Browsing by Author "Loewenthal, Richard Eric"
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- ItemOpen AccessAggressive water attack on carbonated cement materials(1991) Mackintosh, Grant Stewart; Loewenthal, Richard EricAggressive attack on samples was monitored by measuring changes in chemical characteristics of the water exposed to cement concrete samples, inter alia pH, calcium and alkalinity. Over the period of the investigation (100 days) the following observations were found to apply to both brown and white water: (i) Generally uncarbonated OPC experiences significantly higher calcium mineral dissolution rates than both carbonated OPC and 30% fly ash OPC cement concretes. (ii) Once steady dissolution rates were attained, measurements indicated that 30% fly ash OPC and carbonated OPC concrete undergo closely the same calcium mineral dissolution rates. Before these findings are implemented, the following practical considerations need to be addressed: (i) An economic assessment of the benefits of using carbonated OPC, fly ash OPC and carbonated fly ash OPC as a means of resisting aggressive attack. (ii) The investigation should be upgraded from laboratory scale to pilot scale. (iii) The influence of accelerated carbonation on corrosion of steel reinforcing.
- ItemOpen AccessCarbonate chemistry in high salinity waters(1983) Loewenthal, Richard Eric; Marais, Gerrit van RooyenThe primary objective of this investigation was to develop phase equilibrium diagrams for the carbonate system in high salinity waters, i.e. for single aqueous phase, solid-aqueous phase, gasaqueous phase and solid-aqueous-gas phases. Such diagrams have been developed for low salinity waters, viz. Deffeyes and Caldwell-Lawrence diagrams and modifications of these.
- ItemOpen AccessLimestone dissolution kinetics in upflow reactor systems(1995) Kornmüller, Ulrich Christopher Robin; Loewenthal, Richard EricWaters derived from the Table Mountain sandstones are soft and acidic. Consequently they tend to be highly aggressive to cement materials and corrosive to metals. Full stabilization is normally effected using lime and carbon dioxide, this however is expensive and inappropriate in many rural areas. Partial stabilization effected by passing the water through limestone (calcium carbonate) granules appears to be a practical means of reducing aggression and corrosion problems associated with these waters. In this process calcium carbonate into the water increases the pH and the Alkalinity and calcium content. Feasibility of the process in part depends on the rate at which limestone dissolves into the water. This investigation addresses the problem of modelling the kinetics of the dissolution process and calibrating the model by experimentation.
- ItemOpen AccessMathematical modelling of integrated chemical, physical and biological treatment of wastewaters(1998) Musvoto, Eustina Vongai; Ekama, George A; Wentzel, Mark C; Loewenthal, Richard EricThe development of a kinetic-based model to simulate chemical, physical and biological processes in three phase (gaseous-aqueous-solid) mixed weak acid/base systems is described. The chemical processes are expressed in terms of the kinetics of the forward and reverse reactions for the dissociation of the weak acid/bases. In this approach the H⁺ and all the species of the weak acidfbases of interest are included and the pH is calculated directly from H⁺ via pH = -log (H⁺). The advantage of this approach over the alkalinity/equilibrium chemistry approach is that kinetics are used throughout. Also, the approach is general and can be applied to any combination of mixed weak acid/base systems. The kinetic expressions of the carbonate, phosphate, ammonia, acetate and water systems, including the kinetics of the three phase chemical processes viz. precipitation/dissolution of calcium and magnesium phosphates and carbonates and gas stripping/dissolution of O₂, CO₂ and NH₃, were programmed into the AQUASIM shell package to generate simulation results. The chemical processes part of the model was validated by comparing steady state model predictions with those obtained from equilibrium chemistry based models such as STASOFT I and III (Loewenthal et al., 1986, 1991). Virtually identical results were obtained. The kinetic approach allowed integration of the biological kinetic processes of the IAWQ activated sludge model No 1 (Henze et al., 1987), to extend application of the model to situations where precipitation of minerals, stripping of gasses and biological processes take place in an environment where the pH does not remain constant. Where required the interaction between the chemical species and biological processes was included, e.g. CO₂ uptake for autotrophic nitrifier growth and NH₄⁺ uptake for heterotrophic growth and nitrification. Also, literature information on the effect of pH on the maximum specific growth rates of nitrifiers was included.
- ItemOpen AccessModeling of sulfide emission from the Virginia sewer system(2001) Lu, Yue; Loewenthal, Richard Eric; Alexander, Mark GavinRecognizing that attack in the sewer environment invovles five distinct processes occurring simultaneously, each with its own kinetics, any meaningful research can be effected only once the individual processes have been uncoupled and studied separately. The principal objective of this thesis is to predict hydrogen sulfide emission from sewerage along the line of flow for the Virginia sewer field laboratory. Meeting this objective required both an understanding of the flow hydraulics in this sewer environment, and a model (kinetic equation) for hydrogen sulfide emission in terms of the flow characteristics. This thesis presents the relevant theory for predicting hydraulic characteristics (including velocity gradient, G) in gravity flow sewers.
- ItemOpen AccessA one-step ambient temperature ferrite process for treatment of acid mine drainage waters(2005) Morgan, Barak Eli; Loewenthal, Richard EricAcid mine drainage (AMD) waters are low in pH, very high in dissolved iron, high in non-ferrous (mainly heavy) metals and very high in sulphate salinity. As such, AMD waters present a serious environmental problem in the mining regions of South Africa and elsewhere in the world. Treatment of AMD therefore requires pH neutralisation, removal of ferrous and non-ferrous metals and sulphate removal. This thesis addresses the problem of metals removal from AMD. The approach involves pH elevation and partial oxidation of ferrous iron present in AMD so as to precipitate the ferrite magnetite (Fe3O4). Magnetite in turn has the property of incorporating non-ferrous metals into its crystal lattice by cation substitution. Magnetite has several other properties which make its formation an ideal means of metals removal from AMD. Magnetite settles and dewaters extremely well and it is also stable at low pH, making remobilisation of metals into the environment unlikely. Ferrite formation at elevated temperatures (>65°C) is well established and has been successfully used in Japan to remove dissolved metals from laboratory wastes. The challenge insofar as massive volumes of AMD are concerned is to form ferrites at ambient temperatures. A second challenge is to form ferrites at ambient temperature in the presence of calcium, as lime (Ca(OH)2) is the most economical agent available for raising pH, but calcium is known to interfere with magnetite formation. To this end a series of batch and steady-state experiments have been performed in order to establish ambient temperature conditions for ferrite formation from AMD-like waters in both the presence and absence of calcium; as well as in the presence of both calcium and some non-ferrous metals commonly found in AMD (Co, Ni, Zn, Mn). The results represent the first well-described proven demonstration of a continuous flow, steady-state ambient temperature ferrite process which works successfully in the presence of calcium. The process relies upon ( 1) the property of magnetite/ferrite seed to channel the end- products of oxidation of ferrous solutions in the presence of calcium towards magnetite/ferrite formation; and (2) upon a contact stabilisation reactor -- settler sequence which serves to enhance the ferrous intermediate : dissolved calcium ratio in the oxidation reactor so as to overcome the problem of calcium interference in ferrite formation. The feasibility of the process for metals removal from AMD is borne out by a number of robust results pertaining to the quality of the effluent and the density and stability of the resulting sludge. There are several features of the process described here which render it economically attractive in comparison with existing technologies. Salient among these is the role of the contact stabilisation reactor - settler sequence in separating all the metals in the AMD from ~70% of the bulk AMD volume during the first stage of the process. Thus only ~30% of the bulk AMD volume requires further processing resulting in significantly reduced energy, infrastructure and chemical costs. Another feature of economic significance is the production of a commercially valuable end-product.
- ItemOpen AccessPelletization in the upflow anaerobic sludge bed (UASB) reactor(1989) Sam-Soon, Paul Alan Li Nai Sing; Marais, Gerrit van Rooyen; Loewenthal, Richard EricThis investigation was prompted by a study into the feasibility of treating an apple juicing waste water in an upflow anaerobic sludge bed (UASB) reactor system. Past experience with this system suggested that a pelletized sludge would be produced due to the nature of the waste water. This indeed was observed but the system exhibited an unusual feature, a high removal of nitrogen far in excess of that normally found in normal anaerobic processes. This observation stimulated a far reaching investigation into, the behaviour of the pelletized sludge bed, the causes giving rise to pelletization, a biochemical model explaining pellet formation, verification of the biochemical model, criteria for pellet formation, pH control in the pelletized sludge bed, and a kinetic model for the UASB process.