Water. desalination + reuse

May/June 2013

Water. Desalination + reuse

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Page 33 of 51

TECHNOLOGY Is evaporation the answer to inland concentrate disposal? _________ Frederick H Tack, civil engineer, GHD, USA ___ Editor's Note: Increasing brackish water supplies and widening the reuse of wastewater by the use of membranes in the southwestern United States is running up against the limitation of concentrate disposal costs for inland sites. This article explores concentrate management and summarizes the current progress of ongoing research. THE PRACTICE of desalinating brackish water supplies and treating wastewater for reuse by implementing membrane systems continues to increase as available fresh surface water and groundwater supplies become over allocated or diminish. Parallel to this growth is the increased need for cost-effective concentrate management solutions, where concentrate is the byproduct of membrane desalination processes including reverse osmosis (RO), nanofiltration (NF), microfiltration (MF) and electrodialysis (ED) or electrodialysis reversal (EDR). In the southwestern United States, concentrate disposal methods can be the limiting and deciding factor in membrane and treatment process configuration selections. At inland application locations, the costs of concentrate management can become greater than the costs of the treatment system. It is essential that concentrate management research and innovations keep pace with its membrane counterparts. This article explores these concepts and summarizes the current progress of ongoing research that focusing on the technical considerations of the processes and controls in membrane treatment system configuration and the materials and processes used to implement evaporative methods in disposing of the concentrate stream from inland, municipal scale membrane treatment systems. THe Need For INlaNd desalINaTIoN The need for inland desalination consideration is supported on all sides of municipal water budgets. An average of 41% of southwest water portfolios in the study area rely on a sustainable supply of groundwater to meet their communities water needs. As the easiest and most affordable freshwater aquifers diminish, those sources becomes stressed and prompt water managers and policy-makers to take action. Surface water supplies may vary in non-cyclical patterns, which can make them difficult to manage. | 32 | Desalination & Water Reuse | May-June 2013 It is less likely that new surface water sources will be developed without exploring the feasibility of utilizing brackish sources, and noting that an increased reliance on existing surface water supplies may only transfer the stress between the available fresh water sources and may not ultimately alleviate the concerns. Additional considerations include political boundaries and agendas which typically do not uniformly correlate, and tend to apply overlapping constraints which may prevent a community from finding solutions outside their existing influence. Some municipalities and water districts have adopted a safeyield requirement on the remainder of those freshwater aquifers in groundwater management areas, which is a sustainable practice but does not allow for growth of water demand or loss of supply from surface water sources. TecHNIcal coNsIderaTIoN overvIew The variables in selecting concentrate management methods are as unique as the communities they serve. Concentrate disposal volume, flow rate, time-of-day use, climate, regulation and the available area are some of the baseline considerations. Additional operational and maintenance considerations with membrane implementation for RECLAIMED 3% SURFACE 54% RECLAIMED 2% GROUND 43% ARIZONA SURFACE 57% RECLAIMED 5% GROUND 41% NEVADA SURFACE 56% GROUND 39% CALIFORNIA Figure 1. Typical Southwest US municipal water portfolio* * Percentages from an average of 20 cities or large population areas water resources plan 2010, for each region.

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