Since the phasing out of halons, water mist systems have gained attention as a possible alternative form of fire suppression. These ultrafine sprays have both advantages and disadvantages compared to conventional water sprinklers. It has been suggested that one way to improve their performance would be to produce the mist from an aqueous solution of a chemical fire suppressant. Two small-scale experiments were devised to quantify and compare the suppression efficiency of the mists of chemical solutions. Twelve potential chemical suppressants were selected from a review of the literature and delivered into the fires as mists of their solutions at 3-10% m/v concentration; their effect on the time taken to extinguish the flame was recorded. In addition, 90 full scale fire tests were conducted to identify how suppression might best be improved with chemical additives, and a mathematical model was constructed to estimate optimum droplet parameters for various conditions. In the small scale experiments, solutions of KHCO3, other compounds of alkali metals, and seawater showed excellent improvement to the extinction time. On the large scale, a body of research on the comparatively under-studied wood crib fires was compiled, and it was concluded there was scope for using chemically enhanced water mist to provide effective room coverage with fewer nozzles. This research was original in that it studied a range of chemical suppressants which had largely not been tested in the form of water mist additives; it had an emphasis on the application of the results on real fires, quantifying suppression efficiency by the time taken to suppress a flame; the large scale experiments centred around class A fires; it attempted to provide a wide-ranging and systematic approach to the question of chemically enhanced water mist systems by looking at small scale screening tests, full scale fire tests, and modelling.

The abatement of halogenated compounds released from various processes into the environment is now recognized as a pressing environmental issue. Catalytic hydrodehalogenation (HDH) has emerged as a potential technology that can facilitate waste transformation and reuse. In this thesis, a comprehensive study of the critical reaction/catalyst variables is considered for the HDH of a range of haloarenes (chloroand bromo-phenols and chlorobenzenes) using (commercial) Pd/Al2O3 and (laboratory synthesised) Au supported on -Fe2O3 and Fe3O4. Aqueous phase (T = 303 K) HDH is demonstrated to be structure sensitive where smaller Pd particles are intrinsically more active and metal/support interactions have a major impact on reaction selectivity (notably at pH = 3). HDH follows an electrophilic aromatic substitution mechanism: the rate of C–Br bond(s) scission is an order of magnitude greater relative to C–Cl (due to the lower bond dissociation energy). The presence of a second halogen substituent has a deactivating effect (by lowering electron density in the aromatic ring). Solvent (water, organic and water/organic mixtures) effects have been established where, in absence of mass transport limitations, reaction in water delivers significantly higher HDH rates and selectivity is unaffected by solvent composition. A mathematical analysis demonstrates that these effects are principally (ca. 80 % contribution) the result of the variations in solvent dielectric constant where the molar volume represents a secondary consideration. The advantages of a shift from batch to continuous HDH are established in terms of: (i) more efficient gas to liquid H2 transfer; (ii) enhanced HDH rates; (iii) prolongued catalyst lifetime. The potential of HDH as a means of waste transformation to a commercial product is demonstrated in the gas phase (T = 423 K) hydroconversion of 2,4-dichlorophenol into cyclohexanone (over Pd) and 4- chlorophenol (over iron-oxide supported Au). In both cases, a contribution due to spillover hydrogen is established. A comprehensive programme of (Au) catalysts synthesis and characterization, in terms of TPR, H2 chemisorption/TPD, XRD, DRS UV-Vis, SEM/TEM and BET/pore volume measurements is provided and correlated with HDH kinetics. The results presented in this thesis demonstrate the feasibility and flexibility (in terms of operation, rate/selectivity control and product reuse) of catalytic HDH as a progressive means of haloarene waste treatment.

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Methane (CHt) is a greenhouse gas with a global warnling potential. Much is released into the atmosphere from landfill waste disposal sites. Bio-waste compost could be used as cover material to support the microbial oxidation of methane. Mature compost supported higher CH4 oxidation rates than fresher materials (0.42 to 0.01 mg CH4 h-I gol), and was inversely related to NH/. dissolved organic carbon and humic substance concentrations. The diffusivity of CH4 through an aqueous compost extract was on average 64% lower than tl4at observed through dH20, thereby lowering the amount that is available for oxidation by metlianotrophic bacteria. Methanotroph Melhylosinus lrichosporium (OB3b) reproduced less well in a compost extract solution, adhering to humic-like substances in the extract. Use of the 13C stable isotope showed that proportionally less I3C-C02 evolves from the oxidation of 13C-CH4 at high NH/ concentrations (>2000 Jlg gol compost). A landfill-based field experiment identified complex variation in landfill gas: CH4, C02 and N20 concentrations over time and space. Bio-waste compost oxidized CH4 as effectively as he silt material currently used as a cover. A PCR-DGGE protocol was successfully developed to identify methanotrophs in bio-waste compost. DGGE analysis revealed a variety of methanotrophs present in different composts, thereby promoting its use as a landfill cover solution for Ct!4 emissions abatement. Much bio-waste compost is presently produced without a market. Finding alternative applications for this material is an important aspect of maintaining a sustainable waste management system. Its use as a landfill cover appears to be as good as the conventional silt material at promoting CH4 oxidation, but has not been extensively investigated. Further research optimizing the production ofbio-waste compost for landfill cover application has the potential to reduce CH4 emission, but more importantly turns' waste material into a valuable resource.

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