Technology for Cheap Arsenic Removal

City of Cottonwood was required to install arsenic removal systems at 13 well-sites outside the city and four sites within city limits to meet the new EPA safe drinking water standards for arsenic

Arsenic is a naturally occurring element found in groundwater across much of the western United States. The naturally occurring levels of arsenic levels found in raw, untreated groundwater in the Verde Valley range from greater than 70 ppb to less than 10 ppb. 

Well location, depth, geology and the amount of water withdrawn can affect the levels of arsenic found in our groundwater. 

The removal of the arsenic is accomplished by passing water through a vessel that contains a 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. 

When the efficiency of arsenic removal drops to a preset point, the water flow through the vessel is reversed. This reversed flow, or backwash cycle, strips the arsenic coating from the media, which discharges to the sewer system and is pumped to the Mingus Avenue Wastewater Treatment Plant. 

If no direct sewer connection is available, as in the Verde Villages, the arsenic laden backwash is hauled by trailer to a specifically designed sewer connection near the airport. 

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. 

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.

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 backwash water is held in a cone shaped tank while the arsenic solids settle to the bottom. The arsenic solids are then drained from the tank, dried and hauled to a landfill for disposal. The water in the tank is then returned to the start of the treatment process. 

Source: Verde Independent

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