Evaluation of Different Methods to Assess the Hydraulic Behavior in Horizontal Treatment Wetlands

Abstract

While there have been numerous studies on the rate and development of clogging in horizontal subsurface treatment wetlands (HSTWs) and, consequently, the effects on its hydraulic characteristics, research has not shown a clear understanding of the processes. The existing methods for measuring the impact of clogging provide limited information on the extension and degree of the phenomenon. This study aimed to evaluate the capacity of various measurement techniques to assess the degree and variation in space and time of clogging in HSTWs. Hydraulic conductivity at saturation (Ks) measurements were conducted using a newly implemented scheme, the drainage equation method, and traditional tracer tests, which were carried out in a full-scale HSTW system, located in Sicily, Italy, during 2019. After five years of operation, the results highlighted a severe decrease in Ks (<1000 m day−1) in the inlet zone (despite the fact that the filter gravel was replaced in 2017), a very high reduction of Ks along the central path inside the bed, a nonuniform flow through the HSTW, the presence of stagnant zones, and a reduction of the porosity of the bed gravel. Nonetheless, the mean values of the physical–chemical and bacteriological parameters at the hybrid treatment wetland (hybrid TW) outlet indicated that the partial clogging had no significant effect on the quality of the discharged water. Moreover, the results obtained using the different measurement techniques (in terms of both the Ks values and the flow distribution inside the bed) were consistent with each other and with results obtained previously for the same system. Finally, the most efficient combination of methods to assess clogging in HSTWs was identified.

Hydraulic Efficiency of Green-Blue Flood Control Scenarios for Vegetated Rivers: 1D and 2D Unsteady Simulations

“…As depicted in Figure 6, increasing values of Manning's n coefficients were considered for the green-blue scenario I to simulate the growth in biomass area of the examined common reed beds (indicated by the green-yellow rectangles in Figure 6) along Morra Creek, corresponding to an augmentation in leaf area index (LAI), precisely defined as the ratio between the total leaf area distributed on the riverine plants' height (in m 2 ) and the projected ground area (in m 2 ) in the field [12,31,38,39].…”

“…To properly model and simulate the actual biomechanical and botanical traits of riverine vegetation stands at field scale, the analysis of the green volumes involved in their phenological and morphometric evolution over time is essential [30][31][32]. As suggested by previous ecohydraulic studies and reviews [33][34][35], riverine vegetation's canopy morphometric trends can be easily described by the well-known leaf area index (LAI).…”

Monitoring of horizontal subsurface flow constructed wetlands for tertiary treatment of municipal wastewater

“…However, the effects of both solids accumulation and plant root can result in hydraulic malfunction and reduced service life, mainly dealing with clogging issues (Liu et al 2018b ). Hydrodynamics of HSF-CW systems have been studied by many researchers (Licciardello et al 2019 , 2020 ), and internal hydraulic features specific to each HSF-CW unit such as preferential flow in the bottom layer of reed beds (Garcia et al 2003 ) may explain in part overall performance. It should be noted that the predominant physical mechanisms for suspended solids removal are generally flocculation/sedimentation and filtration (Kadlec 2009 ).…”

Initial Stage in Designing Household Constructed Wetlands: Selection of a Suitable Aquatic Plant

“…During acclimatization, the concentration of the greywater gradually increased from 25 to 100%. To characterize the influent and a steady-state system, the following parameters were calculated [25].…”