Thesis (Master of Engineering in Chemical Engineering)--Cape Peninsula University of Technology, 2018. / Globally, water is considered an essential resource as it sustains human, animal and plant life. Water is not only essential for all forms of life but imperative for economic growth. The world’s population is increasing at a disquieting rate, which will result in an increased demand for fresh water and food security. The agricultural industry is the main consumer of global freshwater and utilises fertilisers in order to meet food demands. The demand for water in South Africa (SA) has increased considerably due to the rapid expansion of the agricultural industry, and of the municipal and industrial sectors. Agricultural developments in SA are affected greatly as the country is facing a current drought crisis as a result of low rainfall and large water demands. With an abundance of saline water globally, desalinisation will be a major contributor to solving the global freshwater crisis. With limited fresh water resources accompanied by the agricultural industry as a major consumer, alternative measures are required to desalinate water specifically for agricultural use. Forward osmosis (FO) is a membrane technology that gained interest over the past decade because it has several advantages over pressure-driven membrane processes such as reverse osmosis (RO). FO technology is based on the natural osmotic process which is driven by a concentration gradient between two solutions separated by a semi-permeable membrane. Naturally, water will permeate through the membrane from a solution of low solute concentration or low osmotic pressure (OP) known as a feed solution (FS) to a solution of a higher concentration or higher OP also known as a draw solution (DS). Whilst various research studies have contributed to several advances in FO, several process limitations such as reverse solute flux (RSF), concentration polarisation (CP) and membrane fouling remain problematic, hindering FO for large-scale applications. Further investigation is therefore warranted and crucial in order to understand how to mitigate these limitations to develop/improve future processes. The aim of this study was to evaluate a fertiliser-drawn forward osmosis (FDFO) system by investigating the effects of membrane orientation, system flow rate, DS concentration, and membrane fouling on an FDFO systems performance and energy consumption. The FS used was synthetic brackish water with a sodium chloride (NaCl) content of 5 g/L whereas a potassium chloride (KCl) synthetic fertiliser was used as a DS. The membrane utilised was a cellulose triacetate (CTA) membrane and was tested in forward osmosis mode (FO mode) and pressure retarded osmosis mode (PRO mode) whilst the system flow rate was adjusted between 100, 200 and 400 mL/min. Additionally, the DS concentration was altered from 0.5, 1 and 2 M KCl, respectively. Experiments were performed using a bench scale FO setup which comprised of an i) FO membrane cell, ii) a double head variable peristaltic pump for transporting FS and DS’s respectively, iii) a digital scale to measure the mass of the DS, iv) a magnetic stirrer to agitate the FS, v) two reservoirs for the FS and DS, respectively, vi) a digital multiparameter meter to determine FS electrical conductivity (EC) and vii) a digital electrical multimeter to measure system energy consumption. Each experiment comprised of seven steps i) pre-FDFO membrane control, ii) membrane cleaning, iii) FDFO experiment, iv) post-FDFO membrane control, v) membrane cleaning, vi) membrane damage dye identification and vii) membrane cleaning. Pre- and post-FDFO membrane control experiments operated for 5 h whilst each membrane cleaning procedure operated for 30 min. The FDFO experiment operated for 24 h whilst the membrane damage dye identification operated until a minimum of 10 mL water was recovered. The process parameter which largely contributed to a beneficial system performance and specific energy consumption (SEC) was the increase in DS concentration. Water fluxes increased approximately threefold from a DS concentration increase from 0.5 to 1 M, followed by an additional 30 to 50 % rise in water flux at a DS concentration increase 1 to 2 M. SEC decreased by 58 and 53 % for FO and PRO modes, respectively, with a DS concentration increase from 0.5 to 1 M. An additional 35 and 37 % SEC reduction for FO and PRO modes was obtained for a DS concentration increase from 1 to 2 M. Altering the membrane from FO to PRO did not contribute to a beneficial system performance nor did it improve SEC. However, at a DS concentration of 0,5 M, the PRO mode obtained a 5.3 % greater water recovery compared to the FO mode. Conversely, at a DS concentration of 1 and 2 M, the FO mode achieved 5.4 and 7.0 % greater water recoveries compared to the PRO mode. The increase in flow rate also did not increase system performance significantly, however, a fluctuation in system SEC was observed. Throughout the study, no membrane fouling was observed, however, possible minute traces of membrane fouling could be observed from the membrane surface electron microscope (SEM) images. Additionally, minor changes in post- FDFO membrane control water recovery results were noticed which support the possible occurrence of membrane fouling during the FDFO experiment.

<p>The study shows conclusively that brine composition and concentration is highly variable at these South African power utilities and processes such as RO, contact with ash and CO2 ingress can have an impact upon the overall brine quality. Aq.QA was found to be a more accurate tool for classifying waters according to dominant ions than Stiff diagrams but Stiff diagrams still have the superior advantage of being a mapping tool to easily identify samples of similar composition as well as quickly identify what has been added or what has been removed from a water stream. Chemical speciation could identify effluent streams where CO2 dissolution had taken place.</p>

Thesis (M. Phil.)--University of Hong Kong, 1982.

<p>The study shows conclusively that brine composition and concentration is highly variable at these South African power utilities and processes such as RO, contact with ash and CO2 ingress can have an impact upon the overall brine quality. Aq.QA was found to be a more accurate tool for classifying waters according to dominant ions than Stiff diagrams but Stiff diagrams still have the superior advantage of being a mapping tool to easily identify samples of similar composition as well as quickly identify what has been added or what has been removed from a water stream. Chemical speciation could identify effluent streams where CO2 dissolution had taken place.</p>

Graduation date: 1988

Thesis (DTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2016. / The water desalination process needs large quantities of energy, either directly from fossil fuel or electricity from the national grid. However, these sources of energy significantly contribute to problems such as global warming in addition to creating a drain on the economy, due to their high cost. This dissertation is a description of the research undertaken with the aim of producing a water desalination prototype; a novel approach that was designed using state-of-the-art solar water heating equipment, incorporating the technologies of evacuated tubes and heat pipes. During the execution of the project, various modifications to the original commercially-available solar water heating system were attempted, each aimed at increasing the production of pure water. Finally, the system proved capable of producing a reasonable amount of pure water after twelve lengthy indoor experiments conducted in a laboratory in the department of Mechanical Engineering at the Cape Peninsula University of Technology, Bellville Campus, Cape Town, South Africa. Each experiment lasted five days on the basis of seven hours of exposure to an average amount of simulated solar radiation, followed by seventeen hours daily of inactivity and partial cooling down of the system.

Magister Scientiae - MSc / The study shows conclusively that brine composition and concentration is highly variable at these South African power utilities and processes such as RO, contact with ash and CO2 ingress can have an impact upon the overall brine quality. Aq.QA was found to be a more accurate tool for classifying waters according to dominant ions than Stiff diagrams but Stiff diagrams still have the superior advantage of being a mapping tool to easily identify samples of similar composition as well as quickly identify what has been added or what has been removed from a water stream. Chemical speciation could identify effluent streams where CO2 dissolution had taken place. / South Africa

No description available.

(1) A new model for the mass transfer in Direct Contact Membrane Distillation (DCMD) process is developed. The model is based on Direct Simulation Monte Carlo (DSMC) method. It avoids the over simplification of the resistance mechanisms and hence, give more accurate prediction. The model is validated by means of experiments. The influences of the main parameters in DCMD are also studied, including temperature difference between the feed side and the permeate side, the membrane's thickness and the pore size. Moreover, it is proposed to use aerogel as the membrane material. It is shown that the aerogel's hydrophobic property, low thermal conductivity and high porosity offer a much improved performance over the commonly used membrane material PTFE. The fresh water productivity can reach 10.0 kg/m2 per day. / (2) A new energy harvesting method for converting thermal energy to kinetic energy is proposed. This method is based on the rarefied gas phenomenon called Knudsen effect. By Knudsen effect, a gas flow can be generated from temperature difference. In order to generate Knudsen effect, a special material, aerogel, is used. It is a porous material full of holes of dozens of nanometers. Using Direct Simulation Monte Carlo (DSMC) simulation, it is shown that Knudsen effect still works under atmosphere pressure with aerogel material. Accordingly, a device is designed. Based on the numerical simulation, the device can generate about 70 W kinetic energy when driven by a solar panel with intensity of 1 kW/m2. / (3) A solar desalination system is designed. This system is based on a combination of Knudsen compressor and simple solar still. The Knudsen effect is generated from the aerogel driven by solar radiation. As a result, the system operates at lower pressure resulting in enhanced water evaporation process. Based on the simulation, the evaporation rate is significantly increased. It is found that in a typical summer day in tropic region like Hong Kong, such a system can generate about 5 kg fresh water per 1 m2 solar still per day. This number is about 30% higher than the simple direct solar still. Moreover, the proposed technology can be readily combined with other technologies such as condensation heat recovery to further improve the fresh water productivity. The optimal working condition is also studied. / Energy and water are two of the most important issues in the world today. The social and economic health of the world depends on sustainable supply of both energy and water. Especially, these two critical resources are always inextricably linked. To solve the emerging crisis of energy and water, renewable energy technologies is the key. On the other hand, recent advances in Micro-Electro-Mechanical Systems (MEMS) technology have opened new ways for us to use micro/nano scale physical and chemical effects. It is no doubted that the combination of the renewable energy technologies and micro/nano technologies will have great potential and there are plenty of room to explore. / The research presented in this thesis focuses on extending the micro scale effect to the macroscopic applications. Based on this idea, a new energy harvesting method and two new water desalination technologies are proposed, with computer simulations and experiment validations. These include: / Zhang, Peng. / Adviser: Ruxu Du. / Source: Dissertation Abstracts International, Volume: 72-04, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 123-135). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Deposition of calcium carbonate (CaCO3) and calcium sulfate (CaSO4) causes serious processing problems and limits the productivity of seawater reverse osmosis (RO) desalination. The interactions between CaSO4 and CaCO3 in the dynamic seawater RO systems have been neglected previously because conventional studies mainly focused on individual compounds or mixed compounds in batch systems. The present work evaluates composite fouling behavior of CaSO4 and CaCO3 in a dynamic RO unit. The fouling experiments were performed at constant pressure and velocity by a partial recycling mode which permeate was withdrawn from the system during the recirculation of retentate to simulate the increasing of water recovery level. The fouling phenomena were monitored by the decline of flux. Scanning electron microscopy (SEM) with a combination of elemental dispersive x-ray microanalysis (EDS), and x-ray powder diffraction (XRD) was used to identify the morphological features, chemical compositions and crystalline phases of foulants. The interactions of CaSO4 and CaCO3 were investigated by the comparison between individual CaSO4 or CaCO3 fouling and composite fouling, and by varying SO42-/HCO3- molar ratio of the feed. A recently developed approach, Scaling Potential Index (SPI) incorporated with measured concentration polarization modulus (CP), for assessing the fouling tendency of inorganic salts on the membrane surface was validated in the dynamic tests. In addition, the effectiveness of two generic scale inhibitors, polyacrylic acid (molecular weight =2100, PA) and sodium hexametaphosphate (SHMP) were evaluated. Some of the highlights of the obtained results are as follows: ??????The precipitation kinetics, morphology and adhesive strength of composite scales were different from pure precipitates ??????CaSO4 precipitated as gypsum while CaCO3 precipitated as two crystalline phases: calcite and aragonite ??????The crystalline phases as well as precipitation kinetics were affected by SO42-/HCO3- ratio ??????Scaling Potential Index was able to predict the fouling tendency of CaSO4 and CaCO3 accurately ??????The dosage of PA and SHMP was effective to mitigate fouling Results of this work are significant, not only because they have made contribution to the fundamental understanding of composite inorganic fouling in RO membrane systems which was ignored previously, but also because they may play a key role in the development of scale control.