Desalination of seawater is a widely used technology throughout the world, but is not commonly used in South Africa for domestic water supply. The reasons for this are varied, but very often are based on the assumption that desalination is extremely costly in relation to more traditional water supplies. An economic analysis is undertaken comparing the cost of supplying water to the coastal town of Zinkwazi from various sources including desalination using reverse osmosis. Zinkwazi has an existing borehole water supply that is insufficient to meet current and future demands. The town is also remote from regional bulk surface water infrastructure, which makes it suitable for the investigation of an alternative stand-alone water supply such as desalination. Solving the water supply problems at Zinkwazi is important to Umgeni Water and would support two broad strategic goals of the organisation. Zinkwazi falls within the Ilembe District Municipality, which is an important stakeholder within Umgeni Water's area of jurisdiction. Improving the water supply situation at Zinkwazi is in line with Umgeni Water's goal of assisting Municipalities to meet their developmental objectives. Using desalination to meet this objective is in line with Umgeni Water's goal of using innovative products to alleviate problems of existing customers. Desalination is a multi-billion dollar industry that is growing as traditional surface and goundwater resources become fully utilized and more polluted. Desalination potentially represents a growth opportunity that Umgeni Water, with its expertise in water treatment and supply, could pursue in Africa and Southern Africa in particular. The investigation found that desalination is the most affordable method of supplying water to the town of Zinkwazi and the construction of a desalination pilot plant is recommended for further investigation. / Thesis (MBA)-University of KwaZulu-Natal, Pietermaritzburg, 2005.

Renewable power generation from the controlled mixing of sea and fresh water is relatively unexplored when compared to the development for solar, wind, and other sustainable power alternatives. When global river discharge was taken into account, an estimated 2.6 TW of obtainable energy exists in untapped salinity gradients. Reverse electrodialysis is one proposed power-generating mechanism for harnessing energy from brackish environments and relies on the transport of aqueous salt ions through an apparatus of ion-exchange membranes. In this thesis, operational parameters, including flow direction, salinity composition, and membrane selectivity, are investigated. For optimal performance, I have employed counter-current flow mode with monovalent ion selective membranes and pure 0.5 M NaCl saline solution. The results show that a maximum open circuit voltage (OCV) level of 2.01 V is obtained with an active membrane area of 0.0756 m². The presence of multivalent ions in the feed solutions hinders OCV levels, but the effects are reduced with monovalent-selective membranes. Preliminary results are insightful; in order to increase the commercially viability of this technology, future work is needed to enhance the performance properties of the ion exchange membranes.

Abstract available in PDF copy. / Thesis (M.Sc.-Chemical Engineering)-University of Natal, 1988.

Most common inorganic foulants in RO processes operating on brackish water are calcium carbonate, calcium sulphate and silica. However, silica fouling is the recovery limiting factor in RO system. Silica chemistry is complex and its degree of fouling strongly depends on the silica solubility and its polymerization under different operating conditions of RO process. In several studies carried out in batch and dynamic tests, the presence of polyvalent cations and supersaturation of silica in solutions were found to be the important factors (apart from pH and temperature) that affected the rate of silica polymerization and its induction period. Agitation did increased silica solubility; however, its effect was negligible in presence of polyvalent cations. Alkalization of water solution by coagulants particularly sodium hydroxide was found suitable for silica removal during pretreatment. The presence of magnesium in solution played a key role in silica removal mostly by the mechanism of adsorption to the metal hydroxide. The options of inline mixing (high agitation) for 5 to 10 minutes and microfiltration before RO were found suitable for silica pretreatment. During dynamic tests, the most dominant mechanism for salt deposition (mostly CaSO4) was particulate type in high concentration water solution; while crystallization fouling was the prevailing mechanism of deposition (mostly CaCO3 and silica) in low concentration solution. Silica showed significant effect on size and shape of inorganic salt crystals during coprecipitation. Moreover, the presence of common antiscalants promoted silica fouling. This important finding recommends an extra caution while using antiscalants in case feed water contains silica to a level that can attain saturation near membrane during RO process. A model was developed to predict the silica fouling index (SFI) based on the experimental data for induction period of silica polymerization. The model takes into account the effect of polyvalent cations and concentration polarization near membrane during RO process. It provides a conservative basis for predicting the maximum silica deposition in RO process at the normal operating conditions. A generalised correlation, which was developed for determination of the mass transfer coefficient in RO process, incorporated the effect of temperature change that is usually not considered in previous correlations. A correlation for reduction of silica content in feed water, down to a safe limit of 15 ppm for RO process, was also formulated and validated by the experimental results.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2017. / Water scarcity in South Africa (SA) and more specifically Cape Town, Western Cape, has escalated to disaster levels in 2018. Agriculture and irrigation account for 62% of SA’s accessible potable water (Thopil & Pouris, 2016), and although the agriculture sector plays a pivotal role in SA’s socio-economic development, the future of the sector is dependent on critical issues such as climate variability and population growth (Besada & Werner, 2015). Wine production in SA is an important agricultural activity, contributing great economic value to the agri-food sector. However, despite this, the wine industry is responsible for vast water consumption and the unsafe disposal of winery wastewater, which are critical issues from an environmental and economic standpoint. The ever-imminent crisis pertaining to the limited supply of fresh water from conventional water resources has necessitated the need to develop alternative water resources to supplement an increased water supply, which include the reuse of wastewater, ground water, brackish water (BW) and seawater (SW) desalination. When fresh water supplies are limited, agricultural irrigation is penalised. The reuse of agricultural wastewater as a substitution for potable water irrigation may prove beneficial in areas where water shortages are severe. Forward osmosis (FO) is a developing desalination technology that has received increased attention as a promising lower-energy desalination technology. FO technology relies on the natural osmotic process, driven by a concentration gradient as opposed to significant hydraulic pressures like reverse osmosis (RO). Water is extracted from a lower concentrated feed solution (FS) to a highly concentrated draw solution (DS). The term “lower energy” is only applicable for applications where the recovery of the DS is not required. FO technology offers several advantages. However, the lack of suitable membrane modules and DSs hinder its practical application. FO offers novelty applications in which specialised DSs are selected to serve as the final product water, most notably concentrated fertilisers for direct fertigation. The aim of this study was to evaluate the performance and compatibility of commercially available cellulose triacetate (CTA) and aquaporin biomimetic FO membranes with commonly used fertilisers for direct fertigation within the SA wine industry, using a fertiliser drawn forward osmosis (FDFO) system.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2017. / Similar to the energy crisis, the critical state of the water supply in South Africa (SA) is a combination of (i) resource exhaustion and pollution; (ii) increasing demand; and (iii) poor infrastructure. Despite its importance, water is the most poorly managed resource in the world. The disposal of industrial effluents contributes greatly to the poor quality of water. The textile industry consumes great quantities of water and produces enormous volumes of wastewater which requires appropriate treatment before being released into the environment. In an attempt to address the water issues, research globally has focused on advanced technologies such as desalination to increase limited pure water resources. The need for alternative desalination methods for the production of clean water from alternative water resources, such as seawater and brackish water, has gained worldwide attention. Reverse osmosis (RO) and Nanofiltration (NF) have been used as unswerving approaches to yield freshwater. Forward osmosis (FO) is a developing membrane technology that has increased substantial attention as a possible lower-energy desalination technology. However, challenges such as suitable FO membranes, membrane fouling, concentration polarisation, and the availability of effective draw solutions (DS), limit FO technology. FO is seeking more importance in novel areas where separation and recovery of the DS is not required. The aims of this study was to: i) identify alternative water resources and evaluate their potential as suitable feed solution (FS); ii) Identify dyes and evaluate their potential as suitable draw solutions (DS) at different concentrations; iii) assess the use of aquaporin biomimetic membrane and iv) assess a FO system for the production of dye solutions. Osmotic pressure (OP) is the pressure exerted by the flow of water through semi-permeable membrane, separating two solutions with different concentrations of solute. The DS should always have OP higher than the FS in order to achieve high water flux. Three basic dyes (i.e. Maxilon Turquoise, Red and Blue) and three reactive dyes (i.e. Carmine, Olive Green and Black) were selected, based on their common use in the SA textile industry. The respective dye samples were prepared at different concentrations and dye-to-salt mass ratios ranging from 1:10 to 1:60 and assessed for OP using a freezing point osmometer. A lab-scale FO unit was used for all the studies. Feed and draw channels were circulated in a counter-current flow at a volumetric flow rate of 600 mL/min. Feed solutions(FS) included deionised water (DI) as a control, brackish water (BW), synthetic seawater (SSW) and textile wastewater (TWW) collected from two textile factories. OP of the FS (DI, BW5, SSW and SW, Factory 1 and Factory 2) was 0, 414, 2761, 2579, 1505 and 3308 kPa, respectively. Basic Blue and Reactive Black generated a higher OP compared to other selected dyes in the study and were therefore selected to be used as DS at a 1:10 dye-to-salt ratio and 0.02 M concentration. An aquaporin biomimetic FO membrane (Aquaporin, Denmark) was used for all the experiments conducted in the FO mode.

Water scarcity for agriculture is one of the most important challenges to improve food security worldwide. In this thesis we study the potential to develop a low-cost controller for a small scale brackish desalination plant that consists of proven water treatment technologies, reverse osmosis, cation exchange, and nanofiltration to treat groundwater into two final products: drinking water and irrigation water. The plant is powered by a combination of wind and solar power systems. The low-cost controller uses Arduino Mega, and Arduino DUE, which consist of ATmega2560 and Atmel SAM3X8E ARM Cortex-M3 CPU microcontrollers. These are widely used systems characterized for good performance and low cost. However, Arduino also requires drivers and interfaces to allow the control and monitoring of sensors and actuators. The thesis explains the process, as well as the hardware and software implemented.

Providing sustainable access to water and energy is among the grand engineering challenges in the 21st century. Notably, many pressing issues at the water-energy nexus can be addressed by effective ion separations, such as desalination, nutrient recovery from wastewater, and extraction of energy-related elements from unconventional sources. One tool for such separations is ion-exchange membranes (IEMs), which are charged polymeric thin films. However, conventional IEMs face several performance constraints and fail to achieve ion-specific selectivity. This thesis aims to advance the potential of IEMs for separations at the water-energy nexus. Present-day IEM processes, e.g., electrodialysis (ED) desalination and reverse electrodialysis (RED) power generation, commonly employ the membranes as charge-permselective barriers, transporting oppositely-charged counterions while retaining like-charged co-ions. However, the increase in charge permselectivity is accompanied by a decrease in ionic conductivity, which forms a conductivity-permselectivity tradeoff and crucially limits separation efficiency. This work models IEM conductivity and permselectivity as functions of intrinsic membrane chemical and structural properties, simulating the performance of IEMs in a range of ED and RED operations (Chapter 2). Bulk solution concentration is identified as an external cause for the tradeoff, which confines current IEM applications to sub-seawater salinities. The structure-property-performance analyses reveal membrane water sorption as an intrinsic determinant of the tradeoff, while indicating that increasing ion-exchange capacity and reducing thickness can yield highly selective and conductive IEMs. To depart from this tradeoff, nanocomposite cation-exchange membranes (CEMs) with percolating 1-D sulfonated carbon nanotube (sCNT) network are fabricated (Chapter 3). Membrane conductivity is raised with greater sCNT blending in the polymer matrix (increasing by ≈30% with 20 w/w% incorporation of sCNT), while permselectivity is effectively unchanged (within 2% variation). Further characterization displays sCNT percolation beyond 10 w/w% blending, attributing the conductivity improvement to the interconnected sCNT network. The results imply the potential to advance the conductivity-permselectivity tradeoff with rationally designed nanostructures. Next, this thesis moves from the conventional charge-discriminating selectivity to ion-specific selectivity (Chapter 4), which is urgently needed but underdeveloped due to insufficient understanding of the fundamental transport phenomena. Here, a transport framework is presented to describe counterion migration mobility using an analytical expression based on first principles. The two governing mechanisms are: spatial effect of available fractional volume for ion transport and electrostatic interaction between mobile ions and fixed charges. Mobilities of counterions with different valencies are experimentally characterized, showing high regression R²s with the mobility model. The influence of membrane swelling caused by different counterions is further accounted for, while the frictional effect of electrostatic interaction is quantitatively linked to fixed charged density and dielectric constant of membranes. Additionally, the anion-exchange membrane (AEM) exhibits a weaker electrostatic effect compared to CEMs, which is attributed to the steric hindrance of the quaternary ammonium functional groups. Last, the membrane-level knowledge is extended to two process-level applications, coupling desalination with sustainable energy and desalinating hypersaline brines. This thesis presents a novel low-grade-heat-driven desalination process (Chapter 5), using CEM and AEM Donnan dialysis (DD) stepwise to remove salt ions, e.g. Na+ and Cl-, with a receiver solution of thermally-recoverable solute NH₄HCO₃. NH₄HCO₃ in the streams is later recycled by low-grade heat. The concept is experimentally validated by desalinating brackish water (100mM NaCl) to freshwater salinity (< 17mM). DD desalination of larger ranges of feed and receiver concentrations was then demonstrated, and module-scale analysis quantified the improvements of countercurrent operation to desalination efficiency. Another challenge in water management is the desalination of hypersaline brines. While demand is rapidly increasing, the wider application of hypersaline desalination is held back by considerable technical obstacles. Here, theoretical analyses are carried out to assess the potential of hypersaline ED desalination (Chapter 6). We show that desalination performance is impacted by the interrelated charge-discriminating selectivity and ion-water selectivity of IEMs. The work demonstrates lower energy costs of ED compared to thermal processes, when desalinating 1.0-1.5 M NaCl, and identifies three key performance-determining tradeoffs: conductivity-permselectivity, conductivity-water resistivity, and energy cost-volume reduction factor. To enable highly efficient hypersaline ED, ultra-low swelling IEMs need to be developed. Overall, this work advances mechanistic understanding, membrane development, and process design of IEMs. The thesis contributes insights to breaking conductivity-permselectivity performance constraints and developing highly valued ion-specific selectivity. The informed membrane fabrication and process design provide access to unconventional water sources with less energy input. The findings of the thesis will enable the systematic development of more ion separation processes to address challenges at the water-energy nexus.

Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: When desalinating brackish water by reverse osmosis (RO) or other techniques, high overall water recoveries are essential to minimize brine production and the associated disposal costs thereof. As the overall water recovery increases, concentrations of sparingly soluble salts (e.g. barium sulphate, calcium sulphate) reach levels above saturation, especially near the membrane surface, drastically increasing the scaling propensity. Antiscalants are typically dosed into the feed water to prevent such scaling during RO desalination. However, the carry-over of antiscalant into the concentrate stream can complicate subsequent salt precipitation processes that may be used to increase overall water recovery. These precipitation techniques are sometimes used to reduce the levels of super-saturation in the RO concentrate prior to a subsequent RO desalination step. The purpose of this study was to assess the feasibility of reducing calcium sulphate scaling on RO membranes, by using periodic permeate flushing when feeding a lab-scale RO unit with a supersaturated calcium sulphate solution in the absence of anti-scalant. The overall water recovery was increased by recycling the concentrate, after an intermediate de-supersaturation step. This simulated a multiple-stage RO system, typical of processes used in high-recovery acid mine drainage (AMD) treatment plants. De-supersaturation of the concentrate intermediate was achieved with direct seeded gypsum precipitation, in the absence of any antiscalant. On the membrane surface inside the membrane unit, calcium sulphate concentrations greatly exceeded saturation levels – a combined consequence of the normal concentration process and the well-known surface-based concentration polarisation phenomenon. Therefore, periodic forward-flushing of the supersaturated solution from the membrane unit was performed with permeate. In theory, the periodic flushing removes the highly concentrated layer at the membrane surface during every flush, before scaling can occur. Various flushing regimes were evaluated to assess the effectiveness of the process. A lab-scale desalination unit with a 0.106 m2 flat sheet polyamide RO membrane was designed and constructed. The unit could operate at a feed rate of 12-14 L/h and at permeate fluxes of 12-24 LMH. Super-saturated feed solutions were prepared by mixing sodium sulphate and calcium chloride dihydrate salts with demineralised water, with an initial salinity of ± 5300 mg/L TDS, corresponding to a gypsum saturation index (SIg) of 1.2 for most experiments. The total production time, net permeate production and flux decline were used to compare the flushing efficiency in different experimental runs. Initial tests showed that scaling could be prevented (when operating the unit in full recycle mode, i.e. where both concentrate and permeate were recycled to feed), at flushing frequencies between 12 and 2.4 h-1, when the membrane feed and concentrate were slightly under-saturated (SIg = 0.9) and slightly super-saturated (SIg = 1.1) respectively. However, when switching the same system to non-flushing mode after 24 hours of operation, membrane scaling occurred within 2-3 hours, as indicated by a strong decline in flux. However, when operating the system in concentrate recycle mode (i.e. permeate is withdrawn) with super-saturated feed solutions (e.g. SIg = 1.2), and thus a notably more super-saturated solution in the membrane concentrate, scaling could not be prevented (albeit delayed for some time) with intermittent permeate flushing. A fractional 25-1 factorial design was used to determine which factors had the most significant effect on total production time and permeate production rate, testing five factors: 1) flushing frequency, 2) flushing volume, 3) permeate soak time, 4) permeate flux and 5) instantaneous recovery. The ANOVA analysis showed that total production times were, not surprisingly, primarily affected by the permeate flux, where operation at 24 LMH resulted in a lower net permeate production between 3.0 - 4.2 L, compared to 7.6 - 9.7 L at 12 LMH. Higher permeate fluxes clearly resulted in higher levels of concentration polarisation at the membrane surface, thus increasing the propensity for membrane scaling. Flushing frequency and instantaneous recovery also affected the net permeate production, where 6 h-1 and 10 % were the optimal values respectively within the range of test conditions. The lowest permeate production rate resulted in the highest net permeate volume production (i.e. also longest total production time), confirmed by a least squares regression. In summary: This study showed that periodic permeate flushing could delay the membrane scaling process. However, it failed to prevent membrane scaling completely when operating the system with supersaturated calcium sulphate solutions in the absence of antiscalants. The flushing technique effectively delayed the onset of precipitation, but scaling eventually occurred if the lab-scale RO system was operated in concentrate recycle mode with oversaturated feed solutions (SIg = 1.2). Additional experiments at different cross-flow velocities during permeate flushing, while using an optimised RO test cell flow channel design, are recommended for future studies. / AFRIKAANSE OPSOMMING: Gedurende die ontsouting van brakwater deur tegnieke soos tru-osmose (TO), is ʼn maksimum herwinning van water noodsaaklik om die produksie, en die gepaardgaande kostes van verwydering, van die sout/brak neweproduk te minimeer. Soos die herwinning van water verhoog, so ook verhoog die konsentrasie van moeilik-oplosbare soute (soos bariumsulfaat, kalsiumsulfaat) in die sout konsentraat stroom, totdat die soute uiteindelik superversadiging bereik. Hierdie superversadiging gebeur veral naby die membraanoppervlak, waar dit lei tot ʼn verhoogde kans van presipitasie en skaalvorming. Om dit te voorkom word die voerwater na ʼn TO stelsel tipies gedoseer met antiskaalmiddels. Hierdie antiskaalmiddels verlaat die stelsel saam met die konsentraat, waar hulle gevolglike die presipitasie van soute bemoeilik. Presipitasie van soute uit die konsentraat kan tipies gebruik word om die vlak van superversadiging in die konsentraat te verlaag, waarna verdere TO behandeling gebruik word om selfs ʼn hoër algehele waterherwinning te bewerkstellig. Die doel van hierdie studie was om die vatbaarheid van die vermindering van kalsiumsulfaat (gips) skaalvorming in die afwesigheid van antiskaalmiddels op TO membrane te toets. Dit is bewerkstellig deur ʼn laboratoriumskaal TO eenheid te voer met ʼn superversadigde kalsiumsulfaat oplossing en die membraan periodies met skoon produkwater (permeaat) te was. Die algehele waterherwinning is verhoog deur met ʼn tussenstap die versadigingsvlak van gips in die konsentraat te verlaag, waarna dit hersirkuleer is na die voertenk. Sodoende is ʼn multi-stadium TO stelsel nageboots, soos dit tipies in hoë herwinningsaanlegte, soos met die herwinning van suur mynwater (E: acid mine drainage, AMD), gebruik word. ʼn Verlaging in superversadiging van die konsentraat in die tussenstap is behaal deur die konsentraat direk aan gipskristalle bloot te stel om presipitasie te bewerkstellig in die afwesigheid van enige antiskaalmiddels. Gedurende eksperimente het die soutkonsentrasie op die membraanoppervlak in die TO eenheid superversadigingsvlakke vêr oorskry, as gevolg van die natuurlike konsentrasie proses en die bekende konsentrasie polarisasie oppervlaksverskynsel. Om hierdie superversadiging teen te werk is periodiese saamstroom spoeling van die membraan met skoon produkwater uitgevoer. In teorie het die periodiese spoeling die hoogs gekonsentreerde oplossing van die membraan oppervlak verwyder voor skaalvorming kan plaasvind. Verskillende spoelpatrone is ondersoek om die doeltreffendheid van die spoeling te bepaal. Om die eksperimente uit te voer is ʼn laboratoriumskaal ontsoutingsaanleg met ʼn maklik verwyderbare 0.106 m2 plat-vel poli-amied TO membraan ontwerp en gebou. Die aanleg kan vloeistof voertempo’s tussen 12-24 L/h hanteer en skoon produkwater teen 12-24 LHM lewer. Die superversadigde voer oplossings, soos gebruik in die meerderheid van die eksperimentes is voorberei deur natriumsulfaat en kalsiumchloried-dihidraat soute te meng in gedemineraliseerde water, tot ʼn soutgehalte van ± 5300 mg/L TDS bereik is. Hierdie soutgehalte stem ooreen met ʼn gips versadigingsindeks (E: gypsum saturation index, SIg) van 1.2. Die skoon produkwater totale produksietyd en netto produksie, asook die membraan vloed afname, is gebruik as veranderlikes om die spoel doeltreffendheid tussen eksperimentele lopies te vergelyk. Aanvanklike toetse het getoon dat skalering voorkom is by effens onderversadigde (SIg = 0.9) en effens superversadigde (SIg = 1.1) voer oplossings met die onderskeie spoel frekwensies van 12 en 2.4 h-1, (terwyl die aanleg in algehele hersirkulasie bedryf is, m.a.w. wanneer beide die konsentraat en produkwater gedurig na die voertenk hersirkuleer word). ʼn Effens-superversadigde eksperiment is ook sonder spoeling uitgevoer vir 24 uur. In hierdie geval het skaalvorming binne twee tot drie uur gebeur, soos bevestig deur ʼn skerp afname in die membraan vloed. Skaalvorming kon nie verhoed word terwyl die aanleg bedryf word met superversadigde (SIg = 1.2) voeroplossings en slegs konsentraat hersirkulasie nie (m.a.w. skoon produkwater word opgevang), alhoewel skaalvorming vertraag kon word. Hierdie operasie het tot beduidend meer gekonsentreerde oplossings in die membraan gelei. Om te bepaal watter faktore die grootste invloed op totale produksietyd en netto produksie van skoon produkwater het, is ʼn fraksionele faktoriaalontwerp van 25-1 uitgelê wat vyf faktore toets, naamlik: 1) spoel frekwensie, 2) spoel volume, 3) skoon produkwater weektyd, 4) membraanvloed en 5) oombliklike herwinning. ʼn AVOVA analise het getoon dat totale produksietyd hoofsaaklik deur membraanvloed beïnvloed is, soos verwag kan word. Dit word gestaaf deurdat die aanleg, bedryf teen 24 LMH, slegs 3 - 4.2 L netto produkwater gelewer het, teenoor 7.6 - 9.7 L by 12 LMH. Hoër membraan vloedtempo’s het tot hoër vlakke van konsentrasie polarisasie op die membraanoppervlak gelei, wat ʼn groter neiging tot skaalvorming tot gevolg gehad het. Spoelfrekwensie en oombliklike herwinning het ʼn invloed op die netto produksie van skoon produkwater gehad, met 6 h-1 en 10 % as die onderskeie optimale waardes. ʼn Kleinstekwadraat regressie het aangedui dat die laagste produksietempo van skoon produkwater die hoogste netto produksie van skoon produkwater gelewer het, (asook die langste produksietyd). In opsomming: Hierdie studie het getoon dat gereelde spoeling met skoon produkwater die membraan skaalproses kan vertraag. Gedurende bedryf met superversadigde kalsiumsulfaat oplossings sonder enige antiskaalmiddels is daar gevind dat skaalvorming nie geheel en al vermy kon word nie. Die spoeltegniek, soos gebruik in hierdie studie, het die aanvang van skaalvorming in die laboratorium skaal TO eenheid vertraag, maar bedryf met konsentraat hersirkulasie en superversadigde oplossings (SIg = 1.2) het steeds skaal gevorm. Bykomende eksperimente teen verskeie kruisvloei snelhede gedurende die spoel stap word aanbeveel vir toekomstige studies.

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: This investigation focused on the marine components of large direct seawater intake and brine discharge systems for seawater desalination plants, with the main aim to provide an overall design approach for these components. Due to its complexity, an overall and systematic design approach, addressing all the components (feedwater requirements, plant technology, marine structures and environmental issues) is required to ensure an optimum design. A literature review was done on the various desalination technologies, the main components of a seawater desalination plant, as well as the physical, hydraulic, operational and environmental issues regarding seawater extraction facilities, marine pipelines and discharge structures (diffuser). In order to obtain practical input to the development of an overall design approach, information regarding the marine structures of ten of the largest existing seawater desalination plants throughout the world were obtained and compared with each other and the available technologies. By way of example, the recently designed marine components of a new seawater reverse osmosis desalination plant in Namibia were reviewed and, as part of this thesis, alternative conceptual concepts which will include two additional components (sump and brine reservoir) were designed. The alternative design was compared with the actual design in order to determine the feasibility of the alternative in terms of operation and cost and subsequently provide input to the overall design recommendations. Furthermore, from the literature review it seems that there are still significant uncertainties regarding the required performance of a brine (dense) outfall and this required more attention in terms of environmental and hydraulic performance. Based on the Namibian plant, the diffuser configuration was analysed in terms of its hydraulic and environmental performance and subsequently some general guidance with specific respect to a brine diffuser was developed, which in turn formed part of the overall design approach for the marine components. Finally, the design approach for seawater intake structures, brine outfalls and the connecting marine pipelines is provided in the form of flow diagrams. / AFRIKAANSE OPSOMMING: Hierdie ondersoek handel oor die mariene komponente van groot en direkte toevoer van seewater en die sout-uitvloeisisteme van ontsoutingsaanlegte van seewater. Die doel is om ‘n oorsigtelike ontwerpbenadering vir hierdie component te verskaf. As gevolg van die kompleksiteit, is ‘n oorsigtelike en sistimatiese benadering, wat al die komponente (vereistes vir toevoerwater, tehnologie by die aanleg, mariene omstandighede en omgewingsfaktore) in ag neem noodsaaklik om die beste ontwerp te verseker. ‘n Literêre oorsig is gedoen ten opsigte van die tegnologie van verskeie ontsoutingsmetodes, die hoofkomponente van ‘n seewater-ontsoutingsaanleg, asook die fisiese, hidrouliese, operasionele en omgewingskwessies rakende die fasiliteite om die seewater te onttrek, die mariene pyplyne en die strukture vir die afvloei. Ten einde die optimum ontwerp te ontwikkel, is inligting oor die tegnologie en strukture van tien van die grootste bestaande onsoutingsaanlegte in die wêreld bekom, bestudeer en vergelyk Hulle is met mekaar vergelyk, asook met beskikbare tegnologie. As ‘n voorbeeld is die nuut ontwerpte mariene komponente van die nuwe ontsoutingsaanleg in Namibië, waar ontsouting d.m.v. omgekeerde osmose gedoen word ondersoek en as deel van hierdie tesis, is ‘n alternatiewe konsep, wat twee bykomende komponente – ‘n opvangput en reservoir vir die afloop – ontwerp. Hierdie alternatiewe ontwerp is met die werklike aanleg vergelyk om die uitvoerbaarheid van die onderneming en die koste daaraan verbonde te toets. Dit is gebruik as aanbeveling vir die oorhoofse ontwerp. Uit die literêre oorsig blyk dit dar daar nog groot onsekerheid is oor die vereistes van die (digte) waterafloop en dat meer aandag aan die omgewings- en hidrouliese aspekte gegee moet word. Met die Namibiese aanleg as voorbeeld, is die struktuur van die spreiers t.o.v. hidrouliese werkverrigting en die omgewing ontleed. Voortspruitend daaruit is algemene riglyne vir ‘n spesifieke spreier vir afloopwater ontwikkel, wat op sy beurt weer deel vorm van die oorhoofse ontwerp vir mariene komponente. Laastens is die ontwerp vir die strukture vir seewater-invloei, die afloopwater en die mariene verbindingspyplyne as vloeidigramme aangetoon.