SmartBioH2-BW – Biohydrogen from industrial wastewater and residual streams as a platform for versatile biosynthetic routes

Our approach

The biorefinery is based on two interlinked biotechnological hydrogen production processes:

• Hydrogen (H₂) and other products such as carotenoids are produced in a closed bioreactor using purple bacteria. Carbon dioxide (CO₂) is generated as a by-product.
• Carbon dioxide is fed into the connected microalgae plant. There it is bound in the algae biomass – releasing further hydrogen as well as other products such as starch. In addition to binding the carbon dioxide, the process serves to increase the hydrogen yield and expand the biorefinery's product range.

The biorefinery is to be analyzed and optimized according to ecological, economic and social criteria throughout the entire planning and development process. The project partners are developing a holistic evaluation system that can be transferred to other "biofactories" and that can be used to record the relevant environmental impacts and economic relationships.

On 3 August 2024, the demonstration plant of the SmartBioH₂-BW project was inaugurated by Dr. Andre Baumann, State Secretary in the Baden-Württemberg Ministry of the Environment, as part of his summer tour. Numerous politicians from Rheinfelden, the district of Lörrach and several members of the state parliament also took the opportunity to visit the biorefinery plant. Test operations are now starting under real conditions.

Supplying purple bacteria with light as an energy source for photosynthesis is reaching its limits in large-scale plants. Fraunhofer IGB, coordinator and project partner of SmartBioH2-BW, therefore relies on the so-called “microaerobic dark fermentation”, also known as “dark photosynthesis”, of the purple bacterium Rhodospirillum rubrum. As a result, production is not dependent on the time of day or artificial lighting and the process can be transferred more easily to a larger scale.

Microaerobic dark fermentation with Rhodospirillum rubrum

In dark fermentation, the metabolism of the bacterium is put into a special state in the dark and under microaerobic conditions (low oxygen content), in which photosynthetic membranes are formed even without light. The bacterium turns purple. Instead of sunlight, the bacteria obtain the energy required to produce hydrogen from carbon compounds. Due to the special metabolic state, a higher energy level is achieved.

This additional energy can be used to increase hydrogen production. With microaerobic dark fermentation and the decoupling of H₂ formation from light, it is possible to transfer the process more easily to larger plants.

Implementation in the SmartBioH₂ demonstration plant

In the demonstration plant in Rheinfelden, the purple bacteria are cultivated in a closed stainless steel bioreactor in the absence of light. The carbon substrate used is ethanol, which is contained in large quantities in the rinsing water produced at the site. In addition to hydrogen, further usable carotenoids, the biopolymer PHA and CO₂ are produced as by-products.

A particular challenge during operation is the precise control of the microaerobic conditions during fermentation, as the hydrogen-producing enzymes of the purple bacteria are very sensitive to oxygen.

To avoid the emission of CO₂, the CO₂ generated as a by-product in the purple bacteria module is fed to the connected microalgae plant. Microalgae biotechnology has been studied at Fraunhofer IGB for many years. Microalgae can grow photosynthetically with CO², light and inorganic nutrients, such as ammonium and phosphate, and build up biomass or storage products.

Implementation with automated compact photobioreactor 

In the SmartBioH₂ demonstration plant, microalgae of the species Chlorella sorokiniana are cultivated in a compact photobioreactor illuminated by LEDs. The reactor is characterized by a high degree of automation and offers a large volume in a small space.

The process is operated in such a way that the microalgae produce starch as a usable product from the resulting CO₂. The required nutrients come from a second waste stream produced by Evonik in Rheinfelden: ammonium chloride. 

At a later stage, the species Chlamydomonas reinhardtii will also be cultivated in this photobioreactor in order to provide the biomass for the hydrogen production step using microalgae.

Hydrogen production by means of direct photolysis

In microalgae, hydrogen is produced by direct photolysis: hydrogen and oxygen are generated from water using light energy. One of the challenges is the ongoing removal of oxygen from the system, as oxygen inhibits hydrogen production. 

A completely new type of photobioreactor developed for this purpose will be integrated into the biorefinery later in order to further increase the overall yield of biohydrogen.