydrogen production yields using the continuous release system.  Dr. Zhang was responsible for conducting a thermodynamic analysis of hydrogen production.  We also tested various other substrates such as molasses, cellulose, starch, etc. while Dr. Oh was responsible for testing the sustainability of our heat shocked tomato soil spore suspension over a period of one month.  Dr. Oh also tested the effectiveness of heat shocking and pH on reducing hydrogen consumption (Oh et al. 2003).  I assisted Dr. Oh with the experiments and also initiated the idea since both heat shocking and pH were studied as part of my M.S. thesis (Van Ginkel et al. 2001).

Dr. Logan wrote the manuscript based on these results.

Chapter 3 is the paper, Increased Biological Hydrogen Production with Reduced Organic

Loading, which has been accepted by the journal, Water Research (Van Ginkel and Logan, 2005).  Continuous biohydrogen tests were conducted to observe differences in hydrogen production yield with respect to the glucose loading rate.  Two variables were tested at four levels – glucose (10, 7.5, 5.0, and 2.5 g COD/L) and HRT (10, 5, 2.5, and 1 hr).  We observed that high hydrogen yields can be obtained (2.6±0.2) at the lowest glucose loading rates and attributed these high yields to decreased dissolved hydrogen gas although dissolved hydrogen gas was not measured.  Given the fact that the higher hydrogen yields occur when acetate is the dominant aqueous product compared to when butyrate is produced, higher H2 yields at the lower glucose loading rates were confirmed with the highest acetate to butyrate ratio of 1.1:1. Bacterial flocculation was observed at the higher glucose loading rates and allowed hydraulic detention times of less than one hour.  Of the two variables tested, HRT and glucose concentration, the glucose concentration was found to have a greater effect on hydrogen production than the HRT.

Chapter 4 is the paper, The Inhibition of Biohydrogen Production caused by

Undissociated Acetic and Butryic Acids, which has been submitted to the journal Environmental Science and Technology.  I hypothesized that at high glucose concentrations, the acids produced, specifically the undissociated form of the acid, inhibit hydrogen production.  In continuous tests,

I tested the effect of pH, the addition of acetic and butyric acid to the feed, and the effect of glucose concentrations up to 50 g/L.   We concluded that butyrate was a more effective inhibitor to hydrogen production than acetate although when these two acids were added simultaneously, hydrogen yields were the lowest.  We also concluded that an undissociated butyric acid concentration of > 13 mM is effective in inhibiting hydrogen production.  Hydrogen yields were constant from 10 to 30 g/L, but then decreased when the glucose concentration was increased to 40 g/L.  Solvents were produced at the glucose concentration of 40 g/L indicating that acid inhibition was occurring.  At the glucose concentration of 50 g/L, steady hydrogen production could not be maintained and this was attributed to both acid and substrate inhibition.  We also concluded that self-produced acids are more inhibitory than when the acids were added.

Chapter 5 is the paper, Biohydrogen Production from Food Processing and Domestic

Wastewaters, which has been published in the journal, International Journal of Hydrogen

Energy (Van Ginkel et al. 2004).  I contacted Dr. Robillard, Dr. Ziegler, and Dr. Irudayaraj at Penn State regarding the use of food processing wastewater for biohydrogen production. Subsequently, I contacted an apple processing company, and began biohydrogen production tests using this wastewater.  I also tested hydrogen production from domestic wastewater and observed low H2 yields.  Batch treatability tests were conducted using wastewaters from four more food processing companies.  Dr. Oh assisted with these tests.  We observed a hydrogen production yield from the food processing wastewater of about 1 mol-H2/mol-gluc and concluded that some wastewaters were nutrient limited.  I later conducted a nutrient analysis (nitrogen and phosphorous) of these wastewaters and concluded that two of the wastewaters were indeed nitrogen and phosphorous limited.  We concluded the study by performing batch treatability tests from four different wastestreams from within the potato chip manufacturing facility.  At this time, I also tested to see if the wastewater itself could be used as inoculum.  I heat shocked one of the high solids, potato chip wastestreams and used this as inoculum.  H2 gas was produced.  After three transfers, yields seemed to prove (as measured by gas production) and the H2 percentage in the headspace reached 71% which is higher than in all other batch tests.

1.8 Literature Cited

Alexander, N (2001)  Personal Communication. Nueva Esperanza. El Salvador.

ASCE, American Society of Civil Engineers (2001) Renewing America’s Infrastructure: A Citizens’ Guide. Washington, D.C. http://www.asce.org/reportcard/2005/index.cfm

American Wind Energy Association (2005) http://www.awea.org/pubs/factsheets/WindEnergyAnUntappedResource01-13-04.pdf

Annan, K. (2000) Where the high oil price really hurts. International Herald Tribune. October 3. http://www.un.org/News/ossg/sg/stories/oilprice.htm

Bogte, J.J; Breure, A.M;  Vanandel, J.G; Lettinga, G. (1993) Anaerobic treatment of domestic waste-water in small-scale UASB reactors.  Wat. Sci. Tech. 27 (9): 75-82.

Braun, H. (2004)  Letter to the editor of Popular Science http://www.phoenixprojectfoundation.us/user/Popular%20Science%20Letter.pdf

Cable News Network (CNN). (2005)  Mandela: Rich must feed the poor http://www.cnn.com/2005/WORLD/europe/02/03/mandela.london/

Campbell, C. J. and Laherrere, J.H. (1998) “The End of Cheap Oil”.  Sci Am.  March  p. 78.

http://dieoff.com/page140.pdf/

Caruba, A. (2003) What will this war cost?  Canadian Free Press.  March 17. http://www.canadafreepress.com/2003/inter031703.htm

Cleveland, C.J. and Kaufmann, R.K. (2001)  “Why the Bush Oil (Energy) policy will fail.” October 5, 2001. Center for Energy and Environmental Studies and the Department of Geography at Boston University. http://www.hubbertpeak.com/Cleveland/bushpolicy.htm http://www.oilanalytics.org/policy/policy_bush.html

CIDWT, Consortium of Institutes for Decentralized Wastewater Treatment (2005). Onsite

Consortium. http://www.onsiteconsortium.org/

Crabbenbaum, P.M.; Neijssel, O.M.; and Tempest, D.W; (1985) Metabolic and energetic aspects of the growth of Clostridium butyricum on glucose in chemostat culture. Arch. Micro. 142: 375-382.

Czernik, S; French, R; Magrini, K; and Evans R. at the National Renewable Energy Lab (NREL) (2004)  Hydrogen from Biomass: Process Research U.S. DOE Hydrogen, Fuel Cells and Infrastructure Technologies Program Review. http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/hpd_p5_czernik.pdf

Doremus, M.G.; Linden, J.C.; and Moreira, A.R. (1985) Agitation and pressure effects on acetone-butanol fermentation. Biotech. Bioeng. 27: 852-860

Energy Information Administration (EIA) 2001 World Crude Oil and the Natural Gas Reserves. February 5.; “Long Term World Oil Supply (A Resource Base/Production Path Analysis)”; http://www.eia.doe.gov/emeu/plugs/plworld.html

Freshwater Institute (2005) Decentralized Wastewater Treatment. http://www.freshwaterinstitute.org/?article=2064

Gever, J. (1991) Beyond Oil. University Press of Colorado. Denver, Co.  p. 172.

Gottwald, M., and G. Gottschalk (1985) The internal pH of Clostridiuin acetobutylicum and its effects on the shift from acid to solvent formation. Arch. Microbiol. 143:42-46.

Grady, C.P.L; Daigger, G; and Kim, H.C. (1998) Biological Wastewater Treatment. Second Edition. Revised and Expanded.  Marcel Dekker, Inc., NY.

Grupe, H. and Gottschalk, G. (1992) Physiological Events in Clostridium acetobutylicum during the Shift from Acidogenesis to Solventogenesis in Continuous Culture and Presentation of a Model for Shift Induction. Appl. Env. Micro. 58 (12): 3896-3902

Hodges, L. (1998)  Personal Communication.  Energy and the Environment Class.  Iowa State University.

Houghton, John (1997) Global Warming: The complete briefing. Cambridge, MA: Cambridge University Press.

Hussy, I; Hawkes, F.R; Dinsdale, R; and Hawkes, D.L (2003) Continuous fermentative hydrogen production from a wheat starch co-product by mixed microflora. Biotech. Bioeng. 84(6): 619626.

Intergovernmental Panel on Climate Change (IPCC) (2001)  IPCC Third Assessment Report Climate Change 2001.  World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP). http://www.grida.no/climate/ipcc_tar/wg1/index.htm International Energy Agency (IEA) (2000)  High prices hurt poor countries more than the rich.

Paris. March 20.  www.iea.org/new/releases/2000/oilprice.html

Inyang, H.I. (2004)  Editorial: The Global Ecosystem: Environmental and Socioeconomic Challenges and Opportunities. J. Env. Eng. 130 (9): 923-924.

Iyer, P; Bruns, M.A; Zhang H.S; Van Ginkel, S.W; and Logan, B.E.  (2004) Hydrogen producing bacterial communities from a heat-treated soil inoculum, Appl. Micro. Biotech.  66 (2): 166-173.

Jones, D.T. and Woods, D.R. (1986) Acetone-butanol fermentation revisited. Micro. Rev. 50(4): 484-524.

Kennedy, R.F. Jr. (2003) A bad element. New York Times. February 16. http://www.theocracywatch.org/Bobby_Kennedy_cars_TimesFeb16.html

Kennedy, R.F.Jr. (2002)  Clean Water Under Attack. Testimony before the U.S. Senate. Environment and Public Works Committee. In Recognition of the 30th Anniversary of the

Clean Water Act.  October 8. http://epw.senate.gov/107th/Kennedy_100802.htm

Katoaka, N; Miya, A; and Kiriyama, K. (1997) Studies on hydrogen production by continuous culture system of hydrogen-producing anaerobic bacteria. Wat. Sci. Tech. 36 (6-7): 41-47.

Lettinga, G; van Lier, J.B; van Buuren, J.C.L; and Zeeman, G. (2001) Sustainable development in pollution control and the role of anaerobic treatment. Wat. Sci. Tech. 44 (6): 181-188.

Lloyd, G. and Hassan, G. (2000) Going to sea: Wind goes offshore. Renewable Energy World. January-February. http://www.earthscan.co.uk/defaultREW.asp?sp=&v=3

Logan, B.E; Oh, S.E; and Van Ginkel, S.W. (2002) Biological Hydrogen Production Measured in Batch Anaerobic Respirometers. Env. Sci. Tech. 36 (11): 2530-2535.

Liu, H. and Fang, H.H.P. (2003)  Hydrogen production from wastewater by acidogenic granular sludge.  Wat. Sci. Tech. 47 (1): 153-158.

Lusk, P. (1996.)  Deploying Anaerobic Digesters: Current Status and Future Possibilities. Report prepared for the National Renewable Energy Laboratory under NREL Subcontract No. CAE6-13383-01 and sponsored by the Regional Biomass Energy Program of the US Department of Energy. http://www.biogasworks.com/Reports/weec96.htm

Mizuno, O; Dinsdale, R; Hawkes F.R; Hawkes, D.L; Noike T. (2000) Enhancement of hydrogen production from glucose by nitrogen gas sparging.  Bioresource Tech. 73 (1): 59-65.

Monot, F; Engasser, J.M; and Petitdemange, H. (1984) Influence of pH and undissociated butyric acid on the production of acetone and butanol in batch cultures of Clostridium acetobutylicum.  Appl. Micro. Biotech. 19 (6): 422-426.

Mulder, R. (2005)  Personal Communication.  Paques.  Wagneningen, The Netherlands.

Nandi, R. and Sengupta, S. (1998) Microbial production of hydrogen: An overview. Crit. Rev. Micro. 24(1): 61-84.

Nelson, C. and Lamb, J.  (2002)  Final Report: Haubenschild Farms Anaerobic Digester Updated!  The Minnesota Project. http://www.mnproject.org/pdf/Haubyrptupdated.pdf

Ponting, C. (1991) A green history of the world: The environment and the collapse of great civilizations.  New York. N.Y.  Penguin Books.

Roodman, D.M. (2001) Still Waiting for the Jubilee: Pragmatic Solutions for the Debt Crisis. Worldwatch Paper 155: April 26. http://www.worldwatch.org/pubs/paper/155/.

Ruzicka, M. (1986) The effect of hydrogen on acidogenic glucose cleavage. Wat. Res. 30(10): 2447-2451.

Schwartz, P. and Randall, D. (2003) An Abrupt Climate Change Scenario and Its Implications for United States National Security. October. http://www.ems.org/climate/pentagon_climatechange.pdf Shafer, M. (2004) Personal Communication.  Runnells, Iowa.

Sinclair, N. (2001) Personal Communication.  Kingston, Jamaica.

Soni, B.K. and Jain, M.K. (1997) Influence of pH on butyrate uptake and solvent fermentation by a mutant strain of Clostridium acetobutylicum. Bio. Eng. 17: 329-334.

Speece, R.E. Anaerobic Biotechnology for Industrial Wastewaters, Archae Press., Nashville, Tennessee, 1996.

Terracciano, J.S. and Kashket, E.R. (1986) Intracellular conditions required for initiation of solvent production by Clostridium acetobutylicum. Appl. Env. Micro. 52 (1): 86-91.

Star, C. (1997) Sustaining the human environment: The next two hundred years.  In Jesse H. Ausubel and H. Dalle Langford, eds. “Technological Trajectories and the human environment”.  Washington, D.C.: National Academy Press.

Tompkins, J. (2005)  Wind Power Reconsidered:  Innovations and steep gas prices may at last kick-start wind energy in the U.S.  Pop. Sci. Oct 13, 2004. http://www.popsci.com/popsci/generaltech/article/0,20967,714431,00.html

United Nations (2005) Millennium Ecosystem Assessment: Biodiversity and Human Well– being: A Synthesis Report for the Convention on Biological Diversity. http://www.millenniumassessment.org/en/index.aspx

United Nations Department of Economic and Social Affairs (DESA). (1987) http://www.un.org/documents/ga/res/42/ares42-186.htm.

U.S. Department of Energy.  Energy Efficiency and Renewable Energy. Solar Energy Topics. http://www.eere.energy.gov/RE/solar.html

Van Ginkel, S. W; Lay, J.J; and Sung, S. (2001) Biohydrogen production as a function of pH and substrate concentration. Env. Sci. Tech. 35 (24): 4726-4730.

Van Ginkel, S.W. and Logan, B.E. (2005) Increased biological hydrogen production with reduced organic loading. Wat. Res. Accepted.

Van Ginkel, S.W; Oh, S.E; and Logan, B.E. (2004) Biohydrogen Gas Production from Food Processing and Domestic Wastewaters. Int. J. H2. Energy. In press.

Van Ginkel, S.W. and Logan, B.E. (2005) The inhibition of biohydrogen production caused by undissociated acid concentrations at high glucose concentrations. Env. Sci. Tech. Submitted.

van Lier, J.B. (2005)  Personal Communication. Paques.  Wagneningen, The Netherlands.

van Lier J.B. and Lettinga, G. (1999)  Appropriate technologies for effective management of industrial and domestic waste waters: The decentralised approach. Wat. Sci. Tech40 (7): 171-183.

Youngquist, W.L. (1997) Geodestinies: The inevitable control of Earth resources over nations and individuals.  Published by Halcyon House.

Zeng, A.P; Ross, A; Biebl, H; Tag, C; Gunzel, B; and Deckwer, W.D. (1994) Multiple Product Inhibition and Growth Modeling of Clostridium butyricum and Klebsiella pneumoniae in Glycerol Fermentation.  Biotech. and Bioeng.  44: 902-911.

OPTIMIZATION OF BIOHYDROGEN PRODUCTION FROM FOOD PROCESSING WASTEWATER

Leave a Reply