Average Osmotic Pressure Research Articles

Impact of hydrodynamic conditions on optimum power generation in dual stage pressure retarded osmosis using spiral-wound membrane

The Dual Stage Pressure Retarded Osmosis technique is considered for power generation. The influence of feed flow rates, hydraulic pressure, and pressure drop on mass transfer and solute diffusion in a full-scale membrane model was investigated for the first time to maximize power generation. Dead Sea-seawater, Dead Sea-reverse osmosis brine, reverse osmosis brine-wastewater, and seawater-wastewater salinity gradient resources were investigated for power generation. Results revealed a 71.07% increase in the specific power generation due to the dual-stage pressure retarded osmosis process optimization using Dead Sea-seawater salinity gradient resources. The increase in the specific power generation due to the dual-stage pressure retarded osmosis optimization was 108.8%, 63.18%, and 133.54%, respectively, for Dead Sea-reverse osmosis brine, reverse osmosis brine-wastewater, and seawater-wastewater salinity gradient resources. At optimum operating conditions, using the dual-stage pressure retarded osmosis process as an alternative to the single pressure retarded osmosis process achieved up to a 22% increase in the energy output. Interestingly, the hydraulic pressure at optimum operating conditions was slightly higher than the average osmotic pressure gradients in the dual-stage pressure retarded osmosis process. The study also revealed that power generation in the dual-stage pressure retarded osmosis process operating at constant mass transfer and solute resistivity parameters was overestimated by 2.8%.

Expansion of Ion Effects on Water Induced by a High Hydrophilic Surface of a Polymer Network.

The spatial extent and anion-cation cooperativity of the ion effect on the structure and dynamics of water have long been debated but are still controversial. Previously, we experimentally demonstrated the extensive and cooperative effect of ions on water in a polyamide network by measuring the reflection wavelength (λ) on the ion sensor of poly(N-isopropylacrylamide) (PNIPAAm) hydrogel-immobilized photonic crystals. In the present study, we investigated the influence of the polymer surface on the ion effect by adopting a highly hydrophilic poly(N-isopropylacrylamide-co-N-acryloylaza-18-crown-6) hydrogel as a sensor matrix. In alkaline earth metal salt solutions, the copolymer hydrogel membrane sensor showed the redshift of λ for the specific combination of cations and anions, that is, Ca2+/Cl- and Sr2+/NO3-, which resulted from the concerted binding of ion pairs to the copolymer receptor. In alkali metal salt solutions, the ion sensor showed the blueshift of λ originating from the osmotic dehydration suppressed by the salts. The strength of the ion effect was evaluated by the average osmotic pressure (ΠA) required for the salt-inhibited dehydration in the early stage of hydrogel contraction. From the calculation results of ΠA for the copolymer and PNIPAAm hydrogels, it was found that the high hydrophilic copolymer surface more significantly enhanced the ion effect of structure-making cations (i.e., Li+) compared with borderline (Na+) and structure-breaking (K+ and Cs+) cations. Furthermore, the ion effect exhibited the higher ion cooperativity in combination with chloride anions than with nitrate anions. The enhancement of the long-range cooperative ion effect is derived from the expansion of the interactions between ions, water molecules, and the hydrophilic polymer network.

Addressing drinking water salinity due to sea water intrusion in Praia de Leste, Parana, by a brackish water desalination pilot plant

Seawater intrusion into the Pombas River, source of freshwater to Praia de Leste on the coast of Parana in Brazil presents a problem to the water utility as most water treatment plants in Brazil are conventional. To find a solution to this problem, a pilot plant (1 m3 /h) consisting of ultrafiltration (UF) followed by reverse osmosis (RO) was developed and evaluated. For testing, brackish water was produced with a concentration of 1,500 ± 100 mg/L of total dissolved solids (TDS), mixing seawater and fresh water. To evaluate the water quality, TDS, electrical conductivity, pH, temperature, apparent color, turbidity, alkalinity, total hardness, calcium, chloride and sulfate were monitored. For operational performance, flowrates, osmotic pressure, filtration rate, recovery rate and mass balance were analyzed. On average, the UF system removed 96.4% of turbidity and 98.6% of apparent color; whereas the RO system removed 99.4% of TDS. The overall average recovery (UF and RO) was 45.81% with average osmotic pressure of 8.21 bar, filtration rate of 30.7 L/h/m2 in the UF system and 21.7 L/h/m2 in the RO system. From a water quality point of view, the system was effective in processing brackish into fresh water of high quality.

Impact of membrane orientation on the energy efficiency of dual stage pressure retarded osmosis

The performance of Dual Stage Pressure Retarded Osmosis (DSPRO) was analyzed using a developed computer model. DSPRO process was evaluated on Pressure Retarded Osmosis (PRO) and Forward Osmosis (FO) operating modes for different sodium chloride (NaCl) draw and feed concentrations. Simulation results revealed that the total power generation in the DSPRO process operating on the PRO mode was 2.5–5 times more than that operating on the FO mode. For DSPRO operating on the PRO mode, the higher power generation was in the case of 2 M NaCl-fresh and 32% the contribution of the second stage to the total power generation in the DSPRO. To the contrast, he total power generated in the DSPRO operating on the FO mode was in the following order 5M-0.6M > 5M-0.7M > 2M-0.01 > 2M-0.6 M. Interestingly, single stage process operating on the FO mode performed better than DSPRO process due to the severe concentration polarization effects. The results also showed that power density of the DSPRO reached a maximum amount at a hydraulic pressure less than the average osmotic pressure gradient, Δπ/2, due to the variation of optimum operating pressure of each stage. Moreover, results showed that the effective specific energy in the PRO process was lower than the maximum specific energy. However, the effective specific energy of the DSPRO was larger than that of the single stage PRO due to the rejuvenation of the salinity gradient, emphasizing the high potential of the DSPRO process for power generation.

Force-Induced Unzipping Transitions in an Athermal Crowded Environment

Using theoretical arguments and extensive Monte Carlo (MC) simulations of a coarse-grained three-dimensional off-lattice model of a β-hairpin, we demonstrate that the equilibrium critical force, Fc, needed to unfold the biopolymer increases nonlinearly with increasing volume fraction occupied by the spherical macromolecular crowding agent. Both scaling arguments and MC simulations show that the critical force increases as Fc ≈ φc(α). The exponent α is linked to the Flory exponent relating the size of the unfolded state of the biopolymer and the number of amino acids. The predicted power law dependence is confirmed in simulations of the dependence of the isothermal extensibility and the fraction of native contacts on φc. We also show using MC simulations that Fc is linearly dependent on the average osmotic pressure (P) exerted by the crowding agents on the β-hairpin. The highly significant linear correlation coefficient of 0.99657 between Fc and P makes it straightforward to predict the dependence of the critical force on the density of crowders. Our predictions are amenable to experimental verification using laser optical tweezers.

Osmotic pressure and substrate resistance during the concentration of manure nutrients by reverse osmosis membranes

The objective of the membrane technology presented here is the production of nitrogen concentrates from pretreated swine manure. This paper reports on the effect of osmotic pressure and substrate resistance on transmembrane flux during the concentration of prefiltered swine (PFS) manure by reverse osmosis (RO) membranes. The PFS manure at various concentration levels was filtered by four highly selective polyamide RO membranes with maximum allowable pressures ranging from 41 to 83 bar. The osmotic pressure created by the PFS manure on the RO membranes fitted a second-order equation with respect to manure conductivity or total ammonia-nitrogen (TAN), indicating that the rate of increase in osmotic pressure accelerated as manure was being concentrated. Average osmotic pressure increased by a factor of 6.8, from 5.4 to 36.6 bar, as TAN was increased 5.6 times, from 1.6 g to 9.2 g/l. Substrate-related resistance, which has been attributed to specific membrane–solute interactions even in the absence of flow, tended to increase as PFS manure concentration increased. However, reduction in transmembrane flux during manure concentration was mainly due to increase in osmotic pressure. If the objective of the technology is to concentrate manure in small volumes with high nitrogen concentrations, RO systems have to be equipped with membranes that are able to sustain high applied pressures, because the decrease in flow due to increased osmotic pressure along membrane elements will be substantial.

Tissue stresses and their graviresponsive changes in stems of Reynoutria japonica Houtt

Summary The internodes of Reynoutria (Japanese knotweed) form hollow cylinders in which the epidermis and the underlying collenchyma are under tissue stress (TS) of a tensile type, while most of the compressive TS occurs in the thin-walled peripheral pith. To fulfil static equilibrium, the forces that generate these stresses have equal magnitude, in this case 0.23 N per mm of circumference in vertical stems as measured by restretching tissue peels consisting of epidermis and collenchyma. The tensile TS in the collenchyma and the epidermis amounted to 3 · 106N · m−2, nearly 5 times higher than the average osmotic pressure of cell sap, while the magnitude of the compressive TS in the remaining tissue was on the average 20 times lower. The tensile TS underwent relaxation on the lower side of gravireacting stems. This was demonstrated by a smaller bending of a strip slit from the lower side, and also by measurements of the force required to restretch the peels from this side. In horizontally positioned stems, the tensile force on the lower side decreased by a factor of 3, while the force on the upper side remained unaltered. Relaxation of the tensile TS started in the collenchyma. This relaxation on the lower side of a tilted stem is the first mechanical event occurring during a graviresponse. It causes asymmetry in distribution of TSs in the stem, which brings about a net bending moment.

Freezing Tolerance and Water Relations of Opuntia Fragilis from Canada and the United States

To investigate the influence of winter climate on freezing tolerance at the population level, minimum January air temperatures in the field and cold acclimation determined in the laboratory were compared for Opuntia fragilis. Populations occurred at 20 locations as far north as 56°46' N latitude and at elevations up to 3029 m in Canada and the United States, most of which experience extreme freezing temperatures each winter. Low—temperature responses and water relations of stems were examined in the laboratory at day/night air temperatures of 25°/15°C and 14 d after the plants were shifted to a 5°/—5°C temperature cycle. Cold acclimation averaged 17°C and freezing tolerance averaged —29°C for the 20 populations following a shift to low day/night air temperatures, indicating that O. fragilis has the greatest cold acclimation ability and the greatest freezing tolerance reported for any cactus. Moreover, freezing tolerance and cold acclimation were both positively correlated (r2 ° 0.7) with the minimum temperatures at the 20 locations. Plants lost water during low—temperature acclimation, leading to 30% decreases in cladode and chlorenchyma thickness; the decrease in water content was greater for the five warmest populations than for the five coldest ones. Over the same period, the average osmotic pressure of the chlorenchyma increased from 1.42 to 1.64 MPa, and the relative water content (RWC) decreased from 0.58 to 0.49, but the average osmotic pressure of saturated chlorenchyma was unchanged, indicating no net change in solute content during acclimation. Although the role of water relations in freezing tolerance is unclear, the substantial freezing tolerance and cold acclimation ability of O. fragilis leads to its distribution into regions of Canada and the United States that experience minimum temperatures below —40°C during the winter.

Water relations of Picea abies. II. Determination of the apoplastic water content and other water relations parameters of needles by means of capillary microcryoscopy and the pressure‐volume

Using the pressure volume analysis (PV analysis) on the shoots of Norway spruce (Picea abies [L.] Karst.) and the here presented capillary microcryoscopy of the needle press sap of the same shoots, it was possible to determine the amount of apoplastic water in the needles (Wan) as well as in the defoliated shoots (Was). Additionally, the bulk osmotic pressure at full water saturation in the symplast of the needles and defoliated shoots (πon and πos) was determined. The dependence of the bulk‐averaged turgor pressure (Pt) on the water content and the relationship between the bulk modulus of elasticity of the needles (ɛn) and the bulk‐averaged needle turgor pressure (Ptn) was shown with help of the PV analysis on the whole shoots and defoliated shoots. The study was conducted at the end of the vegetation period in 1987 and during winter 1988.The proportion of Wan in the total needle water content (Wtn) was 14% in September 1987 and 12.5% in March 1988. The respective percentage of Was in Wts were 27% and 25%. The amount of apoplastic water depended on the ratio of the dry weight of defoliated shoots to the dry weight of the whole shoots. A standard mean value for the amount of Wan in the total water content of the shoots (Wt) was therefore not possible. The bulk osmotic pressure at full water saturation in the needle symplasts was –1.9 MPa in September 1987 and –2.2 MPa in winter 1988. The respective values of the bulk osmotic pressures in the symplast of the defoliated shoots (πos) were –1.5 MPa and –1.7 MPa. Thus πon was 0.1 MPa lower and πos 0.3–0.4 MPa higher than the average osmotic pressure during full water saturation in the symplast of the whole shoots (πo).The relation between bulk‐averaged turgor pressure and water content showed that during water loss Ptn dropped more rapidly than the turgor pressure of defoliated shoots (Pts). Consequently the needles were less elastic than the defoliated shoots. The turgor values of whole shoots followed an intemediate course between Ptn and Pts. The flat course of Pts seems to be the main reason for the often observed “plateau” of ψ‐isotherms of whole shoots near full turgor.

Radial and axial turgor pressure measurements in individual root cells of Mesembryanthemum crystallinum grown under various saline conditions

Abstract. Radial and axial turgor pressure profiles were measured with the pressure probe in untreated and salt‐treated intact roots of Mesembryanthemum crystallinum. The microcapillary of the pressure probe was inserted step‐wise into the root tissue 5, 25 and 50 mm away from the root cap. For evaluation of the data, only those recordings on a given root were used in which four discontinuous increases in turgor pressure occurred. These four turgor pressure increases could be related to the rhizodermal cells and to the cells in the three cortical layers. The measurements showed that a radial turgor pressure gradient of the same magnitude (directed from the third cortical layer to the external medium) existed along the root axis. The magnitude of this turgor pressure gradient decreased with increasing salinity (up to 400 mol m‐3 NaCl) in the growth medium. Addition of 10 mol m‐3 CaCl2 to the 400 mol m‐3 NaCl medium partly reduced the salt‐induced decrease in turgor pressure, but only in cells 25–50 mm away from the root tip. Combined with this effect, a small axial turgor pressure gradient was generated, therefore, in the cortex layers which was directed to the root tip. Measurements of the volumetric elastic modulus, ɛ, of the wall of the individual cells showed that the presence of salt considerably reduced the magnitude of this parameter and that addition of Ca2+ to the strongly saline medium partially diminished this decrease. This effect was strongest in cells 50 mm away from the root tip. The magnitude of ɛ of rhizodermal and cortical cells increased along the root axis both in untreated and in salt‐treated roots. The ɛ value was significantly smaller for rhizodermal cells compared to the cortical cells, with the exception of cells 50 mm from the tip. In this tissue, rhizodermal and cortical cells exhibited nearly the same values. The decrease of the ɛ‐values with salt and the increase along the root axis under the various growth conditions could be correlated with corresponding changes in cell volume. Diurnal changes in turgor pressure could not be detected in the individual root cells, with the notable exception of the rhizodermal and cortical cells located in the region 50 mm away from the root tip of the control plants. In these cells, an increase in turgor pressure was observed during the morning hours. Determination of the average osmotic pressure in tissue sections along the roots of control and salt‐treated plants revealed that at 400 mol m‐3 NaCl the osmotic pressure gradient between the tissue and the medium is exo‐directed, provided that the water is not (partly) immobilized.