Xenobiotic organics produced by modern industrial processes resist conventional biological wastewater treatment. Ozone pretreatment to improve biodegradation via partial oxidation is a potential solution for this recalcitrance. Ozone forms no additional sludge, removes colour and has two modes of action that can be utilised according to the wastewater constituents. The preozonation of a variety of wastewaters and model compounds is reviewed here. Of the industrial processes examined, the associated recalcitrant organic compounds were generally halogenated heterocyclic or nitrogenous aromatics, aliphatic polymers or polyaromatics. Initial optimisation of ozone dose ensured the occurrence of partial oxidation, where over 90% parent compound transformation was required to give best results in the subsequent biological process. Ozonation intermediate and end-products included ketones, aldehydes and organic acids that were more biodegradable than the parent compounds. Biodegradability improvement was assessed using TOC, COD, BOD, BOD/COD ratio and OUR. Actual process feasibility and performance was evaluated using various combined ozonation-biodegradation trials; textile dying and finishing effluent being one area of application. Kinetic studies of chemical and biological stages facilitated process optimisation and can assist scale-up. The main factors affecting ozonation performance were pH, the nature and concentration of oxidisable organics, ozone dose, competition between the target compound and biodegradable by-products, the presence of oxidant scavengers, and the efficiency of ozone mass transfer. The formation of toxic or recalcitrant by-products has been found to occur in some cases, necessitating knowledge of wastewater constituents and trials on a site-by-site basis.

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This paper presents the water and contaminant daily simulation model of the total water cycle, called UVQ. The model has been developed to provide a means for rapidly assessing conventional and nonconventional approaches to providing water supply, stormwater and wastewater services to urban allotments, neighbourhoods and study areas. The model is placed the context of other such models developed internationally through a brief literature review. This is followed by a description of the model and output examples, which is used to illustrate the utility of the model. UVQ is an effective preliminary assessment tool for determining the impacts of urban development options on the total water cycle, as well as the performance of a wide range of non-conventional demand and supply side management techniques. It compliments other aspects of an environmental assessment of options, along with more traditional aspects such as infrastructure costing.

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