Frontier Refining, Inc.

In August of 2006 the wastewater treatment plant (WWTP) for the Frontier Oil Refinery in Cheyenne, Wyoming received a new effluent discharge limit that required greater ammonia removal than the plant had historically been able to maintain.

The existing WWTP was unable to sustain MLSS concentrations high enough to maintain the required SRT in the bioreactors. A combined suspended growth and attached growth nitrification process was determined to be the most cost-effective technology for upgrading the existing bioreactors at Frontier Cheyenne Refinery. Frontier examined a number of IFAS suppliers and selected BioPortz carrier media. In June of 2007 during a regularly scheduled refinery turnaround, the bioreactors were retrofitted with effluent screens and BioPortz media was slowly added to their North plant bioreactor. By mid-August the reactor contained 93 m³ (approximately 54,000 square meters) of media and the effects of the additional fixed biomass were already being seen in the plant performance.

Historically their North plant had always performed worse than the South plant, but after the addition of just half of the designed media fill fraction the North plant appeared to nitrify better than the South bioreactor. Additionally the IFAS upgrade helped the plant recover more quickly from major upsets which are a chronic problem due to the complex nature of the refining process. Because of the fixed biomass on the media in the North bioreactor, the North plant recovered nitrification much more quickly than previously, and continued to perform better than the South plant. Integrated Fixed-Film Activated Sludge proved to be an excellent and quick solution to the new nitrification challenge faced by the Frontier refinery.