| Author | Kansakar, Luna Keshari |
| Call Number | AIT Thesis no.EV-07-22 |
| Subject(s) | Constructed wetlands.
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| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Environmental Engineering and Management. |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. EV-07-22 |
| Abstract | The study was conducted with the main aim of understanding the role of the bed media in the removal of the As from the sub-surface flow constructed wetland, focusing the contaminated groundwater. However, the study was conducted with tap water spiked with Arsenic (As2O3) stock solution. In order to fulfill the main target, seven physico-chemical parameters were studied - Iron, Manganese, Sulfate, TOC, ORP, DO and pH together with Arsenic in the three lab scale units two of which were planted with the Vetiver grass as the Constructed Wetland (CW) macrophytes. The analysis of the core sample showed that the highest As concentration, for the particular column near the influent, was found in the topmost layer for all the units which was followed by second layer and finally the third layer. The topmost layer of the first unit contained mixture of 85% sand and 15% soil by volume at the topmost layer and with the plantation. The second unit contained only sand at the topmost layer with the plantation and third unit also had sand in the topmost unit but without the plantation. The second and the third layer for all the units were small gravel and large gravel respectively. The results of sequentially extracted samples presented the much higher proportion of residual form of As in the topmost layer for all the units-CW with the mixture of sand and soil and plantation (58%), CW with sand and plantation (42%) and CW with sand (43%). Residual forms of the As is the As that is found in association with the lattice structure of the material of the system. This fraction is not bioavailable as well as not subjected to the leaching and is the most stable form. Similar results were found for the rhizosphere zone which was found limited to the topmost layer. For the small gravel and large gravel highest proportion was found for the fraction IV which is sulfide bound form, for all the units. There was almost no trace of Fe and Mn in the effluents confirming that these parameters were not leached out during the operation phase. However, the analysis of these parameters in the core sample near the influent point showed the higher concentration in the small gravel layer while the background concentration show very less Fe and Mn concentration in small gravel. This clearly presents the leaching of the Fe and Mn from the top to the second layer. This phenomenon confirms the fate of Fe and Mn in the systems to leach out eventually with time, and also leaching the As associated to this form. The reduction in the concentration of sulfate in the effluent than the concentration going into the system confirmed the retention of sulfate within the system. The removal efficiencies varied for all the three units. The highest was found for the CW with sand and plantation with removal efficiency of 36.21%. Total Organic Carbon (TOC) results showed the leaching out of the organic content from the CW with the mixture of sand and soil with plantation, the one with the highest TOC content of 0.3%. The main conclusion that could be derived from the study is that the constructed wetland system with sand as the top layer, small gravel as middle layer and large gravel as the bottom layer, provided the best condition within the bed media so as to remove As by 93% for the study period of 115 days. |
| Year | 2007 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. EV-07-22 |
| Type | Thesis |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering and Management (EV) |
| Chairperson(s) | Thammarat Koottatep.; |
| Examination Committee(s) | Shipin, Oleg;Preeda Parkpian; |
| Scholarship Donor(s) | Asian Institute of Technology Fellowship |
| Degree | Thesis (M.Sc.) - Asian Institute of Technology, 2007 |