For Utilities With Arsenic Problems, New Tech To The Rescue

New technology may lower arsenic treatment costs as some utilities struggle to meet federal standards over a decade after the U.S. EPA clamped down on the toxic substance.

In 2001, the EPA decreased the maximum allowable arsenic level in drinking water from 50 ppb to 10 and gave companies five years to comply. When the rule passed, the agency argued that this standard is achievable from a cost perspective, but some small utilities have struggled.

The city of Cottonwood, AZ, had to upgrade its technology to meet the standard, and the city took on additional costs to run new processes. But a recent tech upgrade is expected to cut down some of the costs.

When the federal mandate became enforceable, the city was “required to install arsenic removal systems at 13 well-sites outside the city and four sites within city limits to meet [EPA] standards,” according to the Verde Independent. This was not a cheap task.

“The purchase and installation of the arsenic removal systems, piping and required electrical and control upgrades cost $4.9 million with ongoing operations and maintenance expenses of $750,000 annually. Approximately 22 million gallons of water per year are also required to backwash the treatment media,” the report continued.

Arsenic is removed by moving water through manganese dioxide coated granular or resin media. “Over time, the arsenic ions coat the media resulting in a reduction in the efficiency of the resin media's ability to remove arsenic,” the report said.

But installing the technology was not the only cost for Cottonwood, the report said:

Another issue resulting from the removal of arsenic is the added costs associated with the disposal of Biosolids. Arsenic coming into the WWTP concentrates in the treated Biosolids. Prior to the implementation of arsenic treatment, the Biosolids produced by the WWTP were applied to agricultural land growing crops such as sod or animal feed. The increased levels of arsenic in the Biosolids produced by the WWTP are now prohibited from being applied to agricultural lands and must be disposed of in landfills at an additional cost of $4-$5 per ton.

Now, a plant upgrade may lower costs for Cottonwood. “Recently, a new well, reservoir and arsenic treatment system were installed for the Mesquite Hills subdivision through a public/private partnership between the City and VRE Cottonwood LLC. This new system has the capability of removing arsenic from the backwash water before it is discharged to the sewer system,” the report said.

The new technology will hold backwash water in a tank where arsenic can slip to the bottom. Solid arsenic will be drained from the tank and sent to a landfill. The water in the tank is then treated. “By employing this type of process, the volume of water required for arsenic removal is greatly reduced and the volume of arsenic going to the WWTP is also reduced,” the report said.

In the end, that means saving money, the report explained:

By reducing the in-flow levels of arsenic to the WWTP, the levels of arsenic in the Biosolids can be maintained at a level that allows for disposal on agricultural lands, which is a cost reduction to the city. Utility Department Operations staff are closely monitoring the quality of the water produced, the arsenic levels of the backwash water, and the quantity of arsenic solids to be land filled at the Mesquite Hills well-site. If this process is successful, the Utility Department will begin installing similar equipment at other well-sites. The goal is to maintain compliance with the EPA safe drinking water requirements, while maximizing the disposal of Biosolids and the efficient use of precious water resources.

This is what a study of arsenic treatment technology, made possible by EPA funding, found about the varying costs of technologies on the market used by utilities:

Capital investment costs for smaller AM and IR/CF systems varied extensively but mean values of the investment for these two technology types were comparable. Capital investment costs for large AM systems generally were higher than those for IR/CF systems with similar sizes. IX capital investment costs were comparable to the IR/CF costs. The large IR/CF and IX systems were more expensive than the large AM systems because of the use of ancillary equipment and controls, such as contact tanks and iron addition systems for IR/CF and salt saturators and salt supply systems for IX.

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