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The Water Treatment Technology Program Newsletter - No. 8 - Summer 1997


The Water Treatment Technology Program (WTTP) is a basic and applied research program with the primary objective of reducing desalting and water treatment costs to promote application of these technologies to water supplies which are currently not cost-effective to treat. For more information about the WTTP, contact Kevin Price at 303-445-2260. Or visit the WTTP web site at: http://www.usbr.gov/pmts/water/


In November 1996, at the request of the City of Tucson, AZ, the City and the Bureau of Reclamation entered into a cooperative agreement to evaluate the costs and viability of membrane treatment of Central Arizona Project (CAP) water. The City is evaluating membrane treatment as part of its efforts both to use its water resources in the most efficient manner possible and to maintain its historically high water quality. This study reflects Reclamation's mission to perform research to evaluate, improve, and reduce the cost of desalting and other advanced water treatment technologies for the benefit of the water treatment industry, water utilities, and water users. Reclamation also seeks to obtain engineering and cost information regarding advanced treatment of CAP water.

To estimate the costs and viability of membrane treatment of CAP water, the study addresses the following questions:

  • What nanofiltration (NF) or reverse osmosis (RO) membrane types are most appropriate and cost effective?
  • What is the maximum product water recovery that can be achieved while avoiding membrane scaling by the precipitation of sparingly soluble salts? These estimated maximum water recoveries will be verified during onsite pilot operations.
  • Does the City's existing filtration and chloramine disinfection provide adequate pretreatment for the membrane process? The adequacy of existing processes will be evaluated during onsite pilot operations to measure membrane fouling and degradation. If existing treatment does not provide adequate pretreatment, what are the recommended modifications and the associated estimated costs?
  • What is the quantity and composition of the brackish membrane concentrate? Can beneficial use be made of the brackish water concentrate? If not, what are the estimated costs to dispose of this brackish water?
  • What are the approximate costs to implement this enhanced treatment option including cost of pretreatment modifications, membrane treatment, and the use or disposal of the brackish membrane concentrate?
  • If the estimated costs appear potentially affordable, what additional pilot plant, regulatory, and cost questions need to be answered in the next evaluation stage of this water treatment option?

Significant progress has been achieved with respect to preparing for pilot tests using Reclamation's Mobile Treatment Plant (MTP) and screening concentrate disposal alternatives. This progress has been possible through the excellent cooperation and collaboration between a number of parties not only within Reclamation and the City but also from other agencies and interest groups through monthly public meetings. Other contributors include representatives from the Arizona Department of Water Resources, Arizona Department of Environmental Quality, Central Arizona Water Conservancy District, Pima County Wastewater Management, Metro Water District, Tucson Regional Water Council, University of Arizona, Cyprus Sierrita Corporation, Pure Water Coalition, and several engineering firms.

For an inland desalting site such as Tucson, disposal or reuse of the RO/NF concentrate is a critical issue. Screening of concentrate disposal options yielded four alternatives for detailed analyses: deep well injection, discharge to the Gulf of California, reuse at local mines, and blend with effluent from the local wastewater treatment plant (WWTP).

Pilot testing presently focuses on pretreating the surface water to obtain RO/NF feedwater with low particulate concentrations as measured by silt density index (SDI). RO/NF testing in the MTP is scheduled later this summer. In addition to evaluating RO/NF membrane operations, the MTP pilot system will supply concentrate water for evaluating two of the concentrate disposal alternatives: reuse at local mines and blend with effluent from the local WWTP. The MTP pilot system will also supply product water for use in separate City corrosion and taste testing studies.

For more information, contact Reclamation engineers Chuck Moody in Denver at 303-445-2258; or Eric Holler in Tucson at 520-744-5182.


Work on the following three Phase II cooperative agreements continues:


Science Applications International Corp., and VARI-Power Co., jointly built and are testing a new integrated pumping and energy recovery system for RO brackish and seawater desalination systems. Functional evaluation testing of the VARI-RO pump using fresh water began earlier this year. Several component modifications were made based on this testing which have enhanced pump performance and reliability. Also, significant progress has been made in the pump electronic control unit and software that has resulted in nearly pulseless operation and a more user-friendly interface. Seawater functional and operational testing will begin around mid-July at the Naval Facilities Engineering Service Center at Port Hueneme, CA.


Thermal Energy Storage, Inc., built and is presently testing a clathrate freeze desalination pilot system which operates using cold, deep seawater. The goal is to demonstrate that this technology is capable of producing potable water from seawater at a cost favorably comparable to inland sources. Construction of the pilot plant is complete. It will operate on a 24-hour basis through the end of July to demonstrate the desalination capability of the clathrate process. Scaling of the plant to commercial size will be accomplished during the July through September time frame.


The University of Texas at El Paso built and is operating and evaluating a low-pressure, high-recovery RO membrane desalting pilot plant at a Colonias subdivision in East El Paso. Installation and electrical hookup are complete, and the pretreatment and two-stage membrane systems were brought online and are operating well. Interstage ion exchange softening and anti-scalant addition are included to boost product recovery. Once sufficiently concentrated RO reject has accumulated in the adjoining enhanced evaporation ponds, field infiltration tests will be conducted to demonstrate the self-sealing properties of native soils using selected additives. It is hoped that the results of these tests will lead to more economical pond construction methods.


Water from Water is published by Reclamation's Water Treatment Engineering and Research Group - Susan Martella, Editor. For more information about the DesalR&D program, contact Kevin Price at: Bureau of Reclamation, 86-69000, PO Box 25007, Denver CO 80225; phone (303) 445-2260; or e-mail a message to MPrice@usbr.gov.