Optimizing aeration pattern to improve nitrogen treatment performance of ditch wetlands in polder areas around Chaohu Lake, China

Ditch wetlands in polders are planned to attenuate the nitrogen load from paddy fields, mainly resulting in eutrophication of Chaohu Lake, China. The nitrogen treatment performance of ditch wetlands is poor because of the low dissolved oxygen (DO) concentration observed in field. Aeration is often used to improve both DO concentration and nitrogen treatment performance, but aeration pattern needs to be optimized for better treatment performance. A dynamic model was constructed to explore the nitrogen transformation with the DO effect. The simulation results show that through an optimal aeration pattern, the treatment performance of total nitrogen (TN) increased from 3.9% to 23.9% when TN was dominated by ammonium and organic nitrogen (NH4 + ON). The optimal aeration pattern was that the ratio of aeration time to non-aeration time was approximately 1:1, and the aeration cycle period was equal to the experimental period (10 d). The essence of aeration is to ensure that the mass of nitrogen nitrified from NH4 is denitrified, which means that the rate of nitrification is close to that of denitrification. The concentration ratio of (NH4 + ON)/NO3 was a reasonable indicator to determine the aeration time for various composition of TN. Finally, guidelines for drainage water recycling within polders from the point of DO are provided to achieve the objective of nitrogen load reduction in polders. •A model was constructed to explore and optimize aeration pattern for nitrogen treatment.•The ratio of aeration time to non-aeration time was approximately 1:1.•(NH4 + ON)/NO3 can be used to determine the aeration time.•The optimal intermittent aeration pattern is explained from nitrogen transformation.•Guidelines for drainage water recycling within polders from viewpoint of DO are given.