Nitrogen removal in constructed wetlands located in the tropics | |
| Author | Thammarat Koottatep |
| Call Number | AIT Diss. no. EV-99-3 |
| Subject(s) | Sewage--Purification--Nitrogen removal Constructed wetlands |
| Note | A dissertation submitted in partial fulfilment of the requirements for the degree of Doctor of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | This study investigated the strategies for nitrogen (N) removal from constructed wetlands treating a primarily-treated wastewater. The role of N plant uptake and method to enhance N removal through plant harvesting were focused. The experiments were conducted using both laboratory- and pilot-scale constructed wetland units in which cattails (Typha augustifolia) were planted. The hydraulic retention times (HR T) of these constructed wetland units were varied from 2 to 10 d. Data from laboratory- and pilot-scale units without plant harvesting showed that the longer the HRT, the better the N removal efficiencies. With respect to analysis of N mass balance in these experimental units, the N plant uptake and nitrification/denitrification reactions were found to be the major N removal mechanisms in the constructed wetlands accounting for about 43 and 47%, respectively; while the N adsorption, NH3 volatilisation and microbiological uptake had little effects on N removal. With respect to the effects of plant harvesting, it was found from the laboratory-scale data that the constructed wetlands operating at the HRT of 9.8 d and subjected to a plant harvesting interval of 8 weeks had the highest N plant uptake rate of 7.5 kg/ha.d, resulting in the highest TKN mass removal efficiencies of 97%. The short harvesting interval of 2 weeks resulted in lower N plant uptake rate because of the cattail plants were still young (only about 0.80 m in height). The long harvesting interval of 12 weeks also resulted in lower N plant uptake rate because of the age of the plants which became old and did not uptake as much N as young/matured plants. Because the organic biodegradation by heterotrophic bacteria and the sedimentation processes were independent of the cattail growth, the plant harvesting had no effect on the removal of chemical oxygen demand (COD) and suspended solids (SS) in the constructed wetlands. A model based on mass balance equations for N removal in the constructed wetlands was proposed. The modelled results were comparable to the pilot-scale N removal data of the constructed wetland units, and confirming the beneficial effects of N plant uptake in the removal of N from the wastewater. Since the harvested cattails can be used for various beneficial purposes, harvesting of the cattail plants at the suitable interval to improve N removal efficiencies in the constructed wetlands should be undertaken. |
| Year | 1999 |
| Type | Dissertation |
| 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) | Chongrak Polprasert ;Visvanathan, C.; |
| Examination Committee(s) | Ozaki, Hiroaki ;Hansen, Gunner K. ;Denny, Patrick; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1999 |