Water Flux Rate Research Articles

Contrasting effects of inhibitors and biostimulants on agronomic performance and reactive nitrogen losses during irrigated potato production

Urea is the dominant form of nitrogen (N) fertilizer used globally. Various additives have been designed for co-application with urea to improve performance of N-intensive crops including potato (Solanum tuberosum L.). Few if any studies have compared ‘inhibitor’ additives with ‘biostimulants’ designed to enhance plant growth or microbial activity. Over two potato growing seasons (2015–2016) in an irrigated loamy sand in Minnesota, we quantified agronomic performance and N losses as both nitrate (NO3−) and nitrous oxide (N2O) in treatments receiving urea, with and without additives including: nitrification inhibitors dicyandiamide (DCD) or 3,4-dimethylpyrazole phosphate (DMPP), alone or combined with the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT), or a biostimulant containing N-fixing microbes (NFM) by itself or combined with an amino acid blend (AAB). The biostimulants produced modest (˜10%) improvements in tuber yield, under limited conditions, compared to urea alone. However, NFM increased N2O emissions by 32–56%, in contrast to the inhibitors, which decreased N2O emissions by 42–75%. Compared to urea alone, the inhibitors tended to increase soil ammonium and decrease soil NO3− concentrations; however, no differences in soil inorganic N in the upper 0.3 m of the profile were observed with the biostimulants. During the growing season with greater rates of soil water flux (2015), none of the inhibitors decreased NO3− leaching, while NFM increased NO3− leaching by 23%. When AAB was combined with NFM, reactive N losses did not differ from the urea-only treatment. Biostimulants can have unintended impacts on reactive N losses and should be used with caution pending additional study to better understand their effects on biological processes, and to quantify their performance in other agro-ecosystems.

Flux Optimization in Reverse Osmosis via the Solution-Diffusion Model

This paper suggests a new method of predicting flux values at reverse osmosis (RO) desalination plants. The study is initiated by using the solution-diffusion model that is applied to the groundwater source at Abqaiq plant (500 RO plant) at Saudi Aramco, Dhahran, Saudi Arabia in order to calculate the osmotic pressure of the treated water for Shedgum/Abqaiq groundwater. For modelling purposes, the same technique is used to determine the osmotic pressure drops at the same plant configuration and operating conditions when using seawater sources such that of Arabian Gulf and the Red Sea waters. High rejection brackish water RO (BWRO) element Toray TM720D-400 with 8" is the RO membrane type that is used at Abqaiq plant. The calculated osmotic pressures of the three water sources, assuming that they are all treated at Abqaiq plant, are utilized to determine the appropriate flux values as well as membrane resistances of different BWRO Toray membranes. Values of numerous parameters such as water permeability constant, applied pressure, gas constant, water temperature, water molar volume and membrane thickness, water salinity/TDS are taken into account to develop our calculations through the solution-diffusion model. A comparison between low-pressure, standard and high-pressure BWRO Toray membranes performance have been established to select the ideal membrane type for the treatment of water from various sources at Abqaiq plant. The model results confirm an inverse relationship between the membrane thickness and the water flux rate. Also, a proportional linear relation between the overall water flux and the applied pressure across the membrane is identified. Higher flux rates and lower salinity indicate lower membrane resistance which yields to the higher water production. Modelled data predict that BWRO Toray TM720D-440 with 8" membrane is the optimal BWRO membrane choice for the three water sources at Abqaiq plant.

Fabrication of α‐Si3N4‐nanowire/γ‐Y2Si2O7 composite superhydrophobic membrane for membrane distillation

AbstractThis paper reports on the successful fabrication of α‐Si3N4‐nanowire/Y2Si2O7 composite membranes with superhydrophobic properties, aiming to achieve a high performance in membrane distillation. The starting powder mixture of 87 wt% γ‐Y2Si2O7, 5 wt% Si, 3 wt% LiYO2, and 5 wt% ferrocene catalyst was dispersed in a stable suspension, and after being tape‐casted, it was sintered at 1300°C for 4 hours in order to obtain the composite membrane. α‐Si3N4 nanowires with a diameter of about 50 nm were formed, distributed uniformly on the surface and in the pores of the membrane and their presence greatly favored superhydrophobicity. After surface modification with a robust hydrophobic layer of SiNCO nanoparticles, strongly adhered to the surface of the produced membrane, a water contact angle of 153o, was measured. Water desalination experiments, using a sweeping gas membrane distillation (SGMD) device, were conducted. High water flux of 11.91 L/m2/h was achieved for a 4 wt% NaCl feeding solution at 90°C. Stable water flux and rejection rates were recorded in long‐term experiments (>500 hours) using the produced superhydrophobic composite membrane.

The effects of salinity and hypoxia exposure on oxygen consumption, ventilation, diffusive water exchange and ionoregulation in the Pacific hagfish (Eptatretus stoutii)

Hagfishes (Class: Myxini) are marine jawless craniate fishes that are widely considered to be osmoconformers whose plasma [Na+], [Cl−] and osmolality closely resemble that of sea water, although they have the ability to regulate plasma [Ca2+] and [Mg2+] below seawater levels. We investigated the responses of Pacific hagfish to changes in respiratory and ionoregulatory demands imposed by a 48-h exposure to altered salinity (25 ppt, 30 ppt (control) and 35 ppt) and by an acute hypoxia exposure (30 Torr; 4 kPa). When hagfish were exposed to 25 ppt, oxygen consumption rate (MO2), ammonia excretion rate (Jamm) and unidirectional diffusive water flux rate (JH2O, measured with 3H2O) were all reduced, pointing to an interaction between ionoregulation and gas exchange. At 35 ppt, JH2O was reduced, though MO2 and Jamm did not change. As salinity increased, so did the difference between plasma and external water [Ca2+] and [Mg2+]. Notably, the same pattern was seen for plasma Cl−, which was kept below seawater [Cl−] at all salinities, while plasma [Na+] was regulated well above seawater [Na+], but plasma osmolality matched seawater values. MO2 was reduced by 49% and JH2O by 36% during hypoxia, despite a small elevation in overall ventilation. Our results depart from the “classical” osmorespiratory compromise but are in accord with responses in other hypoxia-tolerant fish; instead of an exacerbation of gill fluxes when gas transfer is upregulated, the opposite happens.

Enhanced desalination performance of poly (vinyl alcohol)/carbon nanotube composite pervaporation membranes via interfacial engineering

The dispersion and interfacial interactions between nanofillers and the polymer are two crucial factors affecting the performance of mixed matrix membranes (MMMs). In this study, poly (vinyl alcohol) (PVA) based mixed matrix membranes containing multiwalled carbon nanotubes (MWCNTs) or carboxylic multiwalled carbon nanotubes (C-MWCNTs) were produced via interfacial adhesion, hydrogen bonding or covalent bonding. The desalination performances of the synthesized membranes were compared by the pervaporation (PV) process. A PVA membrane crosslinked with maleic acid (MA) was also prepared for comparison. FESEM and TEM images indicated that the C-MWCNTs were disentangled and dispersed uniformly in the PVA matrix whereas MWCNTs without functional groups readily aggregated. The incorporation of CNTs endowed the PVA/CNT membranes with improved thermal stability, which was confirmed using TGA and DSC measurements. In particular, the altered properties of the PVA/CNT composites enhanced the separation performance compared with the PVA membrane without CNTs. The performance tests showed that the PVA/CNT composite membranes featured remarkably larger water fluxes than control PVA/MA membrane (38.8%–154.1% increase) while maintaining high salt rejection. Thereinto, the overall best performance of 99.91% of salt rejection and 6.96 kg/m2 h of water flux at room temperature (22 °C) was obtained by the PVA/C-MWCNT/MA membrane (19 ± 1 μm thickness) when the feed was synthetic NaCl solution of 35,000 ppm. Kinetic desorption method was applied to compare salt transport properties of the resultant PVA/CNT composite membranes. The salt transport through the PVA/C-MWCNT and PVA/C-MWCNT/MA membranes was significantly restricted with CNT mass fraction. High retention of water flux and salt rejection rates were also obtained by the PVA/C-MWCNT/MA membrane over a 30-h durability test that processed seawater collected from Brighton Beach (Melbourne, VIC, Australia), while the salt rejection for the PVA/C-MWCNT membrane declined with extended operating time indicating that cross-linking of the PVA was necessary for stable MMM performance.

Automated Laboratory Infiltrometer to Estimate Saturated Hydraulic Conductivity Using an Arduino Microcontroller Board

This paper describes the design, calibration and testing processes of a new device named Automated Laboratory Infiltrometer (ALI). It allows to determinate in laboratory, under controlled conditions the saturated hydraulic conductivity (Ks) of altered or unaltered soil samples which is a key parameter to understand the movement of water through a porous medium. The ALI combines the advantages of three different approaches: measures vertical infiltration rates in a soil column, measures the actual volumes of vertically drained water through the soil column, and finally, uses heat as a natural tracer to determinate water flux rates through the porous medium; all those parameters are used to determinate Ks. The ALI was developed using the popular Arduino microcontroller board and commercially available sensors that give the whole system a low cost. Data from the ALI are recorded in a microSD memory so they can be easily read from any spreadsheet software helping to reduce time consuming and avoiding reading errors. The performance of this device was evaluated by comparing the water flow rates determined by the three approaches for which is designed; an excellent correlation among them was observed (worst correlation: R2 = 0.9826 and r-RSME = 0.94%).

Preparation of geopolymer inorganic membrane and purification of pulp-papermaking green liquor

This paper describes a low-cost and highly efficient metakaolin-based geopolymer composite membrane (support + dense layer) at normal pressure and <70 °C. The support was fabricated using geopolymer foam materials and shows a large water flux and good mechanical properties. The dense layer was prepared using a dip-coating process with geopolymer paste on the porous geopolymer support surface. This study explored the influence of the foam agent content on the support membrane microstructure, water flux and compressive strength, and determined that the optimal foam agent content is 1.0 mass%. By adjusting the viscosity of the geopolymer paste in accordance with the water flux and removal rate, the thickness of the dense layer was determined as 500 μm. The composite membrane shows a distribution of pore sizes (approximately 0.09 μm of dense layer), amorphous structure, high permeable water flux (245 kg·m−2·h−1), good interface combination and can be reused. The preliminary ultra-filtration test (0.2 MPa operation pressure) demonstrates that the geopolymer-based composite membrane can effectively treat suspended particles in wastewater and is expected to be applied in the field of wastewater treatment. We then used the composite membrane in the pulp-papermaking green liquor at different temperatures, and it was found that the SS (suspended solids) of the filtrate can be decreased to 3.45 mg/L at 80 °C or to 0.79 mg/L at 30 °C, far below the industrial requirements of green liquor recycling (SS < 20 mg·L−1).

Fabrication of low thermal conductivity yttrium silicate ceramic flat membrane for membrane distillation

This paper reports on the successful fabrication of γ-Y2Si2O7 membranes with low thermal conductivity, which is an important membrane property for achieving high performance in membrane distillation process. Single-phase γ-Y2Si2O7 powder was first synthesized by calcination of SiO2 and Y2O3 powders, with 3 wt% LiYO2 as a sintering aid. The membrane was produced by tape-casting of a suspension of this powder. After sintering at 1300 °C for 4 h, a flat membrane was obtained, which had a thickness of 0.5 mm, 49% porosity, 0.9 μm pore diameter, and low thermal conductivity of 0.497 W/m⋅K at 32 °C, and 0.528 W/m⋅K at 100 °C. The obtained membrane presented hydrophobic features (water contact angle was 132°) after surface modification, which resulted in formation of a strongly adhered robust hydrophobic SiNCO nanoparticle layer on its surface. The resultant hydrophobic membrane was tested in water desalination experiments using a sweeping gas membrane distillation (SGMD) device. High water flux of 10.07 L⋅ m−2⋅ h−1 was achieved for a 20 wt% NaCl feeding solution and a temperature at the feed of 90 °C. Stable water flux and rejection rates were recorded in long-term experiments (>400 h).

Chitin nanowhisker – Inspired electrospun PVDF membrane for enhanced oil-water separation

The requirement of promoting a revolution in filtration technology has led to growing devotion in advanced functional materials such as electrospun membranes for filtering devices as a solution for providing water at lower energy costs. In this study, electrospun polyvinylidene fluoride membranes were fabricated by reinforcing 0.5 and 1 wt. % of chitin nanowhiskers in order to improve their thermal stability, mechanical properties, pure water flux and oil-water filtration performance for the possible application as filtration membranes. Morphological analysis revealed the porous and fibrous structure of membranes which confirmed by BET surface area analysis. Incorporation of chitin nanowhiskers improved the mechanical properties of the membranes such as elongation at break and tensile strength (specifically at 1 wt. % of chitin nanowhisker) while resulted in substantial enhancement of their thermal properties. Furthermore, polyvinylidene fluoride/chitin nanowhisker membranes showed enhanced oil-water separation ability, while reinforcement of chitin nanowhisker led to increase pure water flux rate, which measured as a crucial point in filtration membranes. The oil-water separation results compared with a commercial polyvinylidene fluoride membrane and the results signified the potential of electrospun polyvinylidene fluoride/chitin nanowhisker to be used for filtration application.

Optimization of reverse osmosis flowback water treatment using halotolerant microbes naturally enriched in fractured shales

Flowback water recovered after hydraulic fracturing operations poses a serious environmental concern due to the sheer quantity produced and its toxic chemical composition. Traditional methods of wastewater treatment cannot be used for flowback water treatment due to its high concentration of non-biodegradable dissolved solids. Consequently, alternative technology has been developed to address this problem. Reverse osmosis (RO) treatment is one such example. However, guar gum gelling agents found in flowback water impede membrane permeability and water flux rate of RO, consequently decreasing the efficiency and practicality of this desirable, environment-friendly technology. Previously, a biological solution using activated sludge to degrade guar gum prior to RO treatment was attempted with limited success due to the inhibitory effects of hypersalinity (characterized by high total dissolved solids content) on microbial activity. To solve this problem, several recently discovered strains of bacteria and archaea found to be naturally enriched in fractured shales may be utilized through genetic modification to degrade guar gum under hypersaline conditions. These microbes are naturally halotolerant and thrive under hypersaline conditions, making them prime targets for genetic modification targeting various chemical additives in flowback water. Here, we provide a proof of concept model using these microbes to selectively target guar gum degradation to improve the efficiency of RO treatment.

Study on preparation and performances of cellulose acetate forward osmosis membrane

Cellulose acetate (CA) forward osmosis (FO) membranes were prepared via a phase inversion process. CA was used as membrane material for FO. Acetone and 1,4-dioxane were employed as solvent. Polyvinylpyrrolidone (PVP), maleic acid, and methanol were applied as additives. An orthogonal experiment was performed to optimize the ratio of every component in the casting solution. The membrane with best performance was selected to concentrate an anthocyanin solution. Saturated sucrose solution (about 60°Brix) was fit for using as draw solution in the concentration experiment. Water flux, porosity, and rejection rate were measured to evaluate the membrane properties. Reverse water rinsing was used in cleaning membrane that was fouled by anthocyanin solution. Results showed that under membrane thickness of 100 μm, coagulation temperature at room temperature, and evaporation time of 30 s, the optimum components in casting solution were 13% CA, 45% 1,4-dioxane, 31% acetone, 2% maleic acid, 3% PVP, and 6% methanol. In the concentration experiment, the prepared FO membrane showed water flux of 2.04 L m−2 h−1 and rejection rate of 98.61%. In the membrane cleaning experiment, the water flux of the FO membrane recovered 87.51% after rinsing for 1 h. The prepared membranes and previously published membranes were compared which showed the prepared membrane could significantly improve the rejection rate for anthocyanin solution.

Determinants of blood water δ18O variation in a population of experimental sheep: Implications for paleoclimate reconstruction

Mammalian body, blood and hard tissue oxygen isotope compositions (δ18O values) reflect environmental water and food sources, climate, and physiological processes. For this reason, fossil and archaeological hard tissues, which originally formed in equilibrium with body chemistry, are a valuable record of past climate, landscape paleoecology, and animal physiology and behavior. However, the environmental and physiological determinants of blood oxygen isotope composition have not been determined experimentally from large herbivores. This class of fauna is abundant in Cenozoic terrestrial fossil assemblages, and the isotopic composition of large herbivore teeth has been central to a number of climate and ecological reconstructions. Furthermore, existing models predict blood water, or nearly equivalently body water, δ18O values based on environmental water sources. These have been evaluated on gross timescales, but have not been employed to track seasonal variation. Here we report how water, food, and physiology determine blood water δ18O values in experimental sheep (Ovis aries) subjected to controlled water switches. We find that blood water δ18O values rapidly reach steady state with environmental drinking water and reflect transient events including weaning, seasons, and snowstorms. Behavioral and physiological variation within a single genetically homogenous population of herbivores results in significant inter-animal variation in blood water δ18O values at single collection times (1 s.d. = 0.1–1.4‰, range = 3.5‰) and reveals a range of water flux rates (t1/2 = 2.2–2.9 days) within the population. We find that extant models can predict average observed sheep blood δ18O values with striking fidelity, but predict a pattern of seasonal variation exactly opposite of that observed in our population for which water input variation was controlled and the effect of physiology was more directly observed. We introduce to these models an evaporative loss term that is a function of environmental temperatures. The inclusion of this function produces model predictions that mimic the observed seasonal fluctuations and match observations to within 1.0‰. These results increase the applicability of available physiological models for paleoseasonality reconstructions from stable isotope measurements in fossil or archaeological enamel, the composition of which is determined in equilibrium with blood values. However, significant blood δ18O variation in this experimentally controlled population should promote caution when interpreting isotopic variation in the archaeological and paleontological record.

The osmorespiratory compromise in rainbow trout (Oncorhynchus mykiss): The effects of fish size, hypoxia, temperature and strenuous exercise on gill diffusive water fluxes and sodium net loss rates

In the context of the osmorespiratory compromise, hypoxia and temperature have been little studied relative to exercise, and diffusive water flux rates (as assessed by 3H2O efflux) have received almost no attention. We investigated the effects of fish size, hypoxia, exercise and acute temperature increase on diffusive water flux rates and net sodium loss rates in juvenile rainbow trout. Trout weighing 13–50 g were used to determine the effects of fish size under normoxia. Thereafter 25–50 g trout were selected to assess the effects of different hypoxia levels (3.15, 5.25 and 8.40 KPa), time course of hypoxia (1 h 8.40 KPa, 3 h 8.40 KPa, 1 h 8.40 KPa +1 h normoxic recovery, and 1 h 8.40 KPa + 3 h normoxic recovery), strenuous exercise (5 min) and acute temperature challenge (transfer from 8 °C to 13 °C or to 18 °C). Small fish (13 g) had higher diffusive water flux rates than larger fish, turning over >100% of their fractional body water pool per hour against 34% per hour for 50 g fish. Hypoxic exposure exerted a biphasic effect, increasing the diffusive water flux rate at 8.40 KPa and 5.25 KPa, while returning it to control levels at 3.15 KPa. All the levels of hypoxia increased net Na+ loss. One hour hypoxia (8.40 KPa) increased diffusive water flux rate while prolonged 3 h hypoxia (8.40 KPa), and short or prolonged normoxic recovery returned diffusive water flux rates to control levels. All the treatments over the time course of hypoxia and normoxic recovery increased net Na+ loss rates. Strenuous exercise increased both the diffusive water flux and net Na+ loss rates. Acute temperature rise increased diffusive water flux rates, with Q10 values of 4.03 for 8 to 13 °C and 2.16 for 8 to 18 °C, but the net Na+ loss rate did not change. There was no significant correlation between diffusive water flux rate and net Na+ loss rates at different hypoxia levels, over the course of hypoxia and normoxic recovery, or during acute temperature stress. In contrast, we observed a significant correlation between diffusive water flux and net Na+ loss rates following exercise. Overall, diffusive water flux and sodium loss were regulated differently during acute temperature challenge and hypoxia, while following exercise the two parameters were regulated in a similar fashion.

Fast and efficient separation of seawater algae using a low-fouling micro/nano-composite membrane

High suspended solid loadings due to harmful algal bloom (HAB) pose serious threat to the operation of membrane based desalination plants. Clogging of algal biomass could lead to irreversible damage of the filtration units and eventually disrupting the sustainability of water supply. In this study, we demonstrated a fast and efficient method for separating algae from seawater using a low-fouling micro/nano-composite membrane. The composite membrane was made of a nanoporous nanofiber selective layer on top of a microporous microfiber support layer. The optimized nanoporous selective layer of this composite membrane can effectively separate seawater algae with high efficiency (average 99%) and high flux (3 × 10−5 m3/m2·s) under low operation pressure. More importantly, the membrane exhibits excellent anti-fouling property by maintaining constant water flux and algae rejection rate after a simple backwashing without chemical usage. This superior antifouling property attributes to the underwater superoleophobicity of the composite membrane. These combined merits of fastness, effectiveness and fouling resistance render this membrane-based separation method with greater potential for industrial application.

Synthesis and characterization of mixed matrix membranes incorporated with hydrous manganese oxide nanoparticles for highly concentrated oily solution treatment

AbstractIn this work, ultrafiltration (UF) mixed matrix membranes (MMMs) incorporated with hydrophilic hydrous manganese oxide (HMO) nanoparticles were synthesized and used for the treatment process of a highly concentrated oily solution. The MMMs were fabricated via a phase inversion process and were characterized with respect to physiochemical properties and filtration performances. The results showed that the MMMs demonstrated higher water flux and better oil rejection rates compared to the control membrane (without HMO incorporation) when tested at three different oily solutions with oil concentration in the range of 5000–15 000 ppm. The membrane incorporated with the highest amount of HMO (labelled as MMM‐2) in particular showed the best results even when subjected to 15 000 ppm oily solution filtration, recording water flux of 32.2 L/m2 · h · bar and oil rejection of 82 %. The enhanced performance can be attributed to improved surface hydrophilicity coupled with better structural integrity and higher porosity that contributed to lower degree of oil molecules deposition and greater water transport rate. It was also reported that with the use of a feed spacer during the filtration process, the degree of flux deterioration of MMMs could be further reduced without compromising rejection. The findings of this work indicated the potential of MMMs for the treatment of highly concentrated oily effluent produced from industries, by producing permeate of high quality at reasonably good water permeability.

Extreme water efficiency of Cape gannet Morus capensis chicks as an adaptation to water scarcity and heat stress in the breeding colony

Cape gannet Morus capensis chicks depend entirely on fish prey and metabolic water for water requirements during development. Water loss through evaporative cooling due to heat stress is substantial. We measured water flux and field metabolic rates (FMR) of Cape gannet chicks and adults to determine if gannets developed water saving strategies. The water economy index (WEI, g kJ−1) decreased with chick age according to the model WEI = 0.676 – 0.272 × log10(t), indicating that water efficiency increased with age. At fledging, the WEI of chicks was at the level expected of adult desert birds. Desert birds maintain a low WEI by also having a low FMR, whereas Cape gannet chicks have FMR comparable to other seabird species’ nestling requirements. We propose that maintaining low WEI is adaptive for Cape gannets because (1) chicks need to balance water loss through evaporative cooling, (2) fledglings need to overcome a period of up to a week when they cannot ingest any water and (3) adults spend extended periods in the breeding colony during which water can become a limiting factor. Understanding the physiological mechanism of maintaining low WEI will become increasingly important with future rising temperatures.

Fabrication of Solvent-Resistant Nanofiltration Membrane via Interfacial Polymerization Based on Cellulose Acetate Membrane

Although a great progress has been achieved for the development of NF membranes and technologies and SRNF do show a great potential in the separation of organic components, an NF membrane with good separation performance and good resistance to organic solvents are urgently needed for a more complicated situation in practical. In this study, a kind of solvent-resistant nanofiltration (SRNF) membrane was fabricated via interfacial polymerization on a laboratory optimized cellulose acetate (CA) basic membrane. The effects of interfacial polymerization parameters, such as water phase concentration, immersed time in the water phase and in the organic phase, on the pure water flux and rejection rate of C-2R yellow dyestuffs were investigated. A highest dye rejection rate of 72.9% could be obtained by water phase solution containing 1% m-xylylenediamine (mXDA) and organic phase solution with 0.2% trimesoyl chloride (TMC) under immersed time in water phase of 6 minutes and in organic phase of 40 seconds. This membrane demonstrated better resistance to methyl alcohol compared to commercial membrane. This study may offer an avenue to develop a solvent-resistant nanofiltration membrane.

A low-pressure GO nanofiltration membrane crosslinked via ethylenediamine

Laminate graphene oxide (GO) membranes have received increasing attention recently in the water processing field due to their unique properties. However, the hydration of hydrophilic graphene oxide nanosheets leads to instability of GO membranes in aqueous solutions. In this study, ethylenediamine (EDA) was employed to crosslink GO nanosheets in a GO membrane supported on a brominated polyphenylene oxide (BPPO). In addition, because the O˭C-OH group of GO reacted with the amine group of EDA, the GO layer was firmly bonded to the BPPO substrate, as evidenced by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). EDA crosslinking dramatically improved the stability of the GO membranes. After immersion in water for one month, the prepared BPPO/EDA/GO membranes still retained their flux rates and salt rejection capabilities. The water flux rates and salt rejection capabilities of BPPO/EDA/GO membranes can be tuned by controlling GO loading. At a GO loading of 65mg/m2, the BPPO/EDA/GO membrane achieved a relatively high water flux rate of 4.1L/m2h under a very low transmembrane pressure of 1bar. Additionally, the salt rejection percentages of Na2SO4, MgSO4 and NaCl were 56.2%, 48% and 36.3%, respectively. Moreover, the BPPO/EDA/GO membrane displayed good antifouling and antibacterial properties.

A novel photocatalytic membrane decorated with RGO‐Ag‐TiO2 for dye degradation and oil–water emulsion separation

AbstractBACKGROUNDMembrane separation is a promising process for treatment of dye and oily wastewater if the antifouling capacity and recyclability can be improved. In recent years, the development of photocatalytic materials has provided new methods for research into membrane technology.RESULTSIn this study, a novel photocatalytic membrane decorated with RGO‐Ag‐TiO2 nanomaterial was fabricated by simple vacuum filtration for degradation of dye and separation of oil–water. First, TiO2 nanowires were prepared for more effective photocatalysis, reduced graphene oxide (RGO)‐Ag‐TiO2 was fabricated by a facile hydrothermal reaction, then it was directly decorated on cellulose acetate (CA) membrane using polyethylene glycol and glutaraldehyde.CONCLUSIONThe as‐prepared photocatalytic membrane can simultaneously degrade dye and separate oil–water emulsions under visible‐light irradiation in a short time. The membrane has extremely high water flux (191 L m‐2 h‐1) and rejection rates (almost 100%) of dye–oil–water emulsion. More importantly, the photocatalytic membrane shows excellent antifouling capacity and recyclability, and retains relatively stable dye–oil–water permeation flux (about 27.5 L m‐2 h‐1) and high rejection rates (up to 99%) after six cycles of experiments under visible‐light irradiation. Overall, the photocatalytic membrane opens up new avenues for the treatment of wastewater. © 2017 Society of Chemical Industry

Molecular dynamics modeling of nano-porous centrifuge for reverse osmosis desalination

A concept of the porous graphene membrane centrifuge is proposed aiming at fabrication of large scale, fouling-free desalination machine with nanomaterial-based reverse osmosis modules. The concept as well as strategy of such porous rotating graphene membrane device is approved through molecular dynamics (MD) modeling and simulation of a nano-fluidic device that in order to make a quantitative evaluation. First, an analytical formulation is derived for the critical angular velocity above which the centrifugal force is able to counter-balance osmosis pressure, so that the reverse osmosis (RO) desalination process can proceed. The critical angular velocity derived from this formulation is compared with MD simulated critical angular velocity.Based on MD simulation results, it is shown that the rotating porous membrane device may significantly improve desalination efficiency by combining the centrifugal separation and and the selectivity of porous graphene membrane to achieve reverse-osmosis desalination. Furthermore, we have shown that the proposed desalination device has an intrinsic anti-fouling mechanism, and then we have studied the effect of pore size on the flux rate by conducting simulations with the applied rotating speed. Moreover, we have conducted energy and efficiency analysis for the proposed desalination device model, and we obtained the relationship between fresh water flux rate and the angular velocity, at the same time, with the pore size. By choosing the most efficient angular velocity and the pore size that ensures salt rejection, an optimal nano-fluidic device design is achieved.