pH control in biological systems using calcium carbonate.

Area of Science:

• Biotechnology and biochemical engineering
• Environmental microbiology
• Chemical and process engineering

Background:

• Calcium carbonate (CaCO3) is an abundant and cost-effective alkalinity source for biotechnological applications.
• Controlling pH in microbial processes using CaCO3 as a neutralizing agent presents challenges.
• Understanding pH-determining factors is crucial for optimizing CaCO3 utilization in biotechnology.

Purpose of the Study:

• To identify the dominant processes governing pH in an acid-forming microbial system supplemented with CaCO3.
• To develop and validate a mathematical model simulating pH dynamics in batch fermentation with CaCO3.

Main Methods:

• A mathematical model was constructed incorporating kinetically controlled and equilibrium reactions.
• The model simulated a batch fermentation experiment using finely powdered CaCO3.
• Thermodynamic equilibrium was assumed for speciation, complexation, and precipitation; rate-limited reactions included biological acid production and CO2 mass transfer.

Main Results:

• The model accurately reproduced the experimental pH pattern, validating the chosen reaction set.
• pH establishment was most sensitive to CO2 mass transfer rate, biological acid production rate, CO2 partial pressure, and Ca(+2) concentration.
• Extrapolation to a continuously stirred-tank reactor (CSTR) demonstrated potential pH manipulation strategies.

Conclusions:

• The study successfully identified key factors influencing pH in CaCO3-mediated microbial processes.
• The developed model provides a framework for understanding and controlling pH in biotechnological systems.
• Insights gained can lead to expanded applications of CaCO3 in industrial biotechnology.