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CONTRAFAST is a high rate solids contact process manufactured by Siemens Water Technologies. This process involves internal and external recirculation of solids originating in the untreated water. Untreated water and treatment chemicals first enter a mixed solids contact module, followed by a gravity clarification module using tubes. Clarified water passes through the tubes and a portion of the solids collected in the clarification module are recirculated to the solids contact module. Clarification rates cited by the manufacturer typically are expressed relative to the surface area of clarification, but do not take into account total footprint. Characteristics of the CONTRAFAST system demonstrated during this study include:
  • Hydraulic loading rate (expressed as described above) of up to 12 gpm/ft2 - the reader should note that the process may have been capable of achieving acceptable performance at higher rates, but the 12 gpm/ft2 rate tested was the upper hydraulic limit for the particular pilot unit tested.
  • Median turbidity <1 ntu and 95th percentile turbidity <2 ntu
  • Residual solids of >5 percent solids

Process Schematic (Provided by Siemens Water Technologies, September 2007)

View Typical System Drawings (Provided by Siemens Water Technologies, September 2007)