Challenge: The PA DEP established nutrient cap loads for Lock Haven’s sewage treatment plant (STP). The primary goals of the study were to evaluate viable alternatives for the upgrade of the City’s STP to comply with the nutrient cap loads, upgrade the screening and grit removal operations in the WWTP’s headworks, and UV disinfection alternatives for the replacement of the STP’s chlorine disinfection process, and recommend the best alternatives based on a comparison of construction, operation, and maintenance cost considerations.
Solution: The City determined the STP’s average daily flow capacity was adequate to accommodate growth over the next 20 years; therefore, the design’s average daily flow capacity remained unchanged. Additionally, it was determined the facilities for the removal of solids and grit would be designed for an influent flow rate of 12.0 MGD with 9.0 MGD conveyed to the biological treatment process. Peak flows exceeding 9.0 MGD would be conveyed to an existing wet weather flow storage facility.
Outcome: Two headworks alternatives were considered, and three biological treatment alternatives were developed and evaluated: an activated sludge retrofit, an Integrated Fixed Film Activated Sludge retrofit, and sequencing batch reactors (SBRs). The SBRs (with the addition of alum for TP removal) was the selected biological treatment alternative. A Trojan UV3000 was the recommended UV disinfection system.