Toluene vapour removal in a laboratory-scale biofilter

Area of Science:

• Environmental biotechnology
• Bioreactor engineering
• Air pollution control

Background:

• Industrial processes release volatile organic compounds like toluene into the atmosphere.
• Biofiltration offers a sustainable method for treating toluene-contaminated air streams.
• Acclimatized microbial consortia are key to efficient biofilter performance.

Purpose of the Study:

• To evaluate the performance of a biofilter for toluene removal from synthetic waste air.
• To determine optimal operating conditions for maximizing toluene degradation rates and removal efficiencies.
• To investigate the kinetic limitations of the biofiltration process.

Main Methods:

• Utilized a bench-scale biofilter with a 0.5-m filter bed inoculated with Acinetobacter sp. NCIMB 9689.
• Conducted continuous tests varying influent toluene concentrations (0.1–4.0 g m⁻³) and gas velocities (17.8–255 m h⁻¹).
• Performed macro-kinetic analysis using concentration profiles to identify rate-limiting steps.

Main Results:

• Maximum volumetric toluene removal rate of 242 g m⁻³ h⁻¹ achieved at 127.5 m h⁻¹ superficial gas velocity and 4.0 g m⁻³ inlet concentration.
• High removal efficiencies (>0.9) were obtained at organic loads below 113.7 g m⁻³ h⁻¹.
• Process was diffusion-limited at loads <100 g m⁻³ h⁻¹ and biologically limited at higher loads.

Conclusions:

• Biofilter performance is highly dependent on superficial gas velocity and residence time for effective toluene removal.
• Achieving high toluene removal efficiency necessitates optimized operating conditions, potentially longer residence times than those yielding maximum removal rates.
• Understanding kinetic limitations (diffusion vs. biological reaction) is crucial for designing and operating efficient biofilters.