Impacts of SRT on Particle Size Distribution and Reactor Performance in Activated Sludge Processes

Particle size distribution of the particulates is an essential characteristic of the wastewater quality. Particle size of activated sludge flocs may affect key sludge handling processes including sedimentation, thickening, digestion, and dewatering. This study evaluated the effects of solids retention time (SRT) on particle size distribution, sludge settleability, effluent turbidity, and removals of chemical oxygen demand (COD) and NH4+ -N in a lab-scale Modified Ludzak-Ettinger (MLE) reactor and an integrated fixed film activated sludge (IFAS) reactor. This study also surveyed particle size distribution profile of five full-scale water resource recovery facilities (WRRFs), including high purity oxygen (HPO), step-feed nitrification/denitrification (NDN), and MLE NDN processes. This study provides direct evidence of the effects of SRT on particle size distribution and sludge settleability in lab-scale reactors and full-scale WRRFs.