Downflow denitrification system

A down flow water or wastewater treatment system for removing nitrates from water or wastewater, the system comprising:

• an influent inlet for receiving water or wastewater from a source outside of the treatment system;
• a vessel for containing the water or wastewater, the vessel comprising:
• a first filtration bed comprised of a first filtration media having a first amount of surface area per volume of the first filtration media, the surface area of the first filtration media configured for biological and physical treatment of the water or wastewater;
• a second filtration bed comprised of a second filtration media having a second amount of surface area per volume of the second filtration media, the second amount of surface area being less than the first amount of surface area, the second filtration bed supporting the first filtration bed;
• and
• a support bed, the support bed supporting the second filtration bed;
• one or more nozzles providing fluid communication between the vessel area adjacent to the support bed and the system outlet, the nozzles providing an exit for effluent after traveling through the vessel;
• an effluent outlet, for removing treated water or wastewater from the system;
• one or more inlets for the introduction of air scour and water only backwash into the vessel, the inlets providing air scour and backwash water through the nozzles into the support bed, into the second filtration bed, and subsequently into the first filtration bed, the water only backwash removing at least a majority of nitrogen bubbles trapped in interstices of the first or second filtration bed;
• and
• a carbon source inlet by which a carbon source is introduced into the system in order to support removal of nitrates in the water or wastewater by microorganisms present in the first filtration media.