Yes / Reverse osmosis (RO) has long been recognised as an efficient separation method for treating and removing harmful pollutants, such as dimethylphenol in wastewater treatment. This research aims to study the effects of RO network configuration of three modules of a wastewater treatment system using a spiral-wound RO membrane for the removal of dimethylphenol from its aqueous solution at different feed concentrations. The methodologies used for this research are based on simulation and optimisation studies carried out using a new simplified model. This takes into account the solution-diffusion model and film theory to express the transport phenomena of both solvent and solute through the membrane and estimate the concentration polarization impact respectively. This model is validated by direct comparison with experimental data derived from the literature and which includes dimethylphenol rejection method performed on a small-scale commercial single spiral-wound RO membrane system at different operating conditions. The new model is finally implemented to identify the optimal module configuration and operating conditions that achieve higher rejection after testing the impact of RO configuration. The optimisation model has been formulated to maximize the rejection parameters under optimal operating conditions of inlet feed flow rate, pressure and temperature for a given set of inlet feed concentration. Also, the optimisation model has been subjected to a number of upper and lower limits of decision variables, which include the inlet pressure, flow rate and temperature. In addition, the model takes into account the pressure loss constraint along the membrane length commensurate with the manufacturer’s specifications. The research clearly shows that the parallel configuration yields optimal dimethylphenol rejection with lower pressure loss.

The reverse osmosis performance of cellulose acetate membranes has been examined and analyzed for several aqueous systems where there is a strong attraction between the organic solute and the membrane material. The systems investigated included the aromatic hydrocarbons benzene, toluene, and cumene in single-solute aqueous solutions. Six cellulose acetate membranes, modified by annealing at different temperatures, were studied. Experiments were performed at four pressures (690, 1725, 3450, and 6900 kPa) and at several concentrations (in the range 5 to 260 ppm). The results were found to be markedly different than those observed in the absence of strong solute-membrane affinity. In particular, the solute-water separation decreased rather than increased with increasing pressure and the flux decreased with increasing concentration even though low concentrations, with low osmotic pressures, were studied. Qualitatively, the behavior was explained in terms of a porous membrane mechanism with both solute-membrane affinity and solute mobility varying as a function of solute position with respect to the membrane. The observed reduction in flux was expressed by an empirical equation as a function of concentration of solute in the boundary layer. The experimental results were analyzed quantitatively by several transport models. The irreversible thermodynamics phenomenological transport, solution-diffusion imperfection and extended solution-diffusion relationships generated parameters that were inconsistent with the original formulations of the models. The irreversible thermodynamics Kedem-Spiegler model, solution diffusion model, Kimura-Sourirajan analysis, and the three parameter finely-porous model were functionally unable to represent the data. Only the four parameter finely-porous model and the surface force-pore flow model were consistent with experimental results. From the finely-porous model the partition coefficient was found to be different on the high and low pressure sides of the membrane and this difference was a function of both pore size and solute. For the surface force-pore flow model, the agreement between the model and data was excellent. However, the surface force-pore flow model was considerably more difficult to use. / Ph. D.

In the process of electricity generation, water is used as the working fluid to transport energy from the fuel to the turbine. This water has to be ultrapure in order to reduce maintenance cost on the boilers. For the production of ultrapure water, a desalination process is used. This process consists of an ultrafiltration pretreatment section, two reverse osmosis stages and a continuous electrodeionisation stage. Reverse osmosis desalination plants are, however, inherently inefficient with a high specific energy consumption. In an attempt to improve the efficiency of low recovery seawater applications, energy recovery devices are installed on the brine outlet of the reverse osmosis stages. The energy recovery device recovers the energy that is released through the high pressure brine stream and reintroduces it to the system. The investigated desalination process has a fresh water feed with a salinity of 71 ppm and is operated at recoveries above 85%. The plant produces demineralised water at a salinity lower than 0.001ppm for the purpose of high pressure boiler feed. A thermodynamic analysis determined the Second Law efficiencies for the first and second reverse osmosis sections as 3.85% and 3.68% respectively. The specific energy consumption for the reverse osmosis plants is 353 Wh/m3 and 1.31 Wh/m3. This was used as the baseline for the investigation. An exergy analysis determined that energy is lost through the brine throttling process and that a pressure exchanging system can be installed on all reverse osmosis brine streams. Energy recovery devices are untested in high recovery fresh water applications due to the low brine pressure and low brine flow. It was determined that pressure exchanging systems can reduce the specific energy consumption of the first reverse osmosis stage with 12.2% whereas the second RO stage energy consumption can be improved with 7.7%. The Second Law efficiency can be improved by 25.6% for the first reverse osmosis stage while the efficiency is improved with 18.1% for the second stage. The optimal operating recovery for the PES is between 80% and 90%. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2015

In the process of electricity generation, water is used as the working fluid to transport energy from the fuel to the turbine. This water has to be ultrapure in order to reduce maintenance cost on the boilers. For the production of ultrapure water, a desalination process is used. This process consists of an ultrafiltration pretreatment section, two reverse osmosis stages and a continuous electrodeionisation stage. Reverse osmosis desalination plants are, however, inherently inefficient with a high specific energy consumption. In an attempt to improve the efficiency of low recovery seawater applications, energy recovery devices are installed on the brine outlet of the reverse osmosis stages. The energy recovery device recovers the energy that is released through the high pressure brine stream and reintroduces it to the system. The investigated desalination process has a fresh water feed with a salinity of 71 ppm and is operated at recoveries above 85%. The plant produces demineralised water at a salinity lower than 0.001ppm for the purpose of high pressure boiler feed. A thermodynamic analysis determined the Second Law efficiencies for the first and second reverse osmosis sections as 3.85% and 3.68% respectively. The specific energy consumption for the reverse osmosis plants is 353 Wh/m3 and 1.31 Wh/m3. This was used as the baseline for the investigation. An exergy analysis determined that energy is lost through the brine throttling process and that a pressure exchanging system can be installed on all reverse osmosis brine streams. Energy recovery devices are untested in high recovery fresh water applications due to the low brine pressure and low brine flow. It was determined that pressure exchanging systems can reduce the specific energy consumption of the first reverse osmosis stage with 12.2% whereas the second RO stage energy consumption can be improved with 7.7%. The Second Law efficiency can be improved by 25.6% for the first reverse osmosis stage while the efficiency is improved with 18.1% for the second stage. The optimal operating recovery for the PES is between 80% and 90%. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2015

<p>Hammarby Sjöstad is a new district in Stockholm with high environmental standard. Stockholm Water Company evaluates a local wastewater treatment plant with cutting edge technology. The first step is an experimental treatment plant (Sjöstadsverket) with four parallel lines of treatment, each with a capacity to treat wastewater from 150 persons. Within the membrane technology subproject the possibility of using reverse osmosis (usually called RO) to regain nutrients is examined.</p><p>Reverse osmosis separates the incoming water in a clean permeate and a concentrate that, as the name indicates, is a more concentrated version of the incoming water. Using this method in wastewater treatment, a solution high in nutrients can be obtained without the use of chemical precipitation agent and with no production of sludge. The solution can then be recycled to use on farmland. The disadvantages of the RO technology include high energy consumption and sensitivity to membrane fouling.</p><p>The aim of this study was to investigate the possibility of using RO at Sjöstadsverket and, if possible, to evaluate the chance of obtaining concentrate that can be accepted as a fertiliser and permeate that falls below emission limits. The experiments were carried out with an RO plant with three membranes in series operated in batch mode; the dimensioned permeate flow being 100 l/h. The incoming water was permeate from a membrane bioreactor in the majority of the trial runs.</p><p>The results show that RO can be used in at least one of the lines of treatment. However the permeate exceeds the emission limits (phosphorus: 0,15 mg/l, nitrogen: 6 mg/l) while concentration in the concentrate is still too low. The limiting factor seems to be phosphorus. This could be solved with pre-precipitation of phosphorus or by reconstructing the RO plant to a two-stage system. The quota heavy metal – phosphorus in the concentrate is lower than the limit imposed by the Swedish Environmental Protection Agency but much higher than in human urine.</p> / <p>Som en del i miljöarbetet i Stockholms nya stadsdel Hammarby Sjöstad utvärderar Stockholm Vatten ett lokalt reningsverk med spetsteknologi. I ett första steg har ett reningsverk (Sjöstadsverket) med fyra parallella reningslinjer byggts. Varje linje har kapacitet att rena avloppsvatten från 150 personer. Inom delprojektet membranteknik undersöks möjligheterna att som slutsteg på flera av linjerna återvinna näringsämnen med hjälp av omvänd osmos (eller RO efter engelskans reverse osmosis).</p><p>En RO separerar det inkommande vattnet i ett rent permeat och ett koncentrat som, liksom namnet antyder, är en koncentrerad form av det inkommande vattnet. Inom avloppsvattenrening kan alltså en lösning med hög koncentration av näringsämnen uppnås utan fällningskemikalier och uppkomst av slam. Denna kan sedan återföras till jordbruket. Till teknikens nackdelar hör hög energiförbrukning och stor känslighet för partiklar som kan sätta igen membranen.</p><p>Syftet med denna studie var att undersöka om det går att använda RO på Sjöstadsverket och att i så fall utvärdera koncentratets och permeatets möjlighet att bli accepterat gödselmedel respektive godkänt utloppsvatten. Försöken gjordes satsvis på en anläggning med tre seriekopplade membran dimensionerad för ett totalt permeatflöde på 100 l/h. Det inkommande vattnet var, i nästan alla försök, permeat från en membranbioreaktor.</p><p>Resultaten visar att RO:n kan användas åtminstone på en av reningslinjerna. Däremot kan inte en tillräckligt hög koncentration uppnås i koncentratet utan att gränsvärdena (fosfor: 0,15 mg/l, kväve: 6 mg/l) i permeatet överskrids. Den begränsande faktorn verkar framför allt vara fosfor. Lösningen på problem skulle kunna vara förfällning av fosfor eller en utbyggnad av anläggningen till en två-stegsprocess. Kvoten tungmetallfosfor i koncentratet klarar Naturvårdsverkets gränsvärden för vad som får spridas på åkermark, men är klart högre än i humanurin.</p>

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.

Produced water handling has been an issue of concern for oil and gas producers as it is one of the major factors that cause abandonment of the producing well. The development of effective produced water management strategies poses a big challenge to the oil and gas industry today. The conversion of produced water into irrigation or fresh water provides a cost effective tool to handle excessive amounts of the produced water. In this research we proposed on-site produced water treatment units configured to achieve maximum processing throughput. We studied various advanced separation techniques to remove oil and dissolved solids from the produced water. We selected adsorption as the oil removing technique and Reverse Osmosis (RO) as the dissolved solids removing technique as being the best for our purpose. We performed experiments to evaluate operating parameters for both adsorption and RO units to accomplish maximum removal of oil and dissolved solids from the produced water. We compared the best models fitting the experimental data for both the processes, then analyzed and simulated the performance of integrated produced water treatment which involves adsorption columns and RO units. The experimental results show that the adsorption columns remove more than 90% of the oil and RO units remove more than 95% of total dissolved solids from the produced water. The simulation results show that the proper integration and configuration of adsorption and RO units can provide up to 80% efficiency for a processing throughput of 6-8 gallons per minute of produced water. From an oil and gas producer’s viewpoint output from the produced water treatment system is a revenue generating source. The system is flexible and can be modified for the applications such as rangeland restoration, reservoir recharge and agricultural use.

Hammarby Sjöstad is a new district in Stockholm with high environmental standard. Stockholm Water Company evaluates a local wastewater treatment plant with cutting edge technology. The first step is an experimental treatment plant (Sjöstadsverket) with four parallel lines of treatment, each with a capacity to treat wastewater from 150 persons. Within the membrane technology subproject the possibility of using reverse osmosis (usually called RO) to regain nutrients is examined. Reverse osmosis separates the incoming water in a clean permeate and a concentrate that, as the name indicates, is a more concentrated version of the incoming water. Using this method in wastewater treatment, a solution high in nutrients can be obtained without the use of chemical precipitation agent and with no production of sludge. The solution can then be recycled to use on farmland. The disadvantages of the RO technology include high energy consumption and sensitivity to membrane fouling. The aim of this study was to investigate the possibility of using RO at Sjöstadsverket and, if possible, to evaluate the chance of obtaining concentrate that can be accepted as a fertiliser and permeate that falls below emission limits. The experiments were carried out with an RO plant with three membranes in series operated in batch mode; the dimensioned permeate flow being 100 l/h. The incoming water was permeate from a membrane bioreactor in the majority of the trial runs. The results show that RO can be used in at least one of the lines of treatment. However the permeate exceeds the emission limits (phosphorus: 0,15 mg/l, nitrogen: 6 mg/l) while concentration in the concentrate is still too low. The limiting factor seems to be phosphorus. This could be solved with pre-precipitation of phosphorus or by reconstructing the RO plant to a two-stage system. The quota heavy metal – phosphorus in the concentrate is lower than the limit imposed by the Swedish Environmental Protection Agency but much higher than in human urine. / Som en del i miljöarbetet i Stockholms nya stadsdel Hammarby Sjöstad utvärderar Stockholm Vatten ett lokalt reningsverk med spetsteknologi. I ett första steg har ett reningsverk (Sjöstadsverket) med fyra parallella reningslinjer byggts. Varje linje har kapacitet att rena avloppsvatten från 150 personer. Inom delprojektet membranteknik undersöks möjligheterna att som slutsteg på flera av linjerna återvinna näringsämnen med hjälp av omvänd osmos (eller RO efter engelskans reverse osmosis). En RO separerar det inkommande vattnet i ett rent permeat och ett koncentrat som, liksom namnet antyder, är en koncentrerad form av det inkommande vattnet. Inom avloppsvattenrening kan alltså en lösning med hög koncentration av näringsämnen uppnås utan fällningskemikalier och uppkomst av slam. Denna kan sedan återföras till jordbruket. Till teknikens nackdelar hör hög energiförbrukning och stor känslighet för partiklar som kan sätta igen membranen. Syftet med denna studie var att undersöka om det går att använda RO på Sjöstadsverket och att i så fall utvärdera koncentratets och permeatets möjlighet att bli accepterat gödselmedel respektive godkänt utloppsvatten. Försöken gjordes satsvis på en anläggning med tre seriekopplade membran dimensionerad för ett totalt permeatflöde på 100 l/h. Det inkommande vattnet var, i nästan alla försök, permeat från en membranbioreaktor. Resultaten visar att RO:n kan användas åtminstone på en av reningslinjerna. Däremot kan inte en tillräckligt hög koncentration uppnås i koncentratet utan att gränsvärdena (fosfor: 0,15 mg/l, kväve: 6 mg/l) i permeatet överskrids. Den begränsande faktorn verkar framför allt vara fosfor. Lösningen på problem skulle kunna vara förfällning av fosfor eller en utbyggnad av anläggningen till en två-stegsprocess. Kvoten tungmetallfosfor i koncentratet klarar Naturvårdsverkets gränsvärden för vad som får spridas på åkermark, men är klart högre än i humanurin.

Electrodialysis (ED) experiments were conducted on reverse osmosis (RO)-concentrated solutions of NOM from six rivers. The ED processes successfully recovered 88 11% of TOC, and removed 83% 19% of SO42- and 67% 18% of H4SiO4. More importantly, the molar ratios of SO42- /TOC and H4SiO4 /TOC were reduced to a mean value of 0.0046 and 0.032, respectively, surpassing the goal for removal of SO42- (0.008) and almost achieving the goal for removal of H4SiO4 (0.021). The ED process can lower the SO42- /TOC ratio in samples whose initial SO42- /TOC ratios are already far below the limit of 0.008 used in this study. The coupled RO/ED process that has been described here offers a fast, simple, chemically mild (relative to other methods), and reproducible method of isolation of large quantities of relatively unfractionated, low-ash NOM from freshwaters. RO/ED was also successfully used for isolating and concentrating marine dissolved organic matter (DOM). The effort successfully recovered a median of 72% of the TOC from 200 L samples within six to nine hours of processing through a combination of ED and RO, greatly exceeding the current norm of 30%. The relatively high recovery of DOM implies that classes of DOM previously missing are included in these samples and should yield new insight into the chemistry of marine DOM. Freshwater samples processed by electrodialysis were analyzed for elemental composition and by capillary zone electrophoresis (CZE), 1H and 13C nuclear magnetic resonance spectroscopy (NMR), and electro-spray ionization mass spectrometry (ESI-MS). Bulk elemental composition, 1H- and 13C-NMR, and ESI-MS data provide evidence linking bioavailabilty to the bulk chemistry of NOM: the H/C and N/C molar ratios are positively and strongly correlated with bioavailability, as hypothesized. Using an independent dataset (STORET) of water quality parameters, calculated BOD/TOC ratios were found to be moderately correlated with measured bioavailabilities and can be used as a surrogate for bioavailability of geochemically diverse riverine DOM.

This thesis presents a study to enhance and improve a zero liquid discharge (ZLD) reverse osmosis process that uses seed crystals to promote crystallization of the dissolved salts in the residual brine while it is being treated by identifying those membrane materials that are most suitable for the process. In the study, a one plate SEPA Cell module by GE Osmonics was used to determine which membranes were most susceptible to fouling and/or membrane hydrolysis. A cellulose acetate (CA), polyamide (PA) low MWCO, and PA high MWCO membrane were tested under reverse osmosis conditions. The CA and thin film (TF) membranes were also tested for nanofiltration. The cell was operated under conditions that were determined to be optimum for each membrane by the manufacturer, GE Osmonics. A high pressure, low flow, positive displacement diaphragm pump circulated the saturated calcium sulfate solution with 2 % suspended solids through the cell while the reject and permeate were recycled back to the feed, thereby preserving a saturated solution to promote crystal growth and simulate the seeded reverse osmosis process. The temperature was maintained constant by adding an ice pack to the feed vessel when necessary. The transmembrane pressure differential was maintained constant by adjusting a back pressure valve on the concentrate outlet. The results illustrate that if potable drinking water is the intended use, then the nanofiltration cellulose acetate membrane should be used. If irrigation is the desired use, then the nanofiltration thin film membrane should be used. Overall, the reverse osmosis cellulose acetate membrane was observed to outperform all membranes when all performance parameters were normalized. However, this membrane was observed to be prone to degradation in a seeded slurry and therefore its lifetime should be analyzed further. The polyamide membrane initially had a high water transport coefficient, but fouling led to its rapid decline which was attributed to the membrane’s rough and protrusive surface. A lifetime test on the thin film and cellulose acetate revealed that when operated at their maximum pressure specified by GE Osmonics for a duration of 8 hours that no decrease in rejection occurred.