✎ michka:research:microbial_fuel_cells:bruxelles2 [the libarynth]

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====Experiment "Bruxelles2"====

===Salt Bridges===

I failed a three batches of [[http://www.treehugger.com/slideshows/gadgets/make-microbial-fuel-cell/page/3/#slide-top|salt bridges]] before managing to have one stable made.

The right protocol:
   * Mix 200 ml water, 5 g of agar and 75g of salt in a cooking pan.
   * Bring it to a boil while mixing regularly.
   * Let it boil for a few minutes (not too much, otherwise you will loose your water)
   * Pour the boiling mix in appropriate containers
     * Reused glass jars (with an opening having a size close to the widest diameter of the pot)
     * Glass petri dishes
   * Let them cool down a bit
   * Place them in the fridge for a few hours

What not to do:
   * Use hot water from a kettle and mix everything in a cold pot
     * This induces a very uneven mix, where salt and agar are not well dissolved
   * Let it sit in the pot beore pouring it on top of the substrate
     * Warm liquid may harm the microbes in the substrate
     * Most of the agar and salt will sediment at the bottom of the pot, and your mix will not become a gelatin
   * Do not forget that the fridge step is important !
   * I highly suspect gelatin to be inefficient for this process. My successful batch was made from agar-agar from a chemical provider. I think other sources may be fine, but I have not managed to use them properly yet.

===Mud, Tall===

{{ :michka:research:microbial_fuel_cells:dscf6283.jpg?300 |}}
//Mud samping location - Sint-Jans-Molenbeek, Belgium//

Design details:
   * The mud sample was taken from the waterland at the bottom of Scheutbos Park in Sint-Jans-Molenbeek.
   * Its approximate volume is 50 cl.
   * On top is a highly concentrated Petri-dish-sized salt bridge.
   * On top is filtered water.
   * Electrodes are made of copper from dead batteries. They have an approximate surface area of 100cm2 each.
   * Crocodile clips are clipped on the electrodes and brought out of the pot for measurement.

Results:
   * Tension is unsensitive to oxygen presence, and is in the 300mV range.
   * Current is in the 1-2mA range.
   * Power is therefore in the mW range.

Longer-term results (12 days & more):
   * Tension is stable at 110  mV, but drops when measuring current (and rises up afterwards).
   * Current is stable at 107 microA, but drops after measuring tension (and rises up afterwards).
   * Overall power is therefore around 11 mW.

===Mud, Small===

Design details:
   * The mud sample was taken from the waterland at the bottom of Scheutbos Park in Sint-Jans-Molenbeek.
   * Its approximate volume is 3 cl.
   * On top is a salt bridge the size of the jar.
   * On top is filtered water.
   * Electrodes are made of copper from dead batteries. They have an approximate surface area of 10-20cm2 each.
   * Crocodile clips are clipped on the electrodes and brought out of the pot for measurement.

Results:
   * Tension is sensitive to oxygen presence, and is in the 100mV range when activated, 30 mV at rest.
   * Current is sensitive to oxygen presence, and is very low - about 0.3 mV when activated, dropping to 0.1 mV at rest.
   * Power is therefore in the microW range.

Longer-term results (12 days & more):
   * Tension is stable at 20 mV.
   * Current is stable at 1 microA.
   * Overall power is therefore around 20 microW.

===Vegetable Waste & Compost Tea===

Design details:
   * The substrate is made of vegetable scraps (potatoes, carrotes, zucchinis) covered with compost tea (from FoAM's vermicompost production), and inoculated with a tea spoon of mud from Scheutbos Park.
   * Its approximate volume is 7 cl.
   * On top is a salt bridge the size of the jar (broken during the manipulations).
   * On top is filtered water, which was quickly populated by compost tea from below the salt bridge.
   * Electrodes are made of copper from dead batteries. They have an approximate surface area of 10-20cm2 each.
   * Crocodile clips are clipped on the electrodes and brought out of the pot for measurement.

Results:
   * Tension is sensitive to oxygen presence, and is in the 200mV range when activated, 80 mV at rest.
   * Current is sensitive to oxygen presence, and is very low - about 0.4 mV when activated, dropping to 0.1 mV at rest.
   * Power is therefore in the microW range.

Longer-term results (12 days & more):
   * Tension is stable at 120 mV.
   * Current is stable at 135 microA.
   * Overall power is therefore around 16 mW.

===Conclusion===

* Electrode surface area seems an important feature.
   * Most of the mud in the Tall-Mud design has been sitting here for a week, which may have an influence on community development.
   * Considering electrode area and overall volume, the compost tea design seems very productive.

===Further Designs===
   * Scale-up the vegetable+compost tea design.
   * Look for carbon electrodes, which seem more appropriate
   * Replace salt bridge with paper

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