Introduction: How to Make a Microbial Fuel Cell (MFC) Using Mud

The MudWatt microbial fuel cell (affectionately dubbed the "Dirt Battery") is a device that uses bacteria to convert the organic matter found in mud into electricity. This Instructable will walk you through making your own microbial fuel cell using any MudWatt Science Kit.


To make a MudWatt, you will need:

How the MudWatt Works: The MudWatt is a fun and educational science kit that uses the micro-organisms naturally found in soil to generate electricity. Although invisible to the naked eye, these microbes, with bodies one-tenth the thickness of a human hair, live throughout virtually all soil and sediment on the planet. Among these diverse communities of microbes are particular species that have the unique ability to release electrons outside their bodies as part of their respiration process.

The MudWatt harnesses this remarkable ability by providing these mud-based microbes with two conductive graphite discs, called an anode and cathode. The anode is placed within the mud where the electrogenic microbes can grow, while the cathode is placed on top exposing it to oxygen in the air (see MudWatt diagram below).

Step 1: Making Mud

Put on gloves and find 3-4 handfuls of soil or swamp goo--the smellier the better! Make sure your soil is saturated but not soupy by either adding or pouring off water. Optional: Add extra nutrients to your soil, such as MudWatt packaging, shredded paper products, or food from your fridge.

Key notes: Avoid using soils with little white balls (perlite) which aerate the soil. The bacteria that power the MudWatt are anaerobes that need an environment without oxygen to build healthy communities.

Step 2: Making Electrodes

Bend both wires 90° where the plastic sheath ends. Straighten out the bare end of the wire. The green wire will be used to make the anode, and the orange wire will be used to make the cathode. Insert the bare end of the anode (green) wire into the side of the thin felt disc while wearing the gloves provided. Try to keep the wire from exiting the felt. Repeat this step with the cathode (orange) wire and the thick felt disc.

Step 3: Assembling

Pack an even layer of mud into the bottom of your container, at least 1cm deep. Place the anode (green) you constructed in Step 3 on top of the mud, pressing it down firmly to squeeze out air bubbles. Fill your container with more mud, at least 5cm deep, pressing down firmly to squeeze out air bubbles. Let your mud rest for a few minutes and drain any excess liquid. Finally, place the cathode (orange) gently on top of the mud. Do not cover the cathode with mud.

Step 4: Lidding (for MudWatt Kits That Come With Vessels)

If your kit came with the MudWatt Vessel:

Remove your gloves and attach the Hacker Board into the indentation on the lid. Pass the electrode wires through the lid. Facing the semicircular indentation, the cathode (orange) should be on the left and the anode (green) on the right. Now press the lid down onto the jar to snap it into place.

Step 5: Closing the Circuit

1. Bend and connect the cathode wire (orange) to ‘+’ and anode wire (green) to ‘-’ on the Hacker Board.

2. Connect the long end of the blue (10μF) capacitor to pin 1 and its short end to pin 2. You may need to bend the wires so that they fit snuggly.

3. Connect the LED ‘s long end to pin 5 and its short end to pin 6.

That’s it! You should start seeing the LED blink after a few days, once your MudWatt has developed a healthy community of microbes!

What do these components do?

Hacker Board: The Hacker Board takes the low voltage and low current coming from the MudWatt and converts into short bursts of higher voltage and higher current.

Capacitor: The Capacitor is a little energy storage component. It is able to build up energy as power comes in from the MudWatt, and then discharge that energy in a quick burst to blink the LED.

LED: The Light Emitting Diode (LED) takes the electrons being discharged by the capacitor and converts those electrons’ energy into light energy.

Step 6: Measuring Microbes and Power Output

Download the MudWatt Explorer App on the App Store or Google Play. You’ll be using it to measure, record, and analyze your MudWatt data in the few next steps!

Step 1: Ready, Aim...Measure!

Once your MudWatt’s blinker is blinking, open the MudWatt Explorer App and select Measure from the main menu. Line up the blinker in the target on your screen and the App will automatically measure your power and your population of electric bacteria!

Step 2: Record & Analyze Multiple Measurements

Record several measurements by using the Record button on the Measurement screen, and go to the Analyze section of the app to see how your MudWatt functions over time!

Step 3: Discover a Hidden World

Use your power readings to unlock chapters of a fun and educational comic following Shewy, the Electric Microbe. Discover the magic of microbes as Shewy explores this complex, muddy world.

Step 7: A Closing Note and DIY Resources

Thanks so much to everyone that has commented on our post! When Instructables first invited us to post about the MudWatt, we weren’t sure if it was the right fit, since it is indeed a product, and we were worried our Instructable would end up sounding like an infomercial. But we decided to do it because the MudWatt is designed to be a DIY MFC kit, after all. While we are of course excited when people buy our products, we’re also very excited when we inspire people to pursue their own creation and experimentation. Many people have requested more info for creating their own MFC using off-the-shelf parts. This is completely possible to do, and we’ve provided resources for that below. However, we’ve found that making a true MFC with off-the-shelf components is significantly more expensive than purchasing our components. The MudWatt actually started out using off-the-shelf components, but we've managed to get the price down by ordering materials in very large quantities and processing them ourselves.

We've seen several posts about DIY MFCs in the past, but we've found that these projects include the use of metal meshes, metal brushes, copper wire and other materials that corrode in harsh soil environments. Using these corrosive materials means that you're making a corrosion battery instead of an MFC. That corrosion often occurs at the junction between the electrode material and the wire. This junction can be sealed with epoxy, but this is very difficult to do in practice, especially if you're using high-surface-area or porous electrodes, which you'll need if you want to produce any significant power. The funny thing is that this corrosion will actually produce some significant power, which can be very easily mistaken to be coming from microbial activity.

For making your own DIY MFC, here are some places you can find non-corrosive materials:

Carbon electrodes: http://fuelcellstore.com/fuel-cell-components/gas...

Titanium Wire: http://fuelcellstore.com/fuel-cell-components/gas...

Charge-pump chip (for power an LED/electronics): S-882Z24-M5T1G

We encourage you to use the MudWatt as a launching point for your own research, and we'd be thrilled if you're able to create a true MFC using off-the-shelf materials at a cheaper price. Happy experimenting!

Comments

author
HORSENZEBRA (author)2017-02-11

Works well. Thankyou

author
SHOE0007 (author)2017-01-30

Good attempt for alternative energy. Difficult to scale up and may work better with oxygen exposure. Of course you would have to protect the amplifier from a potential high gain of power. There should be better models out there. This is what I got.

001.jpg
author
enzymeandco (author)2016-09-09

Hi guys !

We got a Mudwatt blinking 1 time/sec here in Cardiff on good old Welsh estuary mud, only 3 days after setup. We are happy !

We tried to order some Seiko S-882Z charge pumps to build some other MFCs, but it seems that the production is now discontinued.

How are you dealing with this issue to continue to produce your HackerBoards ?

Do you have a new reference to advise ?

Thanks in advance for your answer !

author
Merinoide (author)2016-05-22

Firstly, sorry by my english, I know that it not the best.

I have two cuestión:

1) Why use the filter more narrow like a anode? What happen or why not use the big filter like a anode, and the smoller like a cathode.

2) It's possible make more electricity power if in the anode put more wires, like a mesh, inside of anode filter?.

Thank very much.

author
Nknk (author)2016-02-01

hi,

I live in a very cold area. Outside everything is all covered in snow for a few months. Is it OK to collect mud sample in such conditions? Does the freezing temperature kills bacteria in the mud? I tried this experiment with my own MFC, but the voltage is negative (the connections are all correct!). What could be wrong? I'm wondering if the cold/ freezing temperature kills bacteria in the mud/ sludge? If so, where I can get the mud from? Please let me know! Thank you!!

author
MudWatt (author)Nknk2016-02-01

Hi Nknk,

Thanks for your message. Yes, temperature has a big impact on microbial respiration rates, and therefore power in an MFC. Freezing temperatures shouldn't kill the bacteria completely, but it will put them in a pretty dormant state. The best thing to do is to warm up the soil to around body temperature and put some shredded up paper in the soil near the anode. This should help get the bugs going again. As for the negative voltage, hmm... I would make sure that there are no air bubbles near the anode, and no excess water near/above the cathode.

Hope this helps!

author
ThaDee (author)2015-10-09

+1

Like. Been following the PFC but haven’t built anything
(yet).

So you just need to poke the wire in the graphite plate? Or
is the one provided in the kit special somehow?

author
tinee pika (author)ThaDee2016-01-25

one is provided

author
MudWatt (author)ThaDee2015-10-12

That's all you need to do! Our wire is titanium (won't corrode, which is key to making a MFC instead of a corrosion battery), and the graphite plate is just graphite fiber felt. You can get graphite materials from http://www.fuelcellstore.com/ and can experiment with using carbon fiber building materials, as well.

author
ThaDee (author)MudWatt2015-10-23

Been wondering ever sins I first found PFC(plant
fuel cells) how to make the anode and cathode. So super! Tnxz!

author
tinee pika (author)2016-01-25

by the way i have the kit and oe is provided so you dont have to worry to buy oe and in the kit they call it the hacker board and every thing above is provided in the mud watt classic kit

author
tinee pika (author)2016-01-25

nice idea

author
liz_hammack (author)2016-01-17

Looks like a great project to teach kids about alternative energy sources

author
3967 (author)2015-10-13

how practial is this when you scale up, to produce larger output.

How much space to you need for 100 Watthours or 1000watthours ?

author
MudWatt (author)39672015-10-13

MFCs are notoriously difficult to scale, with the power density (Watts per square meter of electrode surface area) decreasing as electrodes get larger. The reason for this is still under debate. The most effective thing to do is to connect multiple smaller MFCs together in series of parrallel to get greater voltage or current respectively. MudWatts will typically produce 50-100 microWatts, meaning that you'd need 1,000,000 MudWatts to get 100 Watts.

author
3967 (author)MudWatt2015-10-14

When the energydesinty is so low, where is the benefit over other powersources like Solar,Wind or chemical energy ?

author
MudWatt (author)39672015-10-14

Great question! MFCs satisfy an energy niche: they can meet low energy needs in remote locations and produce energy as a by-product of waste treatment.

The military and universities install sensors deep in the ocean. The energy requirements of these sensors are relatively low and the cost of replacing batteries extraordinarily high. Microbial fuel cells are excellent sources of energy under these conditions, as they're able to continuously provide power to these sensors without the need for regular replacement. For more reading on MFCs in the ocean: https://cdn.shopify.com/s/files/1/0598/6373/files/...

MFCs are also great technologies where waste is involved. Wastewater treatment and remediation of contaminated groundwater and soil are two examples where we can take advantage of anaerobic conditions to generate electricity in tandem with treatment. These two ubiquitous treatment scenarios provide the conditions necessary for anaerobic microbes, thus enabling microbial-based energy production (typically methane generation, MFCs currently being piloted) that turns waste back into energy, thus closing the loop!

So while MFCs probably aren't going to power the grid like other renewables, they can reduce energy requirements of commercial and municipal-level treatment projects using existing conditions.

author
3967 (author)MudWatt2015-10-15

Ok, but where is the benefit for example against a microgenerator which uses wavemotion as an energy sourc or a lithiumcell which can last 10 years? do these MFCs last forever?

author
MudWatt (author)39672015-10-15

MFCs don't have any moving parts (less risk of failure), and the materials involved will last on "geological" timescales. At the bottom of the ocean, there's a constant influx of nutrients from decaying plant and animal material, which acts as a perpetual fuel source. So, theoretically, they can last forever, so long as there is life on earth. Also, in the deep ocean, the cost of replacing batteries can run over several hundred thousand dollars per node in a wireless sensor network, making operational costs prohibitive for large wireless sensor networks relying on batteries.

author
gmendez3 (author)MudWatt2015-10-15

This technology could be use to power low-energy sensors and create sensor-node-networks to monitor different parameters, for example in hydroponics you could monitor pH, Temperature and Humidity, without having to power every single sensor, etc. Or in Water treatment, you could monitor single spots.

author
gmendez3 (author)MudWatt2015-10-15

This technology could be use to power low-energy sensors and create sensor-node-networks to monitor different parameters, for example in hydroponics you could monitor pH, Temperature and Humidity, without having to power every single sensor, etc. Or in Water treatment, you could monitor single spots.

author
Krisztián PálK (author)2015-10-09

Dear mudwatt, congratulations for your exciting work, I wonder how much milliamps can be harvested in this project? I interested to power a smaller arduino setup with some more functionality, a clock maybe with your mud idea.

author
MudWatt (author)Krisztián PálK2015-10-12

The average is 50-100 microwatts. That may seem small, but we've been able to power simple electronics with LCD (not LED) screens.

author

There is a clock available... I've been looking for a schematic on the hacker board... but haven't found it so far. This is NOT an open source project, definitely a sales pitch for KeegoTech. So far it looks like they are just starting out... I only see one application on the Google APP Store.

author
milkcartonkid (author)2015-10-08

how do you make this without the kit?

author
MudWatt (author)milkcartonkid2015-10-08

Unfortunately, there's no easy way to do this without a kit if you aren't in a research center (we wish there were!). To make electrodes, you need a material that is both electrically conductive and inert. Finding affordable materials that fit the bill is a challenge. Graphite, platinum, and titanium all fall into this category (we use carbon fiber). On our website, you can purchase all of the individual components to make MudWatts, if you want to delve into subbing in your own parts.

author
BeckyH8 (author)MudWatt2015-10-11

If you can use graphite, wouldn't a pencil lead do? I'm sure your kits are very nice, but they cost money, and I have loads of pencils!

author
MudWatt (author)BeckyH82015-10-12

We've heard of other MFCs using graphite rods, including pencil leads. We definitely encourage experimentation with this. You'll want to maximize the surface area of your graphite, so use the loads of the pencils you've got. We'd love to hear your results!

author

Thank you for the idea. I will be making a MFC instructable using re-purposed easy to find materials so need to "buy" a kit. No worries though I'll give full credit.

author
whitsona (author)2015-10-12

Thanks, mudwatt! Even though it's a bit infomercial-ly, I work in a science museum and hadn't run across this product yet. I'm frequently here looking for maker stuff. so, I need this kind of instructable to be welcomed and appreciated here. :-)

author
godfabber (author)2015-10-11

Nice product, but I agree with raygombos, it looks more like an infomercial than a Instructable. I'm pretty sure is possible to make the same experience in a DIY way, without buying the kit. IMHO would be much more cool if you guys teach how to do it with off-the-shelf materials. A lot of people will prefer to buy the kit instead of making it from scratch and you kept the knowledge opened. Keep rocking...:)

author
raygombos (author)2015-10-09

This is an interesting product. Is this an infomercial to sell the MudWatt product or are the board designs opensource so we can build out own?

author
seamster (author)2015-10-08

I'm intrigued! :)

Thank you for sharing the details on how this. Very cool stuff!

author
MudWatt (author)seamster2015-10-08

You're welcome! Thanks for the positive words!

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Bio: We make fun and educational STEM kits that let you play with microbes. Create electricity from the bacteria living in mud, or make bread while ... More »
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