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 Abstract

 

Arsenic Removal from Drinking Water by Adsorptive Media, U.S. EPA Demonstration Project at Wellman, TX, Six-Month Evaluation Report (EPA/600/R-08/080) July 2008

This report documents the activities performed and the results obtained from the first six months of the arsenic removal treatment technology demonstration project in the City of 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 of 10 micrograms per liter (μg/L). Additionally, this project evaluates 1) the reliability of the treatment system (Arsenic Package Unit [APU]-100CS-S-2-AVH), 2) the required system operation and maintenance (O&M) and operator skills, and 3) the capital and O&M cost of the technology. The project also characterizes the water in the distribution system and any residuals produced by the treatment process. The types of data collected include system operation, water quality parameters (both across the treatment train and in the distribution system), and capital and O&M cost.

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, which is an iron-based adsorptive media developed by Bayer AG and marketed under the name of AD-33 by AdEdge. The treatment system was designed for a maximum flowrate of 100 gallons per minute (gpm) and an empty bed contact time of approximately 5.7 minutes per vessel.

Over the six-month operational period, the calculated average flowrate was 121 gpm based on the APU system electromagnetic flow meters/totalizers and hour meter. This calculated average flowrate was significantly greater than the design value and pre-existing master totalizer average of 86 gpm. Based on a one-day flowrate test using a portable ultrasonic flow meter, it was determined that the APU system flow meters/totalizers were the least accurate of the meters. Therefore, the master totalizer was used for the purposes of this performance evaluation, and the use of the APU system flow meters/totalizers was discontinued until the sensor’s K-factors are adjusted to compensate for the inaccuracy.

The AdEdge treatment system began regular operation on August 10, 2006. Between August 10, 2006, and February 9, 2007, the system operated an average of 4.5 hours per day, treating approximately 4,218,200 gallons of water. This volume of treated water was equivalent to about 7,420 bed volumes (BV) based on the 38 ft3 of media in each adsorption vessel.

Total arsenic concentrations measured in the IN samples varied significantly from 6.0 to 45.9 μg/L. Soluble arsenic (V) was the predominate species, ranging from 11.2 to 41.2 μg/L; soluble arsenic (III) concentrations ranged from 0.4 to 1.6 μg/L. A review of the significant variations measured in the IN samples identified that system operations and sampling techniques were likely contributing to the concentration variations. In fact, the after chlorination sample results provided concentrations in a more realistic range and are believed to be more representative of the true water quality. The total arsenic concentrations in the AC samples ranged from 37.5 to 47.2 μg/L. Soluble arsenic (V) in the AC samples remained predominate, ranging from 38.1 to 43.6 μg/L; soluble arsenic (III) concentrations ranged from 0.7 to 2.0 μg/L.

As of February 6, 2007, total arsenic levels in the treated water following Vessels A and B were 1.2 and 1.8 μg/L, respectively at approximately 7,326 BV. Concentrations of vanadium, phosphate, and silica, which could adversely affect arsenic adsorption by competing with arsenate for adsorption sites, averaged 144 μg/L, <10 μg/L (as P), and 44.5 milligrams per liter (as SiO2), respectively, in AC samples. Vanadium existed primarily in the soluble form (at 95 percent) and its concentrations were reduced to <3.2 μg/L in the treated water. Concentrations of iron, manganese, and other ions in raw water were not considered significant enough to impact arsenic removal by the 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 3.3 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 level of 15 and 1,300 μg/L and their levels were not adversely affected by the operation of the system.

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 per gpd) of design capacity. The capital cost also was 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 4.5 hours per day at an average flowrate less than 90 gpm, during the first 6 months of operation, the approximate annual water production was 8,436,400 gallons, and the actual unit capital cost was $1.67 per 1,000 gallons of water.

The O&M cost included only incremental cost 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 first six months of system operation, 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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Thomas Sorg


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