Constructed Wetlands: Perspectives of the Oxygen Released in the Rhizosphere of Macrophytes

Constructed wetland is an economical, efficient and environment friendly technology for the treatment of wastewater. The aquatic plants and microorganisms in constructed wetlands play a key role in the treatment of wastewater. Plants add oxygen during the process of photosynthesis or by direct transport from the atmosphere through their stems and roots to the rhizosphere of constructed wetlands. Moreover, macrophytes provide optimum conditions and surface area for the attachment of microorganisms to perform their activities. The oxygen released in rhizosphere of constructed wetlands has significant impacts on nutrient, gas exchange chemistry, and contaminants removal. In this review, we have compiled the published data to explore the mechanism of oxygen release by the roots of macrophytes in constructed wetlands, rhizospheric oxygen measurement techniques, role of climatic factors, and ability of different macrophytes in oxygenation of rhizosphere in constructed wetlands. Numerous studies have been carried out on enhancing the efficiency of constructed wetlands by modifying design, macrophyte species, and size of wetlands. However, the part of combination of climatic factors, microorganisms, and plant species in augmenting oxygen release in the rhizosphere is not explored so far. Therefore, in this review, we tried for the first time to compile all the parameters effecting oxygen released in the rhizosphere of macrophytes in constructed wetlands that are using worldwide for the treatment of wastewater. Moreover, this review article will provide vital information to all researchers who are working on wastewater treatment by using constructed wetlands.