Modeling and optimization of a solar forward osmosis pilot plant by response surface methodology

Forward osmosis (FO) is a water treatment/separation technology of emerging interest. Due to its complex nature involvingvarious operating parameters, modeling of this separation process is challenging. A solar thermal and photovoltaic-powered FO pilot plant has been optimized by means of a statistical experimental design and response surfacemethodology. Predictive models were developed for simulation and optimization of different responses such as the waterpermeate flux, the reverse solute permeate flux and the FO specific performance index that includes the water and reversesolute permeate fluxes together with the energy consumption. The considered input variables of the FO pilot plant werethe feed flow rate, the permeate flow rate and the temperature. The developed response models have been tested using theanalysis of variance. A Monte Carlo Simulation method has been conducted to determine the optimum operating conditionsof the FO pilot plant. The obtained optimum parameters were confirmed experimentally. Regeneration of the drawsolution can be performed by means of an optimized solar powered reverse osmosis (RO) pilot plant with an optimumFO specific performance index ranging from 25.79 to 0.62 L/g kW h achieved under the FO optimal conditions, 0.83 L/min feed flow rate, 0.31 L/min draw solution flow rate and 32.65 °C temperature. The FO energy consumption is only14.1% the total energy consumption of the FO/RO hybrid system

Ultrafiltration membranes for wastewater and water process engineering: A comprehensive statistical review over the past decade

The primary intention of this review is to showcase and quantify the level of research interest and current research trends, concerning UF membrane applications and processes within the past decade (2009–2018). Detected statistics manifested a resurgent interest in the UF technology on a yearly basis. "Journal of Membrane Science" and "Desalination and Water Treatment" were the primary journals dominating the size of the annual publication among more than 120 ones, with 854 and 683 papers, respectively. Based on ScienceDirect research platform, fouling (27%), modelling (17%) and wastewater (12%), were the dominating research topics and counting for more than half of total scientific articles published (4547 articles) within the specified period of the research. Unsurprisingly, topics like UF membrane fabrication and modification, food processing, hybrid membrane process have disclosed a distinguished growing up trends in terms of annual publications. The current review unrevealed the present-day significance of the UF membranes along with their prospective opportunities for attaining sustainable water industries and materializing the efforts of future researchers into the right orientation

Functional materials in desalination: A review

This paper reviews various functional materials used in desalination. Desalination of the abundant seawater resource has emerged as a promising technology to meet the current fresh water demands. For improved performance, often functional materials such as photocatalysts, electrocatalysts, photothermal materials, sorbents, antibacterial materials and magnetic materials are utilized in thermal, membrane-based and other desalination technologies. With an aim to provide an insight on the existing research on functional materials and the purpose behind using such in desalination, this review collates different research studies of various functional properties and the subsequent materials utilized for those properties. New generation materials such as carbon nanotubes (CNTs) and graphene form a major part, where they exhibit multiple functionalities with improved water transport properties, and thus have been deemed as very attractive enhancers to the desalination technology. Nevertheless, most of the functional materials, such as nano-TiO2, nano-zeolites, graphene, CNTs and magnetic nanoparticles suffer from several limitations such as specialized synthesis techniques, agglomeration, leaching and environmental and health concerns. This review focuses on such challenges and suggests improvements for enhanced incorporation of these in the desalination technology. Lastly, emerging new technologies, advanced fabrication methods and novel functional hybrid materials are reviewed to equip the readers with the latest research trends. Thus, a comprehensive review is essential which will provide current and future researchers an insight on the importance and significance of utilizing functional materials in various desalination technologies

Fabrication and antifouling behaviour of a carbon nanotube membrane

In this work, a novel approach is used to synthesize an iron oxide doped carbon nanotube (CNT) membrane, with the goal of fully utilizing the unique properties of CNTs. No binder is used for the synthesis of the membrane; instead, iron oxide particles serve as a binding agent for holding the CNTs together after sintering at high temperature. The produced membrane exhibited a high water flux and strong fouling resistance. In the first step, CNTs were impregnated with various loadings of iron oxide (1, 10, 20, 30 and 50%) via wet chemistry techniques. Impregnated CNTs were then compacted at 200 MPa and sintered at 1350 °C for 5 h to form a compact disc. The membranes were analysed by measuring their porosity, contact angle, diametrical compression test and water flux. The flux of pure water was observed to increase with an increase in iron oxide content. The permeate flux and rejection rate of sodium alginate (SA) were determined to predict the antifouling behaviour of the membrane. A maximum removal of 90 and 88% of SA was achieved for membranes with a 10 and 1% iron oxide content, respectively, after 3 h. A minor decline in the permeate flux was observed for all membranes after 4 h of operation

Dewatering of POME digestate using lignosulfonate driven forward osmosis

High demand for palm oil results in the production of huge quantities of palm oil mill effluent (POME) wastewater containing a high amount of organics. Currently, this is often processed by anaerobic fermentation, but the waste water still requires further processing. Dewatering of POME digestate could simultaneously recover nutrients for use as organic fertiliser and treat water sufficiently to allow other uses. This work investigates the feasibility of using a forward osmosis (FO) process driven by lignosulfonate draw solutions. It was found that water fluxes for pure water and simulated POME digestate feeds were lower for lignosulfonates than NaCl as draw solutes, but had much lower reverse solute fluxes. Reverse solute flux is of great importance for dewatering of POME digestate, as concentration of salts in the dewatered feed will preclude their use as organic fertilisers. Na lignosulfonate showed both higher water fluxes and lower reverse solute flux than the Ca lignosulfonate. Water fluxes when using the simulated POME digestate were lower than predicted from the directly measured osmotic pressures of the solutions, suggesting increased membrane resistance due to fouling or concentration polarisation effects. In addition, osmotic pressures of organic solutions were measured directly from dead-end filtration measurements. This showed that the relationship between osmolality measured from freezing point depression measurements and osmotic pressure of solutions varies for different solutes, suggesting that osmolality measurements do not give a reliable measure of osmotic pressure when comparing different organic solutions

Enhanced performance of direct contact membrane distillation via selected electrothermal heating of membrane surface

Membrane distillation (MD) is a thermally driven separation process with great potential, but is currently limited by low energy efficiency. Heating of the entire circulating feed represents a major source of energy consumption in MD. Here, we present electrically conductive carbon nanostructure (CNS-) coated polypropylene (PP) membranes as a possible candidate to mitigate energy consumption through selected electrothermal heating of the membrane surface. A membrane for MD was coated with CNS using a tape casting technique. The resulting CNS-PP membrane is hydrophobic, and its smaller pore size and narrow pore size distribution resulted in a higher liquid entry pressure compared to the uncoated PP membrane. An increase in surface temperature was observed when a current was passed through the conductive CNS layer. The CNS layer on the PP membrane acts as an electrothermal heater when an AC potential is applied, and the rate of heating is proportional to the amplitude of applied AC potential. We applied electrothermal heating of these membranes to desalination by direct contact membrane distillation, in conjunction with heating of the circulating feed, and compared the performance with and without application of AC bias at three feed temperatures viz. 40, 50 and 60 °C. Applying a potential across the CNS layer increased permeate flux by 75, 76 and 61% at feed temperatures of 40, 50 and 60 °C respectively, while maintaining a salt rejection of >99%. This increase in flux is accompanied by a reduction in specific energy consumption of greater than 50% for all three feed temperatures. By combining electrothermal surface heating with MD, this study paves the way for smart, low-energy MD systems

Nanocrystalline NiWO4-WO3-WO2.9 Composite Strings: Fabrication, Characterization and their Electrocatalytic Performance for Hydrogen Evolution Reaction

In this study, novel nano crystalline composite strings made from mixed nickel-tungsten oxides (NiWO4-WO3-WO2.9) have been fabricated. The NiWO4-WO3 fibers produced by the electrospinning method were post treated in an argon atmosphere at 800°C which yielded NiWO4-WO3-WO2.9 nanocrystals attached together forming a string-like structure. The presence of WO2.9 phase was confirmed by both the XRD and TEM diffraction pattern analysis. String morphology and structure were found to change with different post treatment conditions such as by changing the calcination temperature from 550°C under oxygen to 800°C under pure argon atmosphere. This material was investigated for electrocatalytic hydrogen evolution reaction (HER) in 0.5 M H2SO4 and 0.1M KOH electrolytes. These composite strings showed good electrocatalytic activity compared to the NiWO4-WO3 fibers reported previously [1]. It was concluded that the presence of WO2.9 phase increases the electrocatalytic activity of the catalyst as compared to the NiWO4-WO3 fibers with over potentials as low as 40 mV and 50 mV in 0.5 M H2SO4 and 0.1M KOH respectively

Effect of Ultrasonic Frequency on the Performance and Cleaning of UF Membranes Used in Sea Water Desalination Pretreatment

This study aims to evaluate the impact of ultrasound (US) on the performance and cleaning of ultrafiltrationmembranes (UF) used in the pretreatment of sea water desalination plants. The effects of ultrasonic frequency onflux and fouling during the ultrafiltration process to saline solutions contaminated with Humic Acid (HA) wereinvestigated. Ultrasonic application had a strong impact on the normal ultrafiltration process, especially at lowfrequency. The estimated increase in the flux were 67% and 38% when applying ultrasonic irradiation on deadend flat sheet ultrafiltration cell at 300 W and frequencies of 28 kHz and 40 kHz, respectively, but there was nosignificant increase in the flux at the upper frequency 100kHz where the flux nearly identical to that wasobtained by stirring only. Upon ultrasonic application, total filtration resistance and reverse resistance, whichinclude concentration polarization and cake layer, were sufficiently reduced as revealed by the quantitativeresistance analysis using resistance in series model. The flux recovery ratio was increased to 72% when 28 kHzfrequency was applied during mechanical and chemical cleaning. Ultrasonic enhancement factor (EUS) washigher by 11% in the online application of US on UF process than that of cleaning process. The application ofultrasound is an effective and promising way to enhance the ultrafiltration and cleaning of fouled membranesused in the pre-treatment of the seawater desalination process