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Problem

Dechlorination & pH Trim: Public water treatment plant required highly effective control to dechlorinate and pH trim in difficult access situation.

Southern Water’s Weirwood Treatment Works supplies direct to the consumer and therefore the highest levels of efficiency and process control are required. Weirwood uses a super-chlorination system which requires effective excess chlorine removal and pH trimming post-treatment.

Whilst the requirements could only be met with a static mixer, there was a potential problem in that no suitable pipework sections existed for making a conventional installation.

Solution

Statiflo engineers examined the problem and came up with the ingenious solution of actually integrating a static mixer into the contact chamber used for the super-chlorination process.

This was effected by building a stainless steel dam across the contact chamber which incorporated a static mixer into its lower edge, the design of which allowed for the fact that only a small head loss was available across the tank.

The final hurdle to be overcome was one of access – only a 460mm man-way existed, thus limiting the size of equipment which could be brought into the chamber.

The situation called for a unique design. The mixer needed to be rectangular in shape, 600mm high and 450mm wide, but because this would have been too large for the man-way, it was split into two halves along the centre line and flanged. This enabled it to pass through the man-way and be re-assembled in situ complete with integral injectors to allow proper dechlorination.

Result

Statiflo’s ability to tailor-make a solution as a normal procedure resulted in the installation being entirely successful despite the numerous limitations the site imposed.

Dechlorination & pH Trim results

Since installation in June 1989, numerous trials have confirmed the continued satisfactory performance of the unit and its ability to maintain set point chlorine concentrations and pH level.

STATIFLO MOTIONLESS MIXER FEATURES OF PRIMARY IMPORTANCE IN THIS CASE STUDY

  • No moving parts for virtually maintenance-free operation
  • Low energy consumption 
  • Low capital cost
  • Eliminates overdosing 
  • Chemical injection rates reduced to a minimum 

Other Statiflo Features

  •  Low pressure drop
  •  Available in all sizes
  •  Eliminates radial gradients
  •  Available in any material
  •  Low shear mixing
  •  Special materials for corrosive applications
  •  No direct energy supply
  •  Meets all QA/QC levels
  •  Available worldwide
  •  Low installed weight
  •  Space saving custom designs in pipe bends
  • Does not require downstream straight pipe for best performance in a matter of weeks.
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