Water & wastewater treatment - Dechlorination & pH Trim – Case Study

PROBLEM

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.

Dechlorination & pH Trim

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 calledfor 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.

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.

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 HISTORY

• No moving parts for virtually maintenance-free operation
• Low energy consumption
• Improved process control & product quality
• Eliminates overdosing
• Designs available for open channel and rectangular duct systems
• Custom designs to meet special requirements

OTHER STATIFLO FEATURES

• Low capital cost
• Predictable blending and dispersion formation
• Chemical injection rates reduced to minimum
• Minimal space requirement
• Manufactured to meet all levels of QA/QC
• Manufactured in all commercially available materials
• Low installed weight
• Completely sealed system
• Eliminates radial gradients
• Approaches ideal plug flow
• Self cleaning
• Processes all pumpable material in laminar or turbulent flow
• Available in small or large diameters
• Can be installed in bends to save space