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We humans have not yet been able to make effective use of renewable biological resources (i.e., biomass). Waste biomass generated by human activities (food waste, livestock manure, sewage sludge, black liquor from paper mills, inedible parts of crops, fishery waste, etc.) and unutilized biomass ( trimmed grass, invasive species, stranded fish/plants/weeds, etc.) have potential to be converted into various resources such as energy, fertilizer, feed and value-added bioproducts. Establishing technologies to convert biomass into resources is indispensable to reduce the environmental impact and develop a resource-recycling society.

Our lab studies environmental biotechnology which utilizes the microorganisms to convert waste biomass into valuable resources. As waste biomass contains a large amount of microorganisms, this process is inevitably not a pure culture system but a complex microbial system with hundreds to thousands species of microorganisms interacting in a complex manner. Our lab is attempting to elucidate the dynamics of these systems using an integrated approach of microbial engineering and bioinformatics, which has been rapidly developing in recent years. We aim to contribute to the construction of a recycling-oriented society by making environmental biotechnology faster, more economical, smaller, and easier to use.


The strength of conducting this research from Nagasaki

Nagasaki Prefecture is a region with a thriving agriculture, forestry and fisheries industry. In particular, In particular, the prefecture ranks second in Japan after Hokkaido in terms of marine fisheries and aquaculture production and output (Source: Nagasaki Prefecture Fisheries Promotion Basic Plan 2021→2025). In Nagasaki, we can work together to build a regional recycling-oriented society in close cooperation with agricultural and fishery businesses. In other words, this is a suitable place to conduct research on technologies to convert agricultural and fishery waste biomass (livestock waste, leftover feed, sludge, and various other organic solid wastes and organic wastewater) into resources. We hope to use our research findings to improve the agricultural, forestry, and fishery industries to make it more sustainable (both locally and globally).

​Research projects conducted so far

Novel ammonia fermentation of aquaculture pond sludge


​Research results (peer-reviewed papers)

In shrimp farming, food and excrement accumulate as sludge, which deteriorates water quality and causes shrimp diseases, thus the sludge must be removed and properly treated. In developing countries, conventional treatment such as composting has achieved certain results, but the product, compost, is inexpensive and therefore not profitable, resulting in an increase in illegal dumping of sludge. Therefore, there is a need to develop a system with high economic incentives. Conventional composting research has focused on maximizing nitrogen retention to increase crop nutrition. However, nitrogen is easily lost through ammonia volatilization and denitrification. Also ammonia emission causes odor problem. In response, we proposed a new ammonia recovery composting system that maximizes the recovery of ammonia gas, i.e., ammonia fermentation, based on the opposite concept. Since ammonia gas is a "clean nitrogen source" that contains no waste/wastewater, it can be used to produce high value-added algae that cost thousands of dollars per kg for raw materials for health supplements. Furthermore, a large amount of CO2 is generated in the process of decomposing organic matter in sludge, which can be supplied as a carbon source for algae, and at the same time, the fermentation residue, or compost, can be used as a soil conditioner. Maximizing ammonia recovery in composting is a novel approach in this field. In this research, we investigated the optimal temperature for accelerating ammonia fermentation, the operation that promotes ammonia volatilization without inhibiting microorganisms, and the microorganisms and enzymes that promote sludge solubilization. 

Robust methane fermentation to substrate load fluctuations


​Research results (peer-reviewed papers)

Anaerobic Digestion (AD) is an environmental technology that uses a complex microbial system to convert organic waste with high moisture content into energy (methane) and nutrients (liquid fertilizer) under anaerobic conditions. Since the daily throughput of raw materials such as food waste fluctuates greatly, a sudden high organic load, or load shock, to the AD fermenter can cause fermentation system to become unstable or fail. For this reason, full-scale systems have been operated at low loads with excessively large facilities by applying excessive safety factors. If a stable AD process can be constructed against these large load shocks, it will be possible to downsize the system. However, it has not been clear whether AD microbiome can withstand repeated load shocks and whether AD microbiome can be resilient to load fluctuations (i.e., repeated load shocks). In this research, we investigated the effects of repeated organic loading shocks on the microbial community of AD, and revealed changes in microbial community composition, metabolic pathways, and microbial networks. Furthermore, we established a method to construct a microbial community that is resilient to AD loading shocks.

Highly efficient methane fermentation of overgrown aquatic plants


The social problems caused by overgrown aquatic weeds have become more serious in Japan and abroad over the past 20 years, and the problems include ecosystem disturbance, foul odor, fishery disturbance, decline in tourism value, and inappropriate recreational use. We have conducted joint research and development on the construction of a recycling-oriented society in Lake Biwa, which is based on the conversion of aquatic weed biomass into resources through AD. In collaboration with researchers from ecology and limnology, we worked on establishing aquatic weed management standards (i.e., establishing the appropriate amount of harvesting aquatic weed) to maintain a healthy aquatic ecosystem, as well as the basic technology to effectively utilize the harvested aquatic weed biomass for AD and microalgae production. More specifically, we have clarified/developed the key parameters determining the methane production from aquatic weeds, a novel AD system that decomposes the easily degradable fraction (i.e., cytoplasm) and hardly degradable fraction (i.e., cell walls) of aquatic weeds at different retention times, enhancing methane yield by alkaline hydrolysis of the hardly degradable aquatic weed by degrading lignin, inhibition and acclimatization of AD microorganisms to the pretreatment by-products, and the effect of dissolved Inhibition and acclimation of AD microorganisms to dissolved lignin, a pretreatment byproduct.

Other research projects conducted in joint research, etc.

  • Search, inoculation and dynamic analysis of useful microorganisms for accelerating composting 

  • Highly efficient cultivation of microalgae using nutrients recovered from organic sludge 

  • Removal of nutrients from organic wastewater by microalgae and high efficiency of algal biomass production 

  • Search for oil-degrading bacteria in methane fermentation of oil-containing wastewater

  • High activation of hydrogen-fermenting microorganisms by adding metal nanoparticles

  • Removal of pretreatment by-products in bioethanol fermentation using non-edible parts of crops as raw materials

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