Hybrid constructed wetland for phosphorus removal in eutrophicated pond water | |
| Author | Ahmed, Ismail Baba |
| Call Number | AIT Thesis no.ET-SUD-17-01 |
| Subject(s) | Constructed wetlands Sewage--Purification--Phosphate removal |
| Note | A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Environmental Engineering and Management with specialization in Environmental Technology and Sustainable Development jointly offered by the Asian Institute of Technology, Thailand and UNESCO–IHE, The Netherlands |
| Publisher | Asian Institute of Technology |
| Abstract | Phosphorus removal in constructed wetlands is largely dependent on removal capacity of its media. The purpose of this research was to formulate synthetic media (SM) for constructed wetland through thermal treatment of clay amended with iron filings (IF), oyster shell (OS), and sawdust (SW), for removing phosphorus in eutrophicated pond waters. Out of the eighteen SMs produced, SM01 – SM06 having OS > 10% wt. developed cracks which led to fragmentation within one week of exposure to air, however, immersing them in water immediately after production did not result into failure, though pH of water increased. In the batch experiment, Phosphorus Removal Efficiency (PRE) and pH of the media showed positive correlation with OS proportion, but negative correlation with IF for all the initial phosphate concentrations tested, though all the correlations were insignificant (p > 0.05). All the formulated media did not fit to Langmuir model, but those with OS < 2% fitted to Freundlich model. At maximum initial phosphate concentration of 4.0 mg P/L, highest (99.9%) and lowest (0.48%) PRE were recorded by SM07 and SM18 at pH of 11.5 and 8.0 respectively. In order to understand the mechanisms involved in phosphorus removal at high and low OS proportion, SM07 (10% OS) and SM15 (1% OS) were subjected to batch kinetic experiments. The kinetic data for the two media were well described by Pseudo First Order (PFO), Pseudo Second Order (PSO), and Intra-particle diffusion model. Phosphorus removal occurred through mechanisms of chemical precipitation and adsorption. In a column experiment conducted for the first three stable media, average phosphorus removal efficiency recorded were SM07 (99.7%), SM08 (99.4%), SM09 (92.2%), and gravel (15.4%). After 30 d, it was only gravel that approached saturation. However, only SM09 leached iron (> 200 mg Fe/L), while iron was not detected in effluents of other columns. In a pilot scale experiment with media SM15, maximum removal performance of 78% Total Phosphorus (TP) was achieved by planted bed at HRT of 3 d with influent TP > 0.5 mg/L. But, internal phosphorus release occurred at influent TP < 0.1 mg/L. First order removal rate constant, k, at HRT of 3 d for planted and unplanted beds were 0.22 and 0.08 m/d respectively. Moreover, in the planted bed, phosphorus removal was achieved through particulate settling and bioaccumulation (56%), plant storage (6%), gravel adsorption (19%), and synthetic media adsorption (19%). But, in unplanted bed, 100% removal was through particulate settling and bioaccumulation. For other parameters, best performances were also achieved at HRT of 3 d. Maximum removals were 67% (COD) and 97% (TSS). However, NO3- recorded net increase greater than 10%. Moreover, iron release from planted bed (9.8 mg Fe/L) and unplanted beds (2.8 mg Fe/L) occurred when effluent Ca concentration approached inlet concentration. |
| Year | 2017 |
| 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 | Energy Technology (ET) |
| Chairperson(s) | Thammarat Koottatep;Bruggen, Hans van |
| Examination Committee(s) | Annachhatre, Ajit P.;Chongrak Polprasert |
| Scholarship Donor(s) | Netherlands Fellowships Programmes (NFP);UNESCO-IHE;Asian Institute of Technology Fellowship |
| Degree | Thesis (M.Sc.) - Asian Institute of Technology, 2017 |