Microalgal Lipid Production Using Light-Dark Recirculation
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Solution Overview
Problem
Existing processes for microalgal lipid production are not economically viable and face challenges in optimizing lipid accumulation while simultaneously removing carbon dioxide from biogas and ammonia nitrogen from digestate, as optimal conditions for these processes do not coincide.
Innovation Solution
A process integrating light/dark cycles through intermittent recirculation between a growth reactor and a shielded absorption column, optimizing conditions such as hydraulic retention time, recirculation flow rates, and gas flow rates to enhance lipid accumulation, carbon dioxide removal, and ammonia nitrogen removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If microalgae are subjected to nitrogen starvation to stimulate lipid accumulation, then lipid production increases, but growth rate decreases and cultivation becomes less economically viable
Solution Approach 1:
The patent implements periodic light/dark cycles by intermittently recirculating culture between a photobioreactor (light phase) and a dark tank (dark phase). During light phases, microalgae perform photosynthesis and grow; during dark phases, lipid accumulation is stimulated. This periodic alternation allows the system to achieve both growth and lipid production, resolving the contradiction between growth rate and lipid accumulation that occurs under continuous nitrogen starvation.
2Productivity
If the photobioreactor is optimized for carbon dioxide uptake, then CO2 removal efficiency increases, but conditions for maximizing lipid accumulation are not met
Solution Approach 1:
The patent divides the cultivation system into two distinct functional units: a photobioreactor optimized for CO2 uptake and photosynthesis, and a separate dark tank for lipid accumulation. By segmenting the system, each component can be optimized for its specific function without compromise. The photobioreactor operates under conditions maximizing CO2 removal, while the dark tank provides conditions optimal for lipid production.
Solution Approach 2:
The system uses periodic recirculation between the photobioreactor and dark tank to alternate between CO2 uptake phase and lipid accumulation phase. During light phases in the photobioreactor, CO2 is efficiently removed; during subsequent dark phases in the tank, lipid accumulation is maximized. This temporal segmentation through periodic action allows both functions to be optimized.
3Quantity of substance
If light/dark cycles are implemented through intermittent illumination of the growth reactor, then lipid accumulation increases, but the process becomes more complex and less economically viable
Solution Approach 1:
Instead of complicating the photobioreactor with intermittent illumination systems, the patent segments the system into a photobioreactor and a separate dark tank. The light/dark cycle is achieved through spatial separation and fluid recirculation rather than temporal illumination control, significantly reducing device complexity while maintaining lipid accumulation benefits.
Solution Approach 2:
The patent introduces a dark tank as an intermediary component that simplifies the implementation of light/dark cycles. Rather than controlling light exposure in the photobioreactor, the system uses the dark tank as a mediator where culture is temporarily held in darkness, achieving lipid accumulation without complex illumination control systems.
4Productivity
If the absorption column is shielded to prevent photosynthetic activity during CO2 absorption, then CO2 removal efficiency increases, but lipid accumulation is reduced during this phase
Solution Approach 1:
The system employs periodic recirculation where culture alternates between the shielded absorption column (CO2 removal phase) and the photobioreactor (growth phase), followed by the dark tank (lipid accumulation phase). This periodic action ensures that when CO2 removal occurs in the shielded column, lipid accumulation is compensated for and enhanced in the subsequent dark tank phase, achieving both objectives over the complete cycle.
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
Simultaneously achieves efficient lipid accumulation, carbon dioxide removal from biogas, and ammonia nitrogen removal from digestate, enhancing economic and environmental sustainability.
Implementation Method 1
microalgae consume the inorganic carbon, due to the photosynthetic activity
Implementation Method 2
The absorption column must be shielded, in order to avoid the photosynthetic activity and therefore the production of oxygen within the same plant in which the methane-rich biogas is insufflated
Implementation Method 3
microalgae are able to remove ammonia nitrogen from the liquid fraction of the digestate
Data Source
Figure 1
AI summary
A process and a plant for the production of microalgal lipids with simultaneous treatment of the liquid and gaseous effluents of anaerobic digestion are described; the process includes the steps of: collecting the digestate and separating the liquid fraction from the dry fraction; mixing, within a loading step, the liquid fraction with water and with the reagents necessary to obtain a culture medium suitable for microalgal growth; continuously feeding the culture medium to the mixing step; simultaneously extracting the effluent from the mixing step to the discharge step; activating a recirculation between the mixing step and the absorption step, maintained in the absence of light; simultaneously extracting the effluent as treated biogas; separating the microalgal biomass from the effluent, for subsequent extraction of the lipids; collecting the digestate and separating the liquid fraction from the dry fraction, wherein this step must be implemented upstream of the process.