Continuous Stirred Tank Reactor with Activated Sludge Recycle
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This Demonstration considers a model for the dynamics of a continuous stirred aeration tank processing activated sludge.[more]
The activated sludge process involves the aeration and agitation of an effluent in the presence of a flocculated suspension of microorganisms that are supported on particulate organic matter. After a predetermined residence time, the effluent is passed to a sedimentation tank where the flocculated solids are separated from the treated liquid.[less]
Contributed by: R. Ricardo Sánchez (August 2022)
Open content licensed under CC BY-NC-SA
The volumetric flow rate entering and leaving the reactor is the sum of the influent and recycle flow rates:
The recycle ratio is defined by:
The reactor residence time is defined as the volume of the reactor divided by the volumetric influent flow rate:
The concentration factor is defined as the ratio of the recycle biomass to effluent biomass concentrations:
: biomass concentration in reactor (),
: substrate concentration (),
: sludge concentration factor (dimensionless),
: recycle ratio (dimensionless).
The model is described in detail in [1, Exercise 3.3.2].
Suggestions for further exploration:
1. Vary the recycle ratio to see how the performance of the process is influenced.
2. Vary the values of the flow rate to see how the process is influenced.
 J. B. Snape, I. J. Dunn, J. Ingham and J. E. Prenosil, Dynamics of Environmental Bioprocesses: Modelling and Simulation, New York: VCH, 1995.