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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Bioremediation of low-permeability, pentachlorophenol-contaminated soil by laboratory and full-scale processes

Havighorst, Mark B. 30 January 1998 (has links)
Ex-situ bioremediation of saturated soil contaminated with pentachlorophenol and 2,3,5,6-TeCP is commonly accomplished by landfarming or by treatment in a bioreactor. Treating saturated, low-permeability soils in bioreactors, without pre-treatment requires a reactor capable of promoting anaerobic and/or aerobic removal of chlorophenols without transferring these contaminants to the aqueous phase. A pilot-scale bioreactor was designed to treat 3.7 cubic meters of contaminated soil with a saturated hydraulic conductivity of 0.12 cm/day. The bioreactor demonstrated significant removal of chlorophenols when soil was infused with a treatment mixture containing imitation vanilla flavoring as an electron donor for reductive dechlorination and primary substrate for aerobic cometabolism. Bench scale studies showed greater overall removal when feed mixtures included an inoculated biomass, or when treatment mixtures were maintained anaerobically prior to use. The combined results of these studies suggest that concentrations of pentachlorophenol and 2,3,5,6-TeCP in soil can be significantly reduced using fill and draw batch reactors, operated for three to five week long cycles, using a variety of treatment mixtures. / Graduation date: 1998
2

Integrated treatment of pentachlorophenol by adsorption using magnetite-immobilized chitin and photocatalytic oxidation. / CUHK electronic theses & dissertations collection

January 2007 (has links)
Chitin is known as an effective biosorbent, which is used to preconcentrate PCP for further treatment. In order to reuse and recover the biosorbent, magnetic separation is a cost-effective alternative to separate the PCP-adsorbed biosorbent (i.e. chitin) from the treated water. Therefore, chitin is immobilized by magnetite prior PCP adsorption. From the immobilization results, the solution pH, temperature, agitation rate do not show great effect on the immobilization of chitin and magnetite. Second, magnetite-immobilized chitin can be formed as quickly as 5 min. Moreover, the interaction of chitin and magnetite is very strong since it is not easy to separate by vigorous shaking, high temperature and changing pH. Although the underlying mechanism of magnetite and chitin is still obscure, the biosorbent is proved to have high stability and reusability. In addition, both Langmuir and Freundlich models indicate that immobilization of chitin by magnetite is favorable with the Langmuir model being the major one. / For PCP adsorption study, it is found that magnetite-immobilized chitin can retain the PCP adsorption ability as free chitin. In accordance with the results, the PCP adsorption of magnetite-immobilized chitin is influenced by altering the parameters of biosorbent concentration, solution pH, temperature, agitation rate, contact time and initial PCP concentration. In general, higher amount of biosorbent gives higher removal efficiency (RE) but lower removal capacity (RC) as more binding sites are available for PCP. The PCP removal is enhanced by lowering pH since uncharged PCP is favorable for adsorption. It is speculated that hydrophobic interaction, hydrogen bonding and electrostatic interaction are involved. In addition, the biosorption efficiency is impeded by high temperature. Evidence shows that the adsorption might be due to the exothermic force such as hydrogen bonding. The biosorption is described as biphasic mechanism with the fast initial phase followed by slow equilibrium phase. For the PCP (10 mg/L) adsorption, the optimized conditions are: 1,500 mg/L of magnetite-immobilized chitin, initial pH 6, 25°C, 200 rpm and 60 min. The RE is 57.9% and RC is 5.4 mg/g. However, the increase in the amount of immobilized chitin (24,000 mg/L) can increase the RE up to 98%. By considering the Langmuir and Freundlich isotherms, the adsorption might be heterogenous, as the correlation coefficient from Freundlich model is higher. / Pentachlorophenol (PCP), a highly chlorinated aromatic organic compound, was widely used as a biocide and is now restrictly used as a wood preservative. PCP is toxic and ubiquitous environmental pollutant. In the present study, integrated treatment of biosorption and photocatalytic oxidation (PCO) using magnetite-immobilized chitin is employed to completely degrade PCP. / To thoroughly remove PCP, PCO is also employed after the biosorption. One hundred % of PCP removal is achieved after 5 h irradiation time, in 100 mL solution at initial pH 9 with 20 mM of H2O2 and 200 mg/L of TiO2. The intermediates of PCP are identified as 2,3,5,6-tetrachlorohydroquinone (TeHQ) and 2,3,5,6-tetrachlorophenol (TeCP) by GC/MS analysis. In addition, the toxicity of sample is monitored by the solid-phase and aqueous-phase Microtox RTM tests, which the toxicity increases and then decreases along the irradiation time. The biosorbent shows no great changes on chitin content and functional groups after PCO. In addition, the results imply that magnetite-immobilized chitin has a good potential to be reused at least for four cycles with high RE and DE. Therefore, the combination of biosorption and PCO treatment was feasible for PCP removal and the system is economic and convenient for repeated use. / by Pang, King Man. / "Oct 2007." / Source: Dissertation Abstracts International, Volume: 69-08, Section: B, page: 4636. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (p. 186-212). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.
3

Demonstration of a permeable barrier technology for the in-situ bioremediation of pentachlorophenol contaminated groundwater

Cole, Jason David 05 May 2000 (has links)
A pilot scale demonstration of a biological permeable barrier was conducted in a pentachlorophenol-contaminated aquifer at a wood preserving facility. A permeable reactor was constructed to fit within a large diameter well. Arranged in series, a cylindrical reactor 24" x 36" (0.61 x 0.91m) (diameter x height) was partitioned to provide three biological treatment zones. Pentachlorophenol (PCP) biodegradation was evaluated under several environmental conditions using a mixed microbial consortium supported on ceramic saddles. Imitation vanilla flavoring (IVF), a mixture of propylene glycol, guaiacol, ethyl vanillin and sodium benzoate, served as the electron donor. In the absence of exogenous substrate, PCP was not degraded in the inoculated permeable barrier. Substrate addition under oxidizing conditions also failed to initiate PCP removal. Anaerobic conditions however, promoted in-situ PCP degradation. PCP reductive dechlorination resulted in the transient production of 3,4,5-trichlorophenol through sequential ortho dechlorinations. Continued carbon reduction at the meta and para positions resulted in 3,4-dichlorophenol and 3,5-dichlorophenol production. Complete removal of all intermediate degradation products was observed. Reactor operation was characterized through two independent laboratory and field companion studies. Experiments were conducted to evaluate (1) the effect of supplemental electron donor concentration (IVF) and (2) the effect of sulfate, a competitive electron acceptor on PCP reductive dechlorination. Results from laboratory and field conditions were consistent. (1) In the presence of an exogenous electron donor, PCP degradation was independent of supplemental donor concentration (10, 25, 50, 100 mg COD/L). However, a comparatively slower rate of PCP degradation was observed in the absence of electron donor. (2) The presence of sulfate was not inhibitory to PCP degradation. However, compared to systems evaluated in the absence of sulfate, slower rates of PCP transformation were observed. Passive operation and low energy requirements, coupled with potential contaminant mineralization suggest that the biological permeable barrier is a highly effective tool for subsurface restoration. / Graduation date: 2000
4

Down-borehole permeable barrier reactor : verification of complete mineralization of pentachlorophenol in a sequential anaerobic-aerobic process

Roberts, David Bradley 10 October 1997 (has links)
Graduation date: 1998
5

Down-borehole permeable barrier reactor : primary substrate selection for aerobic dichlorophenol degradation

Kaslik, Peter J. 14 March 1996 (has links)
In situ bioremediation of pentachlorophenol-contaminated ground water in a sequential anaerobic-aerobic down borehole permeable barrier reactor requires a non-toxic primary substrate for dichlorophenol cometabolism. Serum bottle tests comparing the effectiveness of eight primary substrates for aerobic dichlorophenol degradation showed phenol to be the most effective followed by imitation vanilla flavoring, guaiacol, sodium benzoate, molasses, acetic acid, propylene glycol and ethyl vanillin in propylene glycol. As phenol is a pollutant, imitation vanilla flavoring is the recommended primary substrate for field use. In a second bottle test, 3,4,5-trichlorophenol was not sufficiently biotransformed, emphasizing the need for biotransformation to occur in the anaerobic zone of the reactor. / Graduation date: 1996

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