Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In this work we present a computational study of the properties of water transport across membranes formed of carbon nanotubes (CNT) armchair with different diameters, when subjected to pressure gradients 80-400 MPa. This study was made through the implementation of the method of molecular dynamics code NAMD. The model adopted for our simulation consists of a unit cell containing water molecules that will cross through the reverse osmosis process, 9 carbon nanotubes 20Å in length, using the periodic boundary conditions. The results show a quadratic dependence of the flow on the diameter of the nanotubes. CNT in smaller diameters, the dependence of the flow on the pressure applied is small. This behavior differs for larger diameter nanotubes, where the flow increases linearly with pressure. When analyzing the mean square displacement (MSD) as a function of the diameter of the CNT, we found the occurrence of a regime of ballistic diffusion for all cases. The effect of CNT on the diameter of MSD for the same pressure gradient indicates differences between the coefficients of diffusion of the bulk water and CNT. We found evidence of the occurrence of a non-Fickian transport for this condition of confinement. The analysis flow of water molecules suggests that the CNT membranes can apparently be competitive systems with existing techniques and used on the market for water purification. / Neste trabalho apresentamos um estudo computacional das propriedades de transporte da água através de membranas formadas por nanotubos de carbono (NC) armchair de diferentes diâmetros, quando submetidos a gradientes de pressão de 80 a 400 MPa. A realização deste estudo se deu através da implementação do método de Dinâmica Molecular ao código NAMD. O modelo adotado para a nossa simulação consta de uma célula unitária contendo moléculas de água que irão atravessar, através do processo de osmose reversa, 9 nanotubos de carbono de 20Å de comprimento, valendo-se das condições periódicas de contorno. Os resultados obtidos demonstram uma dependência quadrática do fluxo com o diâmetro dos nanotubos. Em NC de diâmetros menores, a dependência do fluxo com a pressão aplicada é pequena. Este comportamento difere para nanotubos de diâmetros maiores, onde o fluxo aumenta linearmente com a pressão. Quando analisado o deslocamento quadrático médio (MSD) como função do diâmetro dos NC, verificamos a ocorrência de um regime de difusão balístico para todos os casos. O efeito do diâmetro dos NC sobre o MSD, para um mesmo gradiente de pressão, indica diferenças entre os coeficientes de difusão da água bulk e NC. Foram encontradas evidências de ocorrência de um transporte não Fickiano para esta condição de confinamento. A análise da vazão das moléculas de água sugere que as membranas de NC podem, aparentemente, ser sistemas competitivos com as técnicas já existentes e utilizadas no mercado para purificação de água.

Abstract Industrial wastewaters are complex waters, which can contain a large variety of compounds such as heavy metals and salts as well as nutrients, e.g. nitrogen compounds and phosphorous. Prevention of wastewater formation is not always possible and therefore new more efficient water treatment techniques are needed. Legislation also supports the use of more efficient water treatment techniques, which can lead to better purification results and the recovery of valuable compounds from wastewaters. One technique, which has been of interest, is membrane technology. Membrane technology can separate heavy metals, salts and nutrients effectively, also at low concentrations, which is not always possible with conventional water treatment methods. The main disadvantage of membrane technologies is membrane fouling, which reduces the membrane permeate flux and separation efficiency. In this thesis membrane techniques were combined into hybrid processes to increase the efficiency of water treatment to reduce fouling and to widen the application areas of membrane technologies, as well as to increase the awareness of the benefits gained when using hybrid membrane processes in wastewater treatment. Three different hybrid membrane processes were applied. Catalytically active nanofiltration membranes were used to purify real mine wastewaters from harmful compounds, including sulphate. A catalytic layer reduced the membrane fouling tendency. Micellar-enhanced ultrafiltration was applied successfully to the separation of heavy metals from phosphorous-rich wastewater of a fertilizer company to achieve selective separation. In addition, reverse osmosis and membrane distillation were applied to the concentration of heavy metals, a metalloid and nitrogen compounds containing synthetic wastewater efficiently. High volume concentration factor was achieved with the RO-MD process. In this thesis high heavy metal, metalloid, and salt removal efficiencies were achieved with all hybrid membrane techniques. Hybrid membrane techniques were also categorized based on their properties. The study provides new knowledge on hybrid membrane techniques in the removal of inorganic compounds from industrial waters. / Tiivistelmä Teollisuuden jätevedet voivat sisältää kohonneita haitta-ainepitoisuuksia, kuten raskasmetalleja ja suoloja. Teollisuuden jätevedet voivat sisältää myös ravinteita, esimerkiksi typen yhdisteitä ja fosforia. Jätevesien syntymistä ei aina voida ennaltaehkäistä, ja siksi uusille entistä tehokkaammille vedenkäsittelymenetelmille on tarvetta. Lisäksi myös lainsäädäntö vaatii entistä tehokkaampaa vesien puhdistusta, mikä osaltaan edistää entistä tehokkaampien puhdistustekniikoiden kehitystä sekä erotettujen aineiden talteenottoa. Yksi aktiivisen tutkimuksen kohteena oleva vesienkäsittelyssä käytetty menetelmä on kalvoerotustekniikka. Kalvoerotustekniikoilla voidaan erottaa tehokkaasti raskasmetalli-ioneja, sulfaattia ja ravinteita, kuten typpiyhdisteitä teollisuuden jätevesistä myös alhaisissa pitoisuuksissa, missä yleisesti käytettävät menetelmät voivat olla tehottomia. Yksi kalvoerotusmenetelmien ongelma on kalvojen likaantuminen, mikä alentaa kalvojen erotustehokkuutta ja vähentää tuottavuutta. Tässä tutkimuksessa kalvojen likaantumistaipumista on vähennetty yhdistämällä kalvoerotustekniikoita muihin erotusmenetelmiin hybriditekniikoiksi. Tässä työssä on tutkittu kolmea eri hybridimenetelmää. Sinkkioksidilla pinnoitettuja nanosuodatuskalvoja tutkittiin ja verrattiin kaupallisiin nanosuodatuskalvoihin kaivosteollisuuden vesien puhdistuksessa mm. sulfaatista. Katalyyttipinnoite muutti kalvoja vähemmän likaantuviksi, ja näin menetelmän tehokkuus parani. Miselliavusteisella ultrasuodatuksella erotettiin fosforipitoisesta lannoitetehtaan jätevedestä raskasmetalleja selektiivisesti, ja näin mahdollistettiin fosforin uudelleenkäyttö. Kolmannessa tutkimuskohteessa konsentroitiin kalvotislauksen ja käänteisosmoosin yhdistelmällä raskasmetalli- ja typpiyhdisteitä sisältävää synteettistä jätevettä pieneen tilavuuteen. Työssä saavutettiin korkeita raskasmetallien ja suolojen erotustehokkuuksia kaikilla käytetyillä tekniikoilla. Työssä arvioitiin myös yhteenvetona erilaisten hybridimembraanitekniikoiden eroja ja ominaisuuksia ja tekniikoita jaoteltiin menetelmien ominaisuuksien mukaan. Työ antoi uutta tietoa hybridimembraanitekniikoista epäorgaanisten aineiden erotuksessa teollisuuden vesistä.

Komati Power Station has installed a membrane plant consisting of ultrafiltration, double pass reverse osmosis and continuous electro-deionisation to treat cooling tower blowdowns in order to produce demineralised water and to conduct sidestream chemistry control of the cooling water circuit. This plant has replaced the existing ion-exchange plant that was used for the production of demineralised water and thus serves to reduce the loading of mobile salts in the ash dam (90% reduction) by eliminating regeneration effluent from the ion-exchange plant. Due to oil contamination in the cooling water circuit (when oil from oil coolers leaks into the cooling water), the membrane plant was also designed to operate on raw water from either the Nooigdedacht or the Vygeboom Dam or a blend of both dams. This is considered to be an emergency intervention under abnormal conditions to prevent possible irreversible fouling of the membranes due to oil in the cooling water. The Nooigtedach Dam water contains high concentrations of organic matter and is also enriched with nutrients due to raw sewage influent into the Dam water. This poses a challenge with regard to treatment of the high fouling feed water on the membrane plant. Natural organic matter in water has the ability to foul reverse osmosis membranes. This adversely affects the operation of the reverse osmosis process. However, very little information is available regarding the fouling characteristics of natural organic material in the raw and cooling water at Komati Power Station for the reverse osmosis membranes. Therefore, a pilot study was undertaken to determine the influence of natural organic matter on membrane fouling, to optimise the process for the removal of natural organic matter and to assess the ability of two different reverse osmosis membranes to effectively treat the high fouling feed water at Komati Power Station. The ability of a polyethersulphone hollow-fibre ultrafiltration membrane system was first evaluated to remove natural organic matter in the feedwater, by conducting pilot tests, initially without coagulation of the raw water and thereafter with in-line coagulation for organics removal. Jar tests were conducted in the laboratory to determine the most suitable coagulant and dosage for turbidity and natural organic matter removal. Various coagulants were tested and, based on the results of the jar tests, a coagulant (U3000) was identified based on optimal removal of both total organic carbon and turbidity at a dosing level of 20 mg/L. During the operation of the ultrafiltration pilot plant, permeate flow; feed pressure and feed temperature were monitored. Performance of the ultrafiltration membrane was monitored in terms of flux versus time for operation with and without a coagulation process. The results indicated that there was very little total organic carbon removal (maximum removal of 4%) without coagulation and a slight decrease in flux. The flux declined as a result of fouling but could be recovered by performing hydraulic backwashes and CEB procedures. Permeate flux, however, could be maintained at about 90 Lmh (from 642 hours of operation). Since most of the organics passed through the ultrafiltration membrane, it was concluded that the loss in flux was due to colloidal fouling of the membrane. This was observed when the operation was carried out using raw water as feed as well as when cooling water was used. The total organic carbon removal increased to 30% when the plant was operated with inline coagulation. The flux remained relatively stable during the first 600 hours of operation and only decreased significantly during the last 200 hours of operation as a result of fouling. The reduction in flux prior to cleaning was less than the 15% (maximum flux decline of 9.9% during the test period) which is acceptable according to the industry norm of 15%. It appeared that flux could be maintained at around 90 Lmh which was about the same as when no coagulant was applied. The 30% total organic carbon reduction that was obtained was not sufficient to reduce the organics to the level of 6mg/L dissolved organic carbon that was specified by the membrane manufacturer for the standard brackish water reverse osmosis membrane. Two reverse osmosis membranes – the standard brackish water reverse osmosis membrane (BW30-2540) and the extra-low-fouling membrane (BW30XFR-2540) – were assessed in terms of their ability to remove dissolved organic carbon, ease of cleaning of the membrane and the ability to recover flux after cleaning. This was done to establish which membrane is more suited to Komati’s high-fouling feedwater. The evaluation of the performance of the two reverse osmosis membranes was conducted using pre-treated water (filtered water after in-line coagulation, anti-scalant and biocide dosing) as well as using water that was not pre-treated. During operation (under both conditions), the normalised permeate flux, conductivity, dissolved organic carbon and organics absorbing at UV254 were monitored. It was established that in terms of flux decline that the extra low-fouling membrane gave slightly superior performance to that of the standard membrane, achieving longer production runs (up to 5 days compared with 3 days achieved by the standard brackish water membrane) without requiring chemical cleaning. The low fouling membrane achieved better CWF recovery after the cleaning cycles (81.26% Lmh of the virgin membrane on the occasions when there was flux loss) compared to the standard membrane (restored to 77.35% of CWF of the virgin membrane) when using untreated feed water. This performance improved when pre-treated feed water was used and the low fouling membrane’s CWF regained after the CIP was 95.89% which was within the industry norm of a flux recovery of 95%, indicating that the CIP had been effective. It was determined that the TOC rejection of the low-fouling membrane was higher (average TOC rejection of 97%, maximum TOC rejection of 99%) than that of the standard membrane (average TOC rejection of 95.3%, maximum TOC rejection of 97%). Preliminary efforts to optimize the pre-treatment for organics removal in order to reduce organic loading for the RO membranes confirmed that the use of granular activated carbon and use of an organic scavenger resin might not be economically feasible due to the relatively quick TOC breakthrough (8910BV, approximately 18000BV and less than 18000BV for the Filtrasorb 300, Filtrasorb 400 and organic scavenger resin, respectively). Although further investigations should still be conducted, the preliminary results indicate that it would be beneficial to also identify other options that can be further investigated for optimization of organics removal at Komati Power Station. Decline in the normalised flux as well as the evidence of biofouling were witnessed during the pilot operation suggesting that the membranes were fouled. Autopsies were performed on both membranes to identify foulants responsible for the decline in flux that was observed during the pilot study. The results did not indicate an organic foulant on the membrane surface. Biofouling should however, be monitored in the main plant as this was suspected to have resulted in the flux decline during the pilot study. The low fouling membrane demonstrated a better capability to treat the Komati raw and cooling water and would be expected to achieve lower operating costs for the plant (CIP costs and membrane replacement costs) while achieving better organics removal and it is therefore recommended that the low-fouling membranes be used at Komati Power Station as they are superior to the standard membrane and the cost of the low-fouling membranes is comparable to that of the standard membrane. While this would provide somewhat better performance than that obtained with the standard brackish water membranes, it is proposed that further investigation into pre-treatment optimization for organics removal as well as more efficient cleaning solutions be investigated to improve the performance and economics of the main water treatment plant at Komati power Station. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Chemical Engineering / unrestricted

Um método baseado na extração de rRNA, seguido de RT-PCR rRNA 16S, clonagem e ARDRA foi otimizado e validado para a identificação das bactérias ativas em biofilmes. O método foi analisado primeiro com consórcios artificiais de três organismos. As etapas de clonagem e RT não causaram variações importantes na composição destes consórcios, do contrário da etapa de PCR, onde foi necessária a redução de 30 para 10 ciclos para limitar a distorção da proporção de templates. A análise de biofilmes reais indicou que clones dominantes podem ser identificados com o critério de ocorrência de >2% na biblioteca, mas que a reprodutibilidade de análises ainda é insatisfatória, possivelmente devido a fatores como a micro heterogeneidade espacial do biofilme, viés na reação de PCR e formação de mais de um clone de ARDRA por organismo. O armazenamento do biofilme a -20 °C por 2 meses não levou à alterações expressivas em sua composição. O perfil de clones detectado com o kit (Mo Bio) de extração de RNA foi muito diferente do perfil detectado com o método otimizado neste trabalho. / A method based on extraction of rRNA, followed by RT-PCR of 16S rRNA, cloning and ARDRA was optimized and validated for identification of bacteria active in biofilms. The method was first tested with artificial three-membered consortia. Cloning and RT did not lead to significant changes in the composition of the artificial consortia, but a reduction in cycle number in the PCR reaction from 30 to 10 was necessary for limiting the distortion in the proportion of amplicons relative to that of the templates. Analysis of real biofilms revealed that clones from active organisms occurred in frequencies >2% in the clone library, but reproducibility of analysis was unsatisfactory, probably due to factors such as the spatial heterogeneity of colonization of biofilms by microbes, PCR bias and more than one ARDRA clone per organism. Storage of biofilm samples at -20 °C for 2 months did not lead to important changes in composition. Very different clone profiles were obtained in the analysis of the same biofilm sample with the optimized method and with a kit (Mo Bio) for extraction of RNA.

Unrestricted use of reclaimed secondary effluents for irrigation is a major goal in countries suffering from water shortage. Reverse osmosis desalination is used to provide high quality waters with reduced salinity. In order to allow water production with high economic efficiency, fouling in the membrane installation needs to be minimized. Biofouling, caused by microorganisms synthesizing high-molecular biofilms, is of major concern. Biofouling reduces the water production rate and thus increases the costs of the process. Deeper knowledge on its formation and its impact on membrane performance is needed. This is relevant especially for large-scale treatment plants, where process conditions change over length and time and influencing factors on fouling formation occur in combination. Thus, in the present thesis a membrane test cell was developed which enables the investigation of biofouling under validated, representative conditions of full-scale modules. Biofouling was studied in order to determine its impact on membrane performance. Also, appropriate, cost-effective pre-treatment prior to the reverse osmosis process minimizes fouling. Therefore, biofiltration and its suitability as stand-alone pre-treatment was studied when reusing secondary effluents with reverse osmosis. The developed membrane test cell of 1 m length can be assembled with further test cells to simulate a spiral wound module alone, as well as several modules in series in a pressure pipe. The test set-up enables the systematic study of fouling formation integrative over the full length of industrial spiral wound modules. All performance parameters (feed channel pressure drop, permeability/flux, and salt passage) can be monitored over the full length and locally connected to accumulated foulants (non-destructive fouling diagnosis). Validation studies demonstrated that the hydraulic conditions (relationship between pressure drop and flow velocity, as well as the flow profile) are exactly as in real spiral wound modules. Each test cell is a representative, validated system of full-scale dimensions and hydraulics. It was further found that for fouling formation investigations, feed spacers with the same thickness as the feed channel height need to be used. In this way, accurate experimental measurements, especially of feed channel pressure drop, are ensured. With the developed test cells, the impact of biofouling on membrane performance was determined under conditions similar to practice. Biofouling resulted in a decline of all membrane performance parameters. Feed channel pressure drop was affected earliest and most severely, indicating its suitability as a sensitive biofouling monitoring parameter. Salt rejection was moderately impacted by biofouling and influenced by several process parameters, reducing its applicability as monitoring parameter. It was further found, that most biofilm accumulated in the lead parts of the membrane test cells with a declining gradient towards the tail sections. The gradient of biofouling over the length of the membrane installation was directly referred to the declining availability of easily assimilable substrate. It emphasizes the importance to reduce the concentration of biodegradable nutrients in the feed to the membrane installation as suitable strategy to restrict biofouling. The high amount of biofilm deposits in the lead parts caused feed channel pressure drop increase over the lead test cell and affected negatively the performance of the downstream test cells: The tail test cells showed a moderate decline for the permeability (flux) and salt rejection. Biofiltration improved the quality of secondary effluents as tertiary treatment. It successfully reduced the load of substances (microbes, dissolved organic matter, biopolymers, particles) reportedly contributing to fouling of subsequent membrane processes. Especially biopolymers of secondary effluents, which are major membrane foulants, were identified to be completely biodegradable. The biopolymers were estimated to be of colloidal size. Yet, the removal of these organics was suggested to be completely caused by biodegradation; neither filtration nor adsorption mechanisms played a role to retain biopolymers and dissolved organic carbon within the biofilter. However, a combined study of biofiltration and reverse osmosis revealed, that the improving effect of biofiltration as pre-treatment on membrane performance was lower than expected. Although, both biofouling and organic fouling were reduced on the reverse osmosis membrane, only marginal improvement on performance parameters was found. The adsorption of small non-biodegradable substances on the membrane as an organic fouling layer in the early stages of the process, as well as the difference in fouling layer composition were probably reasons for the findings. Thus, the successful application of biofiltration as pre-treatment is highly depending on the feed water source and the foulant layer formation. For the present case biofiltration as stand-alone pre-treatment is not recommended; a combination of biofiltration with subsequent e.g. flocculation and UF could be more beneficial.

>Magister Scientiae - MSc / Coal combustion accounts for over 40 % of the world's energy production and this figure is projected to increase with increasing human population and industrialization. The combustion of coal leads to the generation of waste products such as fly ash (FA), brine from water treatment, bottom ash, slag, flue gas desulphurization products (FGD) and gas emissions such as N20, and C02. The emissions contribute to air pollution and global warming, while FA, brines, and FGD are possible soil and water pollutants. In order to minimize the environmental impact of coal combustion, mitigation of the effects of coal burning processes such as the waste products (FA, brine, bottom ash, slag and FGD) and gas emissions is required. This study investigated utilization of the Secunda FA (class F) and reverse osmosis (RO) Tutuka brine to sequester C02 in an attempt to make coal power production more environmentally sustainable. It was hypothesized that South African FA and brine could sequester C02 through mineral carbonation. A statistical approach was undertaken to optimize the % CaC03 formed from FAlbrine/C02 interaction with input parameters of temperature, pressure, particle size and solid/liquid ratio (S/L) being varied. The ranges adopted for the input parameters were: temperature of 30°C or 90 °C; pressure of 1 Mpa or 4 Mpa; four particle sizes namely bulk ash, > 150 11m, < 20 11m and 20 urn- 150 11m particle size range; S/L ratios ofO.1, 0.5 or 1. The FA! brine dispersions were carbonated in a high pressure reactor varying the above mentioned input parameters. The fresh Secunda FA of various size fractions was characterized morphologically using scanning electron microscopy, chemically using X-ray fluorescence and mineralogically using qualitative X-ray diffraction. The carbonated solid residues on the other hand were characterized using quantitative X-ray diffraction, scanning electron microscopy, thermal gravimetic analysis and Chittick tests. The raw brine from Tutuka together with the carbonation leachates were characterized using inductively coupled mass spectrometry and ion chromatography. Total acid digestion was carried out to evaluate the differences in the total elemental content in both the fresh ash and the carbonated solid residues. The results suggested that South African FA from Secunda belongs to class F based on the CaO content as well as the total alumina, silica and ferric oxide content, while the RO brine from Tutuka were classified as NaS04 waters. Mineral carbonation occurred and ranged between 2.75 % and 6.5 % of CaC03 depending on the input parameters. Two polymorphs of CaC03 were identified in the carbonated residues i.e. calcite and aragonite. The carbonated ash/brine leachates were cleaner with respect to major and trace element concentration compared to raw brine thus the carbonation process could be used to improve the quality of brines generated in the power industry. Removal of the major elements from brine was as follows Ca-74.8 %, Na- 28.7 %, Mg- 98 %, K- 82.9 %, S04- 20.8 %. Hundred percent removal was observed for traces of Fe, Al, Mn, Cu, Zn, Pb, Ni, As, Ti, Sr, Se, Si and N03. However Mo, V, B, and Cl concentrations increased by 72.5 %, 94 %,48.2 % and 7.2 % respectively after carbonation at 90°C, 4 Mpa, S/L ratio of 1 using the bulk ash. The parameters found to be of most significance in the carbonation process were the main effects of temperature, particle size and S/L ratio while the interactions of temperature and particle size as well as the interaction of temperature with S/L ratio were also found to be significant. The statistical approach led to a clear understanding of the effect of each input parameter as well as the ansmg interactions. The conditions of 90°C, 4 Mpa, using bulk ash at a S/L ratio of 1 resulted in the highest yield of % CaC03 with a value of 6.5 %. Theoretically one ton of Secunda FA containing 9.2 % of CaO could sequester 0.083 tons of C02. With the optimized protocol developed in this study bearing in mind that the carbonation efficiency is 75.54%, 1 ton of Secunda FA could sequester 0.062 tons of CO2. This translates to 0.65 % of CO2 produced annually at Secunda plant being sequestered in the FAlbrine dispersions. In other words, 16 tons of FA are required to sequester a ton of C02 annually. It was also observed that carbonation using brine resulted in higher carbonation efficiency than carbonation using water as the Ca2+ component in the brine contributed towards the Ca 2+concentration.

The Master’s Thesis deals with the application of membrane technologies in the production of drinking water from the effluent of a municipal wastewater treatment plant (WWTP). There were two types of pressure-driven membrane processes selected – ultrafiltration and reverse osmosis, to achieve water production of the required quality. For the needs of the diploma thesis, an already existing pilot-scale membrane unit of the ASIO TECH Company l.t.d. was used. There were 44 physical, chemical and microbiological parameters observed to assess the quality of the produced water and also the input water (effluent from the WWTP). None of the afore mentioned parameters exceeded the limit values, more specifically the highest limit values issued by the Decree 70/2018 Coll. However, the produced water cannot be considered as drinking water because of its low mineralisation. Before its potential application in practise, it is therefore necessary to choose an appropriate method of remineralisation as well as to follow all the other legislative requirements for the drinking water, which have already been out of the scope within the Master’s Thesis.

A modified two-element membrane pressure vessel assembly has been used to monitor process operational changes in a full-scale reverse osmosis (RO) water treatment plant (WTP). This study evaluated the effectiveness of the assembly as an on-line monitoring device intended to detect scale formation conditions when connected to an operating RO process train. This study was implemented to support the requirements of a larger University of Central Florida (UCF) research project ongoing at the city of Sarasota’s Public Works and Utilities (City) water treatment facilities located in Sarasota, Florida. During the time-frame of this study, the City was in the process of eliminating their sulfuric acid feed from the pretreatment system of their existing 4.5 million gallon per day (MGD) RO membrane process. The City was motivated to eliminate its dependence on sulfuric acid to reduce operating costs as well as reduce operation health and safety risks associated with the use of the acid as a pretreatment chemical. Because the City was concerned with secondary process impacts associated with acid elimination, additional measures were desired in order to protect the full-scale process. This thesis reports on the design, fabrication and installation of a third-stage two membrane element pressure vessel “canary” sentinel monitoring device (Canary), its effectiveness as an online scaling monitor during full-scale acid elimination, and presents the results of the study. The Canary sentinel device was controlled using the normalized specific flux of the two membrane elements fed by a portion of the second stage concentrate of one of the City’s full-scale RO process skids. Although the Canary demonstrated the ability to detect changes in an RO process operation, scaling did not occur under the conditions evaluated in this study. An autopsy of one iv of the Canary elements revealed that no scaling had occurred during the acid elimination process. Therefore, the Canary was found to be useful in its function as a sentinel, even though no scaling was detected by the device after acid elimination at the City’s full-scale plant had been accomplished.

The use of brackish water and seawater desalination for augmenting potable water supplies has focused primarily on pre-treatment, process optimization, energy efficiency, and concentrate management. Much less has been documented regarding the impact of post-treatment requirements with respect to distribution system. The goals of this study were to review current literature on post-treatment of permeate water, use survey questionnaires to gather information on post-treatment water quality characteristics, gather operation information, review general capital and maintenance cost, and identify appropriate "lessons learned" with regards to post-treatment from water purveyors participating in the Project. A workshop was organized where experts from across the United States, Europe and the Caribbean active in brackish and seawater desalination, gathered to share technical knowledge regarding post-treatment stabilization, identify solutions for utilities experiencing problems with post-treatment, note lessons learned, and develop desalination water post-treatment guidelines. In addition, based on initial workshop discussions, the iodide content of reverse osmosis and nanofiltration permeate from two seawater desalination facilities was determined. The literature review identified that stabilization and disinfection are required desalination post-treatment processes, and typically are considerations when considering 1) blending, 2) re-mineralization, 3) disinfection, and 4) materials used for storage and transport of product water. Addition of chemicals can effectively achieve post-treatment goals although considerations relating to the quality of the chemical, dosage rates, and possible chemical reactions, such as possible formation of disinfection by-products, should be monitored and studied. The survey gathered information on brackish water and seawater desalination facilities with specific regards to their post-treatment operations. The information obtained was divided into seven sections 1) general desalination facility information, 2) plant characteristics with schematics, 3) post-treatment water quality, 4) permeate, blend, and point of entry quality, 5) post-treatment operation, 6) operation and maintenance costs, 7) and lessons learned. A major consideration obtained from the survey was that facilities should conduct post-treatment pilot studies in order to identify operational problems that may impact distributions systems prior to designing the plant. Effective design and regulation considerations will limit issues with permitting for the facility. The expert workshop identified fourteen priority issues pertaining to post-treatment. Priority issues were relating to post-treatment stabilization of permeate water, corrosion control, disinfection and the challenges relating to disinfection by-product (DBP) formation, water quality goals, blending, and the importance of informing the general public. For each priority issues guidelines/recommendations were developed for how facilities can effectively manage such issues if they arise. One of the key priorities identified in the workshop was related to blending of permeate and formation of DBPs. However, it was identified in the workshop that the impact of iodide on iodinated-DBP formation was unknown. Consequently, screening evaluations using a laboratory catalytic reduction method to determine iodide concentrations in the permeate of two of the workshop participants: Tampa Bay and Long Beach seawater desalination facilities. It was found that the permeate did contain iodide, although at levels near the detection limit of the analytical method (8 [micro]g/L).

<p dir="ltr">Reverse osmosis (RO) is emerging as the world’s leading desalination technology due to its superior energy efficiency and the shift towards renewable electrification. However, RO systems need to further improve efficiency, increase operating flux, reach higher salinities (>7.5% w.t.), and minimize component complexity. Treating RO as a dynamical system, this dissertation invents new processes for high-efficiency desalination that achieve milestones for low downtime and high final salinity. It also introduces modeling methods that include more detail (e.g. salt retention, time-varying salinity, concentration polarization, salt transport, temporal multi-staging, etc.) and the first use of certain optimization methods in RO.</p><p dir="ltr">Batch RO is an unsteady, pressure driven process that efficiently desalinates a saline feed volume over time by continuously recirculating the brine through the membrane module. A tank houses the concentrating feed and mediates the streams entering and leaving the membrane module. Most studies so far have concentrated on the high-pressure tank design that requires finite downtime at the end of each stroke. A scalable pressure exchanger batch RO (PX-BRO) configuration using atmospheric tanks that practically has zero downtime and produces permeate even while flushing is first described in this dissertation.</p><p dir="ltr">To achieve high recovery at nominal RO pressures, osmotically assisted RO processes have both sides of the membrane saline and the streams usually in counterflow. The first unsteady osmotically assisted process based on the high-pressure piston tank design, batch counterflow RO (BCFRO) is introduced which dramatically reduces the energy needs. To address the issue of high component count in spatial multi-staging, the first “temporally multi-staged” BCFRO process is also introduced. The new process uses the pressure ex- changer and atmospheric pressure tank design for scalability and operational flexibility.</p><p dir="ltr">For membranes with low salt rejection, it becomes imperative to integrate the salt trans- port dynamics for deciding operating and initial conditions. Trajectory optimization is used to match salinity and volume between stages of temporally multi-staged BCFRO. Treating the process as an optimal control problem, a framework for obtaining time varying flux pro- files that minimize the specific energy consumption is also developed. Both reduced order and discretized models are developed to analyze these new batch RO configurations.</p>