Abstract
Constructed wetlands (CWs) are extensively used as an economical and environmentally friendly sewage treatment under ecological engineering technology. Knowledge of the oxygen in the rhizosphere is of primary importance in understanding the function and regulation of microbial communities and macrophytes. Numerous studies on radial oxygen loss (ROL) have greatly elucidated the mechanism of contaminant removal in CWs. The main sources of oxygen in CWs are atmospheric reoxygenation, macrophyte transmission, and artificial aeration. However, artificial aeration is very expensive, and atmospheric reoxygenation is limited. Therefore, ROL by macrophytes is an essential and economical approach for oxygen input in CWs. In this review, we attempted to study the role of macrophytes in CWs. We described the mechanism of ROL and summarized the methods for determining ROL. We also investigated the role of ROL in contaminant removal in CWs. This review will provide considerable useful information on the oxygen input of CWs.
Highlights
Constructed wetlands (CWs) are extensively used as an economical and environmentally friendly sewage treatment under ecological engineering technology
CWs can generally be divided into three types, namely: free surface horizontal flow (HF), subsurface HF, and subsurface vertical flow (VF)
Oxygen sources can be divided into natural aeration and artificial aeration [6]
Summary
Constructed wetlands (CWs) are extensively used as an economical and environmentally friendly wastewater treatment method under ecological engineering technology [1,2]. CWs are artificial wastewater treatment systems that can be designed and controlled It is a useful approach for the removal of abundant contaminants because of the synergistic effects of soil, macrophyte, and microorganism on the physical, chemical, and biological processes in the wetland system [3]. Filtration includes the natural settlement of particulate contaminants and the settlement of colloidal particles to remove some contaminants Contaminants such as suspended solids can be settled within CWs, including the blocking effect of macrophyte roots and the gravitational interception of solid objects between sand and stone particles. Adding oxygen to CWs can alter the distribution of microorganisms and increase their metabolic efficiency This process has a positive significance for the removal of contaminants in sewage [9]. The input of oxygen in wetlands (especially subsurface HF) is one of the key factors in improving the removal of contaminants. CW oxygen input from macrophytes and its influencing factors, determination, and effects on contaminant treatment are reviewed to better understand the application of oxygen released by the macrophyte root system
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