Trickling Filter Nitrification Performance Characteristics and Potential of a Full-Scale Municipal Wastewater Treatment Facility

The trickling filter solids contact water pollution control facility for the city of Ames, Iowa has successfully nitrified wastewater with trickling filters for the past decade. Both first stage, carbonaceous biochemical oxygen demand removing trickling filters (TFs) and second stage, nitrifying TFs (NTFs) remove significant quantities of ammonia from the wastewater. Based on operating data from January 1999 through December 2001, the average specific ammonia removal rate for the TFs was $1.5\times {10}^{-4}\mathrm{kg}N/\left(d{m}^2\right)$. Most probable number testing confirmed the presence of nitrifiers in the top media layer of both stages of trickling filters. An experiment was performed whereby flows to the TFs and NTFs were varied to test ammonia removal capabilities of the facility. During the experiment, the TFs removed an average of $2.4\times {10}^{-4}\mathrm{kg}N/\left(d{m}^2\right)$ and the NTFs removed an average of $1.5\times {10}^{-5}\mathrm{kg}N/\left(d{m}^2\right)$ due to low loading. Data collected during the study varied with operating conditions. It was compared to and used to calibrate NTF models. An empirical design model poorly fit the data, and a theoretically based model could not be calibrated well with apparent ammonia removal rates. A best-fit equation, dependent on hydraulic loading and influent ammonia concentration (adjusted for recirculation), was regressed directly to the data and is useful for describing nitrification in the Ames WPCF TFs.