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This dissertation investigates how a nominally axisymmetric plume is affected by the presence of ambient turbulence. The results of this investigation are based on laboratory experiments in water. The experiments employ a saline plume released downwards into a tank of fresh water with an oscillating grid positioned near the bottom. A wide range of regimes with increasing levels of ambient turbulence is covered from a quiescent environment to the eventual break-up of the plume. Buoyancy and velocity data were obtained using fluorescent dye and particle tracking, respectively. The response of a plume to ambient turbulence is found to be twofold. The plume centreline position deviates from the perfect vertical and the plume spreading relative to that centreline position increases. Both mechanisms, plume "meandering" and "spreading", combine to create a time averaged plume image in which the plume appears wider. Sophisticated image processing techniques are developed to disentangle the two mechanisms and to quantify their respective contributions to the overall plume spreading. The turbulence-induced plume meandering scales on the ratio of the transversal velocity fluctuation of the background turbulence to the vertical mean velocity on the plume centreline. A simple extension to classical plume theory is proposed to account for the increased plume spreading via enhanced entrainment that becomes dependent on the strength of the ambient turbulence. Although in a quiescent environment the cross-sectional profiles of velocity and buoyancy are close to Gaussian in shape, the actual mechanism of plume spreading involves an inwards erosion of the Gaussian shape from the flanks of the profile by the ambient turbulence. Obviously, a simple extension to classical plume theory does not capture this qualitative change to the shape of the plume profiles. A scaling is proposed instead that links the radial extent to which the Gaussian profile is eroded by the ambient turbulence to the relative magnitudes of the fluctuating velocity in the ambient turbulence and on the centreline of a plume in a quiescent environment.

Phosphate removal from wastewater during treatment is a legal requirement to prevent environmental damage caused by releasing large amounts of nutrients into water courses. The most commonly applied removal methods, due to their ease of use, are based upon precipitation of the phosphate by chemical addition. An alternative method has been developed involving specialised micro-organisms, termed phosphate accumulating organisms (PAO), which take up and store greater than required amounts of phosphate. This process, designated enhanced biological phosphate removal (EBPR), has developed empirically since the observation that cycling the wastewater through anaerobic/aerobic phases selects for these PAO and the phosphate is removed from the liquid. There are still many aspects of the EBPR process that are far from fully understood; these include the identity of the organisms that are responsible for the phosphate uptake and the reasons why plants will occasionally stop removing phosphate. This project addresses these points, firstly by determining the effect of knockout and over-expression of <i>ppk</i> and <i>ppx</i> - genes known to be important in cellular polyphosphate metabolism in <i>Pseudomonas putida</i>, an organism found in sludge, which can accumulate polyphosphate. Previous mutational studies have mostly focused on <i>Escherichia coli </i>and <i>Pseudomonas aeruginosa</i>, which do not proliferate in sewage plants. The effect of the mutations upon growth, polyphosphate production and stress responses were ascertained. It appeared that two separate populations of polyphosphate were present, one being synthesized by polyphosphate kinase, the other by some as yet unidentified pathway. Further investigation of this 'large polyphosphate' established it was not polyphosphate but an unknown contaminating material that co-separated during the extraction procedure. Analysis of this compound suggested it was an exopolysaccharide, similar in character to alginate. The second aspect of the project focussed on the isolation of micro-organisms from a local EBPR plant followed by the selection, identification and characterization of potential PAOs. The development of a fully defined phosphate removing sludge community was attempted, in order to facilitate the study of the process. This was undertaken by operating a two litre bioreactor under EBPR conditions and allowing a self-selected community to develop from the inoculated isolates.

The aim of this research is to investigate the remediation of Methyl Tertiary Butyl Ether (MTBE) and other organics in groundwater by applying photocatalysis as an in-situ process. Photocatalytic degradations of MTBE and some other organics pollutants were proved to be possible. Experimental results suggest that photocatalytic degradation is accurately described by first order kinetics. The efficiency of photocatalytic degradation was expressed as the rate constant or the quantum yield. It was found that complete photocatalytic degradation of MTBE was only possible under aerobic conditions. Intermediates, such as Tertiary Butyl Formate (TBF) and acetone were found in oxygen-limiting photocatalytic degradation of MTBE. It was experimentally deduced that the rate constant of photocatalytic degradation was linearly proportional to the light irradiance and illuminated catalyst surface and inversely proportional to the reactor volume. The quantum yields of photocatalytic degradation of 100 mg/L MTBE solution in the five reactors were measured as 0.23% to 0.71%. The equilibrium adsorption of MTBE on TiO₂ was found to be a linear isotherm. Flow experiments were conducted by circulating MTBE solution between one of the designed reactors and a reservoir. It was found that the reduction of pollutant was a function of the circulation rate, reactor volume and the batch rate constant of photocatalytic degradation in the reactor. Some soil experiments were conducted using one of the designed reactors, which was an underground reactor and some corresponding modelling was done to simulate the transport of MTBE under different flow regimes. It was found that pumping and regional flow facilitated the exchange of water between the reactor and the surrounding soil.

Resource-oriented sanitation systems are designed to recover resources from wastewater while minimizing the demand on other resources, particularly water and energy. This research explores the proposition that such systems offer a more sustainable alternative to conventional waterbourne systems. Its centrepiece is a case study of the world’s largest urban dry sanitation system designed for complete resource recovery, located at the Erdos Eco-Town Project (EETP) in the Inner Mongolia Autonomous Region of China. In the case study, the sustainability of the EETP’s dry system (DRY system) is compared against that of a conventional waterbourne system (WET system) based on technical, environment, economic, and societal indicators. From a technical perspective, the two systems were found to be generally capable of meeting treatment standards and capacity requirements. However, the less technologically mature DRY system requires further improvements particularly with regards to odour control, toilet design, and faecal material handling. The DRY system offers clear environmental advantages such as reduced water consumption, the recovery of valuable resources from domestic wastewater, reduced eutrophication, and reduced toxicity of agricultural soils; however, these benefits come at the cost of higher energy consumption and greater infrastructure requirements. The DRY system requires greater infrastructure and therefore higher capital costs, has higher operational costs, and does not benefit from economy of scale. As a novel technology, however, it does offer the potential for local business development. The WET system performs better based on the societal indicators largely because it is well-established system. The DRY system suffers from low user acceptability due to the more complex design of the urine diversion dry toilets, odours and the prevailing view of the flush toilet as the “gold standard”. An important concern with the DRY system is the health risk associated with its faecal management system.

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