Superfund Research Program
Intensified, High-Rate Reductive Immobilization of Hexavalent Chromium
Project Leader: Fatemeh Shirazi
Grant Number: R44ES031495
Funding Period: Phase II: September 2022 - August 2024
Hexavalent chromium, or Cr(VI), is a highly prevalent contaminant in water resources in the U.S. and worldwide. Research has found that high concentrations of Cr(VI) can be carcinogenic and dangerous for public health. As a result, there is significant demand among water providers and Superfund sites for innovative technologies to reduce Cr(VI) concentrations in water resources in a cost-effective and environmentally sustainable manner. Current technical challenges posed by existing technologies for Cr(VI) remediation include high costs, limited capabilities to achieve low parts-per-billion (ppb) concentrations, and the outsized effects of influent water geochemistry on system performance. Specifically, there is a need for new technologies to reliably reduce Cr(VI) to low parts-per-billion (ppb) levels with lower costs and better performance than existing technologies. This proposed Phase II project builds on successful outcomes from Phase I in which a new biological process technology was developed. The new technology is based on enhanced biological reductive immobilization in which microorganisms reduce soluble, mobile, and highly toxic forms of specific metals to oxidation states at which the metals are very poorly soluble and easily removed from water. In this new technology, specifically chosen natural microorganisms are incorporated inside proprietary polymer composites called biocatalysts. The biocatalysts are designed to retain, control, and maintain a highly active population of the chosen microorganisms inside a bioreactor as part of a compact, high-performance water treatment system. In Phase I support, the Cr(VI)-removal biocatalysts were developed, and a prototype bioreactor was designed, built, and operated. Under continuous flow conditions, the removal of various influent concentrations of Cr(VI) was consistently demonstrated, including more than 99 percent removal to levels below 1 μg/L, which is well below the target concentration of five (5) μg/L. The technology was validated using actual contaminated groundwater with co-contaminants and a technoeconomic analysis was conducted. In Phase II, this new technology is further optimized and then scaled-up for demonstration at a contaminated site. The Phase II project seeks to further establishes the performance and operational parameters for this new technology. In addition, the proposed project positions the new technology for immediate implementation through documenting the technology's long-term operation, conducting stress testing and recovery studies, and assessing detailed maintenance, cost and operation parameters. This new technology addresses a critical need: the reliable treatment of Cr(VI) that cannot be removed cost- effectively using existing technologies. This project's success holds significant promise to become a commercial technology-of-choice for water managers and providers to address Cr(VI) contamination, enhance water security, and promote public health for thousands of communities in the U.S. and around the world.