Water Desalination & RO

Abstract This project aims to design a reverse osmosis (RO) plant in Avra valley that will treat 1,969 L/s of Central Arizona Project (CAP) water with 80% recovery to supply drinking water for Tucson that meets the acceptable standard of 450 mg/L after CAP water and groundwater are blended. The RO unit, preceded by a pre-treatment process, consists of 624 pressure vessels in stage one, 360 in stage two, and six ESPA2+ spiral wound membranes per vessel. An optimized evaporation pond system treats the waste brine that is generated by RO. Evaporation ponds were determined to reduce the environmental impact of the RO process by preventing the brine from being injected back into the aquifer and further contaminating valuable groundwater. The pond system uses PVC-lined ponds, each with a filling time of 2.93 yrs and drying time of 2.87 years. The total capital investment for the plant and evaporation ponds is $99,200,000 with an annual operating cost of $68,800,000. In order to pay for annual costs, the Tucson water customers would have to pay 19% more for their water.

Preface Over the past decade, water scarcity, changes in global climate patterns, and urban growth have led to a great shift in the paradigm of municipal water resource management. Low-cost surface and/or groundwater sources are practically depleted in many highly urbanized regions of the world. Therefore, the water supply planning paradigm is evolving from almost exclusive reliance on traditional freshwater resources toward building an environmentally sustainable diversified water portfolio in which low-cost conventional water sources are balanced with more costly but also more reliable and sustainable water supply alternatives such as desalination. While only 0.5 percent of the world’s available water resources are brackish in nature, brackish water desalination has found widespread application because it allows the production of freshwater at reasonably low cost and energy expenditures. At present, over 77 percent of the existing desalination plants in the United States are brackish water desalination facilities. Approximately 220 brackish water desalination plants produce freshwater for municipal water supplies in states such as Florida, Texas, California, New Mexico, and Virginia. Worldwide, brackish water desalination also contributes to municipal and agricultural water supplies in many arid regions, such as southern Spain, the Middle East, Australia, South America, and southern Israel. Seawater desalination, while more costly at present, allows access to the world’s ultimate water resource—the ocean. This water supply alternative has experienced a continuous exponential growth over the last 20 years, a pattern that is projected to continue well into the next decade. This book provides detailed background information on the planning and engineering of brackish and seawater desalination projects for municipal water supply. While it includes a brief overview of key widely used desalination technologies, it focuses on reverse osmosis (RO) desalination, which at present is the most widely used technology for the production of freshwater from saline water sources. The book’s chapters address practically all aspects of brackish and seawater desalination, from basic principles to planning and environmental review of projects to the design of key desalination plant components such as intake, pretreatment facilities, the reverse osmosis system, post-treatment of desalinated water, and concentrate management. The book also provides guidance and examples for sizing and cost estimation of desalination plant facilities.