This work provides a comparative and genetic analysis of the responses to water stress in desiccation-tolerant and desiccation-sensitive nematodes. Caenorhabditis elegans, a model organism for the study of development, aging, and cell biology was shown to be a desiccation-sensitive organism that survives relative humidities above 40\% for periods of up to seven days. Transcripts from the desiccation-tolerant species Panagrolaimus rigidus AF36 and sp. PS1579, which were expressed uniquely during separate desiccation and osmotic stresses, as well as during recovery from exposure to the dual stresses, were cloned. These sequences were used to search for similarities in the genome sequence data of C. elegans. Putative anhydrobiotic-related transcripts were identified that potentially encode heat shock protein 70, late embryogenic abundant protein, and trehalose-phosphate synthase. Other putative genes that were identified within eight separate libraries encode proteins involved in transcription (histones), protein biosynthesis (ribosomal proteins, elongation factors), protein degradation (ubiquitin, proteases), and transport and cell structure (actin, collagen). Gene ontology analysis of the cloned transcripts revealed that developmental processes are activated during exposure to the stresses as well as during recovery, which may suggest a "rejuvenation" process as a key to survival in Panagrolaimus nematodes. Genes that were up-regulated during desiccation stress in C. elegans were classified as belonging either to an early response (until 12 hours of stress), or to a late response (after 12 hours of stress). The early response was characterized by the up-regulation of a large number of genes encoding mono-oxygenases, which may suggest onset of oxidation stress during desiccation of C. elegans. The late response was characterized by the appearance of transcripts encoding proteins of the immune system, heat shock proteins (protein denaturation), and superoxide dismutases (oxidation damage). Genes in C. elegans that were down-regulated in response to desiccation stress include those encoding proteases and lysozymes (metabolic shutdown). Genes that encode channel proteins (water homeostasis) were found among the transcripts up-regulated during recovery of C. elegans. The up-regulation of gpdh-1 and hmit-1.1, two transcripts linked to hyperosmotic stress, suggest that osmotic stress is experienced by C. elegans. Comparison of these data with those obtained from exposure of C. elegans to a range of other stresses showing that the nematode C. elegans uses specific transcripts for the desiccation response; transcripts that are not induced in other stresses such as heat, anoxia or starvation. In addition, transcripts regulated during desiccation stress of C. elegans were also regulated during dauer formation, which may indicate common stress tolerant mechanisms. Recent studies in mammalian cells and C. elegans have shown that microRNAs are able to degrade and to sequester mRNA especially during stress in so called stress bodies. In this study, C. elegans microRNA knock-outs showed a significant decrease in desiccation stress survival compared to wild type C. elegans which may suggest the importance of microRNAs for stress survival in C. elegans and other organisms. / Ph. D.

Xylitol can be produced from xylose or hemicellulose hydrolysates by either chemical reduction or microbial fermentation. Current technology for commercial production is based on chemical reduction of xylose or hemicellulose, and xylitol is separated and purified by chromatographic methods. The resultant product is very expensive because of the extensive purification procedures. Microbial production of xylitol is being researched as an alternative method for xylitol production. Apart from the chromatographic separation method and activated carbon treatment, no other separation method has been proposed for the separation of xylitol from the fermentation broth. Membrane separation was proposed as an alternative method for the recovery of xylitol from the fermentation broth because it has the potential for energy savings and higher purity. A membrane separation unit was designed, constructed, tested, and successfully used to separate xylitol from the fermentation broth. Eleven membranes were investigated for xylitol separation from the fermentation broth. A 10,000 nominal molecular weight cutoff (MWCO) polysulfone membrane was found to be the most effective for the separation and recovery of xylitol. The membrane allowed 82.2 to 90.3% of xylitol in the fermentation broth to pass through while retaining 49.2 to 53.6% of the Lowry's method positive material (such as oligopeptides and peptides). Permeate from the 10,000 MWCO membrane was collected and crystallized. Crystals were analyzed by HPLC for xylitol and impurities and determined to have purity up to 90.3%. / Master of Science

Thesis (MEng)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: Fouling is readily acknowledged as one of the most critical problems limiting the wider application of membranes in liquid separation processes. A better understanding of fouling layer formation and its monitoring is needed in order to improve on existing cleaning techniques. Plant operation can be optimised if fouling can be monitored by noninvasion means either on the plant itself or on an attached monitoring device. The overall scope of this research was to develop a non-destructive, real-time, in situ visualisation technique or device for concentration polarisation and fouling layer monitoring. Ultrasonic-time-domain-reflectometry (UTDR) was employed as a visualisation technique to provide real-time characterisation of the fouling layer. A 24 cm-long rectangular flat sheet aluminium cell was designed and used as separation device for a desalination system. The experimental results obtained using this module confirmed that there are an excellent correspondence between the flux decline behaviour and the UTDR response from the membrane. The ultrasonic technique could effectively detect fouling layer initiation and growth on the membrane in real-time. In addition to the measurement of fouling, the ultrasonic technique was also successfully employed for monitoring membrane cleaning. Since no real-time permeation data is available during cleaning operations in industrial applications, a UTDR monitoring device may prove to be a very valuable technique in optimising cleaning strategies. The technique was further tested on an 8-inch diameter spiral wrap industrial module and good results were obtained. Stagnant zones, as well as flux flow behaviour inside the module could be determined. However, more research IS needed to fully understand the complex phenomena inside a spiral wrap module. Overall, the UTDR technique and its use in monitoring devices have a major impact in the membrane industry due to its extremely powerful capabilities. / AFRIKAANSE OPSOMMING: Membraan-bevuiling of -verstopping is die grootste struikelblok wat die algemene aanwending van membrane vir verskillende watersuiweringsprosesse negatief beinvloed. 'n Beter begrip van membraan-bevuiling, asook beter metingsmetodes daarvan is nodig om op bestaande skoonmaaktegnieke te verbeter. Die hoofdoel van hierdie studie was die ontwikkeling van 'n nie-destruktiewe-in-lyn visuele tegniek vir die meting van konsentrasie polarisasie en membraan-bevuiling. Deur gebruik te maak van ultrasoniese klank golwe, is 'n tegniek ontwikkel wat 'n direkte visuele aanduiding kon gee van die toestand van membraan-bevuiling binnein die module. 'n Reghoekige aluminium-module, 24 cm lank, is ontwerp en gebou waarbinne die membraan geplaas is vir die skeidingsproses. Resultate dui daarop dat daar 'n uitstekende verband bestaan tussen die afname in permeaatvloei en die ultrasoniese eggo vanaf die membraan. Die ultrasoniese tegniek kon die vorming van en toename in membraan-bevuiling doeltreffend karakteriseer. In teenstelling hiermee, is die tegniek ook suksesvol aangewend om die skoonmaak-proses van membrane te ondersoek. Met min of geen data beskikbaar vir die skoonmaak-proses van membrane in die industriële sektor, het die tegniek enorme potensiaal in die optimisering van bestaande skoonmaak-tegnieke. Die tegniek is verder aangewend op 'n industriële 8-duim deursnee spiraal-module en goeie resultate is verkry. Stagnante sones asook vloed-vloei-patrone binne-in die module kon suksesvol bepaal word. Baie navorsing is egter nog nodig om die ingewikkelde data wat gegenereer word tydens die ondersoek van 'n spiraal-module ten volle te verstaan. Die enorme potensiaal en moontlikhede van die ultrasoniese tegniek kan die begin wees van 'n revolusie in die membraan-industrie.

The water supplies of some small inland communities may come in the form of river systems that offer brackish water. Not fit for immediate human consumption, the water can be further processed using reverse osmosis to be converted into drinking water.In very remote areas there are limited energy resources, and for those areas that lie beyond a municipal distribution grid, renewable energy sources may be used. A reverse osmosis system that operates from the limited power generated by a renewable energy system must do so with the utmost of efficiency. Three methods in improving the efficiency of small-scale reverse-osmosis system are investigated, namely high-pressure pump speed control, feed water heating and vacuum pump based energy recovery.

The rejections of selected N-nitrosamines by commonly used high-pressure nanofiltration (NF) and reverse osmosis (RO) membranes were quantitatively evaluated using a bench-scale cross-flow filtration apparatus. The selected nitrosamines included N-nitrosodimethylamine (NDMA), N-nitrosomethylethylamine (NMEA), N-nitrosopyrrolidine (NPYR), N-nitrosodiethylamine (NDEA), N-nitrosodi-n-propylamine (NDPA), N-nitrosodi-n-butylamine (NDBA) and N-nitrosodiphenylamine (NDPHA). Nitrosamine rejections were evaluated under steady state at elevated feed concentrations, since NDMA rejections were found to be consistent with feed concentrations over three orders of magnitude. The steady-state nitrosamine rejections by NF membranes varied significantly, from 9 to 75%, depending on nitrosamine compounds and tested membranes. For hydrophilic compounds, rejections increased with increasing molecular weight. The nitrosamine rejections by brackish RO membranes reached as high as 97% for higher molecular weight nitrosamines. However, for low molecular weight nitrosamines such as NDMA, rejections as low as 54% were observed. This low level of rejections was attributed to diffusive solute transport being more effective than convective transport. Physicochemical properties such as molecular weight and aqueous diffusivity showed reasonable correlations with nitrosamine permeability constants.

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.

yes / In this paper, a one-dimensional mathematical model based on coupled differential and algebraic equations has been developed for analysing the separation mechanism of a N-nitrosamine in a spiral-wound reverse osmosis process. The model is based on Spiegler and Kedem’s work on mass transport and Darcy’s law and concentration polarization to analyse the pressure drop and mass transfer coefficient in the module feed channel respectively. The model is built using the gPROMS software suite and validated using N-nitrosamine rejection experimental data from the literature, obtained by using a pilot-scale cross-flow reverse osmosis filtration system. Analysis results derived from the model corroborate experimental data.

In the past few years, the contamination by pesticides and heavy metals in surface water and groundwater has increased. Reverse osmosis is a unit process that has demonstrated capacity to remove dissolved pesticides and heavy metals from aqueous solution, and it is therefore worthwhile to consider this treatment process as a potential removal technique for hazardous constituents. The purpose of this investigation was to determine the effectiveness of a field scale reverse osmosis unit, with a spiral wound poly(ether/urea) membrane, in removing pesticides and heavy metals from a contaminated source. The removal efficiency for a single contaminant alone and a part of a mixture was examined. The performance of new and used membranes over time was also investigated. The average removal of pesticides was better than 99 percent. Reverse osmosis separation of pesticides was found to be dependent on the characteristics of the membrane and the physical/chemical properties of the pesticides. Pesticides in the mixed solution were found to behave independently. Sorption of the pesticides onto the reverse osmosis membrane was found to play a major role in the overall removal efficiency. Better than 99 percent average removal was achieved for all the metals except arsenic. The importance of the physical/chemical properties of the metal ions such as solubility, ionic radius, and electronegativity were determined. In tests to compare removal efficiency between new membrane and membrane which had been used, virtually no differences occurred. / Master of Science

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