Project in progress
Automated Microbial Fuel Cell

Automated Microbial Fuel Cell © LGPL

An Arduino-based chemostat controlling cell growth in a MFC (Microbial Fuel Cell). [Currently this page is a WIP, busy being updated.]

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Components and supplies

About this project

[Page still being constructed and updated]

Project Summary

Microbial Fuel Cells (MFCs) are biological batteries which are capable of converting various organic compounds and wastes into useful energy in the form of electricity. This is possible through harnessing the unique respiration pathways of electrochemically active bacteria or exoelectrogens. These bacteria are able to use metal electrodes (among other things) as their final electron acceptors. When coupled to a completed electrical circuit, this results in a battery which runs as long as there are suitable organic compounds available, including waste products from industry and agriculture. Some of the by-products of this process may also be reacted with other compounds to produce useful chemical products.

In order to make an MFC as efficient as possible, the amount of nutrients provided must be finely tuned. This is to ensure that neither too many (requires higher nutrient upkeep) nor too few (reduces yields and power output) bacteria are maintained inside the MFC. Additionally, the constant addition of reactants and removal of by-products produced by the bacteria are also important for maintaining high yields.

Introduction

Microbial fuel cells (MFCs) are devices that utilise the organic oxidation and

reduction of bacteria to produce usable electrical power. This is possible through the unique cellular respiration mechanism found in Geobacter sulfurreducens.

To harness these electrons, an MFC consists of 2 half cells;

1. An anode half-cell containing an anode;

2. A cathode half-cell containing a cathode;

3. The anode and cathode connected via a conductor;

4. The two half cells connected via a Proton Exchange Membrane (PEM).

Figure 1: A two-chamber MFC design

Microbes at the anode oxidise organic fuel, generating protons which pass

through the PEM to the cathode, and electrons which pass through the anode to an

external circuit to generate current

The reaction may be summarised as follows:

At the anode: C2H4O2+2H2O = 2CO2+8H+ +8e-

At the cathode: 8H+ +8e- +2O2 =4H2O

Problem statement and project goals

Problem statement

Large amounts of food and other organic wastes end up in sewage, and act as an untapped energy source. Energy can be generated if these wastes could be utilised. One solution to this problem, is MFC technology. Currently, MFCs are not efficient enough to be implemented on a large scale. In this project, we are automating the operations of an MFC, to optimise energy generation. This can be done through controlling viable cell counts and the flow of chemical products and reactants.

Project goals and timeline

In order to increase power outputs in a MFC, an ammeter will be integrated into the MFC to measure the amount of bacteria interacting with the anode per unit time and determine a continuous flow rate cycle for the nutrient cycle. This aims to also allow the MFC to control the viable cell count in the anode chamber, by increasing or decreasing the nutrient availability to keep cell counts at a desirable level.

Ideally, as a Minimum Viable Product(MVP), the MFC should demonstrate that it can produce more total power output for a set amount of nutrients than a control batch MFC. Additionally, the MFC should demonstrate that it is able to automatically increase/decrease viable cell counts by controlling the nutrient flow rate into the MFC.

Upon achieving the MVP, a planned expansion is to incorporate chemical product synthesis in the product chamber. This would be achieved by using a suitable chemical reactant which shows reactivity with the by-products of the MFC in the cathode chamber. A second continuous flow rate cycle, the product cycle, will be integrated into the cathode chamber, which controls flow rate according to the current flowing between the anode and the cathode chamber. The current would present an ideal rate of reaction, as equal amounts of e- and H+ come from the anode chamber to allow for reactions in the cathode chamber.

Continuous removal of products and addition of reactants will increase the equilibrium constant and result in higher yields (as dictated by Le Chatelier’s Principle). To be considered successful the MFC should demonstrate a higher product yield than a control batch MFC.

In order to achieve these goals, the following team members have been assigned responsibility and oversight for the following tasks:

Fransie Albert Streicher (BSc Chemistry&Biochemistry):

  • Source and obtain Tubing, Tube adaptors, Proton Exchange Membranes, and electrodes for the project.
  • Grow and maintain a culture of G.sulfurreducens for the project.
  • Work with Kaamil-Inaam Naicker on designing a chemical product synthesis plan once the MVP is achieved.
  • 3D printing of components for peristaltic pumps.
  • Source electronic components and their quotes.
  • Program coding and working on mathematical requirements of the project.
  • Reactor design.

Kaamil-Inaam Naicker (BEng Chemical Engineering):

  • Develop a system to control the flow rate of the continuous flow systems (eg: ml/min).
  • Working with Fransie Albert Streicher, develop methods to remove products and keep fresh medium flowing in the nutrient cycle.
  • Working with Fransie Albert Streicher, derive a mathematical model(s) which include but are not limited to describing the flow rate as a function of current readings from the nutrient cycle of the MFC.
  • Program coding and working on mathematical requirements of the project.
  • Reactor design.

Dr Tjaart Kruger :

  • General guidance/supervision/advice

Dr Michal Gwizdala:

  • General guidance/supervision/advice

A planned timeline for the project is as follows:

Custom parts and enclosures

MFC reactor1
Two compartments for the MFC, O ring slots are engraved on either side(2.5mm thick, so get a 3mm thick, 40mm diameter O ring)

look at end plate files for end plates, which go on the sides that arnt joined together.
End Plate1
These end plates are attached to the end of each MFC reactor compartment, on the side where the compartments don't touch,
End Plate2
End plate 1 is on the side with MFC reactor 1, End plate 2 is on the side withMFC reactor 2
MFC reactor2
The other half cell
Peristaltic pump housing
This component is used with a NEMA 17, 1.8DEG step, 1.7A 0.5NM stepper motor, please view the specs of your stepper motor and the one specified in this guide, if they are the same then this can also be used. This is a modified version to fit our stepper motor, the original was made by Great Scott and his guide to making a perstaltic pump can be found here: https://www.instructables.com/id/DIY-Peristaltic-Pump/

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