Design Approach to Extend Longevity of Woodchip Denitrification Bioreactors Treating Wastewater.

Design approach to extend longevity of woodchip denitrification bioreactors treating wastewater

Christine A. Lepine^1,2, Laura Christianson³, and Steven T. Summerfelt¹

¹ The Conservation Fund Freshwater Institute, 1098 Turner Road, Shepherdstown, WV 25443, USA

² Department of Natural Resources and Environmental Sciences, The University of Illinois at Urbana-Champaign, W-503 Turner Hall, 1102 South Goodwin Avenue, Urbana, IL 61801, USA

³ Department of Crop Sciences, The University of Illinois at Urbana-Champaign, AW-101 Turner Hall, 1102 South Goodwin Avenue, Urbana, IL 61801, USA

Woodchip denitrification bioreactors have moved beyond proof of concept as a cost-effective and low-maintenance nitrogen (N) mitigation option for agricultural runoff. Researchers have begun to explore non-traditional applications for this technology, including septic and aquaculture effluent treatment. Ideal conditions for efficient woodchip bioreactor operation include consistent flow, loading rates, and temperature, making bioreactors a promising solution for point-source wastewater high in nitrate-nitrogen (NO₃-N).

However, high total suspended solids (TSS), and chemical oxygen demand (COD) associated with wastewater can potentially alter the hydraulics within a bioreactor. Settled solids and biological growth may clog woodchip pore space, particularly near front-end inlet manifolds, consequently reducing the lifespan of the system. Extending bioreactor longevity is critical for translating this technology into practical wastewater or other high solids loading treatment applications.

Two influent manifold styles (single inlet vs. multiple inlets) installed across four pilot-scale bioreactors (3.8 x 0.76 x 0.76 m) were assessed for their clogging potential. Each manifold design operated with a 24-hour hydraulic retention time and was continuously fed by aquaculture wastewater produced on-site averaging approximately 40-50 mg NO₃-N/L.

Bioreactors were sampled for TSS, COD, and NO3-N. Additional sampling events from in situ wells provided insight into the internal dynamics of these systems. First-year operational results demonstrated no notable differences in N removal (70-100% removal efficiency) or TSS deposition between manifold designs. Continued successful wastewater treatment demonstrates woodchip denitrification bioreactors can effectively perform when loading conditions exceed traditional-use measures.