Abstract
Constructed wetlands (CW) have attracted growing interest in wastewater treatment research in the last 20 years, and have been investigated intensively worldwide. Many of the basic processes occurring in CWs have been qualitatively established; however, much quantitative knowledge is still lacking. In this mini review, the proportionate contributions of the different system components to removal of contaminants are examined. The main objective of this mini review is to provide a more in-depth assessment of the interactions between the porous bed, plants, and microorganisms during the removal of organic contaminants from the water in a subsurface flow CW system. In addition, a unique technique to study the partial contribution to the total removal of contaminants in a CW is described. Future studies in this field will expand our knowledge of any synergistic or antagonistic interactions between the components and facilitate improved CW construction and operation. Here, phenol will be used as a model industrial organic contaminant to illustrate our current understanding of the contributions of the different components to total removal. I will also discuss the various factors influencing the efficacy of bacteria, whether planktonic or as biofilm (on porous bed or plant roots), in subsurface flow CWs.
Highlights
An efficient approach to treating anthropogenic discharge is to create a constructed wetland (CW), which simulates natural marshland or swampland
The gravel-attached biofilm performed as well as the root-attached biofilm, and the phenol removal rate of the planktonic bacteria was found to be 22-fold greater than that of the biofilms, while the performance of the sterile components was inconsequential
It was found that young, thin biofilms developing on roots and gravel performed significantly better than denser biofilms grown on roots and gravel before the experiment began; van Loosdrecht et al [44] attributes this to the poorer ability of dense biofilms for mass transfer of phenols and oxygen
Summary
An efficient approach to treating anthropogenic discharge (e.g., wastewater, effluents from agriculture and industry, stormwater runoff) is to create a constructed wetland (CW), which simulates natural marshland or swampland. Studies suggested that the extent of plant uptake contribution to the overall removal of phenol is insignificant, and indicated that the major role of plants and their root system is to facilitate microbial degradation by providing a suitable habitat for biofilm growth [22,23]. This mini review will discuss the proportionate contribution of each of the CW components—plants roots, porous bed (gravel), and water—to total phenol removal, with and without the contribution of microorganisms
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