New Technologies and Split Treatment Result in Increased Production Capacity and Improved System Performance for Clearwater

T he City of Clearwater (City) owns and operates the reverse osmosis (RO) water treatment plant No. 1 (plant) that was originally constructed in 2003. Similar to many brackish water RO facilities, the City blends pretreated raw water with RO permeate to maximize production while minimizing operational costs. In the case of this plant, the City blends 1 mil gal per day (mgd) of pretreated blend water with 2 mgd of RO permeate; however, the City’s potable water demands exceeded the permitted capacity of the plant. As such, the City relied on Pinellas County to augment its potable water supplies. Concerned with losing more control over the treatment, quality, and cost of its potable water supplies as demands increase, the City sought to increase its potable water independence. To this end, it retained the services of CDM Smith to increase the production capacity of the plant by 50 percent. While the consulting engineering firm that originally designed the plant considered its future expansion, CDM Smith’s vision of the expansion differed significantly. Per the original design, expansion of the plant was predicated upon the installation of additional treatment units, including two new dual-media pressure filter units, one new membrane feed pump, one new RO train, one new blended water transfer pump, and other ancillary systems. As this approach simply called for the duplication of existing treatment processes, no improvements in plant performance or operational enhancements were expected. Furthermore, in order to accommodate the new membrane process equipment, extensive and costly modifications to the existing pre-engineered membrane process building would be required. Following a comprehensive evaluation of the existing plant, CDM Smith developed an alternate approach to the expansion, one that focused on improving and enhancing plant operations while simultaneously increasing its production capacity. Through a series of extensive studies designed to evaluate the performance of various processes, an enhanced split-treatment process emerged as the best approach to meet the City’s needs. Unique features of this project include the implementation of a new arsenic adsorption system, the use of new 440-sq-ft membrane elements to eliminate the necessity of a new RO train and associated building modifications, and the elimination of the ferric chloride coagulation process. This article presents and discusses the original treatment process, factors that were critical to the success of the project, the approach to the process performance studies, the data collected throughout these studies, and the approach to the design of the expansion. In addition, challenges encountered and overcome throughout the course of this project, lessons learned, and select full-scale operating data will also be presented. New Technologies and Split Treatment Result in Increased Production Capacity and Improved System Performance for Clearwater