Euro Green Chemistry-2018-Improved Performance of Soil Microbial Fuel Cell by Adding Earthworms-Hiroshi Yukimoto-Kindai University

摘要

At present, energy demand is enhancing in the world,and it has been reported that 80 percent of the energy supplysource was formed from fossil fuels such as petroleum, coal andnatural gas in 2016. However, this energy supply sources havetroubles such as depletion of petroleum and emission ofgreenhouse gases. Under the situation, demand for renewableand sustainable energy are increasing and the alternative energysources other than fossil fuels are expected .Microbial fuel cellsare strategy that utilize microorganisms as biocatalysts todirectly alter chemical energy to electricity through theoxidization of organic and inorganic matters . MFCs can utilizewastewater and wastes as the fuel source of electricitygeneration and are expected in the current years as anapplication that can produce sustainable energy. There arenumerous kinds of MFCs, and a kind of MFC that use soil asthe fuel source is called soil MFCs (SMFCs). There are diversekinds of bacteria in the soil and the number of bacterial speciesper gram of soil is estimated to be between 2000 to 8.3 million.There exist different bacterial populations, and some bacteria inthe soil such as metal or sulfate-reducing bacteria generateelectricity in the MFCs. while the cathode rests on the surfaceof the soil. Basic principles of MFC and SMFC are same, butthe SMFC doesn’t need proton exchange membrane and it canbe low-cost and easy to be constructed. However, it is a longway to go before the SMFC is practically applied. Onedifficulty is the low power generation by SMFC operation.Numerous studies are being conducted to increase the powergeneration. It has been noticed that increased power generationwas experiential by reducing the internal resistance through theaddition of graphite powder, silica colloid or sodium chloride inthe soil. In other studies, optimization of electrode distance oraddition of substrate such as rice straw was effective for SMFCto enhance the power generation. Most studies for SMFC havebeen focused on soil composition, bacteria in the soil or on theshape and materials of device. Another method for improvingthe power generation was a hybrid system with otherorganisms, such as plants. Joining SMFCs with the rice plant inthe rice paddy field allows the electricity generation efficientlyin the daytime, but it is not at nighttime because of thephotosynthesis. We tried different hybrid systems that usesearthworms, which degrade fallen leaves or plant litter.Moreover, there have been reports that plant growth ispromoted by addition of earthworms to soil and plant pathogensare inhibited by microorganisms derived from earthworms.