Conventional FSBs include five types of flow distribution mechanisms (Summerfelt, 2006); CycloBio fluidized sand bed (CB FSB) is the only type not utilizing a manifold at its top (rotational flow distribution mechanism), whereas the other types do. The CB FSB operates with relatively little head loss across the flow inlet slot than that across the orifices of horizontal pipe manifold flow distri-bution mechanisms (Summerfelt, 2006). Although no floor abrasion has been observed, bottom protection is best to be made. And vac-uum breaker is necessary to enhance security of system. Hence, CBFSBs are commonly used in RAS. However, existing studies about CB FSBs were not systematic. Summerfelt (2006) introduced the mechanism of CB FSBs and the sand selection criteria. Davidson et al. (2008) investigated the efficiency of CB FSBs in wastewater treatment and operation management. Few studies addressed the design of CB FSBs and mostly adopted experimental and theoretical methods. Simulation is a new method which involves low cost, short experiment time, and reduces workload (Sun, 2011; Zhou et al., 2011). Therefore, we studied the design and optimization of CB FSBs with the combination of numerical simulation and experiment validation. We had two aims: (1) improving the efficiency of CB FSBs in wastewater treatment; and (2) minimizing the cost of research.2. Material and methods