This paper presents a novel bioparticle system operated for simultaneous carbon and nitrogen biodegradation, with an anoxic-aerobic bioparticle circulation pattern. In the Circulating Fluidized Bed Biofilm Reactor (CFBBR), bioparticles are slowly transferred from the Riser (Anoxic column) to the Downer (Aerobic column) for enhanced biological nutrient removal (BNR), with bioparticles residing in the Downer prior to recirculation back to the Riser for refreshment. In this study, low shear stress was maintained during all experiments in order to achieve rich biofilm conditions, where predation was encouraged. A lab-scale CFBBR with a 4 L reaction zone was designed to evaluate the circulation effect. Long-term (285 days) performance showed that stable and high-rate chemical oxygen demand (COD) with sodium acetate as the carbon source and total nitrogen (NH4Cl as nitrogen source) conversions were achieved simultaneously, with extremely low sludge production in the 0.034-0.1 gVSS(volatile suspended solids)/gCOD range. These results supported the considerable advantages of the bioparticle process in biological nutrient removal. (C) 2011 Elsevier B.V. All rights reserved.