CO₂ Valorization Technologies
Case Study 3 progress update on bioproduct recovery from CO₂ and digestate at pilot scale
Quick recap
In this blog, we provide a concise overview of the progress made toward the commissioning of CS3, one of the three European Biomethane Innovation Ecosystems (EBIEs) developed within the SEMPRE-BIO consortium.
Regarding CO₂ valorization, we tested two technologies:
- Hybrid fermentation to produce valuable biochemicals (succinic acid) and biopolymers.
- Microalgae and purple phototrophic bacteria (PPB) for alternative protein production.
These biotechnologies aim to recover the waste streams from the anaerobic digestion process of CS-III, i.e., CO₂ from biogas upgrading and the liquid fraction of digestate.
Key Milestones Achieved
Several important milestones have now been reached:
Equipment installation and start-up
Both CO₂ valorization technologies have been implemented at pilot scale (TRL-7).
A 50-L hybrid fermenter coupled to an intensive mass transfer unit (IMTU) has been designed and installed at UVIC’s facilities to produce succinic acid and biopolymers from CO₂.
Regarding microalgae, a 600-L solar photobioreactor (sPBR) has been built for outdoor microalgae cultivation at UVIC, whereas INNOLAB has installed a 1250-L conventional photobioreactor (cPBR) to cultivate green microalgae inside a greenhouse (under artificial illumination).
At UVIC, a 100-L vertical PBR has also been installed for the cultivation of PPB under anaerobic conditions.
Lab scale processes optimization
UVIC has studied the fermentation process at lab-scale for biopolymers and organic acids production. These results have been used for upscaling the process (under evaluation).
UVIC has also studied the cultivation of PPB at lab-scale, obtaining promising results.
Preliminary results on the pilot-scale operation
Through research and experimentation, UVIC and INNOLAB fine-tuned their cultivation methodologies to ensure maximum photosynthetic efficiency when growing in synthetic medium. The use of liquid fraction of digestate and CO₂ from a local biogas facility is under evaluation.
Analysis of the amino acid profile of microalgae
A study has been conducted to ensure that the quality of the cultivated protein is adequate for feeding applications. The biomass from different strains has been tested under both synthetic growth media and digestate conditions.
Evaluation of the digestibility potential of microalgae biomass
The biomass produced in SEMPRE-BIO is being evaluated by simulating the digestibility of their biomass by farm animals.
Next Steps
The next steps of CO₂ valorization technologies focus on optimising the biological processes:
- For the hybrid fermenter, improve the gas-liquid transfer to increase the productivity of succinic acid from CO₂, and liquid fraction of digestate (UVIC)
- Improve the production of microalgae and PPB biomass grown in the liquid fraction of digestate and recovered CO₂ (UVIC, INNOLAB)
- Increase scientific knowledge of the photosynthetic performance of green microalgae under the growing conditions of SEMPRE-BIO project.
- Further optimise the processes
- Complete the analysis of amino acid profiles and digestibility potential of microalgae and PPB biomass.
Long-term Vision
SEMPRE-BIO’s mission is to increase the feasibility and sustainability of anaerobic digestion systems. Anaerobic digestion is a well-established technology with high production potential in Europe, playing a key role in the decarbonisation of the energy sector. However, dealing with its sub-products (residual CO₂ and digestate) is challenging and implies limited deployment of this type of facilities.
Hybrid fermentation or cultivating microalgae/PPB using CO₂ as carbon source and digestate as source of nutrients is a green and sustainable solution to close the nutrient and carbon loops of the digestion process, obtaining added-value bio-product (alternative protein and succinic acid) as by-product, thus minimising socio-economic and environmental impacts.
This solution transforms conventional anaerobic digestion plants into novel biorefinery units where different conversion processes are integrated to obtain multiple bioproducts, with the goal of maximising profitability and reducing waste. This solution opens new business opportunities by closing the loop in the agri-food sector, obtaining energy and feed sources from agri-food wastes.
Preliminary results are promising, and work is ongoing on the optimisation of the production processes. The main barriers to developing a business plan are legislative and social. We are working on developing risk management plans to ensure that the production of alternative protein is safe, as well as on integrating this technology into innovative certification schemes. These instruments can increase the market potential of the solution by providing reliable and transparent information on the characteristics and origin of the feedstocks and bio-products, with the goal of increasing consumer acceptance.
For more information, check the CO₂ valorization video here:
Author: Josué González
Editorial: Lucía Salinas and Laia Mencia
Date: May, 2026
This project has received funding from the European Union’s HORIZON-CL5-2021-D3-03-16 program under grant agreement No 101084297. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the granting authority can be held responsible for them.
