Sustainable biohydrogen production coupled with CO2 capture: the BiH2 biorefinery approach

The global transition toward a low-carbon economy demands innovative strategies that simultaneously address energy production, resource efficiency, and agricultural sustainability. This doctoral research explores the development and application of the BiH₂ technology, an integrated biorefinery platform designed to couple sustainable biohydrogen production with carbon dioxide capture and valorization into high-value co-products. The BiH₂ process is structured into two synergistic phases: (1) dark fermentation using Clostridium beijerinckii DSM 34075, which generates biological hydrogen and valuable co-products such as the fermentation broth (BEFB) enriched with peptides, organic acids, and mineral nutrients; and (2) acetogenic fermentation, which biologically converts CO₂ into additional organic acids through the Wood–Ljungdahl pathway, thereby enhancing carbon efficiency. This dual approach exemplifies a circular bioeconomy framework by transforming both organic substrates and gaseous emissions into renewable energy and value-added compounds. A major focus of this research was the characterization and agronomic evaluation of BiH₂-B, a cell-free biostimulant derived from Phase 1 of the process. Comprehensive chemical analyses confirmed the presence of bioactive molecules and essential nutrients without detectable contaminants. Field trials in apple orchards demonstrated improved fruit weight, dry matter content, and delayed ripening, while controlled chamber experiments revealed that BiH₂-B significantly enhanced stress tolerance in tomato and pepper crops. Specifically, applications at moderate doses (12–15 L ha⁻¹) improved chlorophyll content, biomass accumulation, and reduced tissue damage under cold stress conditions, without phytotoxic effects. The results demonstrate that BiH₂ technology not only provides a sustainable pathway for hydrogen production but also delivers multifunctional agricultural inputs that can mitigate climate-induced abiotic stresses and reduce reliance on chemical fertilizers. This research contributes to bridging renewable energy systems with climate-smart agriculture, positioning the BiH₂ platform as a transformative model for future bioeconomy strategies.