|Arsenic Removal From Drinking Water by Oxidation/Filtration and Adsorptive Media, U.S. EPA Demonstration Project at Clinton Christian School in Goshen, IN, Final Performance Evaluation Report (84 pp, 13.7 MB) (EPA/600/R-10/167) December 2010
This report documents the activities performed for and the results obtained from the arsenic removal treatment technology demonstration project at the Clinton Christian School in Goshen, Indiana. The objectives of the project were to evaluate the effectiveness of AdEdge Technologies AD26/E33 media in removing arsenic to meet the new arsenic maximum contaminant level of 10 micrograms per liter (μg/L). In addition, this project evaluated the:
The project also characterized the water in the distribution system and process residuals produced by the treatment process.
The 25-gallons-per-minute (gpm) AD26/E33 modular arsenic treatment system consisted of two integrated units. First, the AD26 oxidation/filtration unit consisted of three 13-inch by 54-inch vessels, each loaded with 2.3 cubic feet (ft3) of AD26 media. Second, the E33 adsorption unit consisted of two 18-inch by 65-inch vessels, each loaded with 5.3 ft3 of E33 media. AD26 media is a manganese dioxide granular mineral commonly used for iron and manganese removal. E33 is an iron-based adsorptive media developed by Bayer AG for arsenic removal.
Operation of the AD26/E33 system began on May 1, 2008, but logging of operational data did not begin until June 6, 2008. 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. Through the performance evaluation study period from June 6, 2008, through June 19, 2009, the system treated approximately 517,000 gallons (or 6,522 bed volumes [BV]) of water. (Note that BV was calculated based on 5.3 ft3 of E33 in each adsorption vessel.) Daily run times averaged 1.9 hours per day when the school was in session or 1.5 hours per day when the school was not in session. The AD26 unit operated at 16.4 gpm (on average), with an equal amount of water flowing through each of the three oxidation/filtration vessels. The E33 unit operated at 16.0 gpm (on average), with 7.7 and 8.3 gpm of water flowing through each of the two adsorption vessels. Based on the flowrates to the E33 unit, empty bed contact times (EBCTs) varied from 4.1 to 7.3 minutes and averaged 5.0 minutes. This average EBCT was over 61 percent higher than the vendor recommended EBCT of 3.1 minutes for E33 media.
Arsenic concentrations in raw water ranged from 22.2 to 33.4 μg/L and averaged 28.6 μg/L. Soluble arsenic (III) was the predominating arsenic species, with concentrations ranging from 16.3 to 25.6 μg/L and averaging 20.2 μg/L. Upon chlorination, soluble arsenic (III) was oxidized to soluble arsenic (V), which was then adsorbed onto and/or co-precipitated with iron solids. The majority of arsenic (existing mainly in the particulate form) was removed by AD26 media, leaving only 1.2 to 5.0 μg/L (existing mainly as arsenic [V]) to be further removed by E33 media. The system also reduced total iron concentrations from an average of 741 μg/L in raw water to below the method detection limit of 25 μg/L. Total manganese concentrations were reduced from an average of 81.5 to less than 0.1 μg/L. The AD26 unit was backwashed every 70.3 to 72.1 hours, producing 56,810 gallons of wastewater (or 226 gallons per vessel per backwash cycle). During the summer months when the school was not in session and the water use rate was low, the system was backwashed manually when the pressure difference across the AD26 vessels rose to approximately 7 pounds per inch. The E33 vessels were backwashed every 39 to 44 days, producing 3,450 gallons of wastewater. Assuming 10 milligrams per liter (mg/L) of total suspended solids in 56,810 gallons of backwash wastewater produced in one year, approximately 4.7 pounds of solids (including 0.039, 1.5, and 0.21 pounds of arsenic, iron, and manganese, respectively) would be discharged annually.
Comparison of the distribution system sampling results before and after the system startup showed a significant decrease in arsenic concentration from an average of 17.6 to 2.8 μg/L. The arsenic concentrations in the distribution system were either similar to or somewhat higher than those in the system effluent. Iron and manganese also were significantly reduced in the distribution system. Neither lead nor copper concentrations appeared to have been affected by the operation of the system.
The most significant operational issue observed during the performance evaluation study was related to maintaining a target level of free chlorine residuals. Despite repeated efforts to increase chlorine doses, free chlorine residuals were often below the Indiana Department of Environmental Management-required level of 0.2 mg/L (as chlorine).
The capital investment cost for the system was $55,423, including $31,735 for equipment, $11,278 for site engineering, and $12,410 for installation. Using the system’s rated capacity of 25 gpm (36,000 gallons per day [gpd]), the normalized capital cost was $2,216 per gpm ($1.54 per gpd).
The O&M cost included the cost for media replacement and disposal, chemical supply, electricity consumption, and labor. Although media replacement did not occur during the demonstration period, the media replacement and disposal cost would represent the majority of the O&M cost and was estimated to be $2,593 for AD26 and $3,951 for E33. The vendor estimated that both media would have a life expectancy of 8.7 years, which could not be confirmed during the one-year performance evaluation study.
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