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The Desalination and Water Purification Research & Development Program Newsletter - No. 16 - Spring 2000

PROGRAM INFORMATION

The first research results for the Water Desalination Act of 1996, Public Law (PL) 104-298, are coming in. This newsletter showcases only a few of the many projects with reports available by late summer. While the first appropriation for PL 104-298 occurred in October 1997, cost-shared financial assistance agreements were not awarded until September 1998, in order to ensure a strong and fair competition based on the advertised criteria.

The projects discussed in this newsletter represent three major areas meeting the Desalination & Water Purification Research & Development (DWPR) Program's mission to reduce current desalination costs: membrane fouling, innovation, and concentrate disposal. Prevention of membrane fouling can require a significant expense for pretreatment processes. Understanding how a membrane interacts with real world waters is critical to finding ways to prevent fouling. As our understanding improves, membrane processes can be designed to reduce the cost of treating feedwaters.

A second area that could dramatically reduce costs, is the quest for new desalting technologies through sponsoring innovative ideas. In particular, current technologies are very expensive when applied to very small systems, especially in remote locations. Based upon new research results, dewvaporation can economically provide small amounts of water in remote locations. This is mainly due to the low capital cost and the low operation and maintenance requirements.

Concentrate disposal is another major area. One of the greatest variables in the cost of desalination is concentrate disposal. Work is rapidly coming to a close on a study of regulation, current practices, and costs of concentrate disposal in the U.S. This will be a valuable resource for desalting professionals.

For more information about the DWPR Program, contact Kevin Price, Program Manager, at (303) 445-2260, MPrice@usbr.gov, or visit the DWPR web site at: http://www.usbr.gov/pmts/water/research/DWPR/.

HYDROPHILICITY

The University of Nevada-Reno completed a phase I project titled Characterization of the Hydrophilicity of Polymeric Reverse Osmosis and Nanofiltration Membranes: Implications to Membrane Fouling in September 1999, and will complete the phase II project titled Comprehensive Approach to the Prediction of Membrane Fouling in September 2000.

The overall objective of the phase I project was to develop a method for determining actual hydrophilicity by use of an automated goniometer and perform a series of contact angle measurements using polar and apolar liquids. The overall goal was to characterize the hydrophilicity of several water treatment membranes and to relate hydrophilicity to the fouling potential of the membranes.

Using the phase I results, the phase II project will mechanistically examine the adhesion between a colloid and the membrane surface. The main objective is to predict the fouling potential of typical colloidal feed streams on membrane surfaces by evaluating the fundamental surface characteristics of both the membranes and the colloids.

The phase I project successfully developed a method for determining actual hydrophilicity by performing a series of contact angle measurements using polar and apolar liquids. The results are useful in selecting membranes to fit specific applications and in optimizing operation parameters and pretreatment schemes for membrane processes.

When completed, the phase II project will result in a comprehensive approach for evaluating the combined effects of several surface properties. The research will result in numerous implications for reducing membrane fouling, including optimization of feed stream pretreatment, modification of the membrane surface, or selection of the most appropriate membrane based on feed stream characteristics. Final results of these projects are expected to reduce chemical costs for membrane cleaning by 50 percent and decrease membrane replacements costs by 50 percent. In addition, labor costs will be reduced and the amount of chemicals required to pretreat the raw water will be decreased. The total cost reduction will be approximately 20 percent and does not reflect the increase in water production which will be realized.

Final results will also have a positive environmental impact due to increased efficiency of RO and NF membrane processes. Fewer chemicals will be required for pretreatment and cleaning and less energy will be consumed during pumping since the membranes will operate at lower pressures as a result of reduced fouling.

ATMOSPHERIC PRESSURE DESALINATION

Arizona State University completed a phase I project titled Innovative Atmospheric Pressure Desalination in September 1999 and will complete the phase II project titled Carrier-Gas Enhanced Atmospheric-Pressure Desalination in September 2000. Dewvaporation, a relatively new non-traditional and innovative heat efficient tower process, is a specific desalination humidification-dehumidifation application which uses air as a carrier-gas to evaporate water from saline feeds and dew to form pure condensate at constant atmospheric pressure. The phase I research unit is constructed out of thin water wettable plastics to avoid corrosion effects and to reduce equipment cost and is operated at pressure drops of less than 0.2 inches of water. Desalination of mild brackish water (800 mg/L TDS) was demonstrated with a gain output ratio (GOR), also called the energy reuse factor (f), of 11. As a result of successful phase I research, this project received phase II funding to design, build, and test a 1,000 GPD test unit.

The overall objective of the phase I project was to enhance the heat and mass transfer coefficients on the wettable heat transfer wall. The phase II project will focus on novel methods to improve the efficiency of the process and the development of a 1,000 GPD demonstration unit. This work will result in the reduction of operating costs. The phase I successful investigation of the dewvaporation process concluded that: (1) the process is capable of brackish and seawater desalination; (2) the average operating costs for brackish and seawater desalination for small plants ($3.35/1,000 gallons) could be reduced to $1.55 with solar energy and $1.52 with atmospheric steam waste heat; (3) the projected capital cost for a brackish and seawater 1,000 GPD dewvaporation plant would be $2,064; and (4) use of the horizontal serpentine airflow configuration provides excellent distribution needed for heat transfer.

When completed, the phase II project will result in the construction of a mobile 1,000 GPD test plant, which will be tested at sites with brackish water, seawater, or on effluent waters from RO treatment plants. These operations would further demonstrate the economics and versatility of the dewvaporation process. The desalination of saline waters, such as RO concentrate streams and seawater, appear to have the best economic advantage for the dewvaporation process, when compared with other technologies. The dewvaporation technology may find an economic niche and provide an economic advantage over all current desalination technologies for small plant applications. Waters may be produced at about $2-$4/1,000 gals. Capital costs may approach $2 GPD.

CONCENTRATE DISPOSAL

Mickley and Associates continues the study of Membrane Concentrate Disposal: Practices and Regulations. The major objective is to provide the membrane drinking water industry with a valuable and useful reference source focusing on, characterizing, and documenting concentrate disposal practices and regulations on a Federal and state-by-state basis. Thermal desalination will also receive attention.

When completed, the proposed effort will provide a means and a tool for: (1) determining, documenting, and representing the status of the membrane drinking water industry to portray industry growth, define industry trends, and define industry problems and needs; (2) communicating such information to interested parties to highlight the viability and feasibility of membrane produced drinking water, represent the importance, size, growth, and strength of the industry; (3) enabling utilities to set up a network of similar membrane plants that can result in cost reductions and saving during planning, design, and operation; and (4) using the reference source in the evaluation, planning, design, and operation of membrane facilities to avoid past failures and to capitalize on existing successes.

This project will result in publication of a CD ROM containing the project report text, an interactive version of the membrane plant survey database, and an interactive concentrate disposal cost modeling program. The project is not aimed at directly improving the technology but rather at providing information and understanding that will result in improved use of the current technology. This in turn will result in direct cost benefits through cost reduction.

To view previous publications, select the edition you want:

Edition 1 - Spring 1995
Edition 2 - Summer 1995
Edition 3 - Winter 1995
Edition 4 - Spring 1996
Edition 5 - Summer 1996
Edition 6 - Winter 1996
Special Edition - 1996
Edition 7 - Spring 1997
Edition 8 - Summer 1997
Edition 9 - Winter 1997
Special Edition - 1997
Edition 10 - Spring 1998
Edition 11 - Summer 1998
Edition 12 - Winter 1998
Special Edition - 1998
Edition 13 - Spring 1999
Edition 14 - Summer 1999
Edition 15 - Winter 1999
Edition 16 - Spring 2000
Edition 17 - Summer 2000


CONTACT US

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.