Innovation in Seaweed Cultivation to Build a Recycling SocietyIzuru Senaha
＜Series 2 / complete＞
Previously, we talked with Professor Senaha of the University of the Ryukyus, Faculty of Engineering, about utilizing CO2 as a renewable energy source and the state of manufacturing in Okinawa. Part 2 discusses Professor Senaha’s life work, the Project for seaweed cultivation using CO2 dissolution equipment.
Born and raised in Okinawa, he stayed there to continue his studies and research. This dedication to his home prefecture enabled him to make his ideas become reality. We asked Senaha about the circumstances that started this project.
Development of CO2 Dissolution Equipment
First, I want to talk about the CO2 dissolution equipment. So, thermal power plants produce gas emissions. You can trap that exhaust inside a pressurized tank, then spray seawater mist inside. More and more seawater dissolves into the CO2. This gas is mostly composed of CO2 and nitrogen, and the rest is a variety of other chemicals. CO2 dissolves into water more easily than those other gases, and that characteristic means a solubility of 30 times or more. It dissolves into water at least 30 times faster, which allows us to capture just CO2 in a short period of time, as if we were selecting gases.
We tried many methods, through trial and error, and the results was the invention of our CO2 dissolution equipment, which sprays a mist of sea water into exhaust gas to capture CO2. Our dissolution equipment allows us to capture CO2 in a compact and efficient way. Trials conducted at thermal power plants in Okinawa showed a near 100% capture of CO2 from emissions gas into seawater.
However, there was a problem with the development of this equipment. Even if you capture CO2 and trap it inside seawater, you’re basically making carbonated water, so the CO2 is eventually going to escape. That got us thinking about the ideal way to trap CO2, which is to store it inside plants. We also wanted to do something for the sake of Okinawa, which is surrounded by the ocean. That led us to investigate growing seaweed with the CO2 in the seawater to trap it.
Demonstrating the Carbon Recycling System
Right around that time, the Ministry of Economy, Trade & Industry selected us as an incubator project that would reveal the seeds of technology for building a low-carbon society. METI wanted to explore the concept of a complete cycle system that would utilize CO2-grown seaweed as biofuel. In 2012, we performed proof-of-concept trials for 6 months.
These trials demonstrated the potential of the “System for CO2 reduction and reuse of greenhouse gas using marine biomass” by capturing CO2 from gas emissions and using it to cultivating seaweed for biofuel.
Unfortunately, with our current carbon recycling system, the production of biofuel requires 10 times more energy input. We fulfilled METI’s goal of biofuel production, but in reality, I am sorry to say that a carbon recycling system that produces biofuel just isn’t going to happen in real life yet.
Building a Recycling Society
We also found problems related to seaweed cultivation. Current cultivation methods require an enormous amount of energy. As part of the carbon recycling system, the portion of energy required for seaweed cultivation was huge, I would say at least 50%. In other words, if we could reduce the energy required for seaweed cultivation, then we would immediately become closer to realizing biofuel production using carbon recycling systems.
Seaweed peaks around May, so we were frequently pumping more seawater for our seaweed to match that schedule. This process uses so much energy. Fishing and aquaculture industries in Okinawa simple hadn’t considered low-energy methods of seaweed cultivation.
Recycling societies require the creation of systems with stable, low-energy operation. We realized the need to initiate innovation in seaweed cultivation, so we began a project to investigate the mechanization of seaweed cultivation.
From the very beginning, Professor Senaha thought of a process to capture CO2 from gas emissions using CO dissolution equipment, then storing it inside of seaweed. However, the production of biofuel from seaweed requires spending energy. Systems for a true recycling society remain unknown and unverified because there are still many hurdles blocking practical implementation.
Next, Part 3 discusses Professor Senaha’s attempts at innovation in seaweed cultivation.
Interview Date: December 18, 2018
Innovation in Seaweed Cultivation to Build a Recycling Society
Born 1967 in Okinawa. Graduated 1991 from the University of the Ryukyus, Faculty of Engineering, Energy and Mechanical Engineering Department. Continued at the University of the Ryukyus as an assistant after completing his MS Mechanical Engineering in 1993. Awarded PhD Engineering from Nagoya University Graduate School of Engineering in 2001. Returned to the University of the Ryukyus as an associate professor of Engineering in 2006, and accepted a position as full-time professor in 2018. Began research on CO2 reduction and utilization using marine biomass in 2009. His current research project is investigating the early development of seaweeds like sea grapes (umibudo) and Nemacystus decipiens (mozuku) through cooperation with a diverse spectrum of other research institutes to contribute to fields of industry in Okinawa.
Awards & Honors (Selected)
・2009 Contribution to Society Award
・2010 Faculty of Engineering Contributor Award
・2010 IMPRES 2010 Best Poster Award
・2013 Rocky Challenge Award
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