|Arsenic Removal from Drinking Water by Adsorptive Media U.S. EPA Demonstration Project at Wellman, TX Final Performance Evaluation Report (72 pp, 5.58 MB) (EPA/600/R-09/145) December 2009
This report documents the arsenic removal treatment technology demonstration project in Wellman, Texas. The main objective of the project was to evaluate the effectiveness of AdEdge Technologies’ AD-33 media in removing arsenic to meet the new arsenic Maximum Contaminant Level (MCL) of 10 micrograms per liter (μg/L). This project also evaluated the:
The project also characterized the water in the distribution system and any residuals produced by the treatment process. The types of data collected included system operation, water quality parameters (both across the treatment train and in the distribution system), and capital and O&M costs.
The Wellman water system is supplied by five ground water wells. Four are located close to a 110,000-gallon water tank and an underground well-manifold vault. The fifth is located approximately three miles southwest. The combined flowrate from the first four wells is 50 gallons per minute (gpm) and the flowrate from the fifth is 40 gpm. Therefore, the total flowrate is approximately 90 gpm. Operating simultaneously 4 to 6 hours at a time, the wells are used to meet the average daily demand of approximately 26,000 gallons in the winter and 50,000 gallons in the summer.
The newly constructed treatment building is located adjacent to the water tank and underground vault. The treatment system consisted of two 48-inch-diameter, 72-inch-tall carbon steel vessels in parallel configuration, each containing approximately 38 cubic feet (ft3) of E33 pelletized media, an iron-based adsorptive media developed by Bayer AG and marketed by AdEdge Technologies under the name of AD-33. The treatment system was designed for a maximum flowrate of 100 gpm and an empty bed contact time of approximately 5.7 minutes.
Over the performance evaluation period, the average calculated flowrate was 118 gpm, based on readings of two electromagnetic flow meters/totalizers installed on the adsorption vessels and an hour meter interconnected to the flow meters/totalizers. This average calculated flowrate (118 gpm) was significantly greater than that of a master totalizer (91 gpm) installed at the common well manifold and the design flowrate value of 100 gpm.
Based on a one-day flowrate test using a portable ultrasonic flow meter and statistical analysis, it was determined that the electromagnetic flow meters/totalizers were the least accurate of the available meters. Therefore, the master totalizer was used to track the amount of water treated during the performance evaluation study.
The AdEdge treatment system began regular operation on August 10, 2006. Between August 10, 2006, and April 17, 2008, the system operated an average of 5.9 hours per day, treating approximately 14,744,962 gallons of water or 25,938 bed volumes (BV), based on the 76 ft3 of media in both adsorption vessels.
Total arsenic concentrations measured at the common well manifold (IN) varied significantly, ranging from 6.0 to 50.6 μg/L. Soluble arsenic(V) was the predominating species, ranging from 6.1 to 43.8 μg/L; soluble arsenic(III) concentrations ranged from less than the method detection limit (MDL) to 6.0 μg/L. A review of the significant variations measured in the IN samples indicated that system operations and sampling techniques were likely contributing to the variations in concentration. In fact, the after-chlorination (AC) sample results provided concentrations in a more representative range of the true water quality based on historical sampling events. The total arsenic concentrations in the AC samples ranged from 37.5 to 50.0 μg/L. Soluble arsenic(V) in the AC samples remained predominant, ranging from 35.2 to 42.9 μg/L. Soluble arsenic(III) concentrations ranged from less than the MDL to 11.4 μg/L. At the end of this performance evaluation study on April 17, 2008, total arsenic concentrations in the treated water were 6.8 and 2.3 μg/L from Vessels A and B, respectively, less than the target 10-μg/L MCL.
Concentrations of vanadium, phosphate, and silica, which could adversely affect arsenic adsorption by competing with arsenate for adsorption sites, averaged 136 μg/L, less than 10 μg/L (as phosphorus), and 46.2 milligrams per liter (as silicon dioxide), respectively, in the AC samples. Vanadium existed entirely in the soluble form, some of which was removed during the first 10,000 BV. Concentrations of iron, manganese, and other ions in raw water were not considered significant enough to impact arsenic removal by the adsorptive media.
Comparison of the distribution system sampling results before and after operation of the system showed a significant decrease in arsenic concentration (from an average of 38.9 μg/L to an average of 3.2 μg/L). The arsenic concentrations in the distribution system were similar to those in the system effluent. Lead and copper concentrations in the distribution system remained below their respective action levels of 15 and 1,300 μg/L. Overall, their concentrations were not adversely affected by system operation.
The capital investment cost of $149,221 included $103,897 for equipment, $25,310 for site engineering, and $20,014 for installation. Using the system’s rated capacity of 100 gpm (or 144,000 gallons per day [gpd]), the capital cost was $1,492 per gpm (or $1.04 gpd) of design capacity. The capital cost was also converted to an annualized cost of $14,085 per year, using a capital recovery factor of 0.09439 based on a 7 percent interest rate and a 20-year return period. Assuming that the system operated 24 hours a day, 7 days a week at the system design flowrate of 100 gpm to produce 52,560,000 gallons of water per year, the unit capital cost would be $0.27 per 1,000 gallons. Because the system actually operated an average of 5.9 hours per day at an average flowrate of approximately 91 gpm, the approximate annual water production was 11,758,000 gallons, and the actual unit capital cost was $1.20 per 1,000 gallons of water.
The O&M cost included only incremental costs associated with the adsorption system, such as media replacement and disposal, chlorine usage, electricity consumption, and labor. Although media replacement did not occur during the evaluation period, the media replacement cost would represent the majority of the O&M cost and was estimated to be $30,010 to change out both vessels (including 76 ft3 AD-33 media and associated labor for media change-out and disposal).
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