High boron removal polyamide reverse osmosis membranes by swelling induced embedding of a sulfonyl molecular plug

Thin-film composite vapor-gap membrane for pressure-driven distillation

Pressure-driven distillation (PD), as an emerging technology, holds tremendous potential for producing freshwater from nontraditional water sources. In this process, a sufficient hydraulic pressure is applied to drive water evaporation and vapor transport across a vapor-gap membrane. The development of the PD process critically depends on the availability of robust and large-area superhydrophobic membranes. Here, we propose an ultraselective superhydrophobic thin-film composite (TFC) vapor-gap membrane with confined transport channels toward the PD process, which can be manufactured scale-up through a facile swelling-assisted deposition strategy. The TFC-PD membrane demonstrates separation capabilities, achieving near-complete rejections of nonvolatile solutes, including salts, boron, and urea. Featured by a vapor-gap superhydrophobic layer, the TFC-PD membrane exhibits superior chlorine and scaling resistance and maintains stable performance over time without being oxidized or scaling. This work offers notable advancements in the microstructural design of PD membranes and the development of scalable robust TFC membranes for the PD process.

Fouling of Reverse Osmosis (RO) and Nanofiltration (NF) Membranes by Low Molecular Weight Organic Compounds (LMWOCs), Part 2: Countermeasures and Applications

Fouling, particularly from organic fouling and biofouling, poses a significant challenge in the RO/NF treatment of marginal waters, especially wastewater. Part 1 of this review detailed LMWOC fouling mechanisms. Part 2 focuses on countermeasures and applications. Effective fouling prevention relies on pretreatment, early detection, cleaning, optimized operation, and in situ membrane modification. Accurate fouling prediction is crucial. Preliminary tests using flat-sheet membranes or small-diameter modules are recommended. Currently, no specific fouling index exists for LMWOC fouling. Hydrophobic membranes, such as polyamide, are proposed as alternatives to the standard silt density index (SDI) filter. Once LMWOC fouling potential is assessed, suitable pretreatment methods can be implemented. These include adsorbents, specialized water filters, oxidative decomposition, and antifoulants. In situations where pretreatment is impractical, alternative strategies like high pH operation might be considered. Membrane cleaning becomes necessary upon fouling; however, standard cleaning often fails to fully restore the original flow. Specialized CIP chemicals, including organic solvent-based and oxidative agents, are required. Conversely, LMWOC fouling typically leads to a stabilized flow rate reduction rather than a continuous decline. Aggressive cleaning may be avoided if the resulting operating pressure increase is acceptable. When a significant flow rate drop occurs and LMWOC fouling is suspected, analysis of the fouled membrane is necessary for identification. Standard FT-IR often fails to detect LMWOCs. Solvent extraction followed by GC-MS is required. Pyrolysis GC-MS, which eliminates the extraction step, shows promise. The review concludes by examining how LMWOCs can be strategically utilized to enhance membrane rejection and restore deteriorated membranes.

Ultrahydrophilic Inorganic Nanosheet-Based Nanofiltration Membranes for High Efficiency Separations of Inorganic Salts and Organic Dyes

Two-dimensional (2D) inorganic nanomaterials have garnered extensive attention in the fabrication of inorganic nanofiltration membranes due to their unique structures and properties. In this study, we developed a facile process for fabricating large-scale ultrahydrophilic nanofiltration membranes using layered titanate H1.07Ti1.73O4·nH2O nanosheets (HT-ns). A drying deposition process was used to fabricate HT-ns membranes on a poly(tetrafluoroethylene) (TF) substrate. To enhance the bonding strength between the substrate and the deposited HT-ns membrane, the substrate surface was modified with a Cu2+-adsorbed silane monomolecular layer, connecting a negatively charged HT-ns membrane and a positively charged substrate surface. The fabricated HT-ns membrane exhibited an excellent rejection performance for inorganic salts and dye molecules. The ultrahydrophilicity of HT-ns membrane with a low water contact angle of 31° results in an ultrafast water permeance, which is approximately 6 times higher than that of a simple graphene-based nanofiltration membrane. The results open a new avenue to a new category of ultrahydrophilic nanofiltration membranes.

Boron Removal in Aqueous Solutions Using Adsorption with Sugarcane Bagasse Biochar and Ammonia Nanobubbles

Boron is a naturally occurring trace chemical element. High concentrations of boron in nature can adversely affect biological systems and cause severe pollution to the ecological environment. We examined a method to effectively remove boron ions from water systems using sugarcane bagasse biochar from agricultural waste with NH3 nanobubbles (10% NH3 and 90% N2). We studied the effects of the boron solution concentration, pH, and adsorption time on the adsorption of boron by the modified biochar. At the same time, the possibility of using magnesium chloride and NH3 nanobubbles to enhance the adsorption capacity of the biochar was explored. The carbonization temperature of sugarcane bagasse was investigated using thermogravimetric analysis. It was characterized using XRD, SEM, and BET analysis. The boron adsorption results showed that, under alkaline conditions above pH 9, the adsorption capacity of the positively charged modified biochar was improved under the double-layer effect of magnesium ions and NH3 nanobubbles, because the boron existed in the form of negatively charged borate B(OH)4- anion groups. Moreover, cations on the NH3 nanobubble could adsorb the boron. When the NH3 nanobubbles with boron and the modified biochar with boron could coagulate each other, the boron was removed to a significant extent. Extended DLVO theory was adopted to model the interaction between the NH3 nanobubble and modified biochar. The boron adsorption capacity was 36 mg/g at room temperature according to a Langmuir adsorption isotherm. The adsorbed boron was investigated using FT-IR and XPS analysis. The ammonia could be removed using zeolite molecular sieves and heating. Boron in an aqueous solution can be removed via adsorption with modified biochar with NH3 nanobubbles and MgCl2 addition.

Liquid- liquid (Cyclohexanone: Cyclohexanol) separation using augmented tight nanofiltration membrane: A sustainable approach

Organic solvent nanofiltration (OSN) is an incipient technology in the field of organic liquid-liquid separation. The incomplete separations and complexity involved in these, forces many organic liquids to be released as effluents and the adverse effects of these on environment is enormous and irreparable. The work prominences on the complete separation of industrially significant cyclohexanone: cyclohexanol (keto-alcohol oil) and heptane: toluene mixtures. The separations of these above-mentioned organic liquid mixtures were carried out using the fabricated Lewis acid modified graphitic carbon nitride (Cu2O@g-C3N4) incorporated polyvinylidene difluoride (PVDF) composite membranes. These fabricated membranes showed a separation factor of 18.16 and flux of 1.62 Lm-2h-1 for cyclohexanone: cyclohexanol mixture and separation of heptane and toluene mixture (with heptane flux of 1.52 Lm-2h-1) showed a separation factor of 9.9. The selectivity and productivity are based on the polarity and size of the organic liquids. The role of Cu2O@g-C3N4 is influencing the pore size distribution, increased divergence from solubility parameters, polarity, solvent uptake and porosity of the composite membranes. The developed composite membranes are thus envisioned to be apt for a wide range of liquid-liquid separations due to its implicit nature.

Recent advances in boron removal in aqueous media. An approach to the adsorption process and process optimization

The numerous oxidation states of the element boron bring great challenges in containing its contamination in receptor bodies. This scenario increases significantly due to the widespread use of boron compounds in various industries in recent years. For this reason, the removal of this contaminant is receiving worldwide attention. Although adsorption is a promising method in boron removal, finding suitable adsorbents, that is, those with high efficiency, and feasible remains a constant challenge. Hence, this review presents the boron removal methods in comparison to costs of adsorbents, reaction mechanisms, economic viability, continuous bed application, and regeneration capacity. In addition, the approach of multivariate algorithms in the solution of multiobjective problems can enable the optimized conditions of dosage of adsorbents and coagulants, pH, and initial concentration of boron. Therefore, this review sought to comprehensively and critically demonstrate strategic issues that may guide the choice of method and adsorbent or coagulant material in future research for bench and industrial scale boron removal.

Modified os sepiae of Sepiella inermis as a low cost, sustainable, bio-based adsorbent for the effective remediation of boron from aqueous solution

The occurrence of boron in low concentration is essential; however, a higher concentration of boron source in water has a toxic effect on humans as well as have retard effect on agricultural plant growth. Thus, the affordable and facile method to remediate water from higher boron concentrations is highly demanded. This report explores the ability of naturally occurring sustainable bio-waste os sepiae (cuttlefish bone, CFB) as an effective adsorbent for the removal of boron from water. Chemical activation of the os sepiae powder was examined to improve the efficiency of boron adsorption. A batch adsorption study for boron considering various parameters such as chemical modification of os sepiae, pH, initial boron concentration, and the temperature was scrutinized. Untreated (CFB), alkali-treated (CFB-D) and acid-treated (CFB-A) os sepiae powders were investigated and the adsorption capacities reached up to 53.8 ± 0.04 mg/g, 66.4 ± 0.02 mg/g and 69.8 ± 0.02 mg/g, respectively, at optimal pH 8 and 25 °C. Boron adsorption by CFB, CFB-D, and CFB-A were well fitted with the linear Freundlich adsorption isotherm model with a correlation coefficient of 99.4%, 99.8%, and 99.7% respectively. Thermodynamic parameters indicated that the adsorption of boron by CFB is an exothermic process and more feasible at a lower temperature around 25 °C. Moreover, detailed morphological and chemical characterization of the influence of adsorbed boron on adsorbents was conducted and discussed. The Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis spectra confirms the involvement of various functional groups including amino, carbonate (CO₃)^2-, and hydroxyl groups on the adsorbent in the adsorption mechanisms for boron removal. The results indicate that CFB can be an excellent example for the recycling and reuse of biowaste for water remediation.

Advances in Technologies for Boron Removal from Water: A Comprehensive Review

Boron overabundance in aquatic environment raises severe concerns about the environment and human health because it is toxic to various crops and induces many human and animal diseases with long-term consequences. In response to the boron pollution of water resources and the difficulty of eliminating boron from water for production and living purposes, this article summarizes the progress in research on boron removal technology, addressing the following aspects: (1) the reasons for the difficulty of removing boron from water (boron chemistry); (2) ecological/biological toxicity and established regulations; (3) analysis of different existing processes (membrane processes, resin, adsorption, chemical precipitation, (electric) coagulation, extraction, and combined methods) in terms of their mechanisms, effectiveness, and limitations; (4) prospects for future studies and possible improvements in applicability and recyclability. The focus of this paper is thus to provide a comprehensive summary of reported deboronation processes to date, which will definitely identify directions for the development of boron removal technology in the future.

Characterizing Various Produced Waters from Shale Energy Extraction within the Context of Reuse

Environmental concerns with unconventional oil and gas development are frequently centered on elevated water usage and the induction of seismic events during waste disposal. Reuse of produced water for subsequent production well stimulation can effectively address these concerns, but the variability among such samples must be well understood. Twenty-four samples of wastewater from unconventional oil and gas development were collected from south and west Texas to assess their variability and feasibility for direct reuse. Bulk metrics were collected, including total organic carbon, total nitrogen, as well as total dissolved and suspended solids. The profiles of pertinent inorganic constituents were also evaluated. Variations were not only seen between regions but also among samples collected from the same region. For example, the average total organic carbon for Eagle Ford samples collected was 700 ± 500 mg/L, while samples collected from the Permian Basin featured an average total organic carbon concentration of 600 ± 900 mg/L. The Permian Basin total organic carbon ranged from 38 to 2600 mg/L. The total dissolved solids levels had the same variability between regions, with an average value for Eagle Ford of 20,000 ± 10,000 mg/L and a Permian Basin value of 150,000 ± 40,000 mg/L. However, samples were more reproducible within a given region. Collectively, the data indicate that the direct reuse of raw produced water for subsequent production well development without treatment is not feasible based on the reported reuse thresholds. Unconventional development wastewater samples from the Permian Basin were also compared to produced water values from conventional oil and gas wells in the same region, as reported by the United States Geological Survey. Samples collected in the Permian Basin consistently demonstrated lower ionic strength compared to conventional produced water data.

Elucidating the Effect of Aliphatic Molecular Plugs on Ion-Rejecting Properties of Polyamide Membranes

Polyamide RO membranes are widely used for seawater desalination owing to their high salt rejection and water permeability; however, improved selectivity-permeability trade-off is still desired. "Molecular plugs," small molecules immobilized within the polyamide structure, offer an attractive approach; however, their overall effect on polyamide physicochemical properties poses many questions. Here, we analyze the effect of decylamine, a promising plug, and a few charged and uncharged mimics on polyamide films using several in situ techniques. Electrochemical impedance spectroscopy (EIS) reveals a complex pH-dependent response, whereby, upon exposure to amine solution, conductivity first rapidly drops; however, under alkaline conditions, when amine is uncharged, the trend subsequently slowly reverses, and conductivity increases. This slow reversal was observed for noncharged alcohols of similar size as well, but not for larger surfactant molecules. The reversal was assigned to the uptake of plug molecules within polyamide, as opposed to the fast initial drop assigned to surface adsorption. EIS and quartz-crystal microbalance (QCM) results showed that exposure to decylamine under alkaline conditions ultimately led to an irreversible decrease in conductivity, that is, stronger ion rejection, remaining after re-exposure of polyamide to amine-free buffer. This suggests that plug uptake within polyamide resulted in polymer stress, indeed observed in surface stress measurements, and subsequent relaxation. The results indicate that the moderate size of decylamine and conditions minimizing its charge were optimal for irreversible change; however, charge interactions helped maximize its binding within polymer and induce the desired sustained change in selectivity. The results have many potential implications for improving current membrane desalination technology and increasing inherent membrane selectivity toward hard-to-remove species.

Metal-organic framework enables ultraselective polyamide membrane for desalination and water reuse

While reverse osmosis (RO) is the leading technology to address the global challenge of water scarcity through desalination and potable reuse of wastewater, current RO membranes fall short in rejecting certain harmful constituents from seawater (e.g., boron) and wastewater [e.g., N-nitrosodimethylamine (NDMA)]. In this study, we develop an ultraselective polyamide (PA) membrane by enhancing interfacial polymerization with amphiphilic metal-organic framework (MOF) nanoflakes. These MOF nanoflakes horizontally align at the water/hexane interface to accelerate the transport of diamine monomers across the interface and retain gas bubbles and heat of the reaction in the interfacial reaction zone. These mechanisms synergistically lead to the formation of a crumpled and ultrathin PA nanofilm with an intrinsic thickness of ~5 nm and a high cross-linking degree of ~98%. The resulting PA membrane delivers exceptional desalination performance that is beyond the existing upper bound of permselectivity and exhibited very high rejection (>90%) of boron and NDMA unmatched by state-of-the-art RO membranes.

Robust In Situ Fouling Control toward Thin-Film Composite Reverse Osmosis Membrane via One-Step Deposition of a Ternary Homogeneous Metal-Organic Hybrid Layer

Membrane fouling is one of the persistent headaches for water desalination because of the significant detriment to membrane performance and operating cost control. It is a great challenge to overcome such crisis in a facile and robust manner. This work was dedicated to customizing an antifouling thin-film composite (TFC) reverse osmosis (RO) membrane with a polydopamine (PDA)/β-alanine (βAla)/Cu²⁺ ternary homogeneous metal-organic hybrid coating. The metal ions were evenly distributed in a continuous organic network via polydentate coordination. The incorporation of βAla enabled a substantial promotion of the Cu²⁺ loading capacity on the membrane surface. The involved one-step codeposition protocol made the surface engineering practically accessible. The deposition time was optimized to afford an uncompromising permselectivity of the membrane. This novel trinity was a smart blend of anti-adhesive and bactericidal factors, and each component in the all-in-one layer performed its own function. The hydrophilic PDA/βAla phase induced weak deposition propensity of organic foulant and bacteria onto the modified membrane, as elucidated by water flux variation, foulants adhesion profile, and interfacial interaction energy. Meanwhile, the Cu²⁺-loaded surface strongly inactivated the attached bacteria to further alleviate biofouling. Excellent sustainability and stability implied the reliable performance of such trinity-coated membrane in practical service. Given the simplicity and robustness, this work opened a promising avenue for in situ fouling control of TFC RO membranes during water desalination.

Response Surface Methodology for Boron Removal by Donnan Dialysis: Doehlert Experimental Design

The removal of boron by Donnan dialysis from aqueous solutions has been studied according to response surface methodology (RSM). First, a preliminary study was performed with two membranes (AFN and ACS) in order to determine the experimental field based on different parameters, such as the pH of the feed compartment, the concentration of counter-ions in the receiver compartment, and the concentration of boron in the feed compartment. The best removal rate of boron was 75% with the AFN membrane, but only 48% with the ACS membrane. Then, a full-factor design was developed to determine the influence of these parameters and their interactions on the removal of boron by Donnan dialysis. The pH of the feed compartment was found to be the most important parameter. The RSM was applied according to the Doehlert model to determine the optimum conditions ([B] = 66 mg/L, pH = 11.6 and [Cl⁻] = 0.5 mol/L) leading to 88.8% of boron removal with an AFN membrane. The use of the RSM can be considered a good solution to determine the optimum condition for 13.8% compared to the traditional “one-at-a-time” method.

Towards a High Rejection Desalination Membrane: The Confined Growth of Polyamide Nanofilm Induced by Alkyl-Capped Graphene Oxide

In this paper, we used an octadecylamine functionalized graphene oxide (ODA@GO) to induce the confined growth of a polyamide nanofilm in the organic and aqueous phase during interfacial polymerization (IP). The ODA@GO, fully dispersed in the organic phase, was applied as a physical barrier to confine the amine diffusion and therefore limiting the IP reaction close to the interface. The morphology and crosslinking degree of the PA nanofilm could be controlled by doping different amounts of ODA@GO (therefore adjusting the diffusion resistance). At standard seawater desalination conditions (32,000 ppm NaCl, ~55 bar), the flux of the resultant thin film nanocomposite (TFN) membrane reached 59.6 L m^-2 h^-1, which was approximately 17% more than the virgin TFC membrane. Meanwhile, the optimal salt rejection at seawater conditions (i.e., 32,000 ppm NaCl) achieved 99.6%. Concurrently, the boron rejection rate was also elevated by 13.3% compared with the TFC membrane without confined growth.

Recent Desalination Technologies by Hybridization and Integration with Reverse Osmosis: A Review

Reverse osmosis is the leading technology for desalination of brackish water and seawater, important for solving the growing problems of fresh water supply. Thermal technologies such as multi-effect distillation and multi-stage flash distillation still comprise an important portion of the world’s desalination capacity. They consume substantial amounts of energy, generally obtained from fossil fuels, due to their low efficiency. Hybridization is a strategy that seeks to reduce the weaknesses and enhance the advantages of each element that makes it up. This paper introduces a review of the most recent publications on hybridizations between reverse osmosis and thermal desalination technologies, as well as their integration with renewable energies as a requirement to decarbonize desalination processes. Different configurations provide improvements in key elements of the system to reduce energy consumption, brine production, and contamination, while improving product quality and production rate. A combination of renewable sources and use of energy and water storage systems allow for improving the reliability of hybrid systems.

Assessment of different nanofiltration and reverse osmosis membranes for simultaneous removal of arsenic and boron from spent geothermal water

One of the factors that determine agricultural crops' yield is the quality of water used during irrigation. In this study, we assessed the usability of spent geothermal water for agricultural irrigation after membrane treatment. Preliminary membrane tests were conducted on a laboratory-scale set up followed by mini-pilot scale tests in a geothermal heating center. In part I, three commercially available membranes (XLE BWRO, NF90, and Osmonics CK- NF) were tested using a cross-flow flat-sheet membrane testing unit (Sepa CF II, GE-Osmonics) under constant applied pressure of 20 bar. In part II, different spiral wound membranes (TR-NE90-NF, TR-BE-BW, and BW30) other than the ones used in laboratory tests were employed for the mini-pilot scale studies in a continuous mode. Water recovery and applied pressure were maintained constant at 60% and 12 bar, respectively. Performances of the membranes were assessed in terms of the permeate flux, boron and arsenic removals. In laboratory tests, the permeate fluxes were measured as 94.3, 87.9, and 64.3 L m^-2 h^-1 for XLE BWRO, CK-NF and NF90 membranes, respectively. The arsenic removals were found as 99.0%, 87.5% and 83.6% while the boron removals were 56.8%, 54.2%, and 26.1% for XLE BWRO, NF90 and CK-NF membranes, respectively. In field tests, permeate fluxes were 49.9, 26.8 and 24.0 L m^-2 h^-1 for TR-NE90-NF, BW30-RO and TR-BE-BW membranes, respectively. Boron removals were calculated as 49.9%, 44.1% and 40.7% for TR-BE-BW, TR-NE90-NF and BW30-RO membranes, respectively. Removal efficiencies of arsenic in mini-pilot scale membrane tests were all over 90%. Quality of the permeate water produced was suitable for irrigation in terms of the electrical conductivity (EC) and the total dissolved solids (TDS) for all tested membranes with respect to guidelines set by the Turkish Ministry of Environment and Urbanisation (TMEU). However, XLE BWRO, CK-NF and NF90 membranes failed to meet the required limits for irrigation in terms of boron and arsenic concentrations in the product water. The permeate streams of TR-BE-BW, TR-NE90-NF and BW30-RO membranes complied with the irrigation water standards in terms of EC, TDS and arsenic concentration while boron concentration remained above the allowable limit.