The Tetra Denite and DeepBed advanced wastewater filtration systems produce effluent that is safe and cost-effective. The Tetra Denite system combines denitrification and filtration processes for the effective removal of nitrate-nitrogen and suspended solids in a single treatment step. The combined fixed-film biological denitrification process and deep-bed filtration system remove suspended solids to virtually any final effluent requirement with low levels of wastewater return. The small-footprint system integrates well with other plant treatment processes to provide total nitrogen below 3 mg/L and phosphorous removal. The Tetra DeepBed tertiary filtration system provides total phosphorus removal to limits below 0.2 mg/L. Using rounded sand grains with a sphericity of at least 0.8 and a 6-ft media bed allows for up to 2 lb of solids per sq ft of filter surface area before backwashing is required. Sand media is 2 to 3 mm with a maximum uniformity coefficient of 1.4.