New England Floats to the Top - Northeast Innovation Led to Widespread Implementation of DAF

Authors:

  • Matthew Valade – Hazen and Sawyer
  • David Connors – Aquarion Water Company

Dissolved air flotation (DAF) had a strong track record as a robust clarification process in the drinking water treatment industry throughout Europe and Scandinavia as early as the 1970s. Not until 1992 did DAF gain a toehold in drinking water treatment in the US with the first large-scale facility being constructed in Westchester County, NY. Quickly following the first installation, numerous DAF installations were constructed throughout Connecticut and Massachusetts and plans were laid for the construction of a 400-mgd DAF facility to server Boston and the surrounding communities. This paper will review the history of DAF with a particular focus on how the adoption of the clarification process for large scale facilities in New England led to significant changes in the design of DAF tanks (i.e. increased loading rates) and flocculation tanks (i.e. decreased floc time), thereby tremendously reducing the capital costs of DAF facilities.

Historically, one of the perceived disadvantages of DAF compared to other clarification processes is that the energy consumption of the process, primarily due to the requirement of recycling approximately 10% of the process flow at high pressures, is prohibitive.

Recent evaluations of the overall operating cost of systems within a DAF water treatment plant have shown that the relative cost of the DAF system is insignificant compared to the overall operating costs of a water treatment plant, particularly the heating, ventilating and cooling costs (HVAC). (Hoek, 2010). (See figure below). In addition, when considering the treatment process as a whole, increased loading rates, reduced flocculation times, and lower residual solids production result in lower power consumption for a DAF plant compared to other treatment processes such as sedimentation.

This paper will present a comparison of the energy consumption of a DAF plant to a sedimentation plant (both in Connecticut) in order to compare the real life energy requirements of various treatment processes including sedimentation and dissolved air flotation, In addition, a case study of a the design and construction of a 4.0-mgd DAF plant in Madbury, NH that implemented innovative energy design concepts to reduce the overall energy consumption of the DAF plant by nearly 30% as compared to a conventional DAF plant will be presented. The true life cycle assessment considering the energy consumption of the design, construction and operation of a DAF plant will be considered. Factors such as energy required to produce the materials of construction, the chemicals consumed during operation and power required to operate the plant have been considered.

For more information, contact the author at mvalade@hazenandsawyer.com.

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