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Removal of Dissolved Salts and Particulate Contaminants from Seawater: Village Marine Tec., Expeditionary Unit Water Purifier, Generation 1
Citation:
Blumenstein, M., B. Bartley, AND J. Q. ADAMS. Removal of Dissolved Salts and Particulate Contaminants from Seawater: Village Marine Tec., Expeditionary Unit Water Purifier, Generation 1. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-10/013, 2010.
Impact/Purpose:
To inform the public.
Description:
The EUWP was developed to treat challenging water sources with variable turbidity, chemical contamination, and very high total dissolved solids (TDS), including seawater, during emergency situations when other water treatment facilities are incapacitated. The EUWP components include feed pumps, a UF pretreatment system, a one or two pass RO desalination system with an energy recovery device, storage tanks, and product pumps. It has chemical feed systems for optional pretreatment coagulation and post treatment chlorination. Clean-in-place systems (CIP) are included with the UF and RO skids. During this verification test, coagulation pretreatment was employed, but chlorination was not evaluated. Design specifications indicate that the UF system alone has a production capacity up to 250,000 gallons per day (gpd) from a fresh water source with up to 500 mg/L TDS and a temperature of 25°C. The combined UF and RO system is designed to produce from 98,000 gpd up to 162,000 gpd, depending on the TDS of the source water and the recovery settings of the RO process. The testing site was the Seawater Desalination Test Facility (SDTF) operated by the Naval Facilities Engineering Service Center (NFESC) at Naval Base Ventura County (NBVC) in Port Hueneme, California. The source water was from an open ocean intake in the Port of Hueneme, a deep-water port. The port has no appreciable fresh water outlets; therefore, the water closely resembles that of the Pacific Ocean with respect to salinity. The UF system reduced turbidity from a mean of 1.34 NTU in the raw water to a mean of 0.06 NTU in the UF filtrate, as measured by the daily grab samples. The 95% confidence level shows that filtrate turbidity can be expected to be in the range of 0.05 to 0.07 NTU. The RO system provided little additional reduction of the turbidity levels, with the RO permeate having a mean turbidity of 0.05 NTU, based on the grab samples collected each day. The RO system reduced the dissolved ions in the water, as measured by conductivity. The mean conductivity in the RO permeate was 592 μS/cm, while that for the RO feed was 51,380 μS/cm. The RO unit reduced the conductivity by a mean value of 98.9%. The direct measurements of TDS show that the concentration in the RO permeate was in the 280-300 mg/L range, compared to 34,000-39,000 mg/L in the RO feed. TDS was reduced by 99%, as measured in the RO permeate. Sodium was reduced by 98% and chloride was reduced by 99%. These data are consistent with the conductivity data. The other inorganic materials measured such as hardness, alkalinity, metals, sulfate, and phosphorus were also reduced in the RO permeate. The UF system had no impact on the pH of the water with the feed water having a mean pH of 7.78 and the filtrate having a mean pH of 7.73. The RO system did lower the pH, the permeate having a mean pH of 6.29. Pressure decay tests were used to document UF membrane integrity. Bacillus endospores and total coliforms were measured in the UF feed and filtrate to provide data on the microbial reduction achieved by the UF system. In-line analyzers also collected particle count data from the feed and filtrate streams as an additional measurement/indicator of membrane integrity and the capability of the system to remove particulate and microbial contaminants. Pressure decay tests on the UF system were performed on most operating days during the verification test. The mean pressure decay rates ranged from 0.02 to 0.15 psig/min. The overall mean pressure decay rate was 0.08 psig/min. These direct integrity test results were indicative of membrane modules with no significant observable breaches. The particle counters recorded the particle counts in the UF feed and UF filtrate every five minutes, and stored the data for transfer to a personal computer. The mean 2-3 µm particle count for the feed water was 5,559/mL, with a range of 53-17,843/mL. The UF filtrate had a mean 2-3 µm particle count of 42/mL, with a range of 0-773/mL. The UF system reduced the 2-3 µm particles by a mean value of 2.3 log10. However, the maximum particle count of 773/mL may not be indicative of the typical UF separation performance. The UF system went through a backflush cycle every half-hour, and during these backflushes the particle counts were still being recorded. Consequently, the filtrate particle count data included numerous spikes. The backflushes were not time-stamped, so the spikes due to backflushes could not be identified with certainty and removed from the data set. The mean 3-5 µm particle count for the UF feed was 3,616/mL, with a range of 1,355-9,505/mL. The filtrate had a mean 3-5 µm particle count of 22/mL, with a range of 1-352/mL. Again, spikes due to backflushes could not be identified with certainty. The UF system reduced the 3-5 µm particles by a mean value of 2.5 log10. Bacillus endospores and total coliform levels in the seawater were low during the test, with geometric mean concentrations of 64 CFU/100 ml and 10 CFU/100 ml, respectively. The UF system reduced the Bacillus endospores to a geometric mean of 1.3 CFU/100 ml. No total coliforms were found in any UF filtrate samples. The UF filtrate endospores counts were 1 or <1 CFU/100mL on all but two days. The UF system had a mean endospore log reduction of 1.6 log10. The mean UF feed water flow rate was 249 gpm. The UF water recovery was 89.2% based on the mean feed water and filtrate flow rates. Over the 28 calendar-day verification test, the RO feed water totalizer showed 4,673.3 kgal of water was fed to the RO unit. Based on the daily percent recoveries for each Array (typically Array 1 at 61% and Array 2 at 50%), the total volume of permeate produced was approximately 2,671 kgal, giving an average of 98.9 kgal/day over 28-day test. Antiscalant was added to the RO feed water throughout the test. The mean dose rate was 5.7 mg/L versus a target feed of 5 mg/L. The RO system did not appear to experience any scaling or fouling problems during the test. The S&DSI varied from -0.71 to -0.84 during the test. This indicates that the concentrate was a non-scaling water (S&DSI <0.0 is non-scaling). The combination of non-scaling water and the addition of antiscalant reduced or eliminated the problems of scaling on the RO membranes. The system operated consistently throughout the test with little change in flows or pressures.
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REMOVAL OF DISSOLVED SALTS & PARTIC CONTAM FROM SEAWTR: VILLAGE MARINE TEC., EXPED UNIT WTR PURIFIER, GEN 1VERIFICATION STATEMENT