SUCCESSFUL FULL-SCALE IMPLEMENTATION OF A BIOLOGICAL AERATED FILTER FOR SECOND STAGE NITRIFICATION

The Freeport, Illinois Wastewater Treatment Plant received new effluent ammonia limits and a compliance schedule in the 1997 renewal of its NPDES permit. The facility had a high-rate activated sludge system incapable of meeting the new limits without capital improvements. An evaluation of alternatives identified a second stage nitrifying biological aerated filter (BAF) as the best option. A BAF system was competitively procured and constructed. The 1,065 m3/hr (6.75 mgd) second stage nitrifying BAF has been in service since October 2001 and has allowed the facility to successfully meet its new NPDES permit requirements.Ammonia, cBOD5, and TSS data from both a critically loaded performance test and from the first 30 months of operation are presented and used to illustrate the level of treatment achieved by the Freeport BAF. An analysis of historic data illustrates that the system has responded well to fluctuations in influent ammonia load. The impact of ammonia removal on facility power usage is examined.