A Sustainable Approach to Low Pressure Reverse Osmosis Concentrate Management

Abstract

Population increases within the city of Ormond Beach, Fla., increased demands on the city's existing 8-mgd conventional lime-softening water treatment plant. Because of deteriorating raw water quality, the city's consultant conducted a pilot study and completed preliminary and final designs for a 4-mgd low pressure reverse osmosis (LPRO) expansion. A critical aspect of the project focused on managing the concentrate stream. Although concentrate characteristics are functions of raw water quality, membrane selectivity, and system operating conditions, LPRO concentrate is generally characterized by elevated values of total dissolved solids, chloride, total hardness, organic carbon, and/or color. The concentrate management strategy implemented for the project consisted of blending LPRO concentrate with reclaimed water at the city's wastewater treatment plant (WWTP), which augmented reclaimed water supplies with an unused resource without consuming the WWTP's treatment capacity.