Solar-driven surface-heating membrane distillation using Ti3C2Tx MXene-coated spacers.

The emergence of two-dimensional (2D) MXenes as efficient light-to-heat conversion materials offers significant potential for solar-based desalination, particularly in photothermal interfacial evaporation, enabling cost-effective solar-powered membrane distillation (MD). This study investigates solar-powered MD afforded by a photothermally functionalized spacer, which is built by spray-coating Ti3C2Tx MXene sheets on metallic spacers. 2D Ti3C2Tx MXene gives an ultrahigh photothermal conversion efficiency; thereby, by Ti3C2Tx MXene-coated metallic spacer, this rationally designed spacer allows for a localized photothermal conversion and interfacial feed heating effect on the membrane surface, especially for MD operation. As a feed spacer and a photothermal element, Ti3C2Tx MXene-coated metallic spacer exhibited stable enhanced water flux of up to 0.36 kg·m-2h-1 under one sun illumination for a feed salinity of 35 g·L-1, corresponding energy conversion efficiency of 28.3 %. Overall, the developed photothermal Ti3C2Tx MXene-coated spacers displayed great potential in enhancing the performance, scalability, and feasibility of solar-driven MD process, paving the way for further development of photothermal elements that can be implemented in solar MD applications.

Electrothermal interfacial evaporation through carbon-nanostructured composite membranes.

High energy demand required in membrane distillation (MD) process to heat feed water and maintain the necessary temperature gradient across the membrane presents a challenge to widespread adoption of MD. In response to this challenge, surface heating membrane distillation (SHMD) has emerged as a promising solution. SHMD can employ solar or electrical energy to directly heat the membrane and feed, eliminating the need for an external heat source to heat feed water. In this study, we explore electrothermally-driven interfacial evaporation using a multi-walled carbon nanotube (MWCNT)-based composite membrane and further envision its utilization for high-efficient SHMD. Upon application of voltage, the resistance of the MWCNT leads to the conversion of electrical energy into heat, which is then uniformly transferred to feeds. The MWCNT-based composite membrane exhibited an evaporative water flux of up to 2.34 kg m-2h-1 with an associated energy efficiency of 61% and demonstrated outstanding localized surface heating performance. The employed membranes exhibited no significant variations in either resistance or surface temperature, regardless of the direction of the applied electric field. Energy parameters from the electrothermal membranes showed quantitative agreement with values reported for various electrothermal MD systems, suggesting the potential of the composite membranes in energy-efficient and cost-effective localized heating MD applications.

Comprehensive review on pH and temperature-responsive polymeric adsorbents: Mechanisms, equilibrium, kinetics, and thermodynamics of adsorption processes for heavy metals and organic dyes.

Wastewater treatment technologies have been developed to address the health and environmental risks associated with toxic and cancer-causing dyes and heavy metals found in industrial waste. The most commonly used method to mitigate and treat such effluents is adsorption, which is favored for its high efficiency, low costs, and ease of operation. However, traditional adsorbents have limitations in terms of regeneration and selectivity compared to smart adsorbents. Smart polymeric adsorbents, on the other hand, can undergo physical and chemical changes in response to external factors like temperature and pH, enabling a selective adsorption process. These adsorbents can be easily regenerated and reused with minimal generation of secondary pollutants during desorption. The unique properties acquired by stimuli-responsive adsorbents have encouraged researchers to investigate their potential for the selective and efficient removal of organic dyes and heavy metals. This comprehensive review focuses on two common stimuli, pH and temperature, discussing the fabrication methods and characteristics of smart adsorbents responsive to these factors. It also provides an overview of the mechanisms, isotherms, kinetics, and thermodynamics of the adsorption process for each type of stimuli-responsive adsorbent. Finally, the review concludes with discussions on future perspectives and considerations.

Porous Ti3C2Tx MXene Membranes for Highly Efficient Salinity Gradient Energy Harvesting.

Extracting osmotic energy through nanoporous membranes is an efficient way to harvest renewable and sustainable energy using the salinity gradient between seawater and river water. Despite recent advances of nanopore-based membranes, which have revitalized the prospect of blue energy, their energy conversion is hampered by nanomembrane issues such as high internal resistance or low selectivity. Herein, we report a lamellar-structured membrane made of nanoporous Ti3C2Tx MXene sheets, exhibiting simultaneous enhancement in permeability and ion selectivity beyond their inherent trade-off. The perforated nanopores formed by facile H2SO4 oxidation of the sheets act as a network of cation channels that interconnects interplanar nanocapillaries throughout the lamellar membrane. The constructed internal nanopores lower the energy barrier for cation passage, thereby boosting the preferential ion diffusion across the membrane. A maximum output power density of the nanoporous Ti3C2Tx MXene membranes reaches up to 17.5 W·m-2 under a 100-fold KCl gradient at neutral pH and room temperature, which is as high as by 38% compared to that of the pristine membrane. The membrane design strategy employing the nanoporous two-dimensional sheets provides a promising approach for ion exchange, osmotic energy extraction, and other nanofluidic applications.

Negative Pressure Membrane Distillation for Excellent Gypsum Scaling Resistance and Flux Enhancement.

Membrane distillation (MD) has potential to become a competitive technology for managing hypersaline brine but not until the critical challenge of mineral scaling is addressed. The state-of-the-art approach for mitigating mineral scaling in MD involves the use of superhydrophobic membranes that are difficult to fabricate and are commercially unavailable. This study explores a novel operational strategy, namely, negative pressure direct contact membrane distillation (NP-DCMD) that can minimize mineral scaling with commercially available hydrophobic membranes and at the same time enhance the water vapor flux substantially. By applying a negative gauge pressure on the feed stream, NP-DCMD achieved prolonged resistance to CaSO4 scaling and a dramatic vapor flux enhancement up to 62%. The exceptional scaling resistance is attributable to the formation of a concave liquid-gas under a negative pressure that changes the position of the water-air interface to hinder interfacial nucleation and crystal growth. The substantial flux enhancement is caused by the reduced molecular diffusion resistance within the pores and the enhanced heat transfer kinetics across the boundary layer in NP-DCMD. Achieving substantial performance improvement in both the scaling resistance and vapor flux with commercial membranes, NP-DCMD is a significant innovation with vast potential for practical adoption due to its simplicity and effectiveness.

Antiscaling 3D printed feed spacers via facile nanoparticle coating for membrane distillation.

Surface modification of feed spacers rather than membranes may hold more merit as an antiscaling strategy in membrane distillation (MD), as it avoids compromising the functionality of MD membrane. In this work, an antiscaling polyamide 3D printed spacer was developed for MD. The surface of the printed spacer was coated with fluorinated silica (FS) nanoparticles synthesized via a sol-gel process. The sol-gel approach used to synthesize the FS nanoparticles is considered a convenient and easy approach for engineering the spacer's surface structure and roughness. The performance of the FS coated printed surface was evaluated against other coating materials of different chemical properties. The coated surfaces were characterized using water contact angle measurements, ATR-FTIR, Raman, FESEM-EDX, atomic force and 3D microscopes. The 3D printed surface's microscale roughness and hydrophobicity increased, while its surface-free energy decreased with FS nanoparticles coating. The antiscaling performance of uncoated and FS coated spacers was then assessed in a direct contact MD process, using a scale-inducing aqueous solution of calcium sulfate as its feed. The scalant (Ca2+) attachment on the FS coated spacer was 0.24 mg cm-2, 74% lower than on the uncoated 3D spacer (0.95 mg cm-2). Also, by using the antiscaling FS coated spacer, scaling on the membrane surface dropped by 60%. The predominant factors that helped minimize scaling with FS coating were microscale roughness-induced hydrophobicity and reduced surface-free energy that weakened the scalant 's interaction with the spacer surface.

Polyvinylidene fluoride (PVDF)-α-zirconium phosphate (α-ZrP) nanoparticles based mixed matrix membranes for removal of heavy metal ions.

The removal of heavy metal ions from industrial wastewater is essential as they pose serious threats to human health and the environment. In this study, novel poly(vinylidene fluoride) (PVDF)-alpha-zirconium phosphate (PVDF-α-ZrP) mixed matrix membranes (MMM) were prepared via the phase inversion method. Membranes with different α-ZrP nanoparticles (NPs) loadings (0.25, 0.50, 0.75, or 1.00 wt%) were fabricated. The impacts of α-ZrP NP loading on the membrane's morphology, functionality, surface charge, and hydrophilicity were evaluated. Fourier-transform infrared and the energy-dispersive X-ray spectroscopy were performed to verify the presence of α-ZrP NPs in the fabricated membranes. The PVDF membranes became more hydrophilic after incorporating the α-ZrP NPs. The thermal and mechanical stability and porosity of the PVDF-α-ZrP MMM were higher than those of the pristine PVDF membrane. The increased hydrophilicity, pore size and porosity and reduced surface roughness of the PVDF-α-ZrP membrane led to significant flux increase and reduced fouling propensity. The PVDF-α-ZrP membrane containing 1.00 wt% α-ZrP was capable of removing 42.8% (Cd2+), 93.1% (Cu2+), 44.4% (Ni2+), 91.2% (Pb2+), and 44.2% (Zn2+) from an aqueous solution at neutral pH during filtration.

Recent Developments in the Rational Fabrication of Thin Film Nanocomposite Membranes for Water Purification and Desalination.

Efforts have been rendered by researchers to address water purification and desalination challenges through membrane separation processes. However, the trade-off phenomenon in permeability and selectivity constrained the membranes' usage. Recent advances made in fabricating membranes, especially thin film nanocomposite (TFN) membranes using functionalized nanofillers, have high performance in water purification and desalination. In this review, state-of-the-art thin film composite (TFC) membranes in water purification and desalination along with their drawbacks are discussed. The urgent demands as an alternative of TFC membranes are highlighted for high-performance membranes. Then, the fabrication and development of high permeability and selectivity of TFN membranes are discussed. Thin film nanocomposite membranes manufactured using rational nanofillers are systematically summarized. Finally, the applications of TFN membranes in water purification and desalination are reported.

Macro-corrugated and nano-patterned hierarchically structured superomniphobic membrane for treatment of low surface tension oily wastewater by membrane distillation.

A hierarchically assembled superomniphobic membrane with three levels of reentrant structure was designed and fabricated to enable effective treatment of low surface tension, hypersaline oily wastewaters using direct contact membrane distillation (DCMD). The overall structure is a combination of macro corrugations obtained by surface imprinting, with the micro spherulites morphology achieved through the applied phase inversion method and nano patterns obtained by fluorinated Silica nanoparticles (SiNPs) coating. This resulted in a superomniphobic membrane surface with remarkable anti-wetting properties repelling both high surface tension water and low surface tension oils. Measurements of contact angle (CA) with DI water, an anionic surfactant, oil, and ethanol demonstrated a robust wetting resistance against low surface tension liquids showing both superhydrophobicity and superoleophobicity. CA values of 160.8 ± 2.3° and 154.3 ± 1.9° for water and oil were obtained, respectively. Calculations revealed a high liquid-vapor interface for the fabricated membrane with more than 89% of the water droplet contact area being with air pockets entrapped between adjacent SiNPs and only 11% come into contact with the solid membrane surface. Moreover, the high liquid-vapor interface imparts the membrane with high liquid repellency, self-cleaning and slippery effects, characterized by a minimum droplet-membrane interaction and complete water droplet bouncing on the surface within only 18 ms. When tested in DCMD with synthetic hypersaline oily wastewaters, the fabricated superomniphobic membrane demonstrated stable, non-wetting MD operation over 24 h, even at high concentrations of low surface tension 1.0 mM Sodium dodecyl sulfate and 400 ppm oil, potentially offering a sustainable option for treatment of low surface tension oily industrial wastewater.

High-Flux, Antifouling Hydrophilized Ultrafiltration Membranes with Tunable Charge Density Combining Sulfonated Poly(ether sulfone) and Aminated Graphene Oxide Nanohybrid.

In this work, a new protocol was developed for creating charge-tuned, hydrophilic hybrid ultrafiltration (UF) membranes with high flux, rejection rate, and fouling resistance. The membranes were fabricated using a combination of sulfonated poly(ether sulfone) (SPES) and aminated graphene (GO-SiO2-NH2) nanohybrid via the non-solvent-induced phase separation (NIPS) method. The GO-SiO2-NH2 nanohybrid was first synthesized using GO nanosheets and 3-aminopropyl triethoxysilane (APTES) through the covalent condensation reaction at 80 °C and was thoroughly characterized. Then, 2-8 wt% of the nanohybrid was incorporated into the matrix of SPES for the fabrication of the hybrid membranes. The resulting membranes were characterized using an electrokinetic analyzer, a contact angle goniometer, and Raman, field emission scanning electron microscopy-energy-dispersive X-ray spectrometry (FESEM-EDX), and atomic force microscopy experiments. The porosity, charge density, and surface morphology were altered, and the hybrid membranes became more hydrophilic after the incorporation of the nanohybrid. The pure water flux of the hybrid membranes systematically increased with the loading amount of the nanohybrid. The pure water flux of the hybrid membrane containing 6 wt% GO-SiO2-NH2 nanohybrid at a 2 bar feed pressure was 537 L m-2 h-1, about 3-fold that of pristine membrane (186 L m-2 h-1). The fouling resistance of the hybrid membranes was evaluated and confirmed using several representative foulants, including bovine serum albumin, humic acid, sodium alginate, and a synthetic solution of natural organic matter (NOM). The fabricated membranes were capable of removing more than 97% of NOM, without a compromise of their rejection rate.

Implementation of two multiphase flow methods in modeling wetting of microporous hydrophobic membranes.

Pore wetting phenomenon plays a critical role in a porous media and is critical in various processes. For instance, liquid entry pressure (LEP) is one of the critical characteristics of hydrophobic membranes used in membrane distillation (MD) processes. In this study, pore-scale models were developed to assess the accuracy of two multiphase flow computational fluid dynamics (CFD) methods, as modeling tools for predicting two-phase flow in microporous MD membranes. Finite element method (FEM)-based phase field (PF) method (which was applied in the COMSOL package) and finite volume method (FVM)-based volume of fluid (VOF) method (which was applied in Star-CCM+) were the selected CFD tools for the implementation. The boundary conditions of the models were first set based on the experimental procedure for measuring the LEP, as given in the literature. Then, the models were used to capture the LEP under the gradually increased water pressure. Critical tuning of CFD parameters of each tool (such as mesh size, mesh type, and interface thickness) was conducted to investigate their influence on the LEP prediction accuracy and the water/air interface representation at the pore entrance. CFD model results were presented and compared with both experimental LEP data and the calculated value using the Young-Laplace equation (YLE). Both CFD tools were capable of capturing the water/air interface. LEP result from the VOF model showed good agreement with the experimental data, but the PF model overestimated the LEP value closer to the theoretical YLE value. For both approaches, the adjustment of the interface thickness was critical. In the VOF method, a realistic interface thickness could be achieved by adjusting both mesh size and time step simultaneously. In contrast, PF simulations were less mesh sensitive. The accuracy of the VOF model was better due to its mass conservation condition at the interface.

Photothermal Membrane Distillation for Seawater Desalination.

Thermoplasmonic effects notably improve the efficiency of vacuum membrane distillation, an economically sustainable tool for high-quality seawater desalination. Poly(vinylidene fluoride) (PVDF) membranes filled with spherical silver nanoparticles are used, whose size is tuned for the aim. With the addition of plasmonic nanoparticles in the membrane, the transmembrane flux increases by 11 times, and, moreover, the temperature at the membrane interface is higher than bulk temperature.

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.

Eggshell: A green adsorbent for heavy metal removal in an MBR system.

Presence of heavy metals as well as different metal ions in treated wastewater is a problem for the environment as well as human health. This paper aims to investigate the possibility to combine an MBR (membrane biological reactor) with an adsorption process onto powdered eggshell and eggshell membrane in order to improve metal removal from wastewater. The first step of the experimental analysis consists of the evaluation of the compatibility between the two processes. Then, a study about sorbent concentration and size effect on fouling was conducted, because the use of this kind of sorbent could affect membrane performance. The second step of the work concerns the check up of eggshell removal capacity as a function of sorbent size, achieved treating an aqueous solution containing Al(3+), Fe(2+) and Zn(2+) as water pollutants. Finally, synthetic wastewater, containing the metal species, was treated by two alternative process schemes: one of them performs the metal uptake in a dedicated adsorption unit, before the MBR. In the second, the two processes take place in the same unit. Results demonstrate that the optimization of the first option could be a solution to MBR upgrading.

Solid waste management in the hospitality industry: a review.

Solid waste management is a key aspect of the environmental management of establishments belonging to the hospitality sector. In this study, we reviewed literature in this area, examining the current status of waste management for the hospitality sector, in general, with a focus on food waste management in particular. We specifically examined the for-profit subdivision of the hospitality sector, comprising primarily of hotels and restaurants. An account is given of the causes of the different types of waste encountered in this sector and what strategies may be used to reduce them. These strategies are further highlighted in terms of initiatives and practices which are already being implemented around the world to facilitate sustainable waste management. We also recommended a general waste management procedure to be followed by properties of the hospitality sector and described how waste mapping, an innovative yet simple strategy, can significantly reduce the waste generation of a hotel. Generally, we found that not many scholarly publications are available in this area of research. More studies need to be carried out on the implementation of sustainable waste management for the hospitality industry in different parts of the world and the challenges and opportunities involved.

Membrane technology in microalgae cultivation and harvesting: a review.

Membrane processes have long been applied in different stages of microalgae cultivation and processing. These processes include microfiltration, ultrafiltration, dialysis, forward osmosis, membrane contactors and membrane spargers. They are implemented in many combinations, both as a standalone and as a coupled system (in membrane biomass retention photobioreactors (BR-MPBRs) or membrane carbonation photobioreactors (C-MPBRs). To provide sufficient background on these applications, an overview of membrane materials and membrane processes of interest in microalgae cultivation and processing is provided in this work first. Afterwards, discussion about specific aspects of membrane applications in microbial cultivation and harvesting is provided, including membrane fouling. Many of the membrane processes were shown to be promising options in microalgae cultivation. Yet, significant process optimizations are still required when they are applied to enable microalgae biomass bulk production to become competitive as a raw material for biofuel production. Recent developments of the coupled systems (BR-MPBR and C-MPBR) bring significant promises to improve the volumetric productivity of a cultivation system and the efficiency of inorganic carbon capture, respectively.

Modeling and comparative assessment of municipal solid waste gasification for energy production.

Gasification is the thermochemical conversion of organic feedstocks mainly into combustible syngas (CO and H(2)) along with other constituents. It has been widely used to convert coal into gaseous energy carriers but only has been recently looked at as a process for producing energy from biomass. This study explores the potential of gasification for energy production and treatment of municipal solid waste (MSW). It relies on adapting the theory governing the chemistry and kinetics of the gasification process to the use of MSW as a feedstock to the process. It also relies on an equilibrium kinetics and thermodynamics solver tool (Gasify(®)) in the process of modeling gasification of MSW. The effect of process temperature variation on gasifying MSW was explored and the results were compared to incineration as an alternative to gasification of MSW. Also, the assessment was performed comparatively for gasification of MSW in the United Arab Emirates, USA, and Thailand, presenting a spectrum of socioeconomic settings with varying MSW compositions in order to explore the effect of MSW composition variance on the products of gasification. All in all, this study provides an insight into the potential of gasification for the treatment of MSW and as a waste to energy alternative to incineration.

A review of residential solid waste management in the occupied Palestinian Territory: a window for improvement?

Solid waste is considered an urgent environmental health issue in the Palestinian Territory. The aim of this paper was to analyse the current status of residential solid waste (RSW) management in the Palestinian Territory, with the objective of identifying windows for improvement. The study is based on a national household sample survey in the Palestinian Territory, which was conducted by the Palestinian Central Bureau of Statistics (PCBS). The results of this study revealed various interesting trends. For example, while about 90% of households in the Palestinian Territory receive solid waste collection service, about 50% of the households receive this service three times per week or less, leaving a chance for waste pile-up and litter generation. Organic waste (including food waste) was found to account for more than 90% of RSW, providing an opportunity for waste utilization through composting or biogas generation. Additional efforts are required, and some were suggested in this paper, in order to improve the current situation of Palestinian residential solid waste management.

Enhanced solid waste management by understanding the effects of gender, income, marital status, and religious convictions on attitudes and practices related to street littering in Nablus - Palestinian territory.

Litter is recognized as a form of street pollution and a key issue for solid waste managers. Nablus district (West Bank, Palestinian Territory), which has an established network of urban and rural roads, suffers from a wide-spread litter problem that is associated with these roads and is growing steadily with a well-felt negative impact on public health and the environment. The purpose of this research was to study the effects of four socio-economic characteristics (gender, income, marital status, and religious convictions) of district residents on their attitudes, practices, and behavior regarding street litter generation and to suggest possible remedial actions. All four characteristics were found to have strong correlations, not only with littering behavior and practices, but also with potential litter prevention strategies. In particular, the impact of religious convictions of the respondents on their littering habits and attitudes was very clear and interesting to observe.

Influence of socio-economic factors on street litter generation in the middle east: effects of education level, age, and type of residence.

Street littering is considered an important environmental health issue in the Middle East. This problem is growing steadily and is attracting great concerns within the communities. The purpose of this paper, which focuses on Nablus district (Palestinian Territory), is to measure the perception and opinion of residents toward littering, in addition to studying prevailing attitudes and practices on littering. This was achieved using an interview survey approach. The influence of three socio-economic factors; level of education, age, and type of residence, on the littering behaviour of individuals was studied. As a result, possible remedial actions have been suggested. The data presented in this work can be considered as one piece of information, which can be compiled with other future data to design an effective litter control programrhe for Middle Eastern countries.