Effects of solids accumulation and plant root on water flow characteristics in horizontal subsurface flow constructed wetland

摘要

Void space clogging of horizontal subsurface flow constructed wetlands (HSSF CWs) can result in hydraulic malfunction and reduced service life. In this study, the effect of solids accumulation and root growth on the hydrodynamics of the HSSF CWs was evaluated by tracer tests. The experimental HSSF CWs were designed to be unplanted, uniformly planted and linearly planted to investigate the role of Iris (I. pseudacorus) root and the effects of different planting patterns. Results showed that the traditional design of HSSF CW was easy to develop the preferential bottom flow, and the solids accumulation near inlet zone aggravated the fast bottom flow throughout the whole systems. Plant root impeded the upper layer flow at the initial stage and promoted the uniform flow in the severe clogging situation. Consequently, the water flow was more uniform in the linearly planted (dispersion number (d) = 0.16) and uniformly planted (d = 0.13) systems than the unplanted system (d = 0.10) at the final stage. The opening of new void spaces by root growth and the upward water drag induced by plant transpiration was responsible for such phenomenon.