The Potential of Sewage Treatment through Constructed Wetlands in Northeast India: A Critical Review

The benefits of economical treatment systems and global demand for introducing sustainable way of environmental management, the Constructed Wetlands (CWs) treatment of domestic sewage is rising rapidly all over the globe. The Total nitrogen in the sewage is the summation of Organic Nitrogen, Nitrate Nitrogen, Nitrite Nitrogen and Ammonium Nitrogen. Ammonification, Matrix Adsorption, Nitrification, Denitrification, Plant Uptake and Ammonia Volatilization are the principle involved for total nitrogen removal in the treatment of sewage using CWs. This paper provides a comprehensive review by comparative analysis of effects of type and nature of flow system, wetland structures, types of Macrophyte, removal mechanisms, Aeration, Step-feeding and other key operational parameters and conditions for the enhance removal of total nitrogen in CWs.

Effects of nutrient addition, recovery thereafter and the role of macrophytes in nutrient dynamics of a Mediterranean shallow lake: a mesocosm experiment

Eutrophication in coastal wetlands has increased greatly because of human impact, reducing water quality and affecting aquatic plants. The aim of the present study was to investigate the eutrophication of Mediterranean wetlands and their possible recovery. An in situ mesocosm nutrient enrichment experiment was performed in a coastal shallow lake from eastern Spain, holding dense Chara meadows. In this lake, 36 mesocosms were installed and fertilised weekly with four levels of N and P addition over an 8-week period from June to August. Mesocosms fertilised with the two higher levels (N:P ≥5:0.5mgL–1) shifted to turbid status with macrophyte loss before Week 4. Saturation concentrations were similar under these two conditions, with averages ~1.0mgL–1 total particulate P and 700µgL–1chlorophyll-a reached in the last 3 weeks. After 5 weeks of the experiment, macrophytes were removed from the mesocosms without nutrient addition and those fertilised with 1:0.1mgL–1 N:P. Macrophyte removal resulted in a release of phosphate and ammonium from sediments, enhancing eutrophication. Three months after stopping nutrient addition, high nutrient and chlorophyll concentrations persisted in the highly fertilised mesocosms, but decreased in the low fertilised mesocoms, which shows that restoration of eutrophic Mediterranean shallow lakes depends to a great extent on previous external loads.

Responses of periphytic diatoms to mechanical removal of Pistia stratiotes L. in a hypereutrophic subtropical reservoir: dynamics and tolerance

The Itaqui reservoir in Paraná state, southern Brazil, is dominated by the floating macrophyte Pistia stratiotes L. and is used for recreation and irrigation. The reservoir's excessive plant cover suggests an extreme trophic state and interferes with multiple uses. The aims of this study were to determine the trophic state of the reservoir water and to document the limnological conditions and the composition of the periphytic diatom community before and after the mechanical removal of macrophytes. As each diatom species has certain autoecological requirements in a given geographic area, another objective of the study was to identify diatoms that can be considered tolerant of the reservoir's trophic state in a substropical environment. Local water samples collected for physical and chemical analyses, including estimates of chlorophyll a, showed the hypereutrophic status of the reservoir before and after macrophyte removal. Environmental conditions exceeded acceptable values for fishing and irrigation, providing a clear example of how the inadequate management of water resources can directly reduce their usefulness. Trimestral sampling was carried out between May 2008 and February 2009. For quantitative analyses, biofilms were scrubbed off glass slides submerged for 30 days at a depth of approximately 40 cm. Diatom samples were cleaned with potassium permanganate and hydrochloric acid and mounted on permanent slides with Naphrax. All individuals found in random transects under three replicates were identified and counted up to a minimum of 600 valves. Thirteen species tolerant of eutrophication were selected. Four species mostly known from low-nutrient sites may be considered tolerant of eutrophic conditions. The composition of the diatom community was influenced by seasonal changes in temperature and rainfall. Canonical Correspondence Analyses confirmed a correlation between higher diatom densities and the increased photic zone following macrophyte removal.