pH-Based FCA Control for Fermentation Overfeeding
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Solution Overview
Problem
In industrial fermentation processes, particularly in fed-batch fermentations, controlling the carbon feed rate is critical to prevent overfeeding, which can lead to loss of batches and reduced productivity due to the production of unwanted side products. Existing methods, such as frequency content analysis using dissolved oxygen signals, may not be robust enough to handle process irregularities and require specialized equipment.
Innovation Solution
The method involves monitoring and adjusting the carbon feed based on pH disturbances caused by adding a limiting substrate, using Fourier transformation of the pH signal to quantify metabolic activity and adjust the carbon feed rate accordingly, thereby optimizing carbon utilization efficiency without overfeeding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dissolved oxygen (DO) signal is used for FCA control, then carbon feed can be controlled to prevent overfeeding, but the method lacks robustness during process irregularities and requires specialized equipment
Solution Approach 1:
The patent replaces the dissolved oxygen (DO) measurement system with a pH measurement system. Instead of using DO electrodes and oxygen-based FCA control, the invention uses pH electrodes to monitor carbon feed metabolism. This substitution eliminates the need for specialized DO measurement equipment and provides more robust control during process irregularities such as stirring problems or oxygen supply issues, as pH measurement is less susceptible to these disturbances.
2Productivity
If carbon feed rate is increased to maintain productivity, then production output improves, but overfeeding occurs leading to unwanted byproduct formation
Solution Approach 1:
The patent implements feedback control by continuously monitoring the pH signal in response to carbon feed addition and using this information to adjust the feed rate. The pH response to feed pulses provides real-time information about the culture's substrate uptake capacity. When pH changes indicate approaching saturation, the system automatically reduces feed rate to prevent overflow metabolism and acetate formation, thereby maintaining high productivity without byproduct formation.
Solution Approach 2:
The patent employs periodic pulsing of the carbon source followed by analysis of the pH response. By adding carbon feed in controlled pulses and measuring the pH response to each pulse, the system can determine the maximum carbon dosing rate without overfeeding. This periodic action allows the culture to metabolize the carbon source completely during each pulse interval, preventing overflow metabolites while maintaining high overall productivity.
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
This approach is more robust and reliable, capable of maintaining process control during irregularities like stirring or oxygen supply issues, and can be used under conditions where oxygen-based methods fail, ensuring high productivity and preventing unwanted byproduct formation.
Implementation Method 1
measuring the disturbance in the pH of the fermentation broth
Implementation Method 2
The FCA signal is obtained by pulsing the carbon source and subsequently analyzing the response in the dissolved oxygen (DO) signal
Data Source
AI summary
Disclosed is a method for controlling the carbon feed to a fed-batch fermenter based on the disturbance of the pH signal following the addition or a limiting substrate.