Materials

The goal of this project was to use easily materials easily accessible in developing nations. To achieve that aim, old 2 liter soda bottles were used as containers, carbon rods used as electrodes, Nafion 117 as the proton exchange membrane (PEM), a phosphate buffer to maintain pH in the cathode chamber, and PVC piping and coupling. Additional materials included hot glue, tape, copper wires, and a multimeter. PEM's may be acquired naturally through chicken eggs, whereas carbon rods are found in non alkaline batteries, thus both essential materials could be acquired in less developed nations. Additionally, any plastic containers, tubes and conductor could be used. Hot glue and tape was used to hold the assembly together, but any adequate material could suffice. Finally, the multimeter was used to test the electricity generated from the Microbial Fuel Cell (MFC), but would be replaced by the target device in actual usage. Finally, the waste water used was dirty pond water taken from a creek, and the cell culture used was lactobacillus, taken from yogurt. In actual use, waste water used may be dirty sewage such as excrement and trash in water. Lactobacillus occurs naturally, especially in many dairy products. A further wide range of bacterium may also be used.

Method

Holes were cut in the same place in both soda bottles, such that a PVC attachment could be placed laterally. The two PVC segments were fed through the holes and secured using tape and hot glue to form a watertight seal. The PEM was stretched over one end of the PVC segment and then both segments were attached to each other using the coupler, thus locking the PEM in place. The Carbon rods were sanded and then soaked in distilled water to increase effectiveness. In the Anode chamber, yogurt and dirty pond water was placed inside. The cathode chamber was filled with freshwater and a 7.7pH phosphate buffer. Finally, carbon rods were placed in both chambers, and attached to wires that lead to the multimeter. The multimeter was checked every 6 hours. A video camera was set to record the multimeter at night using the lowest framerate, no sound, and low resolution, such that we could check the readings in the morning by jumping to the right time.

Control

Setup was kept in a windowless garage over a period of several days where the temperature ranged from (low) 7-9C and (high) 25-28C (13-17 April), as temperature affects the growth of lactobacillus (Siegrist). A catholyte, the phosphate buffer maintained the pH of the Cathode chamber. A small flourescent lamp was turned on next to the setup, which allowed the camera to record, and to to maintain the light level of the setup.

Additional Safety

The waste water was safely disposed of and the anode chamber thoroughly cleaned afterwards. Carbon rods were purchased as chemicals in batteries could potentially have been hazardous to health if not opened correctly.