Bioelectrochemical enhancement of nitrogen removal in bioretention systems

Overview

Urban stormwater bioretention systems often underperform in nitrogen removal because traditional heterotrophic denitrification requires supplemental carbon sources and can export residual pollutants. This research proposes a bioelectrochemical approach that enriches electroactive nitrogen-processing microorganisms directly within bioretention cells. By applying low-energy electrical input from on-site solar panels, the system promotes autotrophic denitrification on cathodes and supports anammox bacteria capable of converting ammonium and nitrite into nitrogen gas under anaerobic conditions. The result is improved nitrogen removal performance in both existing and newly constructed bioretention infrastructure without the need for external chemical inputs.

Technical specifications

• Cathode-driven autotrophic denitrification: Electroactive denitrifiers enriched on the cathode reduce nitrate in the upper, unsaturated layer of bioretention cells using supplied electrons.
• Anode-supported microbial respiration: In the internal water-saturated zone (IWSZ), electroactive microbes transfer electrons to the anode, supporting both heterotrophic denitrification and electroactive anammox activity.
• Anammox integration: Anammox bacteria capable of extracellular electron transfer remove ammonium and nitrite from incomplete nitrification and denitrification, producing nitrogen gas under anaerobic conditions.
• Renewable energy integration: Carbon electrodes are powered by on-site solar panels, enabling low-energy, self-sustaining operation.
• Microbial community control: Anode potential manipulation allows targeted cultivation of desired denitrifier and anammox populations.
• No external carbon or pollutant addition: The system avoids the need for supplemental organic carbon and does not introduce additional pollutants.

Technology readiness level

The technology is at an early-to-mid research and development stage. Bioelectrochemical systems have previously demonstrated promising nitrogen removal results in wetlands and low-concentration wastewater treatment. Future validation will proceed in two phases: first, rapid enrichment of electroactive nitrogen-processing bacteria using mesocosm columns with carbon electrodes and solar-powered cycling, with biofilm community analysis every 10 to 20 cycles; second, system performance assessment using simulated stormwater at varying nitrogen concentrations, flow rates, and durations to determine nitrogen removal rates and establish scale-up parameters.