Effect of Floc Size on Selection of Phosphate-Accumulating Organisms (PAO) in Wastewater Treatment Systems Without a Strictly Anaerobic Zone

Phosphate-accumulating organisms (PAOs) are commonly used in enhanced biological phosphorus removal (EBPR) to remove phosphorus from wastewater. Selection for PAOs in a wastewater treatment plant (WWTP) is typically obtained by providing strict cyclic anaerobic/aerobic conditions in order to give PAOs a metabolic advantage over ordinary heterotrophic organisms (OHOs). This thesis explores the question “can large flocs enhance selection for PAOs under non-ideal conditions, both in conventional activated sludge (CAS) and EBPR systems?” “Non-ideal conditions” refer to the lack of a strictly anaerobic zone.The hypothesis was selection for PAOs occurs in CAS and EBPR systems as long as flocs have an interior zone alternating between anaerobic/anoxic and aerobic.It was expected that larger flocs will more readily supply the required anaerobic/anoxic conditions and this was explored through computer numerical simulations. In our simulations, floc size had little significant influence on selection for PAOs, but bulk substrate concentrations did.