Effects of plant roots on the hydraulic performance during the clogging process in mesocosm vertical flow constructed wetlands

Abstract

The aim of this study was to evaluate the effects of plant roots (Typha angustifolia roots) on the hydraulic performance during the clogging process from the perspective of time and space distributions in mesocosm vertical flow-constructed wetlands with coarse sand matrix. For this purpose, a pair of lab-scale experiments was conducted to compare planted and unplanted systems by measuring the effective porosity and hydraulic conductivity of the substrate within different operation periods. Furthermore, the flow pattern of the clogging process in the planted and unplanted wetland systems were evaluated by their hydraulic performance (e.g., mean residence time, short circuiting, volumetric efficiency, number of continuously stirred tank reactors, and hydraulic efficiency factor) in salt tracer experiments. The results showed that the flow conditions would change in different clogging stages, which indicated that plants played different roles related to time and space. In the early clogging stages, plant roots restricted the flow of water, while in the middle and later clogging stages, especially the later stage, growing roots opened new pore spaces in the substrate. The roots played an important role in affecting the hydraulic performance in the upper layer (0-30 cm) where the sand matrix had a larger root volume fraction. Finally, the causes of the controversy over plant roots' effects on clogging were discussed. The results helped further understand the effects of plant roots on hydraulic performance during the clogging process.

Domestic Wastewater Depuration Using a Horizontal Subsurface Flow Constructed Wetland and Theoretical Surface Optimization: A Case Study under Dry Mediterranean Climate

“…As a result of this drying episode, the following months showed an abnormal behavior for the BOD 5 value, a circumstance that can be related to the possible formation of preferential flow paths in the HF-CW bed that would have decreased the HRT. Other authors reported that an excessive root growth may cause the unbundling of the bed, encourage the creation of preferred paths and short circuits and open new pore spaces in the substrate [30,33]. From December 2013, a tendency to return to the proper working order of the CW was observed.…”

Efeito da vegetação em sistemas alagados construídos para tratar águas residuárias da suinocultura

“…Quanto à remoção de demanda bioquímica de oxigênio (DBO) e de sólidos suspensos totais (SST), não se constatou diferença entre os SACs (p>0, 05), no entanto a eficiência de remoção de demanda química de oxigênio (DQO) foi diferente entre os SACs orgânica, mineralização de nutrientes e remoção de patógenos, bem como funcionam como intermediárias em processos físicos e químicos como filtração, adsorção, precipitação e sedimentação (BRIX, 1994;1997;BIAŁOWIEC;JANCZUKOWICZ;RANDERSON, 2011;SHELEF;GROSS;RACHMILEVITCH, 2013). Apesar de controvérsias, autores como Hua et al (2014) e Matos et al (2015), entre outros, têm demonstrado que a planta e seu sistema radicular também contribuem para o aumento do tempo de vida útil das unidades, pela atenuação do progressivo processo de obstrução do meio poroso.…”

Analysis of conservative tracer measurement results using the Frechet distribution at planted horizontal subsurface flow constructed wetlands filled with coarse gravel and showing the effect of clogging processes

“…-deposition of the particles (Batchelor and Loots 1996;Sani et al 2013;Knowles and Davies 2011), -microbial biomass activity (Tanner and Sukias 1995;Sani et al 2013), -root density and condition (Breen and Chick 1995;Hua et al 2014), -mechanical compaction of filter media (Winter and Goetz 2003), -chemical precipitation (Winter and Goetz 2003), and -gas blocking (Langergraber et al 2003).…”