Multiple linear modeling of outflow nitrogen dynamics in vertical-flow constructed wetlands under two different operating states

•An assumption concerning first-order removal rate constant (k) was proposed and validated.•Vertical-flow wetland state shift impacted N removal.•Temperature presented heavier impact on k compared to the other factors.•A new approach to simulate wetland outflow might be provided.

This paper proposed an assumption that the area-based first-order removal rate constant (k) of constructed wetland (CW) could be linearly determined by multiple influencing factors based on the classic k-C* model. The assumption was further validated by STELLA® using datasets from nine-batch pilot-scale vertical-flow CWs treating aquaculture wastewater under two different operating conditions: i.e., submersed state (SS) and non-submersed state (NS). A before-and-after comparison indicated that wetland state shift impacted N removal. Under SS, TN was mainly removed by sedimentation coupled with nitrification/denitrification, while under NS, it was mainly through sedimentation. Factor loadings showed that temperature presented heavier impact on k compared to the other factors. The simulations reflected the variation trend of observations well but the model precision was poor. Sensitivity analysis revealed that the dynamic model was more sensitive to the influencing factors under NS than it was under SS with temperature, pH and concentration having relatively higher SI compared to the other factors. Overall, this work might provide a new approach to simulate outflow and could be used for system design, prediction or optimization.