Enhanced denitrifying biofilter technology for stormwater nitrate removal

Overview

This technology addresses a critical challenge in stormwater management: the removal of nitrate, the most difficult nitrogen species to capture in passive biofiltration systems. Conventional woodchip biofilters suffer from carbon limitation because the slow decomposition of lignocellulosic biomass under flooded, anoxic conditions restricts the availability of soluble carbon needed to fuel denitrification. The proposed solution leverages two complementary strategies—brown rot fungi inoculation and enhanced between-storm ventilation—to accelerate the oxygen-dependent breakdown of lignin-rich biomass into labile carbon substrates. This approach enables more robust denitrification during storm events and the resulting flooding and anoxia in biofilter layers, offering a scalable, low-cost method for improving water quality in agricultural and urban stormwater treatment applications.

Technical specifications

Key features:

• Fungal bioaugmentation using brown rot fungi strains to accelerate lignocellulose decomposition into soluble, labile carbon forms
• Enhanced ventilation via perforated PVC pipes connecting woodchip layers to the surface, promoting aerobic conditions during dry periods
• Periodic oxic-anoxic cycling that increases dissolved organic carbon concentrations, including acetate and other labile substrates
• Layered biofilter design consisting of 30 cm loamy sand over 20 cm sand/woodchip media with a 10 cm submerged zone maintained by an elevated outlet
• Validated nitrate removal rates ranging from 8 to 40 g N m-3 d-1 depending on aeration conditions, compared to continuously flooded baseline systems
• Compatibility with established biofiltration infrastructure, requiring only low-cost lignocellulosic amendments such as woodchips or plant residues

Technology readiness level

The technology has progressed through initial laboratory validation, with demonstrated nitrate removal improvements in both batch and flow-through experimental systems. Current results show that enhanced aeration during dry periods can achieve removal rates sufficient to meet typical stormwater treatment targets of 1–2 gpm per square foot at influent nitrate concentrations of 1.5 mg N/L. The next phase involves constructing full-scale laboratory biofiltration cells to compare enhanced ventilation, fungal bioaugmentation, and control conditions in triplicate using real stormwater. Effluent analysis for nitrogen and carbon species will validate performance under realistic storm event conditions. The approach is built on established biofilter designs and low-cost materials, positioning it favorably for pilot-scale demonstration and eventual deployment in existing stormwater treatment infrastructure.