|Arsenic Removal From Drinking Water by Adsorptive Media, U.S. EPA Demonstration Project at LEADS Head Start Building in Buckeye Lake, OH, Final Performance Evaluation Report (EPA/600/R-11/002) January 2011
This report documents the activities performed and the results obtained for the arsenic removal treatment technology demonstration project at Licking Economic Action Development Study (LEADS) Head Start School in Buckeye Lake, Ohio. The objectives of the project were to evaluate the:
The Kinetico system consisted of two 18-inch by 65-inch sealed vessels connected in series to treat up to 10 gallons per minute (gpm) of water. Water supplied from a well was temporarily stored in a 120-gallon pressure tank, softened through a water softener, chlorinated with a sodium hypochlorite solution, and retained in a 120-galloon contact tank. Following the contact tank, chlorinated water flowed through the two adsorption vessels, each loaded with 4.5 cubic feet of ARM 200, an iron oxide/iron hydroxide media. At the design flowrate of 10 gpm, the system would yield a hydraulic loading rate of 5.6 gpm per square foot and an empty bed contact time (EBCT) of 3.3 minutes in each vessel. Because of on-demand operation of the system, actual flowrates through the treatment system could not be measured. Based on visual observations during site visits, it was determined that the actual flowrates were much lower than 10 gpm. Therefore, the actual hydraulic loading rates were much lower and the actual EBCTs were much longer than the design values.
The system operated from June 28, 2006, to February 24, 2010, treating approximately 303,200 gallons (or 9,000 bed volumes) of water. Daily use rates averaged 450 gallons, compared to 675 gallon rate provided by the school. Source water contained 5.5 to 20.5 μg/L of arsenic, existing predominately as soluble arsenic (III), averaging 79 percent of the soluble arsenic. Ten-μg/L arsenic breakthrough following the two adsorption vessels did not occur during the almost four years of operation. The highest arsenic concentration measured after treatment was 1.4 μg/L.
Significantly elevated total trihalomethanes (TTHM) and haloacetic acids (HAA5) were measured in the vessel effluent soon after system startup. Examination of system operating conditions and disinfectant by-product (DBP) data revealed that the exceedances coincided with elevated chlorine residuals levels at or above 4.4 milligrams per liter (as chlorine). The results of laboratory column studies suggested that ARM 200 media had the ability to promote TTHM and HAA5 formation, but only with the presence of chlorine and total organic carbon in its influent. The increase found in the laboratory was not on the same order as observed onsite. Therefore, the results of the column studies did not totally explain the elevated DBP concentrations observed onsite.
Comparison of distribution system water sampling results before and after system startup showed a significant decrease in arsenic concentration at the two sampling locations during the 12 monthly sampling events. Arsenic concentrations were reduced from an average baseline level of 15.2 μg/L to an average of 1.3 μg/L. In general, arsenic concentrations in the distribution system water were somewhat higher than those measured in the treatment system effluent. Some dissolution and/or re-suspension of arsenic might have occurred in the distribution system. Lead and copper levels were well below their respective action levels in the distribution system water both before and after system startup.
The capital investment cost included $10,435 for equipment, $11,000 for site engineering, and $5,820 for installation. Using the system’s rated capacity of 10 gpm (or 14,400 gallons per day [gpd]), the capital cost was $2,725 per gpm (or $1.89 per gpd). The annualized capital cost was $2,572 per year based upon a 7 percent interest rate and a 20-year return. The unit capital cost was $0.49 per 1,000 gallons, assuming the system operated continuously 24 hours per day, seven days a week at 10 gpm. At the current use rate of approximately 82,500 gallons per year, the unit capital cost increased to $31.36 per 1,000 gallons.
The O&M cost included only incremental cost associated with the adsorption system, such as media replacement and disposal (for 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. Because the media was not replaced during the performance evaluation study, the O&M cost to supply water to the Head Start Building in one year when using ARM 200 media was estimated based on an assumed re-bedding cost for the lead vessel.
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