Harmful Contaminants, Innovative Solution

Perchlorate Contamination

The Magna Water District provides drinking water and wastewater treatment for the City of Magna, Utah. Drinking water is drawn from wells where dissolved solids, minerals and salts, and naturally occurring arsenic are persistent problems.

During routine testing in 1997, trace elements of perchlorate were found in one well at the Barton Well Field. A plume from the defense industry had contaminated the groundwater with perchlorate. Because of the rapid-moving nature of plumes, the entire Barton Well Field was shut down for fear of further contamination.

Naturally occurring arsenic levels at the Barton Well Field were between 8 and 18 μg/L. In 2001, the EPA adopted a new arsenic standard of 10 μg/L, replacing the old standard of 50 μg/L, and requiring compliance by January, 2006. While the EPA had not made a final regulatory determination by setting a maximum contaminant level (MCL) for perchlorate, the Magna Water District took a proactive approach and began looking for a perchlorate-remediation solution that could also provide arsenic removal. (The EPA most recently declared an interim health advisory of 15 μg/L in January, 2009.)

A series of studies were conducted over the course of the next several years to evaluate processes for simultaneous arsenic and perchlorate removal. Following the studies, the engineer concluded that electrodialysis reversal (EDR) was the most cost-effective contaminant removal system. Typically, EDR systems are used for desalination and to remove charged particles (lead, copper, chromium, and nitrates). Magna installed the first EDR for arsenic and perchlorate removal.

Equipment Selection

After the removal of perchlorate and other contaminants from the drinking water, the concentrated waste stream required disposal. If perchlorate is not destroyed, it will continue to pollute the environment and drinking water supplies. Magna, in conjunction with Carollo Engineers, developed a biological process to destroy perchlorate. The concentrated reject stream from the EDR was combined at a 1.5:1 ratio with screened wastewater and allowed to react anaerobically. Vertical pressure filters were the best treatment-housing-equipment option to provide this anaerobic reaction. In 2007, WesTech was contracted to supply six vertical pressure vessels for digestion (12 ft diameter x 9.5 ft long).

WesTech’s vertical pressure filters were filled with 54 inches of Granular Activated Carbon (GAC) media. Because of the media depth, the underdrain design needed to be modified for the system. The unique header and lateral underdrain design developed by WesTech, in collaboration with Carollo, ensured uniform distribution of flow in the vessels. With WesTech’s extensive experience in designing and constructing pressure filters, the large diameter vessels and media depth were customized to match the water quality and remove perchlorate.

Due to its porous nature, GAC was an optimal growth media where the wastewater developed a biofilm around it. When perchlorate-contaminated water passed over the media, the oxygen starved bacteria consumed the oxygen in the perchlorate, breaking the O-Cl bonds and destroying it.

The biodestruction of blended residual oxidants (BIOBROx) process provided sustained perchlorate and arsenic removal below detection with much shorter detention times (10 minutes) than traditional methods (6 to 24 hours). In addition, BIOBROx is lower in cost due to lack of aeration requirement and the fact that it is contained within a smaller footprint than traditional biological processes.

Customer Satisfaction

As perchlorate is difficult and costly to track, nitrate levels are routinely monitored. In a pilot study completed before plant operation began, when nitrate levels were below 0.05 mg/L, perchlorate levels were non-detectable.

The Magna Water District has received recognition for its forward thinking and role in advancing water treatment technology. By destroying perchlorate, Magna created an environmentally friendly treatment process.

In a letter to the water district, Senator Orrin Hatch said, “It is exciting to know that the project continues to be an efficient and cost-effective solution to the problem.”

“The simultaneous removal of arsenic, perchlorate, and TDS by EDR, followed by the biodestruction of perchlorate in the concentrate represents a unique approach to a complex water quality problem.”