The potential of using biological nitrogen removal technique for stormwater treatment

Biological nitrogen removal (BNR) may provide permanent elimination of nitrogen pollutants by conversion to nitrogen gas. However, few studies have explored the potential of BNR for the removal of nitrogen from stormwater even though this technique has been broadly applied for wastewater purification. Urban runoff is characterized by its low strength and high dissolved oxygen content, which poses multiple challenges to effective BNR. In this study, mathematical modeling indicated that for most runoff input concentrations, complete nitrogen removal within a 0.5-day hydraulic retention time could be achieved if a critical organic carbon concentration is provided in the influent of steady-state bioretention systems. An appropriate amount of organic carbon is required to simultaneously create spatial aerobic and anoxic conditions for successful stormwater BNR in the layered structures of biofilms that are formed on bioretention media and inhabited with syntrophic BNR communities. Because organic carbon is normally limiting in stormwater denitrification processes, anammox becomes an especially important pathway for stormwater BNR. An analysis of influent runoff concentrations from the National Stormwater Quality Database suggested that 71.1% runoff could have nitrogen pollutant removed via partial nitritation followed by anammox. The adequacy of dissolved oxygen, ammonia and alkalinity in stormwater for successful BNR was also evaluated. It was concluded that adjusting influent organic content to a critical value determined in this study should suffice the stormwater BNR requirement of steady-state bioretention systems. Bioaugmentation is required to expedite the bioretention system startup.