|Arsenic Removal From Drinking Water by Adsorptive Media, U.S. EPA Demonstration Project at Brown City, MI, Six-Month Evaluation Report (EPA/600/R-06/004) January 2006
This report describes the activities and results of the first six months of the arsenic removal treatment technology demonstration project in Brown City, Michigan. The objectives of the project are to evaluate the:
The project is also characterizing the water in the distribution system and residuals produced by the treatment system process.
The STS treatment system started on May 11, 2004, and continued to operate through November 30, 2004, with an average operational time of approximately 4.8 hours per day, or a 20 percent utilization rate. The design capacity of the treatment system with two APU-300 units in parallel is 640 gallons per minute (gpm). During the time frame, approximately 29,711,000 gallons (13,096 bed volumes) of water were treated.
The system continued to operate through the six-month demonstration period with only a few minor repairs and adjustments. The flow rate, pressure data, and other operational parameters were within the vendor specifications after a system retrofit, which was performed in late April/early May 2004. The system continues to operate within the vendor equipment specifications.
Arsenic in the source water existed as:
Per the vendor's recommendations, raw water was fed directly through the adsorption vessels without prechlorination to evaluate the capacity of the SORB 33T media for arsenic (III) adsorption.
Over the six-month period, total arsenic concentrations in raw water ranged from 9.5 to 28.7 µg/L and in treated water from 0.5 to 8.7 µg/L. In early November, as the treatment system throughput was approaching 12,500 bed volumes, a spike up to 8.7 µg/L of total arsenic was measured in the treated water. However, by November 30, the total arsenic concentrations dropped to 2.4 to 4.1 µg/L in the treated water. The treated water remained below 10 µg/L for approximately 20,000 bed volumes, which will be further discussed in the final evaluation report.
Comparison of the distribution system sampling results before and after the operation of the APU-300 system showed a decrease in arsenic concentrations at each of the sampling locations. Total arsenic levels in the distribution system decreased from 7.2 to 13.3 µg/L before treatment to 3.0 to 6.1 µg/L after treatment. Iron levels decreased to nondetect levels, while manganese levels increased slightly. Lead and copper concentrations did not appear to have been affected by the operation of the system.
Four backwash water samples were collected during the first six months of system operation. With the exception of one event, dissolved arsenic concentrations in the backwash water were significantly lower than in the raw water and ranged from 4.9 to 9.9 µg/L, indicating removal of arsenic by the media during backwash. Soluble iron levels were typically lower than in the raw water, while manganese concentrations correlated more closely with the influent concentrations.
The capital investment cost of $305,000 included $218,000 for equipment, $35,500 for site engineering, and $51,500 for installation. Using the system's rated capacity of 640 gpm (921,600 gallons per day [gpd]), the capital cost was $477 per gpm ($0.33 per gpd) and equipment-only cost was $340 per gpm ($0.24 per gpd). These calculations do not include the cost of a building addition to house the treatment system.
O&M costs included only incremental costs associated with the APU-300 system, such as media replacement and disposal, chemical supply, electricity, and labor. Although not incurred during the first six months of system operation, the media replacement cost represented the majority of the O&M cost and was estimated to be $53,600 for both APU-300 units (which represented 320 cubic feet of media). This cost was used to estimate the media replacement cost per 1,000 gallons of treated water as a function of the projected media run length to the 10-µg/L arsenic breakthrough. O&M costs will be refined once the actual throughput and cost at the time of the media replacement become available.
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