Influent salinity affects substrate selection in surface flow constructed wetlands.

Shenyan Zhou,Shuqing An,Juan Du,Qiming Li,Ran Zhao,Chen Chen,Qianqian Lu,Dehua Zhao,Miao Zhang

doi:10.1007/s11356-021-15036-5

Shenyan Zhou, Shuqing An + Show 7 more

Open Access

https://doi.org/10.1007/s11356-021-15036-5

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Abstract

To identify the effect of influent salinity on substrate selection, a study was conducted in pilot-scale surface flow constructed wetlands (SFCWs). Compared with gravel and sand SFCWs, soil SFCWs performed similarly or worse at low salinities, while at high salinities, soil SFCWs performed similarly or better in removal efficiency (RE) of salt, total nitrogen (TN), total phosphorous (TP), and chemical oxygen demand (COD). Soil generally increased macrophyte growth (especially at high salinity) in terms of biomass, leaf chlorophyll concentration, root activity, and root catalase and superoxide dismutase activities. A general decrease in bacterial α-diversity in the rhizosphere was observed at high salinity, while compared with gravel or sand, soil improved rhizosphere bacterial community stability at varying salinities. At high salinity, compared with that of gravel or sand, the soil support of macrophytes and rhizosphere microorganisms increased pollutant RE in SFCWs. This finding highlights the necessity of varying substrate selection in SFCWs with influent salinities for both increasing pollutant RE and reducing input cost, with soil recommended at high influent salinity.

Highlights

In constructed wetlands (CWs), especially in surface flow CWs (SFCWs) with relatively low purification function (PF) per surface unit when compared with subsurface flow CWs (SSFCWs) filled with large amounts of natural or artificial external substrates (ESs), the role of macrophytes should not be neglected because macrophytes can improve the PF of CWs by direct absorption, absorption, sedimentation, degradation of root biofilm and improvement of the rhizosphere environment through root radial oxygen loss (ROL) and organic matter secretion (Sun et al, 2019; Zhao et al, 2018a)
In the selection of substrates for surface flow constructed wetlands (SFCWs), both the purification ability of the substrate and the influence of the substrate on macrophyte growth, which probably vary with environmental stresses, should be considered
At low salinity (0.8‰), no significantly different removal efficiencies (REs) were obtained between the three treatments for either total nitrogen (TN) or total phosphorous (TP) (Fig. 1B and 1C)

Summary

Introduction

In constructed wetlands (CWs), especially in surface flow CWs (SFCWs) with relatively low purification function (PF) per surface unit when compared with subsurface flow CWs (SSFCWs) filled with large amounts of natural or artificial external substrates (ESs) (such as gravel, sand and ceramsite), the role of macrophytes should not be neglected because macrophytes can improve the PF of CWs by direct absorption, absorption, sedimentation, degradation of root biofilm and improvement of the rhizosphere environment through root radial oxygen loss (ROL) and organic matter secretion (Sun et al, 2019; Zhao et al, 2018a). To improve the PF and mitigate clogging of wetlands, ES was recommended to replace or partially substitute for the native soil for SFCWs or the top layers of subsurface/vertical flow CWs to increase the absorption and attached biofilm degradation of the substrates (Iamchaturapatr et al, 2007; Zheng et al, 2016; Zheng et al, 2014). This design idea has been widely used in the improvement of natural wetlands and the construction of CWs (Wang et al, 2018).

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