To realize a carbon-recycling society based on sustainable cultivation, it is necessary to reduce greenhouse gases such as methane and nitrous oxide (N₂O) generated in crop production at carbon cultivation sites. Additionally, there is a need to establish a supply chain based on a new industry for turning waste into reusable resources (“venous industry”), which will process difficult-to-use waste from fuel production and materials development to create valuable products. Moreover, the new carbon cycle based on sustainable cultivation must be accompanied by a parallel nitrogen and phosphorus cycle, since such nutrient components are intertwined with the new carbon cycle. In light of the above, it will be essential to develop technologies to reduce greenhouse gases from rice paddies and establish innovative waste recycling systems that create new environmental values, including healthy circulation of nitrogen and phosphorus (SDGs 12.3-5), in order to accomplish greenhouse gas reduction and a recycling-based society based on carbon cultivation. To achieve these objectives, the following five research items will be addressed.
Reduction of greenhouse gas emissions in rice cultivation by integrating water management with the application of fermentation residues and carbides
Targeting rice paddies as sites for carbon cultivation, we will promote research on paddy rice cultivation methods that minimize greenhouse gas emissions. Specifically, we will integrate methods of fertilizer application using fermentation residues and carbides, as well as water-saving management methods that incorporate IoT and machine learning. The biomass to be applied is the residue from the decomposition of organic matter contained in rice straw by anaerobic microorganisms (fermentation residue) and carbide made from the fermentation residue, which is effective in reducing CO₂ and CH4 emissions. In addition, water-saving water management that harnesses IoT and machine learning will also serve to reduce N2O emissions. By integrating methane fermentation residue and carbide with appropriate fertilizer application and water management, we aim to significantly reduce methane and N₂O emissions during rice cultivation.
Establishment of high-efficiency biogas recovery technology from mixed waste such as biomass utilization residue and livestock waste
We will establish methane fermentation technology to generate and recover methane at high efficiency and high speed by mixing herbaceous biomass such as rice straw harvested from rice paddies, raw municipal garbage, and waste from the livestock and food industries. The proportion of organic matter and nitrogen that is biased toward each type of biomass is adjusted by mixing different waste sources to achieve high efficiency in methane fermentation. Anaerobic fermentation produces carbon dioxide and methane, and we aim to develop a methane fermentation system combined with a gas separation membrane capable of concentrating methane. High-purity methane gas will be used as a raw material for power generation and valuable products.
Establishment of technology to utilize methane fermentation residues as carbon adsorbents
We aim to carbonize methane fermentation residues and develop adsorbents that adsorb and collect nitrogen and phosphorus. Submerging such adsorbents in barn wastewater containing high concentrations of nitrogen and phosphorus is expected to retain high concentrations of these elements. We will evaluate the effectiveness of the adsorbent with concentrated nitrogen and phosphorus when applied to paddy fields, its performance as a slow-release fertilizer, and its contribution to reducing methane emissions during paddy rice cultivation. On the other hand, drying or other forms of heating are required to produce carbides. Such processes consume energy, and there are concerns that they may lead to CO₂ emissions. As a way to avoid such concerns, we will consider a carbonization system that uses waste heat from biogas power generation. The new system will aim to reduce the consumption of fossil fuels. In addition, we will work on reforming adsorbents. Biomass-derived carbide has excellent ammonia adsorption capacity, but its performance for phosphorus adsorption needs to be improved. Therefore, we are working to improve the ammonia.
