Purification Of Oily Wastewater Research Articles

Double network cross-linked hydrogel coating membrane with photocatalytic self-cleaning performance for efficient oil-water separation

Oil-water separation is one of the most attractive areas in the field of energy and the environment. However, the synthesis of oil-water separation membranes with high separation efficiency and anti-fouling via simple methods is still a challenge. In this work, a double network with tannic acid and g-C3N4 cross-linked gelatin hydrogel coating membrane was prepared via ultrasound and coating. The prepared hydrogel had excellent mechanical properties and swelling resistance and also endowed the membrane with underwater superoleophobicity. For stratified oil-water mixtures, the separation flux achieved 40,355 ± 1957 L·m−2·h−1 and separation efficiency higher than 99 %. Moreover, after 40 cycles, there was no decrease significantly in separation performance. For oil-in-water emulsions, the separation efficiency is >99.90 % under gravity. The adsorption of MB by the GE-CNTA-PP membrane conformed to a pseudo-first-order kinetic process (R2 = 0.99906), which was consistent with the Langmuir isothermal adsorption model (R2 = 0.99932). The contaminated membrane could self-clean via photocatalytic reaction, which mechanism was explained through theoretical investigation of the band structure of g-C3N4 by DFT. Due to these obvious advantages, the practical application of the gelatin-based hydrogel membrane in the purification of oily wastewater is promising.

Cellulose cryogels from herbal residues for oily wastewater purification

Recycling herbal residues for oily wastewater purification is a potential way to use the wastes to treat wastes. Cellulose extracted from herbal residues is a fine material for cryogel fabrication. However, the cellulose cryogels were not suitable for oily wastewater treatment due to their amphiphilicity. To address this issue, the cryogels were modified with methyltrimethoxysilane (MTMS), which made them hydrophobic and reduced their surface energy. In this study, the herbal residues (Ficus microcarpa L. f) were used in cryogel preparation for the first time. The cryogels exhibit super lightweight and low density. The modified cryogels show excellent sorption capacity for free oils, especially silicone oil (51.22 g/g), and outperformed some recent sorbents. They also effectively separated water-in-toluene emulsion stabilized by Span 80, with a separation efficiency of 98.57 % and a flux of 1474.67 L/m2h. This study demonstrated a novel application of waste herbal residues in the field of environmental remediation.

Super-amphiphobic arabic gum-based coatings on textile for on-demand oily and dye wastewater treatment

Different membrane materials have broadly been constructed for oil-containing water separation, but most of preparation routes involve corrosive or toxic chemicals and especially many materials have only single superwetting property. Herein, a novel and eco-friendly cellulose-based textile membrane is developed by incorporating the composite coating consisting of arabic gum (AG), attapulgite (APT), and iron (Fe) onto cellulose textiles. The functionalized textile is superoleophobic underwater and superhydrophobic underoil. As a result, the textile prewetted with water or oil can be employed to separate light oil layer/water and heavy oil layer/water mixtures, respectively, and the separation efficiency to the two types of mixtures is larger than 98.3 %. Results also reveal that the decorated textile possesses superior stability and recyclability in purifying oily wastewater. More importantly, such coated textile is capable of filtrating water-soluble contaminants (dyes) from polluted water. Due to the versatility and environmental compatibility of product as well as the accessibility as agricultural and forestry product as raw materials, the advanced textiles may offer effective solutions to oily wastewater purification and water-soluble contaminant removal.

Preparation and characterization of electrospun PVDF/PVP/SiO2 nanofiber membrane for oil-water separation

For oily wastewater purification, polyvinylidene fluoride (PVDF) nanofiber membranes have been widely noticed for their excellent mechanical strength and corrosion resistance. However, it is prone to serious oil fouling problems during use, resulting in reduced flux and inability to be used repeatedly. It has become a hot research topic to develop simple methods to realize its hydrophilic modification for oily wastewater treatment to address this problem. Herein, a novel separation membrane was prepared by doping polyvinylpyrrolidone (PVP) and hydrophilic silica nanoparticles (SiO2 NPs) into PVDF using a facile one-step electrospinning method. The modified membrane shows hydrophilicity, water contact angle (WCA) is 0°, oleophobicity in water, and oil contact angle (OCA) is more than 145° and has good separation efficiency and flux for both oil-water mixtures and emulsions. After 30 times of mixture and emulsion separation tests, the separation efficiency is above 99.5 % and 97 %, respectively, showing good separation and reusability. Besides, compared with hydrophilic modification methods such as surface coating and grafting, the proposed modification method is simpler and has great potential in treating oily wastewater.

Rod-like MIL-53(Fe) intercalated MXene nanosheets lamellar composite membrane for the purification of multi-component oily wastewater

The complicated oily wastewater containing hazardous organics post a great challenge to the membrane separation technology. Herein, a multilayer porous multifunctional MXene/MOF composite membrane with high permeability and photocatalytic degradation performance was prepared by embedding rod-shaped MIL-53(Fe) into layered MXene nanosheets and self-assembling them onto porous polyacrylonitrile fibrous mat. It was found that the embedment of rod-like MIL-53(Fe) with rough nanostructures could effectively avoid the dense physical stacking of MXene nanosheets and regulate the layer spacing, which was conducive to the enhancement of water channel and permeability of membrane. Moreover, the hydrophilic modification of TA could render the super-wetting feature (WCA=0°, UOCA>150°) and enhance the oil resistance of the membrane. Thence, the composite membrane exhibited favorable separation flux (904.3 ∼ 1226.5 L·m−2·h−1) and retention rate (99.06 ∼ 99.62%) for different O/W emulsions. In addition, the coupling of rod-like MIL-53(Fe) and MXene nanosheets endowed the composite membrane with efficient photocatalytic performance, which could degrade various dyes contained in oily wastewater (CV: 62.4%, MeB: 99.0%, CR: 79.5%, MO: 84.1%). Overall, this study opens up a new way for the preparation of super-wetting and multi-functional fibrous composite membrane, showing the broad application prospects in the purification of multi-component oily wastewater.

High mechanical CuO@stainless steel mesh for continuous and durable separation of surfactant-stabilized viscous and light/heavy-mixed oily emulsions in liter-scale

High mechanical filtration membranes, which can continuously and durably separate surfactant-stabilized viscous and light/heavy-mixed oily emulsions with high separation efficiency, are highly desirable for existing oily wastewater remedy. Herein, an all inorganic FM, by decorating CuO microrods standing on stainless steel mesh (SSM), has been designed to fulfill this challenge. Our FM exhibits both superwetting surface and high mechanical performance (tensile strength: ∼250 MPa). Furthermore, driven by the robust thermal stability of our FM (≥ 800 °C at oxygen atmosphere), combustion (<10 s) via alcohol flame, can be used to solve the oil fouling issue without deteriorating their original filtration performance. Prompted by these advantages aforementioned, our FM displays high oil rejection efficiency (>99 %) towards diverse surfactant free/−stabilized oil-in-water emulsions with good flux (> 10,500 L m−2 h−1 bar−1) via dead-end setup in millilitre-scale. Besides, continuous and durable separation of surfactant stabilized viscous (soybean oil) and light (hexane)/heavy (dichloroethane)-mixed oil/water emulsions in liter-scale with good cycling stability and same separation efficiency compared to these of emulsions via dead-end setup in millilitre-scale aforementioned, has been also achieved. These outstanding functions make our FM hold excellent potential for practical complex oily wastewater purification.

Robust Zwitterionic Poly(imidazolium)-Coated PVDF Membrane for Oily Water Treatment with Antibacterial and Anti-Biofouling Performances

Membrane fouling remains a major challenge during oily wastewater purification, resulting in reduced water flux and separation efficiency. Zwitterionic polymers have been introduced to the PVDF membrane and shown their fouling resistance ability. However, most current zwitterions lack bactericidal effects and tend to be fouled by the attachment of bacteria and biofilm formation in long-term service. Herein, a synthetic zwitterionic poly(imidazolium), poly(ZIM-co-VTS), was introduced onto the PVDF membrane by co-assembly with polydopamine (PDA) and tetraethyl orthosilicate (TEOS) as a silica source. The in situ covalent bond can be formed between the catechol from PDA and silanol groups from both TEOS and imidazole-based polymers. Further, Fe3+ cross-linking contributes to the robust chemical stability of modified PVDF. The as-prepared coating exhibits superhydrophilicity and underwater superoleophobicity under harsh conditions (pH = 1 and 13), remaining high separation efficiency (>99%) toward various surfactant-stabilized oil-in-water emulsions without an apparent water flux (>1013 L m–2 h–1 bar–1) decline. More importantly, the cationic imidazolium in poly(ZIM-co-VTS) endues the excellent bacterial killing efficiency toward Staphylococcus aureus (4.5 log10 reduction) and Escherichia coli (4.7 log10 reduction). The zwitterionic poly(imidazolium)-modified PVDF exhibited long-term durability with anti-biofouling properties and was a promising candidate for practical oily wastewater remediation.

A simple surface modification method to prepare versatile PVDF electrospun nanofibrous felts for separation, sterilization and degradation

The discharge of oily effluents from industrial production and crude oil spills at sea result in significant water pollution, posing a major danger to the environment and human health. Due to the tiny droplet size, emulsion separation is a difficult task in the separation and purification of oily wastewater. Polydopamine (PDA) and TiO2 nanoparticles were coated on the surface of polyvinylidene fluoride (PVDF) electrospun nanofibrous to increase surface roughness, and then the low surface energy substance octadecylamine (ODA) was grafted. As a result, a superhydrophobic PVDF@PDA/TiO2@ODA nanofibrous felts with a water contact angle of 168.1° has been developed. Because of their three-dimensional porous structure, the nanofibrous felts have a porosity of up to 72.9 %. The tensile strength of a series of reinforced PVDF@PDA/TiO2@ODA nanofibrous felts reaches 30.06 MPa, which is useful for maintaining the stability of the nanofibrous felts during the pressure separation. The oil and water in the emulsion are entirely separated due to the selective permeability induced by the strong superhydrophobic and superlipophilic properties. The separation efficiency of over 99 % and flow flux of above 1100 L·m−2·h−1 are achieved. The performance of the nanofibrous felts in inhibiting bacterial growth was then investigated, and it is found that a significant inhibition circle appeared in the flat dish diffusion method, with a bacteriostasis rate exceeding 99 %. This result demonstrates that PVDF@PDA/TiO2@ODA nanofibrous felts have excellent antimicrobial properties. Finally, UV–vis absorption spectroscopy was employed to demonstrate the good catalytic degradation of organic dyes by PVDF@PDA/TiO2@ODA nanofibrous felts. PVDF@PDA/TiO2@ODA nanofibrous felts have a variety of applications in the deep separation and purification of oily wastewater due to these characteristics.

Simple and eco-friendly fabrication of highly tolerant chitosan/alginate@sepiolite hybrid films on nylon textile for oil/water separation in harsh conditions

Because of the need of achieving efficient separation to oil/water mixture, the construction of separation coating with good mechanical strength and chemical resistance are highly desired. Although many polysaccharide-based coating for oil/water separation have been prepared, the poor durability and the environmentally unfriendly preparation process greatly restrict their applications. Herein, sepiolite (SP) was introduced into chitosan/alginate (CS/AG) matrix to produce nacre-like composite films with superb robustness and stability via a simple and green layer-by-layer (LbL) self-assembly technique. After the composite films are fabricated on nylon textile (NT), the hydrophilicity and underwater superoleophobicity of the NT surface are significantly improved. The composite coating also reveals excellent oleophobic stability after being subjected to corrosive liquids immersion, high-temperature treatment, strong abrasion, and organic solvents immersion. Furthermore, the modified NT is able to separate oil/pure water, oil/cold corrosive water, and oil/hot corrosive water mixtures with high filtration efficiency (>98.3 %). Especially, the separation to oil/hot corrosive solution mixtures can be repeated at least 40 times without obvious decrease of separation efficiencies. This investigation offers a new and eco-friendly strategy to prepare SP coating-based membrane materials with good superhydrophilicity, mechanical property, and recyclability for oily wastewater purification.

Modified porous membrane with high solar-to-thermal conversion and oil resistance performance for solar steam generation

The utilization of solar steam generator via photothermal conversion is a sustainable and highly sufficient solution for addressing long-standing water scarcity. Due to its extensive optical absorption, dopamine has been considered as a promising photo-thermal conversion material. In this work, by co-depositing Fe3+ and 3-glycidyloxypropyltrimethoxysilane (KH550) with polydopamine (PDA), a high-performance, low-cost, and scalable modified membrane (called PVDF/[email protected]@Fe3+) with superior oil resistance was developed. Under one sun illumination, the resulting PVDF/[email protected]@Fe3+ membrane generated solar steam with a high efficiency of 90.33% and a high evaporation rate of 1.40 kg m−2 h−1. More importantly, the evaporation rate still performs well even in oil-contaminated water due to the improvement of hydrophilicity and anti-fouling capabilities of the modified membrane. In oil-in-water emulsion, the evaporation rate approaches 1.33 kg m−2 h−1 and the evaporation efficiency reaches 85.49%. This study demonstrated that solar steam generation using PVDF/[email protected]@Fe3+ membrane could be a viable option for seawater and oily wastewater purification.

Structured electroplating sludge derived membrane for one-step removal of oil, metal ions, and anions from oil/water emulsions

The effective simultaneous treatment of hazardous waste sludge and complex oil/water emulsions in one way is urgently desired but still a challenging issue. Herein, this work for the first time presents a green and efficient strategy to fabricate an electroplating sludge (ES) derived multifunctional self-supporting membrane for the one-step removal of emulsified oils, soluble metal ions, and anions in complex oily wastewater. Due to low cost of ES and sustainability of the solvent selected in fabrication process, the large-scale application of the membrane is easily to promote. The assembled hierarchical nanostructure endowed robust underwater superoleophobicity of the membrane even under various corrosive aqueous environments, as well as excellent ultra-low oil adhesion and anti-oil-fouling performance, without chemical modification. Significantly, the multifunctional membrane possessed desirable simultaneous separation efficiency for five typical oil-in-water emulsions (>99.4%, high oil/water selective wettability), including crude oil-in-water emulsion with high viscosity (>99.6%), Cu2+ (>96.1%, surface complexation and ionic exchange), and Cl- (>92.7%, electrostatic attraction). Therefore, this green, low-cost, and multifunctional membrane not only allows the large-scale resource utilization of hazardous waste sludge, but also effectively solves the problems of complex oily wastewater purification.

Electrophoretic coalescence behavior of oil droplets in oil-in-water emulsions containing SDS under DC electric field: A molecular dynamics study

The presence of oil droplets in oil-in-water (O/W) emulsions seriously affects the efficiency of wastewater purification, and the appropriate addition of surfactants can effectively improve the demulsification process. In this paper, the electrophoretic coalescence behavior of oil droplets containing anionic surfactant sodium dodecyl sulfate (SDS) under a direct current (DC) electric field was studied based on molecular dynamics (MD) simulations, and four typical stages of oil droplet migration coalescence were defined. The weak interactions between SDS and water and between SDS and n-hexane are mainly van der Waals interactions, while a small number of hydrogen bonds are formed between SDS and water and between water molecules internally. With the increase of electric field strength (E), the deformation of oil droplets after aggregation increases, and the contact angle with the electrode plate becomes smaller. The interfacial tension between oil and water decreases and then increases with increasing surfactant concentration, reaching a minimum value of 32.52 mN/m when the number of SDS molecules (n) around each oil droplet is 55. When E = 1.2 V/nm and n = 55, the coalescence time of oil droplets reaches the minimum value of 2.425 ns. The migration rate of oil droplet far from the anode is greater than that of oil droplet near the anode, which is due to the larger combined forces on the former. The results reveal the microscopic mechanism of oil droplet migration and coalescence under the coupling effect of DC electric field and anionic surfactant, which could provide theoretical guidance for the improvement of oily wastewater purification process.

Mineralized cupric phosphate/alginate gel alternately multilayer-wrapped nanofibrous membrane with robust anti-crude oil pollution for oily wastewater purification

The high oil-adhesion of crude oil results in flux decline. Therefore, the purification of crude oil/water emulsions is an ongoing and arduous challenge. To improve oil stain resistance and reusability, alginate gel and mineralized Cu3(PO4)2 were alternately layer-by-layer self-assembled on a thermally stabilized PAN/PEI nanofibrous membrane. Inspired by a natural formation water purification system, the hydrophilic and antifouling ‘soil-stone’-like hierarchical structures were constructed. The prepared membrane has excellent mechanical properties (Modulus:198.36 MPa) and large specific surface area. In addition, the synergistic effect of the alginate gel layer and mineralized copper phosphate endows the membrane with excellent underwater superhydrophobicity and outstanding anti-oil-fouling properties, so the (Alg/CuP)6-PAN/PEI membrane can effectively separate crude oil-in-water emulsions and other various SDS-stabilized oil-in-water emulsions, with a high separation efficiency of approximately 99.5%. In the continuous test of separating 1000 mL emulsion, the flux and separation efficiency have no obvious attenuation, and the flux recovery rate (FRR) reach up to 98.4%. Furthermore, the modified membrane has good mechanical and chemical stability in environments with ultrasonic waves, salt, solvents, bases and weak acids, showing great promise in the decontamination of actual oily wastewater.

Blow-Spun Nanofibrous Membrane for Simultaneous Treatment of Emulsified Oil/Water Mixtures, Dyes, and Bacteria

Membrane separation is of great significance due to its unique performance in treating wastewater. However, the simultaneous treatment of oily emulsions and other complex pollutants in water remains challenging. Herein, we have proposed a simple strategy to prepare a multifunctional titanium dioxide/silver nanoparticles/polyacrylonitrile (TiO2/AgNPs/PAN) nanofibrous membrane. The experimental results showed that the combination of the hierarchical structure composed of PAN nanofibers and Ag/TiO2 nanoprotrusions contributed to the superhydrophilicity and superoleophobicity (UOCA = 153.3 ± 2.0°). Further, the nanofibrous membrane exhibited a rapid gravity-driven permeate flux (>1829.37 ± 83.51 L m-2 h-1) and an ultrahigh separation efficiency (>99.9%) for the surfactant-stabilized oil/water emulsions. Moreover, due to the synergistic effect between the PAN fibers and TiO2/Ag heterojunction, Rhodamine B dye in water can be removed quickly and efficiently (up to 97.67% in 90 min). More importantly, the obtained nanofibrous membrane exhibited ultrahigh stability in different harsh environments. The design of superoleophobic nanofiber membrane with a high separation efficiency and high photocatalytic activity has great potential for practical applications in the purification of oily wastewater.

Remediation of saline oily water using an algae-based membrane

Petrochemical industry generates large amounts of oily wastewater that requires effective treatment methods. Among all, membrane filtration techniques have been receiving more attention, due to easy operation and low energy consumption. One of the issues is that the oily wastewater also contains high level of salinity. Thus, preparation of dual function membrane to be used for purification of saline oily wastewater is an attractive option. Inspired from fish scales, we prepared an underwater superoleophobic membrane using microalgae coated on steel mesh which can also be used in water desalination. In order to fix microalgae biofilm on the surface of steel mesh, PVA polymer and glutaraldehyde as crosslinking reagent was used. The salts can also be removed using microalgae biomass coated on steel mesh by the adsorption process. The prepared membrane demonstrated high efficiency (above 98%) for oil-water separation with the highest water flux of 30225.0 L m−2 h−1. Under optimized conditions, algae-based mesh exhibited salt rejection of (98.6 ± 0.5) %. Due to its simplicity, low cost and great performance in both oil-water separation and water desalination, the as-prepared membrane could find broad applications for commercial purposes.

Effect of inorganic salt concentration and types on electrophoretic migration of oil droplets in oil-in-water emulsion: A molecular dynamics study

Oil-in-water (O/W) wastewater generally contains inorganic salt ions, which cause energy consumption in the process of electric demulsification. To reveal the influence mechanism of inorganic salt ions on the micro movement of oil droplets in O/W emulsion, the electrophoretic migration of oil droplets with different ion concentration was studied based on molecular dynamics simulation. The results showed that Na+ adsorbed the negative charge on the surface of the oil droplets while Cl- repelled it, leading to a decrease in the electrophoretic mobility and deformation of the oil droplets with the increase of ion concentration. The inhibitory effect of three inorganic salts on oil droplet electrophoretic migration was MgCl2 > CaCl2 > NaCl. The weak interaction between oil, water and ions was mainly van der Waals interaction. When the NaCl concentration was 0.4 mol/L, the oil–water interfacial tension was at its maximum value of 85.14 mN/m. and the deformation degree of oil droplets reached the minimum values of 0.45. The formation of hydrated ions reduces the freedom of water molecules. The above findings uncovered the effect of inorganic salt ions on the electrophoretic migration of oil droplets in O/W emulsions under a DC electric field, which can provide theoretical guidance for the purification of oily wastewater from the molecular level.

A passive-active combined strategy for ultrafiltration membrane fouling control in continuous oily wastewater purification

Membrane-based technology has been confirmed as an effective way to treat emulsified oily wastewater, however, membrane fouling is still one of practical challenges in long-term operation. Herein, a novel passive-active combined strategy was proposed to control membrane fouling in continuous oily wastewater purification, where the δ-MnO2 decoration layer helped to reduce the total fouling ratio (passive strategy for fouling mitigation) and the catalytic cleaning effectively removed the irreversible oil fouling (active strategy for fouling removal). The functional membrane was prepared via in-situ modification, referred to as δ-MnO2@TA-PES. The morphology, crystalline phase, chemical structure and surface properties of the membranes were systematically characterized. Compared with PES, the δ-MnO2@TA-PES possessed superhydrophilicity, enhanced electronegativity and narrowed pore size. The δ-MnO2@TA-PES achieved high water permeation flux of 723.9 L·m − 2·h − 1·bar−1, excellent oil rejection with separation efficiency above 98.5% for various emulsions, and durable anti-oil-fouling performance with FRRb of 98.0%. Notably, the oil cake layer fouling on δ-MnO2@TA-PES was greatly alleviated owing to its enhanced surface properties. In addition, δ-MnO2@TA-PES showed high cleaning efficiency in the peroxymonosulfate (PMS) cleaning process, where the radical and nonradical pathways occurred simultaneously. And the active substances generated in the nonradical process (especially 1O2) were considered as the main contributor to the reduction of irreversible fouling. Overall, the novel strategy of fouling control ensured the efficient operation of ultrafiltration membranes for the continuous oily wastewater purification.

Green multifunctional PVA composite hydrogel-membrane for the efficient purification of emulsified oil wastewater containing Pb2+ ions

To date, most existing engineering materials have difficulty simultaneously separating oil/water and removing heavy metals from complex oily wastewater. In response to this challenge, a novel multifunctional composite hydrogel membrane (named PVA-CS-LDHs) was fabricated by incorporating chitosan (CS) and nanohydrotalcite (LDHs) into a polyvinyl alcohol (PVA) hydrogel. This material was developed using an easy yet versatile strategy of freezing and salting-out, which can enable the formation of a PVA-CS-LDH hydrogel membrane in one step and endow the PVA-CS-LDHs with high strength, excellent stretchability, favourable shape recoverability, and an ideal 3D microstructure. The PVA-CS-LDH membrane can purify emulsified oil and metal ions simultaneously with a separation efficiency of 99.89 % for emulsified oil and a removal efficiency of 97.44 % for Pb2+ ions. Additionally, the high-efficiency, multifunctional, high-antifouling and eco-friendly properties of the PVA-CS-LDH membrane make it a promising hydrogel material for both emulsified oil separation and heavy metal ion removal. Thus, this material provides critical application potential that can address scientific and technological challenges in complex oily wastewater purification.

Surface modified basalt membrane as a photothermal material for improved oily wastewater solar evaporation

ABSTRACT Oily wastewater is produced from many processes in petrochemical, food, pharmaceutical, mining, and metal industries. Proper management of oily wastewater discharges is required to mitigate their environmental impacts. Basalt fabric has been reported as being uniquely suitable for oily wastewater purification via solar evaporation due to its robust structure and surface chemistry. In this study, an efficient, low-cost, and scalable 3D photothermal evaporator was prepared by surface modification of basalt fabric with TiO2 nanoparticles for oily wastewater treatment and solar steam generation. The basalt membrane was coated with two types of TiO2 (Degussa P25 and nitrogen-doped TiO2) to enhance its hydrophilicity and photocatalytic properties important for fouling control. The basalt membranes were then tested for their impacts on water evaporation under various salinities and concentrations of gasoline constituents and crude oil. In pure water, the modified membrane system achieved an evaporation rate of 1.65 kg‧m−2‧h−1 under 1 sun irradiation, which is higher than the theoretical value of 1.47 kg‧m−2‧h−1 due to the 3D nature of the structure capable of harvesting energy from the environment. Crude oil significantly decreased the evaporation rate of the unmodified basalt membrane. However, the coating of TiO2 nanoparticles was found to ameliorate the fouling effect by increasing the membrane evaporation efficiency from 0.75 kg‧m−2‧h−1 to 1.42 kg‧m−2‧h−1 in a 2.0 g/L oily water composition. This technology is promising as a new approach to manage oily wastewater storage tanks and evaporation ponds in industry in addition to improving the efficiency of resource recovery.

A freestanding dual-cross-linked membrane with robust anti-crude oil-fouling performance for highly efficient crude oil-in-water emulsion separation

Hydrogel membranes generally possess weak mechanical properties, and the membrane surface is susceptible to abrasion, which results in the loss of superwetting properties and oil/water separation ability. Therefore, we prepared a flexible freestanding membrane using a dual-cross-linking approach. A mixed solution of sodium alginate (SA) and polyvinyl alcohol (PVA) was covalently and ionically cross-linked with borax and calcium chloride (CaCl2) to form a hydrogel, and sodium carbonate (Na2CO3) solution was then added to synthesize calcium carbonate (CaCO3) in situ. The combination of covalent and ionic cross-linking improves the tensile strength. The prepared SA/PVA/borax/CaCO3 (SPBC) membrane maintained excellent superwetting properties and oil/water separation ability, even after abrasion. The SPBC membranes have broad application prospects in the oily wastewater purification owing to their numerous advantages, such as cost effectiveness, high separation efficiency, and improved mechanical strength.