Enhanced nitrogen removal and mitigation of nitrous oxide emission potential in a lab-scale rain garden with internal water storage

Abstract

The rain garden is a low impact development design for stormwater management. Nitrate was difficult to be removed in conventional rapid-filtration rain garden, and sometimes even with net nitrogen release, resulting in the potential nitrous oxide (N2O) emission. This study aimed to compare the conventional rapid-filtration rain garden (CON) and modified rain garden with internal water storage (IWS) in terms of the nitrogen removal, N2O emission, and the bacterial community composition. Two lab-scale rain gardens (CON and IWS) were designed and studied in simulated rainfall experiments. The IWS design showed an advantage over CON in nitrogen removal, with the total nitrogen (TN) removal efficiency of 91.3%–91.4% compared to 18.0%–53.7% in CON. For N2O emission, IWS exhibited a lower emission potential of 0.2%–0.3% of TN removed (with emission rate of 0.41–0.74 mg N2O-N/m2/h) compared to 0.2%–0.7% of TN removed in CON (with emission rate of 0.24–0.29 mg N2O-N/m2/h). Phyla of Actinobacteria, Acidobacteria, Bacteroidetes, Chloroflexi and Proteobacteria dominating in both IWS and CON. A significant difference of microbial composition was found at the genus level, especially the potential denitrifiers including Candidatus Solibacter, Haliangium, Hyphomicrobium, Lentimicrobium and Terrimonas. The different abundance of these functional denitrifiers in IWS and CON may contribute to their different nitrogen removal efficiency and N2O emission potential. This study highlighted that rain garden with IWS as an optimal option for enhancing nitrogen removal and mitigating N2O emission from stormwater systems.