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- Hyperosmolality-mediated peritoneal microvascular vasodilation is linked to aquaporin function. [Journal Article, Research Support, Non-U.S. Gov't]
- Adv Perit Dial 2014.:63-74.
Glucose-based peritoneal dialysis (PD) solutions dilate the parietal and visceral peritoneal microvasculature by endothelium-dependent mechanisms that primarily involve hyperosmolality. This PD-mediated dilation occurs by active intracellular glucose uptake and adenosine Al receptor activation, and by hyperosmolality-stimulated glibenclamide-sensitive potassium channels. Both pathways invoke NO as a second messenger for vasodilation. We hypothesized that during crystalloid-induced osmosis, the osmotic water flux through the transendothelial water-exclusive aquaporin 1 (AQP1) channels is the primary mechanism whereby the endothelium is being stimulated to instigate hyperosmolality-driven vasodilation. Four microvascular levels (diameters in the range 6 - 100 microm) were visualized by intravital videomicroscopy of the terminal ileum in anesthetized rats. Microvascular diameters and flow were measured after topical exposure to a 5% hypertonic mannitol or 2.5% glucose-based PD solution, at baseline and after brief tissue pre-treatment (with 0.1% glutaraldehyde for 10 seconds) or after combined tissue pre-treatment and pharmacologic blockade of AQP1 with HgCl2 (100 micromol/L). Vascular endothelial integrity was verified by the response to acetylcholine (10(-4) mol/L) and sodium nitroprusside (10(-4) mol/L). The hyperosmolar solutions both caused rapid and sustained vasodilation at all microvascular levels, which was not altered by tissue pre-treatment. Inhibition of AQP1 completely abolished the mannitol-induced vasodilation and markedly attenuated the PD fluid-mediated vasodilation. Neither glutaraldehyde pre-treatment nor HgCl2 affected tissue integrity or endothelial cell function. We conclude that the peritoneal microvascular vasodilation caused by hyperosmolar PD fluid is instigated by the osmotic water flux through AQP1. Clinical PD solutions have components other than hyperosmolality that can induce endothelium-dependent peritoneal microvascular vasodilation independent of the AQP1-mediated osmosis.
- Process optimization for osmo-dehydrated carambola (Averrhoa carambola L) slices and its storage studies. [Journal Article]
- J Food Sci Technol 2014 Oct; 51(10):2472-80.
An osmotic-dehydration process protocol for Carambola (Averrhoacarambola L.,), an exotic star shaped tropical fruit, was developed. The process was optimized using Response Surface Methodology (RSM) following Central Composite Rotatable Design (CCRD). The experimental variables selected for the optimization were soak solution concentration (°Brix), soaking temperature (°C) and soaking time (min) with 6 experiments at central point. The effect of process variables was studied on solid gain and water loss during osmotic dehydration process. The data obtained were analyzed employing multiple regression technique to generate suitable mathematical models. Quadratic models were found to fit well (R(2), 95.58 - 98.64 %) in describing the effect of variables on the responses studied. The optimized levels of the process variables were achieved at 70°Brix, 48 °C and 144 min for soak solution concentration, soaking temperature and soaking time, respectively. The predicted and experimental results at optimized levels of variables showed high correlation. The osmo-dehydrated product prepared at optimized conditions showed a shelf-life of 10, 8 and 6 months at 5 °C, ambient (30 ± 2 °C) and 37 °C, respectively.
- Endoscopy supply water and final rinse testing: five years of experience. [JOURNAL ARTICLE]
- J Hosp Infect 2014 Sep 28.
The penultimate stage in endoscope reprocessing is the final rinse with water following terminal disinfection. This requires a degree of microbiological and chemical control of the quality of the final rinse water.To report experience gained over five years of testing, reporting and managing the quality of final rinse water for endoscopic devices.Three endoscope reprocessing units, each comprising five endoscope washer-disinfectors (EWDs) supplied by two reverse osmosis (RO) water units, were subjected to weekly monitoring and control of final rinse water quality. EWDs were subjected to nightly thermal self-disinfection, and RO units were subjected to periodic sanitization with peracetic acid. Final rinse water samples were processed periodically for total viable counts (TVCs), Pseudomonas spp., endotoxins, conductivity, environmental mycobacteria and Legionella spp.Over the five-year study period (2008-2013), no Pseudomonas spp., environmental mycobacteria or Legionella spp. were isolated from endoscopy rinse water. All conductivity readings were below 30μs/cm. Endotoxin levels fluctuated over the recommended cut-off of 0.25EU/mL, with no correlation with TVCs. Trend analysis of TVCs established alert and action limits. Apart from the supply water of one EWD becoming contaminated with Aspergillus spp., there have been no interruptions to operational capacity of the endoscope reprocessing units.Quality control principles coupled with appropriate thermal and chemical disinfection of EWDs resulted in the achievement of microbiological standards for final rinse water. A co-ordinated team approach between the microbiology department, infection control department, endoscope unit managers and estates department is required to achieve this degree of success.
- Assessing the utility of testing aluminum levels in dialysis patients. [JOURNAL ARTICLE]
- Hemodial Int 2014 Oct 13.
Plasma aluminum (Al) is routinely tested in many dialysis patients. Aluminum exposure may lead to acute toxicity and levels in excess of ∼2.2 μmol/L (60 μg/L) should be avoided. Historically, toxicity has been caused by excessive dialyzate Al but modern reverse osmosis (RO) water should be Al free. Nevertheless, many units continue to perform routine Al levels on dialysis patients. This single-center study retrospectively analyzed Al levels in plasma, raw water feed, and RO product between 2010 and 2013 using our database (Nephworks 6) with the aim of determining the utility of these measurements. Two thousand fifty-eight plasma Al tests in 755 patients (61.9% male, mean age 64.7 years) were reviewed showing mean ± SD of 0.41 ± 0.30 μmol/L. One hundred eleven (5.4%) tests from 61 patients had Al levels >0.74 μmol/L and 45 (73.8%) of these patients were or had been prescribed Al hydroxide (Al(OH)3 ) as a phosphate binder. Seven patients had Al concentrations >2.2 μmol/L with no source of Al identified in 1 patient. One hundred sixty-six patients taking Al(OH)3 (78.7% of all patients on Al(OH)3 ) had levels ≤0.74 μmol/L, the odds ratio of plasma Al > 0.74 μmol/L on Al(OH)3 was 9. The cost of plasma Al assay is $A30.60; thus, costs were $A62,974.80 over the study period. Despite RO feed water Al levels as high as 48 μmol/L, Al output from the RO was almost always undetectable (<0.1 μmol/L) with dialyzate Al levels > 2.2 μmol/L only 3 times since 2010, and never in the last 3 years. Routine unselected testing of plasma Al appears unnecessary and expensive and more selective testing in dialysis patients should be considered.
- Bacterial bioluminescence response to long-term exposure to reverse osmosis treated effluents from dye industries. [Journal Article]
- Can J Microbiol 2014 Oct; 60(10):661-8.
The bacterial bioluminescence assay is one of the novel means for toxicity detection. The bioluminescence response of 2 marine bioluminescent bacteria was tested upon their long-term exposure to 9 different reverse osmosis (RO) rejects with varying chemical composition sampled from various dye industries. Bioluminescent bacteria were cultured in the RO reject samples, at different concentrations, and their growth rate and luminescence was measured for 24 h. The RO reject samples caused sublethal effects upon exposure and retarded the growth of bacteria, confirming their toxic nature. Further, continuation of the exposure showed that the initial luminescence, though reduced, recovered and increased beyond the control cultures irrespective of cell density, and finally decreased once again. The present study emphasizes the need of evolving a long-term exposure assay and shows that the method followed in this study is suitable to evaluate the toxicants that exert delayed toxicity, using lower concentrations of toxicants as well as coloured samples.
- Biofouling and Microbial Communities in Membrane Distillation and Reverse Osmosis. [JOURNAL ARTICLE]
- Environ Sci Technol 2014 Oct 8.
Membrane distillation (MD) is an emerging desalination technology that uses low-grade heat to drive water vapor across a microporous hydrophobic membrane. Currently, little is known about the biofilms that grow on MD membranes. Here, we use estuarine water collected from Long Island Sound in a bench-scale direct contact MD system to investigate the initial stages of biofilm formation. For comparison, we studied biofilm formation in a bench-scale reverse osmosis (RO) system using the same feed water. Each of these membrane desalination systems exposes the natural microbial community to vastly different environmental conditions -- high temperatures with no hydraulic pressure in MD and low temperature with hydraulic pressure in RO. Over the course of 4 days, we observed a steady decline in bacteria concentration (nearly 2 orders of magnitude) in the MD feed reservoir. Even with this drop in planktonic bacteria, one case of a 50 % flux decline in MD over 12 h with pre-filtered sea water was observed. Biofilm morphologies on MD and RO membranes were markedly different. MD membrane biofilms were heterogeneous and contained several colonies, while RO membrane biofilms, although thicker, were a homogenous mat. Phylogenetic analysis using next-generation sequencing of 16S ribosomal DNA showed significant shifts in the microbial communities. Bacteria representing the orders Burkholderiales, Rhodobacterales, and Flavobacteriales were most abundant in the MD biofilms. Based on the results, we propose two different regimes for microbial community shifts and biofilm development in RO and MD systems.
- An osmolyte-based micro-volume ultrafiltration technique. [JOURNAL ARTICLE]
- Lab Chip 2014 Oct 6.
This paper discusses a novel, simple, and inexpensive micro-volume ultrafiltration technique for protein concentration, desalting, buffer exchange, and size-based protein purification. The technique is suitable for processing protein samples in a high-throughput mode. It utilizes a combination of capillary action, and osmosis for drawing water and other permeable species from a micro-volume sample droplet applied on the surface of an ultrafiltration membrane. A macromolecule coated on the permeate side of the membrane functions as the osmolyte. The action of the osmolyte could, if required, be augmented by adding a supersorbent polymer layer over the osmolyte. The mildly hydrophobic surface of the polymeric ultrafiltration membrane used in this study minimized sample droplet spreading, thus making it easy to recover the retained material after separation, without sample interference and cross-contamination. High protein recoveries were observed in the micro-volume ultrafiltration experiments described in the paper.
- In-situ biofilm characterization in membrane systems using Optical Coherence Tomography: Formation, structure, detachment and impact of flux change. [JOURNAL ARTICLE]
- Water Res 2014 Sep 16.:243-254.
Biofouling causes performance loss in spiral wound nanofiltration (NF) and reverse osmosis (RO) membrane operation for process and drinking water production. The development of biofilm formation, structure and detachment was studied in-situ, non-destructively with Optical Coherence Tomography (OCT) in direct relation with the hydraulic biofilm resistance and membrane performance parameters: transmembrane pressure drop (TMP) and feed-channel pressure drop (FCP). The objective was to evaluate the suitability of OCT for biofouling studies, applying a membrane biofouling test cell operated at constant crossflow velocity (0.1 m s(-1)) and permeate flux (20 L m(-2)h(-1)). In time, the biofilm thickness on the membrane increased continuously causing a decline in membrane performance. Local biofilm detachment was observed at the biofilm-membrane interface. A mature biofilm was subjected to permeate flux variation (20 to 60 to 20 L m(-2)h(-1)). An increase in permeate flux caused a decrease in biofilm thickness and an increase in biofilm resistance, indicating biofilm compaction. Restoring the original permeate flux did not completely restore the original biofilm parameters: After elevated flux operation the biofilm thickness was reduced to 75% and the hydraulic resistance increased to 116% of the original values. Therefore, after a temporarily permeate flux increase the impact of the biofilm on membrane performance was stronger. OCT imaging of the biofilm with increased permeate flux revealed that the biofilm became compacted, lost internal voids, and became more dense. Therefore, membrane performance losses were not only related to biofilm thickness but also to the internal biofilm structure, e.g. caused by changes in pressure. Optical Coherence Tomography proved to be a suitable tool for quantitative in-situ biofilm thickness and morphology studies which can be carried out non-destructively and in real-time in transparent membrane biofouling monitors.
- Impact of organic nutrient load on biomass accumulation, feed channel pressure drop increase and permeate flux decline in membrane systems. [JOURNAL ARTICLE]
- Water Res 2014 Sep 16.:227-242.
The influence of organic nutrient load on biomass accumulation (biofouling) and pressure drop development in membrane filtration systems was investigated. Nutrient load is the product of nutrient concentration and linear flow velocity. Biofouling - excessive growth of microbial biomass in membrane systems - hampers membrane performance. The influence of biodegradable organic nutrient load on biofouling was investigated at varying (i) crossflow velocity, (ii) nutrient concentration, (iii) shear, and (iv) feed spacer thickness. Experimental studies were performed with membrane fouling simulators (MFSs) containing a reverse osmosis (RO) membrane and a 31 mil thick feed spacer, commonly applied in practice in RO and nanofiltration (NF) spiral-wound membrane modules. Numerical modeling studies were done with identical feed spacer geometry differing in thickness (28, 31 and 34 mil). Additionally, experiments were done applying a forward osmosis (FO) membrane with varying spacer thickness (28, 31 and 34 mil), addressing the permeate flux decline and biofilm development. Assessed were the development of feed channel pressure drop (MFS studies), permeate flux (FO studies) and accumulated biomass amount measured by adenosine triphosphate (ATP) and total organic carbon (TOC). Our studies showed that the organic nutrient load determined the accumulated amount of biomass. The same amount of accumulated biomass was found at constant nutrient load irrespective of linear flow velocity, shear, and/or feed spacer thickness. The impact of the same amount of accumulated biomass on feed channel pressure drop and permeate flux was influenced by membrane process design and operational conditions. Reducing the nutrient load by pretreatment slowed-down the biofilm formation. The impact of accumulated biomass on membrane performance was reduced by applying a lower crossflow velocity and/or a thicker and/or a modified geometry feed spacer. The results indicate that cleanings can be delayed but are unavoidable.
- Electro-osmosis of non-Newtonian fluids in porous media using lattice Poisson-Boltzmann method. [JOURNAL ARTICLE]
- J Colloid Interface Sci 2014 Sep 10.:186-193.
Electro-osmosis in porous media has many important applications in various areas such as oil and gas exploitation and biomedical detection. Very often, fluids relevant to these applications are non-Newtonian because of the shear-rate dependent viscosity. The purpose of this study was to investigate the behaviors and physical mechanism of electro-osmosis of non-Newtonian fluids in porous media. Model porous microstructures (granular, fibrous, and network) were created by a random generation-growth method. The nonlinear governing equations of electro-kinetic transport for a power-law fluid were solved by the lattice Poisson-Boltzmann method (LPBM). The model results indicate that: (i) the electro-osmosis of non-Newtonian fluids exhibits distinct nonlinear behaviors compared to that of Newtonian fluids; (ii) when the bulk ion concentration or zeta potential is high enough, shear-thinning fluids exhibit higher electro-osmotic permeability, while shear-thickening fluids lead to the higher electro-osmotic permeability for very low bulk ion concentration or zeta potential; (iii) the effect of the porous medium structure depends significantly on the constitutive parameters: for fluids with large constitutive coefficients strongly dependent on the power-law index, the network structure shows the highest electro-osmotic permeability while the granular structure exhibits the lowest permeability on the entire range of power law indices considered; when the dependence of the constitutive coefficient on the power law index is weaker, different behaviors can be observed especially in case of strong shear thinning.