Evaluation of Ceraflow-50 as a Filtration Media for Hexavalent Chromium Treatment - Case Study
Pilot testing was conducted to evaluate the relative performance of 4 filter media, including Ceraflow-50, as part of a reduction coagulation filtration (RCF) treatment process for the removal of hexavalent chromium (Cr(VI)) from groundwater. This evaluation was conducted at multiple well sites for a water utility in California.
The RCF process achieves Cr(VI) removal by reduction to the less soluble trivalent chromium (Cr(III)) using a reductant – i.e., ferrous iron, coagulation, followed by filtration of the chromium laden particulate. Following the reduction step, any remaining ferrous iron is oxidized to ferric hydroxide via aeration or chlorine addition, and then filtered, removing the chromium particles. RCF for Cr(VI) removal is akin to arsenic removal with coagulation filtration with the exception of the reduction step and the use of ferrous, rather than ferric iron as a coagulant.
This investigation compared the efficacy of four different filter media designs for use in the RCF process (See Table 1). For the impacted utility, significant capital cost savings could be realized by reduction of (1) the requisite filter area, and (2) instantaneous back wash volume. In this instance the backwash volume was important as the utility could discharge backwash waste to sewer, however the existing sewer capacity is limited and therefore either costly sewer main improvements or on-site equalization would be required. If Ceraflow-50 were effective, the filter area could be reduced by as much as 50% and the instantaneous backwash volume by 75% when compared to a traditional dual media design.
Pilot Test Results
Total Chromium Removal:
With all four media designs, with optimal ferrous doses and contact times, filtered water total chromium targets of 4 μg/L could be reliably achieved.