📋 Case Study

Bioethanol Fermentation Tank Cascade Control (POET LLC, Iowa)

Yeast viability drop after 36 h due to ethanol toxicity and CO₂-induced pH shift

🏗️ Project Overview

Improving ethanol yield and reducing diacetyl off-flavor in 2M-gal SSF fermenters

🎯 Challenge

Yeast viability drop after 36 h due to ethanol toxicity and CO₂-induced pH shift

🔧 Design Approach

pH-triggered nutrient feed cascade with real-time glucose/ethanol Raman probes and variable agitation setpoint scheduling

📐 Design Diagram

AI-generated project design illustration

📐 Key Calculations

Specific Growth Rate (μ)

μ = d(lnX)/dt

Result: 0.18 h⁻¹

Indicates optimal feeding window

Ethanol Inhibition Constant (K_i)

μ = μ_max / (1 + [EtOH]/K_i)

Result: 82 g/L

Defines maximum tolerable titer before lysis

📊 Results

Yield increased from 92% to 97.4% theoretical; diacetyl reduced to <0.1 ppm; 11% shorter batch time

💡 Lessons Learned

• •Bioreactor control must integrate metabolic kinetics with transport limits
• •Online spectroscopy enables true first-principles feedback

✅ Key Takeaways

• 1Bioreactor control must integrate metabolic kinetics with transport limits
• 2Online spectroscopy enables true first-principles feedback