Boosting Blue Carbon sequestration in marine ecosystems through seaweed and seagrass using nutrient-enriched treated sewage water

The Roots of My Commitment to Energy and Environmental Innovation

Sumikura: During my time in university, I chose electric power and high voltage as my research focus. As you may know, electric power and energy have a great impact in the world, so much so that it can even be sources of conflict. I wanted to contribute to this vital field in some way. While pursuing my master’s degree, I began job hunting with a particular focus on renewable energy research. However, at the time, “renewable energy” was not yet a widely recognized term. When I discussed my aspirations with my faculty advisor, I was told that environmental technologies hadn’t yet emerged as a viable business sector. Nevertheless, he believed that in the future, environmental technology would become indispensable—and that major heavy electric machinery manufacturers would likely play a key role in this transformation.

When I was considering a career at Hitachi, I spoke with an alumnus from my university about my future interest in the environmental field and renewable energy. At that time, there was no department at Hitachi specifically focused on environment-related themes, but I learned that the water field was closely related to environmental issues and came to focus my research on water-related topics. After joining Hitachi, I was assigned to a department specializing in water and sewerage systems. While my academic background was in electric power centered on electromagnetics, working in water treatment required knowledge of chemistry and biology fields that I had only encountered briefly during general education courses. As a result, I had to learn these subjects from the ground up.

My research journey began with sewage treatment, then expanded to reclaimed wastewater, and later to seawater desalination. I also gained experience in production engineering by working on improving a production process at a Hitachi affiliate that manufactures desalination equipment. This diverse experience has led me to my current work in technology development for the Sewage Blue Carbon Scheme.

Kenneth: After graduating from university in Malaysia and working there as an engineer, I heard from my father about scholarship opportunities offered by Japan’s Ministry of Education, Culture, Sports, Science and Technology. I decided to apply—and was fortunate enough to be accepted. As someone who loves anime, I was genuinely excited at the chance to study in Japan! [laughs]

In graduate school, I majored in energy science and pursued my doctorate degree by conducting research on renewable biomass. When I first arrived in Japan, my Japanese language skills were limited, and to make things even more challenging, the people around me spoke the Kyoto dialect, which was difficult to understand. Realizing I needed to improve my language abilities to succeed in Japan, I joined the badminton club—not so much to play badminton, but to practice Japanese! Looking back, I have many fond memories of that experience. After passing the Japanese Language Proficiency Test, I began considering a career in Japan. When Hitachi started recruiting researchers in the renewable field, I applied and was delighted to be accepted.

About six months after joining Hitachi, I was assigned to the Sewage Blue Carbon Scheme project. Although the research was quite different from what I had done in graduate school, I adapted quickly, not only because of similarities like the lab instrument operations, but also thanks to the thoughtful and thorough support from Kageyama-san in our department.

To be honest, I wasn’t quite sure what to make of the seaweed experiments at first—I didn’t even know what Blue Carbon was. Growing up in the capital of Malaysia, I had never seen or handled seaweed before. But as I progressed with the experiments and learned more, I gradually realized that this was extremely interesting and meaningful research. Many of my peers who joined Hitachi simply focus on simulations in the lab. In contrast, I spend some of my working hours out by the beach collecting seaweed—probably the only researcher at Hitachi who’s allowed to go to the beach during working hours! [laughs]

Promoting Blue Carbon capture through treated sewage water management

Sumikura: Blue carbon refers to the carbon captured by marine ecosystems and stored either on the ocean floor or in the deep sea. Seaweed and seagrasses absorb carbon dioxide (CO2) through photosynthesis, converting it into organic matter. Some of this organic matter then sinks to the ocean floor or deep sea, where it can be stored for long periods of time.

This process is part of a broader global effort to achieve carbon neutrality by 2050. Since it is impossible to reduce carbon emissions to absolute zero, the goal is to reach a balance by both reducing emissions and actively capturing carbon. Alongside improving energy efficiency, there are initiatives including converting sewage sludge into energy, expanding renewable energy use, and advancing incineration technologies; however, in many cases CO2 emissions are inevitable.

This reality has led to growing interest in negative emissions technologies—methods that remove CO2 from the atmosphere. While afforestation, or planting trees to absorb CO2, is widely known, increasing attention is being given to ocean-based carbon storage methods, namely Blue Carbon.

Compared to afforestation, Blue Carbon has a significant advantage. When trees die or degrade, the stored carbon may be released back into the atmosphere, posing a risk of CO2 re-emission. In contrast, Blue Carbon stored on the ocean floor can remain isolated for hundreds or even thousands of years, providing a more stable and long-lasting carbon sink.

Kenneth: Blue carbon accumulates in ecosystems such as seaweed forests, seagrass beds, marshes, tidal flats, and mangrove forests. Seaweed and seagrasses absorb CO2 as they grow. Moreover, the organic matter they produce contains a substance called refractory dissolved organic carbon (RDOC), which resists decomposition back into CO2, making it especially effective for long-term carbon storage.

Sumikura: In oceans with abundant seaweed and seagrass beds, there are plenty of habitats for fish to spawn and hide, which contributes to the recovery and health of the marine ecosystem. To increase these vital habitats, concrete blocks are being placed to encourage the formation of new seagrass beds. Another promising strategy involves managing treated sewage water: by carefully regulating the amount of nutrient salt such as nitrogen and phosphorus in the discharge treated sewage water, these nutrients nourish phytoplankton and seagrass, which in turn foster the growth of shellfish and fish that rely on them.

Since 2017, Hitachi has been providing an energy-efficient sewage treatment control system that uses information and communication technology (ICT) for precise prediction and regulation. This system carefully controls the air flow supplied to treatment tanks, optimizing blower operation to stabilize treated water quality while reducing electricity consumption.

The Sewage Blue Carbon Scheme aims to manage the quality of treated sewage water so that appropriate nutrient salt levels remain in the discharged treated sewage water. The scheme also involves measuring the amount of Blue Carbon absorbed by marine ecosystems, such as seagrass beds, analyzing this data, and feeding the results back to the sewage treatment plant for ongoing optimization. The goal is that, by successfully establishing Blue Carbon management and control technology, it will become possible to maintain suitable nutrients in discharged water (aligning with water quality standards) without placing undue burden on plant operators, ultimately increasing Blue Carbon sequestration.

Kenneth: Hitachi has already developed advanced sewage treatment plant control technology. Our current focus is on analyzing the impact of nutrient salts on seagrass beds and developing a system to accurately measure Blue Carbon.

Sumikura: In addition to coastal areas, we aim to utilize the foundations of offshore wind power plants farther out at sea by installing seagrass bed formation blocks, thereby creating large seaweed forests.

Developing measurement methods and clarifying the relationship between nutrient salts and seaweed growth

Sumikura: In the Sewage Blue Carbon Scheme, I am responsible for blue carbon measurement during the verification tests, working alongside Askari-san from the same research department. The measurement system must capture a variety of components, but since expertise in ocean data measurement is limited within Hitachi, we are collaborating with partner companies experienced in this field. Together, we are developing a monitoring system that leverages Hitachi’s strengths while incorporating their specialized knowledge.

Kenneth: I am conducting fundamental experiments to observe how the growth of seaweed cultivated in artificial seawater responds to the addition of nutrient salts. The goal is to gather foundational data to support the development of a Blue Carbon Cyber-Physical System (CPS). Currently, there is insufficient quantitative data on how nutrient salts in treated sewage water influence seaweed growth. Our aim is to gather this essential data and create mathematical models that can predict changes in seaweed growth rate. For example, when nitrogen levels increase by one unit, the model can quantify the corresponding increase in seaweed growth rate and ultimately estimate the increase in carbon fixation. These models will then be integrated into the CPS. Looking ahead, I hope to run CPS simulations that predict how much seaweed will grow in specific ocean areas as a result of discharged treated sewage water with elevated levels of nitrogen and phosphorus. If successful, this will enable highly accurate feedback for optimizing sewage treatment plant operations.

Because seaweed is a living organism, studying its growth requires careful attention and diligence. As we encounter various challenges, we continuously learn and refine our experimental setup. Through these efforts, we have found that seaweed grown in water enriched with treated sewage containing nutrient salts increases in weight by about 1.6 times compared to seaweed grown without added nutrients.

However, if the levels of nutrient salts remaining in the water are too high, it can trigger algal blooms, which have harmful effects on the marine environment. This highlights the importance of evaluating whether the nutrient balance is appropriate within the CPS —not only for promoting seaweed growth but also for maintaining the overall environmental health.

Hitachi’s R&D environment where involvement with people drives research

Sumikura: At Hitachi labs, we have experts across a wide range of fields. Since water is an interdisciplinary area, it draws on knowledge from many different disciplines. I believe it’s a great advantage to be part of a company where specialists from various fields are available to provide deeper insights and guidance, helping us refine our projects further.

Kenneth: One aspect I truly appreciate about working at Hitachi is the culture of openness and support. There are many helpful people around, and I’m especially grateful for how my seniors and managers patiently and thoroughly share their knowledge and experience with me.

Sumikura: I’m currently working in the same lab as Kageyama-san, Kenneth-san, and Askari-san. Although Kenneth-san’s seaweed cultivation experiments and my research on the measurement system are not directly connected, I often offer advice from my perspective as a fellow lab member.

Kenneth: Sumikura-san is always in the lab and teaches me a wide range of things. She has guided me in scientific skills, such as using various measurement instruments, as well as everyday matters like the waste separation rules. When I encounter difficulties understanding those rules, I will always ask her for assistance. [laughs]

Sumikura: During research, there are occasions when you want to use measurement instruments or other tools that your own department may not have, simply to explore different methods. At Hitachi, with its many specialized laboratories, it’s possible to conduct research by collaborating across departments—sharing instruments, expertise, and knowledge.