Multi-Scale Individual-Based Model of Microbial and Bioconversion Dynamics in Aerobic Granular Sludge

Aerobic granular sludge is a novel compact biological
wastewater treatment technology for integrated removal
of COD (chemical oxygen demand), nitrogen, and phosphate
charges. We present here a multiscale model of aerobic
granular sludge sequencing batch reactors (GSBR) describing
the complex dynamics of populations and nutrient
removal. The macro scale describes bulk concentrations
and effluent composition in six solutes (oxygen, acetate,
ammonium, nitrite, nitrate, and phosphate). A finer scale,
the scale of one granule (1.1 mm of diameter), describes the
two-dimensional spatial arrangement of four bacterial
groupsheterotrophs, ammonium oxidizers, nitrite oxidizers,
and phosphate accumulating organisms (PAO)using
individual based modeling (IbM) with species-specific
kinetic models. The model for PAO includes three internal
storage compounds: polyhydroxyalkanoates (PHA), poly
phosphate, and glycogen. Simulations of long-term reactor
operation show how the microbial population and activity
depends on the operating conditions. Short-term dynamics
of solute bulk concentrations are also generated with results
comparable to experimental data from lab scale reactors.
Our results suggest that N-removal in GSBR occurs
mostly via alternating nitrification/denitrification rather
than simultaneous nitrification/denitrification, supporting
an alternative strategy to improve N-removal in this promising
wastewater treatment process.