Supercritical fluid extraction of PCBs from tropical soils | |
| Author | Chompoonut Chaiyaraksa |
| Call Number | AIT Diss. no. EV-97-02 |
| Subject(s) | Polychlorinated biphenyls Soils--Analysis |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctoral of Technical Science |
| Publisher | Asian Institute of Technology |
| Abstract | Supercritical carbondioxide was used to extract three planar and three mono-ortho PCBs from three tropical soil types which were different in character. The effect of pressure, temperature, methanol modifier, soil moisture content, pH and concentration on the extraction were investigated. Kinetic of the extractions was discussed. Sorption experiment was used to explain the supercritical extraction phenomena. The Freundlich model was used to quantify the sorption of PCBs in soil. The stepwise linear regression was used to predict which factors affected the sorbed of PCBs onto soils. The recovery yield, impurity, solvent consume, toxic waste problem, health, accidental risk, cost, time and labor intensive of the extraction by Soxhlet conventional method and SFE method were compared. The optimum supercritical extraction condition were used to extract the real contaminated site. Application of the supercritical extraction method for soil remediation was evaluated in term of cost. At constant temperature (40°C), elevating the fluid density from 0.25 to 0.8 g/ml. resulted in enhanced extraction efficiency of compounds on all soils. Clay content and soil constituents played a major role for the adsorption and the supercritical extraction of the selected PCBs from all soils. In addition the selected planar congeners were sorbed stronger to soil and were extracted harder than the selected mono-ortho congeners. The PCB properties were found to have greater effect on the extraction yield than soil properties. Increased the temperature from 40°C to 100°C at constant pressure (167 bar) were found to have negligible effect on the recoveries of all congeners. Adding methanol at 3-10% highly increased the yield of planar PCBs. The methanol modifier increased the yield by the most of PCB-126. However modifier decreased the recovery yield of PCB-156. For PCB-105 and PCB- 189, the modifier could not improve their yield significantly. The three and five percentage of methanol mostly gave the same effect to the extraction. In some case, the five percentage of methanol could give approximately 30% higher yield than three percentage. The effect of seven and ten percentage were less than three and five percentage. The optimum percentage conditions of methanol modifier to the extraction of all congeners in all soil type was identified and presented. On the soil moisture content, the 5% water increased yield of PCB-105 and PCB-189. The 5% water had no effect to the extraction of PCB-77 and PCB-169 but started to reduce yield of PCB-126. Adding water 15-25% reduced yield of all congeners. The pH was found to have no effect on the SFE due mainly to their persistence property. Extraction of 0.2 ng/g. PCB contaminated soils gave lower yield than extraction from 20 ng/g. PCB contaminated soils. The possible reasons and explanation were provided and discussed. Findings from this study indicate that when SFE was employed forty minutes of time for extraction was an optimum dynamic condition of all congeners from all soils at 40°C temperature and 0.8 g/ml. fluid density. In terms of efficiency to remove PCBs from the contaminated sites, both SFE and Soxhlet extraction techniques yield quite similar results. The amounts detect for different congeners include PCB-77, PCB-105, PCB-126, PCB-156, PCB-169, and PCB-189 were 7.95, 4.31, 0.21, 0.60, 0 and 0.03 respectively. Based upon the overall evaluation performed during this study, SFE technique was recommended over the Soxhlet technique because of its superior in the following categories such as recovery yield, impurity, solvent consume, toxic waste problem, health, accidental risk, cost, time and labor intensive. To apply the SFE to soil remediation, the scale up extractor is required for further study. The cost estimation of the scale up (600g. soil size) extraction process was approximately 245- 345 Baht/sample. |
| Year | 1997 |
| 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) | Preeda Pakpian;Samorn Muttamara; |
| Examination Committee(s) | Apisit Eiumnoh;Reutergardh, Lars Baetz;Gambrell, Robert P.; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1997 |