|Arsenic Removal From Drinking Water by Adsorptive Media, U.S. EPA Demonstration Project at Spring Brook Mobile Home Park in Wales, ME, Final Performance Evaluation Report (EPA/600/R-10/012) March 2010
This report documents the activities performed and the results obtained for the arsenic removal treatment technology demonstration project at Spring Brook Mobile Home Park (SBMHP) in Wales, Maine. The objectives of the project were to evaluate the:
The project also characterizes water in the distribution system and residuals produced by the treatment process.
The ATS system consisted of two parallel treatment trains, each having four 10-inch by 54-inch sealed polyglass columns connected in series to treat up to 7 gallons per minute (gpm) of water per train. Water supplied from a developed spring was stored in two 120-gallon pressure tanks and then passed through a 25-micrometer sediment filter, and one oxidation and three adsorption columns in each train. Each oxidation column was loaded with 1.5 cubic feet (ft3) of A/P Complex 2002 oxidizing media, which consisted of an activated alumina substrate and metaperiodate complex. Each adsorption column was loaded with 1.5 ft3 of A/I Complex 2000 adsorptive media, which consisted of an activated alumina substrate and a proprietary iron complex.
Based on the design flowrate of 7 gpm for each train, the empty bed contact time (EBCT) in each column was 1.6 minutes and the hydraulic loading rate to each column was 13 gallons per minute per square foot (gpm/ft2). Because the actual average flowrate through a treatment train over the entire demonstration study was lower at 6.1 gpm (on average), the actual EBCT was longer at 1.9 minutes per column and the hydraulic loading rate was slightly lower at 11.2 gpm/ft2.
Between March 7, 2005, and August 29, 2007, three media runs were evaluated. The system operated an average of 3.7 hours per day for a total of 2,564 hours, treating approximately 1,834,990 gallons of water. Source water contained 34.6 to 50.2 μg/L of arsenic, existing predominately as soluble As(III), averaging 91 percent of the soluble arsenic.
During Media Run 1 (March 7 to September 26, 2005) and Media Run 2 (September 27, 2005 to February 17, 2006), the oxidation columns were loaded with A/P Complex 2002 media and the adsorption columns were loaded with A/I Complex 2000 media. Oxidation of soluble As(III) was achieved through reactions with sodium metaperiodate (IO4-) within the oxidation columns, producing soluble As(V) and I- as end products. The oxidation columns remained effective for soluble As(III) oxidation throughout Media Runs 1 and 2, typically lowering soluble As(III) concentrations to less than 1.5 μg/L following the oxidation columns. Up to 124 μg/L of iodine (as I-) were measured in the oxidation and adsorption columns effluent, most likely caused by leaching of metaperiodate, which followed an apparent decreasing trend. The oxidizing media also showed a significant adsorptive capacity for arsenic, averaging 0.14 micrograms (μg) of As per milligram (As/mg) of dry media. Complete arsenic breakthrough from the oxidation columns occurred after processing about 56,000 gallons of water per treatment train (or 5,000 bed volumes [BV], 11.2 gallons per BV).
Ten μg/L arsenic breakthrough following the three adsorption columns occurred after processing approximately 171,000 gallons of water (per train), equivalent to 5,100 BV (i.e., 4.5 ft3 or 33.6 gallons per BV), if considering the three adsorption column as one large column. Complete arsenic breakthrough from the three adsorption columns took place after processing approximately 213,000 gallons of water (or 6,300 BV, if considering the three adsorption column as one large column). Arsenic loadings on the adsorption columns ranged from 0.18 to 0.28 μg of As/mg of dry media (averaged 0.23 micrograms per milligram [μg/mg]), compared to the measured spent media results of 0.17 μg/mg using inductively coupled plasma-mass spectrometry (ICP-MS). The 0.23 μg/mg result was about 1.6 times of that measured for oxidizing media as mentioned above, and close to the values observed for the same adsorptive media at another EPA arsenic demonstration site in Susanville, California.
For Media Run 3, ATS oxidizing media were replaced with Filox-RTM and adsorptive media were replaced with GFH and CFH-12 (with GFH in Train A and CFH-12 in Train B). Filox-RTM also was effective in converting soluble As(III) to soluble As(V) throughout the 52-week evaluation period; soluble As(III) concentrations were typically lowered to less than 1.2 μg/L. Unlike the ATS oxidation media, Filox-RTM had little to no adsorptive capacity for arsenic.
During Media Run 3, the system effluent reached 10 μg/L of arsenic after treating approximately 391,000 gallons (or 11,600 BV, if considering the three adsorption columns as one large column) in Train A (GFH) and 516,000 gallons (or 15,300 BV, if considering the three adsorption columns as one large column) in Train B (CFH).
After Media Run 2, the spent ATS media in one oxidation and three adsorption columns were sampled for Toxicity Characteristic Leaching Procedure (TCLP) test and ICP-MS analyses. The spent ATS oxidizing and adsorptive media passed the TCLP test and could be disposed off at a sanitary landfill. However, the vendor recycled the spent media into another product, thus saving the disposal cost. Spent GFH and CFH media were not subject to TCLP before the end of this performance evaluation study.
Comparison of distribution system water sampling results before and after system startup showed a significant decrease in arsenic concentration at the three sampling locations during the 11 monthly sampling events. Arsenic concentrations were reduced from an average baseline level of 35.8 μg/L to an average of 1.1 μg/L for the first three months after system startup. Afterwards, arsenic concentrations increased to above 10 μg/L and then to the influent levels due to arsenic breakthrough from the treatment system. In general, arsenic concentrations in distribution system water mirrored those in treatment system effluent. Lead and copper levels were low in the distribution system water; however, low pH values could significantly increase lead and copper levels.
The capital investment cost included $10,790 for equipment, $1,800 for site engineering, and $3,885 for installation. Using the system’s rated capacity of 14 gpm (or 20,160 gallons per day [gpd]), the capital cost was $1,177 per gpm (or $0.82 per gpd). The annualized capital cost was $1,555 per year based upon a 7 percent interest rate and a 20-year return. The unit capital cost was $0.21 per 1,000 gallons, assuming the system operated 24 hours per day, 7 days a week at 14 gpm. At the current use rate of 955,450 gallons per year, the unit capital cost increased to $1.63 per 1,000 gallons.
The O&M costs included only incremental costs associated with the adsorption system, such as media replacement and disposal (for both oxidizing and adsorptive media), electricity consumption, and labor. The unit O&M cost was driven by the cost to replace the spent media as a function of the media run length. Supplying water to SBMHP in one year would require $45,382, $4,082, and $2,849 O&M cost when using ATS A/P Complex 2002/A/I Complex 2000, Filox-R/GFH, and Filox R/CFH-12 media, respectively. It is apparent that using either Filox-R/GFH or Filox-R/CFH-12 media can result in significant cost savings.
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