Engineering conditions of constructed wetlands for cadmium removal and toxicity reduction | |
| Author | Varangkana Visesmanee |
| Call Number | AIT Diss. no.EV-08-6 |
| Subject(s) | Cadmium--Physiological effects Constructed wetlands |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Environmental Engineering and Management Inter-University Program on Environmental Toxicology, Technology and Management |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. EV-08-6 |
| Abstract | This study was conducted to investigate the long-term performance of subsurface-flow constructed wetland (SFCW) units treating a wastewater containing Cadmium (Cd). The hydraulic retention time (HRT) was found to have significant effects on the chemical oxygen demand (COD) and total nitrogen (TN) removal, SFCW units operating at the HRT of 8 days yielded the best treatment efficiencies with COD and TN removal of 93 and 94 %, respectively and the first order kinetic coefficient (k₂₀) of COD and TN removal were found to be 0.23 and 0.24 d⁻¹, respectively. The Cd removal efficiencies of SFCW units operating at the HRT of 1, 3, 5 and 8 days were found to be 50, 92, 98 and 99 % corresponding to the average effluent Cd concentrations of 8.3±0.6, 1.8±0.4, 0.7±0.6 and 0.2±0.1 mg/L, respectively. The Cd was removed about 70-77 % by retaining in SFCW beds due to such mechanisms as adsorption, sedimentation and filtration. Most of retained Cd in SFCW wetland media was found to be in the Fe/Mn bound and residual fractions that would remain insoluble in SFCW beds. However, plant uptake also played the role for Cd removal which was contributed about 62S %. The Cd fractions in the SFCW effluent were mostly found in the Cd ion. The Cd complex form was found to increase with increasing HRTs, Based on adsorption mechanism only, the maximum Cd adsorbed on the SFCW media was found to be 78 g, which was later used to calculate breakthrough times of Cd in the SFCW effluent. The calculated breakthrough times of the SFCW units operating at the HRT of 1, 3, 5 and 8 days were found to be 56, 166, 278 and 433 days, respectively. However, the observed Cd breakthrough times from the experiments were found to be longer than the calculated values which were probably caused by other mechanisms such as sedimentation, filtration and plant uptake. The XTT cytotoxicity test with T47D human breast cancer cells suggested the effluent from SFCW units operating at the HRTs of 5 and 8 days could reduce Cd toxicity; while Microtox technique by bioluminescent bacteria showed the toxicity reduction of the effluent for all HRTs |
| Year | 2008 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. EV-08-6 |
| 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 ;Jutamaad Satayavivad (Co-Chairperson) |
| Examination Committee(s) | Apinya Thiantanawat ;Gallardo, Wenresti |
| Scholarship Donor(s) | Chulabhorn Research Institute ;Mahidol University ;Asian Institute of Technology Fellowship |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology - Chulabhorn Research Institute - Mahidol University, 2008 |