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 from carbon cultivation sites while producing crops. In addition to this, there is a need to establish a supply chain based on a new venous industry that processes difficult-to-use waste from fuel production and materials development and also produces valuable products from the waste. In addition, the new carbon cycle based on sustainable cultivation must be accompanied by a parallel cycle of nitrogen and phosphorus, since nutrient components such as nitrogen and phosphorus are intertwined with the new carbon cycle. In light of the above, it can be said that the construction of technologies to reduce greenhouse gases from rice paddies and the establishment of innovative waste recycling systems that create new environmental values, including healthy circulation of nitrogen and phosphorus (SDGs 12.3-5), are essential to achieve greenhouse gas reduction and a recycling-based society based on carbon cultivation. To achieve these objectives, the following five research items will be addressed in Issue
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, IoT and machine learning water-saving water management will also work 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
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, municipal raw garbage, and waste from the livestock and food industries. The proportion of organic matter and nitrogen that is biased toward each 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 absorbents
Carbonize methane fermentation residues and develop adsorbents that adsorb and collect nitrogen and phosphorus. By submerging this adsorbent in barn wastewater containing high concentrations of nitrogen and phosphorus, it is expected to retain high concentrations of nitrogen and phosphorus. 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, heating, such as drying, is required to produce carbides. This process consumes energy, and there are concerns that it 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.
