Mixing characteristics and liquid circulation in a new multi-environment bioreactor

Area of Science:

• Environmental Engineering
• Biochemical Engineering
• Fluid Dynamics

Background:

• Understanding hydrodynamics and mixing is crucial for optimizing bioreactor performance.
• Multi-environment bioreactors offer advantages for sequential biological processes.
• Air-lift bioreactors are efficient for promoting mixing and oxygen transfer.

Purpose of the Study:

• To investigate the theoretical and experimental aspects of hydrodynamics and mixing in a new air-lift multi-environment bioreactor.
• To analyze mixing characteristics, residence time distribution, and liquid circulation between aerobic, microaerophilic, and anoxic zones.
• To determine the impact of influent and air flow rates on bioreactor performance.

Main Methods:

• Theoretical analysis of liquid displacement and circulation patterns.
• Experimental investigation of mixing characteristics using parameters like axial dispersion coefficient and Bodenstein number.
• Evaluation of residence time distribution and its ratio to hydraulic retention time (t m/HRT).

Main Results:

• The ratio of mean residence time to hydraulic retention time (t m/HRT) decreased with increased air flow rate.
• Mixing parameters (Bodenstein number) showed a linear relationship with superficial gas velocity.
• Liquid circulation between zones was efficient, with minimal escape (<1.5%) per cycle, decreasing at higher air flow rates.

Conclusions:

• The air-lift bioreactor design facilitates efficient mixing and liquid circulation across different zones.
• Optimized air and influent flow rates are critical for maximizing bioreactor performance and wastewater treatment efficiency.
• The study provides a correlation between mixing parameters (Bodenstein number) and fluid dynamics (Froude number).