Systematic errors in data evaluation due to ethanol stripping and water vaporization.

Area of Science:

• Biotechnology and Biochemical Engineering
• Process Engineering and Optimization
• Environmental Monitoring and Measurement

Background:

• Bioreactors often neglect the phase partitioning of water and ethanol, leading to systematic errors in measurements.
• Off-gases from bioreactors contain both water and ethanol vapor, impacting gas analysis and process efficiency.
• Existing condensation systems show limited effectiveness in reducing ethanol vapor loss.

Purpose of the Study:

• To investigate systematic errors in bioreactor measurements caused by unaddressed water and ethanol vapor partitioning.
• To evaluate the efficacy of condensers in reducing ethanol loss via vaporization.
• To explore alternative methods, such as absorption, for minimizing ethanol stripping in bioreactors.

Main Methods:

• Mathematical modeling using mass balance and partition equations to predict vapor partitioning.
• Experimental validation of model predictions in bioreactors with and without condensers.
• Testing a modified bioreactor setup utilizing the condenser as an absorption column for continuous cultures.

Main Results:

• Neglecting water vapor in off-gas can lead to overestimation of oxygen consumption rates by a factor of 3.
• Condensers have a minimal impact on reducing ethanol vapor content due to high condensate concentrations.
• Ethanol evaporation can account for over 20% of the ethanol production rate, with stripping reduced by a factor of 4 using an absorption setup.

Conclusions:

• Systematic errors in bioreactor measurements are significant when water and ethanol vapor partitioning is ignored.
• Condensation is inefficient for recovering ethanol; absorption offers a more effective solution for reducing vapor stripping.
• Modifying bioreactors to use condensers as absorption columns can substantially improve ethanol recovery and measurement accuracy.