The effectiveness of reverse osmosis (RO) membrane systems may be compromised due to fouling, of which biofouling (excessive growth of biomass) is the most troublesome. Effective control of biofouling is essential to improve membrane performance and reduce operating costs. The periodic application of chemical cleaning agents is possibly the most widely practiced method of biofouling control in RO membranes. This research investigated advanced chemical cleaning strategies for biofouling control. The first part of this study concluded that short-term accelerated biofouling studies using lab-scale membrane fouling simulators (MFSs) are a representative and suitable approach for the prediction of long-term biofouling development in membrane systems. Thereon, the superior efficiency of urea as an alternative to conventional chemical cleaning agents was demonstrated (i) at lab-scale using MFSs, (ii) for full-scale industrial spiral-wound membranes and (iii) for multiple cleaning cycles during long-term operation. Periodic chemical cleaning with urea resulted in better restoration of membrane performance, higher biomass inactivation, enhanced biofilm solubilization and removal, disintegration of extracellular polymeric substances (EPS) particularly proteins, and a considerable reduction of key biofilm-forming bacteria. This research presented enhanced chemical cleaning strategies aiming to increase the removal of biofilms, reduce biomass accumulation and its impact on membrane performance, and delay fresh biofilm formation.

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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

No / The reverse osmosis (RO) desalination process to make fresh water from seawater has been studied here. First, a model for the process is developed. Sensitivity of different operating parameters (feed flow rate, feed pressure) and design parameters (internal diameter, total number of tubes) on the recovery ratio are studied via repetitive simulation. Finally, an optimisation framework for the process is developed so as to maximize the recovery ratio or a profit function using different energy recovery devices, subjectto general constraints. The optimal operating parameters (feed flow rate, feed pressure) and design parameters (internal diameter, total number of tubes) are determined by solving the optimisation problem using an efficient successive quadratic programming (SQP) based method. The optimal values for the decision variables depend on the constraints introduced, and are also sensitive to variations in water and energy prices, as well as feed concentration. The use ofthe emerging energy recovery devices is widely justified, reporting much higher reductions in operating costs than the traditional technology used for this purpose. Using a pressure exchanger device, it is possible to reduce energy consumption by up to 50%.

No / Reverse Osmosis (RO) process is widely used for seawater desalination. In this work, we considered a small scale SWRO (Spiral Wound Reverse Osmosis) desalination unit which is enough to cover the need of a medium size hotel complex at Limassol city in Cyprus. The pH of the seawater in the region is 7.95 and the temperature varies from 17 to 27 °C. The aim of this study is to identify the configuration of the RO process and the optimum operating parameters such as pH and pressure that can minimise the total annualised cost of the process subject to acceptable quality of freshwater in terms of boron concentrations throughout the year. For this purpose, the mathematical model for boron rejection developed earlier by the authors is used but incorporates cost functions. The model is based on solution-diffusion model which can describe solvent and solute transport mechanism through the membranes. With the variation of seasonal seawater temperature, the key finding of this study was that by choosing the right combination of pH and pressure, substantial economical savings up to 16 % could be achieved.

Yes / The Reverse Osmosis (RO) process has been expansively used in water treatment as a result of its low energy consumption compared to thermal distillation processes, leading to reduced overall water production cost. Evaluation and minimisation of energy consumption (expressed in kWh/m3 of fresh water production) in a medium-scale spiral wound brackish water RO (BWRO) desalination plant of the Arab Potash Company (APC) are the main aims of this research. The model developed earlier by the authors has been integrated to simulate the process and achieve the main aims. Energy consumption calculations of low salinity BWRO desalination plant, with and without an energy recovery device, have been carried out using the gPROMS software suite. In other words, this research evaluated the impact of adding an energy recovery device on the RO process energy consumption of the APC, which is introduced for the first time. Also, the effects of several operating conditions of BWRO process include the feed flow rate, pressure and temperature on the performance indicators, which include the energy consumption and total plant recovery at different energy recovery device efficiencies, were studied. The simulation results showed that the total energy consumption could be reduced at low values of feed flow rates and pressures and high values of temperatures. More importantly, there is an opportunity to reduce the total energy consumption between 47% and 53.8% compared to the one calculated for the original design without an energy recovery device.

No / In this work, a reverse osmosis (RO) desalination process operating under batch mode is considered experimentally. The effect of operating parameters, such as pressure and feed salinity on the permeate quantity and salinity is evaluated. In addition, the water permeability constant, Kw, which is one of the main parameters that affect the optimal design and operation of RO processes is evaluated as a function of changing feed salinity and pressure using the experimental data and two literature models. A strong pressure dependence of the water permeability constant is observed in line with earlier observations. Interestingly, a strong concentration dependence of the water permeability constant is also observed which has always been neglected or ignored in the literature. Finally, for a given pressure, concentration dependent correlations for Kw are developed and are used in the full process model (described by a system of ordinary differential and algebraic equations) for further simulation studies and to validate the experimental results.