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Arsenic Removal from Drinking Water by Adsorptive Media U.S. EPA Demonstration Project at Chateau Estates Mobile Home Park in Springfield, OH
Six-Month Evaluation
March 2007

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This report documents the activities performed for and the results obtained from the first six months of the arsenic removal treatment technology demonstration project at the Chateau Estates Mobile Home Park at Springfield, OH. The objectives of the project are to evaluate the effectiveness of AdEdge Technologies' AD-33 media in removing arsenic to meet the new arsenic maximum contaminant level (MCL) of 10 g/L. Additionally, this project evaluates the reliability of the treatment system (Arsenic Package Unit [APU]-250), the required system operation and maintenance (O&M) and operator skill levels, and the capital and O&M cost of the technology. The project also characterizes the water in the distribution system and process residuals produced by the treatment process.

The 250 gal/min (gpm) APU-250 treatment system consisted of two integrated units referred to as AD-26 oxidation/filtration and AD-33 adsorption systems. The AD-26 pretreatment system was for iron and manganese removal, followed in series by the AD-33 adsorption system for arsenic removal. Both the AD-26 oxidation/filtration and AD-33 adsorption systems were skid-mounted, each comprised of three carbon steel pressure vessels of similar construction and configuration but different sizes.

AD-26 media was a manganese dioxide mineral commonly used for oxidation and filtration of iron and manganese. Because chlorine was added prior to the AD-26 system, it helped precipitate soluble iron, oxidize As(III) to As(V), and form arsenic-laden solids, which were then filtered by the AD-26 media. The pre-treated water was subsequently polished by the AD-33 media, an iron-based adsorptive media developed by Bayer AG for arsenic removal.

The APU-250 system began regular operation on September 21, 2005. 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 cost. Through the period from September 21, 2005, to March 26, 2006, the system treated approximately 8,184,000 gal (about 9,540 bed volumes) of water with the daily run time ranging from 3.7 to 15.1 hr/day and averaging 9.2 hr/day. For the most part, the AD-26 system operated at the well pump flowrates with water supplied by two alternating wells at 130 and 90 gpm. The AD-33 system operated based on demand from the distribution system, ranging from 9 to 56 gpm and averaging 33 gpm. Because of the low flowrates, long empty bed contact times (EBCT), averaged at 25.8 min, were experienced by the AD-33 system.

The system reduced total arsenic levels from between 9.5 and 31.3 g/L (averaged 21.5 g/L) in raw water to <10 g/L in the treated water. As(III) was the predominating arsenic species in raw water, ranging from 5.6 to 24.7 g/L and averaging 16.4 g/L in both wells. The majority of arsenic was removed in the particulate form by the AD-26 media, leaving only 0.5 to 2.0 g/L, existing mainly as As(V), to be further polished by the AD-33 media. The system also reduced total iron concentrations from an average of 1,000 g/L to less than the method detection limit (MDL) of 25 g/L, while the total manganese concentrations decreased from an average of 40.2 to 0.1 g/L.

The AD-26 system was backwashed initially every two days for 15 min with a 2-min service-to-waste rinse, producing approximately 5,640 gal of wastewater per backwash event. During a power outage, the backwash settings were reset to default values, prompting the system to produce almost twice as much wastewater per backwash event. This problem was resolved by manually adjusting the backwash settings, which, after a short time, were further reduced to every three days for 9 min with a 90-sec rinse. Assuming that 82 mg/L of total suspended solid (TSS) was produced in 6,000 gal of backwash wastewater, approximately 4 lb of solids (including 0.02, 1.45, and 0.03 lb of arsenic, iron, and manganese, respectively) would be discharged during each backwash event. The AD-33 system was backwashed only once during the first six-months of operation.

Comparison of the distribution system sampling results before and after the system startup showed a significant decrease in arsenic concentration (from an average of 23.7 to 2.0 g/L). The arsenic concentrations in the distribution system were similar to 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 was related to the chlorine injection system. In spite of repeated efforts on fine-tuning the chlorine injection system and even reconfiguring the system piping to allow the injection to be controlled by well pump flowrates instead of on-demand flowrates, as much as 4 and 3.8 mg/L (as Cl2) total and free chlorine, respectively, were measured in the treated water, which were significantly higher than the 1.5 and 1 mg/L (as Cl2) of total and free residuals targeted for the treatment. The vendor continued to troubleshoot this problem.

The capital investment cost for the system was $292,252, including $212,826 for equipment, $27,527 for site engineering, and $51,899 for installation. This cost included the cost, paid for by the Park owner, to upgrade the system size from 150 to 250 gpm to meet the Ohio Environmental Protection Agency's (Ohio EPA's) redundancy requirement, upgrade the pressure vessel construction material from fiberglass reinforced plastic (FRP) to carbon steel, and add a chlorine injection and control system. Using the system's rated capacity of 250 gpm (360,000 gal/day [gpd]), the capital cost was $1,170 per gpm of design capacity ($0.81/gpd) and equipment-only cost was $851 per gpm of design capacity ($0.59/gpd).

The O&M cost included only incremental cost associated with the oxidation/filtration and adsorption system, such as media replacement and disposal, chemical supply, 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 $34,230 and $13,140 to change out the AD-33 and AD-26 media, respectively.

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Thomas Sorg

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