Steady-state analysis of activated sludge processes with a settler model including sludge compression

Area of Science:

• Environmental Engineering
• Biochemical Engineering
• Process Systems Engineering

Background:

• Analyzing steady states of coupled bioreactor-settler systems is complex.
• Existing reduced models often oversimplify settler dynamics.

Purpose of the Study:

• To develop a simplified, yet accurate, reduced model for a bioreactor coupled to a settler.
• To improve the steady-state analysis of such systems, incorporating realistic settling phenomena.

Main Methods:

• Developed a reduced model for a completely stirred-tank bioreactor and a settling tank with recycle.
• Incorporated compressive and hindered settling using the Bürger-Diehl model.
• Replaced a complex ordinary differential equation with an approximate algebraic equation for simplified analysis.

Main Results:

• The novel algebraic equation simplifies steady-state analysis of the entire plant.
• The model accurately accounts for sludge blanket location and limiting flux capacity.
• Steady-state concentrations, solids residence time, and wastage flow ratio are shown to be functions of the recycle ratio.

Conclusions:

• The simplified algebraic approach offers more realistic solutions compared to previous reduced models.
• This method enhances the ability to analyze and optimize bioreactor-settler systems.
• The model's flexibility allows for analysis under various growth kinetics and operating conditions.