Lake DeForest Water Treatment Plant Enjoying Benefits of High-rate Dissolved Air Flotation System

United Water began seeking an upgrade of the plant's aeration and sedimentation basins to a higher rate clarifier in order to improve overall water quality and taste.

Owned and operated by United Water New York, the 20 mgd Lake DeForest Water Treatment Plant is fed by a 1000-acre reservoir and provides 33% of Rockland County's drinking water.

In 2001 United Water began seeking an upgrade of the plant's aeration and sedimentation basins to a higher rate clarifier in order to improve overall water quality and taste, filter run times and plant efficiency.

A pilot study of Infilco Degremont's AquaDAF Dissolved Air Flotation System was initiated in order to confirm operating criteria. Specifically, the owners were looking for efficient removal of solids, TOC, algae and color, with a consistent clarifier effluent of less than 1 NTU.

In mid-2002 evaluation of pilot results was completed and confirmed Infilco Degremont's AquaDAF system operated at exceptionally high loading rates of up to 16 gpm/ft2.

Even at such a high rate, little coagulant was needed and sludge production was minimal. Based on the pilot success a design-build team of Infilco Degremont, United Water and Black & Veatch Construction began full-scale design, and startup was achieved in less than seven months, by June 2003.

This was Infilco Degremont's first high-rate dissolved air flotation facility built in the U.S.

System description

Conventional aeration and sedimentation basins were replaced by AquaDAF clarifiers, which are followed by mixed media filtration.

With filtered turbidity of less than 0.1 NTU, the system is producing turbidity three times lower than the plant's previous conventional treatment system while operating at a loading rate of 12 gpm/ft2.

The AquaDAF system at Lake DeForest utilizes hydraulic flocculation. Two very small, unpacked saturators operate at a design recycle rate of 10%. A patented false floor creates a dynamic vortical flow pattern within the basin. Low in maintenance, the only submerged moving part is the effluent weir used for desludging.

About the author: Judi Harrison is a Marketing Specialist for Infilco Degremont located in Richmond, Virginia