The removal of particulate material in the aeration basin of the activated sludge process is mainly attributed to bioflocculation and hydrolysis of particulate substrate. The bioflocculation process in the aeration tank of the activated sludge process occurs only under favorable conditions in the system and several common operational parameters affect its performance. The principal objective of this research was to observe the effect of MLSS, SRT and EPS on the removal of particulate substrate by bioflocculation. A first order particulate removal expression, based on flocculation, accurately described the removal rates for supernatant suspended solids and colloidal COD. Based on the results presented in this investigation, a mixed liquor concentration of approximately 2,200 mg/L, an SRT of at least 3 days and a contact time of 30 minutes are needed for relatively complete removal of the particulate substrate in a plug flow reactor.