Effect of intermittent operation on performance of a solar-powered membrane distillation system

Modification of the distribution of humic acid complexations by introducing microbubbles to membrane distillation process for effective membrane fouling alleviation

Membrane fouling caused by inorganic ions and natural organic matters (NOMs) has been a severe issue in membrane distillation. Microbubble aeration (MB) is a promising technology to control membrane fouling. In this study, MB aeration was introduced to alleviate humic acid (HA) composited fouling during the treatment of simulative reverse osmosis concentrate (ROC) by vacuum membrane distillation (VMD). The objective of this work was to explore the HA fouling inhibiting effect by MB aeration and discuss its mechanism from the interfacial point of view. The results showed that VMD was effective for treating ROC, followed by a severe membrane fouling aggravated with the addition of 100 mg/L HA in feed solution, resulting in 45.7% decline of membrane flux. Analysis using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and zeta potential distribution of charged particles proved the coexistence of HA and inorganic cations (especially Ca2+), resulting in more serious membrane fouling. The introduction of MB aeration exhibited excellent alleviating effect on HA-inorganic salt fouling, with the normalized flux increased from 19.7% to 37.0%. The interfacial properties of MBs played an important role, which altered the zeta potential distributions of charged particles in HA solution, indicating that MBs adhere the HA complexations. Furthermore, this mitigating effect was limited at high inorganic cations concentration. Overall, MBs could change the potential characteristics of HA complexes, which also be used for other similar membrane fouling alleviation.

Distributed desalination using solar energy: A technoeconomic framework to decarbonize nontraditional water treatment

Desalination using renewable energy offers a route to transform our incumbent linear consumption model to a circular one. This transition will also shift desalination from large-scale centralized coastal facilities toward modular distributed inland plants. This new scale of desalination can be satisfied using solar energy to decarbonize water production, but additional considerations, such as storage and inland brine management, become important. Here, we evaluate the levelized cost of water for 16 solar desalination system configurations at 2 different salinities. For fossil fuel-driven plants, we find that zero-liquid discharge is economically favorable to inland brine disposal. For renewable desalination, we discover that solar-thermal energy is superior to photovoltaics due to low thermal storage cost and that energy storage, despite being expensive, outperforms water storage as the latter has a low utilization factor. The analysis also yields a promising outlook for solar desalination by 2030 as solar generation and storage costs decrease.

New Materials and Phenomena in Membrane Distillation

In recent decades, membrane-based processes have been extensively applied to a wide range of industrial processes, including gas separation, food industry, drug purification, and wastewater treatment. Membrane distillation is a thermally driven separation process, in which only vapour molecules transfer through a microporous hydrophobic membrane. At the operational level, the performance of membrane distillation is negatively affected by wetting and temperature polarization phenomena. In order to overcome these issues, advanced membranes have been developed in recent years. This review, which focuses specifically on membrane distillation presents the basic concepts associated with the mass and heat transfer through hydrophobic membranes, membrane properties, and advances in membrane materials. Photothermal materials for solar-driven membrane distillation applications are also presented and discussed.

The advent of thermoplasmonic membrane distillation

Freshwater scarcity is a vital societal challenge related to climate change, population pressure, and agricultural and industrial demands. Therefore, sustainable desalination/purification of salty/contaminated water for human uses is particularly relevant. Membrane distillation is an emerging hybrid thermal-membrane technology with the potential to overcome the drawbacks of conventional desalination by a synergic exploitation of the water-energy nexus. Although membrane distillation is considered a green technology, efficient heat management remains a critical concern affecting the cost of the process and hindering its viability at large scale. A multidisciplinary approach that involves materials chemistry, physical chemistry, chemical engineering, and materials and polymer science is required to solve this problem. The combination of solar energy with membrane distillation is considered a potentially feasible low-cost approach for providing high-quality freshwater with a low carbon footprint. In particular, recent discoveries about efficient light-to-heat conversion in nanomaterials have opened unprecedented perspectives for the implementation of sunlight-based renewable energy in membrane distillation. The integration of nanofillers enabling photothermal effects into membranes has been demonstrated to be able to significantly enhance the energy efficiency without impacting on economic costs. Here, we provide a comprehensive overview on the state of the art, the opportunities, open challenges and pitfalls of the emerging field of solar-driven membrane distillation. We also assess the peculiar physicochemical properties and synthesis scalability of photothermal materials, as well as the strategies for their integration into polymeric nanocomposite membranes enabling efficient light-to-heat conversion and freshwater.

Direct contact membrane distillation as an approach for water treatment with phenolic compounds

Membrane distillation is a well-established technology for non-volatile components retention, but the removal of volatile and semi-volatile substances in trace concentration, such as phenols derivates commonly found in surface waters, requires further comprehension. In this context, the direct contact membrane distillation (DCMD) performance was assessed for the retention of fifteen phenolic compounds in surface water by different operating conditions of temperature (40, 50, and 60 °C), feed concentration (3, 5, 7, and 10 μg L^-1), and permeate recovery rate (30, 50 and 70%). Kruskal Wallis confirmed a significant difference (p < 0.05) between the global removal of phenolic compounds at different temperatures. The increase in temperature led to a reduction in all compound's removal. As expected, a positive correlation (r_Spearman>0.8) between the compounds' volatility and their losses was observed. Regarding the feed concentration and the recovery rate, there was no statistical difference between the removal values obtained for the phenolic compounds. This indicates the DCMD strength for that application. However, a trend for flux decay was noticed as the recovery rate (RR) increased, confirmed by temporal trend analysis and Mann-Kendall tests, although the flux decay was relatively low (J/J₀ = 0.89). Aiming for a greater removal and to avoid a reduction in process performance, it is recommended to work with 40 °C as feed temperature and a RR prior to the flux decay (RR<30%). Nonetheless, the technology was efficient and did not compromise the permeate quality with >90% efficiency in pollutants removal, even for higher temperatures and RR.

Prospective Methodologies in Hybrid Renewable Energy Systems for Energy Prediction Using Artificial Neural Networks

This paper presents a comprehensive review of machine learning (ML) based approaches, especially artificial neural networks (ANNs) in time series data prediction problems. According to literature, around 80% of the world’s total energy demand is supplied either through fuel-based sources such as oil, gas, and coal or through nuclear-based sources. Literature also shows that a shortage of fossil fuels is inevitable and the world will face this problem sooner or later. Moreover, the remote and rural areas that suffer from not being able to reach traditional grid power electricity need alternative sources of energy. A “hybrid-renewable-energy system” (HRES) involving different renewable resources can be used to supply sustainable power in these areas. The uncertain nature of renewable energy resources and the intelligent ability of the neural network approach to process complex time series inputs have inspired the use of ANN methods in renewable energy forecasting. Thus, this study aims to study the different data driven models of ANN approaches that can provide accurate predictions of renewable energy, like solar, wind, or hydro-power generation. Various refinement architectures of neural networks, such as “multi-layer perception” (MLP), “recurrent-neural network” (RNN), and “convolutional-neural network” (CNN), as well as “long-short-term memory” (LSTM) models, have been offered in the applications of renewable energy forecasting. These models are able to perform short-term time-series prediction in renewable energy sources and to use prior information that influences its value in future prediction.

A Critical Review of Membrane Wettability in Membrane Distillation from the Perspective of Interfacial Interactions

Hydrophobic membranes used in membrane distillation (MD) systems are often subject to wetting during long-term operation. Thus, it is of great importance to fully understand factors that influence the wettability of hydrophobic membranes and their impact on the overall separation efficiency that can be achieved in MD systems. This Critical Review summarizes both fundamental and applied aspects of membrane wetting with particular emphasis on interfacial interaction between the membrane and solutes in the feed solution. First, the theoretical background of surface wetting, including the relationship between wettability and interfacial interaction, definition and measurement of contact angle, surface tension, surface free energy, adhesion force, and liquid entry pressure, is described. Second, the nature of wettability, membrane wetting mechanisms, influence of membrane properties, feed characteristics and operating conditions on membrane wetting, and evolution of membrane wetting are reviewed in the context of an MD process. Third, specific membrane features that increase resistance to wetting (e.g., superhydrophobic, omniphobic, and Janus membranes) are discussed briefly followed by the comparison of various cleaning approaches to restore membrane hydrophobicity. Finally, challenges with the prevention of membrane wetting are summarized, and future work is proposed to improve the use of MD technology in a variety of applications.

Synergy of biofuel production with waste remediation along with value-added co-products recovery through microalgae cultivation: A review of membrane-integrated green approach

Development of advanced biofuels such as bioethanol and biodiesel from renewable resources is critical for the earth's sustainable management and to slow down the global climate change by partial replacement of gasoline and diesel in the transport sector. Being a diverse group of aquatic micro-organisms, algae are the most prominent resources on the planet, distributed in an aquatic system, a potential source of bioenergy, biomass and secondary metabolites. Microalgae-based biofuel production is widely accepted as non-food fuel sources and better choice for achieving goals of incorporation of a clean fuel source into the transportation sector. The present review article provides a comprehensive literature survey as well as a novel approach on the application of microalgae for their simultaneous cultivation and bioremediation of high nutrient containing wastewater. In addition to that, merits and demerits of different existing conventional techniques for microalgae culture reactors, harvesting of algal biomass, oil recovery, use of different catalysts for transesterification reactions and other by-products recovery have been discussed and compared with the membrane-based system to find out the best optimal conditions for higher biomass as well as lipid yield. This article also deals with the use of a tailor-made membrane in an appropriate module that can be used in upstream and downstream processes during algal-based biofuels production. Such membrane-integrated system has the potential of low-cost and eco-friendly separation, purification and concentration enrichment of biodiesel as well as other valuable algal by-products which can bring the high degree of process intensification for scale-up at the industrial stage.