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At least 109 records · Page 6Linked to original sources
PubMed2005

Ultraviolet irradiation to preserve high reverse osmosis water quality.

AIMS: The use of ultrapure dialysate decreases hemodialysis patients' morbidity. Bacterial and endotoxin content of reverse osmosis (RO) water is usually lowered or eliminated by a combination of bacterial filtration and regular disinfection of the distribution. Whether bacterial filtration may be replaced by UV irradiation is unknown. MATERIALS AND METHODS: One, and subsequently two UV lamps were inserted in a complex RO water distribution circuit, devoid of bacterial filters. RO water bacterial content was checked weekly between RO water distribution disinfections. RESULTS: With one UV lamp on the departure of the RO water circuit, bacterial results remained negative (< 1 cfu/ml) till the second week after disinfection. Disinfection of the circuit was required every four weeks to comply with the AAMI Guidelines (< 200 cfu/ml). Failure of the lamp was followed by bacterial growth (up to 500 cfu/ml), promptly aborted after replacement of the failed lamp. Subsequent addition of a second UV lamp on the return line of the water circuit kept bacteria < 1 cfu/ml for up to five weeks. Endotoxin levels remained < 0.125 EU. CONCLUSIONS: UV irradiation preserves a low RO water bacterial/endotoxin content in the distribution line and is not associated with a measurable endotoxin increase.

Disinfection↗
PubMed1999

Quantitative structure-activity relationship (QSAR) analysis of surfactants influencing attachment of a Mycobacterium sp. to cellulose acetate and aromatic polyamide reverse osmosis membranes.

A series of 23 neutral, anionic, and zwitterionic surfactants were tested at a concentration of 0.1% wt/vol for their influence on attachment of a Mycobacterium sp. to cellulose acetate (CA) and polyamide (PA) reverse osmosis (RO) membranes. Four cell attachment bioassays were used: (1) semiconcurrent addition of surfactant and bacteria to RO coupons (standard assay); (2) surfactant pretreatment of RO membranes (membrane pretreatment assay); (3) surfactant treatment of adsorbed cells (detachment assay); and (4) surfactant pretreatment of mycobacteria (cell pretreatment assay). Seventeen surfactants inhibited attachment to PA membranes, whereas 15 inhibited attachment to CA in standard assays and, in 13 cases, the same surfactant inhibited attachment to both PA and CA. Despite greater cell attachment to PA than CA, surfactants were typically more effective in the former membrane system. More surfactants were effective in impairing cell attachment than in promoting detachment and a number enhanced attachment in membrane pretreatment assays, suggesting surface modification of RO membranes. Cell pretreatment inhibited attachment to CA membranes, suggesting the bacterial surface was also a target for detergent activity. Multivariate regression and cluster analyses indicated that critical micellar concentration (CMC) was positively correlated with Mycobacterium attachment in CA and PA standard assays. Surfactant dipole moment and octanol/water partitioning (LogP) also contributed to detergent activity in the PA system, whereas dipole moment, molecular topology (i.e., connectivity indices), and charge properties influenced activity in the CA system. Influential variables in membrane pretreatment assays included the LogP, topology indices, and charge properties, whereas CMC played a diminished role. Surfactant dipole moment was most influential in CA membrane detachment assays. Increasing system ionic strength by LiBr addition strengthened inhibition of cell attachment to CA membranes by dodecylbenzene sulfonic acid (DBSA) and promoted DBSA adsorption to CA surfaces as indicated by attenuated total reflection Fourier-transform infrared spectrometry. Results indicate that inhibition of bacterial attachment to RO membranes may be maximized by manipulating surfactant molecular structure to optimize surface adsorption behavior.

Bacterial Adhesion↗
PubMed2001

[Various effects of prostaglandin E2 on reabsorption of water and urea in the amphibia osmosis-regulating epithelium].

Principal similarities between molecular pathways providing the enhancement of water and urea reabsorption under the action of argininvasotocin (AVT) in amphibian urinary bladder suggest that prostaglandin E2 (PGE2) could be a negative regulator of urea transport. To analyse this hypothesis, the role of PGE2 in regulation of urea transport was studied in isolated frog (Rana temporaria L.) urinary bladder. The urea permeability (Pu) was determined from the rate of efflux of (14) Curea from mucosal to serosal solution in isoosmotic conditions. The water permeability was measured in separate experiments in presence of an osmotic gradient. In contrast to water permeability, we were unable to demonstrate any inhibitory effect of 10-1000 nM PGE2 on AVT-stimulated urea transport using a variety of protocols. It was found that basolateral PGE2 exposure (10 nM-1 microM) caused an increase in Pu with no effect on osmotic water flow. The PGE2 effect was markedly inhibited by phloretin, a specific inhibitor of urea transporter. Sulprostone, an EP1/EP3 prostaglandin E2 receptor agonist, had no effect on Pu suggesting the contribution of EP2/EP4 receptor subtypes. In presence of osmotic water flow, the AVT-induced urea transport was significantly higher. This water flow-dependent urea permeability was inhibited by PGE2 although the inhibitory effect was less pronounced in comparison to the action of PGE2 on osmotic water flow. On the basis of these results we can make a conclusion that PGE2 has different role in regulation of water and urea transport in the frog urinary bladder. PGE2 could be considered as a stimulator of urea transport and an inhibitor of osmotic water flow activated by the AVT. The ability of PGE2 to regulate various types of cAMP-dependent transport by different mechanisms seems to be based on the presence of multiple basolateral PGE2 receptor subtypes in amphibian osmosis-regulatory epithelium.

Absorption↗
PubMed2002

Fouling of reverse osmosis and nanofiltration membranes by dairy industry effluents.

Fouling experiments of nanofiltration (NF) and reverse osmosis (RO) are reported for treatment of the effluent of chemical-biological treatment plant and the original effluent of dairy industry respectively. In the experiments, a thin film composite type of spiral wound was used and fitted with flowmeters and pressure sensors. The feed water was stored into a feed tank and passed a fine filter and was pumped to membrane. Brine and permeate were recirculated back to the feed tank. Membrane fouling was investigated with 16 and 30% water recovery of a single membrane at different pressures and flowrates for RO and NF membranes respectively. Fouling is evaluated with a relationship between relative flux (J/Jo) which is the ratio of the flux at any time during the fouling test to the initial flux and relative resistance (Rf/Rm) which is the ratio of fouling (cake) layer resistance to clean membrane resistance. Turbidity, conductivity, chemical oxygen demand (COD), total suspended solids (TSS) and total hardness were measured in the feed and permeate side of each membrane. The effluent total hardness concentrations of chemical-biological treatment plant were found greater than the influents. The results are presented in terms of the relative flux as a function of time related to hydrodynamic conditions and pollution characteristics of wastewater. The permeate water flux of RO membrane decreases more rapidly than NF membrane, the relative flux decreases with increasing the fouling layer resistance, Rf onto membrane surface. 50% the drop of permeate flux was observed for RO and NF membranes after 50 h and 80 h of operation, respectively. The fouling rate increases with an increase in the concentration of the wastewater constituents in the dairy industry. The relative flux decreased 10 and 20% with increasing chemical oxygen demand (COD) from 5,000 mgl-1 to 10,000 mgl-1 and from 45 mgl-1 to 450 mgl-1 for RO and NF membranes, respectively after 45 h of time. Fouling of membranes resulted in 100% increase of specific energy consumption as the relative permeate fluxes of NF and RO membranes decreased 30 and 40% respectively. The average of specific energy consumption was obtained at 6 and 10 kWhm-3; consequently, operational costs were estimated at U.S. $0.45 m-3 and U.S. $0.75 m-3 for NF and RO units respectively. Also, operational cost for chemical-biological treatment was found at U.S. $0.30 m-3.

Agriculture↗
PubMed2002

Dsorption of estrone on nanofiltration and reverse osmosis membranes in water and wastewater treatment.

Adsorption of the trace contaminant estrone, a natural hormone and commonly abundant in surface waters and in treated as well as untreated wastewaters, to eight commercial nanofiltration and reverse osmosis membranes was investigated under well defined conditions. Experiments were conducted in stainless steel stirred cells by spiking trace levels (100 ng x L(-1)) of estrone into five different matrices, namely MilliQ water, a bicarbonate solution, synthetic natural waters containing natural organics, and secondary effluent. Results show that estrone is adsorbed to the membranes to varying degrees with extent of adsorption influenced by the feedwater composition with different mechanisms of association controlling adsorption to different membrane types. Increase in membrane resistance is typically observed to result in decrease in extent of estrone adsorption.

Adsorption↗
PubMed2004

Combined membrane bioreactor (MBR) and reverse osmosis (RO) system for thin-film transistor-liquid crystal display TFT-LCD, industrial wastewater recycling.

In TFT-LCD industry, water plays a variety of roles as a cleaning agent and reaction solvent. As good quality water is increasingly a scarce resource and wastewater treatment costs rises, the once-through use of industrial water is becoming uneconomical and environmentally unacceptable. Instead, recycling of TFT-LCD industrial wastewater is become more attractive from both an economic and environmental perspective. This research is mainly to explore the capacity of TFT-LCD industrial wastewater recycling by the process combined with membrane bioreactor and reverse osmosis processes. Over the whole experimental period, the MBR process achieved a satisfactory organic removal. The COD could be removed with an average of over 97.3%. For TOC and BOD5 items, the average removal efficiencies were 97.8 and 99.4% respectively. The stable effluent quality and satisfactory removal performance were ensured by the efficient interception performance of the UF membrane device incorporated with biological reactor. Moreover, the MBR effluent did not contain any suspended solids and the SDI value was under 3. After treatment of RO, excellent water quality of permeate were under 5 mg/l, 2.5 mg/l and 150 micros/cm for COD, TOC and conductivity respectively. The treated water can be recycled for the cooling tower make-up water or other purposes.

Bioreactors↗
PubMed2005

Use of fouling resistant nanofiltration and reverse osmosis membranes for dyeing wastewater effluent treatment.

Dyeing wastewater was post-treated by using nanofiltration (NF) and reverse osmosis (RO) membranes. To reduce membrane fouling, poly (vinyl alcohol) (PVA) with a neutral charge was coated on NF and RO membranes. The effect of surface charge and surface roughness on membrane fouling was investigated. Dyeing wastewater was pre-treated by using coagulation, activated sludge process, and MF process to investigate the effect of the pre-treatment on the membrane fouling. It is demonstrated that the extent of fouling is significantly influenced by the surface roughness and the surface charge on the NF and RO membranes. A membrane with a smooth and neutral surface was fouled less. The pre-treatment was essential for avoiding NF and RO membranes fouling. The quality of the final permeate was acceptable for water reuse.

Bioreactors↗
PubMed2005

Design considerations for wastewater treatment by reverse osmosis.

Reverse Osmosis is finding increasing use for the treatment of municipal and industrial wastewaters due to the growing demand for high quality water in large urban areas. The growing success of membranes in this application is related to improved process designs and improved membrane products. Key factors which have been determined to result in successful operation of large-scale plants will be discussed. Factors which play a key role in the use of RO membranes include ultra or microfiltration pretreatment, low fouling membranes, flux rate, recovery and control of fouling and scaling. In particular, high flux rates can be used when UF or MF pretreatment is used. These technologies remove most of the suspended particles that would normally cause heavy fouling of lead elements. Typically, fluxes in the range of 17-21 lmh lead to cleaning frequencies in the range of 3-4 months. By combining the use of membrane pretreatment and chloramination of the feed water through chlorine addition, two of the primary sources of RO membrane fouling can be controlled. The use of chloramine has become a proven means to control biofouling in a membrane for wastewater applications. The other significant problems for RO membranes result from organics fouling by dissolved organics and scaling due to saturation of marginally soluble salts. The former can be a significant problem for membranes, due to the strong attraction forces. To some extent, these can be mitigated by making the membrane surface more hydrophilic or changing the charge of the membrane surface. To minimize fouling, many plants are turning to low fouling membranes. Extensive studies have demonstrated that the membrane surface is hydrophilic, neutrally charged over a broad pH range, and more resistant to organic adsorption. Also, an analysis of the potential scaling issues will be reviewed. In particular, calcium phosphate has been found to be one of the key scalants that will limit RO system recovery rate. Calcium phosphate concentrations can reach high values in many wastewaters, and scaling of this compound is not often modeled in most RO projection software. Various process options will be presented to evaluate the most economic means of avoiding phosphate scaling. Finally, data from major RO wastewater treatment plants will be presented to show how the RO membranes operate under actual conditions, utilizing many of these design features. Long-term data from the 2.6 mgd Bedok demonstration Plant demonstrate that the RO membranes operate consistently on wastewater. Experiences from the 8.5 mgd (32,000 m3/day) Bedok and 10.5 mgd (40,000 m3/day) Kranji plants will also be presented. These large plants started operation in the fall of 2002 and have demonstrated an effective means to reclaim high quality water from difficult source waters, such as municipal wastewaters.

Bioreactors↗
PubMedDate not supplied

The production of pharmaceutical grades of water using continuous deionization post-reverse osmosis.

Continuous deionization (CDI) devices to purify water have recently become available. CDI and reverse osmosis (RO) equipment can form the key elements of water treatment trains that produce ultrapure water, without the need for the chemical regenerants associated with batch ion-exchange processes. CDI systems used as downstream polishers of RO product water have been found to be effective for the removal of trace ionic contaminants. Recently, CDI technology was extended, and devices are now capable of removing dissolved carbon dioxide without the requirement of pH adjustment. Examples from a number of installations are provided. CDI systems have been found to reduce the levels of total oxidizable carbon as well. Field experiences are provided and discussed. RO/CDI systems can be maintained to provide product water with low levels of bacteria and pyrogens. The results of a nine-month study of a system designed to produce pharmaceutical grade water are provided.

Drug Industry↗
PubMed1974

Osmosis in cortical collecting tubules. ADH-independent osmotic flow rectification.

The present experiments were designed to evaluate the effects of varying the osmolality of luminal solutions on the antidiuretic hormone (ADH)-independent water and solute permeability properties of isolated rabbit cortical collecting tubules. In the absence of ADH, the osmotic water permeability coefficient (cm s(-1)) P(f) (l-->b), computed from volume flows from hypotonic lumen to isotonic bath, was 20 +/- 4 x 10(-4) (SEM); the value of P(f) (b-->l) in the absence of ADH, computed from volume flows from isotonic bath to hypertonic lumen, was 88 +/- 15 x 10(-4) cm s(-1). We also measured apparent urea permeability coefficients (cm s(-1)) from (14)C-urea fluxes from lumen to bath (P(DDurea) (l-->b)) and from bath to lumen (P(DDurea) (b-->l)). For hypotonic luminal solutions and isotonic bathing solutions, P(DDurea) (l-->b) was 0.045 +/- 0.004 x 10(-4) and was unaffected by ADH. The ADH-independent values of P(DDurea) (l-->b) and P(urea) (b-->l) were, respectively, 0.216 +/- 0.022 x 10(-4) cm s(-1) and 0.033 +/- 0.002 x 10(-4) cm s(-1) for isotonic bathing solutions and luminal solutions made hypertonic with urea, i.e., there was an absolute increase in urea permeability and asymmetry of urea fluxes. Significantly, P(DDurea) (l-->b) did not rise when luminal hypertonicity was produced by sucrose; and, bathing fluid hypertonicity did not alter tubular permeability to water or to urea. We interpret these data to indicate that luminal hypertonicity increased the leakiness of tight junctions to water and urea but not sucrose. Since the value of P(f) (b-->l) in the absence of ADH, when tight junctions were open to urea, was approximately half of the value of P(f) (l-->b) in the presence of ADH, when tight junctions were closed to urea, we conclude that tight junctions are negligible paracellular shunts for lumen to bath osmosis with ADH. These findings, together with those in the preceding paper, are discussed in terms of a solubility-diffusion model for water permeation in which ADH increases water solubility in luminal plasma membranes.

Animals↗
PubMed2001

Continuous preconcentration system for nitrate ions using anionic reverse osmosis tubes coupled to an ion chromatograph.

A continuous preconcentration system for nitrate ions was developed using cation exchange tubing made from Nafion perfluorosulfonic acid membrane. This method is based on ion exclusion effects and reverse osmosis phenomena. The system was evaluated by connecting it to an ion chromatograph. The concentration ratios could be increased by raising the pressures between the two sides of the cation exchange tubing. Twenty-fold concentration of nitrate ion was achieved when the pump pressure was 20 x 10(5) Pa. The relative standard deviations of the preconcentration ratio at four different pump pressures, 5, 10, 15 and 20 x 10(5) Pa were 1.2-2.8% (n = 5).

Journal Article↗
PubMed2004

Preparation of alpha-alumina-supported mesoporous bentonite membranes for reverse osmosis desalination of aqueous solutions.

In this study, mesoporous bentonite clay membranes approximately 2 microm thick were prepared on porous alpha-alumina substrates by a sol-gel method. Nanosized clay particles were obtained from commercial Na-bentonite powders (Wyoming) by a process of sedimentation, washing, and freeze-drying. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption were employed for membrane characterization. It was found that the content of solids, concentration of polymer binder, and pH value of the clay colloidal suspension had critical influences on membrane formation during the dip-coating process. The membranes were tested for reverse osmosis separation of a 0.1 M NaCl solution. Both water permeability and Na(+) rejection rate of the supported membranes were comparable to those of the compacted thick membranes reported in the literature. However, due to the drastically reduced membrane thickness, water permeance and flux of the supported membranes were significantly higher than those of the compacted thick membranes. It was also observed that the calcination temperature played a critical role in determining structural stability in water and desalination performance of the clay membrane.

Journal Article↗
PubMed2006

Coupling reverse osmosis with electrodialysis to isolate natural organic matter from fresh waters.

Reverse osmosis (RO) has proven to be an effective method for the concentration of natural organic matter (NOM) from fresh waters, but an undesirable consequence of this process is the co-concentration of some inorganic solutes. Accordingly, current practice yields solutions of NOM that, upon desalting and freeze-drying, are converted into dry solids containing finely dispersed sulfuric acid and silicic acid (H(4)SiO(4)). These acids will contribute to the apparent carboxylic and phenolic contents of NOM, leading to an overestimation of both. NOM may also be chemically altered by sulfuric acid, which reacts strongly with many classes of organic compounds. The sulfur content and ash content of NOM will be elevated in the presence of sulfuric acid and H(4)SiO(4). The goal of this study is to develop and test a method in which the removal of water by RO is coupled with the removal of salts by electrodialysis (ED). Like RO, ED is a relatively mild treatment that enables the desalting of NOM solutions without subjecting those samples to conditions of extremely high or low pH. The end product of the coupled process is a desalted, concentrated liquid sample from which low-ash NOM can be obtained as a freeze-dried solid material. In this study, the efficacy of ED for desalting NOM is evaluated using concentrated synthetic river waters and actual concentrated (by RO) river waters. Under optimal operating conditions, both sulfate and silica can be largely removed from RO-concentrated solutions of riverine NOM with only an average loss of 3% of total organic carbon.

Adsorption↗
PubMed1995

Typhoid fever from water desalinized using reverse osmosis.

In May 1992, 81 bacteriologically confirmed cases of typhoid fever (TF) were identified in all districts of Tabuk City in northwestern Saudi Arabia. Attack rates (AR) in residential districts ranged from 0.9-10.3 per 10,000. Confirmed cases included 9 workers in the city's referral hospital, King Khalid Hospital (AR 140/10,000), 2 in families of medical staff, 57 in the community (AR 4.4/10,000) and 13 in a local military cantonment (AR 0.8/10,000). The outbreak began with the onset of TF in the three areas within 5 days, continued for 7 weeks, and ended 2 weeks after chlorination began. Among water sources, the odds ratio (OR) was highest (2.6; 95% confidence interval [CI] 1.25-5.39) for water purchased from reverse osmosis (RO) plants, especially RO plants supplied by one well (ASUW) (OR = 7.05; 95% CI 2.51-20.7). The aquifer for ASUW lay partially beneath a depression where city sewage collected. Unchlorinated water samples from ASUW 1 month after the outbreak ended yielded coliforms. ASUW probably became contaminated with Salmonella typhi when KKH demand overtaxed the aquifer and drew in surface water. Membranes in RO plants using this unchlorinated well water could then become fouled with S. typhi. RO plants, which are common throughout Saudi Arabia, need close monitoring. Water for RO must be prechlorinated to prevent microbiologic fouling of the membranes.

Adolescent↗
PubMed2005

Biofilm formation characteristics of bacterial isolates retrieved from a reverse osmosis membrane.

High-quality water purification systems using reverse osmosis (RO) membrane separation have faced a major challenge related to biofilm formation on the membrane surface, or biofouling. To understand this issue, the biofilm formation characteristics of four bacterial isolates previously retrieved from an RO membrane treating potable water were investigated. Biofilm formation of all four isolates occurred to different extents in microtiter plates and could be related to one or more cell properties (hydrophobicity, surface charge, and motility). For Dermacoccus sp. strain RO12 and Microbacterium sp. strain RO18, bacterial adhesion was facilitated by cell surface hydrophobicity, and for Rhodopseudomonas sp. strain RO3, adhesion was assisted by its low surface charge. Sphingomonas sp. strain RO2 possessed both twitching and swarming motilities, which could be important in mediating surface colonization. Further, strains RO2, RO3, and RO12 did not exhibit swimming motility, suggesting that they could be transported to RO membrane surfaces by other mechanisms such as convective permeate flow. The biofilm formation of RO2 was further tested on different RO membranes made of cellulose acetate, polyamide, and thin film composite in continuous flow cell systems. The resultant RO2 biofilms were independent of membrane surface properties and this was probably related to the ex-opolysaccharides secreted bythe biofilm cells. These results suggested that RO2 could colonize RO membranes effectively and could be a potential fouling organism in RO membranes for freshwater purification.

Bacterial Physiological Phenomena↗
PubMed2006

Use of reverse osmosis membranes to remove perfluorooctane sulfonate (PFOS) from semiconductor wastewater.

Perfluorooctane sulfonate (PFOS) and related substances are persistent, bioaccumulative, and toxic, and thus of substantial environmental concern. PFOS is an essential photolithographic chemical in the semiconductor industry with no substitutes yet identified. The industry seeks effective treatment technologies. The feasibility of using reverse osmosis (RO) membranes for treating semiconductor wastewater containing PFOS has been investigated. Commercial RO membranes were characterized in terms of permeability, salt rejection, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and membrane surface zeta potential (streaming potential measurements). Filtration tests were performed to determine the membrane flux and PFOS rejection. Over a wide range of feed concentrations (0.5 - 1500 ppm), the RO membranes generally rejected 99% or more of the PFOS. Rejection was better for tighter membranes, but was not affected by membrane zeta potential. Flux decreased with increasing PFOS concentration. While the flux reduction was severe for a loose RO membrane probably due to its higher initial flux, very stable flux was maintained for tighter membranes. At a very high feed concentration (about 500 ppm), all the membranes exhibited an identical stable flux. Isopropyl alcohol, present in some semiconductor wastewaters, had a detrimental effect on membrane flux. Where present it needs to be removed from the wastewater prior to using RO membranes.

Alkanesulfonic Acids↗
PubMed2006

Electro-osmosis at inhomogeneous charged surfaces: hydrodynamic versus electric friction.

Electrokinetic methods are efficient in probing the electrostatic surface properties of charged systems. However, anomalies observed in experiments indicate that the classical electrokinetic theory should be reconsidered. Using Green's function methods and hydrodynamic simulations, we investigate electro-osmosis driven by electric-field-induced ion motion near a charged planar substrate with smooth or rough boundary. First, a reformulation of electro-osmotic theory for planar charged surfaces employing Green's functions shows that the Helmholtz-Smoluchowski (HS) relation between electrostatic potential and solvent velocity is exact for smooth surfaces, even in the presence of ion correlations. Deviations from HS theory are caused by combined hydrodynamic and electric surface friction, as our hydrodynamic simulations of ions at smooth and corrugated charged surfaces in lateral electric fields demonstrate. Within the simulations, hydrodynamic interactions are treated in the continuum limit and the presence of a no-slip boundary condition at the surface is taken into account. While electrofriction is relevant in highly charged system and/or for multivalent ions, hydrodynamic friction is dominant in systems with moderate surface charge density and/or low ionic valency. We also derive the effective electrokinetic surface charge from the electro-osmotic solvent profiles, which is substantially reduced when compared with the bare value and shows qualitative agreement with the experimental tendency.

Journal Article↗