The objective of this project was to develop a suitable procedure for the design, control and optimisation of the Tubular Filter Press. To this end, the following objectives were defined for this study: • To extend or improve upon the constant pressure compressible cake filtration model, predictive solution procedure, and standard laboratory characterisation techniques requlred to obtain the empirical model parameters, presented in Rencken (1992). A new generalised area contact constant pressure compressible cake filtration model was developed for both the internal cylindrical and planar filtration geometries. The model utilises a heuristically developed area contact function which relates the interparticle contact area to the solids compressive pressure within the cake. If the area contact is zero, the model reduces to the conventional point contact model as presented in Rencken ( 1992). The sludge used in this investigation was found to exhibit a negligible degree of area contact. A new pseudo variable pressure solution procedure was developed, that is an extension of the constant pressure solution procedure, to account for the initial variable pressure stage of the Tubular Filter Press operation. The pseudo variable pressure solution procedure was found to account accurately for the initial filtration behaviour observed during the pressurisation period of the Tubular Filter Press. However for the normal operation of the Tubular Filter Press. the difference between the output of the pseudo variable pressure and constant pressure solution procedures, was found to be insignificant. Wall friction in compression-permeability (C-P) cell tests was identified as a main source of error. The significance of wall friction was investigated using a specially constructed C-P cell. that enabled the transmitted pressure through the cake sample to be measured. The accuracy of the characterisation which had been corrected for the effects of wall friction, was found to improve the prediction of the filtration behaviour of the sludge significantly. The direct shear test was identified and documented as a feasible experimental procedure to determine the coefficient of earth pressure at rest. The coefficient of earth pressure is unique to the non-planar filtration geometries. The coefficient of earth pressure at rest was determined for the sludge used in this investigation. • To incorporate the constant pressure compressible cake filtration model and the associated predictive solution procedures into a user-friendly computer programme that will facilitate the design and optimisation of full-scale plants. The predictive solution procedures were incorporated into the Windows 95 computer programme, COMPRESS, that can be used for any constant pressure compressible cake dead-end filtration application where the filtration geometry is planar or internal cylindrical. A control and optimisation strategy for the continuous operation of the Tubular Filter Press has been proposed. To develop a regressive solution procedure, and incorporate this procedure into a user-friendly computer progranune, that will enable the empirical model parameters. normally obtained from standard laboratory-scale tests, to be obtained from actual filtration data. A regressive solution procedure was developed that utilises a direct search optimisation technique that is an extension of the COMPLEX method. The regressive solution procedure was incorporated into the Windows 95 program, REGRESS. The program utilises filtration data from any dead-end constant pressure filtration application of either planar or internal cylindrical geometry. REGRESS provides an effective means for determining the true physical or plant specific filtration characteristics of the sludge. The regressive solution procedure also enables the parameters specific to the new area contact model to be determined. The sludge characterisation obtained from regressing on filtration data was found to be a significant improvement in predicting the filtration behaviour, than the characterisation obtained from the standard non-filtration laboratory-scale methods, even after the C-P cell data had been corrected for the effects of wall friction. The programs COMPRESS and REGRESS should greatly assist in the design. control and optimisation of the Tubular Filter Press process. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.

University press publishing was introduced in sub-Sahara Africa around the mid 1950s as the new independent countries strived to accelerate the pace of education and training of their peoples with the sole purpose of the rapid socio-economic development of their countries. Just like their universities, African university presses were modeled after their American and European counterparts. Like all genres of publishing, scholarly publishing in Africa has not been cushioned from the challenges imposed by economic factors. In fact publishing in Africa enjoyed a short boom in the early 1970s, but due to the serious socio-economic downturns in most of these countries, starting from the early 1980s, these gains have been halted and in some cases reversed. This study examines the policies and practices of six sub-Saharan Africa university presses. It is a multi-site case study to establish how far the presses have adopted and/or adapted their policies to suit the environment and circumstances of Africa. The study investigates the extent to which constraints facing them affect their publishing efforts, their coping strategies, and the possible avenues of reducing the effect of these constraints. Several data collection methods were employed including on-site visits, interviews, and observations at three of the presses, and a mail survey of all six presses. There is a serious absence of competition and cooperation between the presses surveyed. There are no aggressive fund raising strategies, yet the survey showed financial constraint as the most crucial factor that impedes the development of their publishing activities. The presses do not have press publishing areas or press lists, which define the subject areas in which each of them concentrates its publishing. None of the presses has a formal written policy on manuscript acquisition. The study confirms that university presses publish mainly in the humanities and social sciences. Views on a unique African model of a university press are divided. The issue of author-publisher relationship is high on the presses agenda, especially as African scholars seek publishing avenues with African presses. Opinion on publishing non-scholarly materials was divided but swayed towards getting the needed profits to support non-profitable but essential publishing by the university press. For the majority of the presses, the most important publishing category is undergraduate textbook, and direct sales is the most popular means of marketing their works. The presses have succeeded at selling between 25-65% of their output. The study concludes that the coping strategies adopted by the presses in the face of harsh environmental conditions include the introduction of ICTs, changes in the treatment of authors, editorial policy on publishing non-scholarly materials, staff levels and use of outsourcing, and different approaches to sources of funding. It recommends a consortium of African university presses based at the micro level on Specialization, Cooperation, and the adoption of ICTs especially print-on-demand technologies. Each press must operate as a Trust in order to enjoy autonomy as a private company, but be registered as a non-profit organization. At the macro level funding must be vigorously sourced through donor agencies including The African Development Bank. Governments should prioritize book publishing, the development and stocking of libraries, encourage reading, set up regional university presses, and introduce book and publishing components into research project funds. The study recommends further research into the effect of technological developments on university press publishing in Africa, a follow up study in 10 years to see how university presses in Africa are surviving, and a detailed study of university press consortia and the implications for tertiary education in Africa.

The tubular filter press is a novel tubular configured filter press for the filtration or dewatering of sludges. The unique features of the filter press are: (i) during the cake deposition cycle, cake is deposited on the internal walls of a self-supporting array of horizontal collapsible porous fabric tubes; (ii) during the cake removal cycle, cake is dislodged from the tube walls by means of a roller cleaning device and the dislodged flakes of cake are hydraulically transported out of the tubes by the feed sludge which is simultaneously re-circulated at a high flow rate through the tubes. The two main problems experienced on a prototype tubular filter press, which was erected at a water treatment plant to dewater the sludge from the clarifier underflow, were: (i) tube blockage problems during the filtration cycle; (ii) low cake recoveries (high cake losses) during the cake removal cycle. The following objectives which were defined for this study, were regarded as fundamental prerequisites for any solution of the two main problems: (i) to develop a predictive dead-end internal cylindrical model for compressible cake filtration inside a porous tube; (ii) to investigate the cake losses during the cake removal cycle of the tubular filter press; (iii) to develop a predictive unsteady-state internal cylindrical cross-flow microfiltration model for a non-Newtonian sludge which, when filtered, produces a very compressible cake. (An alternative to dead-end filtration during the filtration cycle of a tubular filter press is low axial velocity cross-flow filtration). On the basis of the objectives the study was divided into three separate investigations. To date no one has developed a model which incorporates the cylindrical configuration of the filter medium for dead-end compressible cake filtration inside a porous tube. The most comprehensive model for dead-end external cylindrical compressible cake filtration is that of Tiller and Yeh (1985). This model was adapted for internal cylindrical compressible cake filtration. In essence the model by Tiller and Yeh (1985) requires the solution of a system of two ordinary differential equations in order to calculate the radial variation of solids compressive and liquid pressures in a compressible filter cake deposited externally on a cylindrical surface. The relevant equations were derived for internal cylindrical compressible cake filtration and it was found that one of the differential equations changes from: dPl/dr = H1/2nrK (external cylindrical) to dPl/dr = H12nrK (internal cylindrical). The other differential equation remains unaltered for internal cylindrical compressible cake filtration. A batch of waterworks clarifier sludge from the prototype tubular filter press was used for experiments to evaluate the performance of the internal cylindrical filtration model. The cake produced by the filtration of this sludge had to be characterized for the model. Compression-permeability data were obtained over a wide solids compressive pressure range. A Compression-Permeability (C-P) cell was used for high solids compressive pressures (10 kPa<_ ps<_400 kPa) and settling tests were used for low solids compressive pressures (0,0065 Pa <_ ps < 525,6 Pa). The cake was found to be very compressible (compressibility coefficient = 0,989). Empirical equations of the form, K' = Fps - b and (1 - E) = B pbs , were derived from the C-P cell and settling tests to relate permeability and porosity to solids compressive pressure. The equations were slightly different to those proposed by Tiller and Cooper (1962). The predictions by the internal cylindrical compressible cake filtration model were compared to the results of constant pressure internal cylindrical filtration experiments, at filtration pressures of 100 kPa, 200 kPa and 300 kPa, using the waterworks clarifier sludge. The internal diameter of the filter tube which was used for the experiments was 26,25 mm. The model accurately described the results of the filtration experiments in terms of volume of filtrate, average cake dry solids concentration, filtrate flux and internal cake diameter. The differences between external cylindrical, internal cylindrical and planar compressible cake filtration were highlighted. Since the tubular filter press is a novel process, the cake losses during the cake removal cycle have not been investigated before. An investigation was therefore conducted into the cake losses which occur during the cake removal cycle. The same batch of clarifier sludge was also used for the investigation of cake losses during the cake removal cycle at filtration pressures of 100 kPa and 300 kPa. It was found that significant cake losses occurred due to: (i) the shear of the cleaning fluid prior to the action of the rollers (losses varied between 10 % to 20 % of the deposited cake dry solids); (ii) the combined action of the rollers when dislodging the cake and the hydraulic conveyance of the dislodged flakes of cake (losses varied between 30 % to 40 % of deposited cake dry solids). A new shear model, which was developed, accurately predicted the cake losses and increase in internal cake diameter and average cake dry solids concentration, which occurred due to the shear of the cleaning fluid. For the shear model the sludge (cake) rheology was determined using a capillary-tube viscometer. It was found that the sludges exhibited Bingham plastic behaviour in the solids concentration range: 3,58 % m/m <_Cs <_16,71 % m/m. The cake losses due to the action of the rollers and hydraulic conveyance of the dislodged flakesof cake decreased markedly as filtration pressure and filtration time were increased, while a decrease in path length for hydraulic conveyance of dislodged cake flakes resulted in a mild decrease in these cake losses. A literature review revealed that to date only one mathematical model (Pearson and Sherwood, 1988) is available for the unsteady-state cross-flow microfiltration of a non-Newtonian sludge which, when filtered, produces a compressible cake. A new unsteady-state internal cylindrical axial convection shear model (for laminar flow of the feed sludge) was developed for cross-flow microfiltration of a Bingham plastic sludge which, when filtered, produces a very compressible cake. Similar to the approach by Pearson and Sherwood (1988) this model is a combination of the dead-end internal cylindrical compressible cake filtration model and the "cleaning fluid" shear model. The major difference between the new model and the model by Pearson and Sherwood (1988) is that unlike the convection-diffusion model of Pearson and Sherwood (1988), diffusive and shear induced diffusive back-mixing of particles were assumed to be negligible. The existence of a shear plane within the cake forms the basis of the model. Those cake layers with a yield stress less than the shear stress exerted by the flowing feed sludge at the inner cake wall are convected along the shear plane. It was assumed that the axial convection of the solids in the moving cake layer along the shear plane is the sole mechanism for removal of solids deposited at the cake surface. The model was compared to the results of cross-flow microfiltration experiments at one filtration pressure (300 kPa) and cross-flow flow rates of 0,84 l / min; 1,58 l / min; 2,43 l / min and 4,44 l /min. The model accurately described the variation of filtrate flux, internal cake diameter and average cake dry solids concentration during the unsteady-state time period. The model, however, had to be "extended" by incorporating empirical equations for changes in permeability and porosity (due to further cake compaction) to obtain a good fit between the model and experimental results during the pseudo steady-state time period. The results of all three investigations provide a greater understanding of the cake deposition process (during both dead-end and cross-flow filtration modes) and the cake removal process for the tubular filter press. This should assist in finding solutions to the two main problems which were experienced on the prototype tubular filter press. / Thesis (Ph.D.)-University of Natal, Durban, 1992.