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The Desalination and Water Purification Research & Development Program Newsletter - No. 21 - Winter 2001

AWARDS & CONTRACTS FOR FY01

In FY01, Reclamation's Desalination and Water Purification Research Program (DWPR) awarded six contracts for research: four for studies and two for pilot plants.

STUDIES

Novel Membrane and Device for Direct Contact Membrane Distillation. This continues previously funded work with the New Jersey Institute of Technology to develop appropriate membrane systems for a direct contact membrane distillation device. This year, the project's objectives are to develop laboratory modules of composite hydrophobic porous hollow fiber membranes, determine the water vapor permeance of these fibers, and develop preliminary economic estimates for these devices. The study will also look at long term performances of membranes and investigate desalinating saline water at 60 - 90 degrees Centigrade.

Predicting Membrane Flux Decline Using Parameters Derived from Field Flow Fractionation Measurements. This new study with the Colorado School of Mines is to improve methods to predict fouling. Using flow-based field flow fractionation techniques, researchers plan to develop a new engineering model to predict membrane fouling. This is expected to improve costs and provide greater ease of use of membranes.

Impact of Magnetic Fields on Reverse Osmosis Separation. This new study with the University of South Florida will examine whether the effect of magnetic fields on the quantum numbers, velocity, and waters of hydration associated with ionic species will cause beneficial changes in ion permeation of membranes. The study objectives are to determine the effects of the magnetic field on pure water permeability, on reverse osmosis separation, and on production rates and salt permeation with various salts.

Removal of Biofilm and Other Foulants from Spiral Wound Reverse Osmosis Membranes. This new study with Novaflux Technologies, Inc., will examine whether a lean dispersion of water droplets in the air (1:500) makes an effective cleaning agent for removing foulants (particularly biofilms) from membrane surfaces. The study's objectives are to investigate cleaning single 8-inch elements and up to three elements in series at existing plants and to do an economic assessment.

PILOT PLANTS

Various Membrane Bioreactor Systems for Water Reclamation. This new program with the City of San Diego will examine the membrane bioreactor, one of the promising technologies being considered for wastewater reclamation. The program's objective is to evaluate new membrane bioreactor systems (Kubota, U.S. Filter/Jet Tec) at the pilot plant level. The program will also evaluate the suitability of reverse osmosis for treating membrane bioreactor system effluent, demonstrate the membrane bioreactor/reverse osmosis/ultra-violet train for Title 22 approval, update costs estimates for membrane bioreactor applications, and optimize membrane bioreactor processes.

Membrane Pretreatment for Seawater Reverse Osmosis Desalination. In this new program, Aqua Resources International will evaluate the performance of MF and UF as pretreatment for seawater reverse osmosis systems. Recently developed high-quality, commercial systems can provide reliable, well-filtered source water at a reasonable price. The program's objectives are to evaluate the performance of combined systems for seawater desalination and to determine the cost benefits of these membranes compared with conventional pretreatment over the life cycle of the plant.

CONCENTRATE DISPOSAL CD IS HERE!

Mickley and Associates completed Membrane Concentrate Disposal: Practices and Regulations. This reference manual is a valuable source to characterize and document concentrate disposal practices and regulations on a federal and state basis. We now have a CD containing the project report text, an interactive version of the membrane plant survey database, and an interactive concentrate disposal cost-modeling program.

Regulations and cost are the primary factors for selecting an alternative for concentrate disposal such as surface water and sewer, evaporation pond, deep well, spray irrigation, and zero discharge. The report, database, and cost models will be a valuable resource for members of the water treatment community to plan and design alternatives for concentrate disposal in membrane treatment projects.

The study examined membrane concentrate disposal practices in the U.S. and determined that membrane technology has grown dramatically to address water quality issues and to treat water to attain drinking water standards. The use of desalting membranes to treat lower quality water sources is increasing. There are several ongoing concerns regarding disposing of desalting plant, including:

  • Suitable disposal options vary by site and are complicated by changing regulatory requirements and limited resources for water treatment plants.
  • The public and some regulators may wrongly think that membrane concentrates are "hazardous wastes."
  • Surface and ground water quality continues to deteriorate, resulting in concentrates with higher levels of contaminants.

These environmental concerns must be addressed so that these technologies can continue to grow to meet the water quantity and quality challenges facing the U.S. Please download from the DWPR web site http://www.usbr.gov/pmts/water/research/DWPR/, or contact Susan Martella at (303) 445-2257 for the report with the attached CD.

THE TALE OF THE "TAIL" - Pore Size Standardization

Varying pore sizes in ultrafiltration membranes allows spores such as anthrax or cryptosporidium to slip through membranes. The closer we can come to exact and small pore sizes, the more spores we can remove. Membrane manufacturers and end users have come together under the auspices of the North American Membrane Society's Sponsored R&D Committee to create a standard protocol for measuring the pore size distribution of UF membranes. Now vendors and users set these standards together.

The quest for new and improved membranes for pressure-driven (MF and UF) membrane separations processes invariably leads through the "pore-size distribution" or molecular mass cut-off (MWCO). As with all separation processes, membranes have two key figures-of-merit: speed (flux) and selectivity. Beyond making a thinner skin, membrane manufacturers must strive to create as many pores per unit area as they can. Moreover, the physical and chemical processes that govern the formation of pores are not perfectly uniform (especially in the manufacturing milieu). This leads us to the "tail" of the pore size distribution.

For all intents and purposes, all commercial, porous membranes have a distribution of pore sizes that are steeply bounded at the smallest radii but with a significant tail into the larger pore diameter region the tail can also contain a small peak indicating a 'bimodal' pore size distribution. Numerous modeling calculations have shown how dramatically a few pores at the larger size end of the pore size distribution can affect the selectivity of the membrane separation. For example, if one is concerned with removing viral (e.g. smallpox) or microbial pathogens (e.g., anthrax or cryptosporidium) from water, a figure of merit for selectivity is often the LCR, which is defined as the log (bulk concentration/permeate concentration). Dan Boggs at Baxter Healthcare analyzed a variety of cases of viral removal with "tight" UF membranes and illustrated that relatively few 0.5 micron "defects" can cause loss of over 2 orders of magnitude in the LCR. What are a relative few defects? Well, a UF membrane may have a pore density ~1 x 1011 pores/cm2, and a few defects are only ~5 x 103.

The metrology research conducted at the National Institute of Standards and Technology in Boulder, CO has two major components: (1) develop more sensitive and reproducible liquid-liquid porosimetry methods measure the geometrical pore size distribution, and (2) more completely investigate the correlative power between the geometric measurements and the "solute" challenge measurements (e.g., MWCO). The project got underway in May 2001 and is anticipated to run for three to four years (depending on the number and committment level of the sponsors).

Initial efforts this first year have benchmarked an apparatus to reproducibly meter very low volumetric flows (@100 nL/s) of pore-fluid displacing fluids while measuring the dynamic response of the differential pressure. A variety of calibrating fluids and membranes have been developed and are being tested. In addition, several apparatuses for measuring solute retention have been assembled. The NIST research team feels confident that these efforts will make it easier for all membrane users to "chase down the tail." Contact John Pellegrino at (303) 497-3416.

YES, WE STILL MAKE HOUSE CALLS - Mobile Water Treatment Plant

Reclamation's Mobile Water Treatment Plant (MTP) is contained in a small trailer that travels to test various water treatment processes. Reclamation's Technical Service Center, Advanced Water Treatment Program, uses the MTP to provide technical assistance to small, rural, and Native American communities with limited financial resources. This assistance finds ways to remove potential health risks from their water supplies and meet increasingly stringent water quality regulations. The MTP helps determine the optimum water treatment process at that particular location to achieve the desired water quality. For qualified communities, a supporting staff of engineers and technicians will travel with the MTP to address water treatment problems and recommend solutions. Reclamation and the community cost-share on a 50-50 basis.

The MTP is equipped to demonstrate most conventional and advanced treatment processes (including membranes) at a total production rate of 6 gallons per minute. The MTP is configured so that any combination of processes can be linked. Processes are computer controlled so that they can run 24 hours a day. Reclamation can supply operators, but local utilities are encouraged to participate.

Dennis Watt, Hydrologist in Reclamation's Lower Colorado Region, is enthusiastic about the trailer, "I believe the trailer benefits Reclamation by providing an opportunity for local water treatment research staff to work directly with the MTP staff to solve problems, first hand with real world trade-offs, I believe, is a big difference from academia. The MTP helps differentiate Reclamation's water treatment research staff from research institutes. Also, new technology transfer will occur faster if it can be demonstrated at a real treatment plant with relatively little cost. The MTP gives Reclamation exposure to communities that may not realize all that Reclamation can do in water treatment and other areas."

With the MTP, Reclamation staff can evaluate existing water resources, water quality, and water treatment; perform pilot-scale testing for water treatment options, and provide results, analyses. We also provide recommendations including a feasibility level design and cost estimate for the optimum water treatment scheme. For more information or to schedule the MTP, contact Bob Jurenka at (303) 445-2254.

MICROBUBBLES COLLECT EXCESS AIR

Excess levels of dissolved air can damage aquatic ecosystems. Fish get gas bubble disease (GBD) from high concentrations of nitrogen in the water, resulting in large and costly fish kills. As this water quality problem affects Reclamation projects such as Grand Coulee and other dams along the Columbia River system, Yellowtail Dam, Alamosa Franklin Eddy Canal, Tracy Fish Collection Facility, and others, Reclamation's Technical Service Center's (TSC), Water Treatment Engineering & Research Team, is conducting research into a solution.

Microbubbles in flows act as collectors for excess air. These bubbles, formed by a technique developed by the TSC, are less than a micron in diameter. Introducing microbubbles may provide a cost-effective and practical solution.

This treatment technique has been explored in a laboratory environment for the past two years and successfully field tested in 2000 in Alamosa, Colorado. Supersaturated water, by definition, has total dissolved gas (TDG) levels higher than 100 percent. Acceptable levels of TDG are about 110 percent. In field testing, microbubbles lowered levels by 35 percent, thereby approaching acceptable levels of TDG.

Minimizing power consumption, amount of air used, diffuser size, and capital and operation and maintenance costs are needed to make this technology practical. In 2001, TSC made significant advances toward meeting these demands.

Reclamation has received a U.S. patent on this treatment method and is continuing to conduct laboratory and field investigations. This year, study objectives are to:

  • Evaluate dissolved air concentrations, gas/water flow rates, and diffuser surface areas
  • Improve diffusers for large-scale and long-term use
  • Reduce operation and maintenance costs
  • Do further field testing at Alamosa and investigate testing locations on the Columbia River.

This technology may offer a low cost, practical alternative to modifying facilities to protect the environment from GBD and other damage to aquatic ecosystems. Reclamation is looking for further opportunities to test this intriguing and promising approach to reducing high levels of dissolved air.

BIOFILMS AND BIOFOULING

The National Science Foundation (NSF) established Engineering Research Centers to encourage multi-disciplinary research and increase U.S. industrial competitiveness. The Center for Biofilm Engineering (CBE) at Montana State University, Bozeman, was established in 1990 to foster a new approach to university engineering and science education.

At the CBE, multidisciplinary research teams work on industrially relevant problems and find potential applications for microbial biofilm formation. The multi-disciplinary approach allows microbiologists, engineers, computer scientists, and others to approach problems from many angles to develop multi-faceted solutions which can work in many areas. For example, CBE engineers, microbiologists, and statisticians have recently developed a protocol to optimize adding biocides to pools and spas.

The challenge here was to find the best dosing strategy for a system with a bulk fluid reservoir (the pool or spa) and a porous media filter which can harbor microbial growth. Though developed for recreational waters, these findings can help us understand and control biofilm growth in other complex systems, such as drinking water treatment. Likewise, our drinking water research has improved our understanding of how microbes interact with metal substrata, thereby helping advance our corrosion research.

The CBE has graduated from the NSF seed funding to become a foundation for research. Reclamation and 20 other companies pay subscription fees to sponsor research and educational initiatives. Funding from NSF, National Institute of Health (NIH), and other federal, state, and local agencies as well as corporations and universities help support specific research projects. This partnership approach has lead to open sharing of knowledge and allows the research community to build on what has been learned.

Reclamation's partnership with the CBE is mutually advantageous. Kevin Price, Manager of the Water Treatment Engineering & Research Team, says "Since Reclamation has joined, the CBE has broadened its interests and has produced good proposals to fund that would otherwise never have come to Reclamation's attention."

The larger research effort in biofilms has now pointed down pathways to look at natural organic matter/biofilm interactions, which affect virtually every surface in the environment. The results from the research done to reduce natural organic matter fouling and biofouling on membranes is also being extrapolated to explain biofilm reactions in a much broader sense (e.g., when the biofilms and their processes occur in virtually every aqueous environment).

This research led to biological pretreatment that can reduce fouling in membrane systems. CBE investigators proposed a technology to increase the biological stability of water to be further processed by reverse osmosis membranes The technology will improve membrane productivity by complementing existing processes in a pretreatment train while reducing dependence on extensive use of disinfectants. The approach is ecologically sound because it uses biological processes to control subsequent biological activity. We are focusing on controlling biofouling in an engineered system rather than allowing it to occur in undesirable locations. The process is based on the experiences of the drinking water industry where biological filtration is being used to:

  • Reduce concentrations of natural organic matter
  • Decrease disinfectant demand
  • Reduce downstream fouling of the distribution system.

Using a biological treatment process in a RO system design should be considered as a way to reduce operation and maintenance costs and more efficiently run a water treatment plant.

Reclamation and the CBE hope that this effort will be one of many cooperative, multi-disciplinary ventures to address biofilm problems and applications. Anne Camper, research team leader within the CBE and Associate Professor for Civil Engineering, and Associate Dean for Research and Graduate Education, in the College of Engineering, looks to a promising future, "The Center has really appreciated the opportunity to interact with Reclamation. We think it has been a fruitful collaboration, and we hope to do more in the future." Contact Anne Camper at (406) 994-4906 for further information.

DWPR PROGRAM

The DWPR program focuses on: (1) Research and studies on desalination technologies and related issues that push the state of the art forward so costs can be reduced, and (2) Development and demonstration activities to test technological advancements, confirm economics, and gain public acceptance.

For more information, contact
Kevin Price, Group Manager, Water Treatment Engineering Research Team, 86-68221
Bureau of Reclamation
Technical Service Center
P.O. Box 25007
Denver CO 80225
FAX (303) 445-6329
WaTER@do.usbr.gov

Or refer to our program web site:

Desalination and Water Purification Research and Development Program: http://www.usbr.gov/pmts/water/research/DWPR/.


CONTACT US

Water from Water is published by Reclamation's Water Treatment Engineering and Research Group - Susan Martella, Editor. For more information about the DWPR 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.