Leave it to the microbes: microbial energy generation as a solution to
meet our energy needs
Jane Doe
Microbiology
4/22/19
Executive summary
The global energy demand is predicted to increase by 28% from 2017 to 2040. As more
people gain reliable access to electricity, and overall global use increases, we must find ways to
sustainably meet the growing demand. Right now, the projected growth in energy capacity is
dominated by fossil fuels, with renewables contributing some, but not nearly enough to
significantly reduce our carbon emissions. Therefore, it is vital that we pursue alternative
mechanisms of renewable energy generation
One alternative is microbial energy generation, or the use of bacteria and other
microorganisms to generate energy in a form that is usable by humans. There are several
technologies available to do this. One is biofuels, liquid fuels generated from corn or other
organic feedstocks using the power of microbial fermentation. Biofuels can also be created by
using photosynthetic algae to harvest sunlight and convert it into biodiesel. Microbes can also
produce electricity directly from organic material. Bacteria such as Shewanella and Geobacter
can strip electrons off of organic compounds and transfer them to extracellular electrodes, where
they flow through a resister to generate an electric current. The newly discovered microbial
metabolism of flavin-based bifurcation, once it is further studied and understood, will likely be
harnessed in a similar way. Finally, anaerobic digestion can produce energy from wastewater.
Microbes digest the organic material in wastewater and convert it to methane, which can then be
burned to heat the wastewater treatment plant and power water treatment processes.
Introduction and background
Producing enough energy to supply a growing population is one of the greatest
challenges of the 21st century. According to the Energy Information Administration, global
energy use will grow 28% in the next 20 years, and our energy generation capacity must grow
along with the demand. Right now, fossil fuels are the main source of energy around the world,
but in order to maintain a healthy planet, that must change in the coming decade.
Energy use varies widely throughout the world. Nations in Sub-Saharan Africa and parts
of Asia use far less energy, due in part to the lack of reliable power throughout many rural areas.
However, this is changing due to modernization, and growth of energy availability in these
countries is one of the main drivers. It is predicted that this demand will be met with increased
use of liquid fossil fuels, natural gas, and some renewables, while coal use will fall. Though the
outlook on renewable energy is positive, the truth is that things are not changing fast enough.
According to the recent report by the Intergovernmental Panel on Climate Change, we only have
12 years to drastically reduce our dependence on fossil fuels before the earth hits a tipping point
and we see large-scale and irreversible changes to our global ecosystem, as well as threats to
millions of lives, cultures, and homelands. We need to accelerate the pace of our transition to
renewable energy, which requires us to explore all available methods of renewable energy
generation.
To complete the transition to renewables, we will need to take advantage of a variety of
energy sources, because no one source can produce the entire global energy load. The wind does
not blow constantly, the sun only shines during the day, and nuclear energy is fraught with
controversy. Therefore, the incorporation of other energy sources into the mix is vital. One
option for additional energy is microbial energy generation, which uses bacteria to produce
energy in various forms.
There are a number of benefits to microbial energy generation. Humans have been
harnessing the power of bacteria for centuries to produce fermented foods and fix nitrogen for
our crops, so we already understand the basic principles of utilizing microbes. Microbial energy
generation is scalable and often very cheap, and bacterial energy generation methods do not use a
lot of land for their processes. Finally, once a microbial energy system has been set up, it
requires very little maintenance to keep producing energy. One must simply feed it, keep it at the
right temperature, and extract the end products.
There are several examples of microbial energy generation technology available right
now. The most widely used is biofuels, which are produced by fermentative microbes that turn
corn and other cellulosic products into ethanol. Algae can also harness energy from sunlight and
produce biofuels. Another microbial energy source is microbial fuel cells, which use the natural
electron generation of bacteria to produce an electric current, similar to a battery. Anaerobic
digestion is used in wastewater treatment plants to produce methane from waste. Finally, a
recently discovered microbial metabolic strategy called flavin-dependent bifurcation has shown
potential for an additional microbial energy generation method.
The concept of microbial energy generation is particularly exciting to me, a microbiology
major about to start a graduate program studying bioremediation. The idea of using microbes to
solve human-created problems is something that I think about daily and plan to base my career
on. While I will not directly be studying the use of microbes to generate energy, this idea is
something I may study in the future, or that I could tie into another microbial-based
environmental solution.
While the field of microbiology does not face any unique energy-related issues, we, like
all industries, would benefit from an energy infrastructure that is no longer reliant on fossil fuels.
In addition, limiting climate change is important for microbiologists because a shift in the
climate could result in changes to microbial communities across the planet. If we want to achieve
a future without fossil fuels and maintain the balance of global bacterial communities, it is
important that all potential energy sources are explored, even those that are so small, we can’t
see them. Thus, I believe that microbiology and microbial energy generation will be an important
part of a renewable energy future.
Discussion of the issue
The shift to microbial energy generation, and renewable energy sources in general, is
being driven by a variety of factors. Most prevalently is our need to reduce fossil fuel use. It
involves a variety of sectors and stakeholders, including researchers studying microbial
metabolisms, technology companies designing products to harness the energy from microbes,
and the people who will benefit from the technology. The beneficiaries include global citizens as
a whole, who will benefit from a safer and cleaner planet, and people in rural areas who will
benefit from access to consistent electricity. The transition to renewable energy also involves the
government, who is responsible for distributing grants to those researchers pursuing microbial
energy generation. All of these groups have worked together to produce a number of innovative
technologies that harness the power of bacteria to produce energy in various forms.
One of the primary microbial-based methods of energy generation is the production of
biofuels. Biofuels are generated by the microbial fermentation of feedstocks to ethanol in largescale bioreactors. The microbes responsible are generally anaerobic organisms that transform
sugars into alcohols. The most common feedstock used is corn, but other products including
sugar cane, molasses, and a variety of cellulosic material can also be used. Due to the variety of
feedstocks, there is also a great variety in the microbes involved in ethanol generation, but they
tend to fall into a few genera, including Zymomonas, Leuconostoc, and the well-known yeast
Saccharomyces cerevisiae. Specialized E. coli that have been engineered to contain genes for a
fermentative metabolism can also be used. Regardless of how it is produced, ethanol is used as a
liquid fuel in vehicles. This fuel is desirable because it can fit directly into our existing
infrastructure and can even be sold in traditional gas stations. Though specialized motors are
required to use high concentrations of ethanol, the motors are a modification on existing
technology rather than a completely new invention. Thus, biofuels can easily be integrated into
our existing system.
In addition to the use of fermentative organisms, biofuels can also be produced using
another microbe: algae. This photosynthetic organism is capable of processing sunlight into
energy, and storing up to 50% of that energy as oil. Algae also grow at an incredible pace,
sometimes doubling in as little as 24 hours. The algae can be processed into biodiesel and serve
as another source of renewable liquid fuel that can feed into our existing infrastructure. Algae is
a carbon neutral biofuel, because the organisms pull carbon dioxide out of the atmosphere as
they grow, so burning biodiesel in vehicles does not release new carbon.
Another technology that can be utilized to generate energy from bacteria is the microbial
fuel cell. This technology harnesses soil microbes to produce electricity. Some species of soil
bacteria, including Shewanlla oneidensis and Geobacter sulfurreductens, generate their energy
by removing electrons from organic compounds. Sometimes, they transport these electrons out of
the cell and into the surrounding soil. This is where the technology comes in. Like a battery, the
microbial fuel cell has positive and negative terminals, termed the cathode and anode
respectively. Bacteria strip electrons off soil organic compounds, producing negatively charged
electrons and positively charged hydrogen ions. The electrons are then shuttled to the anode,
while the positively charged hydrogen ions are pushed through a membrane toward the cathode.
The electrons are pushed through a resistor as they move towards the cathode, which generates
electricity. Finally, they rejoin the hydrogen ions at the cathode. The movement of these
electrons generates electricity that can be harnessed to power technology the same way that a
battery can. The advantage to microbial fuel cells is that they can use a variety of compounds for
their energy source. One pilot study produced energy from maple syrup crop residues and found
that the conversion efficiency was 50%, which demonstrates the potential that microbial fuel
cells can provide.
A recent discovery may allow scientists to tap into an additional source of electrical
energy from microbes. This discovery is a type of microbial metabolism called flavin-based
bifurcation. In this mechanism, microorganisms strip electrons off organic molecules and store
them on a flavin molecule. Up to 1 volt of electric potential energy can be stored at one time.
This microbial energy can be harnessed similarly to the microbial fuel cell, by capturing the
electrons stripped from the organic molecules and directing them through a resistor, creating an
electrical charge. It has also been proposed that microbes could be engineered to utilize these
pathways more efficiently, or to synthesize hydrogen and liquid fuels in addition to electrons, but
more research is needed before these applications can be pursued. With both traditional and
flavin-based mechanisms available for use in microbial fuel cells, this technology presents a vast
untapped energy resource that could be harnessed in a variety of ways.
One of the most important applications for microbial fuel cell technology is in the
developing world. In Sub-Saharan Africa, only 26% of residents have access to a reliable electric
grid, but many more own a mobile phone and have no way to charge it except by walking,
sometimes for hours, to the closest village with electricity. The microbial fuel cell would help to
solve this problem by providing isolated villages with a source of renewable electricity. Students
at Harvard used a small graphite anode, a chicken wire cathode, and animal manure as a source
of organic material to create a fuel cell that costs only $10 and can provide a community with a
decade of energy if properly maintained. This fuel cell could serve a whole village, helping to
power cell phones, radios, and small light sources. This technology is vital for helping create
independence for rural communities without the need for any fossil fuel use.
One final method of microbial energy generation is the use of methane-producing
organisms in anaerobic digesters. This technology is used in some large-scale wastewater
treatment plants, where anaerobic bacteria produce methane from wastewater. The treatment
plants, according to a variety of sources, use anywhere between 1 and 4% of the total electricity
in the US. Meanwhile, at the plants, up to 50% of operating costs go to electricity. This
electricity use can be significantly reduced by increasing the use of anaerobic digestion in
treatment plants.
In anaerobic digestion, a specially chosen community of microbes is housed in a large,
anoxic tank, where they convert waste products into methane at a rate of 190-240 Nm3/ton of
organic matter. The methane can then be burned on-site to generate energy. Currently, the
methane generated in plants is used to provide space heating and to warm wastewater during the
pretreatment step, but the use of methane could also be expanded to meet other energy needs in
the plant. If the US took full advantage of its microbial energy potential at just its largest 100
wastewater treatment plants, they could save 41 million barrels of oil and 18 millions tons of
CO2 from entering the atmosphere every year
In addition to its industrial use at wastewater treatment plants, anaerobic digestion is also
utilized on a small scale to generate biogas in rural areas such as India. The digesters can use
crop residue, animal manure, and wastewater to produce methane gas for cooking and home use.
3.7 million home-use digesters have already been installed, and there is potential for up to 12
million total installations. Anaerobic digestion could also be used on a larger scale to process
these types of waste from industries across the nation. Overall, biogas has great potential for a
consistent and reliable energy source for India. This is important because, as one of the major
contributors to the growing energy demand, transitioning India to renewable energy sources will
help mitigate potential additions of greenhouse gases into the atmosphere and serve as a model
for other developing nations.
Future actions
There are several barriers to microbial energy generation that must be overcome before
we can utilize these technologies on a broader scale. The first is that more research is needed to
take full advantage of these technologies. For newer discoveries such as flavin-based energy
generation, more basic research must be conducted to better understand the processes. For
technologies like anaerobic digestion that have been employed for several years, additional
research is vital to make the technologies cheaper and more efficient.
The major barrier to all of this research is securing sufficient funding. As a future
microbiologist, I know that obtaining funding for my research will be one of the most difficult
parts of my work. If we want to adopt microbial energy generation technologies on a larger scale,
then we will need financial support in the form of government grants and funding from nongovernmental agencies. The funding should be available to all researchers working to create
better methods of sustainable energy generation, but specific grants should be set aside for
microbial energy generation in order to encourage microbiologists to pursue this type of
research.
The next step is to pilot new technologies in a real setting. The focus should be on
implementing the technologies in rural areas that have a difficult time accessing energy from the
grid. In addition, we should start by installing these technologies in the countries where we will
see the biggest growth in energy demand in the coming decades, such as India and China, in
order to help them initiate a more rapid transition to clean energy.
Finally, to implement these technologies on a broader scale, we will likely require a
cultural shift in the way we think about microbes. Currently, people associate microbes with
disease and uncleanliness. There is an overall negative connotation surrounding microbiology,
because people are only aware of the negative effects of a few microbes rather than the variety of
products that these small creatures can produce. A good way to change public perception would
be to encourage dialogue and education about microbes, especially to school-aged children. We
could start by talking about the bacterial products like yogurt and beer that people consume on a
regular basis, then introduce newer technologies and assure people of the safety of the bacteria
involved in the processes.
In order to implement and expand the use of microbial energy generation by 2025, there
are several steps that can be taken. People who support microbial energy generation can offer
financial support to research institutions developing the technology, or to companies that are
working to implement the technology in the real world. Concerned citizens can lobby their local
governments and municipal wastewater treatment plants to include or expand their anaerobic
digestion efforts and to make sure that the methane gas from these processes is captured and used
efficiently. Finally, we can work on teaching people about the benefits of microbes. One way to
do this is by teaching about microbiology in schools to young children. Including microbiology
in the curriculum, even a simple activity like culturing bacteria from around the classroom, will
help teach children that not all bacteria are dangerous. Hopefully, this will pave the way for a
new generation of microbiologists that want to study the positive attributes of bacteria, rather
than just their ability to cause disease.
Our growing population has created an undeniable need for an increased energy
generation capacity, and it is clear that if we want the planet to be livable in the future, the
energy will need to come from renewable sources. It is important to consider all available energy
sources, as one or two technologies alone will not be able to meet our needs. One energy source
that has been explored and could be greatly expanded is the use of microbes to generate
electricity. There are a variety of microbial-based energy generation techniques available that
can be utilized to help meet our energy needs. These technologies are being studied and
implemented right now, and I am confident that in the future, microbes will play a significant
part in generating clean, renewable energy to power the world.
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