Scientists at Pacific Northwest National Laboratory (PNNL) have developed a new approach to converting solar energy, water, and CO2 into small molecule precursors, fatty acids, lipids, proteins, and other value-added products. The approach uses binary cultivation, inside photobioreactors, to facilitate growth by creating a closed system in which the metabolic by-products of one organism are used to fuel the metabolism in the other. The technology is available for licensing.
Utilization of phototroph-heterotroph binary cultures rather than mono-cultures provides a self-sustaining environment in closed photobioreactors allowing for the key metabolic processes to be optimized for maximum productivity. During the process, oxygen as well as carbon and energy source(s) for the heterotrophic organism is uniformly produced in the liquid culture, ensuring absence of shock by periodic excess or deficiency of nutrients and oxidants that conventional types of cultivation usually suffer. In turn, the heterotrophic organism consumes oxygen produced as the result of photosynthesis, thus dramatically decreasing mass transfer energy expenditure and simplifying photobioreactor design and operation.
The approach allows the utilization of various carbon sources ranging from CO2 from power plants to municipal wastes. Binary cultures also allow utilization of readily-engineered heterotrophic strains for major biotechnology products using CO2 and light instead of commodities such as glucose, sucrose, and agricultural feedstocks. Binary cultivation also provides ways to improve biomass production process using closed photobioreactor systems. Existing photobioreactors require high mass transfer to deliver CO2 into its liquid phase and remove oxygen into its gas phase, and must be opened periodically to complete the process. PNNL’s truly closed system requires less mass transfer, thus requiring less energy to optimize the system’s productivity.
PNNL’s modular photobioreactor technology and binary cultivation process is a true step change platform. It shows promise for applications including protein production, pharmaceuticals, biofuels, amino acids, vitamins, and animal foods, where its efficiency at producing useful materials could make these and other high value products less expensive. Because of the robustness of the phototroph-heterotroph association, the binary cultivation provides a novel platform for the development of consolidated bio-processing methods leading to production of carbon-neutral energy at reduced economic and energetic costs.
Advantages
- The system cost-efficiently optimizes mass transfer (CO2 delivery and O2 removal)
- The processes of photosynthesis and photosynthate conversion into a target product are spatially separated
- Designed to be compact and modular, the system eliminates the need for huge bioreactors, easing transportation and setup challenges while preserving scalability
- The process enables 100 percent consumption of carbon sources and produces no waste; the only outputs are chemicals applicable to various high value applications
- If contamination occurs in a modular system, smaller volumes allow for more efficient handling of the contaminated matter.
PNNL Photobioreactor
In addition to developing novel cultivation approaches, PNNL designed a novel cutting-edge custom light enclosure for photobioreactors that blocks ambient light from entering while providing high-intensity light using energy-efficient light emitting photodiodes. Combined with the binary cultivation, the new photobioreactor system allows precise control over the metabolic and energy status of a culture, thus dramatically increasing the light conversion efficiency and productivity.
PNNL Photobioreactor Process
Co-culturing of phototrophic and heterotrophic organisms allows for the utilization of different carbon sources ranging from CO2-enriched flue gas to municipal wastes, carbon capture, and production of value-added products. Successful growth of the binary culture is based on the production of O2 by the phototroph which supports the growth of the heterotrophic partner and subsequent utilization of the organic substrate by the heterotroph to produce a stoichiometric amount of CO2.
