Microbial Fuel Cell-Raitong Organics

Abstract

A microbial fuel cell (MFC) is a device that produces electrical energy from anaerobic bacteria. The energy produced is both clean and renewable. Currently, microbial fuel cells are not economically feasible either to produce or maintain. Over a decade of research has been put into the development of microbial fuel cells, but no one has yet been able to produce a fuel cell that offers a positive return on investment.

Team 108 was tasked by Raitong Organics to develop a MFC. The team configured a design made of polyvinyl chloride (PVC), activated carbon, carbon cloth, and zip ties. The average voltage produced per fuel cell during testing was 0.148 volts, and the average current produced was 1.48 milliamp (mA). The power density of the fuel cell is 5.48 milliwatts per meter squared (mW/m2 ). The fuels cells are modular, adjustable, and easily modifiable.

Testing data indicate that our design is capable of producing enough electricity to be able to power low voltage applications. All of the customer requirements and engineering specifications required by the sponsor were met. Overall, the team demonstrated the effectiveness of our design by providing consistent data.

Introduction:

• Project Scope:

Microbial fuel cells show tremendous promise as an energy resource for the future. They’re renewable and they produce clean energy. However, there are currently no large scale microbial fuel cells in use. Researchers and engineers are hard at work, but current designs produce only very low current and therefore are not useful for most practical applications. Our team has been given the task of designing a cell for large scale use that will meet a set of customer requirements. The specific customer requirements can be seen in Table 1.

• Contributors:

Our team is composed of three group members. Madison Smith is our team’s chief analyst. He is responsible for material testing, researching, and data recording. Nicholas Saputra is the team’s chief designer. He is responsible for designing the microbial fuel cell, building a solidworks model, and assembling the prototype. Francis Dickson is the project manager. He is tasked with contacting the sponsor and advisor, planning and coordinating meetings, and overseeing the work that needs to be done.

The team’s advisor is Professor Sharp. She was given the role due to her connections with humanitarian work overseas. She is currently assisting developing countries with sustainable water and energy systems projects. She is also a professor in mechanical engineering.

Professor Liu is the team’s main source of information. She has researched microbial fuel cells for over a decade. Professor Liu teaches biological and ecological engineering at Oregon State University. She does research in sustainable energy production, environmental biotechnology, and wastewater treatment.

• Sponsor:

Our team’s sponsor is Raitong Organics Farm in Thailand. They provided the team with a budget of $1000. The team’s project mentor is Bryan Hugill. Bryan is the co-founder of Raitong Organics. Raitong Organics is a Thai social enterprise in Sisaket Province in northeast Thailand. The farm is serving as a model for farming methods that are organic and ecologically-sensitive.

Design Process:

• Process:

In order to develop a justifiable design, the team designed a technical portfolio. The work for the technical portfolio was divided into four revisions. The first revision included a team charter, a list of roles and responsibilities, a work breakdown structure, and a project schedule. The second revision included a house of quality, a list of engineering specification justifications, and a list of applicable codes and standards. The third revision included a SolidWorks, a bill of materials, and testing procedures. The fourth revision included the results and updates,

• Customer Requirements:

Using the sponsor’s expectations, the team developed a list of customer requirements. In addition, weights were assigned to the requirements so that the team could identify which requirements were most important. The weights were determined by asking the sponsor a series of questions. Table 1 shows the customer requirements and their assigned weights.

• Engineering Specifications:

The engineering specifications were determined from the customer requirements. Also, in addition to the engineering specifications, a target, tolerance, and units were included for precision. Table 2 illustrates the engineering specifications.

• House of Quality:

The house of quality was developed from the customer requirements and the engineering specifications. The importance of the house of quality is that it shows which engineering specifications are most important.

• Codes and Compliances:

After developing the house of quality, the team did research on codes to stay compliant with international law. The team primarily used the International Plumbing Code. No electric codes were required as the device is not connecting to the main grid. Instead, the MFC will connect to an existing solar panel inverter. An inverter is a device that turns direct current into alternating current.

Discussion:

• Components:

According to Professor Liu, all microbial fuel cells are composed of three components. Those three components are the anode, the cathode, and anaerobic bacteria [2]. The anode is the negatively charged component, and the cathode is the positively charged component. Batteries are also composed of three components as well. A battery is composed of an anode, a cathode, and an electrolyte bridge. A MFC is similar, however the bridge is replaced by an oxidation reaction. An oxidation reaction is a chemical reaction in which oxygen causes another compound to lose electrons.

• Anode Selection:

Professor Liu noted that the anode is the most important part of the MFC [2]. At the anode, electrons are produced by anaerobic bacteria. Anaerobic bacteria is bacteria that grows without being in the presence of oxygen. The flow of these electrons from the anode to the cathode produces electricity. Due to the fact that the anode needs to be made of a material that both transfers electrons and allows anaerobic bacteria to grow, the material choices were limited.

Professor Liu informed us of a few options that were already currently being used for the anode in her research projects. She found that a few materials work well, but none of them are economically viable for large scale power production. Among the materials that she tested, she found that carbon cloth and carbon felt were the most economically viable [2].

Despite the fact that none of the tested anodes were economically viable, the team was not able to uncover any additional materials that worked well. The team found that neither approaches suited the project well due to cost. Instead, the team found that the cathode design worked well for the anode.

• Cathode Selection:

The cathode is responsible for allowing the electrons produced at the anode to produce a current. The cathode does this through an oxidation reaction with the air. According to Professor Liu, the only material she has found that is economically viable is activated carbon [2]. Activated carbon is not sold in a form that would be useful as a cathode, however. Due to this, the team designed a cathode from scratch. The cathode consists of a wire mesh, glue, and activated carbon. The activated carbon is glued to the wire mesh to produce the team’s cathode. The reasoning behind this is that the wire mesh enhances the current, and the activated carbon allows for the oxidation reaction to take place with the air.

• Anaerobic Bacteria Selection:

The anaerobic bacteria for the MFC has to be provided by the environment. Therefore, if the MFC is placed in an environment that does not produce anaerobic bacteria then the device will not work. In addition, because not all anaerobic bacteria is the same, the fuel cell will produce different results in different locations [2].

• Power Production:

The anode is mainly responsible for power production. The team used activated carbon to attract bacteria on the anode. Activated carbon in the design finalized allows bacteria to produce electricity at a rate of 5.48 milliwatts per meter squared (mW/m2 ) [2]. In comparison, a Lumex SSL-LX5093IT LED requires 0.125 watts to power, as indicated in [3]. That means that multiple cells would have to be stacked together to increase power generation.

• Enclosure Materials:

The device will be made of a PVC housing. PVC is strong, will not corrode when exposed to sewage, and floats. The PVC will be in the form of half inch tubing. The anode, and the cathode, will both connect to the PVC housing and be lowered in the housing for the sewage.

• Sizing:

The sewage treatment facility is made up of four tanks next to each other. The size of the tanks are 1350mm (L) x 1000 mm (W) x 1000 mm (H). Four microbial fuel cells will be developed to fit each tank in order to maximize electrical output. A full scale MFC will be 1000 mm (L) x 1000 mm (W) x 1000 mm (H). There will be nine activated carbon steel mesh anodes equally spaced at 100 mm apart. The spacing ensures that the anodes do not compete for the microbes. Each MFC will therefore produce 9 mW. The prototype developed in this project utilizes much smaller dimensions. The anode and cathode of the prototype is 20 cm (L) x 20cm (W). This means that the cell constructed is roughly a fifth of the size of the full scale model.

• Capacitor:

A capacitor is an electrical storage device similar to a battery. The MFC will utilize a high voltage capacitor to insure that electricity is not being wasted when electricity is not needed. For the purpose of this report, a small capacitor, 10 microfarads, was used during testing.

• 3D Model:

After the materials were decided upon, the team developed a series of models to help illustrate the design graphically. The SolidWorks model can be seen in Figure 1.

• Mooshimeter:

A mooshimeter is a device that works like a digital multimeter and stores data to a SD card. Unlike a digital multimeter, the mooshimeter can record data generated by the MFC over a long period of time and send data to a mobile device.

3.11.Configuration:

The PVC frame will be held together by couplings. The activated carbon will be attached to a piece of steel mesh which will be one meter by one meter. The activated carbon attached to the steel mesh will represent the cathode. The additional piece will then be attached on top of the frame with zip locks. The anodes will be a steel mesh with activated carbon cut to size (one meter by one meter). The anodes will be attached lengthwise across the frame and stretched tight with a clamp. Zip locks will then connect the anode. Once the fuel cell is configured, electrical wires will be attached both to the cathode and anodes by twisting the wire on. At the end of the cathode wire, the capacitor will be connected. The capacitor will be connected by twisting electrical wires together. The fuel cell will then be ready to be connected to an inverter provided by the customer.

Constraints:

• Budget:

The team was given an assigned budget of $1000 dollars. The budget being so low, the team focused on trying to develop the lowest costing MFC possible, while still completing all of the given customer requirements listed in Table 1. The minimum cost of the materials needed to make a MFC that will power a small electrical device is shown in the bill of materials in Figure 2. This value given accounted for all the materials necessary for the completion of this project. Based on the data from Figure 2, the total cost of materials for the MFC is $117.39.

• Economic Viability:

The cost of electricity varies greatly by location. In Thailand, electricity costs 12 cents per kilowatt-hour, as indicated in [1]. The ideal MFC designed using the data collected, produces 109.6 mW, which is approximately 10.96 e-4 kilowatt-hours. The sponsor intends to use the MFC nonstop, which means, based on the cost of electricity in Thailand, it would take over 100 years for the investment on the cell to break even. That estimate assumes maintenance is not required either.

• Maintenance:

The anode and cathode needs to be replaced approximately every two years according to Professor Liu [2]. The other materials are not necessary to be replaced, but will be either recycled or trashed at the end of the microbial fuel cell’s life. The exact maintenance time was not able to be tested during the duration of the project due to time constraints.

Results:

• Testing Process:

The MFC was placed through a series of 6 tests. The tests were designed to see if the MFC met the customer requirements and engineering specifications. Therefore, the tests were scaled as either pass or fail.

• Testing Procedure 1 and Results:

Testing procedure 1 tested the ability of the MFC to continuously generate power during a 15 minute time period. To perform this procedure the MFC model was put in a mixture of 20.0L of water and 600mL of soil, which mimics the environment of the wastewater, allowing the anodes to react with the bacteria in the water. The MFC was then connected to a digital multimeter. As shown in Figure 3, the MFC cell constructed continuously generated power during the 15 minute time trial. Testing procedure 1 demonstrated the teams abilities to meet engineering specifications 2 (continuous power generation).

• Testing Procedure 2 and Results:

Testing procedure 2 tested the ability of the MFC to prevent objects from clogging the current wastewater treatment system setup at Raitong Organics. It was also deemed necessary for water to be able to go through the cell and into the system since it would not hinder the treatment process. To test this testing procedure, the team used beads to mimic the small objects that may come into contact with the wastewater treatment system. The beads were put inside a bucket that contained 1000 mL of water and than poured onto the MFC. The goal of this testing procedure is to ensure that no less than an average of 90% of water and no more than 3 beads could make it through the steel mesh. The data collected from this testing procedure is shown in Table 3. The table shows that the team’s design passed. More than 90% of the water that was poured onto the MFC was found in the bucket. Also, an average of 1 bead penetrated through the cell. All other obstacles were stopped. This addressed both engineering specification 1 and 3 (solid waste filter and unrestricted fluid flow).

• Testing Procedure 3 and Results:

Testing procedure 3 was designed to check the functionality of the anode and cathode after prolonged exposure to water. To accomplish this, a small prototype of the MFC was assembled and left submerged under the wastewater for 26 days. After 26 days, the MFC was set up and the voltage production was recorded. As shown in Figure 4, the MFC was still able to generate power after prolonged exposure in water. The only issue was that the voltage produced initially was much lower than a brand new cell. This difference could have resulted from material degradation or from the molds found on the cathode and anode surfaces. Even with these circumstance, the MFC showed continuous power generation from the trial and passed the testing procedure fulfilling engineering specification 5 (product lifetime).

• Testing Procedure 4 and Results:

Testing procedure 4 was designed to confirm the ability of the capacitor to properly store electricity. The setup of testing relied on a DC circuit which meant that the capacitor could only allow current to pass once charged. Knowing this, the input voltage was compared to the output voltage once the capacitor was charged. The average of these voltages was calculated and then compared to each initial voltage produced to see that it fell within 15% of one another. This testing procedure for the experiment was deemed a success fulfilling engineering specification 6 (capacitor presence). The results are shown in Table 4.

• Testing Procedure 5 and Results:

Testing procedure 5 was designed to check the ability of the MFC to record testing data for prolonged periods of time. A mooshimeter was selected as the recording tool and captured all the necessary data for a 3 day testing period. During that testing period the Mooshimeter collected and stored data for the trial. At the end of that testing period the data was recorded and analyzed. Figure 5 shows the data recorded. The Mooshimeter successfully recorded each data point and passed the testing procedure. By passing the testing procedure it has been shown that the MFC system designed would meet engineering specifications 7 and 8 (data collection over time and data storage on an SD card). A benefit from this large sample size was an accurate average voltage production for the MFC design. The voltage average determined from this test was found to be 0.148 volts with an average current production of 1.50 mA.

• Testing Procedure 6 and Results:

Testing procedure 6 was designed to ensure that the average time of assembly was not greater than 45 minutes. To test this each group member was timed constructing the main components of the MFC design.The main components for our construction of the MFC is the two electrodes and the frame. The two electrodes were made out of grounded up activated carbon attached to the stainless steel mesh. The average construction time from this test was found to be 27 minutes as shown in Table 5. The average time for construction of the MFC was less than 45 minutes and resulted in the design passing testing procedure 6 therefore meeting engineering specification 4 (MFC is easy to install).

Conclusion:

• Value:

The MFC is a device that produces electrical energy from anaerobic bacteria. The energy produced is both clean and renewable. However, at present, the team’s MFC is not economically feasible either to produce or maintain. Over a decade of research has been put into the development of microbial fuel cells, but no one has yet been able to produce a fuel cell that offers a positive return on investment. Unfortunately, the team’s current design is not cost effective either. Future reiterations of this project could attempt to focus on single issues within the design. This could range from electrode material selection to circuit management in order to help stabilize voltage production. Iterations like this would further the work done by Team 108 and allow Raitong Organics to further their goals of bettering the community and leading local innovation in the Sisaket province.

The results from our trials indicate that our design could be capable of producing enough electricity to be able to power low voltage applications. All of the customer requirements and engineering specifications were met. Overall, the team demonstrated the effectiveness of our design by providing consistent data.

7. References:

[1] “Electricity Charges in Thailand.” ID Card for Foreigners in Thailand, Udon Thani | Udon-News.com, udon-news.com/en/main/electricity-charges-in-thailand

[2] Liu, H. (2018, October 25). Microbial Fuel Cell Research [Personal interview].

Professor Interview

[3] “Lumex SSL-LX5093IT.” Allied Electronics & Automation, www.alliedelec.com/lumex-ssl-lx5093it/70127636/?mkwid=sFaSAw0ku&pcrid=30980760979&pkw=&pmt=&gclid=EAIaIQobChMI5-bSgbD73gIVyR6tBh2_JQEjEAYYASABEgJ_bvD_BwE.