AWWA ACE58249

Rapidly increasing water demands and limited water resources are motivating municipalities, such as Las Vegas, to evaluate beneficial use of more difficult to treat water sources. Approximately 20% of the Las Vegas Valley is underlain by shallow, often brackish groundwater that has been designated a geologic hazard by the State of Nevada due to its salinity, the need for construction dewatering, its impact on existing structures, and its water quality impacts on the Las Vegas Wash and Lake Mead. In an effort to augment the potable water supply and reduce geologic hazard, Southern Nevada Water Authority (SNWA) identified the shallow groundwater system as a potential source of potable water in its 1994 Integrated Resource Plan (IRP). A prepilot study was conducted to compare alternatives for treatment and brine disposal. It was assumed that local regulations and the lack of an ocean outfall would limit brine disposal to zero liquid discharge options, i.e. solar ponds or brine treatment. Desalination with reverse osmosis (RO) membranes and vapor compression distillation (VCD) of the brine was the highest rated treatment alternative in the prepilot study. A subsequent pilot study was conducted to evaluate the feasibility of RO and VCD treatment. A concurrent desktop study was executed to compare the performance and cost of treatment alternatives to those established for RO in the pilot study. Several of the alternatives included treatment processes ahead of RO to reduce hardness and increase RO recovery, and each was evaluated with VCD to achieve zero liquid discharge. The alternatives were as follows: softening followed by RO; high efficiency reverse osmosis (HERO(TM)), a patented process by Aquatech; and, electrodialysis reversal (EDR). The results of the RO pilot study and the desktop study of treatment alternatives are reported in this paper. Includes tables, figures.