| Summary: | The Biologically Engineered Single Sludge Treatment (BESST) system is a small package wastewater treatment plant, which is designed to reduce influent concentrations of ammoniacal nitrogen, biochemical oxygen demand and total suspended solids, to a standard fit for discharge into controlled waterways. This thesis examines the treatment performance of the BESST, while operating under steady state and disruptive conditions, and assesses the contribution of physicochemical and microbiological factors to treatment efficacy. The design of the BESST was based on principles of activated sludge processes, and comprised of an anoxic area, an aerobic area, and an upflow clarifier. In each area of the system, physico-chemical and microbiological profiles were distinct from the other areas. The influent delivered to the system was municipal sewage, delivered from the start of the wastewater treatment works within which the prototype BESST was located. The influent was generally high in concentrations of biochemical oxygen demand, and was highly variable in nature. At times, this was reflected in effluent quality, particularly when disruptive events were occurring, such as mechanical failure. However, good levels of reduction in concentrations of ammoniacal nitrogen, biochemical oxygen demand and total suspended solids were observed throughout the treatment period, and the system demonstrated a good level of robustness with regard to mechanical failure and experimental changes to sewage control parameters. Transformations of nitrogen and phosphorus were performed by bacteria in the biomass of the system, and were analysed throughout the sampling period by qualitative, culture based and molecular microbiological methods. Culture based techniques were shown to be a valuable monitoring tool, but were not representative of the actual community in the BESST. Molecular methods provided a higher resolution of microbial populations present during treatment, but it was not possible to correlate data obtained from culture based methodology with that obtained using molecular techniques. Enhanced phosphorus removal trials were performed during the study period, in order to facilitate the production of an effluent very low in concentrations of total phosphorus. The trial suggested that enhanced removal of phosphorus was possible in the BESST, and found the most dominant morphotype accumulating polyphosphate, to be that of filamentous bacteria. The study produced a large and complex dataset, which presented difficulties in the analysis of interactions between variables. Suggestions are presented to overcome such difficulties. The BESST is presented in this study as a package wastewater system which is able to successfully perform biological nutrient removal in a robust manner, the interrogation of which has led to a greater contribution to knowledge of small wastewater treatment systems and the reactive nature of the chemical and biological processes occurring within them.
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