NOVELTY - A biologically active reactor system comprising submerged denitrification reactor(s) comprising upright walls defining compartment and a floor, submerged aerated filter(s) comprising biologically aerobic microorganisms for oxidation of organic matter and deep bed denitrification filter(s) for removal of suspended solids and denitrification of oxidized nitrogen, is new.    USE - The system is used for the oxidation of organic matter and denitrification of oxidized nitrogen, in the treatment of wastewater (claimed).    ADVANTAGE - The invention eliminates backwashing requirements and its associated capital cost savings, and provides ease of operation and maintenance without interruption of operation by backwashing. Avoiding the use of fine media in the submerged filters and reactors eliminates the high head loss, air, and water distribution problems, and potential plugging typically associated with biological aerated filters.    DETAILED DESCRIPTION - A biologically active reactor system comprises submerged denitrification reactor(s) (30) comprising upright walls (33, 43) defining at least one compartment (34, 44) and a floor (31, 41), submerged aerated filter(s) (40) comprising biologically aerobic microorganisms for oxidation of organic matter in fluid communication with the reactor, and deep bed denitrification filter(s) (60) for removal of suspended solids and denitrification of oxidized nitrogen and in fluid communication with the submerged aerated filter. The media bed comprises coarse, mineral media particles and a fixed biological film comprising biologically anoxic active microorganisms.    An INDEPENDENT CLAIM is also included for submerged denitrification filtration comprising feeding the reactor with wastewater influent, piping the effluent wastewater stream from the reactor into a submerged aerated filter, and piping the remaining effluent from the submerged aerated filter to a deep bed denitrification filter for removal of suspended solids and denitrification.    DESCRIPTION OF DRAWING(S) - The figure shows a biologically active reactor system.    Pre-treatment unit (20)    Submerged denitrification reactor (30)    Floor (31, 41)    Upright walls (33, 43)    Compartment (34, 44)    Submerged aerated filter (40)    Piping (42, 52)    Clarification unit (50)    Deep bed denitrification filter (60)