Grantee Research Project Results
Final Report: Photosynthetic Biohydrogen, An All-Worlds Solution to Global Energy Production
EPA Grant Number: SU833168Title: Photosynthetic Biohydrogen, An All-Worlds Solution to Global Energy Production
Investigators: Frymier, Paul , Alliowe, Nickyla M. , Bruce, Barry , Lowe, Chris , Thompson, Latoyia , Macdonald, Linda , Raeiszadeh, Mehrsa , Counce, Robert
Institution: University of Tennessee
EPA Project Officer: Hahn, Intaek
Phase: I
Project Period: October 1, 2006 through April 30, 2007
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2006) RFA Text | Recipients Lists
Research Category: P3 Challenge Area - Air Quality , Pollution Prevention/Sustainable Development , P3 Awards , Sustainable and Healthy Communities
Objective:
A growing problem in the undeveloped, developing, and industrialized worlds is securing a sustainable, abundant energy supply sufficiently concentrated for practical use. The current standard of living enjoyed by the industrialized world is a result of inexpensive, plentiful energy sources. In third world countries, the lack of access to this energy leads to a poor quality of life for many people and competition for energy resources.
Hydrogen can be produced by several methods. The most common current practice produces hydrogen by steam reforming of methane. This method is not sustainable because it depends on non-renewable reserves of methane. This project focuses on producing hydrogen sustainably using the microalgae Chlamydomonas reinhardtii to split water by photosynthesis. This photosynthetic route uses a simple technology that can be easily adapted for application in the developed and developing worlds.
This project proposed two major tasks: first, perform a design study to size and determine the operating and capital costs for a bioreactor system for the large scale production of photosynthetic biohydrogen, and second, design and build a laboratory scale bioreactor system. The large scale system is sized to produce sufficient hydrogen for transportation for a small city of 100,000 people, which was determined to be approximately 46 million kilograms of hydrogen annually. This figure uses the rule of thumb that one kg. of hydrogen contains roughly the same amount of energy as a gallon of gasoline and assumes the existence of automobiles with gas mileage ratings on hydrogen (in mile/kg) similar to current gasoline mileage (in miles/gallon).
Summary/Accomplishments (Outputs/Outcomes):
Early design work indicated that some process assumptions needed to be validated in the laboratory, so a series of experimental studies were conducted. The initial laboratory scale experiments were based largely on experimental studies from the relevant research literature (Melis et al, 2000). A three stage process was used and included an algal growth stage, sulfur deprivation and anaerobiosis, and hydrogen production. The initial experimental studies indicated that the algae could be grown on either carbon dioxide or acetic acid as a sole carbon source and that acetic acid supported the highest cell densities and growth rates. Also, it was determined that active pH control was a less expensive and more accurate method of controlling the pH during the growth phase when compared to the use of a pH buffer.
The design study incorporated the results of the experimental work and the final design determined an “at the plant gate” cost for hydrogen produced with current technology of about $40/kg hydrogen. Transportation costs are estimated to add approximately $2.80/kg hydrogen for off-site storage, distribution, and delivery. The design is based on a 4 day fed-batch production cycle. The study identified major cost factors and targets for future research studies.
Finally, the design team built a laboratory scale version of the process to validate experimentally that the process was technically feasible. The best-case experiment produced approximately 0.2 mL hydrogen/L culture volume/hour, about an order of magnitude lower than that found in the best cases from the research literature.
Conclusions:
Photobiological hydrogen production was cited in the 2004 NRC/NAE report “The Hydrogen Economy as having the potential to be the most efficient mechanism for the biological production of hydrogen. In order for the benefits of a biologically based approach to hydrogen production to be realized, our study indicates that costs must be reduced. There are many potential research and process alternative targets identified in the study, including optimization of the fluid and gas handling layout, as well as further experimental work to determine allowable purge rates, and alternate carbon feed sources. Potential Phase II work will examine these alternatives as well as the use of recently generated mutant strains that could lead to order of magnitude hydrogen evolution rate increases.
If eventually implemented, the use of a biologically produced transportation fuel could reduce/eliminate the need of gasoline from petroleum. It may be expanded for use in other sectors outside of transportation in the future. If gasoline was replaced by biologically produced hydrogen, the following quantifiable benefits would be realized for a population of 100,000 people: the elimination of 892 million pounds of carbon dioxide, 18.9 million pounds of methane, and 52 million pounds of nitrogen oxides per year.
Proposed Phase II Objectives and Strategies:
The design study in Phase I concluded with a process that provides hydrogen at a cost of about $43 per kg hydrogen (including off-site storage and distribution, and subject to the requisite approximations and assumptions in the study). Using the rule of thumb that a kilogram of hydrogen is roughly equivalent in energy content to a gallon of gasoline, that is over 16 times the March 11, 2007 average cost per gallon of regular gasoline in the US ($2.57/gallon). Previously published back-of-the envelope calculations indicated that this cost could have been as little as $0.57 or as much as $439.00. We found, however, that these previous studies did not accurately account for physiological requirements of the algae and process requirements for producing a fuel at the quantity required. Therefore, we realized the value of the study was in its ability to accurately identify areas of opportunity for creating a transportation future based on sustainably produced hydrogen. The remaining challenges to be pursued in Phase II are therefore to:
- identify the major remaining factors in the cost of producing hydrogen from algae and consider additional process alternatives
- identify major process and algal physiology assumptions and experimentally determine bounds on process alternatives affected by these assumptions
- identify potential biomolecular innovations for improving process yields and rate
- perform a life-cycle assessment of the economic best-case design
- demonstrate in a pilot scale system that the final improved process can generate hydrogen at a yield and rate significantly higher than that currently achievable.
Understanding the implications of process alternatives and physiology considerations from Phase I are critical to obtaining a cost effective method of producing biohydrogen. However, there are physical limits to the current process that are determined by the selection of the particular algal strain. Implementation on a large scale without additional order-of-magnitude improvements is unlikely. In order to truly close the loop on the hydrogen-based transportation economy, revolutionary innovation will be required in addition to the evolutionary innovation discussed above. Phase II proposes to incorporate revolutionary innovation in genetic engineering and mutation selection into the process to develop these order-of-magnitude cost reductions.
Supplemental Keywords:
sustainable fuels production, biophotolysis, biohydrogen, algae, Chlamydomonas reinhardtii, process analysis, cost analysis, economic analysis,, RFA, Scientific Discipline, Sustainable Industry/Business, Sustainable Environment, Environmental Chemistry, Technology for Sustainable Environment, Environmental Engineering, algae, photobioreactor, sustainable development, environmental sustainability, alternative fuel, energy technology, alternative energy source, biofuel, biohydrogen, pollution preventionThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.