NOVELTY - Wastewater treatment system comprises a submerged attached growth bioreactor (10), an equalization tank (30) connected to the bioreactor, and a clear well (40) connected to the bioreactor. The bioreactor has an inlet connected with an equalization tank outlet; a deep-bed sand filter with an underdrain adjacent to a bioreactor bottom; a support gravel bed; filter media; and a plenum below the underdrain. The plenum interconnects to an adjacent bioreactor outlet in a bioreactor side wall.    USE - The system is used for treating wastewater (claimed) containing nitrogen compounds, e.g. ammonia and organic nitrogen compounds.    ADVANTAGE - The system has a single-unit, single-zone bioreactor for combined removal of organics and nitrogen while operating in both a down flow and up flow mode with intermittent aeration to the filter. The nitrogen compounds in the wastewater are reduced to an environmentally acceptable level prior to discharge of the wastewater. The bioreactor is simple to operate and maintain. The wastewater flow through the filter is in two directions, i.e. down flow (forward flow) and up flow (reverse flow). The hydrostatic pressure, created by the differential liquid levels within the tanks, is the driving force of the forward flow through the system, through the clear well inlet pipe into the clear well first inlet through the clear well. Flow through the bioreactor alternates between down-flow and up-flow. The system is operated as a continuous flow process. Some of the flow cycles through the bioreactor filter, treated effluent from the clear well, is discharged continuously. The intermittent aeration of the bioreactor provides sufficient air for the removal of organics and nitrification, and minimizes the amount of excess so that denitrification occurs within the same reactor. The use of the bioreactor for biological nutrient removal provides the system with a small foot print due to its ability to operate with high concentrations of biomass. The submerged attached growth bioreactor produces high quality feed water to the microfiltration unit, which will allow higher flux rates through the membrane unit and thus a reduced total membrane area requirement. It provides biological separation and solids separation of the biomass.    DETAILED DESCRIPTION - Wastewater treatment system comprises a submerged attached growth bioreactor having a bottom, a top, and a side wall interconnecting the bottom and top, in which the bottom, top and side wall define a hollow, bioreactor interior (14). The bioreactor has a first inlet (15) connected with an equalization tank outlet. The bioreactor interior has a deep-bed sand filter (16) with an underdrain adjacent to the bioreactor bottom, a support gravel bed (18), filter media (19), and a plenum below the underdrain. The plenum interconnects to an adjacent bioreactor outlet in the bioreactor side wall. An equalization tank is connected to the bioreactor. It has a bottom, a top, and a side wall interconnecting the bottom and top, in which the bottom, top and side wall define a hollow, equalization tank interior (34). It has an influent inlet for receiving wastewater from a source external to the equalization tank and into the equalization tank interior. A clear well is attached to the bioreactor. It has a side wall interconnecting a bottom and top, in which the bottom, top and side wall define a hollow, clear well interior (44). It has a first inlet with an inlet pipe connected to the bioreactor outlet. The clear well interior has a first pump system (47) on the clear well bottom. The first pump system is connected to the clear well first inlet and is adapted to provide reverse flow from the clear well interior back through the bioreactor interior. The clear well interior has a second pump system (48) on the clear well bottom. The second pump system is interconnected to a clear well discharge outlet (49). It is adapted to discharge the contents of the clear well interior out through the discharge outlet.    DESCRIPTION OF DRAWING(S) - The figure is a block diagram of a submerged attached growth bioreactor system.    Bioreactor (10)    Bioreactor interior (14)    First inlet (15)    Sand filter (16)    Support gravel bed (18)    Filter media (19)    Equalization tank (30)    Equalization tank interior (34)    Clear well (40)    Clear well interior (44)    First pump system (47)    Second pump system (48)    Discharge outlet (49)