need help asap with the MFC

Thread Starter

maliha tamkeen

Joined Jan 6, 2016
Project link

We were using 2 MFCs to compare the power output after adding the salt.For the first trial we used store bought potting soil(Nature's Care Organic Potting Soil Water Conserve).

Below are the power output measurements

Below are voltage current measurements at the first day

Voltage and current after adding the salt on day 13 are

Distilled water-0.3microA


1g soil-8.66mA

5g soil-36.8mA

As you can see that the power out is low,so the LEDs for both MFCs did not blink.The internal resistance was high.The temperature was not constant .It was 68-72F.

The output of 1g salt is more than 5g salt(as expected).

During the second trial we soil we used the top soil from some one's backyard.We checked with them that there was no pesticides used.

Below is the link of the power output.

Below is the voltage and current of MFCs measure each day

Below is the current and voltage measure on the first day

Voltage and current after adding salt on day 13

Distilled water-o.1mA

1g soil-3.38mA,3.21mA,3.5mA

5g soil-14.46mA,14.55mA,14.79mA

We used heat wrap to keep the temperature constant at 72F at the time of taking reading.Throughout the day, temperature was 68-72F.The LED of 1g blinked.

On the day we added salt LED blinks are as follows

Temperature- Time between blinks

71F -30

73 -18

74.5 -15

74 -12

75 -10

78 -8

The temperature was recorded each day .The second MFC's LED(5g soil) never blinked.We tried switching LEDs and chip.It worked fine for 1g,but did not work for 2nd MFC.

As you can see that the power output of 5g salt is more than 1 g soil(which is opposite to first trial).The internal resitance of 1g salt is 4700ohms.Internal resistance of 5g soil decresed to 470 then went back to 1000ohms.

Our Hypothesis was the power output of 1g is more than 5g.

We also tried using using mud watt app for our second trial,but the results were not compatible with power output readings.

2nd day-8W,4W,3W

6 day-3W

13 day-3W

12 day 8w

The point is LEDs blinks were not uniform.How do we epresent the LEDs blinks output?

Which output was expected to be more ,1g salt or 5 g salt?

What do we explain for the opposite output of 2 trials.

Why is the output of topping soil so low?

Why did the internal resistance of 2nd MFC change?

We have 3 weeks left for Science fair and almost 2months for regional Science fair?Should we do one more trial with top soil and 10g salt ?

We were thinking about using soil under river for another trial .Is it a good idea?What do we show as 3 types of soil.First was potting soil,2nd consists of clay.Does it make sense to do do third trial with river soil as it may again consists of clay with bacteria rich soil.What explanation we should give for LED of 2nd MFC not blinking .

Thankyou so much.

Waiting for your reply before the next step.




Joined Sep 9, 2010
I hear lots of experiments and data, but no hypothesis or goal. And it's almost impossible to understand what you did.

If your hypothesis is that there is some optimum added salt level, you should collect data with at least 3 test levels, for as many soil types as you have time for. (You cannot show an optimum with just two levels.) If you think conductivity is the key parameter, you probably ought to measure it, don't you think? And there are different salts that could supply conductivity without as much toxicity as salt.

You seem to be measuring power output, but there are no obvious measurements of it. You need voltage and current against time.

If there really is such a thing as a microbial fuel cell, I would suppose it depends heavily on the organism(s) being grown. Can you get the effect with a single organism, or do you need complementary organisms? Do you have any idea what organisms are involved or is this a compost-pile experiment? What fuel is being converted to MFC power?

And I suppose you should prepare yourself to answer questions about carbon generation.

Thread Starter

maliha tamkeen

Joined Jan 6, 2016
  • Microbial fuel cell vessels (2)
  • Anodes (2)
  • Cathodes (2)
  • Hacker boards (2)
  • Capacitors (2)
  • LEDs (2)
  • Digital clock/thermometer to be powered by the microbial fuel cell (1)
  • Set of 7 resistors
  • Alligator clips and jumper wires (2)
  • Digital multimeter (1)
  • Nitrile gloves (1 pair)

My hypothesis is that the power output of the MFC with 5 g of salt will be higher than the one with 1 g of salt.
I, however, also understand what you mean to say. Perhaps I should make a graph of voltage and current vs. time. Like I said before, I have already been measuring the voltage and the current and have put it into Google Sheets. I did not graph it compared to time though.
I need help for why the LED for 5 g of salt is not blinking. Also, the digital thermometer that was provided with the MFC kit did not light up or work. Do I need another capacitor for the digital thermometer? Or can I use the same one that I used for the LED?
Finally, how can I connect the 2 MFC's in parallel? In series? How can I measure their power output once they are connected?


Joined Sep 9, 2010
To get much help here, you'll need to sketch out a schematic. I can't speak for everyone, but I've got too many other things going on to spend time researching how these things work, how they're set up and connected and all. The same diagram you might use to present your project might go a long way here to help people understand. Right now, we have no idea why LEDs blink or anything you asked about.


Joined Sep 9, 2010
I think it's one of those flashers that slowly charges the cap and then switches to discharge the cap through the LED. I forget what they call them but they're also used with DC motors to make a bug-like jumper.