Engineered Bioretention for Removal of Nitrate from Stormwater Runoff

TLDR

Bioretention units are simple, plant‑ and soil‑based low‑impact facilities for treating stormwater runoff, but conventional designs do not attenuate nitrate. This study evaluated a reengineered bioretention concept that incorporates a continuously submerged anoxic zone with an overdrain to remove nitrate via microbial denitrification. The authors conducted a four‑phase experimental program, including column studies, loading tests, dormant‑period viability assessments, and pilot‑scale trials, to develop design information for the engineered system. Results showed that newspaper is the most effective electron‑donor substrate, the system remains viable after extended dormancy, and pilot‑scale tests achieved up to 80 % nitrate plus nitrite removal, demonstrating the potential of engineered bioretention for urban stormwater nitrogen treatment.

Abstract

A bioretention unit is a simple, plant‐ and soil‐based, low‐impact treatment and infiltration facility for treating stormwater runoff in developed areas. Nitrate, however, is not attenuated in conventional bioretention facilities. Thus, this study systematically evaluated a reengineered concept of bioretention for nitrate removal via microbial denitrification, which incorporates a continuously submerged anoxic zone with an overdrain. Experimental studies were performed in four phases. In the first two phases, column studies demonstrated that, overall, newspaper is the best solid‐phase electron‐donor substrate for denitrification out of the set studied (alfalfa, leaf mulch compost, newspaper, sawdust, wheat straw, wood chips, and elemental sulfur) based on superior nitrate removal and effluent water quality. The nitrate loading and hydraulic loading studies in the second phase provided design information. In the third phase, system viability after 30‐ and 84‐day dormant periods was evaluated in column studies, demonstrating that newspaper‐supported biological denitrification should be effective under conditions of intermittent loadings. Finally, in the fourth phase, pilot‐scale bioretention studies demonstrated the effectiveness of the proposed design, showing nitrate plus nitrite mass removals of up to 80%. These results indicate that engineered bioretention for the removal of nitrogen from stormwater runoff has the potential for successful application as an urbanstormwater treatment practice.