Primary clarifier effluent is pumped to the two first stage trickling filters. Underflow from the first stage trickling filters is pumped to two second stage trickling filters. Here the removal of organic material from the wastewater is continued. Effluent from the second stage trickling filters next passes through the solids contact basin, a modification of the activated sludge process. This is a small aeration basin where the wastewater is aerated, promoting the growth of microorganisms which further break down organic material and begin converting ammonia in the wastewater to nitrite and nitrate.
Wastewater flows from the solids contact basin to two final clarifiers.
In these basins the wastewater is again under quiescent conditions, which allow the suspended solids to settle to the bottom of the tank. These solids are returned to the reaeration basin, where the mixed liquor is aerated to provide oxygen to the microorganisms. Specific bacteria grow on the media of these filters to convert ammonia in the wastewater to nitrate. This process is utilized in order to meet the plant effluent limitations on ammonia concentrations discharged to the receiving stream. Some of the clarifier effluent is routed around the NTF's, based on the level of ammonia removal required at any particular time of the year .