Effective diffusion coefficients of glucose in artificial biofilms

Area of Science:

• Biophysical Chemistry
• Environmental Science
• Chemical Engineering

Background:

• Biofilm structure influences solute transport.
• Accurate measurement of diffusion coefficients is crucial for understanding microbial processes.
• Fourier transform infrared (FTIR) spectrometry offers potential for in-situ measurements.

Purpose of the Study:

• To demonstrate a novel method for determining the effective diffusion coefficient (De) of an inert solute in biofilm.
• To quantify the effect of biomass concentration on glucose diffusion in a simulated biofilm.
• To utilize horizontal attenuated total reflection (HATR) FTIR for real-time diffusion measurements.

Main Methods:

• Simulated biofilms were created using 1% agarose hydrogel films with varying activated sludge biomass concentrations.
• Glucose diffusion was monitored using horizontal attenuated total reflection (HATR) coupled with Fourier transform infrared (FTIR) spectrometry.
• The effective diffusion coefficient (De) was calculated using Fick's Law based on measured glucose concentrations and film thickness.

Main Results:

• The effective diffusion coefficient (De) of glucose in biomass-free agarose films was determined to be 6.46 ± 0.21 x 10⁻⁶ cm²/s.
• Glucose diffusion was significantly impeded by the presence of biomass.
• De values decreased with increasing biomass concentration: 6.38 ± 0.22 x 10⁻⁶, 6.08 ± 0.23 x 10⁻⁶, and 5.62 ± 0.17 x 10⁻⁴ cm²/s for 0.45%, 0.90%, and 1.80% biomass, respectively.

Conclusions:

• HATR-FTIR is a viable technique for measuring solute diffusion in biofilms.
• Biomass concentration is a critical factor controlling solute transport within biofilms.
• This method provides valuable insights into mass transfer limitations in microbial systems.