Green hydrogen based succinic acid and biopolymer production in a biorefinery: Adding value to CO2 from acidogenic fermentation

Dark fermentative biohydrogen (bio-H2) production is usually associated with the formation of CO2 and organic acids as by-products. Although bio-H2 is an attractive low-carbon renewable fuel, generation of CO2 during production limits its use in certain applications. Nevertheless, these gases can be used for the production of various chemicals and materials, which are currently being manufactured from fossil carbon feedstocks. Therefore, in the present work we report an integrated approach for effective utilization of this bio-H2 and CO2 generated during acidogenic fermentation (AF) for the production of bio-based succinic acid (SA) using bacterial strain C. amalonaticus. In addition, the organic acids generated in the effluent after AF were converted into polyhydroxyalkanoates (PHA) using enriched mixed microbial consortia. Results show that continuous supply of CO2 positively affected SA production (14.7 g L-1) in comparison to control operation (12.07 g L-1) where CO2 was supplied at the beginning of the cycle. Bio-H2 acted as an effective electron donor for the formation of reduced end product, SA. The organic acids were effectively utilized and 23 gPHB/g DCW (dry cell weight) was achieved. Among the acids acetic acid was consumed in major proportion followed by butyric and valeric acids. The biopolymer obtained was a homopolymer of polyhydroxybutyrate (PHB), which was confirmed using FTIR analysis. The biopolymer also depicted good thermal properties, which was analyzed by TGA, DSC and DTA analysis. This work represents a successful attempt to develop an integrated system capable of simultaneously producing biobased SA and PHA, both, valuable bio-based products with a huge market potential.

Automated summary

This study presents an integrated approach for utilizing bio-H2 and CO2 produced during fermentation to produce bio-based succinic acid and polyhydroxyalkanoates efficiently. The results show that continuous supply of CO2 positively influenced succinic acid production, while organic acids were effectively converted into biopolymer with good thermal properties. This integrated system offers the potential to simultaneously produce valuable bio-based products with a huge market potential.