Economic development has its price, and sometimes calls for major upgrades to a community’s wastewater treatment facilities. In Fort Dodge, Iowa, that was the case where expansion of new Cargill and CJ Bio America plants in a nearby industrial park required additional capacity and BOD and TKN removal capabilities at the Fort Dodge Water Pollution Control Facility (FDWPCF). The two agricultural production plants added about five million gallons a day of flow to the FDWPCF, and increased BOD and TKN loadings by 100 and 300 percent, respectively.
To meet the new treatment requirements, Fort Dodge chose to expand the biological treatment technology it had been using for several years - the VLR® System from Evoqua. Essentially, a oxidation ditch tipped on its side, the VLR not only saved on construction costs and footprint requirements when compared to conventional treatment, it gave the Fort Dodge plant the ability to simultaneously nitrify and denitrify.
“We selected the VLR system back in 1998 when we faced new ammonia limits,” explains Mike Trotter of McClure Engineering Company, Fort Dodge, the design firm on the project. “We decided to install suspended growth biological technology to replace our old two-stage trickling filters. We looked at several biological processes, and the VLR system offered more flexibility, he says, noting that the design team and the city were looking ahead to anticipated nutrient removal requirements in the future."
Two VLR systems were originally installed and a third has been added in the new project, which also includes a new final clarifier, pumping stations, aerobic digester, and blower and chemical building, plus rehabilitation of the existing UV disinfection system. In addition, a new SmartBNR™ process control system, supplied by Evoqua, uses DO and ORP monitors in each tank to control the operation of the discs, blowers, and internal recycle pumps.
Ready for the Future
The total project cost was $23 million to increase primary treatment capacity to 12.0 MGD and secondary treatment to 18.6 MGD with plant start-up in mid-2014. Mike Trotter with McClure Engineering notes that the VLR system installation will enable the plant to remove phosphorus biologically (if required in the future) without having to add any more tanks. At the moment, it’s not clear whether more production facilities will be added to the industrial park, but if they are, the FDWPCF will be prepared. “The VLR is the best application for dealing with total nitrogen and phosphorus limits in the future,” Trotter says.