Across California and the western U.S., utilities are confronting a growing challenge: how to effectively remove hexavalent chromium (Cr(VI)) from drinking water sources. With California setting a Maximum Contaminant Level (MCL) of 10 ppb for Cr(VI), the pressure is on for municipal utilities to choose the right treatment technology—one that delivers reliable results, meets regulatory thresholds, and balances cost with operational feasibility.
The City of Glendale, CA, has been a national leader in addressing this challenge. Through a multi-year research and demonstration program, Glendale conducted one of the most comprehensive evaluations of Cr(VI) treatment technologies to date. Their findings offer invaluable insights for utilities navigating similar decisions—and reinforce why Reduction-Coagulation-Filtration (RCF) deserves strong consideration as a preferred solution.
A Groundbreaking Study on Cr(VI) Treatment
In partnership with the Water Research Foundation and engineering firm Hazen and Sawyer, the City of Glendale evaluated four potential technologies for Cr(VI) removal:
- Weak Base Anion Exchange (WBA)
- Strong Base Anion Exchange (SBA)
- Reverse Osmosis (RO)
- Reduction-Coagulation-Filtration (RCF)
Their goal was not just to assess performance, but to compare each technology’s operational complexity, residuals management, cost, and long-term viability for groundwater treatment at municipal scale.
RCF, a process involving chemical reduction of Cr(VI) to Cr(III) followed by coagulation and filtration, emerged as one of the top performers—particularly in sites where it was possible to dispose of backwash water via a nearby sanitary sewer connection.
What Makes RCF So Effective?
RCF adapts a conventional drinking water treatment framework by introducing a reducing agent (typically ferrous iron) upstream. The process involves:
- Reduction: Ferrous iron converts Cr(VI) to Cr(III), a less toxic and less mobile form.
- Coagulation: Cr(III) forms flocs that can be captured through filtration.
- Filtration: Granular media or microfiltration captures the chromium-laden particles.
One of the key strengths highlighted by Glendale’s study is that RCF does not require exotic materials or high-pressure membranes. Utilities familiar with traditional coagulation and filtration processes can integrate RCF with moderate upgrades. Even more compelling, RCF can often be retrofitted into existing iron and manganese treatment systems—something ATEC has demonstrated successfully in the field.
ATEC’s Track Record with RCF
At ATEC, we’ve long recognized RCF’s value as a flexible, high-performance solution for groundwater systems facing Cr(VI) contamination. Our approach builds on the foundational science validated in Glendale by engineering systems that are:
- Scalable: From 20 GPM wellheads to 5,000 GPM treatment facilities, ATEC’s RCF systems are modular and right-sized for the community served.
- Reliable: With over 500 installations across North America and systems running since 1996, ATEC brings operational proof—not just theory.
- Cost-effective: By leveraging existing iron/manganese vessels, many systems avoid greenfield construction, reducing both capital costs and time to deploy.
- Low Maintenance: Media beds typically last over 20 years, and with minimal sludge generation, residuals are manageable through simple sewer discharge or landfill.
For example, in Las Lomas, CA, ATEC retrofitted existing iron and manganese vessels to also treat hexavalent chromium using RCF, achieving compliance with California’s 10 ppb standard while maintaining uninterrupted service. The system has been operating successfully since 2015.
Head-to-Head: How RCF Compares to Other Technologies
The Glendale research team found that all four technologies evaluated could technically meet the 10 ppb MCL, but each came with tradeoffs:
| Technology | Advantages | Drawbacks |
|---|---|---|
| RCF | • Conventional process • Reliable removal • Adaptable to existing systems Low waste | • More complex chemical feed • Requires backwash management |
| WBA | • Lower capital cost for small systems • Simple operation | • Less effective in high TOC/silica waters • Regenerant disposal |
| SBA | • High capacity for Cr(VI) • Effective even at low concentrations | • Brine disposal concerns • Not selected by Glendale |
| RO | • Broad contaminant removal | • High energy use • Expensive • Concentrate disposal challenges |
The conclusion? RCF is especially attractive when utilities seek a proven technology that aligns with conventional treatment paradigms, minimizes waste, and in some cases may also enables a retrofit of existing system components rather than a fully greenfield solution.
Water Quality Matters—But RCF Is Resilient
The Glendale team also explored how water chemistry influences RCF performance. Key findings:
- pH Sensitivity: RCF is most effective at pH <8, but higher pH can be managed with increased iron doses.
- TOC and Silica: Elevated levels can impact floc formation and filtration performance, though bench testing showed RCF can still perform under these conditions with proper design.
- Chlorination Compatibility: Unlike aeration, chlorine can be used as an oxidant after reduction, enabling flexibility in design while minimizing reformation of Cr(VI) from Cr(III).
These insights mirror what ATEC has observed in the field: with the right engineering support, RCF can be tailored to a wide range of groundwater chemistries.
Understanding Cost and Scale
Glendale’s cost analysis estimated capital and O&M costs across a range of system sizes. While WBA showed lower initial costs for very small systems (<100 GPM), RCF gained a clear cost advantage as system size increased. Notably:
- RCF (with backwash recycling) was more economical than WBA for systems over 500 GPM.
- Annualized cost per acre-foot of treated water was highly competitive, especially when blending was not an option.
ATEC systems reflect these efficiencies in practice. By optimizing footprint, offering standardized skid-based designs, and leveraging existing infrastructure, we deliver systems that meet budgets and timelines—even for rural or cash-strapped communities.
Final Takeaways for Utilities
The City of Glendale’s work should be applauded not only for its technical rigor but for its transparency. Their demonstration of RCF’s capabilities gives water utilities across the country a roadmap for compliance with confidence.
For communities wrestling with Cr(VI) contamination, the message is clear:
- RCF is a practical, adaptable, and cost-effective solution.
- The technology has moved well beyond pilot testing—ATEC and others have proven it at scale.
- With new regulations and increasing scrutiny of groundwater quality, now is the time to act.
- ATEC stands ready to help communities assess their options and deploy right-sized RCF systems that protect public health and make the most of limited resources.
Further Reading & References
- City of Glendale, “Final Report on Chromium 6 Treatment Evaluation” (2013)
- Water Research Foundation Projects 4445 & 4450
- Blute et al., “Reduction/Coagulation/Filtration for Hexavalent Chromium Removal from Drinking Water,” Glendale, AZ Presentation