AWWA MTC64578

Brine disposal for inland desalination is a daunting challenge due to the lack of the options that are typically available for coastal communities. In addition, a desert community such as Southern Nevada must consider alternatives for recovery of water from all treatment processes. The Virgin and Muddy Rivers were evaluated by Southern Nevada Water Authority (SNWA) as a new potable water source for a 70 mgd treatment facility. These waters pose extremely challenging water quality conditions. High levels of inorganics, metals, total dissolved solids, and other contaminants require use of advanced treatment methods, such as reverse osmosis, to meet state and federal treatment standards. Brine production, handling, and disposal is clearly a key consideration for SNWA and was carefully evaluated during the course of SNWA's investigation into use of these water sources. Because of the need for complex treatment processes and the difficulty of residual discharge, innovative and ingenious options were analyzed to meet water quality standards and provide the project recovery rate of at least 92%. Various processes were evaluated, including multi-stage reverse osmosis (RO), mid-stage ion exchange, and/or lime softening for optimizing recovery. Zero discharge options were developed and, as expected, brine disposal was found to be the highest cost for the plant. Even though the Nevada climate is ideal for brine evaporation, the anticipated brine flow rate of 5 mgd resulted in brine disposal capital costs between $130 million to $500 million. Developing a near zero liquid discharge facility requires understanding the relationship among the various available treatment options and brine disposal options. This paper describes the advantages, disadvantages, costs and methods of application which were analyzed for the Virgin and Muddy Rivers. Treatment schemes evaluated in this project will advance the database of projects available to utilities looking at challenging water sources in arid climates and striving for zero liquid discharge. Includes table, figures.