The best indicator of hydraulic short-circuiting and mixing of constructed wetlands

Hydraulic residence time (HRT) distribution intuitively reflects flow pattern of constructed wetlands. HRT is able to reflect the merits of flow state clearly. Short-circuiting and mixing are the most important factors on HRT, exerting a significant effect on the flow pattern of wetlands. These two conditions must be avoided in wetlands construction and management. Therefore, it is necessary to select the best indicators measuring short-circuiting and mixing for understanding the flow pattern and the hydraulic performance of wetlands. This paper analyzes numerous indicators reflecting the degree of short-circuiting and mixing, displaying that t 10 and Morril index t 90 / t 10 are optimal indicators measuring short-circuiting and mixing, respectively, according to truncation and stability analysis based on tracer data. Data analysis showed that when water depth dropped, t 10 increased and t 90 / t 10 reduced gradually, indicating the improvement of short-circuiting and mixing. These results were fully consistent with the analysis results of hydraulic parameters, such as effective volume ratio e and the number of serial mixing tanks N . The excellent indicators of short-circuiting and mixing provide theoretical basis for reasonable design and evaluation of constructed wetlands, contributing to promote the hydraulic performance and purification effect.