A medium and system for enhanced bioremediation of ammonium and fluorochemicals using polymer-coated iron particles

Background

The field of environmental remediation, particularly the removal of ammonium and persistent fluorochemicals such as per- and polyfluoroalkyl substances (PFAS), has become increasingly critical due to the widespread contamination of soil, groundwater, and wastewater by these pollutants. Ammonium, a common byproduct of agricultural runoff and wastewater discharge, contributes to eutrophication and poses toxicity risks to aquatic ecosystems. PFAS, often referred to as “forever chemicals,” are synthetic compounds used in a wide array of industrial and consumer products. Their strong carbon-fluorine bonds render them highly resistant to natural degradation processes, resulting in their accumulation in the environment and potential adverse health effects in humans and wildlife. The urgent need for effective, scalable, and sustainable remediation technologies is driven by the persistence, mobility, and toxicity of these contaminants.

Current approaches to ammonium and PFAS remediation face significant limitations. Conventional biological treatment methods, such as nitrification-denitrification for ammonium and activated sludge processes for PFAS, often fail to achieve complete removal, especially for highly recalcitrant PFAS. Chemical oxidation and advanced physical treatments (e.g., granular activated carbon, ion exchange, or high-pressure membranes) can be costly, generate secondary waste streams, or are ineffective against short-chain PFAS and complex mixtures. In situ remediation using iron-based amendments is hindered by poor transport through soils, rapid aggregation, and inhibition by dissolved iron species. Additionally, the acidic conditions required for certain biological processes can further reduce the mobility and reactivity of remediation agents, limiting their effectiveness in real-world applications. These challenges highlight the need for innovative solutions that can overcome the fundamental barriers of electron transfer, contaminant accessibility, and operational stability in diverse environmental settings.

Technology

This technology is an advanced bioremediation medium designed to simultaneously degrade ammonium and persistent fluorochemicals, specifically per- and polyfluoroalkyl substances (PFAS), in contaminated soil, water, sludge, and sediments. It utilizes iron particles, such as ferrihydrite or goethite, coated with negatively charged polymers like polyacrylic acid, which serve as electron acceptors for Feammox bacteria—most notably Acidimicrobiaceae bacterium A6—or their enzymes. The medium also includes an electron donor, such as ammonium or hydrogen, to drive the biochemical process. The polymeric coating on the iron particles imparts a negative surface charge, enhancing colloidal stability and transport through porous media, while also mitigating the inhibitory effects of dissolved Fe(II) by promoting its sorption. This setup facilitates efficient electron transfer, enabling the bacteria to oxidize ammonium and reduce Fe(III) to Fe(II), while concurrently driving the reductive dehalogenation and defluorination of PFAS.

What differentiates this solution is its integrated approach to overcoming key challenges in environmental remediation of both nitrogenous and fluorinated contaminants. The negatively charged polymer coating not only accelerates electron transfer and reaction rates but also ensures the iron particles remain mobile and bioavailable in diverse environmental conditions, particularly in acidic and anoxic settings where traditional iron phases would aggregate or become immobilized. By reducing charge transfer resistance and preventing Fe(II) inhibition, the technology sustains high microbial activity and contaminant degradation rates. Experimental validation demonstrates that this system significantly outperforms uncoated iron media, achieving higher rates of ammonium oxidation and PFAS breakdown, as well as enhanced defluorination. Its adaptability to both batch and continuous reactor systems, and its ability to support robust microbial communities, make it a scalable and effective solution for the remediation of challenging environmental pollutants.

Benefits

• Enhanced degradation of ammonium and persistent fluorochemicals (PFAS) through improved bioremediation efficiency.
• Accelerated electron transfer rates due to polymer-coated iron particles reducing charge transfer resistance.
• Mitigation of Fe(II) inhibition by sorption onto negatively charged polymer coatings, sustaining microbial activity.
• Improved transport and stability of iron particles in soil and groundwater via negative surface charge and colloidal stability.
• Increased bioavailability of iron to Feammox bacteria and enzymes, enhancing microbial-driven reactions.
• Effective operation under a wide range of environmental conditions (pH 2–8, temperature 4–35°C).
• Scalable application for in-situ and ex-situ remediation of contaminated soil, water, sludge, and sediments.
• Simultaneous removal of nitrogenous waste and defluorination of PFAS, addressing multiple pollutants concurrently.

Applications

• Groundwater PFAS remediation
• Wastewater treatment plant upgrades
• Soil decontamination at industrial sites
• Sewage sludge PFAS removal

Additional info

This technology utilizes *Acidimicrobium* sp. Strain A6 to catalyze the Feammox process, coupling ammonium oxidation with ferric iron reduction to drive PFAS dehalogenation. The system employs iron particles encapsulated in negatively charged polymers, such as polyacrylic acid. This coating lowers charge transfer resistance, enhances electron transfer, and mitigates Fe(II) inhibition via sorption. The resulting negative zeta potential improves colloidal stability and transport through porous media for effective bioremediation.