In 2001, the Lexington Fayette Urban County Government West Hickman Creek Wastewater Treatment Plant in Nicholasville, Ky., was starting Phase II of its third upgrade since 1972, when the state imposed a phosphorus limit.
Total phosphorus hovered around 6 mg/l, but the permit required 1 mg/l monthly average and 2 mg/l daily maximum from May through October. Engineers from Tetra Tech, the Lexington-based company designing the expansion, converted the anaerobic digesters to aerated sludge holding tanks and the primary clarifiers to biological phosphorus removal (BPR) fermentation tanks.
They also modified the two-staged activated sludge nitrification system and added two final clarifiers, chlorine
