The Millwood Water Treatment Plant in Westchester County, about 60 kilometres (35 miles) north of New York City, was commissioned in August 1993. This plant is the first dissolved air flotation (DAF) plant in the United States which uses the DAF technology and concepts that have become the industry standards in Europe and Australia. The $19-million plant was built to treat a previously unfiltered supply, to meet the requirements of the new federal Surface Water Treatment Rule.

This paper describes the project in its entirety: starting from the planning, pilot testing, and process selection; proceeding to the means of overcoming resistance to a “new” process and obtaining regulatory body approvals; and outlining the design, process criteria, construction, and start-up of the plant. Operating results are also presented. The plant treats soft, slightly colored, generally low turbidity water which experiences occasional turbidity spikes of 100 NTU or more. The treatment process comprises two-stage mixing, three-stage flocculation, dissolved air flotation, ozonation for primary disinfection, dual-media filtration, and post-treatment with chlorine, sodium hydroxide, orthophosphate and fluoride. Flotation sludge is dewatered in on-site freeze/thaw lagoons for off-site disposal in a landfill.