Delaware County Regional Water Quality Control Authority Sludge Thickening, Grease Thickening, and Odor Control System

In response to a failing sludge thickening system for a 44 million gallons per day (MGD)-wastewater treatment plant, Weston designed a new system with improved thickening technology and flexibility to expand the system as the plant flows increase.

The Delaware County Regional Water Quality Control Authority (DELCORA) Western Regional Treatment Plant was using dissolved air flotation (DAF) to thicken waste activated sludge (WAS) prior to dewatering and incineration. Two of the four DAF systems failed, and one of the DAF tanks was operated without dissolved air injection. This particular DAF tank operated without the air injection that was used to store and separate scum from the primary clarification system and trucked in grease from restaurants and food preparation facilities. Weston was tasked to evaluate several alternatives for sludge thickening and grease concentration, prepare design drawings, specifications, and contract documents, and provide construction services.

After an alternative technology evaluation, Weston selected the sludge thickening alternative that included three new 2-meter gravity belt thickeners (GBTs) (one of which is a future spare) staged over one of the decommissioned DAF tanks. For the grease concentration system, Weston recommended to rebuild the two DAF systems and operate them without the dissolved air injection. It is intended that one tank will serve as the primary tank for grease acceptance and treatment, and the other tank will remain empty in standby mode for use as needed. The new recommended odor control system is a biological trickling filter (biofilter) that replaced the old caustic scrubber unit.

To ensure that WAS thickening operations did not halt because of a critical failure of this existing equipment, we conducted system modifications in phases. The design and installation of the GBTs provided DELCORA with the capability to expand the plant capacity to 50 MGD. The upper and lower skimmers were redesigned to provide a more efficient removal of the floating grease and removal of solids settling on the bottom of the tanks. The new odor control system, a biological trickling filter located outside, south of the existing sludge storage tanks, has replaced an old caustic scrubber and eliminated the chemical cost hazards associated with chemical handling.

Weston also assisted DELCORA in the construction bid phase and provided construction management services. All systems have been in successful operation since 2014.