|Arsenic and Uranium Removal From Drinking Water by Adsorptive Media, U.S. EPA Demonstration Project at Upper Bodfish in Lake Isabella, CA, Final Performance Evaluation Report (EPA/600/R-10/165) December 2010
This report documents the activities performed during and the results obtained from the performance evaluation of an arsenic and uranium removal technology demonstrated at Upper Bodfish in Lake Isabella, California. The objectives of the project were to evaluate the:
The project also characterized water in the distribution system and process residuals produced by the treatment system.
The HIX system, designed by VEETech for the Upper Bodfish site, consisted of two trailermounted, single-stage fiberglass-reinforced plastic vessels, each capable of treating up to 50 gallons per minute (gpm) of flow. The vessels were 42 inches in diameter and 60 inches in height; each contained 27 cubic feet (ft3) of ArsenXnp, a hybrid anion exchange resin impregnated with hydrous iron oxide nanoparticles manufactured by Purolite. During normal operation, one vessel was put into service while the other was on standby.
During the performance evaluation study from October 12, 2005, through March 23, 2007, the HIX system operated for a total of 9,713 hours, treating approximately 13,561,950 gallons of water from the Upper Bodfish Well CH2-A. The average daily run time was 18.5 hours per day and the average daily production was 25,783 gallons per day (gpd). System flowrates ranged from 20 to 30 gpm and averaged 23 gpm, which was 46 percent of the system design flowrate of 50 gpm. The lower flowrates resulted in longer empty bed contact times (i.e., 6.7 to 10.1 minutes) and lower hydraulic loading rates (i.e., 2.1 to 3.1 gpm per square foot).
Source water from Well CH2-A contained 34.3 to 50.0 μg/L of total arsenic with arsenic (V) being the predominating species at an average concentration of 41.9 μg/L. Source water also contained 26.6 to 38.9 μg/L of total uranium, with concentrations exceeding the 30-μg/L MCL most of the time. In addition, source water had near-neutral pH values of 6.7 to 7.2, 88 to 145 milligrams per liter (mg/L) of alkalinity (as calcium carbonate), 36 to 51 mg/L of sulfate, and 39.5 to 47.5 mg/L of silica.
Total arsenic concentrations in treated water were reduced initially to less than 0.1 μg/L and gradually increased to just over 10 μg/L after treating approximately 33,100 bed volumes (BV) of water through Vessel 1, and 31,700 BV through Vessel 2. These run lengths were 66 percent and 59 percent higher than the vendor-estimated run length of 20,000 BV. Meanwhile, uranium was completely removed to below the method detection limit of 0.1 μg/L throughout the study period. A laboratory rapid small-scale column test on the Upper Bodfish water using the ArsenXnp media achieved a similar run length of 28,000 BV for arsenic and over 50,000 BV for uranium. The HIX system did not require backwashing due to an insignificant headloss buildup across the adsorption vessel.
Comparison of the distribution system water sampling results before and after system startup showed significant decreases in arsenic concentration at all three sampling locations, including one residence in the historic Lead and Copper Rule (LCR) sampling network and two non-LCR residences. Arsenic concentrations measured at the taps of these residences mirrored the breakthrough behavior of arsenic in the plant effluent, but were in general higher than those of the plant effluent. Although uranium concentrations in the distribution system were not measured during the baseline sampling and after system startup, its concentrations after system startup were expected to be low because uranium was completely removed by the treatment system. The HIX system did not appear to have any effects on other water quality parameters in the distribution system.
The only residual generated by the HIX system was 54 ft3 of spent media. Due to the presence of uranium, the spent media was classified as a technologically enhanced, naturally occurring radioactive material (TENORM). Because uranium is considered a source material, the uranium laden spent media may be subject to the Nuclear Regulatory Commission’s (NRC’s) licensing requirements for storage, transportation, and disposal.
The vendor originally proposed to regenerate the spent media at an offsite facility and then return the regenerated media to the site for reuse. However, the offsite regeneration would be possible only if the spent media residual stream contains less than 0.05 percent of uranium. Otherwise, the spent media would be considered a low-level radioactive waste (LLRW) or a nonexempt material and may have to be partially regenerated onsite (in order to lower the uranium content to less than 0.05 percent) before offsite regeneration. Another approach would be to completely regenerate the spent media onsite to remove both uranium and arsenic. Both regeneration approaches would produce uranium and arsenicladen liquids that would have to be hauled away due to lack of an onsite disposal method. These approaches would greatly increase complexity and cost, thus rendering media regeneration an unworkable option.
As a mixed waste, the spent media was subject to waste profiling and radiological analysis. The spent media passed the federal Toxicity Characteristic Leaching Procedure and the California Soluble Threshold Limit Concentrations tests, but failed the California Total Threshold Limit Concentrations test for arsenic. As such, it was classified as a California hazardous waste (although not a Resource Conservation and Recovery Act waste). Results of the radiological analysis were compared against the federal requirements for an exempt source material based on the concentration, radioactivity, and quantity of uranium:
Because the spent media met all three requirements, it was deemed an “unimportant quantity” and was exempt from applicable NRC regulations. Although the spent media, as an exempted material, might be disposed of at a solid waste, hazardous waste, or LLRW landfill or any landfill licensed by a state to accept TENORM, it was difficult if not impossible to locate a solid waste landfill that would accept the mixed waste with a radioactivity over 200 pCi/L. After 13 months of effort, different contractors were secured to collect and analyze spent media samples and extract the spent media from the adsorption vessels. The spent media was transported in 10 55-gallon high-density polyethylene drums to a facility in Turlock, California, for temporary storage and was disposed of five months later at a U.S. Ecology facility in Grandview, Idaho, as an exempt nonhazardous material.
Upon completion of the performance evaluation study, the host site, Cal Water, decided to close Well CH2-A, drill two new wells, and install a new 150-gpm HIX system for arsenic treatment. Cal Water also elected not to request transfer of the trailer-mounted system to the company. After removal of the spent media from the adsorption vessels, the trailermounted system was hauled away from the site to Battelle by a subcontractor.
The capital investment cost was $114,070, which included $82,470 for equipment, $12,800 for engineering, and $18,800 for installation. Using the system’s rated capacity of 50 gpm, the capital cost was $2,281 per gpm (or $1.58 per gpd).
The O&M cost for the HIX system would include media regeneration or replacement (including disposal) and labor for routine system operation. Spent media regeneration was proposed but not performed; thus, its cost could not be evaluated. The spent media was not replaced with virgin media due to removal of the treatment system from the site. Nevertheless, the media replacement cost was estimated to be $38,271 based on the cost for virgin media and spent media disposal. By averaging the media replacement cost over the useful life of the media (i.e., 13,089,671 gallons), the cost per 1,000 gallons of water treated was $2.92 per 1,000 gallons. The HIX system did not require electricity to operate. Routine activities to operate and maintain the system consumed only 50 minutes per week and the estimated labor cost was $0.13 per 1,000 gallons of water treated.
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