Biological nitrogen removal of stormwater

Abstract.

Biological nitrogen removal (BNR) allows for permanent elimination of nitrogen pollutants in the form of nitrogen gas. However, very few studies have explored the potential of BNR for stormwater nitrogen removal even though this technique has been broadly applied for wastewater treatment. The stormwater runoff is characterized by its low strength and high dissolved oxygen content, which pose multiple challenges to effective BNR. The mathematical modeling effort carried out in this study for the first time revealed that over 90% national stormwater runoff has the potential to achieve compete nitrogen removal in steady-state bioretention systems within 0.5-day hydraulic retention time by syntrophic BNR communities in the layered structure of biofilms that are formed on packing media as long as a critical organic carbon concentration is provided in the influent. An appropriate amount of organics is required to simultaneously provide aerobic and anoxic conditions for successful stormwater BNR. Due to the prevalent organic carbon limitation in stormwater for denitrification, anammox becomes an especially important pathway for stormwater BNR. The adequacy of dissolved oxygen, organic carbon, and ammonia in stormwater for successful BNR was also elucidated in this study. It was concluded that the steady-state performance of a bioretention system with influent organic content optimization should suffice stormwater BNR requirement. Yet, bioaugmentation is required to expedite the bioretention system startup.