Abstract: A pre-fabricated, self-contained biological fluidized bed apparatus for the treatment of wastewater, which offers easy and uniform expansion for various types of commercially available media, by means of a conical bottom and a single, non-clogging flow distribution pipe. Besides the biological treatment accomplished within the fluidized bed, this reactor provides mechanical solids/gas/liquid separation and upflow sludge blanket clarification to improve effluent quality. Additional unique features of this apparatus are a rotating surface skimmer and an excess sludge collection and thickening device powered by an externally mounted drive. With this reactor configuration, anaerobic and anoxic biological treatment and subsequent clarification are achieved in a single enclosed tank.