Determination of carbon dioxide evolution rate using on-line gas analysis during dynamic biodegradation experiments

Area of Science:

• Environmental Microbiology
• Biochemical Engineering
• Analytical Chemistry

Background:

• Respirometry, particularly oxygen uptake, is vital for microbial activity assessment but limited in anaerobic or insoluble substrate conditions.
• Carbon dioxide (CO2) measurement via gas balance is an alternative, but observed CO2 evolution rate (OCER) can deviate from biological CER in dynamic systems due to transfer limitations.
• Accurate CER determination is crucial for understanding microbial processes in various environments, including wastewater treatment.

Purpose of the Study:

• To develop and validate a mathematical model for accurately calculating the biological carbon dioxide evolution rate (CER) in dynamic microbial systems.
• To account for chemical and physical transfer limitations affecting CO2 measurements in short-term batch experiments.
• To improve the reliability of respirometry data obtained from non-stationary conditions.

Main Methods:

• A mathematical model based on mass balance equations was developed, incorporating CO2 chemical equilibrium and liquid phase pH evolution.
• Mass transfer from the liquid to the gas phase was described, and the analysis system's response time was evaluated.
• Global mass transfer coefficients (KLa) for CO2 and oxygen were determined and compared, using a laboratory-scale reactor with activated sludge microorganisms.

Main Results:

• The proposed model successfully predicted gaseous response disturbances during pH changes.
• Global mass transfer coefficients (KLa) for CO2 and oxygen were determined, aiding in hydrodynamic assumptions.
• The model accurately determined CER in non-stationary conditions during batch experiments with activated sludge.

Conclusions:

• The developed mathematical model effectively corrects for transfer limitations in CO2 measurements during dynamic respirometry.
• This approach enables accurate determination of biological carbon dioxide evolution rate (CER) even in challenging, non-stationary batch experiments.
• The validated model enhances the utility of respirometry for studying microbial activity in environmental and industrial applications.