Floating treatment wetlands (FTWs) use plants’ roots for water quality improvement. The plants are supported by a buoyant structure deployed at the water surface. The roots form a porous zone beneath the structure and remove pollutants carried in suspension through filtering, absorption and uptake. This paper used CFD simulation to model FTWs arranged in series and spanning the channel width and to study the effects of root length and spacing between FTWs on flow distribution and mass removal. The root zone was modelled as a porous media, and removal was computed using first-order decay, for which a range of removal constants was tested. Longer roots increased the reactive volume of the root zone, which increased the fraction of pollutant inflow entering the FTWs. Increasing the distance between FTWs allowed greater mixing between water that went through and beneath the upstream FTW. This increased the concentration entering each FTW, which enhanced mass removal per FTW. However, a larger distance between FTWs reduced the number of FTWs in the channel, reducing the reactive volume. In the tradeoff between mixing and reactive volume, the reactive volume was more important, such that total removal in the channel increased with longer roots and more units of FTW (shorter gap distance). However, removing the gap entirely was detrimental, as FTWs in series removed more mass than a continuous FTW of same volume. This study points to two design recommendations for FTWs in series. First, if resources for building FTWs are not limiting, but the channel length is, it is preferable to prioritize higher reactive volume (shorter gap distance) to achieve maximum removal per channel length. Second, if resources for FTWs are limiting, but channel length is not, it is better to place the FTWs with a longer gap distance, preferably along enough to allow mixing over the full depth between FTWs, as this will achieve maximum removal per FTW.

浮动处理湿地 (FTW) 使用植物的根来改善水质。这些植物由部署在水面上的浮力结构支撑。根部在结构下方形成一个多孔区域，通过过滤、吸收和吸收去除悬浮中的污染物。本文使用 CFD 模拟对串联排列并跨越通道宽度的 FTW 进行建模，并研究 FTW 之间的根长和间距对流量分布和质量去除的影响。根区被建模为多孔介质，并使用一阶衰减计算去除，并测试了一系列去除常数。较长的根增加了根区的反应体积，从而增加了进入 FTW 的污染物流入比例。增加 FTW 之间的距离允许通过上游 FTW 和下方的水之间的更大混合。这增加了进入每个 FTW 的浓度，从而提高了每个 FTW 的质量去除。然而，较大的 FTW 之间的距离减少了通道中 FTW 的数量，从而减少了反应体积。在混合和反应体积之间的权衡中，反应体积更重要，因此通道中的总去除量随着根越长和 FTW 单位越多（间隙距离越短）而增加。然而，完全消除间隙是有害的，因为串联的 FTW 比相同体积的连续 FTW 消除了更多的质量。本研究为串联的 FTW 提出了两个设计建议。首先，如果构建 FTW 的资源不受限制，但通道长度是，最好优先考虑更高的反应体积（更短的间隙距离），以实现每个通道长度的最大去除量。其次，如果 FTW 的资源有限，但通道长度不受限制，则最好将 FTW 放置为具有更长的间隙距离，最好沿足够长的距离以允许在 FTW 之间的整个深度上混合，因为这将实现每个 FTW 的最大去除。