Science Buddies: "Ask an Expert"

Here's part 2.

Part III

Part IV

Part V.

Hello Donna!

Yeah, thanks for looking over those additional MFC construction directions. Unfortunately I have never soldered anything before and do not have a glue gun. I will compare the different methods and talk to my dad about his opinion.

Wow - I'm speechless! This paper is looking very helpful and by the way you state it's purpose, I think it'll be wonderful! I will definitely look for newer papers as well. Thanks so much for your kindness!

Okay, so my goal by the end of today is to completely understand the MFC itself - anode, cathode, circuit, salt bridge. It's kind of confusing because when some references explain the MFC and describe the process, they mention some terms I'm not familiar with and haven't read on yet. I also want to finalize the materials I will be using and which MFC design I will use.

Just one question: I looked over the HowStuffWorks article on Fuel Cells (http://auto.howstuffworks.com/fuel-effi ... /printable) and I am surprised that they never mention the word 'bacteria' once! I realized that this article is specifying to cars, but then I looked over this article (http://science.howstuffworks.com/body-g ... /printable) and it specifically mentions the MFC and bacteria. So why do they never mention bacteria in the Fuel Cell article? They mention the anode/cathode/PEM design and everything else...

Thanks so, so, so much!

Hi Irregular,

You do ask good questions. A fuel cell is a unit that generates electricity. Only a microbial fuel cell uses living bacteria to generate the electrons. Read the first page of the review article carefully because it does a good job of defining what a microbial fuel cell is; it is a sustainable production of electron production at the anode electrode and consumption at the cathode. All other types of fuel cells are not microbial fuel cells. One of the stated purposes of the review article was to define standard terminology, so do look at the article carefully and use the terms the same way the author does.

What type of engineering does your father do? Do you have someone available who can show you how to drill, solder, and construct an electrical device? It is very helpful to have someone show you how the first time you learn a new technique. Doing water-tight gluing and soldering wires are techniques that improve with experience.

Donna Hardy

Hello Donna!

My, that makes things a whole lot easier to understand. Okay, so I've got that cleared. Since there are so many references out there, I think that sometime during or at the end of this week, whenever possible, I will write up a piece describing the MFC which I can use in my Research Paper. This 'piece' will explain the MFC itself - the parts of the MFC, as well as how the MFC works.

As for the scientific paper, I am eager to start reading it. With school and everything, I'm going to print it off so I can read it whenever possible and refer to it. It sounds amazingly helpful.

My father is a mechanical engineer by profession, and he works for a company which produces rubber. So his company is mostly chemistry-based. He will be able to do the drilling, but I will ask him about soldering. Honestly, I'm not sure whether he knows how to do it or does it at his plant. I will get back to you on that ASAP.

Lastly, I am thinking of a possible place where I can conduct my experiment. I don't want to risk doing it in the kitchen/house, so I'm thinking perhaps my garage? What do you recommend?

Thank you very much for you help, Donna

EDIT: In case my father or anyone I know doesn't have any soldering experience, I have a video I can use to guide me: http://blog.makezine.com/archive/2007/0 ... ake_v.html. (It's the MP4 link)

Also, I found two scientific papers via Wikipedia's article on MFC's.
1) http://www.pnas.org/content/104/47/18871.full.pdf+html
2) http://www.nature.com/ismej/journal/v1/ ... 20074a.pdf

I have briefly skimmed through them, and find them interesting. As to my understanding, the first one is based more on hydrogen, though the MFC is important. What do you think?

Lastly, I was reading the MFC article from Wikipedia (http://en.wikipedia.org/wiki/Microbial_fuel_cell) and scrolled down to the "See Also" section. There are links to other Wikipedia articles with terms I haven't studied at all. About all of them relate to hydrogen - why is that? Do you recommend I study those terms?

Hi Irregular,

Are there any electrical engineers at your father’s company? I think I will see if we can find a science buddy expert on electrochemistry to help on this project.

It’s good to be thinking about the details of your experiment. You have not worked with anaerobic bacteria before, but you should know they are all aromatic and you definitely don’t want to work with them in the house. Your family would complain. What is the temperature is the garage?

I didn’t have time to look at the 19 minute video on soldering, but that’s enough time to cover this subject and get you started. I recommend doing a few practice solders before working on your device.

You are doing a great job in finding references. The first reference describes hydrogen producing microbial fuel cell and it authored by Bruce Logan, one of the authors on the MFC review article. In a hydrogen fuel cell, an external voltage is added to the electricity produced in the anode chamber, and the cathode chamber is anaerobic instead of aerobic. The second article looks like another review article and I will read it tonight.

Donna Hardy

Hello Donna!

Yes, I checked with my dad and he said that there are electrical engineers at his plant. He also said that he has only soldered once or twice in his childhood with a soldering expert. Thanks for the help!

When we bought our house the previous owner had built a considerably stable garage. Thus it does not block out much cold. I would say that the temperature depends on the weather, maybe one or two degrees above the temperature. Is there a specific temperature at which I should work with the bacteria?

Okay, so those two papers aren't related to my MFC project and I do not have to read them, correct?

What do you think of the terms I found on Wikipedia?

Lastly, I was reading the MFC article from Wikipedia (http://en.wikipedia.org/wiki/Microbial_fuel_cell) and scrolled down to the "See Also" section. There are links to other Wikipedia articles with terms I haven't studied at all. About all of them relate to hydrogen - why is that? Do you recommend I study those terms?

Hi Irregular,

Good. Your Dad is a mechanical engineer and he can give you advice on the design and construction of the MFC; an electrical engineer can advise you about the electrical circuitry. Why don't you give the design you are planning to use to both engineers and ask for suggestions on the materials, construction, and possible problems you might encounter? They might be able to suggest using alternative materials that would work better or be less expensive.

Most of the temperatures we've seen in the literature range from 20 to 30 degrees Centigrade. The one paper that cited an optimum temperature when using Rhodopherax ferrireducens was 25 degrees C, which a 77 degrees F, or like a room that is a little too warm. Generally, for every 10 degree C change in temperature up to the optimum temperature the rate of bacterial growth doubles. If the temperature is too high, the bacteria die; it it's too low, they just slow down. So if your temperature was significantly below 20 degrees Centigrade, your bacteria might not be able to grow and metabolize quickly enough to generate electrons. What temperature range do you expect in your garage this month? Is there any way to add a little heat?

You are correct; you don't have to read the hydrogen fuel cell paper. A hydrogen fuel cell is a type of microbial fuel cell that yields hydrogen gas; you are making one that will generate electricity. The other paper is a review paper and you have the information available in other papers. You should be aware of the different types of microbial fuel cells, but just concentrate on the papers that relate to your project. You can ignore all references about hydrogen fuel cells for now.

The following link from the Wikipedia site contains a very clear explanation of why Rhodopherax works better than other bacteria to generate electrons in an MFC:

http://www.scq.ubc.ca/microbial-fuel-ce ... ireducens/

How are you doing on collecting materials for your MFC?

Donna Hardy

Hello!

I will talk to my dad about materials, construction and possible problems as you mentioned. I will ask him if it is possible if he can contact an electrical engineer to look at the electrical circuit.

Hmm.. that's an interesting point. I will discuss the temperature issue with my parents and inform you of my decision. Thanks!

Thanks for clarifying my hydrogen fuel cell confusion Additionally, I printed the article on the bacteria to read and refer to. Unfortunately I will not be able to identify my bacteria. If I could, however, I would definitely consider using this bacteria and altering my MFC to suit the bacteria. So I guess this article will help me in thinking about my MFC itself and the results (efficiency, for example),correct?

A few materials needed for the MFC will have to be researched and purchased. For example, I will probably have to order the carbon cloth online. However, basic materials such as the multimeter, alligator clips, anode/cathodes materials, fish tank, etc. will be easier to purchase. I will think about whether using boxes, bottles or jars will be better for my experiment (for the anode/cathode).

Wow, indeed background research is essential, extremely beneficial and helpful. I am still reading more and more information based on the MFC and key experiment terms. Do you recommend any mathematical concepts which I should study? For example, the Rhodopherax MFC article quotes:

The stoichiometry of glucose oxidation and iron reduction is as follows:

Oh my, how much can I ever thank you for all your help!?!?!?

EDIT: I found a Final Report a student wrote based on single-chambered MFCs. I am not looking at his analysis, but I looked at the part which he classified as Literature Review in his report. Would this be the background research section? As you scroll down, he mentions many mathematical equations which I am unfamiliar with. Do they relate to my subject? He mentions topics such as " Root-Finding Numerical Methods", "Parameter Estimation", the "Monod model", for example.

Report link: http://www.engr.psu.edu/ce/enve/logan/b ... roject.pdf

Hi,

I can't get at the PDF right now; my computer died and I am on an exceedingly old one that can't really handle PDFs. However:

The "equation" you saw in the other paper is an example of something called stoichiometry. It's a method chemists use to keep track of molecules. For example, what this particular stoichiometric equation says is that if you take a molecule of glucose (C6H12O2) and combine it with six molecules of water (H2O) and 24 molecules of a specific type of iron (Fe), the reaction they are studying results in the production of carbon dioxide (CO2), water, and a slightly different type of iron.

I think that this is probably a little advanced for your age category--most people do not learn this until a chemistry class in high school.

As to the PDF you mentioned, as I said, I cannot see it, but a parameter estimate makes me think that they created a mathematical model to simulate some process that was going on in the fuel cell. Again, I think that this is a little beyond your grade level and that you do not need to worry too much about this; if I were judging a science fair, I would definitely not expect you to be able to do anything like that in middle school.

However, if you want to know more, we would be happy to help--it's not as if I'm not saying don't learn it; instead, I don't want you to feel as if your project will be unsuccessful if you don't understand stoichiometry or mathematical modeling as a middle-schooler .

Hi Irregular,

You did a great job in advising Kirby on his last minute project! That was very kind of you to spend your time to share your experience in planning science fair projects. I think you have a great future as a science buddies advisor.

If you get a chance to talk or e-mail the electrical engineer, ask for ideas on how to lower the resistance of the circuit. This is a common problem reported in many of the papers we have been reading and high resistance limits the usefulness of many MFC’s. It’s also why the soldering technique is important; to make sure the electrical connections are secure. Ohm’s law of electricity explains the why low resistance is preferred in an MFC:

http://en.wikipedia.org/wiki/Ohm's_law

Look at the formula: I (current) = V(voltage)/R (resistance)

You will be measuring current and voltage with your multimeter. You can see that if the electrical resistance is high, then the current (flow of electrons) is reduced, so ideally you want a low resistance in your circuit. An electrical engineer would be able to tell you if what you could do to have the lowest possible resistance.

You should order the carbon cloth as soon as possible to make sure this item does not hold up your project. You might want to telephone the company and make sure the item is in stock and will ship immediately. Try not to order something that is on backorder.

What about a mediator? What are you planning to use to mediate the transfer of electrons from the bacteria to the salt bridge?

The equation for glucose oxidation and iron reduction definitely applies to your project, but the equation for your apparatus might feature a different electron donor and acceptor. This particular equation shows how electrons are generated from the reduction of Fe III to Fe II, and this would apply to your project if you were to add FeIII (iron chloride) to the anaerobic chamber. According to the references, adding iron helps increase the flow of electrons, but it is used up and has to be regenerated. You will need an equation to describe whatever electron acceptor you will be using and I will explain this in more detail very soon.

The final report from one of Bruce Logan’s students contains some useful equations for evaluating an MFC and would be optional for you. For your project I think that Ohm’s law will be sufficient to describe and measure your results. However, if you are interested and if you have time after you complete your project, you can come back to this article and see if you want to try applying any of the equations to your system.

Donna Hardy

I just read the Science Buddies project and it has a few flaws in terms of electrical measurements.

I haven't gone through this entire thread to see what your hypothesis is and what materials you are going to be using.

If you are going to be running multiple samples concurrently, my first thought would be to utilize your meter to measure current and when the meter is not connected to a given apparatus, to short the annode and cathode leads together.

The impedance (resistance) of your DVM on a millivolt scale can easily be higher or lower than the impedance of the apparatus and should different samples have different impedances that are higher and lower than the impedance of your meter, huge measurement errors will result.

By using the DVM on a DC micro or milli Amp scale, the meter is gauranteed to have a lower impedance than any of your samples.

In any case, you need to have some "load" between the annode and cathode at all times during your experiment (except for brief periods when you are putting the meter in and out of the circuit.

If you fail to provide an external electron path between the annode and the cathode chambers, the microbial activity in the annode chamber could easily drive the chemistry to a different state. Understanding all of the anerobic microbial organic chemistry possibilities in your samples is well beyond any of our abilities (expert and you alike) because we can't know exactly what is in your samples without analyzing them which is well beyond your time and budget.

You can reduce the impedance of the cathode chamber by adding salt; however, that will likely kill any microbial activity in the cathode chamber so it depends on exactly what you are testing on whether that is a good or bad idea. Living cells need the chemistry of surrounding fluid to be isotonic with the intracellular fluid to prevent the cell walls from bursting from ionic pressure.

Hello Melissa, Donna and Craig!

Thank you so much for your helpful advice! I am nearly finished my background research and have printed all of your replies. Once I finish background reading, I will be able to understand some concepts/terms better and will reply back to your comments and concerns.

Thanks for your patience, sorry for the late reply!

Quick question for Donna:

I have finished reading about electrons, protons and neutrons. Should I read about the combination of atoms, bonding, etc?

Hi Irregular,

Thanks for Craig for posting his helpful comments and suggestions for measuring the current on your MFC and for always using a external load between and anode and cathode electrode. I think you can add salt to the cathode chamber to reduce the impedance/resistance, as he suggests because the anaerobic bacteria will be growing in the anode chamber.

There is lots of information that you need to understand for this project, but don’t worry if everything is not completely clear at this point. After you have had physics and chemistry in high school, the scientific concepts on this project will make more sense. I think you should read the articles you have, and try to understand as much as you can, and go ahead and start building the MFC, using the directions from the Logan group at Univ of Pennsylvania, since they seem to have the most experience in this area.

The chemistry that you should read for this experiment involves respiration, or the chemical breakdown of food to produce energy. Here is a website that explains the chemistry of respiration of organisms that use oxygen. The process of respiration for aerobic organisms like humans, involves the transfer of electrons from the food source (sugar) to oxygen:

http://www.rsc.org/education/teachers/l ... ration.htm

Here’s the important formula for this process, involving several intermediate steps, which are not included. This equation just shows the beginning and end of the process.

C6H12O6 + 6O2 6CO2 + 6H2O + energy (ATP)
(sugar/glucose) + oxygen carbon dioxide + water

The important background fact for your project is than in this equation the sugar is oxidized (loses electrons) and the oxygen is reduced (gains electrons).

Anaerobic bacteria use sugar as an energy source, but they don’t use oxygen at the final electron acceptor. Instead, there are many types of bacteria that use all sorts of molecules as an electron acceptor.

http://en.wikipedia.org/wiki/Microbial_metabolism

Here are some examples from the wikipedia article:

• Manganic ion (Mn4+) reduction to manganous ion (Mn2+)
• Selenate (SeO42-) reduction to selenite (SeO32-) and selenite reduction to inorganic selenium (Se0)
• Arsenate (AsO43-) reduction to arsenite (AsO33-)
• Uranyl ion ion (UO22+) reduction to uranium dioxide (UO2)
In each of the examples above, the charge number (e.g.2+, 4+)of the element on the left shows that it has fewer electrons (oxidized state) than the (reduced) element on the right.

The charge of an element is described as the oxidation sate, and the following website explains this concept:

http://en.wikipedia.org/wiki/Oxidation_state

The purpose of the MFC is to capture the electrons that are produced by the bacteria and measure the flow of electrons from the anode to the cathode electrode. This is what electrical current is; the flow of electrons.

http://en.wikipedia.org/wiki/Electric_current

The challenging part of this project will be to keep the bacteria growing (and respiring) as rapidly as possible and keep the resistance/impedance low so that there will be a measurable current.

From your reading, do you have any ideas what you could do to keep the bacteria metabolizing? Also, do you have any ideas of what you could actually do with the electricity that is produced by a typical MFC?

Also, in you local area, are there any local water sources that are high in nitrate, iron, sulfur, arsenic, or any other elements? These water sources might be a good source of samples of anaerobic bacteria for your project.

Let us know if you have any questions.

Donna Hardy

Thanks all of you, Melissa, Donna and Craig for your helpful informational responses. I have indeed read them and printed them off for reference. Sorry for the late reply - I have been so, very busy with background reading, projects, homework and other activities.

I provided my father with a list of materials needed to purchase and he is looking into them. I am planning on having all the materials, latest, preferably by Sunday. Thanks so much for the references, they were amazing resources and helped me understand the processes I found most complex, respiration, oxidation+reduction, etc.

As for the electrical circuitry, I am still reading and looking into possibilities. I understand how resistance will be important to consider.

For metabolization, I am thinking about using a mix of compounds, as they seem effective according to one of my resources. Although very effective, using a substrate like sugar will be wasted as it is a usable and important resource. Using organic compounds are better as they are considered 'waste'. Mixing the difference compounds seems effective enough. I will be testing the benthic+topsoil bacteria, and am thinking of possibly changing my idea of temperature variable to a variable of metabolization material - maybe acetate in one, organic compounds in the other? So much to decide on!

I am not sure if I will be able to identify the elements in the water. I am using water from a small lake in a nearby park and will see if a park information sign somewhere might describe the lake and possibly any elements.

Lastly, before I forget, I just have a few questions:
1) Why does bacteria in the MFC HAVE to be anaerobic, as aerobic bacteria produces more energy?
2) In human respiration, glucose is used... is this because of the energy in the glucose? How is the glucose obtained? Do we consume it form of food or is there glucose in our body? What is used in replacement of glucose in bacteria. (The references about respiration talk about human respiration and bacterial respiration, so I got a little confused..)

Thanks for your help, so, so much!

Hi Irregular,

You have good questions. Here are some answers.

1) Why does bacteria in the MFC HAVE to be anaerobic, as aerobic bacteria produces more energy?

Look at the equation for aerobic respiration on this page above in my last post. The electrons are transferred to oxygen and water, a neutral product, is the end product. In anaerobic respiration, some other molecule such as iron accepts the electron and the product is another charged ion. The MFC steals some of the electrons from the anaerobic respiration process to create a flow of electrons. I have not seen a reference on this topic, but apparently the electrons from the anaerobic respiration are more available at the surface of the bacterial cells to be transferred to the medium. With aerobic respiration, the electrons are not as readily available. Additional study on this topic could be a subject for a future science fair project.

Aerobic respiration yields more energy from a molecule of glucose, but there are many environments where oxygen is not available, and bacteria have developed the ability to survive without oxygen. They can't get as much energy per molecule of glucose, but they survive very well.

2) In human respiration, glucose is used... is this because of the energy in the glucose? How is the glucose obtained? Do we consume it form of food or is there glucose in our body? What is used in replacement of glucose in bacteria.

Humans and aerobic bacteria essentially utilize glucose the same way to produce energy. Glucose is a simple sugar that humans and bacteria obtain from food. Complex carbohydrates that humans and bacteria consume such as potatoes, bread, and cookies are broken down to the individual sugars such as glucose and the sugar is then metabolized to produce energy and the leftover electrons are transferred to an oxygen atom. With anaerobic bacteria, the process is about the same, but the electrons are transferred to elements other than oxygen. Some of the references you are reading have described other food sources that can be added to the MFC that anaerobic bacteria can utilize for energy, such as acetic acid (vinegar), Bacteria are very flexible in their choice of food/energy sources and can use just about anything.

For your experimental plan, I think you are planning too many independent variables. Varying the food/energy source could be one project. Varying the temperature would be another. Comparing results with different sources of bacteria would be a third project. I recommend picking one independent variable and running that experiment. Repeat results. Then you can go to the next topic. You don’t have time to do everything this year, but you can think about continuing this project in the future.

Donna Hardy

Hello Donna!

Thank you very much for your answers, I will use them for reference and they really helped me understand. The anaerobic/aerobic bacteria sounds very interesting and you are right - it would make a wonderful future project!

Some additional questions:

1) For this MFC project, is it needed to study and learn about fermentation?
2) From my understanding, the electron acceptor will be the mediator - methyl blue, for example. The electron donor - will it be the substrate (food for bacteria..) or the bacteria itself?

I am reviewing my decision for materials, design, mediator, variable, etc. I will proceed to start my experiment this week or coming weekend.

Thanks for your help, time and patience!

EDIT: Below is my explanation of "Benthic" from my Research Paper. I have gone through many sources explaning the MLA format (including Science Buddies resources), precisely ones mentioning website citation. For websites which contain no author, it is suggested to use a short title of the reference. Do you think my explanation is appropriate? I have expanded on the website title, organization, URL, etc in my bibliography.

The term “benthic” refers to anything associated with the floor/bottom of a mass of water, which can range from a pond, to an ocean (Benthic Habitat). Organisms living in the benthic zone, including plants and animals, are named “benthos” (Benthic Zone). Precise benthic zones range according to location, depth, and biological communities, physical and structural features (Benthic Habitat). The soil lining the bottom of the water floor is particularily important for bethos and biological activity (Benthic Zone). The benthic zone is generally known for usually being pitch dark and oxygen deficient (Classifying Lakes).

The benthic zone is generally split into 4 depths. Figure 1 shows the varying levels of the benthic zone. The hadal zone is respectively named after the Greek underworld God Hades (Benthic Zone). The abyssal zone never receives sunlight, so the temperature is around 0-3 °C (Benthic Zone). The hadal, abysmal and bathal zones contain extreme pressure and depth that mapping organisms is difficult (Benthic Zone). The nearshore habitats can range from rippled sandflats, sea grass beds and coral reefs (Benthic Habitat).

Benthos organisms have adapted to the high water pressure, darkness and cannot survive in higher water zones (Benthic Zone). Benthic species include microscopic organisms and many forms of macroinvertebrates, such as anaerobic bacteria (Classifying Lakes). Benthos are classified by job (producing/consuming), location (on top of soil, just above soil), size (bigger than 1 mm, less than 1mm by bigger than 32 µm, less than 32 µm). Energy is obtained from organic matter which drifts to the benthic zone from higher water levels (Benthic Zone).
Benthic habitats are important because…

1. They provide protection and shelter for animals
2. Benthic organisms maintain water quality
3. Benthic organisms aid in organic matter breakdown
4. Many benthic organisms are food sources to diverse animals (Benthic Habitat)

Benthic Level Depth
Hadal Zone 6,000 m deep
Abyssal Zone 2,000 – 6,000 m deep
Bathyal Zone 200 – 2,000 m deep
Nearshore/Estuarine Zone Less than 200 m deep
Figure 1 – based on information from “Benthic Zone” and “Benthic Habitat Mapping”

Hi Irregular,

Yes, I think you've got it! The food (carbon source-sugar, vinegar, etc) is the electron donor and the mediator accepts the electrons until they can be transferred to the cathode electrode. The bacteria are living organisms and they are getting energy for cell metabolism from the food.

Your description of the benthic zones is comprehensive and excellent; however, it's all of the information is not necessarily related to your project so you may consider revising it a little. The benthic zones refer that you have described refer to the ocean, and since you will be collecting your samples from a lake, I assume that it is a fresh water lake and does not contain salt water. Is this correct? We have not seen any MFC references that use salt water microorganisms. The reason you are collecting from the benthic zone is to obtain anaerobic bacteria. The bottom of a lake usually has a mud layer and there may be oxygen at the surface of the lake bottom, but conditions become anaerobic just a centimeter or two deep into the mud. That's where you will find the best organisms for a MFC. Many lakes are shallow enough that light can filter down, and if so there may be photosynthetic anaerobic bacteria that can transfer electrons to many types of electron acceptors (sulfide, nitrate, etc.) Why don't you try looking for a few references that describe the type of bacteria found in the benthic layer of fresh water lakes, and I'll do the same? That would provide appropriate background for your research paper.

Donna Hardy

Hello Donna!

Presently, I am a little confused with a few things. I have been reading this website (http://www.ccsf.edu/Departments/Biology ... /metab.htm), and it describes Glycolysis, The Krebbs Cyle, Electron Transport Chain, Chemiosmosis and Fermentation. Do you recommend me learning those terms? This link (http://www.microbialfuelcell.org/www/in ... nisms.html) and it describes fermentation as well. From my understanding, I think I just need to learn respiration from that webpage, right?

Hmm.. I totally understand what you are saying and will remember that when obtaining bacteria. I have found a few references, but am not particularly sure if they are related to benthic bacteria in freshwater lakes.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC374433/
http://books.google.ca/books?id=0dF3Ct- ... er&f=false
http://www.jstor.org/pss/4251075
http://www.springerlink.com/content/u16ucay13cg8165l/
http://www.microbiologyprocedure.com/mi ... aries.html
http://www.ingentaconnect.com/content/b ... 4/art00023
http://www.sciencedirect.com/science?_o ... fb14abb95d
http://www.ncbi.nlm.nih.gov/pubmed/17876654
http://www.int-res.com/articles/meps/43/m043p001.pdf
http://en.wikipedia.org/wiki/Aquatic_ec ... Freshwater
http://mason.gmu.edu/~klargen/111lectec ... ring04.htm
http://www.ucmp.berkeley.edu/exhibits/biomes/marine.php

Hi Irregular,

The first reference includes details about microbial respiration and electron transport, so is definitely related to your topic. However, it includes lots of details that you don’t need to know for now and you will understand better after you have had chemistry and biochemistry classes. The second reference, however, is perfect because it has just enough detail to show how electrons are generated during bacterial respiration, and it includes concerns related to MFC’s, like the availability of an electron acceptor and the fact that the generation of electricity depends on rapid microbial metabolism. You can base your research paper on the second reference and fill in with details from other sources if you would like to include additional information. Please note that the second reference mentions the fact that not everything is understood about how microbes transfer electrons, so this is an area for future research.

You did a really good job of searching for literature on the growth of benthic freshwater anaerobic bacteria. There are a couple of intriguing references that I can’t access, and the rest are on marine samples or don’t seem to have any information that would be useful for your project.

I found a couple of references with some information, but not much. There don’t seem to be a lot of papers on this topic. I’ll keep looking:

This is an abstract to reports a number of carbon sources that are utilized by a couple of anaerobic bacteria from freshwater sediment (acetate, butyrate, glucose, fumarate, benzoate) and lists their electron acceptors (sulfate and nitrate). The optimum temperature was about 30 degrees C. This is relevant because the carbon sources and electron acceptors would be suitable for use in your MFC, and the optimum temperature information is useful also.

http://www.springerlink.com/content/2h18w3n0023l0376/

Here is the Wikipedia website describing obligate anaerobes, the microorganisms that are inhibited if exposed to oxygen. The useful information in this citation is the list of electron acceptors. Please note that sulfate gives the most favorable energy yield of all of the potential molecules, so this would be a good choice for an MFC because it would generate the most electrons per molecule of food.

http://en.wikipedia.org/wiki/Obligate_anaerobe

Donna Hardy

Wow, thanks so much for your feedback and links! I will read them and include information related to my project in my research paper.

One more concern..

irregular wrote:Presently, I am a little confused with a few things. I have been reading this website (http://www.ccsf.edu/Departments/Biology ... /metab.htm), and it describes Glycolysis, The Krebbs Cyle, Electron Transport Chain, Chemiosmosis and Fermentation. Do you recommend me learning those terms? This link (http://www.microbialfuelcell.org/www/in ... nisms.html) and it describes fermentation as well. From my understanding, I think I just need to learn respiration from that webpage, right?

Thanks a bunch!

donnahardy2 wrote:Hi,

It's really difficult to suggest a topic for you to do, but I do sympathize because selecting the topic is the hardest part of the project sometimes. I would recommend reading through all of the project ideas on the science buddies website that are related to your field of interest and selecting one that meets your time and resource requirements:

http://sciencebuddies.com/science-fair- ... l?From=Tab

For example, here are some projects that could be completed within two months:

http://sciencebuddies.com/science-fair- ... A&from=TSW

http://sciencebuddies.com/science-fair- ... A&from=TSW

http://sciencebuddies.com/science-fair- ... A&from=TSW

Remember that you want to ask a question that can be answered by doing a controlled experiment. And, even though you are short on time, do take time to do background reading on your topic as this will help you design a better experiment.

Good luck and do let us know if you have questions on the science behind your project or designing your experiment.

Donna Hardy

Do that and also don't panic you will do fine. Take in all the other comments and go for the gold.

Hi Silverlake!

I have already chosen my topic, thanks for your interest in helping! I was currently talking to Donna about some research material. Thanks again!

Donna: Please look at my post above. It is re-quoted below:

irregular wrote:Wow, thanks so much for your feedback and links! I will read them and include information related to my project in my research paper.

One more concern..

irregular wrote:Presently, I am a little confused with a few things. I have been reading this website (http://www.ccsf.edu/Departments/Biology ... /metab.htm), and it describes Glycolysis, The Krebbs Cyle, Electron Transport Chain, Chemiosmosis and Fermentation. Do you recommend me learning those terms? This link (http://www.microbialfuelcell.org/www/in ... nisms.html) and it describes fermentation as well. From my understanding, I think I just need to learn respiration from that webpage, right?

Thanks a bunch!

Hi Irregular,

Sorry if I was not clear in my reply to your inquiry about the glycolysis/respiration websites. This is my reply that I intended to address your questions about these references:

"The first reference includes details about microbial respiration and electron transport, so is definitely related to your topic. However, it includes lots of details that you don’t need to know for now and you will understand better after you have had chemistry and biochemistry classes. The second reference, however, is perfect because it has just enough detail to show how electrons are generated during bacterial respiration, and it includes concerns related to MFC’s, like the availability of an electron acceptor and the fact that the generation of electricity depends on rapid microbial metabolism. You can base your research paper on the second reference and fill in with details from other sources if you would like to include additional information. Please note that the second reference mentions the fact that not everything is understood about how microbes transfer electrons, so this is an area for future research."

The second website www.microbialfuelcell.org/www/in covers the basic biology for your project; respiration and electron transport are the basis for the MFC.

Donna Hardy

Hello Donna!

Ah, I guess I just got a little confused there! I'm not sure if I accidentally missed that or something. Thanks!

Hmm.. just a few additional questions:

a.What is the purpose of the oxidizing material in the cathode? Once the electrons have reached the electrode in the cathode what happens? This is based on the Wikipedia article on Microbial Fuel Cells. (http://en.wikipedia.org/wiki/Microbial_fuel_cell)
b. I have researched a few inexpensive aquarium pumps to remove oxygen from the anode. Does this one look usable for the project to you? If many pumps are needed, I am considering possibly asking the store for a donation. I'm not sure that they will be agreeable to donate, however, since they are a pet store. http://www.petsmart.com/product/index.j ... oduct+Type
c. The link for the carbon cloth website is not seeming to work. The link is www.etek-inc.com as the Science Buddies and Bruce E Logan carbon cloth reference suggests.
d. For my research paper, under History of Similar Experiments, what kind of experiments should I list/explain/describe? The Science Buddies for sure.. how many more? Maybe mention Bruce E. Logan and some experiments by children? How many experiments should I mention? In how much depth should I mention each experiment?
e. In your opinion, which variable will be appropriate for my experiment? I've narrowed it down to 3 - bacteria (topsoil+benthic bacteria), temperature or substrate? I am more hooked onto the bacteria and substrate options. The concerns of doing two variables is that 1) more time will be needed and it will be more complex 2)I will need to spend more money.

I am a little behind schedule though will aim to finish my research paper, build my hypothesis, decide variable(s) and buy materials by Saturday. On Saturday-Sunday I will start by MFC construction and run it.

Thank you very, very much Donna, I appreciate your time and patience greatly!

a.What is the purpose of the oxidizing material in the cathode? Once the electrons have reached the electrode in the cathode what happens?

I'll try to tackle this question and leave the rest for others.
From an electrical circuit perspective, the definition of a cathode is a negatively charged electrode that will supply electrons to an external circuit.

From an inorganic chemistry perspective, most of the cathode chamber is a solution that contains ions. In order for a negative ion to donate its electron to the cathode electrode, something else must change state. In inorganic chemistry, this is typically done by via a class of chemical reactions referred to as oxidation / reduction reactions. In all oxidation reduction reactions, something is oxidized and something else is reduced. The thing that changes states is ususally an atom that changes valance states (or how many electrons it shares with other atoms).

For a simple example, lets look at Iron oxides, Fe2 O3 and Fe O. Oxygen typically has a valance of -2 (it is missing two electrons to fill its outer electron shell orbitals). This meanst that Fe has valance +3 in the first case and +2 in the second (in other words the number of electrons that each Fe atom is sharing with the oxygens to form the oxide molecules. The chemical change between these two oxides is a change in valance state of the iron or the loss or gain of an electron from an ionic or electrical perspective.

Now to the most likely organic chemistry equation involved (equation one in your citation), the anerobic (without oxygen) break down of a sugar:
C12H22O11 + 13H2O ---> 12CO2 + 48H+ + 48e-
48 hydrogen atoms gave up electrons to the cathode. This produced 48 H+ ions that have to find some negative ion to pair up. In other words, they need 24 oxygens (or some other "oxidizer", e.g. something that behaves like oxygen in an oxidation / reduction reaction)

This is a LOT to understand without learning a lot of chemistry. It starts with learning a bit about the atomic structure, how electron clouds or shells behave, and chemical equations and oxidation reduction reactions.

Hopefully other experts will tackle your other questions.

Hi Craig and Donna!

My, Craig, thanks very much for the thorough explanation!It is indeed complex since I'm only in grade 7! I am grasping the equation a little better now. I have added extra questions below in my list of questions.

FOR DONNA AND OTHER EXPERTS IF NEEDED:

irregular wrote:b. I have researched a few inexpensive aquarium pumps to add more oxygen into the cathode. Does this one look usable for the project to you? If many pumps are needed, I am considering possibly asking the store for a donation. I'm not sure that they will be agreeable to donate, however, since they are a pet store. http://www.petsmart.com/product/index.j ... oduct+Type
c. The link for the carbon cloth website is not seeming to work. The link is http://www.etek-inc.com as the Science Buddies and Bruce E Logan carbon cloth reference suggests.
d. For my research paper, under History of Similar Experiments, what kind of experiments should I list/explain/describe? The Science Buddies for sure.. how many more? Maybe mention Bruce E. Logan and some experiments by children? How many experiments should I mention? In how much depth should I mention each experiment?
e. In your opinion, which variable will be appropriate for my experiment? I've narrowed it down to 3 - bacteria (topsoil+benthic bacteria), temperature or substrate? I am more hooked onto the bacteria and substrate options. The concerns of doing two variables is that 1) more time will be needed and it will be more complex 2)I will need to spend more money.

f. From my comprehension, in the cathode, I can make a hole to add the aquarium air pump as the electron acceptor. But won't this oxygen get into the salt bridge, into the anode? Then the oxygen won't be able to stay to serve as an electron acceptor.. and the anode will contain air...
g. Next, according to Bruce E Logan's article, the electrons and protons which meet in the cathode, combined with the oxygen produce water. But isn't a hydrogen molecule needed to combine with water molecule to produce a water molecule? If hydrogen is in the MFC, where does it come from? For a quantity of water to be produced, more than one molecule of water must be present! Glucose+oxygen produce water though.. in aerobic respiration..hmm..
h. In terms of wastewater as the source of bacteria, how does the water become usable and clean after the MFC process? Is the 'clean' water the generated water in the cathode? Because the wastewater in the anode will still contain bacteria...
i. I will be using a conductive solution in the cathode - saltwater, right? When the electrons and protons reach the cathode, what will the conductive solution do? After reading one reference, I thought that it was saying that the protons+electrons will oxidize the saltwater, then reduce the oxygen (kind of like the substrate and mediator?) which will produce water. Am I correct?

Since reducing the internal resistance in the MFC is important, I did a little bit of research. I came to this paper which looks related to my project: http://www.springerlink.com/content/ep11306017977711/. My father has a machine breakdown at work so he does not have very much time to explain some concepts to me, specifically the electrical circuitry, etc

I know I have a lot of questions - sorry if I'm asking too much! I have done research but I can't seem to get a clear answer for some things.. I guess I'm just quite passionate and curious! Thanks so, so much!