Three nitrifying trickling filters (NTF's), provide ammonia removal to meet monthly variable effluent limitations. Each NTF is 105-feet in diameter and contains 24 vertical feet of plastic cross-flow media. The filters rest on a base of fill approximately 6 feet above grade to allow gravity flow from the NTF's to the Denitrification Filters Influent Pump Station. NTF structural design allows routine flooding and backwashing of the units to control nuisance organisms associated with the nitrification process. Sodium hydroxide can be applied to raise the pH during flooding for snail control. Secondary effluent is applied over the media surface by a 4-arm, hydraulically driven rotary distributor.
The three covered nitrifying trickling filters serve a dual function, oxidizing ammonia to meet effluent water quality standards and biologically treating odorous sulfur compounds in the exhaust air from the dissolved air flotation thickeners, the centrate return tank and the solids handling building. Forced air ventilation systems transfer foul air from three dissolved air flotation thickeners, the solids handling building and a centrate equalization tank to the three NTF's. Geodesic dome covers enclose the NTF tanks, ensuring uniform distribution of foul air over the biofilm surface, preventing short-circuiting and enhancing odor treatment. The combined foul air from both sources discharges into the top of the NTF enclosure, moving downward through the media with the wastewater flow. Treated air drawn from underneath the NTF media is discharged to the atmosphere through a centrifugal fan. Foul air flow to each NTF unit is approximately 9,900 cfm. Use of the nitrifying biofilm for foul air treatment avoids the cost for another expensive chemical scrubbing system.
Four variable speed, 24-mgd vertical column pumps lift secondary effluent to the NTF distributors. The pump station can recycle nitrified effluent to increase wetting rates. Two pumps allow bypass of a controlled portion of the secondary effluent to the disinfection complex in order to provide the required amount of ammonia necessary for efficient disinfection of the wastewater. Electric variable speed drives and other support equipment are housed in a separate support building.