Biological Nutrient Removal Improvements, Springettsbury Township, PA

Springettsbury WWTP

BH designed a Biological Nutrient Removal upgrade of the existing Springettsbury Township WWTP at the designed flow rate of 15.0 MGD with a peak flow of 37.0 MGD. The upgrade was necessary to comply with the proposed effluent nutrient limits required by the Chesapeake Bay Strategy. The WWTP had to comply with nutrient effluent discharge limits of 6.0 mg/L and 0.8 mg/L for total nitrogen and total phosphorous respectively.

In order to save capital expense and because there was limited area for expansion, BH selected an innovative technology to create the environment for BNR without building additional tanks. First, the existing primary clarifiers were converted to anaerobic selectors for phosphorus removal. We were able to reuse these tanks at very little additional cost since the Township never used the primary clarifiers.

Second, the existing aeration tanks were converted to Integrated Fixed-Film Activated Sludge (IFAS) tanks in order to more efficiently use the tanks. The first stage is an anoxic stage where nitrates are recycled and converted to nitrogen gas (denitrification). The second stage is an IFAS tank packed with plastic media providing a surface for nitrifying bacteria to grow. The increased population of microorganisms is able to treat the increased load of nutrients. The third and final stage is a re-aeration stage for carbonaceous BOD removal and further nitrification.

The existing gas chlorine disinfection system was replaced with a UV disinfection system. The existing chlorine contact tank was modified for installation of the UV equipment. One half of the existing chlorine contact tank was converted to a UV disinfection tank.

The Enaqua UV system was installed where the plant effluent flows through parallel banks of plastic tubes. The UV bulbs are arranged around the tubes with UV light being transmitted through the tubes. Cooling fans blow air across a water cooled heat exchanger and the cool air is circulated around the UV bulbs to dissipate their heat. The source of the cooling water is UV effluent, which is pumped through the heat exchanger. Two UV units are provided in separate channels with sufficient room in the channels to provide side access for maintenance. The side panels can be removed from each unit to provide access to the flow tubes. The UV bulbs are mounted on racks which can be lifted vertically from the unit.

The capacity of the UV system is 37 MGD. The UV system control panel is tied via Ethernet to the WWTP central control system for full monitoring of all UV system parameters. The UV effluent is discharged to two utility water reservoirs and to a post aeration cascade.

A fiberglass building was constructed over the entire UV tank to protect the utility water pumping system from freezing, to house the electrical and storage room areas, and to protect maintenance personnel from the elements. Installation of the UV system has been completed.