The Fairplay Sanitation District was challenged in meeting their ammonia permit limits and wanted a process that would produce a stable effluent in a small footprint. Influent water temperatures were regularly recorded in between 6°C and 10°C. Due to these cold temperatures, nitrification was not being achieved on a consistent basis. Additionally, the District had to factor in the issue of the groundwater table rising and falling as well as the alkalinity of the wastewater that is needed for nitrification.
The Fairplay Sanitation District Plant consisted of over 3 million gallons of aerated lagoon treatment. The plant sits at approximately 10,000 ft of elevation. The harsh climate with cold temperatures the majority of the year leads to an inconsistent ammonia removal. The lagoons brought additional challenges including excess algae growth in the summer and freezing in the winter.
In 2005 the City began planning to upgrade the facility to a fully mechanical plant. The main objectives were to build an easily operated mechanical plant in a small footprint that could be covered to allow for heat retention as well as protection from the extreme elements for the operators.
The resulting IFAS facility is 125,000 gallons of aerobic volume with two rectangular clarifiers. This portion of the facility is outside and covered. The remaining footprint encompasses the headworks, pumps, laboratory, and ancillary equipment. The new flow scheme consists of headworks including a 3 mm spriral screen and grit removal; 2 trains each of 1 anoxic reactor and 2 aerobic reactors containing the AnoxKaldnes K1 media; secondary clarification; and UV disinfection. The existing lagoon 3 was converted to an aerobic digester for waste activated sludge (WAS).
The IFAS reactors are 15’ x 15’ x 16’ SWD with percent media fills of 65% in the first reactor and 38% in the second. The design MLSS is 3,000 mg/l. The biological system is designed to treat screened influent down to 10 mg/l soluble BOD₅ and 1.0 mg/l effluent NH₃-N. The return activated sludge (RAS) rate has a maximum of 100% of influent flow, and the internal recycle design rate is 70%.
The plant is designed to have comparable manpower requirements as the previous lagoon system. An operator makes a walk-through each day and spends a half day on site two times per week. Due to the remote location and harsh climate, the focus of this plant design was on simplicity and consistent performance with little operator attention.
Fairplay, CO - case study