Abstract

This report documents the activities performed during and the results obtained from the first six months of the arsenic removal treatment technology demonstration project at the Spring Brook Mobile Home Park in Wales, Maine. The objectives of the project are to evaluate the effectiveness of an Aquatic Treatment System, Inc. (ATS) As/1400CS arsenic removal system in removing arsenic to meet the new arsenic maximum contaminant level of 10 micrograms per liter (µg/L), the reliability of the treatment system, the required system operation and maintenance (O&M) and operator's skills, and the capital and O&M costs of the technology. The project also characterizes the water in the distribution system and process residuals produced by the treatment process.

The ATS system consisted of two parallel treatment trains, each consisting of one 25-micrometer sediment filter, one 10-inch-diameter, 54-inch-tall oxidation column, and three 10-inch-diameter, 54-inch-tall adsorption columns connected in series. The columns were constructed of sealed polyglass and loaded with 1.5 cubic feet (ft³) each of either A/P Complex 2002 oxidizing media (consisting of activated alumina and sodium metaperiodate) or A/I Complex 2000 adsorptive media (consisting of activated alumina and a proprietary iron complex). Based on a design flow rate of 7 gallons per minute (gpm) through each train, the empty bed contact time in each column was 1.6 minutes (or 4.8 minutes for three columns in series) and the hydraulic loading rate to each column was 13 gallons per minute per square foot.

Between March 3 and September 9, 2005, the system operated an average of 3.4 hours per day for a total of 638 hours, treating approximately 480,000 gallons of water. This volume throughput was equivalent to 21,400 bed volumes (BVs) based on the 1.5-ft³ BV in a lead adsorption column or 7,143 BVs based on the 4.5-ft³ combined BV in the three adsorption columns. The oxidation columns were effective at converting arsenic (III), the predominating arsenic species, to arsenic (V) throughout the six-month period, typically lowering the arsenic (III) concentrations from an average of 29.4 ± 6.7 to <1 µg/L. The oxidation of arsenic (III) to arsenic (V) was achieved presumably through reaction with sodium metaperiodate. Iodide (I-) analysis in the treated water was not conducted during the first six months of the study. Subsequent samples collected during the continuation of this study show elevated iodide concentrations as high as 124 µg/L following the oxidizing and adsorption columns. The oxidation columns also showed some adsorptive capacity for arsenic (i.e., 0.14 micrograms per milligrams of media), initially removing arsenic to <1 µg/L. By about 5,000 BVs (based on the 1.5-ft³ BV in an oxidation column), arsenic had completely broken through the oxidation columns.

Arsenic concentrations after the lead columns reached 10 µg/L at approximately 6,000 BVs (based on the 1.5-ft³ BV in the lead adsorption column) from Train A and just under 5,000 BVs from Train B, and reached complete breakthrough at approximately 10,000 BVs and 9,000 BVs, respectively, from each train. Arsenic breakthrough from the lead columns occurred much sooner than projected (at 32,700 BVs) by the vendor. High pH values of the source water (ranging from 8.0 to 8.7) was thought to be the major factor for early arsenic breakthrough from the adsorption columns. Arsenic concentrations after the second set of lag columns reached 10 µg/L at approximately 15,000 BVs through both treatment trains, and reached complete breakthrough at about 19,000 BVs. The adsorptive capacity of the media was estimated to be 0.2 µg of arsenic per milligram of media.

Several anions, including silica, sulfate, alkalinity, and fluoride were present in raw water at concentrations significant to potentially compete with arsenic for adsorption sites. Silica was consistently removed from 10.8 milligrams per liter (mg/L) to 0.6-5.5 mg/L by (and did not reach complete breakthrough from) the oxidation and adsorption columns throughout the first six months of system operation. Even after the arsenic removal capacity was completely spent, the oxidation columns and the lead adsorption columns continued to show some capacity for silica removal. Of the other competitive anions, both media showed little or no removal capacity for sulfate or alkalinity. The treatment system removed fluoride from about 0.5 to <0.1 mg/L initially, but fluoride completely broke through the oxidation and lead adsorption columns within 2,000 BVs.

Aluminum concentrations (existing primarily in the soluble form) in the treated water following the oxidation columns were about 20 to 30 µg/L higher than those in raw water, indicating leaching of aluminum from the oxidizing media. However, the concentrations were below the secondary drinking water standard for aluminum of 50 to 200 µg/L.

Comparison of distribution system sampling results before and after operation of the As/1400CS system showed a significant decrease in the average arsenic concentration at each of the three sampling locations during the first three months of system operation. During this period, arsenic concentrations were below 2.0 µg/L at all sampling locations. After the third month of operation, as arsenic began to break through the treatment system, the concentrations at the distribution locations also increased, exceeding the 10 µg/L target value. Neither lead nor copper concentrations appeared to have been affected by the operation of the system and remained well below the action levels of 15 µg/L for lead and 1.3 mg/L for copper.

The capital investment cost of $16,475 included $10,790 for equipment, $1,800 for site engineering, and $3,885 for installation. Using the system's rated capacity of 14 gpm (or 20,160 gallons per day [gpd]), the capital cost was $1,177 per gpm of design flow (or $0.82 per gpd).

O&M cost included only incremental cost associated with the adsorption system, such as media replacement and disposal (for both oxidizing and adsorptive media), electricity consumption, and labor. Incremental cost for electricity consumption was negligible. Although media replacement and disposal was not performed during the first six months of operation, the estimated cost was $2,465, $4,015, and $5,565 for changing out two, four, or six columns, respectively. Cost curves were constructed one each for replacing two, four, or six columns at a time to estimate media replacement cost per 1,000 gallons of water treated as a function of the media working capacity.

Contact

Thomas Sorg

See Also

Arsenic Research

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