Mitigating membrane wetting in the treatment of unconventional oil and gas wastewater by membrane distillation: A comparison of pretreatment with omniphobic membrane

Hydratable Janus Membranes with Robust Antiwetting Pores for Stable Membrane Distillation of Saline Oily Wastewater

Janus membranes, composed of a hydrophilic surface layer and a hydrophobic substrate, are potential candidates for membrane distillation (MD) to prevent organic substance induced wetting in saline oily wastewater treatments. However, owing to insufficient hydrophobicity of pore surfaces, traditional hydrophobic substrates suffer from pore wetting and limited MD performance stability when saline water penetrates through the hydrophilic layer. Herein, we present a Janus polyvinylidene fluoride (PVDF) nanocomposite membrane with robust pore surface antiwettability for stable MD desalination of saline oily wastewater. Hydrophobic silica (SiO2) nanoparticles are used to build nanostructures on pore surfaces to significantly enhance their hydrophobicity for preventing pore wetting. The superhydrophilic tannic acid/Fe (TA/Fe) layer provides a hydratable surface to promote water molecule absorption, facilitate the evaporation rate, and effectively impede oil/surfactant/gypsum contaminants. As a result, the TA/Fe-PVDF/SiO2 Janus membrane shows stable desalination (32 h) with a high flux of 25.2 kg m-2 h-1 and salt rejection (>99.9%) for saline oily solution. This work provides a promising approach to develop high-performance Janus membranes with antiwetting ability for stable saline oily wastewater treatment.

Corrosion-resistant omniphobic coating for low-carbon steel substrates using silica layers enhanced with ethylenediamine tetraacedic acid

The present work develops a highly liquid repellent, i.e. omniphobic, coating designed specifically for metallic substrates like low carbon steels and evaluates its potential as a barrier to corrosion. Polydimethylsiloxane (PDMS) chains are grafted to an intermediary silica layer via the hydrolysis and polycondensation of a difunctional chlorosilane monomer, resulting in a contact angle hysteresis of ∼3° when deposited on unpolished low carbon steel substrates. However, the use of chlorosilanes to fabricate the omniphobic PDMS can corrode steel. To circumvent this, the coating uses a phosphate buffer solution to partially neutralize the silica precursor solution, and ethylenediamine tetraacedic acid (EDTA) to passivate any released Fe ions. The inhibition of corrosion is evidenced visually and by unchanging surface metrology parameters even after two months following coating deposition. Potentiodynamic polarization data indicate that the omniphobic layer provides a barrier to water ingress, as evidenced by a current density of ∼10-6 A cm-2, two orders of magnitude lower than the steel coated with the silica but without the PDMS chains. Electrochemical impedance spectroscopy data indicates the absence of an inductive loop (i.e. no ongoing corrosion) and a high polarization resistance of 40 000 Ω cm2 for the omniphobic coating. This work not only indicates that omniphobic grafted polymer chains like PDMS exhibit anti-corrosion properties, but also provides a method for depositing such coatings onto metals without corroding the substrate, even when using chlorosilane precursors that evolve hydrochloric acid.

Advances in membrane distillation for wastewater treatment: Innovations, challenges, and sustainable opportunities

Water pollution and the growing demand for zero liquid discharge solutions have driven the development of advanced wastewater treatment technologies. Membrane distillation (MD) is a promising thermal-based process capable of treating high-salinity brines and wastewater. This review provides an in-depth analysis of MD configurations, operating principles, and membrane characteristics while addressing key challenges such as fouling and pore wetting which hinder large-scale implementation. To overcome these limitations, various membrane fabrication and modification strategies, including physical and chemical approaches, have been explored. The integration of MD with other processes (hybrid MD) for wastewater treatment is also examined. A comprehensive discussion on the mechanisms of organic, inorganic, and biological fouling and their impact on MD performance is presented. Additionally, recent advancements in antifouling strategies, including surface modifications, novel materials, and operational optimizations, are reviewed. Furthermore, the review critically analyzes membrane wetting, its governing mechanisms, and mitigation techniques. By summarizing the current challenges and future prospects, this work provides valuable insights into improving MD performance for practical applications. The findings serve as a foundation for further research and technological advancements in the field of wastewater treatment using MD.

Mineral scaling induced membrane wetting in membrane distillation for water treatment: Fundamental mechanism and mitigation strategies

The scaling-induced wetting phenomenon seriously affects the application of membrane distillation (MD) technology in hypersaline wastewater treatment. Unlike the large amount of researches on membrane scaling and membrane wetting, scaling-induced wetting is not sufficiently studied. In this work, the current research evolvement of scaling-induced wetting in MD was systematically summarized. Firstly, the theories involving scaling-induced wetting were discussed, including evaluation of scaling potential of specific solutions, classical and non-classical crystal nucleation and growth theories, observation and evolution of scaling-induced processes. Secondly, the primary pretreatment methods for alleviating scaling-induced wetting were discussed in detail, focusing on adding agents composed of coagulation, precipitation, oxidation, adsorption and scale inhibitors, filtration including granular filtration, membrane filtration and mesh filtration and application of external fields including sound, light, heat, electromagnetism, magnetism and aeration. Then, the roles of operation conditions and cleaning conditions in alleviating scaling-induced wetting were evaluated. The main operation parameters included temperature, flow rate, pressure, ultrasound, vibration and aeration, while different types of cleaning reagents, cleaning frequency and a series of assisted cleaning measures were summarized. Finally, the challenges and future needs in the application of nucleation theory to scaling-induced wetting, the speculation, monitoring and mitigation of scaling-induced wetting were proposed.

Biodegradability enhancement of waste lubricating oil regeneration wastewater using electrocoagulation pretreatment

As a sustainable management of fossil fuel resources and ecological environment protection, recycling used lubricating oil has received widespread attention. However, large amounts of waste lubricating-oil regeneration wastewater (WLORW) are inevitably produced in the recycling process, and challenges are faced by traditional biological treatment of WLORW. Thus, this study investigated the effectiveness of electrocoagulation (EC) as pretreatment and its removal mechanism. The electrolysis parameters (current density, initial pH, and inter-electrode distance) were considered, and maximal 60.06% of oil removal was achieved at a current density of 15 mA/cm2, initial pH of 7, and an inter-electrode distance of 2 cm. The dispersed oil of WLORW was relatively easily removed, and most of the oil removal was contributed by emulsified oil within 5-10 μm. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that effective removal of the biorefractory organic compounds could contribute to the improvement of biodegradability of WLORW. Thus, the 5-day biochemical oxygen demand/chemical oxygen demand ratio (BOD5/COD) was significantly enhanced by 4.31 times, which highly benefits future biological treatment. The routes of WLORW removal could be concluded as charge neutralization, adsorption bridging, sweep flocculation, and air flotation. The results demonstrate that EC has potential as an effective pretreatment technology for WLORW biological treatment.

A review of the development in shale oil and gas wastewater desalination

The development of the shale oil and gas extraction industry has heightened concerns about shale oil and gas wastewater (SOGW). This review comprehensively summarizes, analyzes, and evaluates multiple issues in SOGW desalination. The detailed analysis of SOGW water quality and various disposal strategies with different water quality standards reveals the water quality characteristics and disposal status of SOGW, clarifying the necessity of desalination for the rational management of SOGW. Subsequently, potential and implemented technologies for SOGW desalination are reviewed, mainly including membrane-based, thermal-based, and adsorption-based desalination technologies, as well as bioelectrochemical desalination systems, and the research progress of these technologies in desalinating SOGW are highlighted. In addition, various pretreatment methods for SOGW desalination are comprehensively reviewed, and the synergistic effects on SOGW desalination that can be achieved by combining different desalination technologies are summarized. Renewable energy sources and waste heat are also discussed, which can be used to replace traditional fossil energy to drive SOGW desalination and reduce the negative impact of shale oil and gas exploitation on the environment. Moreover, real project cases for SOGW desalination are presented, and the full-scale or pilot-scale on-site treatment devices for SOGW desalination are summarized. In order to compare different desalination processes clearly, operational parameters and performance data of varying desalination processes, including feed salinity, water flux, salt removal rate, water recovery, energy consumption, and cost, are collected and analyzed, and the applicability of different desalination technologies in desalinating SOGW is qualitatively evaluated. Finally, the recovery of valuable inorganic resources in SOGW is discussed, which is a meaningful research direction for SOGW desalination. At present, the development of SOGW desalination has not reached a satisfactory level, and investing enough energy in SOGW desalination in the future is still necessary to achieve the optimal management of SOGW.

Coaxial Electrospun Nanofibrous Membranes for Enhanced Water Recovery by Direct Contact Membrane Distillation

Membrane distillation (MD) is an emerging technology for water recovery from hypersaline wastewater. Membrane scaling and wetting are the drawbacks that prevent the widespread implementation of the MD process. In this study, coaxially electrospun polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP) nanofibrous membranes were fabricated with re-entrant architecture and enhanced hydrophobicity/omniphobicity. The multiscale roughness was constructed by incorporating Al2O3 nanoparticles and 1H, 1H, 2H, 2H Perfluorodecyltriethoxysilane in the sheath solution. High resolution transmission electron microscopy (HR-TEM) could confirm the formation of the core-sheath nanofibrous membranes, which exhibited a water contact angle of ~142.5° and enhanced surface roughness. The membrane displayed a stable vapor flux of 12 L.m−2.h−1 (LMH) for a 7.0 wt.% NaCl feed solution and no loss in permeate quality or quantity. Long-term water recovery from 10.5 wt.% NaCl feed solution was determined to be 8−10 LMH with >99.9% NaCl rejection for up to 5 cycles of operation (60 h). The membranes exhibited excellent resistance to wetting even above the critical micelle concentration (CMC) for surfactants in the order sodium dodecyl sulphate (SDS) (16 mM) > cetyltrimethylammonium bromide (CTAB) (1.5 mM) > Tween 80 (0.10 mM). The presence of salts further deteriorated membrane performance for SDS (12 mM) and Tween-80 (0.05 mM). These coaxial electrospun nanofibrous membranes are robust and can be explored for long-term applications.