What Is Algae Biomass Energy, and How Can Wakame and Kombu Play a Role?

Watanabe

Broadly speaking, algae refer to organisms—other than terrestrial plants—that primarily live in water and perform photosynthesis. One unique feature of algae is that they lack the distinct structures found in plants, like roots, leaves, and stems.

Algae are all around us in daily life. Familiar examples include wakame seaweed and kombu kelp. These are considered macroalgae because they’re relatively large. On the other hand, there are also very small types called microalgae. These range in size from just a few micrometers (µm) to a few hundred micrometers and can only be seen under a microscope.

*1 µm is one-thousandth of a millimeter.

What’s fascinating about algae is that there are species that don’t necessarily fit neatly into these definitions or characteristics. In fact, scientists estimate there are anywhere between 300,000 and 10 million species of algae in nature, yet only about 40,000 have been identified so far.

Watanabe

Algae biomass energy is a type of renewable energy that uses the oil, or bio-crude oil, found in algae cells. It’s gaining global attention as a sustainable alternative to fossil fuels.

One of its key advantages is its carbon-neutral nature. Algae absorb carbon dioxide from the atmosphere and release oxygen during photosynthesis. So, even when algae biomass is burned for energy, the overall amount of carbon dioxide in the atmosphere doesn’t increase significantly.

When people hear the term biomass, they often think of grain-based biomass made from crops such as corn. While grain biomass was popular for a time, it has a significant downside—it competes with the food supply. The more crops that are used for energy production, the less there is available as food, leading to potential price increases. Algae biomass, however, avoids this issue entirely.

In terms of productivity, algae biomass outperforms grain-based alternatives by a wide margin. For instance, a hectare of corn can produce about 172 liters of oil per year. In comparison, algae can yield approximately 136,900 liters of oil per year. While these numbers are just examples, they highlight the remarkable efficiency of algae for oil production. Our current project involves cultivating algae at a sewage treatment plant, eliminating the need to build new facilities. This approach not only reduces production costs but also makes the process more sustainable.

Watanabe

The possible applications are incredibly diverse. Algae oil can be used in cosmetics, plastics, resin products, and even animal feed. One of the most exciting recent developments, however, is its potential as a source for sustainable aviation fuel (SAF).

In fact, the Ministry of Economy, Trade and Industry has announced plans to mandate that 10% of the fuel used at Japanese airports must be SAF by 2030. This initiative is part of a broader effort to reduce carbon dioxide emissions, and it’s keeping both airlines and oil wholesalers very busy. Algae biomass is emerging as a promising candidate to help meet these ambitious goals.

Watanabe

Let me explain step by step. My journey began with studying algae in general. I’ve been researching algae for nearly 50 years, and they’re far more complex and fascinating than most people realize. They rarely get much attention, but without algae, life as we know it today wouldn’t exist.

Here’s why: algae played a crucial role in creating Earth’s atmosphere. About 5 billion years ago, the atmosphere was mostly carbon dioxide. Then, roughly 3 billion years ago, photosynthetic algae—specifically cyanobacteria—appeared, and everything started to change. Through photosynthesis, cyanobacteria began releasing oxygen into the atmosphere. Over time, this oxygen accumulated, eventually forming the ozone layer. The ozone layer shielded the planet from harmful ultraviolet rays, making it possible for life to move from water onto land.

Watanabe

Exactly. I believe that without studying algae, we can’t solve many of the pressing issues related to the global environment. In a way, algae hold the future of the Earth in their hands. Is there any research topic more compelling than this? It’s hard to simply call it “romantic” (laughs).

We started researching algae biomass around 2005. At the time, oil prices had been rising since the previous year, and there were widespread concerns that oil resources are running out. To address this, people began looking into biomass alternatives made from corn and sugarcane. However, competition with food supplies became a significant drawback for grain biomass. As discussions about alternative materials took place globally, algae biomass emerged as the only viable option.

That said, this field was virtually unexplored in Japan. So, we decided to take the lead, stepping into uncharted territory and launching our research in earnest.

Watanabe

The United States was actually the first to start researching algae biomass. After the first oil crisis in the 1970s, the US Department of Energy launched a project called the Aquatic Species Program.

The project lasted about 18 years, but eventually stalled as crude oil prices stabilized at lower levels. Even ExxonMobil, a major oil company, invested heavily in algae biomass research. However, in 2013, they publicly stated that it would take at least another 25 years before it could be commercially viable.

More recently, China has been ramping up its research efforts and expanding its presence in the field. But as with our project, the biggest challenge remains overcoming high production costs. Currently, crude oil costs around 80 yen per liter. To compete, algae-derived fuel would need to be priced at a similar level. If production costs were to reach 500 or 600 yen per liter, it would simply be too expensive for anyone to use.

Watanabe

We’re developing a system to produce algae oil using sewage treatment plants. Sewage contains large amounts of organic matter, nitrogen, and phosphorus—essentially the perfect “food” for algae. The algae consume these nutrients while performing photosynthesis, which not only helps them grow but also purifies the sewage in the process. This significantly lowers the cost of removing organic matter, nitrogen, and other waste.

In other words, it’s a win-win system that combines large-scale algae cultivation with sewage treatment. The project is based on research from the University of California, Berkeley, which demonstrated that algae oil could be produced at a cost lower than that of crude oil.

Sewage treatment plants are, of course, critical infrastructure for daily life. Japan has more than 2,000 such facilities, and studies suggest that cultivating algae in just one-third of these could yield 136 million tons of oil annually—the same amount as Japan’s yearly crude oil imports. Once the algae are cultivated, they’re concentrated into pellets and converted into oil using high-temperature, high-pressure processing.

Watanabe

When we first started, we worked primarily with Botryococcus and Aurantiochytrium. Algae oil is generally similar to edible oil, but these two species produce a hydrocarbon oil, the main component of petroleum. The extracted oil is exceptional because it can be used as fuel almost directly. On top of that, they are easy to cultivate and have high oil productivity. In a sense, Botryococcus and Aurantiochytrium are the elite algae.

However, as the project progressed, we began to encounter their limitations. These elite algae are highly sensitive to environmental changes, with their growth rate dropping significantly in colder regions with low temperatures. Maintaining optimal conditions to cultivate them incurs additional running costs. While managing them in a controlled lab environment isn’t an issue, scaling up to industrial production is not practical.

This led us to focus on indigenous algae—species naturally found around sewage treatment plants. Indigenous algae are well-adapted to the local climate and environment, which gave us the idea that they might be capable of year-round cultivation.

When we tested this hypothesis in a demonstration experiment, the results confirmed it: the indigenous algae grew steadily throughout the year. Since then, we’ve moved forward with a polyculture approach, combining elite algae with indigenous algae.

Watanabe

When that decision came through, I felt a sense of relief—finally, our efforts were recognized by the government. The funding we received was used to conduct a demonstration experiment at the Kokaigawa Tobu Wastewater Treatment Facility in Ibaraki Prefecture. The goal was to cultivate algae using primary treated sewage water, which has had most of the pollutants removed. We set up a 100-liter container and tested how well algae would grow under natural conditions. The experiment proved that algae can thrive even in water where sunlight struggles to penetrate deeply.

This project wouldn’t be possible without collaboration. We’re working alongside oil refining companies and sewage treatment plants, and as we look to scale up, we’ll need to procure a significant amount of hydrothermal liquefaction equipment, which processes the algae under high-temperature and high-pressure conditions.

Watanabe

Absolutely. After all these years, algae have become like a lifelong partner (laughs). Research has its challenges, but my passion for algae has kept me going.

Algae are everywhere on Earth, and sewage treatment plants are essential infrastructure worldwide. This means our project has the potential to be replicated not only across Japan but also globally. While we still face hurdles with production costs, if we can overcome them and make algae-based energy viable, the impact on global energy supply would be immense. By reducing competition for energy resources, we could also help prevent conflicts, making algae a potential contributor to world peace. It’s a bold idea, but considering the potential algae hold, it’s not far-fetched.