Wastewater System pH Control

Client—TransAlta Centralia Generation, Centralia, Washington

TransAlta operates a coal-fired electrical power generation plant located six miles northeast of Centralia, Washington. TransAlta’s new NPDES permit issued in 2010 requires effluent discharged to Big Hanaford Creek or Pond 3E to have a pH in the range of 6-9. The previous effluent pH limit range was 6-10 based on grab samples taken twice per month for compliance. TransAlta has not had a problem meeting the effluent pH limit of 10 but frequently pH levels are in the range of 8.8 to 9.3. To ensure compliance with the tighter effluent pH limits a pH control system was required.

Gibbs & Olson was authorized to review the facility’s process wastewater treatment effluent to Big Hanaford Creek and Pond 3E, evaluate pH control alternatives and make a recommendation with preliminary design criteria and opinions of cost as to which pH control method should be implemented. After evaluating the available data and the potential pH control systems, Gibbs & Olson recommended moving forward with design and installation of a carbon dioxide (CO2) pressurized solution feed system to provide pH control. A preliminary schematic and opinion of cost for the recommended CO2 system was included in the pre-design report.

TransAlta immediately rented a full scale pilot system to meet the NPDES permit requirements for pH in 2011. This system performed well and TransAlta authorized Gibbs & Olson to proceed with design of the permanent CO2 treatment system.