Stabilization of landfill leachate by an integrated electrochemical and natural system | |
| Author | Variga Sawaittayotin |
| Call Number | AIT Diss. no.EV-06-2 |
| Subject(s) | Sanitary landfills--Leaching Sewage--Purification--Organic compounds removal |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy |
| Publisher | Asian Institute of Technology |
| Abstract | Landfill leachate is wastewater emanated from sanitary landfills treating a variety of municipal and industrial solid wastes. Due to anaerobic conditions and long retention time prevailing in sanitary landfills, landfill leachate normally contains high concentrations of organic matters, nutrients and heavy metals which, if not properly collected and treated, can cause serious pollution to nearby surface and groundwater sources. The presence of heavy metals at high concentrations in landfill leachate usually causes toxic effects to microbes, making it difficult to he treated biologically. Experiments were conducted to test the feasibility of applying an integrated electrochemical (EC) and natural system for treating leachate collected from a municipal landfill site. This integrated system Was postulated to be effective for landfill leachate treatment through the EC reactions, as a pre-treatment. in heavy metal removal, and, subsequently, through the natural systems, such as constructed wetlands (CW), for organic and nutrient removal. The EC treatment involves the application of direct-current power supply to electrode plates installed in an electrolyte solution. The EC reactions occurring between electrode plates (anode and cathode) result in the formation of hydroxide ions effective in precipitating the heavy metals by forming metal hydroxides. The pre-treated effluent from the EC reactor which should contain less heavy metals, but mainly organic and nutrients (N and P), is further treated in a CW system. CW is an artificial wetland whose bed is lined with non-permeable membrane to avoid inflow/outflow of wastewater. The bed is usually filled with sand and gravel media to support growth of emergent aquatic plants. Waste stabilization in CW beds is accomplished mainly through the reactions of bacteria growing on the plants roots/stems and on the media utilizing oxygen transferred the plant leaves to the root zones. N is removed by mtriflcationldenitriflcatiotl reactions and plant uptake, while P is removed by precipitation and plant uptake. The results obtained from the batch EC experiments showed the efficiencies of Cd and Mn removal to be more than 99 and 97 %, respectively, when the landfill leachate was treated in a pilot-scale EC reactor. The EC operating conditions were maintained at the following conditions: operation times, 2-60 min; electric currents, 5-10 ampere; and specific area of iron electrode, 46.51 m2/m3. The Cd concentrations were reduced from 1000 to less than 1 ug 1-1, while Mn was reduced front 6370 to l8Oug 1-1. In addition, the leachate color was also reduced from 600 to 80 ADMI unit during the EC treatment. Due to the high pH conditions prevailing in the EC reactor, up to 11, the fecal coliform concentrations were reduced from 1600 MPN/100 ml to non-detectable. There were about 80 % of P removal through precipitation with the hydroxide sludge, but N removal was found to be' insi eniticant. Experiments to investigate the feasibility of applying constructed wetlands to treat a sanitary landfill leachate containing high nitrogen (TN) and bacterial contents were conducted. Two-pilot scale subsurface-flow CW (SFCW) units located at the Asian Institute of Technology. Thailand, campus. were fed with a synthetic wastewater and landfill leachate collected from a nearby sanitary landfill. Under the tropical conditions (temperature of about 30 ' C), the SFCW units operating at the hydraulic retention time (HRT) of 8 days yielded the best treatment efficiencies with BOD; removal of 91 %, TN removal of 96 %. total and fecal coliforms (TC and FC) removal of more than 99 %. Cadmium removal in the SFCW bed was found to he 99.7 %. 'file treatment performance was found to follow first-order reaction rate, in which the k20, values of BODS, COD, IN, TC, FC and Cd were 0.201, 0.121, 0.247, 0.346 and 0.354 and 0.690 d-1, respectively. Mass balance analysis. based on TN contents of the plant hiomass and dissolved oxygen (DO) and oxidation-reduction potential (ORP) values, suggested that 88 % of the input TN were uptaken by the plant hionrrss, 8 % removed by others reactions and adsorption on the wetland media, while the remaining 4 % were discharged with the effluent. Fluorescence in-situ hybridization (FISH) results revealed the predominance of bacteria including heterotrophic and autotrophic bacteria responsible for BOD5 removal. Because of the rather row DO and negative ORP values, nitrifying bacteria was not found to he present in the SFCW beds. The experimental results demonstrated the feasibility of applying the integrated system to treat landfill leachates with high efficiencies of heavy metal, color and organic removal. The EC unit could remove the heavy metals contained in the leachate through precipitation as metal hydroxides. The SFCW units were able to remove organic matter, nutrient and pathogen contents to within the effluent standards for disposal or reuse. This integrated system was found to be effective in treating the landfill leachate and should help to prevent ground and surface water pollution |
| Year | 2006 |
| 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 |
| Examination Committee(s) | Aramaki, Toshiya.;Shrestha, Rajendra P.;Shipin, Oleg.;Satoh, Hiroyasu. |
| Scholarship Donor(s) | National Science and Technology Development (NSTDA) |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2006 |