Mixotrophic Fermentation for High Carbon Yield
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Solution Overview
Problem
Current microbial fermentation methods for producing bioproducts, such as biofuels, face challenges in maximizing feedstock conversion efficiency and minimizing CO2 losses, leading to increased operating costs and limited economic viability, particularly in autotrophic and mixotrophic fermentation processes.
Innovation Solution
A supplemented mixotrophic fermentation method involving a naturally acetogenic organism, a fermentation medium with a carbon source metabolized at a controlled rate and a non-sugar reductant like hydrogen, CO, or methanol, which enhances carbon yield and reductant efficiency, thereby reducing CO2 emissions and increasing bioproduct production, specifically ethanol, in a fermentation broth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If autotrophic fermentation is used to ferment gaseous substrates, then substrate conversion is attempted, but substrate concentration and product titer remain low, increasing isolation-related operating costs
Solution Approach 1:
The patent combines autotrophic and heterotrophic fermentation pathways into a mixotrophic system, allowing organisms to simultaneously utilize gaseous substrates (CO, CO2, H2) and organic substrates (sugars, glycerol). This merging enables the system to achieve both high substrate conversion efficiency from gases and high product titers through the synergistic contribution of both metabolic pathways.
Solution Approach 2:
The fermentation system is designed to perform multiple functions: it can ferment gaseous substrates for carbon fixation, metabolize organic substrates for rapid growth and product formation, and adjust its metabolic mode based on substrate availability. This multi-functionality allows the system to overcome the limitations of pure autotrophic fermentation while maintaining cost-effectiveness.
2Loss of substance
If mixotrophic fermentation is used to produce bioproducts, then CO2 loss is reduced, but feedstock and pre-treatment costs remain high, affecting economic viability
Solution Approach 1:
The patent optimizes key parameters including the ratio of gaseous to organic substrates, pH, temperature, and dissolved oxygen levels to maximize carbon yield while minimizing CO2 loss. By carefully controlling these parameters, the system achieves high efficiency carbon conversion without requiring expensive specialized feedstocks or complex pre-treatment processes.
Solution Approach 2:
The system utilizes readily available, low-cost substrates such as syngas from industrial processes and common sugars or glycerol. The mixotrophic organisms naturally regulate their own metabolism to optimize carbon utilization, reducing the need for expensive external intervention or specialized feedstock preparation.
3Speed
If sugar is used as carbon source in mixotrophic fermentation, then rapid metabolism occurs, but CO2 production increases, reducing carbon yield to bioproducts
Solution Approach 1:
Instead of relying solely on sugar metabolism, the system uses a partial contribution from gaseous substrates (CO, CO2, H2) to supplement carbon fixation. This partial action from alternative substrates reduces the overall CO2 production from sugar metabolism while maintaining rapid growth rates, thereby improving carbon yield to bioproducts.
Solution Approach 2:
The patent converts the harmful effect of CO2 production from sugar metabolism into a beneficial process by incorporating CO2-fixing pathways. The CO2 generated during sugar fermentation is re-fixed by the mixotrophic organisms through autotrophic pathways, converting this waste product into additional biomass and bioproducts, thereby reducing net CO2 emissions and improving carbon efficiency.
4Productivity
If non-sugar reductants (CO, methanol, H2) are added to fermentation medium, then carbon yield and reductant efficiency improve, but process complexity increases
Solution Approach 1:
The patent segments the substrate feed into separate streams: gaseous substrates (CO, CO2, H2) and organic substrates (sugars or glycerol). This segmentation allows independent optimization of each substrate type and simplifies process control, as each can be fed and regulated separately based on its specific requirements and availability.
Solution Approach 2:
The mixotrophic organism acts as an intermediary that integrates multiple substrate types and metabolic pathways. It naturally coordinates the utilization of gaseous and organic substrates, managing the complexity of simultaneous metabolism through its inherent regulatory mechanisms, thereby simplifying the overall process design and control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method achieves a carbon yield of at least 67% and reductant efficiency of over 100%, with a weight/weight ratio of ethanol to CO2 greater than 1.05, significantly improving the economic viability of bioproduct production by minimizing waste and optimizing resource utilization.
Implementation Method 1
A supplemented mixotrophic fermentation method is disclosed including providing a naturally acetogenic organism; providing a fermentation medium comprising a carbon source that is metabolized by the native form of the organism
Implementation Method 2
Mixotrophic fermentation, which therefore combines aspects of autotrophic fermentation and heterotrophic fermentation, has also been utilized for the production of bioproducts and has advantages over, for example, autotrophic fermentation. For example, mixotrophic fermentation may result in reduced loss of CO2 produced during fermentation, thereby allowing more complete conversion of an initial carbon source into acetyl-CoA and/or other bioproducts.
Data Source
AI summary
Supplemented mixotrophic method. A mixotrophic fermentation method is disclosed including providing a naturally acetogenic organism; providing a fermentation medium comprising a carbon source and a supplemented non-sugar reductant; and culturing the organism in the fermentation medium, where both the carbon source and the non-sugar reductant are metabolized and a fermentation broth is formed, which contains at least one carbon-containing bioproduct.