Unpacking compaction: Effect of hydraulic pressure on alginate fouling

Forward Osmosis Desalination Using Thermoresponsive Ionic Liquids: Bench-Scale Demonstration and Cost Analysis

Forward osmosis (FO) desalination using thermoresponsive ionic liquid (IL)-water mixtures is a promising technology for treating nontraditional water sources. However, its demonstration has primarily been at the lab-scale, with water flux and recovery values that are not representative of realistic applications. In this work, the performance of tetrabutyl-phosphonium trifluoroacetate (P4444TFA), as well as a new dual draw of P4444TFA with tetrabutyl-ammonium trifluoroacetate (N4444TFA) is characterized. The dual draw combines the higher osmolality of one IL with the lower critical solution temperature (LCST) of the second IL to outperform its constituents at the same total concentration of IL in water (70 wt %). Experiments were first performed in a lab-scale coupon tester to understand the effects of draw osmotic pressure and viscosity on water flux through the membrane. Bench-scale experiments were then performed in an element tester with a 1 m2 membrane area to evaluate the performance of IL-based FO for the desalination of produced water feed from oil and gas. Specifically, 10 kg of IL-water draw solution was used with 3 kg of real produced water feed, resulting in water recoveries of 60% with initial and final water fluxes of 14 LMH and 3 LMH, respectively. The bench-scale experimental results were used as inputs for a cost analysis, yielding a levelized cost of water (LCOW) of $1.18 per m3. This reveals the potential of IL-based draw solutions for cost-effective desalination of challenging feedwaters using FO.

Advances in Membrane Separation for Biomaterial Dewatering

Biomaterials often contain large quantities of water (50-98%), and with the current transition to a more biobased economy, drying these materials will become increasingly important. Contrary to the standard, thermodynamically inefficient chemical and thermal drying methods, dewatering by membrane separation will provide a sustainable and efficient alternative. However, biomaterials can easily foul membrane surfaces, which is detrimental to the performance of current membrane separations. Improving the antifouling properties of such membranes is a key challenge. Other recent research has been dedicated to enhancing the permeate flux and selectivity. In this review, we present a comprehensive overview of the design requirements for and recent advances in dewatering of biomaterials using membranes. These recent developments offer a viable solution to the challenges of fouling and suboptimal performances. We focus on two emerging development strategies, which are the use of electric-field-assisted dewatering and surface functionalizations, in particular with hydrogels. Our overview concludes with a critical mention of the remaining challenges and possible research directions within these subfields.

Existing Filtration Treatment on Drinking Water Process and Concerns Issues

Water is one of the main sources of life's survival. It is mandatory to have good-quality water, especially for drinking. Many types of available filtration treatment can produce high-quality drinking water. As a result, it is intriguing to determine which treatment is the best. This paper provides a review of available filtration technology specifically for drinking water treatment, including both conventional and advanced treatments, while focusing on membrane filtration treatment. This review covers the concerns that usually exist in membrane filtration treatment, namely membrane fouling. Here, the parameters that influence fouling are identified. This paper also discusses the different ways to handle fouling, either based on prevention, prediction, or control automation. According to the findings, the most common treatment for fouling was prevention. However, this treatment required the use of chemical agents, which will eventually affect human health. The prediction process was usually used to circumvent the process of fouling development. Based on our reviews up to now, there are a limited number of researchers who study membrane fouling control based on automation. Frequently, the treatment method and control strategy are determined individually.

Enhancing the Permselectivity of Thin-Film Composite Membranes Interlayered with MoS2 Nanosheets via Precise Thickness Control

The demand for highly permeable and selective thin-film composite (TFC) nanofiltration membranes, which are essential for seawater and brackish water softening and resource recovery, is growing rapidly. However, improving and tuning membrane permeability and selectivity simultaneously remain highly challenging owing to the lack of thickness control in polyamide films. In this study, we fabricated a high-performance interlayered TFC membrane through classical interfacial polymerization on a MoS₂-coated polyethersulfone substrate. Due to the enhanced confinement effect on the interface degassing and the improved adsorption of the amine monomer by the MoS₂ interlayer, the MoS₂-interlayered TFC membrane exhibited enhanced roughness and crosslinking. Compared to the control TFC membrane, MoS₂-interlayered TFC membranes have a thinner polyamide layer, with thickness ranging from 60 to 85 nm, which can be tuned by altering the MoS₂ interlayer thickness. A multilayer permeation model was developed to delineate and analyze the transport resistance and permeability of the MoS₂ interlayer and polyamide film through the regression of experimental data. The optimized MoS₂-interlayered TFC membrane (0.3-inter) had a 96.8% Na₂SO₄ rejection combined with an excellent permeability of 15.9 L m^-2 h^-1 bar^-1 (LMH/bar), approximately 2.4 times that of the control membrane (6.6 LMH/bar). This research provides a feasible strategy for the rational design of tunable, high-performance NF membranes for environmental applications.

Improvement of Properties and Performances of Polyethersulfone Ultrafiltration Membrane by Blending with Bio-Based Dragonbloodin Resin

Polyethersulfone (PES) is the most commonly used polymer for membrane ultrafiltration because of its superior properties. However, it is hydrophobic, as such susceptible to fouling and low permeation rate. This study proposes a novel bio-based additive of dragonbloodin resin (DBR) for improving the properties and performance of PES-based membranes. Four flat sheet membranes were prepared by varying the concentration of DBR (0-3%) in the dope solutions using the phase inversion method. After fabrication, the membranes were thoroughly characterized and were tested for filtration of humic acid solution to investigate the effect of DBR loading. Results showed that the hydrophilicity, porosity, and water uptake increased along with the DBR loadings. The presence of DBR in the dope solution fastened the phase inversion, leading to a more porous microstructure, resulted in membranes with higher number and larger pore sizes. Those properties led to more superior hydraulic performances. The PES membranes loaded with DBR reached a clean water flux of 246.79 L/(m2·h), 25-folds higher than the pristine PES membrane at a loading of 3%. The flux of humic acid solution reached 154.5 ± 6.6 L/(m2·h), 30-folds higher than the pristine PES membrane with a slight decrease in rejection (71% vs. 60%). Moreover, DBR loaded membranes (2% and 3%) showed an almost complete flux recovery ratio over five cleaning cycles, demonstrating their excellent antifouling property. The hydraulic performance could possibly be enhanced by leaching the entrapped DBR to create more voids and pores for water permeation.

News on alginate recovery by forward osmosis: Reverse solute diffusion is useful

The water content in the recycled alginate solutions from aerobic granular sludge was nearly 100%. Forward osmosis (FO) has become an innovative dewatering technology. In this study, the FO concentration of sodium alginate (SA) was investigated using calcium chloride as a draw solute. The reverse solute flux (RSF) of calcium ions in FO had a beneficial effect, contrary to the findings of previous literature. The properties of the concentrated substances formed on the FO membrane on the feed side were analyzed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, verifying that calcium alginate (Ca-Alg), which can be used as a recycled material, was formed on the FO membrane on the feed side owing to the interaction between SA and permeable calcium ions. Water flux increased significantly with the increase in calcium chloride concentration, while the concentration of SA had little influence on the water flux in FO. Based on this discovery, we propose a novel method for the concentration and recovery of alginate, in which the RSF of calcium ions is utilized for recovering Ca-Alg by FO, with calcium chloride as a draw solute.

Formation of Water-Channel by Propylene Glycol into Polymer for Porous Materials

In this study, a porous membrane with a cellulose acetate (CA) matrix was fabricated using propylene glycol with a water pressure treatment without a metal salt as an additive. The water pressure treatment of the fabricated CA membrane with propylene glycol yielded nanopores. The nanopores were formed as the additives in the CA chains led to plasticization. The weakened chains of the parts where the plasticization occurred were broken by the water pressure, which generated the pores. Compared to the previous study with glycerin as an additive, the size of the hydration region was controlled by the number of hydrophilic functional groups. When water pressure was applied to the CA membrane containing propylene glycol as an additive, the hydration area was small, so it was effective to control the pore size and the number of nano pores than glycerin. In addition, the number of nanopores and pore size could be easily adjusted by the water pressure. The porosity of the membrane was increased owing to the trace amount of propylene glycol, confirmed by scanning electron microscopy (SEM) and porosimetry. The interaction between the CA and propylene glycol was verified by Fourier-transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). Consequently, it was the optimum composition to generate pores at the CA/propylene glycol 1:0.2 ratio, and porosity of 69.7% and average pore diameter of 300 nm was confirmed. Since it is a membrane with high porosity and nano sized pores, it is expected to be applied in various fields.

Solar Desalination Using Thermally Responsive Ionic Liquids Regenerated with a Photonic Heater

Growing global water demand has brought desalination technologies to the forefront for freshwater production from nontraditional water sources. Among these, forward osmosis (FO) is a promising two-step desalination process (draw dilution and regeneration), but it is often overlooked due to the energy requirements associated with draw regeneration. To address this limiting factor, we demonstrate FO desalination using thermally responsive ionic liquids (ILs) that are regenerated using a renewable energy input, that is, solar heat. To efficiently harness sunlight, a simple photonic heater converts incoming irradiation into infrared wavelengths that are directly absorbed by IL-water mixtures, thereby inducing phase separation to yield clean water. This approach is markedly different as it uses radiative heating, a noncontact mode of heat transfer that couples to chemical functional groups within the IL for rapid energy transfer without a heat exchanger or secondary fluid. Overall, a solar-thermal separation efficiency of 50% is achieved under unconcentrated sunlight, which can be increased to 69% with the thermal design. Successful desalination of produced water from oil wells in Southern California highlights the potential of solar-powered IL-FO for energy-efficient and low-cost desalination of complex brines for beneficial water reuse.

Fouling propensity of novel TFC membranes with different osmotic and hydraulic pressure driving forces

The feasibility of Forward Osmosis (FO) as an alternative treatment technology to current membrane processes is believed to hinge on its reported lower fouling propensity. In this study, the impacts of constant osmotic pressure and hydraulic pressure driving forces on membrane fouling were investigated using a novel approach. In each case the cake layer was modelled accounting for all concentration polarisation effects and effective driving force. Compared to the widely employed method of using a non-constant osmotic pressure difference during bench-scale fouling experiments, maintaining a constant osmotic pressure led to 50% more alginate deposited on the same membrane surface (from 13.7 to 21.7 g/m²). This was attributed to a stronger osmotic driving force at the active layer interface and enhanced fouling due to a greater reverse flux of Na⁺ ions. An applied hydraulic pressure of 1 bar already changed fouling cake deposition and the cake structural parameter shrunk by 224 and 83 μm for the two thin-film composite membranes tested. A detailed analysis of the model however demonstrated that it needs further development, incorporating pore size, porosity and tortuosity of the foulant cake to enable drawing reliable conclusions on the causality of cake layer compaction.

Evidence, Determination, and Implications of Membrane-Independent Limiting Flux in Forward Osmosis Systems

A stepwise method for determining limiting flux and limiting osmotic pressure and a constant osmotic pressure method to validate the limiting flux were developed. First, five of the most commonly used FO membranes were characterized for water permeability ( A), solute permeability ( B), and structural parameter ( S). During both stepwise and constant osmotic pressure fouling experiments, membrane fouling constrained water flux to a singular, common upper limit, the limiting flux, for all membranes despite very different A and A/ B values for the membranes. Conversely, there was not an upper limit to reverse salt flux. It was observed that reverse salt flux increases as S decreases; however, this does not mean that higher S values are desirable. Higher S values (> ∼600 μm) also increase dilutive internal concentration polarization, which is recognized as the major impediment to achieving high FO water flux. For osmotic processes where membrane fouling occurs, membrane transport parameters A and B may not be useful performance indicators, and the goal of improving water flux by developing highly permeable, highly selective membranes may not be realistic. Instead, optimizing fouling mitigation strategies, hydrodynamics at the membrane surface, and membrane module configuration may be more promising alternatives for improving performance.

Effect of artificial cell miniaturization on urea degradation by immobilized E. coli DH5α (pKAU17)

Second generation E. coli DH5α (pKAU17) was successfully encapsulated by means of atomization (MA), inkjet printing (MI) and double-encapsulation (DDMI) for the purpose of urea degradation in a simulated uremic medium at 37 °C. Experimentally determined values of the effectiveness factor are 0.83, 0.28 and 0.34 for the MI, MA and DDMI capsules, respectively, suggesting that the catalytic activity of the E. coli DH5α (pKAU17) immobilized in MI capsule (d = 52 μm ± 2.7 μm) is significantly less diffusion-limited than in the case of the MA (d = 1558 μm ± 125 μm) and DDMI (d = 1370 μm ± 60 μm) bio-encapsulation schemes at the 98.3% CI. The proposed novel double encapsulation biofabrication method for alginate-based microspheres, characterized by lower membrane degradation rates due to secondary containment is recommended compared to the standard atomization scheme currently adopted across immobilization-based therapeutic scenarios. A Fickian-based mechanism is proposed with simulations mimicking urea degradation for a single capsule for the atomization and the inkjet schemes.

Inorganic fouling mitigation by salinity cycling in batch reverse osmosis

Enhanced fouling resistance has been observed in recent variants of reverse osmosis (RO) desalination which use time-varying batch or semi-batch processes, such as closed-circuit RO (CCRO) and pulse flow RO (PFRO). However, the mechanisms of batch processes' fouling resistance are not well-understood, and models have not been developed for prediction of their fouling performance. Here, a framework for predicting reverse osmosis fouling is developed by comparing the fluid residence time in batch and continuous (conventional) reverse osmosis systems to the nucleation induction times for crystallization of sparingly soluble salts. This study considers the inorganic foulants calcium sulfate (gypsum), calcium carbonate (calcite), and silica, and the work predicts maximum recovery ratios for the treatment of typical water sources using batch reverse osmosis (BRO) and continuous reverse osmosis. The prediction method is validated through comparisons to the measured time delay for CaSO₄ membrane scaling in a bench-scale, recirculating reverse osmosis unit. The maximum recovery ratio for each salt solution (CaCO₃, CaSO₄) is individually predicted as a function of inlet salinity, as shown in contour plots. Next, the maximum recovery ratios of batch and conventional RO are compared across several water sources, including seawater, brackish groundwater, and RO brine. Batch RO's shorter residence times, associated with cycling from low to high salinity during each batch, enable significantly higher recovery ratios and higher salinity than in continuous RO for all cases examined. Finally, representative brackish RO brine samples were analyzed to determine the maximum possible recovery with batch RO. Overall, the induction time modeling methodology provided here can be used to allow batch RO to operate at high salinity and high recovery, while controlling scaling. The results show that, in addition to its known energy efficiency improvement, batch RO has superior inorganic fouling resistance relative to conventional RO.

A review of polymeric membranes and processes for potable water reuse

Conventional water resources in many regions are insufficient to meet the water needs of growing populations, thus reuse is gaining acceptance as a method of water supply augmentation. Recent advancements in membrane technology have allowed for the reclamation of municipal wastewater for the production of drinking water, i.e., potable reuse. Although public perception can be a challenge, potable reuse is often the least energy-intensive method of providing additional drinking water to water stressed regions. A variety of membranes have been developed that can remove water contaminants ranging from particles and pathogens to dissolved organic compounds and salts. Typically, potable reuse treatment plants use polymeric membranes for microfiltration or ultrafiltration in conjunction with reverse osmosis and, in some cases, nanofiltration. Membrane properties, including pore size, wettability, surface charge, roughness, thermal resistance, chemical stability, permeability, thickness and mechanical strength, vary between membranes and applications. Advancements in membrane technology including new membrane materials, coatings, and manufacturing methods, as well as emerging membrane processes such as membrane bioreactors, electrodialysis, and forward osmosis have been developed to improve selectivity, energy consumption, fouling resistance, and/or capital cost. The purpose of this review is to provide a comprehensive summary of the role of polymeric membranes in the treatment of wastewater to potable water quality and highlight recent advancements in separation processes. Beyond membranes themselves, this review covers the background and history of potable reuse, and commonly used potable reuse process chains, pretreatment steps, and advanced oxidation processes. Key trends in membrane technology include novel configurations, materials and fouling prevention techniques. Challenges still facing membrane-based potable reuse applications, including chemical and biological contaminant removal, membrane fouling, and public perception, are highlighted as areas in need of further research and development.