Glendale looks at microfiltration to reduce chromium-6 levels

The California utility Glendale Water & Power has demonstrated two successful methods for removing hexavalent chromium from drinking water. However, it has now started to evaluate microfiltration in advance of anticipated lower chromium-6 maximum levels.

The Metropolitan Water District of Southern California (MWDSC) reveals in its February 2011 newsletter that Glendale has developed two facilities that effectively remove chromium-6, made infamous by Erin Brockovich and recently found at elevated levels in more than 30 US public water systems, using weak-base anion (WBA) exchange and reduction-coagulation-filtration (RCF).

As the presence of chromium-6 in drinking water throughout Los Angeles County was making the news in the year 2000, Glendale started up the Glendale Operable Unit (GOU), a treatment facility that was part of the Environmental Protection Agency (EPA) Superfund to clean up the San Fernando Groundwater Basin from Volatile Organic Compounds (VOC). After a year of public debate, expert testimony and studies of various alternatives, a self-imposed chromium-6 limit of 5 ppb allowed the GOU to continue to operate. 

Since then Glendale has conducted the only research of its kind, says MWDSC, to remove chromium-6 from groundwater. The research moved from bench-scale testing to pilot-scale and, eventually, demonstration.

The WBA facility treats a 425 gpm (1,600 L/min) groundwater well that is part of the GOU. It has two exchange-vessels in lead and lag, and a carbon-dioxide feed system for pH control. The influent chromium-6 concentration is 40 ppb, the effluent is currently at 2 ppb and resin change-out takes place when the effluent reaches 5 ppb.

The RCF facility is a 100 gpm (380 L/min) system with a ferrous sulfate feed for reduction, mixing and aeration tanks, polymer feed and dual-media filters. Backwash water uses a fabric filter media in a dewatering container for sludge densification. The influent chromium-6 concentration is 80 ppb with the effluent in the range 1-6 ppb.

The effort has been supported by senators Dianne Feinstein and Barbara Boxer and representative Adam Schiff. Numerous partners have provided funding: EPA, the state of California, the Water Research Foundation, the National Water Research Institute, the Association of California Water Agencies and the cities of Los Angeles, Burbank and San Fernando, for a total of US$ 5.6 million thus far (MWDSC has provided in-kind funding).

When the study began, the goal was to reduce chromium-6 concentrations to less than 5 ppb. The state of California has recently issued a draft Public Health Goal of 0.02 ppb, which, while not enforceable, influences public opinion and may result in a lower Maximum Contaminant Level (MCL) than previously anticipated.

For the treatment technologies being tested to consistently achieve levels below 1 ppb, it is necessary to evaluate microfiltration as part of the RCF system. Further, for the state of California to establish an MCL, it is necessary to understand the limits and cost of removal for the various technologies.

Glendale has already prepared the scope of the research needed to study the effectiveness of microfiltration and to understand the cost of treatment, and estimates this additional effort will cost about US$ 1.6 million.