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Removal of Perchlorate and Bromate in Conventional Ozone/GAC SystemsUrbana, ILSource: 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 determine whether conventional ozone/granular activated carbon systems can be modified to remove perchlorate and bromate without sacrificing system performance. Objective The goal of this research is to determine whether the conventional ozone/GAC process can be operated in a manner that will accomplish the removal of perchlorate in drinking water sources. The research should be concentrated on removing perchlorate to below the drinking water action levels of 4-18 ?g/L. Perchlorate removal should be done without interfering with the system performance for its other functions, such as chemical oxidation of contaminants, disinfection, biological stabilization and adsorption. Because the conditions required for bromate removal may be similar to those required for perchlorate removal, bromate removal should also be investigated. Specific objectives are: to determine whether perchlorate and bromate are removed by the chemical reactions associated with the application of the oxidant and its reactions with activated carbon; to determine whether the ozone/GAC process can be modified so that perchlorate and bromate can be removed by chemical means; and, to determine whether the process can be modified to remove perchlorate and bromate biologically. Background Perchlorate and bromate are thermodynamically unstable in water. However, their activation energies for reaction with water to produce chloride and bromide, respectively, are very high. Therefore, their reaction rates at ambient conditions and in dilute solutions, are negligible. However, the presence of a catalyst can speed up these reactions. Such a catalyst may be either inorganic or biological. The chloride in perchlorate is at its highest oxidation state, so there is no possibility of removing perchlorate by oxidizing it. The best option for destroying both perchlorate and bromate appears to be to use them as electron acceptors, and thus to reduce them to other forms, such as chloride and bromide, respectively. Activated carbon is a reduced form of carbon that can supply electrons for reduction processes, but research is needed to determine the best way to condition the activated carbon surface so that the desired chemical reactions can take place. Research is also needed to demonstrate that the activated carbon surface is not fouled by natural organic matter. Studies should be done to determine whether removal of perchlorate and bromate can occur by this means. 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 Ozonation prior to GAC treatment generally increases the amount of biological activity in the adsorber (GAC) by converting a portion of the natural organic matter into biodegradable compounds. Research is needed to determine if the biological activity can remove bromate and perchlorate. Critical questions related to the biological reduction of bromate and perchlorate include: 1) is it possible to develop a biofilm that will result in the removal of both chemicals in a reasonable time, 2) what are the procedures and time required to develop the biofilm, 3) what are the chemical concentrations that must be maintained and operating procedures that must be used to maintain the biofilm, and 4) are any of the other functions (disinfection, adsorption, biological stabilization) of the ozone/GAC processes impeded if it is also used for removal of these species? Bench scale studies will be used to determine whether removal will occur and, if so, under what water quality conditions. There seem to be multiple roles activated carbon can take in the reduction of perchlorate. Activated carbon can either supply electrons for reduction processes from the reduced form of carbon, or facilitate the development of a biofilm that can enhance biological reduction of perchlorate and bromate. For these reasons, this RFP requests that bench-scale experiments be conducted to determine the technical feasibility and treatment conditions necessary for the planning of larger-scale studies. The following research activities should be considered: Activated Carbon Studies. Conduct a preliminary assessment of the ability for fresh/virgin GAC (with and without preozonation) to reduce perchlorate and bromate in natural waters. Determine the extent that natural organic matter prevents perchlorate and bromate reduction. Determine the effect of biological growth on the removal of perchlorate and bromate by GAC after ozonation. Determine whether presence or addition of ammonia and resulting nitrification may help to create sufficient reducing conditions for treatment of perchlorate and bromate. The researcher may also explore the ability of other reduced surfaces, e.g., iron, etc. to supply electrons for reduction processes. Ozonation Studies. Explore water quality conditions under which ozonation may result in by-products (e.g., peroxide, aqueous electrons) that donate electrons sufficiently to facilitate the product of selected ozone byproducts that can contribute to perchlorate and bromate. Preventing adverse effects. The addition of inorganic or organic substances could promote biological growth in the distribution system, introduce undesirable tastes and odors to the water, or cause other adverse effects. Special emphasis should be given to determining whether sufficient electron donors will be available after ozonation of natural water so that the addition of a substance such as ethanol for this purpose can be avoided. Top priority must be given to experiments that show that the desired removals can be achieved without adding inorganic or organic substances. Any detrimental effects of developing reducing conditions should be investigated. The results of this study should be summarized in a final report. In addition to documenting Phase I activities and results, this report should also be suitable for use in Phase II activities. The goal of Phase II (not directly funded in this RFP) will be to develop design data and operating procedures to accomplish the desired perchlorate and bromate 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 Promising approaches to reducing perchlorate and bromate will be investigated in detail. The process needs to be refined at the bench scale, and a pilot study will need to show that the process will work at a larger scale. The pilot scale conditions should be representative of those encountered in field operations. The goal of this research will be to develop design data and operating procedures to accomplish the desired removals. Successful pilot scale work should also include characterization of the GAC biofilm itself. Such issues as the distribution of the biofilm, type of dominant bacteria (aerobic, facultative, anaerobic) and sensitivity to water quality changes should be investigated. 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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