Sustainable Bioconversion of CO2 to Polyhydroxyalkanoates Biopolymer by Anaerobic Mixed Bacteria in a Single-Stage Gas Fermentation (CO2BIOPOL)
Lead Research Organisation:
UNIVERSITY OF SOUTH WALES
Department Name: Faculty of Computing, Eng. and Science
Abstract
The increasing carbon dioxide (CO2) emissions are a significant contribution to global warming and climate change. The carbon capture and utilisation (CCU) strategy has emerged to convert the CO2 to carbon-based chemicals through gas fermentation to move towards a low-carbon economy. An interesting case for CCU is to produce intracellular biopolymers such as polyhydroxyalkanoates (PHA) from CO2 feedstock by anaerobic microorganisms. PHA holds several industrial and bulk applications, and it has been recognised as long-term sustainable green alternatives to petrochemical plastics since they are entirely biodegradable and biocompatible. This project is developing the concept of a novel biotech process for the sustainable bioconversion of CO2 into PHA by anaerobic mixed microbial cultures (MMC) via single-stage gas fermentation using novel high-rate gas transfer reactors. First, the project aims to investigate the appropriate anaerobic microbial communities for PHA synthesis. Secondly, intensification of PHA production conditions by selecting and controlling operating parameters along with PHA chain length elongation and medium-chain-length PHA synthesis by anaerobic MMC. Thirdly, optimised PHA production conditions will be evaluated under pilot-scale level along with cost-benefit analysis to demonstrate the sustainable long-term PHA production via single-stage gas fermentation. The proposed project is significant in terms of PHA production from renewable feedstocks (CO2) and would be an asset in the development of the bioeconomy within UK and European biotech industries. PHA production from CO2 would be an example of sustainable future clean technologies to save natural resources and energy.
Organisations
| Description | So far, anaerobic PHA production has been achieved directly from CO2 without any other carbon source, yields and efficiencies are still being evaluated. In addition, single cell protein is a co-product of the fermentations. SCP can be used for animal feed. The increasing carbon dioxide (CO2) emissions significantly contribute to global warming and climate change. The carbon capture and utilisation (CCU) strategy has emerged as a sustainable approach to convert CO2 into value-added carbon-based chemicals, fostering the transition to a low-carbon economy. One of the most promising applications of CCU is the microbial synthesis of polyhydroxyalkanoates (PHA), a class of biodegradable and biocompatible biopolymers that serve as sustainable alternatives to petrochemical plastics. This project, CO2BIOPOL, aimed to develop a novel biotechnological process for converting CO2 into PHA through single-stage gas fermentation using anaerobic mixed microbial cultures (MMC) in high-rate gas transfer reactors. The project focused on identifying suitable microbial consortia, optimising PHA production conditions, and scaling up the process for long-term sustainable production. Industrial PHA production is predominantly carried out using aerobic pure culture fermentation with high-cost sugar substrates. This project introduced an effective alternative by utilising anaerobic MMC, either in the form of natural or synthetic consortia, which require lower investment and operating costs while supporting circular economy principles. While previous studies demonstrated the potential of anaerobic MMC for PHA synthesis in wastewater treatment and other refinery processes, the bioconversion of CO2 to PHA through gas fermentation remains in its infancy. Traditionally, multiple fermentation stages are needed to produce PHA from CO2, and this project sought to eliminate this limitation by developing a single-stage gas fermentation process. Through this approach, knowledge gaps in anaerobic MMC-based PHA synthesis were systematically investigated using both natural MMC derived from anaerobic digestate and synthetic microbial consortia composed of photoautotrophic bacteria. Since CO2 is the most oxidised C1 gas feedstock, it requires an external energy source for reduction into more usable intermediates. To address this, a minor portion of H2 was introduced to support PHA synthesis in natural MMC systems. For photoautotrophic production, nitrogen gas (N2) was used for nitrification, as nitrogen-fixing purple non-sulfur bacteria (PNSB) formed the core of the synthetic microbial consortium for CO2-to-PHA conversion. A significant achievement of this project was the development of a one-stage production method for PHA using single-stage gas fermentation, which represents an advancement in microbial biotechnology. Additionally, new microbial resources, such as freshwater PNSB, were identified as promising candidates for PHA synthesis under photoautotrophic conditions. This research also opened important new questions regarding the interactions within a photoautotrophic microbial consortium and its ability to synthesise PHA using only CO2 as a carbon source. Another critical challenge identified was the competition between PHA synthesis and co-product formation, particularly methane (CH4) and organic acids, when using MMC derived from anaerobic digestate. Production of CH4 was slightly suppressed for one week when the bioprocess was amended with lovastatin, which particularly inhibits the methanogens. However, organic acid synthesis remains highly challenging and requires extensive process optimisation. Hence, the need to channel microbial metabolism away from CH4 and organic acid production toward PHA biosynthesis remains a key research focus. The project's objectives were largely met; however, several technical and methodological challenges had to be overcome. One of the primary difficulties was optimising microbial consortia that could efficiently fix CO2 while simultaneously synthesising PHA. Many naturally occurring anaerobic microbes lack direct CO2-to-PHA conversion pathways, necessitating metabolic engineering or synthetic biology interventions. Maintaining stable and selective enrichment of MMCs capable of both acetogenic CO2 fixation and PHA biosynthesis required precise control of reactor conditions, including pH, redox potential, and hydrogen partial pressure. Efficient gas-liquid mass transfer was also essential, as CO2 solubility in liquid media is inherently low. The bioconversion process heavily relied on electron donors such as H2 or organic acids, which required sophisticated reactor configurations, including pressurised systems and membrane bioreactors. Additionally, PHA accumulation is often substrate-limited under anaerobic conditions, necessitating careful feeding strategies to balance microbial growth and polymer storage. Equipment-related issues, such as delays in PHA characterisation due to the breakdown of gas chromatography instruments, also impacted the timeline for achieving specific deliverables. Despite these challenges, the research has led to notable collaborations and partnerships. During the course of the project, the research fellow established collaborations with institutions in Estonia, Poland, India, Taiwan, and South Korea, leading to the submission of a consortium project worth 3.5 million euros to the European Commission. Furthermore, increased research capability was achieved through specialised training in state-of-the-art methodologies at the host institute, including C1 gas fermentation, anaerobic bioprocess design, and advanced analytical techniques such as gas chromatography (GC/FID, GC-TCD, GC-FPD), ion chromatography, ICP-MS, CHNSO analysis, and online Fourier transform near-infrared (FT-NIR) spectroscopy. A review article titled "Autotrophic Bacterial Production of Polyhydroxyalkanoates Using Carbon Dioxide as a Sustainable Carbon Source" was submitted to Frontiers in Bioengineering and Biotechnology, and an additional research article is currently in preparation based on the project's findings. Looking ahead, the findings from CO2BIOPOL provide a strong foundation for future advancements in CO2-based PHA production. The research has demonstrated the feasibility of converting CO2 into bioplastics through single-stage gas fermentation, a significant step toward industrial application. To further develop and commercialise this technology, the research fellow has applied for the Green Future Fellowship to bridge the gap between laboratory research and industrial-scale implementation. Scaling up this process will require the utilisation of industrial CO2 off gas, ensuring sustainability and economic viability. Engaging industry stakeholders, conducting techno-economic assessments, and regulatory evaluations will be critical in advancing CO2-based bioplastic production. Ultimately, this research contributes to a sustainable bioeconomy by promoting clean biotechnological solutions to mitigate CO2 emissions while producing environmentally friendly bioplastics. |
| Exploitation Route | CO2 can be sourced from numerous sectors. PHA can be utilised for sectors such as packaging, medical, cosmetic, energy etc. PHA is a sustainable biopolymer with good biodegradability efficiencies in numerous environments. PHA can be biochemically recycled. SCP can be used for animal feed. |
| Sectors | Agriculture Food and Drink Chemicals Energy Environment Healthcare Manufacturing including Industrial Biotechology Pharmaceuticals and Medical Biotechnology |
| Description | In other research applications in collaboration with potential future partners. |
| First Year Of Impact | 2023 |
| Sector | Agriculture, Food and Drink,Chemicals,Manufacturing, including Industrial Biotechology |
| Description | Biotechnologies Delivering Circularity and Net Zero. Promoting Women in STEMM and gender equality, Wales in India, 25th November 2024 |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Present the R&D and impact delivered related to Biotechnologies Delivering Circularity and Net Zero. Presented at the event entitled 'Promoting Women in STEMM and gender equality', Wales in India, 25th November 2024 |
| Year(s) Of Engagement Activity | 2024 |
| URL | https://www.wales.com/news/india/webinar-promoting-women-stemm-and-gender-equality |
| Description | Biotechnologies Driving Circular Economies and Net Zero. Welsh Secretary of State Event. Welsh Research and Development Reception. Lancaster House, London, 17th October 2023 |
| Form Of Engagement Activity | Participation in an activity, workshop or similar |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Policymakers/politicians |
| Results and Impact | Presentation: Biotechnologies Driving Circular Economies and Net Zero. Welsh Secretary of State Event. Welsh Research and Development Reception. Lancaster House, London, 17th October 2023 |
| Year(s) Of Engagement Activity | 2023 |
| URL | https://www.gov.uk/government/news/welsh-universities-showcase-cutting-edge-research-and-innovation |
| Description | Introduction to Gas Fermentations R&D. Environmental Biotechnology Network and Carbon Recycling Network. Gas Fermentations Workshop, Manchester 27-28th March 2024 |
| Form Of Engagement Activity | A formal working group, expert panel or dialogue |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Other audiences |
| Results and Impact | Gas Fermentations Workshop, to introduce USW R&D work on Gas Fermentations R&D to a high profile academic/private sector audience. The event was organised by the Environmental Biotechnology Network and Carbon Recycling Network. Manchester 27-28th March 2024 |
| Year(s) Of Engagement Activity | 2024 |
| URL | https://ebnet.ac.uk/wp-content/uploads/sites/343/2024/07/Joint-GF-wkshop-Combined-report-v2.pdf |
| Description | Technologies Delivering Circularity and Net Zero, Delegation from Bavaria Visit to the Hydrogen Centre, University of South Wales, Baglan, 16th January 2025 |
| Form Of Engagement Activity | Participation in an open day or visit at my research institution |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Introduce our R&D Activities to a Delegation from Bavaria. Others present including Welsh Government officers.Technologies Delivering Circularity and Net Zero, Delegation from Bavaria Visit to the Hydrogen Centre, University of South Wales, Baglan, 16th January 2025 |
| Year(s) Of Engagement Activity | 2024 |
| Description | Turning Wastes Into Resources. Academic Delegations from Vietnam Visiting Welsh Universities USW 16th May 2023 |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Other audiences |
| Results and Impact | Presentation to academic colleagues from Vietnam entitled 'Turning Wastes Into Resources'. 16th May 2023. |
| Year(s) Of Engagement Activity | 2023 |