Environmental Remediation: Removal of polycyclic aromatic hydrocarbons Dissertation
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Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous persistent semi-volatile organic compounds. They are contaminants that are resistant to degradation and can remain in the environment for long periods due to their high degree of conjugation, and aromaticity. PAHs are present in industrial effluents as products of incomplete combustion processes of organic compounds. Petroleum, coal and shale oil contain extremely complex mixtures of these PAHs, and their transport and refining process can also result in the release of PAHs. It is therefore prudent that such effluents are treated before discharge into the environment. In this project, different approaches to the treatment of PAHs have been investigated. Hydrous pyrolysis has been explored as a potential technique for degrading PAHs in water using anthracene as a model compound. The experiments were performed under different conditions of temperature, substrate, redox systems and durations. The conditions include oxidising systems comprising pure water, hydrogen peroxide and Nafion-SiO2 solid catalyst in water; and reducing systems of formic acid and formic acid / Nafion-SiO2 / Pd-C catalysts to assess a range of reactivities. Products observed in GCMS analysis of the extract from the water phase include anthrone, anthraquinone, xanthone and multiple hydro-anthracene derivatives (Paper I). In addition a modified version of the Nafion-SiO2 solid catalyst in water oxidising system was tested; and reducing systems of formic acid and formic acid / Nafion-SiO2 / Pd-C catalysts were adopted for the conversion of a mixture of anthracene, fluorene and fluoranthene. The rate of conversion in the mixture was high as compared to that of only anthracene (Paper II). Also the use of LECA (Lightweight expanded clay aggregates) as an adsorbent (Paper III) for PAHs (phenanthrene, fluoranthene and pyrene) removal from water has been successfully achieved as well as photodegradation (UV) studies of fluorene in different aqueous media (Paper IV).
Paper I: Nkansah, M. A., Christy, A. A. & Barth, T. (2011) The use of anthracene as a model compound in a comparative study of hydrous pyrolysis methods for industrial waste remediation. Chemosphere, Volume 84 (4): 403- 408. Full-text not available in BORA. The published version is available at: http://dx.doi.org/10.1016/j.chemosphere.2011.03.061Paper II: Nkansah, M. A., Christy, A. A. & Barth, T. (2012) Catalytic oxidation and reduction of polycyclic aromatic hydrocarbons (PAHs) present as mixtures in hydrothermal media. Polycyclic Aromatic Compounds (In press). The paper is available at: http://hdl.handle.net/1956/6104Paper III: Nkansah, M. A., Christy, A. A., Barth, T. & Francis, G.W. (2012) The use of lightweight expanded clay aggregate (LECA) as sorbent for PAHs removal from water, Journal of Hazardous Materials, 217- 218: 360-365. Full-text not available in BORA. The published version is available at: http://dx.doi.org/ 10.1016/j.jhazmat.2012.03.038Paper IV: Nkansah, M. A., Christy, A. A., Barth, T. Francis, G.W. (2012). Preliminary photochemical studies of fluorene in various aqueous media (Manuscript). Full-text not available in BORA.