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Treatability of Perchlorate-Containing Water by Reverse Osmosis and NanofiltrationBoulder, COSource: 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 ranges treatable by reverse osmosis and nanofiltration, and will evaluate effects of water quality parameters on process performance and perchlorate removal. Objective To determine the removal/rejection of perchlorate by RO (reverse osmosis) and NF (nanofiltration); to evaluate the effects of water quality parameters on process performance and removal of perchlorate using RO and NF; to determine the maximum feedwater recovery of perchlorate using RO and NF (usually limited by salt solubility); and to characterize the concentrate stream and investigate concentrate treatment and disposal options. Background A recently-developed analytical method can detect perchlorate contamination down to a concentration of 4 micrograms per liter (4 ppb). Application of this method has resulted in the detection of perchlorate in a variety of ground and surface waters in California, Nevada, and Utah. In some areas, perchlorate has been found in excess of the State of California Department of Health Services provisional action level of 18 micrograms per liter (18 ppb). This has resulted in the shutdown of some water supply sources. Consequently, there is substantial interest among water utilities to minimize exposure to this chemical in drinking water. RO and NF are established water treatment technologies used for the removal of contaminants such as salts, disinfection by-product precursors, nitrates, and selected pesticides. While it is anticipated that these processes may be effective for the removal of perchlorate, there is little to no peer-reviewed data that demonstrates their applicability to perchlorate contamination at concentrations of 1000 micrograms per liter (1 mg/L) and lower. Moreover, there is no information on the impact of background water quality matrices on the removal of perchlorate using RO and NF. Membrane separation processes for perchlorate removal will result in the production of up to 20 percent concentrate. One issue of concern in using membrane separation processes is the potential for losses of excessive quantities of water with the disposal of the concentrate. The potential for the presence of cocontaminants in the concentrate require that consideration be given to how to dispose of concentrates with significant levels of hazardous materials present (i.e., metals and/or radioactive components). There may be considerable regulatory concern in disposing of the waste and concerns with worker safety. Research Approach Perchlorate contamination of drinking water is currently impacting at least 12 million consumers in the U.S. 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: the success of Phase I, availability of funding for Phase II, and PAC and AWWARF approval of the detailed scope of work for Phase II. AWWARF reserves the right to issue an RFP (Request for Proposals) for Phase II work if this is deemed appropriate. Phase I As a part of Phase I, the researcher will perform a literature review. This literature review should identify past and ongoing research related to the removal of chemical species similar to perchlorate (such as, but not limited to, nitrate and bromate). As part of the review, the researcher will estimate the efficacy of perchlorate removal based on membrane composition and charge and on the potential for ion-coupling of perchlorate (in the presence of low perchlorate concentrations). The researcher should also find information on the effect of other water quality parameters on perchlorate removal. Because perchlorate is an oxidant, the researcher should investigate the potential for long-term oxidation damage to NF and RO membranes. The researcher will conduct a bench-scale membrane screening study in order to assess: Applicable feedwater concentrations and achievable permeate levels. (The researchers can expect to work with perchlorate feedwater concentrations of up to 1 mg/L. This concentration upper limit represents realworld perchlorate concentrations that utilities find in their source waters.) Impact of selected water quality parameters (i.e., ionic strength, TDS/conductivity, hardness, alkalinity, total organic carbon, pH, and temperature) on perchlorate removal efficiency. Natural waters should be used for testing where possible although it is recognized that tests with model waters may be necessary. The researcher will determine which feedwater quality to use to perform the membrane testing. Pretreatment that may be necessary, and the conditions under which pretreatment may be necessary, to decrease membrane fouling or increase the rejection of perchlorate The mechanism for the removal of perchlorate Impact of membrane polymer type on perchlorate rejection The researcher will also characterize concentrate production from the RO and NF bench systems. The researcher should optimize RO and NF processes so that a minimum volume of concentrate solution is produced in order to minimize water losses. The researcher will identify contaminants of concern with regard to concentrate disposal or reuse and determine possible treatment options to improve disposal permitting or reuse. The researcher will also identify regulatory and chemical barriers to those treatment options. Finally, the researcher should conduct bench-scale feasibility testing of the possible treatment options. The results of Phase I work will 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 (which is not directly funded in this RFP) would be to develop design data and operating procedures to accomplish the desired removal of perchlorate at pilot- and full-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 Following completion of the bench-scale work from Phase I, a separate pilot-scale project should be initiated in the year 2000. Phase II of this study will focus on the pilot-scale testing of promising membrane treatment schemes to: 1. Confirm perchlorate removal efficiencies that were determined at bench-scale 2. Optimize membrane system operational conditions 3. Minimize generation of the concentrate stream The researcher will also investigate and employ membrane system pretreatment. A minimum of one groundwater and one surface water should be employed at this scale, with these waters representing either the most difficult to treat, or the most prevalent water quality that has been impacted by perchlorate. The Crafton-Redlands Plume in Redlands, California area will be a required pilot-scale study site for Phase II work. As a part of Phase II, pilot testing of concentrate treatment methods would also be conducted. It is expected that the reject treatment process employed will be that which was most promising during Phase I. 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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