Team:Nanjing NFLS/Project
Currently, there are 4 common ways to treat waste water: physical water treatment, chemical water treatment, sludge treatment, and biological water treatment. There are mainly 7 ways to produce green energy: solar energy, wind power, geothermal, hydroelectricity, tide energy, bioenergy and hydrogen. A microbial fuel cell (MFC) is a device that converts chemical energy to electrical energy by the action of microorganisms [5], a rising technology to treat wastewater and produce clean electricity energy. Power output is too low compared with practical uses; shape and size of the reactors are relative large considering the unit electric power; electrodes and external circuits have high resistance; and find suitable microorganisms or a consortium of microorganisms, etc. All of these pose serious questions on the ability of MFCs for various applications. Nowadays the major bottleneck of MFC is low power generation. The anodic electron transfer pathway and mechanism offer to be the most critical and decisive players in predicating the overall efficiency and electrical performance of an MFC.[8] Therefore, in our project, we try to modify the transfer pathway in these aspects: 1) intracellular electron generation; 2) electron across the bacterial surface; 3) extracellular electron transfer to anode. We also try to improve other characteristics of MFCs, like the waste water treatment in cathode, the safety, the hardware, etc. Since MFC is a typical application integrating engineering principles and biological mechanisms, we try to extend the bioengineering application by identifying genes responsible for the three aspects above, and by overexpression to enhance the electricity output. Moreover, using overexpression methods are more reliable (do not significantly influence the gene regulation) and more less expensive (do not use additional materials but all produced by bacteria themselves). [1] “Four Effective Processes to Treat Waste Water”, from www.eponline.com, Feb 08,2018
Background
Current ways to deal with waste water
1) Physical water treatment involves processes like sedimentation, aeration and filtration. All these processes can remove solids from the water. However, the physical treatment can only deal with relatively large particles in water, and the design of expensive membrane filtration system can differ significantly. Membrane clogging is also likely to happen very often.
2) Chemical treatment utilizes oxidizing agent like chlorine or ozone to kill bacteria and prevent the bacteria from reproducing, thus purify the water. However, chemical treatment is an additive process. Adding these substances can be quite complex and require extensive jar testing. The dosages need to be fairly exact in order to properly process the influent optimally.
3) Sludge treatment includes a combination of thickening, digestion and dewatering processes, therefore make the sewage easier to dispose. However, this process needs at least three tanks to operate, and temperature changes affect the tank greatly. In addition, the cleaning of the tanks is a hassle.
4) Biological water treatment uses microorganisms to metabolize organic matter in the wastewater. It can be divided into three categories: aerobic processes, anaerobic processes and composting. The application of microorganisms for the biodegradation of organic contaminants is simple, economically attractive and well accepted by the public [1] [2] [3].Current ways to produce green energy
1) Solar energy uses polysilicon cells to convert sunlight into electricity. It’s most used in providing hot water and ventilation systems. Homeowners, businesses can both benefit from solar energy by installing a home solar system or commercial solar panels.
2) Wind power can be tapped by using wind turbines. When the wind blows, the power generated by the turbines goes to offset the need for utility-supplied electricity. But it takes a large area to build a system of expensive wind turbines.
3) Geothermal can be sourced close to the surface or from heated rock and reservoirs of hot water miles beneath our feet. Power plants harness these sources to generate electricity, but they are limited to the geological conditions and it needs to lay out tubes to transport the heat.
4) Hydroelectricity taps the kinetic energy of the river by building dams and store water in reservoirs, which has an additional use to adjust the uneven distribution of water resources in time.
5) Tidal energy, from the ebbs and flows of the tides, is a promising method, since nearly 70% of the Earth surface is covered by ocean, this method has. However, it may do unpredictable damage to the coastal zone ecosystem.
6) Hydrogen is high in energy yet produces little or no pollution when burned, while the use of hydrogen power is still limited because the current cost is quite high and hydrogen is difficult for storage[4].
7) Bioenergy is a type of energy derived from biomass and living organisms to create energy. It does no harm to the environment because it uses the surface carbon instead of the buried carbon, so it won’t emit excess carbon into the atmosphere. Under optimal conditions in living organisms, the energy transfer efficiency can to intensively high compared with traditional methods. But there is still a long way to go before massive application. The basics of MFC
Most MFCs consist of the anode, the cathode, the external circuits and the separator, just like the normal chemical fuel cell. The anode chamber and the cathode chamber are physically separated by the anion exchange membrane (AEM)[6].
In a typical MFC, microbes in anode chamber can produce electrons during the oxidation of substrate (from various carbon sources, even waste water). Subsequently, the electrons are transferred directly or indirectly to anode, and then fluxing to cathode through external wires. The protons traveled through the membrane to reach the cathode. In this way, the electrons and protons extracted during bacterial substrate catabolism combine with electron acceptors (often O2) at the cathode[7]. Current drawbacks of MFC
Our goals and how to achieve
[2] “Wastewater Treatment: Sludge Treatment and disposal”, from www.britannica.com, Jan 22, 2010
[3] “Advantages and disadvantages of techniques and used for waste water treatment”, Gregorio Crini, Eric Lichtfouse. Environmental Chemistry Letters, Spring Verlag, 2019, 17(1)
https://hal.archives-ouvertes.fr/hal-02082890
[4] “A complete guide to 7 renewable energy sources” from www.us.sunpower.com
[5] Introduction from “Microbial Fuel Cell”, Debabruta Das
[6] Introduction from “Microbial Fuel Cell”, Debabruta Das
[7] Allen, R.M.; Bennetto, H.P. (1993). "Microbial fuel cells: Electricity production from carbohydrates". Applied Biochemistry and Biotechnology. 39–40: 27–40.
[8] Wei, J., Liang, P., & Huang, X. (2011). Recent progress in electrodes for microbial fuel cells. Bioresource Technology, 102(20), 9335–9344.