Water and wastewater treatment produce sludge that is dewatered prior to disposal in order to reduce disposal costs. This work combined mathematical modelling of thickeners, filters and centrifuges with accurate measurement of sludge dewatering properties to give improvements in operation, design and control of such devices, including increased throughput and reduced water content. / The theoretical basis of this work was the phenomenological solid-liquid separation theory of Buscall and White, 1987, in which the local volume fraction dependent properties of compressive yield stress, Py(φ), and hindered settling function, R(φ) (which, when combined, give the solids diffusivity, D(φ)), describe the material behaviour in compression. The local conservation equations were given in vector notation, converted to one-dimension, and applied to piston-driven filtration. A range of models of plate-and-frame filter presses and solid-bowl centrifuges were developed. Simple visual basic programs were written to provide operators and designers access to filter model predictions. / Filtration and settling tests were used to measure the material characteristics for water and wastewater treatment sludges from a range of industrial sites, including different coagulants and coagulation conditions, with weekly and seasonal variations. The results showed that ferric-based water treatment sludges have very little variability, while alum sludges can exhibit some changes in properties. New qualitative and quantitative methods were developed for wastewater sludges, which exhibit atypical filtration behaviour. The production of synthetic sewage sludge showed that this is caused by the extracellular polymeric constituent. / The material characteristics were used to predict the throughput and cake solids for filter presses, centrifuges and continuous thickeners. The filter models were validated at a range of water treatment plants, and used to investigate the optimisation and control of press performance. A modified-Darcy’s law, which was validated using model predictions, was used to determine the membrane resistance from on-site measurements. / The centrifuge models included one-dimensional transient and continuous, and two-dimensional continuous decanting models. Algorithms for the solution of the one-dimensional models were developed for both the un-networked and networked cases, and the results for a simple example illustrated. The development of the decanting centrifuge model included conversion of the conservation equations to helical coordinates, consideration of the viscous flow of the centrate down the spiral formed by the blades of the scroll, the movement of the solids due to differential speed of the scroll and the sedimentation-consolidation of the solids due to the centrifugal acceleration. / Civil engineering consolidation theory and testing methods were outlined and compared to filtration. The relevant dewatering parameters were related via a simple equation. The material characteristics of a kaolin sample were measured using oedometer and pressure filtration testing and compared using the derived relationship. / Overall, this represents several important developments in the understanding of water and wastewater sludge dewatering, especially the measurement of water treatment sludge characteristics at a range of sites and with seasonal variations, the development of analysis techniques to determine wastewater sludge characteristics, and the development or adaptation of new or existing models of filters, centrifuges and thickeners. Considerable cost savings were made possible by understanding both the material behaviour and the dewatering device.
| Identifer | oai:union.ndltd.org:ADTP/269940 |
| Date | January 2005 |
| Creators | Stickland, Anthony D. |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
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