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  Arsenic Removal From Drinking Water by Adsorptive Media, U.S. EPA Demonstration Project at Woodstock Middle School in Woodstock, CT, Final Performance Evaluation Report (EPA/600/R-11/059) May 2011

This report documents the activities performed for and the results obtained from the arsenic removal treatment technology demonstration project at the Woodstock Middle School in Woodstock, Connecticut. The objectives of the project were to evaluate the:

  • Effectiveness of Adsorbsia GTO media in removing arsenic to meet the new arsenic Maximum Contaminant Level of 10 micrograms per liter (μg/L)
  • Reliability of the treatment system
  • Required system operation and maintenance (O&M) and operator skill levels
  • Capital and O&M costs of the technology

The project also characterized the water in the distribution system and process residuals produced by the treatment process.

The 20-gallons-per-minute (gpm) arsenic treatment system consisted of two 24-inch by 72-inch lead/lag vessels. Rather than the design quantity of 7.5 cubic feet, each vessel was loaded with 7.0 cubic of Adsorbsia GTO media, a titanium oxide-based adsorptive media developed by Dow Chemical Company for arsenic removal. Operation of the system began on February 10, 2009, but logging of operational data did not begin until March 10, 2009. The types of data collected included those for 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 March 10, 2009 through September 30, 2010, the system treated approximately 544,600 gallons of water supplied by two wells (No. 1 and No. 2). Daily run times averaged 1.0 hour per day. Based on two flow meters installed at the inlet to the adsorption vessels, system flowrates ranged from 14.7 to 16.9 gpm and averaged 16.4 gpm, equivalent to an average empty bed contact time (EBCT) of 3.2 minutes and an average hydraulic loading rate of 5.2 gpm per square foot. The design EBCT and hydraulic loading rate were 2.8 minutes and 6.4 gpm per square foot, respectively.

Arsenic concentrations in raw water ranged from 17.9 to 29.3 μg/L and averaged 24.7 μg/L. Soluble arsenic(V) was the predominating arsenic species, with concentrations ranging from 15.5 to 22.4 μg/L and averaging 19.6 μg/L. Both soluble arsenic(V) and soluble arsenic(III) were removed by Adsorbsia GTO media, but breakthrough at 10 μgL from the lead vessel occurred rather early at 7,600 bed volumes (BV). BV was calculated based on 7.0 cubic feet of media in the lead vessel. No plausible reason is offered to explain the short run length.

Comparison of the distribution system sampling results before and after the system startup showed a significant decrease in arsenic concentration from an average of 23.1 to 2.3 μg/L. The arsenic concentrations in the distribution system were either similar to or somewhat higher than those in the system effluent. Neither lead nor copper concentrations were affected by the operation of the system.

The capital investment cost for the system was $51,895, including $30,215 for equipment, $10,110 for site engineering, and $11,570 for installation. Using the system’s rated capacity of 20 gpm (28,800 gallons per day [gpd]), the normalized capital cost was $2,594.75 pre gpm ($1.80 per gpd). The O&M cost included the cost for media replacement and disposal and labor. A cost curve was created to project the cost for media replacement and disposal based on the media run length experienced during an adsorption.

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