A bioelectrochemical and microbial system for anaerobic ammonium oxidation and biodegradation of persistent contaminants

Background

The management of nitrogen pollution and the remediation of persistent organic contaminants are critical challenges in environmental engineering, particularly in the context of wastewater treatment and soil decontamination. Ammonium, a common byproduct of agricultural runoff, sewage, and industrial effluents, poses significant risks to aquatic ecosystems and human health due to its role in eutrophication and toxicity. Simultaneously, per- and polyfluoroalkyl substances (PFAS) have emerged as a class of “forever chemicals” that resist conventional degradation processes, accumulating in water, soil, and living organisms. The recalcitrant nature of PFAS, combined with the widespread occurrence of ammonium pollution, underscores the urgent need for innovative, efficient, and sustainable treatment technologies that can address both types of contaminants under real-world conditions.

Current approaches to ammonium removal, such as aerobic nitrification and denitrification, require substantial energy inputs for aeration and often generate greenhouse gases as byproducts. Anaerobic processes like Feammox rely on the addition of ferric iron, which leads to the accumulation of iron sludge—a secondary waste stream that is costly and challenging to manage. For PFAS, existing remediation methods, including activated carbon adsorption, ion exchange, and advanced oxidation, are either ineffective at achieving complete mineralization or are prohibitively expensive and energy-intensive. Moreover, these technologies typically transfer PFAS from one medium to another rather than destroying them, resulting in persistent environmental liabilities. The limitations of current methods highlight the need for solutions that can operate under anaerobic conditions, minimize secondary pollution, and achieve true contaminant mineralization without excessive operational costs or waste generation.

Technology

This bioelectrochemical system is designed for the simultaneous anaerobic oxidation of ammonium and the biodegradation of persistent per- and polyfluoroalkyl substances (PFAS) in contaminated water, soil, and sludge. At its core, the technology leverages the unique metabolic capabilities of the Feammox bacterium Acidimicrobiaceae sp. A6, which colonizes an electrically conductive anode within a reactor. The anode, made from materials such as graphite or metal, serves as the primary electron acceptor—eliminating the need for ferric iron and preventing iron sludge accumulation. The system operates under a broad range of pH (2–9) and temperatures (4°C–35°C), and can utilize various electron donors, including ammonium, hydrogen, or organic matter. The bacteria facilitate the oxidation of ammonium and, through specialized enzymes, catalyze the reductive dehalogenation of PFAS, breaking down these contaminants into harmless end-products like fluoride, carbon dioxide, and water. The reactor is adaptable for both in situ and ex situ applications, supporting industrial wastewater treatment and environmental remediation efforts.

What differentiates this technology is its integration of microbial electrochemical processes with the metabolic versatility of Acidimicrobiaceae sp. A6, enabling the complete mineralization of highly recalcitrant contaminants under anaerobic conditions. Unlike traditional methods that require continuous addition of ferric iron or oxygen—leading to operational complexity and secondary waste—this system uses an anode as a reusable electron sink, streamlining the process and reducing costs. The ability of A6 to directly transfer electrons to the anode and to express specific reductive dehalogenases allows for efficient breakdown of PFAS, achieving up to 97% defluorination in experimental trials. The system’s flexibility in electron donors, broad operational range, and demonstrated scalability make it a robust solution for addressing two major environmental challenges: nitrogen pollution and persistent organic contaminants. Its energy efficiency, minimal chemical input, and avoidance of secondary pollution position it as a significant advancement in sustainable remediation technologies.

Benefits

• Enables anaerobic oxidation of ammonium without the need for ferric iron, reducing sludge production and chemical inputs.
• Effectively biodegrades persistent and toxic PFAS contaminants through reductive dehalogenation, achieving up to 97% defluorination.
• Operates efficiently under a wide range of pH (2–9) and temperature (4°C–35°C) conditions, enhancing versatility for various environments.
• Utilizes bioelectrochemical reactors with conductive anodes to facilitate direct electron transfer, improving process efficiency and stability.
• Supports treatment of diverse pollutants including chlorinated solvents, hydrocarbons, and heavy metals, broadening remediation applications.
• Applicable for both in situ and ex situ remediation of contaminated water, soil, and sludge, enabling flexible deployment strategies.
• Reduces energy consumption compared to traditional nitrification and iron-based Feammox processes by eliminating oxygen and iron supplementation.

Applications

• PFAS-contaminated groundwater remediation
• Industrial wastewater PFAS removal
• Anaerobic ammonium-rich sludge treatment
• Soil remediation at contaminated sites

Additional info

This bioelectrochemical system utilizes *Acidimicrobiaceae* sp. A6 to facilitate Feammox-driven anaerobic ammonium oxidation and reductive dehalogenation of per- and polyfluoroalkyl substances. Using a conductive anode as the primary electron acceptor, reductive dehalogenases mineralize persistent contaminants into fluoride, carbon dioxide, and water. Operating between pH 2–9 and 4°C–35°C, this technology eliminates iron sludge accumulation, providing a scalable solution for wastewater treatment and soil remediation.