A Sustainable Approach to Low Pressure Reverse Osmosis ConcentrateManagement: Reclaiming and Reusing a Valuable Resource

摘要

Population increases within the city of Ormond Beach placed increased demands on the city’srnexisting 8.0‐million‐gallon‐per‐day (mgd) conventional lime softening water treatment plant. Combinedrnwith deteriorating raw water quality due to salt water intrusion and upconing, the city retained thernservices of CDM to conduct a pilot study and complete the preliminary and final design for a 4.0‐mgdrnlow pressure reverse osmosis (LPRO) expansion. In 2006, the final design of the LPRO expansion wasrncompleted and construction activities commenced. In Janaury 2008, the expansion was first placedrnonline and all construction activities concluded a few months later.rnThe most innovative aspect of this project focused on the management of the concentraternstream. Traditionally, concentrate is considered an undesirable waste stream, which presents arnsignificant obstacle to implementation. While the specific characteristics of concentrate are functions ofrnraw water quality, membrane selectivity, and operating conditions, LPRO concentrate is generallyrncharacterized by elevated values of total dissolved solids (TDS), chloride, total hardness, organic carbon,rnand color. Conventional methods of concentrate management include, but are not limited to, deep‐wellrninjection, discharge to a surface water body, discharge to a sanitary sewer, or discharge directly to thernheadworks of a waste water treatment plant (WWTP).rnThe successful permitting of an innovative and sustainable method of managing up to 1.0 mgdrnof concentrate produced by Ormond Beach’s LPRO expansion was made possible by a collaborativerneffort by the city, the Florida Department of Environmental Protection (FDEP), and CDM. This uniquernmethod of concentrate management provided for the blending of the LPRO concentrate with reclaimedrnwater at the city’s WWTP. The most significant benefit associated with the implementation of thisrnconcentrate management strategy included the ability to reuse this previously unutilized resource andrnaugment reclaimed water supplies without consuming treatment capacity of the WWTP.rnOperating data collected over the past 17 months demonstrate the success of this innovativernand sustainable method of concentrate management. Since the startup of the LPRO expansion, the city’srnreclaimed water supplies have increased by approximately 0.4 mgd. While the use of reclaimed water isrnheavily affected by local precipitation rates, approximately 50 percent of the LPRO concentrate isrnreclaimed on average and during periods of high reclaimed water demand, 100 percent of the LPROrnconcentrate is reclaimed. The TDS and chloride values of the blended reclaimed water have increased asrna result of concentrate blending; however, no adverse effects to the vegetation or soil structure havernbeen observed. This paper will discuss the permitting efforts and challenges associated with thernimplementation of this innovative method of concentrate management, the first 17 months of operatingrndata, and lessons learned throughout the course of this project.