Orica Australia Pty Ltd

Use of a Magnetic Ion Exchange Resin to Improve DBP Precursor Removal and Reduce Coagulant Usage at Lee County`s OLGA WTP

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Courtesy of Orica Australia Pty Ltd

The 5 MGD Olga WTP in Lee County, Ft Myers, treats water from the Caloosahatchee River where TOC and color levels range from 15-25mg/L and 80-350 Pt Co Units respectively. This surface water presents many treatment challenges and treatment costs are high with alum doses in excess of 200mg/L required during times of the year to provide an adequate treated water quality.

As part of Lee County’s treatment plant reservoir and plant improvements for the Olga Water Treatment Plant (WTP), Parsons has been contracted to replace the current alum coagulation feed system with a ferric sulfate coagulation feed system. In order to determine chemical feed rates and their impact on water quality, disinfection and the formation of disinfection by-products, three days of on-site jar testing were conducted at the Olga WTP. MIEX® ion exchange resin was also evaluated for enhanced removal of dissolved organic carbon (DOC). DOC serves as the precursor matter in the formation of disinfection by-products with the addition of chlorine. Aluminum sulfate (alum), powder activated carbon (PAC) and polymer in conjunction with ferric sulfate were also tested. Following the jar tests a 6-week trial was conducted to further investigate MIEX® treatment followed by coagulation with ferric sulfate.

To determine the impacts these treatment regimes have on disinfection, both chlorine dioxide and chlorine decay tests were performed on optimum treated waters from the jar testing and pilot plant trial.  For waters treated with ferric sulfate and MIEX® followed by ferric sulfate, disinfection by-product formation potentials were conducted using chlorine to estimate the concentrations of trihalomethanes and haloacetic acids that would be formed if chlorine were used for primary disinfection.  This paper will discuss the results of the bench testing and MIEX® pilot plant trial conducted at Lee County’s Olga WTP and compare water quality data and operating costs of the treatment alternatives
investigated by Parsons.

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