The Salisbury Township WWTP in Gap, Pennsylvania, utilized a conventional activated sludge system prior to being retrofitted with an AquaPASS Phased Activated Sludge System in May 2008. The upgrade was necessary in order to comply with the Chesapeake Bay Initiative for local impaired waterways, requiring stringent permit limits on effluent total nitrogen and total phosphorus by 2010. The plant’s conventional system was not designed for nutrient removal and required only secondary limits of 20 mg/L BOD5, 30 mg/L TSS, 6 mg/L NH3-N, and 2 mg/L TP. Salisbury experienced constant upsets during peak wet-weather flow conditions that required operator intervention to prevent solids from rising over the effluent weir. In addition, the conventional system could no longer handle the increased hydraulic loadings from the area’s rapid population growth of about 11.5% in the past nine years.

Since the previous upgrade occurred in 1999, it was important to evaluate alternative technologies that would not only meet the new treatment objectives but also operational, process and construction aspects including: utilizing the existing concrete structures, preserving the current hydraulic profile, allowing continued operation throughout installation, and reducing operation and maintenance requirements.

Salisbury and its consulting engineer, ARRO Consulting, Inc., began investigating several technologies in 2005 and ultimately selected the AquaPASS Phased Activated Sludge System for its ability to combine prominent features of both batch and continuous-flow processes into a singular treatment process. This offered Salisbury the temporal and spatial process control it needed. Installation of the AquaPASS system was complete in May 2008. Salisbury was the first treatment plant to install AquaPASS technology. 

Download the full case study to learn more.