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Abstract : Measures to Increase Recoveries and Avoid Concentrate Disposal: Principles to Control Scaling and Reduce Concentrate Disposal in Reverse Osmosis Applications
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Abstract: The present work is aimed at development of a new approach to reduce RO concentrate flow and to increase recovery. The described techniques enable us to remove calcium carbonate from RO concentrate by means of "seed" сrystallization. These proposed techniques use "open channel" spiral wound membrane modules that can directly treat water with high scaling and fouling potentials without pretreatment. The experimental procedure is described and experimental plots are presented that describe precipitation kinetics. The test membrane unit was operated in circulation mode and recovery values reach 95% or higher. RO concentrate constantly passed through the precipitation reactor where seed crystals were contained. Seed crystal formation was initiated by injecting caustic solution to RO concentrate. The driving force for crystal growth was constantly created by RO process due to increase of calcium and carbonate ion concentration values. Fouling control is achieved by providing sufficient cross flow velocities, flushings and cleanings. Coagulated suspended matter after membrane flushes is collected, sedimented and finally dewatered. The concentrated solution that contains rejected salts and impurities constitutes no more than 1 per cent of initial feed water volume and can be withdrawn together with wet sludge as a sludge moisture. The described technical procedure enables us to completely utilize concentrate and produce quality product water, softened water and sludge. Keywords: Reverse osmosis concentrate, concentrate utilization, calcium carbonate precipitation, seed crystallization.Download Full Article |
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Abstract: We produced microcapsules of alginate-poly(L)lysine-alginate (APA)with diameters on the order of 10 µm. To characterize their mechanical properties, we conducted an experiment on the parallel-plate compression of a microcapsule and modeled its deformation. In the modeling task, the microcapsule was assumed to be a spherical liquid-filled elastic membrane with negligible bending stiffness and permeability. The membrane thickness was estimated by applying Reissner’s linear elastic theory to the experimental force-displacement relationship during loading in the small displacement region. The initial stretch of the membrane was taken into account; it was mainly caused by the osmotic pressure difference across the membrane. The initial stretch of the microcapsule was determined by fitting the calculated and experimental force-displacement relationships during loading at small to medium displacements. At large displacements, the calculated force was smaller than the experimentally measured force because of fluid permeation across the APA membrane. The calculated and experimentally imaged shapes of the deformed microcapsule were compared. The effects of varying the membrane thickness on the force-displacement and transmural pressure-displacement curves were shown, and the limitations of applying the present deformation model were examined. Keywords: Microcapsule, compression, modeling, mechanical characterization, initial stretch. |
Abstract : Mitigating Low-Pressure Membrane Fouling by Controlling the Charge of Precipitated Floc Particles
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Abstract: Fouling presents the most significant obstacle to optimal low-pressure membrane plant performance. The occurrence of fouling tends to decrease production rates (flux), increase chemical usage incurred during clean-in-place (CIP) process, increase energy costs, shorten membrane life and reduce recovery. Fouling may be of organic or inorganic nature, necessitating more frequent dual chemical cleaning procedures. Regardless of the nature of the foulants, particulate loading onto the membrane fiber surface has been identified as a common mechanism of deteriorating performance. Particulates and colloidal materials such as turbidity, natural organic material (NOM), algae and precipitated coagulant floc accumulate on the membrane surface and disrupt the laminar flow of water through the element. Particulates can either attach or adhere to the membrane surface through electrostatic attraction. One method of reducing this fouling mechanism is to employ controlled coagulation as a direct feed or coupled with a clarification step prior to membrane process. Coagulation can attract and retain naturally occurring particulates and colloidal materials via charge neutralization. Then, by controlling the charge of precipitated floc particulates to align with the surface charge of the membrane element, both types of fouling can be mitigated. This Paper summarizes two demonstrations featuring a pressure feed and a submerged vacuum ultrafiltration (UF) system. Keywords: Coagulant, Floc, Particulate, Flux, Electrostatic.Download Full Article |
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Abstract: Four distinctive Ceramic membranes have been synthesized using bentonite and Egyptian clay with the expansion of melamine. The addition of melamine (~ 1% by wt.) enhanced the porosity, density, the thermal stability and water permeability of the membranes made from bentonite or Egyptian clay while decreasing the chemical stability of either bentonite or Egyptian clay membranes. The most noteworthy level of decrease in COD (94.7%) is acquired for the concentration of 200ppm with saturating flux of 4.63 E-05 (m3/m2.s) utilizing (B+M) membrane. The cost of the four manufactured clay membranes was assessed based on raw materials used in the present investigation. Keywords: Oily water, emulsion, ceramic membrane, melamine. |
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Abstract: Molecularly imprinted nanofiber membranes were fabricated from chitin and print molecule of phenylalanine derivative by simultaneously applying an alternative molecular imprinting and an electrospinning. The D-enantiomer imprinted nanofiber membrane preferentially incorporated the D-enantiomer and selectively transported D-enantiomer and vice versa. The permselectivity was exponentially increased with the increase in the membrane thickness, implying that multi-stage cascade membrane separation was carried out within the nanofiber membrane. The present study led to the conclusion that a molecularly imprinted nanofiber membrane is one of suitable membrane forms for the separation membrane with relatively high flux and permselectivity. Keywords: Cascade separation, Chitin, Chiral separation, Molecularly imprinted membrane, Molecular imprinting, Multi-stage cascade membrane separation, Nanofiber, Optical resolution.Download Full Article |