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- EDTA: a synthetic draw solute for forward osmosis. [JOURNAL ARTICLE]
- Water Sci Technol 2014 Nov; 70(10):1677-1682.
The draw solution is the driving force of the forward osmosis (FO) process; however, the solute loss of the draw solute to the feed side is a general, financial limitation for most applications. The anthropogenic amino acid ethylenediaminetetraacetic acid (EDTA) was investigated as a draw solution for FO. At concentrations of approximately 1.0 osmol/kg, EDTA demonstrated comparable water fluxes (Jv = 5.29 L/m(2) h) to the commonly used salt, NaCl (Jv = 4.86 L/m(2) h), and both produced better water fluxes than glucose (Jv = 3.46 L/m(2) h). EDTA showed the lowest solute loss with Js (reverse solute loss or solute leakage) = 0.54 g/m(2) h. The molecular weight, degree of ionisation and charge of EDTA played a major role in this efficiency and EDTA was therefore well rejected by the membrane, showing a low Js/Jv ratio of 0.10 g/L. Owing to the low solute loss of EDTA and its resistance to biodegradation, this compound has the potential to be used as a draw solute for FO during long periods without requiring much replenishment.
- Principles of cryopreservation. [Journal Article]
- Methods Mol Biol 2015.:3-19.
Cryopreservation is the use of very low temperatures to preserve structurally intact living cells and tissues. Unprotected freezing is normally lethal and this chapter seeks to analyze some of the mechanisms involved and to show how cooling can be used to produce stable conditions that preserve life. The biological effects of cooling are dominated by the freezing of water, which results in the concentration of the solutes that are dissolved in the remaining liquid phase. Rival theories of freezing injury have envisaged either that ice crystals pierce or tease apart the cells, destroying them by direct mechanical action, or that damage is from secondary effects via changes in the composition of the liquid phase. Cryoprotectants, simply by increasing the total concentration of all solutes in the system, reduce the amount of ice formed at any given temperature; but to be biologically acceptable they must be able to penetrate into the cells and have low toxicity. Many compounds have such properties, including glycerol, dimethyl sulfoxide, ethanediol, and propanediol.In fact, both damaging mechanisms are important, their relative contributions depending on cell type, cooling rate, and warming rate. A consensus has developed that intracellular freezing is dangerous, whereas extracellular ice is harmless. If the water permeability of the cell membrane is known it is possible to predict the effect of cooling rate on cell survival and the optimum rate will be a trade-off between the risk of intracellular freezing and effects of the concentrated solutes. However, extracellular ice is not always innocuous: densely packed cells are more likely to be damaged by mechanical stresses within the channels where they are sequestered and with complex multicellular systems it is imperative not only to secure cell survival but also to avoid damage to the extracellular structure. Ice can be avoided by vitrification-the production of a glassy state that is defined by the viscosity reaching a sufficiently high value (~10(13) poises) to behave like a solid, but without any crystallization. Toxicity is the major problem in the use of vitrification methods.Whether freezing is permitted (conventional cryopreservation) or prevented (vitrification), the cryoprotectant has to gain access to all parts of the system. However, there are numerous barriers to the free diffusion of solutes (membranes), and these can result in transient, and sometimes equilibrium, changes in compartment volumes and these can be damaging. Hence, the processes of diffusion and osmosis have important effects during the introduction of cryoprotectants, the removal of cryoprotectants, the freezing process, and during thawing. These phenomena are amenable to experiment and analysis, and this has made it possible to develop effective methods for the preservation of a very wide range of cells and some tissues; these methods have found widespread applications in biology and medicine.
- Bidirectional Diffusion of Ammonium and Sodium Cations in Forward Osmosis: Role of Membrane Active Layer Surface Chemistry and Charge. [JOURNAL ARTICLE]
- Environ Sci Technol 2014 Nov 24.
Systematic fundamental understanding of mass transport in osmosis-driven membrane processes is important for further development of this emerging technology. In this work, we investigate the role of membrane material and surface charge on bidirectional solute diffusion in forward osmosis (FO). In particular, bidirectional diffusion of ammonium (NH4+) and sodium (Na+) is examined using FO membranes with different materials and surface charge characteristics. Using an ammonium bicarbonate (NH4HCO3) draw solution, we observed dramatically enhanced cation fluxes with sodium chloride feed solution compared to that with deionized water feed solution for thin-film composite (TFC) FO membrane. However, the bidirectional diffusion of cations did not change, regardless of the type of feed solution, for cellulose triacetate (CTA) FO membrane. We related this phenomenon to the membrane fixed surface charge by employing different feed solution pH to foster different protonation conditions for the carboxyl groups on the TFC membrane surface. Membrane surface modification is also carried out with the TFC membrane using ethylenediamine to alter carboxyl groups into amine groups. The modified TFC membrane, with less negatively charged groups, exhibited a significant decrease in the bidirectional diffusion of cations under the same conditions employed with the pristine TFC membrane. Based on our experimental observations, we propose Donnan dialysis as a mechanism responsible for enhanced bidirectional diffusion of cations in TFC membranes.
- 2-Bromo-4-methylphenol, a Compound Responsible for Iodine Off-Flavor in Wines. [JOURNAL ARTICLE]
- J Agric Food Chem 2014 Nov 20.
This study focuses on an off-flavor in wines treated by an acidification technique involving ion-exchange resins. Applying reversed-phase HPLC on a C18 column to a contaminated wine extract resulted in 25 fractions in dilute alcohol medium, and only one, fraction 19, presented this off-flavor. Its composition was analyzed using gas chromatography coupled to olfactometry (GC-O) and mass spectrometry (GC-MS), leading to the identification of 2-bromo-4-methylphenol for the first time as a compound associated with an "iodine" aroma in white, rosé, and red table wines. Contaminated wines presented a wide range of levels, with maximum concentrations of 28900, 7556, and 48000 ng/L and minimum values of 260, 35, and 63 ng/L in white, rosé, and red wines, respectively. Sensory studies investigating 2-bromo-4-methylphenol gave very interesting results. Individual thresholds ranged from 0.15 to >77.4 ng/L in reverse osmosis water, from 0.4 to >193.5 ng/L in white wine, from 0.5 to >774 ng/L in rosé wine, and from 0.5 to >774 ng/L in red wine. The very wide distribution of individual thresholds suggested the presence of two populations, sensitive and nonsensitive, with a bimodal frequency distribution. The odor descriptions quoted by the more sensitive group characterized 2-bromo-4-methylphenol using terms with "iodine" connotations in both the reverse osmosis water and red wine matrices. The descriptors for commercial wines naturally affected by this defect were seafood, iodine, mud, and fish.
- Facile Fabrication of Freestanding Ultrathin Reduced Graphene Oxide Membranes for Water Purification. [JOURNAL ARTICLE]
- Adv Mater 2014 Nov 18.
Freestanding ultrathin rGO membranes, with thicknesses down to 17 nm, are fabricated via a facile approach using hydroiodic acid vapor and water-assisted delamination. These unique membranes provide the potential for addressing the key challenge that limits the performance of current forward osmosis membranes.
- Preconcentration of ammonium to enhance treatment of wastewater with the partial nitritation/Anammox process. [JOURNAL ARTICLE]
- Environ Technol 2014 Nov 17.:1-24.
Abstract The anaerobic ammonium oxidation (Anammox) process is one of the most cost-effective technologies for removing excessive nitrogen compounds from effluents of wastewater treatment plants. The study was conducted to assess the feasibility of using ion exchange and reverse osmosis methods to concentrate ammonium to support partial nitritation/Anammox process, which so far has been used for treating only wastewater with high concentrations of ammonium. Upflow anaerobic sludge blanket reactor (UASB) effluents with 40.40, 37.90 and 21.80 mg NH4-N/L levels were concentrated with ion exchange method to 367.20, 329.50 and 187.50 mg NH4-N/L respectively which were about 9 times the initial concentrations. Reverse Osmosis (RO) method was also used to concentrate 41.0 mg NH4-N/L of UASB effluent to 163 mg NH4-N/L at Volume Reduction Factor 5. The rates of nitrogen removal from respective reverse osmosis pre-treated concentrates by partial nitritation/anammox technology were from 0.60, 1.10 and 0.50 g N/m(2)day. The rates were largely influenced by initial nitrogen concentration. However rates of RO concentrates were 0.74, 0.92 and 0.81 g N/m(2)day even at lower initial NH4-N concentration. It was found out from the study that higher salinity decreased rate of nitrogen removal when using partial nitritation/anammox process. Dissolved oxygen concentration of ∼1 mg/L was optimal for the operation of the partial nitritation/anammox process when treating ion exchange and reverse osmosis concentrates. The result shows that ion exchange and reverse osmosis methods can precede a partial nitritation/anammox process to enhance the treatment of wastewater with low ammonium loads.
- Spiral precipitation patterns in confined chemical gardens. [JOURNAL ARTICLE]
- Proc Natl Acad Sci U S A 2014 Nov 10.
Chemical gardens are mineral aggregates that grow in three dimensions with plant-like forms and share properties with self-assembled structures like nanoscale tubes, brinicles, or chimneys at hydrothermal vents. The analysis of their shapes remains a challenge, as their growth is influenced by osmosis, buoyancy, and reaction-diffusion processes. Here we show that chemical gardens grown by injection of one reactant into the other in confined conditions feature a wealth of new patterns including spirals, flowers, and filaments. The confinement decreases the influence of buoyancy, reduces the spatial degrees of freedom, and allows analysis of the patterns by tools classically used to analyze 2D patterns. Injection moreover allows the study in controlled conditions of the effects of variable concentrations on the selected morphology. We illustrate these innovative aspects by characterizing quantitatively, with a simple geometrical model, a new class of self-similar logarithmic spirals observed in a large zone of the parameter space.
- Removal of nitrogen compounds from landfill leachate using reverse osmosis with leachate stabilization in a buffer tank. [JOURNAL ARTICLE]
- Environ Technol 2014 Nov 20.:1-7.
In this paper, a removal of nitrogen compounds from a landfill leachate during reverse osmosis (RO) was evaluated. The treatment facility consists of a buffer tank and a RO system. The removal rate of N─NH4, [Formula: see text] and [Formula: see text] in the buffer tank reached 14%, 91% and 41%, respectively. The relatively low concentration of organic carbon limits N─NH4 oxidation in the buffer tank. The removal rate for the total organic nitrogen (TON) was 47%. The removal rate in RO was 99% for [Formula: see text], 84.1% for [Formula: see text] and 41% for [Formula: see text]. The accumulation of [Formula: see text] may be the result of a low pH, which before the RO process is reduced to a value of 6.0-6.5. Besides it, the cause for a low removal rate of the [Formula: see text] in the buffer tank and during RO may be free ammonia, which can inhibit the [Formula: see text] oxidation. The removal rates of total inorganic nitrogen and TON in the RO treatment facility were similar being 99% and 98.5%, respectively.
- Demineralization of drinking water: Is it prudent? [Journal Article, Review]
- Med J Armed Forces India 2014 Oct; 70(4):377-9.
Water is the elixir of life. The requirement of water for very existence of life and preservation of health has driven man to devise methods for maintaining its purity and wholesomeness. The water can get contaminated, polluted and become a potential hazard to human health. Water in its purest form devoid of natural minerals can also be the other end of spectrum where health could be adversely affected. Limited availability of fresh water and increased requirements has led to an increased usage of personal, domestic and commercial methods of purification of water. Desalination of saline water where fresh water is in limited supply has led to development of the latest technology of reverse osmosis but is it going to be safe to use such demineralized water over a long duration needs to be debated and discussed.
- A novel miniature dynamic microfluidic cell culture platform using electro-osmosis diode pumping. [Journal Article]
- Biomicrofluidics 2014 Jul; 8(4):044116.
An electro-osmosis (EOS) diode pumping platform capable of culturing cells in fluidic cellular micro-environments particularly at low volume flow rates has been developed. Diode pumps have been shown to be a viable alternative to mechanically driven pumps. Typically electrokinetic micro-pumps were limited to low-concentration solutions (≤10 mM). In our approach, surface mount diodes were embedded along the sidewalls of a microchannel to rectify externally applied alternating current into pulsed direct current power across the diodes in order to generate EOS flows. This approach has for the first time generated flows at ultra-low flow rates (from 2.0 nl/s to 12.3 nl/s) in aqueous solutions with concentrations greater than 100 mM. The range of flow was generated by changing the electric field strength applied to the diodes from 0.5 Vpp/cm to 10 Vpp/cm. Embedding an additional diode on the upper surface of the enclosed microchannel increased flow rates further. We characterized the diode pump-driven fluidics in terms of intensities and frequencies of electric inputs, pH values of solutions, and solution types. As part of this study, we found that the growth of A549 human lung cancer cells was positively affected in the microfluidic diode pumping system. Though the chemical reaction compromised the fluidic control overtime, the system could be maintained fully functional over a long time if the solution was changed every hour. In conclusion, the advantage of miniature size and ability to accurately control fluids at ultra-low volume flow rates can make this diode pumping system attractive to lab-on-a-chip applications and biomedical engineering in vitro studies.