|Arsenic Removal From Drinking Water by Adsorptive Media, U.S. EPA Demonstration Project at Lead, South Dakota, Final Performance Evaluation Report (EPA/600/R-10/179) December 2010
This report documents the activities performed and the results obtained from the arsenic removal treatment technology demonstration project at Lead, South Dakota. The main objective of the project was to evaluate the effectiveness of SolmeteX’s adsorptive media system in removing arsenic to meet the new arsenic maximum contaminant level (MCL) of 10 μg/L. In addition, this project evaluated the:
The project also characterized the water in the distribution system. The types of data collected included system operation, water quality (both across the treatment train and in the distribution system), process residuals, and capital and O&M costs.
The demonstration study was divided into two study periods. Study Period I extended from April 4, 2008, to November 29, 2009; Study Period II extended from November 30, 2009, to May 23, 2010.
Study Period I focused on evaluating the performance of ArsenXnp media. At the end of Study Period I, the lead vessel was replaced with LayneRT and the flow through the vessels was switched (such that the lag vessel containing partially exhausted ArsenXnp media was placed in the lead position and the former lead vessel containing virgin LayneRT media was placed in the lag position) before Study Period II began. ArsenXnp is an engineered hybrid inorganic/organic sorbent manufactured by Purolite. The media consists of hydrous iron oxide nanoparticles impregnated into 300 to 1,200 micrometers anion exchange resin beads. LayneRT is a newer generation of the hybrid media.
The treatment system consisted of two 42-inch by 72-inch fiber glass vessels in series configuration, each containing approximately 28 cubic feet (ft3) of adsorptive media. The treatment system was designed for a peak flowrate of 75 gallons per minute (gpm) and an empty bed contact time (EBCT) of approximately 2.8 minutes per vessel. Over the performance evaluation period, the actual average flowrate was at 71.5 gpm in Study Period I and 69.2 gpm in Study Period II, corresponding to an EBCT of 2.9 and 3.0 minutes, respectively.
In Study Period I, the treatment system operated for a total of 7,154 hours, treating approximately 27,978,780 gallons (or 133,590 bed volumes [BV]) of water. (Unless mentioned otherwise, bed volumes were calculated based on 28 ft3 of media in one vessel.) The average daily operating time was 12.0 hours per day and the average daily water production was 46,866 gallons per day (gpd).
In Study Period II, the treatment system operated for a total of 1,787 hours, treating approximately 7,231,940 gallons (or 34,530 BV) of water. The average daily operating time was 10.5 hours per day and the average daily water production was 42,541 gpd. Due to leaks from the distribution system, the amount of daily water production in both study periods was significantly higher than the design value of 9,000 gpd. During the 25-month demonstration study, the District located and fixed several leaks from the distribution system.
Total arsenic concentrations in source water ranged from 16.9 to 26.3 micrograms per liter (μg/L), and averaged 21.6 μg/L. Soluble arsenic (V) was the predominating species with concentrations ranging from 18.6 to 23.1 μg/L and averaging 20.8 μg/L. In Study Period I, arsenic breakthrough at 10 μg/L following the lead vessel occurred after treating 14,725,250 gallons (or 70,310 BV) of water, which was about 8 percent higher than the 65,000 BV working capacity projected by the vendor. By the end of Study Period I, total arsenic concentrations in the system effluent were reduced to 5.8 μg/L. At this point, the system had treated approximately 27,978,780 gallons of water (i.e., 133,590 BV based on 28 ft3 of media in one vessel, or 66,795 BV based on 56 ft3 of media in both vessels). Study Period II ended when the system effluent contained only 0.5 μg/L of total arsenic.
Comparison of the distribution system sampling results before and after system startup showed a significant decrease in arsenic concentration (from an average of 22.5 to 1.1 μg/L). The average lead concentrations reduced from 2.0 μg/L in baseline samples to 0.8 μg/L; the average copper concentration reduced from 164 μg/L to 46.2 μg/L.
The capital investment cost of $87,892 included $60,678 for equipment, $14,214 for site engineering, and $13,000 for installation. Using the system’s rated capacity of 75 gpm (or 108,000 gpd), the capital cost was $1,172 per gpm (or $0.81 per gpd) of design capacity. The unit capital cost would be $0.21 per 1,000 gal if the 75-gpm system operated around the clock. Based on an average daily operating time of 12.0 hours per day and an average system flowrate of 71.5 gpm, the unit capital cost increased to $0.44 per 1,000 gallon at this reduced rate of use.
The O&M cost included only the cost for media replacement and disposal, electricity consumption, and labor. The media replacement cost represented the majority of the O&M cost. The unit O&M cost is reported in graphical form as a function of projected media run length.
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