Proof by Szeged researchers – pure hydrogen can be produced by algae in a sustainable manner

Hydrogen (H₂) is used by the oil, chemical and food industry in a large scale. At present, the substance is mostly produced from natural gas at the cost of producing huge quantities of carbon-dioxide (CO₂) during the process. Hydrogen functions as a protective or tracer gas, as well as a cooling agent. Hydrogen, which can be stored as a gas or a liquid, could be utilized as an energy source or fuel if we were able to produce it in large quantities without considerable CO₂-emission.

During photosynthesis, green algae (such as Chlamydomonas reinhardtii) produce sugars using light and water, but are also able to produce hydrogen. Concerning living organisms, theoretically this is the most efficient method for transforming sunlight into chemical energy. Naturally occurring green algae are capable of this process at a 13% efficiency rate, which is far better than biomass-based renewables.

How do algae produce hydrogen?

In natural circumstances, photobiological hydrogen production lasts only for some minutes. Green algae often get into environments lacking oxygen during the night, which triggers the production of hydrogenase enzymes. When the sun rises, hydrogen production begins. However, the large quantities of oxygen produced during photosynthesis inactivate the hydrogenase enzymes, and hydrogen production ceases.

The process of hydrogen production can be lengthened by stressing the algae, for example by depriving them of sulphur. However, this process cannot be utilized from a biotechnological point of view, as it is not effective enough. Furthermore, the lack of sulphur is such a strong stress factor that it kills cells in a few days. “Owing to these facts, it was questionable whether algae will ever be utilized for industrial hydrogen production” – says Szilvia Zita Tóth, senior research associate at the Molecular Photobioenergetics Momentum (Lendület ) Group in the Biological Research Centre in Szeged.

Single celled green algae Chlamydomonas reinhardtii under a microscope Credit: MTA BRC

“The basis of the method developed by our team is that no carbon source is provided for the algae, i.e. they get no carbon-dioxide during the hydrogen producing phase. Consequently, the electrons and protons delivered by the photosynthetic electron transport take part in hydrogen production instead of carbon-dioxide fixation. This method does not stress the algae to a great extent, and the photosynthetic apparatus works properly after several days. Additionally, it is self-evident that the method does not require an organic or an inorganic carbon source. Thirdly, this method is more efficient than the earlier method employing sulphur deprivation” says Szilvia Zita Tóth. She discussed these developments in Trends in Biotechnology together with Iftach Yacoby, the leader of the Laboratory of Renewable Energy Studies at Tel Aviv University in an article entitled Paradigm Shift in Algal H₂ Production: Bypassing Competitive Processes. The hydrogen production method developed by the Szeged research group were described in detail in an article published in Biotechnology for Biofuels in 2018.

Precision breeding and photobioreactor design

In order to produce hydrogen effectively for industrial purposes, the efficiency of hydrogen production by the algae must be maximized. To achieve this, both the hydrogen and the oxygen produced must be extracted from the alga culture as rapidly as possible. For this, a special photobioreactor is needed.

In Mediterranean desert areas, 7726 MJ solar energy arrives at one square meter annually. Using wild type alga species, if theoretical efficiency is reached, approximately 7 kilogramgs of hydrogen can be produced. However, the efficiency of hydrogen production can be enhanced by precision breeding of alga species, as reported by the study. It is an important factor that alga cultures should tolerate natural light exposure during hydrogen production.

Experiments at the Szeged Biological Research Centre are pursued in small photobioreactors. The hermetically sealed glasses are monitored for several days, measuring the level of hydrogen and oxygen production by gas chromatography. The photobioreactor volume has recently been increased. Highly concentrated alga cultures are placed in the photobioreactor as a thin film now and gas volume has also been increased. “Our latest goal is automation, so that we could measure hydrogen and oxygen production online. The next step is to build a greenhouse photobioreactor in one or two years. This is a scale change, and such a reactor must be automated, naturally” added the researcher.

Members of the Molecular Photobioenergetics Momentum (Lendület ) Group, Szilvia Zita Tóth in the mid front row Credit: MTA BRC

The scientist said her basic research interest includes photosynthesis and vitamin C metabolism. Earlier the research group proved that vitamin C affects the hydrogen production of algae. They went step by step from basic, exploratory research towards applied research. An important landmark on this route was when they filed a European Patent Application in 2017 (Valéria Nagy and Szilvia Zita Tóth, PCT/EP2018/053115). They are looking for industrial partners to be able to complete the next step.

Photobioreactor Credit: MTA BRC

“I never thought that I would once be negotiating with multinational companies about the application of my scientific results. However, if in the course of basic research new and new possibilities open up for the researcher, these should be exploited” says Szilvia Zita Tóth.

However, she warns that expectations should not be very high. They emphasized in their article that their research is still ongoing. It cannot be guaranteed that their method for hydrogen production proves to be profitable at an industrial scale, and can produce enough hydrogen for the car industry. “As for industrial production, there are several factors that cannot be foreseen. It is possible that our method proves to be useful for special purposes. Let us considre the food industry, which uses large quantities of hydrogen. Hydrogen produced by algae is extremely pure and comes from a biological source.”