Nutrient Removal by Floating Treatment Wetlands Under Different Spatial Arrangement Modes: a Field Study

Floating treatment wetlands (FTWs) are a management method to improve urban rivers, but most studies have been carried out at laboratory, micro, and meso levels, so it is necessary to study full-scale FTWs as a method to improve urban water bodies. In this experiment, the purification effects of water temperature (WT), dissolved oxygen (DO), ammonia nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N), total phosphorus (TP), chemical oxygen demand (COD_Mn), and chlorophyll-a (Chl-a) under staggered arrangement (SA) and centered arrangement (CA) were evaluated. It was found that the DO concentration and removal rate of COD_Mn, Chl-a, and TP in the SA were significantly higher than those in the CA in months with heavy rainfall. However, interestingly, for TP, August showed the opposite trend. The removal rates of NH₄⁺-N and NO₃^--N were significantly different throughout the test period. The biomass growth values of shoots and roots of plants in the FTWs were 0.40 ± 0.03 kg/m² and 1.38 ± 0.07 kg/m² in the SA and 0.32 ± 0.07 kg/m² and 1.26 ± 0.30 kg/m² in the CA. The increments of N absorbed by plants in the SA and CA were 7.08 ± 0.49 g/kg and 6.83 ± 0.07 g/kg, respectively, and the increments of P were 0.57 ± 0.02 g/kg and 0.32 ± 0.07 g/kg, respectively, which indicated that the growth status of plants in the FTWs in the SA was slightly better than that in the CA. In summary, the hybrid-constructed FTWs of both arrangements can effectively improve the water quality of urban rivers, and the effect of the SA was greater than that of the CA. The purification effect of in situ tests under different arrangement modes of hybrid-constructed FTWs was evaluated, which provides guidance and support for the field layout of FTWs in rivers in the future.