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 Cooling Tower Blowdown Treated to Achieve NPDES Permit Levels

 Challenge

A utilities company in Texas discharged their cooling tower blowdown to a surface water source.  New National Pollutant Discharge Elimination System (NPDES) permit levels were enacted and the discharge now contained copper levels in excess of the new limit.

The copper is believed to have come from the makeup water source as well as leaching from the cooling system.  The new permit requirements called for a substantially lower limit of 53 ppb copper.

 Solution

To meet permit requirements, Evoqua Water technologies proposed the use of ion exchange for heavy metals removal. Following initial laboratory and pilot testing it was determined that activated carbon would be added prior to the ion exchange vessels to remove biocides and to protect the cation resin. In order to increase the efficiency of the resin to remove copper, the pH of the blowdown water was reduced to <4; following the ion exchange vessels, the pH was increased to 6 for discharge.

The final system included:

  • Complete turnkey service contract including ASME code stamped 30 cubic foot vessels, USF ion exchange resin, and resin loading and removal operations.
  • The system is designed in a lead lag configuration.


When copper readings from the system reach a predetermined level, Evoqua service technicians replace the exhausted vessels ensuring that the customer never exceeds their discharge limits.

Exhausted resin is transported to Evoqua RCRA permitted facility for regeneration and metal recovery.  All residuals from the regeneration process are sent for secondary treatment and recovery; no waste goes to a landfill.  The regenerated resin is then shipped back to the customer for reuse.

 Results

  • Evoqua provided the utilities company with one system to treat multiple cooling towers, saving both capital investment and physical site space.
  • Off-site generation and Evoqua's local service provide this customer with the advantage of simple operation and no increase in manpower requirements.
  • The pH chemical feed systems were designed to take advantage of chemicals already used at the plant saving money and storage space.  

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