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Treatability of Perchlorate in Groundwater Using Ion Exchange TechnologyHouston, TXSource: American Water Works Association Research Foundation (AWWARF) Information, December 2000, and AWWARF website, available at http://www.awwarf.com/research/perch.htm. Project Summary: The following text was excerpted from information supplied by American Water Works Association Research Foundation (AWWARF), December 2000, and AWWARF website, available at http://www.awwarf.com/research/perch.htm: This research will develop and optimized ion exchange process to address low concentration perchlorate contamination of groundwater. Objective Develop and demonstrate an optimized ion exchange process to treat low concentration perchlorate contamination of groundwater (less than 1,000 micrograms per liter). Costs of plant equipment and costs of operation, generation of waste brines and rinse water and waste disposal costs should be minimized. The process must be suitable for use by public water treatment utilities. Key items of investigation will be the choice of ion exchange resins, the process, the regenerant and regeneration method, product water quality, and water system compatibility of the treated water. Background In a recent Aerojet study addressing perchlorate contamination at their Rancho Cordova site, Aerojet started with a screening of available treatment technologies. From this screening ion exchange technology seemed the most viable for effective treatment of large quantities of contaminated water. Aerojet then devoted considerable effort to develop an ion exchange treatment system for perchlorate contamination. However, the Aerojet work ended with the development of a biological treatment process. Issues to consider in development of an ion exchange treatment process for perchlorate include the following. Perchlorate has a high affinity for ion-exchange resins. The perchlorate ion is weakly hydrated in aqueous solutions and will therefore prefer attachment to hydrophobic resins. The perchlorate ion has a stronger affinity for resins than the nitrate ion. The high affinity of perchlorate for resins leads to low leakages from the resin, but it also leads to difficulties in the use of sodium chloride as a regenerant. This will lead to low regeneration efficiencies and low perchlorate in the waste brine. It can be reasonably concluded that nitrate selective resins (Triethyl, Tripropyl and Tributyl substituted resins and highly cross linked resins) which are hydrophobic may not be useful for perchlorate removal because of regeneration difficulties. However, hydrophilic resins such as weak base resins with primary, secondary, or tertiary amine functional groups in the hydrogen chloride form or gel type strong base resins bearing one or more hydroxyl groups may show less affinity for perchlorate and therefore allow more efficient regeneration using sodium chloride. A preferred resin for perchlorate has not been selected. Competition with other anions and the relative selectivity of perchlorate in various drinking waters has not been determined. Selectivity orders, however, can be assumed from published literature and may change depending on drinking water composition. The best resin to use, the method of regeneration of the resin, and regenerant disposal are key issues to resolve. A nitrate ion exchange process with brine denitrification and reuse has been developed and may be modified to satisfy project objectives. The combination of ion exchange and biological treatment of waste brines to remove perchlorate may be a practical solution that will allow several cycles of waste brine reuse. Nitrate and arsenic are present in many groundwaters. The effect of these contaminants on any process developed for treatment of perchlorate by ion exchange is unknown. Similarly, the effect of perchlorate on existing ion exchange plants removing nitrate or arsenic is also unknown. Final concentrations of perchlorate in treated water should be in the range of 18 micrograms per liter or less. The California Department of Health Services established a provisional action level for perchlorate in drinking water of 18 micrograms per liter. Research Approach Perchlorate contamination of drinking water is currently impacting at least 12 million consumers. Effective treatment technologies for perchlorate removal or destruction are needed immediately. In order to expedite the research process, this project will be undertaken in two phases with the intent that the contractor selected for Phase I will continue as the contractor for Phase II. Phase II continuation of the project will be contingent upon several factors including: success of Phase I, availability of funding for Phase II, and PAC and AWWARF approval of the detailed scope for Phase II work. The AWWA Research Foundation reserves the right to issue a Request for Proposals (RFP) for Phase II work if this is deemed appropriate. The Crafton-Redlands Plume in the Redlands, California area will be required to be investigated as a pilot-scale study site in Phase II. Phase I As a part of this project the researcher will perform a literature review. This literature review should identify past and ongoing ion exchange research related to the removal of perchlorate, or chemicals similar to perchlorate, such as nitrate and bromate. As part of the review, attempts should be made to identify ion exchange resin characteristics of interest. If possible, these characteristics should be cross-referenced to expected water quality parameters of interest. Additional project activities should include the following. 1. Establish the composition of at least three test waters based on the occurrence of perchlorate in the environment. The test waters should contain variations of chloride, sulfate, perchlorate, and alkalinity. Nitrate and arsenic should also be considered for consideration in some test waters. The use of actual perchloratecontaminated water, possibly spiking with perchorate, sulfate, nitrate, volatile organic compounds or other contaminants to simulate other percholorate contaminated waters may also be considered. 2. Select representative resins from available strong and weak base resins. The use of NSF-approved resins or other resins approved by regulatory agencies for drinking water applications are preferred unless valuable research data can be obtained from unapproved resins. 3. Screen representative resins using column tests. Measure adsorption and regeneration for at least three cycles after a mass balance is demonstrated for the process. Choose regenerant and regenerant concentration. 4. Perform bench-scale testing to establish optimum empty bed contact time, quality of the effluent, and quality of the spent regenerant. Establish the effect of water quality parameters on the media. Demonstrate that process data shows that mass balances of perchlorate and nitrate are achieved. Address media fouling issues, especially as related to naturally occurrring organics. The use of both fixed bed and moving bed bench scale tests should be considered for this work. 5. Establish conditions for biological degradation of perchlorate in regenerant. Determine suitability of regenerant for reuse. 6. Combine ion-exchange and biological degradation components in a single bench-scale system. Run for at least three cycles after material balances for perchlorate and nitrate are obtained. 7. Practical methods of on-line monitoring of perchlorate levels in the treated water should be considered for this work. Alternatively, other methods of determining the amount of water which can be treated for perchlorate contamination by a given ion exchange process should be demonstrated. 8. Prepare a pilot-scale system design with a capacity of approximately 500,000 to 1,000,000 gallons per day to verify bench-scale results. The characteristics that should be considered in the design of this pilot scale system should include the following:
In addition to documenting Phase I activities and results, the final Phase I report should also be suitable for use in Phase II activities. The goal of Phase II (not directly funded in this RFP) would be to develop design data and operating procedures to verify the desired perchlorate removals at pilot scale. A brief description of currently anticipated Phase II activities is presented below. Additional details concerning Phase II activities will be developed in the course of Phase I work. Phase II Phase II of this study will primarily focus on pilot scale testing of promising ion exchange treatment schemes. Pilot-scale work will be done on several groundwaters from actual water supplies, with the focus on confirmation and optimization of the system operational conditions. Phase II will also address treatment of the waste stream. The general intent will be to verify the perchlorate removal efficiencies determined at the bench scale, optimize system operational conditions, characterize the waste stream, and minimize generation of the waste stream. Additional Info Source: American Water Works Association Research Foundation (AWWARF) Information, December 2000, and AWWARF website, available at http://www.awwarf.com/research/perch.htm. |
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