The capability of biological nutrient removal from wastewater of a novel laboratory-scale twin fluidized-bed bioreactor (TFBBR) was studied. The work showed approximately 96% organic matter, 84% nitrogen, and 12% phosphorus removal efficiencies in the first three phases of the study at influent synthetic municipal wastewater (SMW) flow rates of 150, 190, and 240 L/d, with corresponding organic loading rates of 1.3, 1.7, and 2.3 kg COD m(-3) d(-1) nitrogen loading rates of 0.14, 0.18 and 0.25 kg N m(-3) d(-1). The TFBBR effluent was characterized by <1.0 mg NH4-N/L, <4.3 mg NO3-N/L, <6 mg TN/L, <6 mg SBOD/L, and 6-10 mg VSS/L. For the three phases, biomass yields of 0.06, 0.066, and 0.071 g VSS/g COD were observed, respectively, which was a significant further reduction in yield compared to the liquid-solid circulating fluidized-bed bioreactor technology developed and patented by this research group, of 0.12-0.16 g VSS/g COD. The very low yield was due to a longer solid retention time of 72-108 d.