Solid-liquid separation is an important unit operation in many industrial processes. Research on the process optimisation and technical advancement of this operation is crucial to ensure a reliable and economical process. Work include developments in filtration theory and understanding of suspension behaviour are constantly investigated to ensure the process reaches the target. / In this work, enhancement in dewatering was quantified with the use of shear. Shear, in this context, is a mechanism used to deform a suspension network such as the action of raking in thickeners. In order to understand the inter-play between shear and dewatering for colloidal networked suspension, the relationship between shear and compression rheology was investigated. / The effect of shear was investigated in two situations, which are the presence of shear during and before dewatering. The former was achieved by applying an electric field to a suspension during (in-situ to) dewatering and the latter was achieved through varying shear condition for flocculated suspensions prior to dewatering. The analysis of dewatering properties was then performed by applying the consolidation theory of Landman and White (Landman et al. 1995; Landman and White 1997). / The materials used in the study were two types of colloidal metal oxide particles namely AKP-30 alumina and Ajax kaolin. They were chosen due to their physical differences such as particle size and shape. The dispersion state of these suspensions from coagulated to dispersed, was fully controlled by manipulation of the particle surface chemistry. This changed the suspension micro-structure. Flocculated suspensions were prepared by the addition of a non-ionic, high molecular weight polyacrylamide to the coagulated AKP-30 alumina suspension. / The study on shear rheology was investigated by employing steady shear and small amplitude oscillatory shear (SAOS) measurements. The use of these two methods allowed quantitative interpretation of a network deformation of a suspension which involved the transition between solid-like behaviour (before yielding) and liquid-like behaviour (after yielding). The network deformation can be characterised as either being of a brittle or ductile type. The use of Lissajous figures also aided the understanding of the deformation. / The shear rheology of the metal oxide suspensions was found to depend critically on the extent of the inter-particle interactions. Both dispersed and coagulated suspensions show different rheological properties. In the case for coagulated suspensions, rheological parameters such as the shear and compressive yield stresses, and elastic modulus plateau value, all scaled, which indicate that these parameters arise from particle interaction. This is in contrast to the understanding of shear rheology on freshly flocculated suspension which is still limited, particularly for concentrations at close the gel point. The shear rheology of flocculated suspension was then compared to that of coagulated suspensions. Various degrees of flocculation conditions were investigated. Network deformation was found to show an identical pattern to that of coagulated suspensions but the network strength was found to increase with shear rate. / The dewatering properties of dispersed and coagulated AKP-30 alumina and Ajax kaolin suspensions were compared. It was found that dispersed suspensions have lower compressibility (i.e. produce a higher final solids concentration at the same applied pressure) and permeability compared to coagulated suspensions. Comparison between the two model suspensions shows that AKP-30 alumina suspensions have better dewatering qualities compared to kaolin suspensions. The effect of flocculation conditions for AKP-30 alumina suspension was found to dramatically affect the settling rate but had only a small effect on dewatering at higher solids. / A combination of dewatering methods was used and they gave excellent results for the prediction of the dewatering characteristics of suspensions for a wide range of solids concentration from close the gel point up to close to the maximum close packed concentration. Finally, electrically enhanced dewatering (EED) for Ajax kaolin suspension was compared to that of normal dewatering. Results showed significant dewaterability enhancement at pressures below 10 kPa. The application of EED was also investigated for an industrial sample of water treatment sludge. Similar results were noted as for Ajax kaolin, with an increase of equilibrium solids concentration and permeability with EED at a given pressure. In this context, EED delivered promising results in improving the dewatering properties of difficult-to-dewater suspensions.

The world's brown marine algae, or kelps, have a great potential for agricultural use. Over 14 million tonnes of kelp are estimated to be available for harvesting every year, but only 6.3% is harvested, mostly for food products or alginate extraction. The inclusion of kelp in an animal's ration has been found by several researchers to have a beneficial effect on the animal's health and productivity. High concentrations of kelp in an animal's ration, however, can have detrimental effects on the animal's health due to toxic levels of certain inorganic salts. / By including a dewatering operation in the production of dried kelp meal, much of the soluble salts present in the kelp will be removed with the filtrate. The filtrate would also be valuable as a source of potassium, trace minerals, and phyto-hormones for crops. Energy costs for dewatering are also much lower than for drying. Because kelp is difficult to dewater using conventional methods, a combined fields technique using electro-osmosis and mechanical pressure was investigated. / Electric current and pressure were both found to have a significant positive effect on dewatering. Dewatering resulted in significantly lower ash and available carbohydrate fractions, while having no other significant effect on kelp meal composition. The combined fields dewatering resulted in significant total energy savings over conventional dewatering or drying alone. / The combined fields dewatering process was successfully scaled up to a continuous process using a prototype roller press. The press was able to produce a press cake with up to 32% solids. The continuous process resulted in significantly lower ash content and significantly higher protein. The total energy to produce kelp meal with the roller press was found to be about half of the energy required for drying alone.

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This thesis concerns design of two pieces of suspension dewatering equipment (i.e. transient batch settlers and steady state continuous gravity thickeners). In a transient batch settler, very slow densification of aggregates within the suspension is considered whilst the drag on the solids in the suspension is assumed to be negligible. The interface of the suspension is then determined by a balance between gravity and the gradient of the compressive yield stress of the gelled suspension. The compressive yield stress functional form in general could be either a weakly gelled formula, or a strongly gelled formula. These formulae differ in the way they behave for solids concentrations in the neighbourhood of the suspension gel point. The effects of the above two gel formulae, the evolution of the compressive yield stress functional form over time during aggregate densification, different initial suspension heights, and different initial feed solids volume fractions upon the predictions of consolidated bed structures and solids volume fractions obtained at the bottom of a batch settler, and upon the evolution of the heights of the suspension and the consolidated bed have been explored. A sufficiently tall initial suspension height might lead to insignificant increases in the solids volume fractions obtained at the bottom of batch settlers after time-dependent aggregate densification. The interfaces of the suspension and the consolidation zone coincide after aggregate densification if the gel point, which increases with time, is larger than the initial feed solids volume fractions. Moreover, the maximum permitted underflow solids fluxes predicted from steady state thickeners have been investigated and compared. Pre-shearing of aggregates which densifies aggregates to have smaller diameters upon entering the thickener is necessary if large underflow solids fluxes and small underflow solids volume fractions are specified. The solids volume fraction at the top of the consolidated bed which is the densified gel point is influenced by the extent of pre-shearing of aggregates. An algorithm for determining this densified gel point has also been developed. In reality, thickeners contain not just a consolidating bed, but also a hindered settling region above it. When the hindered settling region is considered in a thickener, the effects of the extent of aggregate densification that has occurred in the hindered settling region and how that impacts upon thickener performance and sludge rheological properties have been explored in this thesis. A new algorithm for predicting the densified gel point obtained at the top of the consolidated bed has been developed when the hindered settling region is present. The effects of underflow solids volume fractions, aggregate densification rate parameters and pre-shearing of aggregates upon the predictions of maximum permitted underflow solids fluxes, sludge rheological properties, and thickener performance have been explored. The predictions of thickener performance using both the weakly and strongly gelled formulae have also been achieved. In cases where it is possible to neglect the hindered settling region, substantial increases in the maximum permitted underflow solids fluxes, and substantial decreases in the consolidated bed heights and the total solids residence times have been achieved after aggregate densification for a comparatively small underflow solids volume fraction. The benefits arising from aggregate densification are more modest if the underflow solids volume fraction is larger. On the other hand, when the hindered settling region is included, more densification of aggregates occurring in the hindered settling region might lead to taller consolidated bed heights for a specified suspension flux and a specified aggregate densification rate parameter due to higher underflow solids volume fractions.

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The treatment of municipal, industrial and agricultural wastewater produces a semi-liquid mixture known as sludge. The costs associated with pumping, transporting, treating, storing, and disposing of sludge are significant. Therefore, sludge dewatering techniques are employed to increase the solids content of the material by separating the solid and liquid components, thus reducing the overall volume requiring further handling. Non-mechanical dewatering methods require large areas of land and favorable climatic conditions, while mechanical dewatering technologies require significant capital investment and ongoing operation and maintenance by highly trained personnel. Due to these shortcomings, the conventional methods of sludge dewatering are not applicable to scenarios where: the quantity of sludge is small, there is limited budget, there are land restrictions, or dewatering is performed seasonally. An alternative approach that has recently attracted considerable attention is the use of dewatering fabrics; specially engineered textiles supplied in the form of very large bags into which the sludge is pumped. The concept itself is simple, pressure inside the bag pushes the free water through the fabric while the solid material is retained within. Unfortunately, these products have exhibited poor dewatering performance for certain feed materials. In this work, a series of ‘next-generation’ engineered dewatering fabrics featuring elongated ‘slit’ pores were produced using laser cutting techniques. A comprehensive analysis of the effect of the filter properties on dewatering performance was performed using sludge sourced from two different operations: municipal wastewater treatment and precious metal mining. / Thesis / Master of Applied Science (MASc) / In recent years, the use of engineered dewatering fabrics has emerged as a viable alternative to conventional methods of sludge dewatering in numerous application areas including municipal wastewater, mining, and pulp and paper. Previous studies have focused on the development of empirical ratios between dewatering performance and the porous properties of the textile material. The limitation of this approach is that the latter is difficult to characterize using currently available techniques due to the complex, nonuniform pore structure of conventional woven and nonwoven dewatering fabrics. In this study, a series of dewatering fabrics were produced using advanced microfabrication techniques featuring well-defined slit-pore geometries. Full-factorial design-of-experiment frameworks were employed to evaluate the effects of slit-pore dimensions and slit-pore spacing on cake layer development and key dewatering performance metrics. Laboratory scale dewatering performance tests were performed using both anaerobic digested sludge from the Woodward Avenue Wastewater Treatment Plant in Hamilton, Ontario and metal precipitate sludge from a nickel-copper mine in Ontario, Canada. The results from this study provide new insights into the importance of the cake layer in geotextile dewatering and the impact of pore geometry, porosity, and polymer performance on cake layer development.

The solid-solid separation processes employed by modern coal preparation plants require large amounts of process water that must be removed from the surfaces of particles using mechanical dewatering equipment. Unfortunately, the existing processes that are used to dewater fine particles are inefficient in terms of moisture reduction and/or solids recovery. Many coal preparation plants are forced to discard fine coal particles because of the inability of existing technologies to reduce the moisture content of this product to an acceptable level. In light of this problem, a new ultrafine dewatering process called hyperbaric filter centrifugation (HFC) has been developed. This novel method combines centrifugation and pressure filtration within a single process to substantially reduce moistures over what can be achieved using conventional dewatering systems. In the current study, steady-state and dynamic dewatering models were developed in order to be able to simulate the behavior of the HFC technology. The steady-state model, which was based on grain-size properties, used empirical expressions to predict product moistures. On the other hand, the dynamic model was based on fundamental theories of filtration and centrifugation. Although the dynamic model provided a better understanding of the working principles of the process, the steady-state grain model produced more accurate equilibrium moisture predictions. Therefore, the steady-state model was used to further investigate the effects of several parameters on cake moistures. As such, the steady-state model was useful for scale up and design purposes. The steady-state dewatering model was also used to perform an economical analysis of potential applications of the HFC technology. The model was used to investigate a variety of new circuit designs that have the potential to be commercially applied in the coal industry. The results clearly showed that this new technology would allow coal companies to process difficult-to-dewater ultrafines using the HFC process, while coarser solids would be more appropriately dewatered using conventional technologies such as vacuum filters or screenbowl centrifuges. This "split dewatering" concept would provide substantially higher profitability due to lower moistures and higher recoveries of ultrafine solids than could be achieved using a single dewatering process. Laboratory- and pilot-scale versions of this technology has been constructed and tested at the facilities of Mining & Minerals Engineering Department of Virginia Tech. Results of this testing program showed that 30-50% lower moisture values than the ones obtained using conventional mechanical dewatering processes could be achieved with the HFC technology. Based on these promising results, a pilot-scale prototype unit, which was tested successfully at several commercial U.S. coal plants, was also constructed by Decanter Machine, Inc. Finally, the process of developing of this novel technology was successfully completed with the sale of the first full-scale commercial unit by Decanter Machine, Inc. to a major U.S. coal producer. / Ph. D.

Production of biogas is one of several alternatives to meet sustainable energy solutions and waste management. However, managing the by-product (digestate) can be problematic with its high handling costs. Digestate from wet co-digestion biogas plants contains large volumes of water, causing high transportation costs and low concentration of the valuable nutrients. An alternative to try and reduce the associated costs is by processing the digestate. Processing the digestate for volume reduction allow for more economic and resource efficient ways of handling the product. This master thesis was performed on an initiative from Tekniska verken AB and address digestate handling from Linköping biogas plant, a large co-digestion biogas plant in Sweden. The project aimed to find a feasible, more resource efficient management of their digestate by looking at digestate processing alternatives.The approach systematically evaluated a large number of processing techniques by both literature and communication with TvAB or experts. A selection of techniques were further evaluated were studies in laboratory and a market analysis on digestate provided complementary information, aiding the economical evaluation. Results suggest that processing by centrifuge is a viable, economic option when digestate management is costly and a liquid fraction can be recirculated in the process. It has the potential to significantly reducing digestate management costs. Other processing alternatives may be beneficial if transportation distance can be greatly reduced and/or synergies can be found, but the findings in this project suggest that only treatment with centrifuge is of interest. The results are subject to a number of conditions (such as size of the plant) and assumptions (such as recirculation of a liquid fraction) and therefore need individual adaption to be applicable at any specific plant. Conclusive remarks are that although site specific conditions affect the choice of processing, a project such as this may help reducing the necessary time spent on evaluation. Both research process and results may provide valuable findings for similar evaluations in any industry.

Thesis (M.S.)--Washington State University, August 2007. / Includes bibliographical references (p. 73-77).