United States Environmental Protection Agency Municipal Environmental Research Laboratory Cincinnati OH 45268 Research and Development EPA-600/S2-81-115 Oct. 1981 Project Summary Inorganic Contaminant Removal from Drinking Water by Reverse Osmosis Martin R. Huxstep The removal of inorganic contami- nants from drinking water was studied using two reverse osmosis (RO) treat- ment systems. A high pressure (400 psi) and low pressure system (200 psi). each having a rated capacity of 1.82 L/sec (28.9 gpm) of product water, were used to evaluate their capability for removing various inor- ganic contaminants.' A groundwater was spiked with varying concentra- tions of fluoride, nitrate, arsenic III, and arsenic V, and runs of 2 to 5 days ware conducted to determine rejec- tions. Removal data were also col- lected on the natural constituents in the feed water of total dissolved solids, hardness, calcium, magnesium, chloride, sodium, and sulfate. . For all contaminants and natural constituents measured, the high pres- sure system operated at 265 to 359 psig more effectively removed the inorganic contaminants than did the low pressure system operated at 163 to 187 psig. High pressure system removals ranged from 80 to 99 per- . cent; low pressure, from 10 to 85 percent. Percent removals varied with the ion measured, but the order, from best to worst, was about the same for each system. The order for the high pressure system was: (1) arsenic V, (2) fluoride, (3) nitrate, and (4) arsenic III. For the low pressure system: (1) arsenic V, (2) fluoride, (3) arsenic III, and (4) nitrate. Percent removal was also independent of the initial concentra- tion. This Project Summary was devel- oped by EPA's Municipal Environmen- tal Retearch Laboratory. Cincinnati, OH. to announce key findings of the research project that is fully docu- mented in 'a separate report of the same title (see Project Report ordering information at back). Introduction RO has been used successfully for desalting sea waterand brackish waters for many years. Compared with other drinking water treatment methods, its relatively high cost has limited its application in this field. Technological advances, however, have generated considerable interest for use on drinking waters with high total dissolved solids and on those having specific contami- nants that cannot be easily removed by other methods. One major advantage of RO is its effectiveness to remove almost all inorganic substances. Information is generally available on the rejection capabilities for the common natural . constituents in drinking water, such as sodium, chloride, or sulfate, but lacking on the rejection of specific contaminants such as arsenic and selenium. This study was undertaken to develop . data on removing the inorganic con- taminants included in EPA National Interim Primary Drinking Water Regula- tions by RO. Tests were conducted using two parallel pilot plant RO sys- tems: (1) a low pressure (200 psi) system housing low rejection mem- ------- branes and (2) a high pressure (400 psi) system with high rejection membranes. Test runs lasting from 1 to 5 days were carried out by spiking a natural ground- water with known concentrations of contaminants and measuring their removal by each RO system. Removal data were also obtained on some of the natural constituents in the feed water such as total dissolved solids, calcium, magnesium, chloride, sodium, and sulfate. The results of the first series of tests for the removal of fluoride, nitrate, arsenic III, and arsenic V are reported in this first progress report. Results Because of several problems, unre- lated to the RO systems, the two systems were operated under three slightly different sets of operating conditions (pressure). The test data on the natural substances suggest, however, that these changes did not significantly influence the performance of the sys- tems for removing the spiked contami- nants. As was anticipated, the test data show a very significant difference in the capabilities between the two RO sys- tems for removing all spiked and natural constituents monitored. The low pres- sure system, which requires about one- half the energy used by the high pressure system, achieved rejections of about 50 percent or less than that achieved by the high pressure system. Data also show that rejection of the contaminants on a percent basis was independent of the feed concentration and the order of effectiveness for removing spiked and natural constituents was nearly the same for each system (Table 1). Conclusions The investigation clearly indicated that the high pressure system was Table 1. Percentage Removal of Natural and Spiked Constituents Monitored Reverse Osmosis Systems, % Removal Constituents High Pressure Low Pressure Natural Sulfate Magnesium Calcium Total Hardness Radium-226 Total Dissolved Solids Chloride Sodium >99 96-98 96-98 97-98 97 93-96 87-95 88-93 82-84 63-67 64-67 64-66 62 45-52 42-45 36-44 Spiked Arsenic V Fluoride Nitrate Arsenic III 91 -98 90-93 76-80 63 - 70 77-81 56-62 6-24 12-35 significantly more effective for removing all substances measured. The low pres- sure system achieved a very wide range of removals and was very ineffective for removing nitrate and arsenic III. Because of its low rejection charac- teristics, the low pressure system is ofily effective on source water having contaminant concentrations slightly above the maximum contaminant levels (MCL). The high pressure system, al- though it requires about twice the energy, is much more effective, and blending of feed and product waters could be accomplished to affect the difference in energy costs. The full report was submitted in ful- fillment of Cooperative Agreement No. RC-805207 by Charlotte Harbor Water Association, Inc., under the sponsorship of the U.S. Environmental Protection Agency. Martin R. Huxstepis with the Charlotte Harbor Water Association, Inc., Harbour Heights, FL 33950. Thomas J. Sorg is the EPA Project Officer (see below). The complete report, entitled "Inorganic Contaminant Removal from Drinking Water by Reverse Osmosis," (Order No. PB 81-224 420; Cost: $8.00, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA2216t Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Municipal Environmental Research Laboratory U.S. Environmental Protection Agency Cincinnati, OH 45268 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 Postage and Fees Paid Environmental Protection Agency EPA 335 Official Business Penalty for Private Use $300 RETURN POSTAGE GUARANTEED 00003,89 liZT, U.S. GOVERNMENT PRINTING OFFICE: 1981 — 757-012/7352 ------- |