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

Abstract

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.

Wastewater Treatment Potentials of Vegetated Beds with <i>Brillantaisia cf. bauchiensis</i> Hutch & Dalz and <i>Polygonum salicifolium</i> Brouss ex Wild in the Western Highlands of Cameroon

“…The growth parameters increased very slowly during the domestication phase as the plants were still struggling to adapt in their new but more polluted environment Wastewater is rich in nutrients that enrich and nourish the soil. Plants growing in wastewater constructed environment make use of these nutrients for their growth and development [15] [17]. The plants species in the CW showed increase in plants height and diameter has a function of the rich nitrate and phosphate habitat that the plants absorded for its metabolism.…”

“…They are capable of stabilizing the substrate in constructed wetland (CW) by providing good condition for physical filtration and a huge surface bacteria growth and removal. Some wetland macrophytes like Echinochloa pyramidalis, E. crus-pavonis, Fuirena umbellata and Leersia hexandra amongst others have been tested for domestic wastewater treatment and these macrophytes under stress conditions of pollution produced high biomass in CW which can be valourised [12]- [17].…”

Nitrate availability affects denitrification in Phragmites australis sediments

“…Rooted macrophytes act as "ecosystem engineers" for N removal (Jones, Lawton, & Shachak, 1994;Vila-Costa et al, 2016) by influencing denitrification in several ways: for example, by (i) increasing organic matter accumulation (i.e. root exudates, decaying plant biomass, trapped suspended material), thus providing labile organic carbon whose mineralization promotes anoxic conditions (Hang et al, 2016;Schoelynck et al, 2017;Taylor, Moore, & Scott, 2015); (ii) releasing oxygen in the rhizosphere and establishing oxic−anoxic interfaces where the coupling of aerobic and anaerobic processes (such as organic N mineralization, nitrification, and denitrification) occurs (Rehman, Pervez, Khattak, & Ahmad, 2017;Soana et al, 2015); and (iii) promoting microbial population growth and diversity through the provision of submerged surfaces (e.g., stems and leaves) available for colonization (Soana, Gavioli, et al, 2018;Toet, Huibers, Van Logtestijn, & Verhoeven, 2003). Denitrification results in permanent removal of bioavailable N. Thus, assessing this process is a pivotal scientific and management task for decreasing eutrophication of aquatic ecosystems in human-impacted watersheds.…”

Plant Growth Promoting Rhizobacteria Impact on Typha latifolia and Phragmites australis Growth and Dissolved Oxygen

“…New ways are being searched for, to treat wastewater with the help of both natural and constructed wetlands . Besides many other factors, the oxygen concentration in the rhizosphere added by the macrophytes performs a significant part in wastewater treatment processes and becomes a limiting factor in various wetlands where organic waste requires abundant oxygen for its degradation.…”

“…The oxygen released from its roots was measured directly proportional to the rate of photosynthetic oxygen production in plant shoots. It was also determined that the ability of this plant to add oxygen and to its rhizosphere was found greater in the growing and smaller plants than the larger plants, moreover, oxygen release from floating macrophytes help to treat wastewater …”