Chapter 7 - Advances in Nanostructured Membranes for Water Desalination

Recent developments on nanostructured polymer-based membranes

The recent development of membrane-based water desalination and purification technologies shows new approaches to meeting global demand for freshwater. Carbon-based nanomaterials have shown great potential in various desalination technologies. Such materials are suitable for membrane separation, offering advantageous structure, mechanical properties and porosity. In the present molecular dynamics study, water desalination via reverse osmosis is simulated using a new sp2-carbon membrane. It is found that the membrane under consideration demonstrates a very good rate of ion rejection and a reasonably good water flux, which grows with increasing temperature.

Desalinated seawater is the primary source of drinking water in Qatar. Among all present desalination technologies, reverse osmosis (RO) has been demonstrated as one of the most feasible processes. However, the main limitation with RO and other membrane-based techniques is costly operation and maintenance associated with membrane scaling, fouling, and degradation. Advanced membranes that enable ultrafast permeation while maintaining good mechanical properties, are very important to facilitate both water purification and desalination technologies. Low-dimensional nanomaterials such as carbon nanotubes, cellulose nanocrystals and graphene oxide (GO) have been tested in membranes due to their good mechanical properties and amenable surface functionalization. Specifically, GO nanosheets have recently emerged as a new material for ultrathin, high-flux and energy-efficient sieving membranes due to GO's unique two-dimensional atomically thin structure, outstanding mechanical strength and good flexibility, as well as good dispersion in aqueous solutions. However, selectivity and stability of fully wetted GO membranes in cross-flow conditions has remained challenging and solubility of GO can also lead to membrane disintegration under operation conditions. Herein we present MXenes [1], a new class of 2D carbides, as new promising membrane materials for water desalination applications. For this purpose, Ti3C2-based MXene membranes have been prepared by a vacuum-assisted filtration technique. In order to detect the permeated ions and molecules, we have performed electrical conductivity measurements and UV-Vis analyses. The results have shown that MXene membranes are selective towards ions of different size/charge, such as Cu2+, Mg2+, Na+, K+, SO42-, and Cl-. The permeation data have also shown a cut-off trend around 4 A, and species of a larger size have been sieved out. The transport mechanism through MXene membrane films has been therefore size and charge selective due to the presence of the interlayer slit pores and the negative charges on the hydrophilic Ti3C2-based MXene film surfaces. In this study, we compare MXene membranes with GO membranes to better understand differences in their water desalination performance. Indeed these novel membrane composites are expected to improve the flux, increase the salt rejection efficiency and decrease adhesion of the adsorbed particulates and organic molecules, thus mitigating fouling. Reference: 1.M. Naguib, V.N. Mochalin, M.W. Barsoum, Y. Gogotsi, MXenes: A New Family of Two-Dimensional Materials, Advanced Materials, 26, 992-1005 (2014)

Hybrid membrane system for desalination and wastewater treatment : Integrating forward osmosis and low pressure reverse osmosis

Mechanical properties of water desalination and wastewater treatment membranes

Countries which do not have adequate supply of freshwater sources like Kuwait resort to using desalination plants to meet their demand. Kuwait had used Multi-flash desalination (MSF) plants sine the 50's of the last century to satisfy its ever increasing demand. Many new and more efficient and cost effective desalination technologies are currently available. Kuwait is in the process of building new desalination plants, and has to seize this opportunity to consider using other desalination technologies instead of MSF plants. In this work, an attempt to make to bring to the attention to the decision maker the performance and suitability of the different technologies using a fuzzy multi-criteria decision making technique. The preference is based on six criteria (factors) for comparing three commercially available desalination technologies, i.e., Multi-stage flash (MSF), Multi-effect desalination (MED), and Reverse osmosis (RO). The study found that the amount of energy used in these plants should be most important selection criteria followed by the amount of pretreatment required. The most preferred technology is RO according to this study.

Multi-criteria sustainability assessment of water desalination and energy systems — Kuwait case

Desalination and atmospheric water harvesting technologies are highly desirable to produce freshwater for daily life activities and alleviate the global water crisis. Efforts to improve these have mostly been based on better engineering or materials design, but a comparison of their energy performance over a theoretical optimum is not well consolidated. This research conducts a meta-analysis that comparatively assesses existing atmospheric water harvesting and desalination technologies by evaluating the energy optimality in terms of the Gibbs free energy principle derived theoretical limit. After a review of the various existing technologies in these two classes, energy optimality, defined as the theoretical minimum specific energy consumption divided by the specific exergy consumption, is used as the metric to make a comprehensive and fair comparison of the various desalination and atmospheric water harvesting technologies. Results show that the vapor compression cycle and hybrid technologies-based atmospheric water harvesters have higher energy optimality of 12%, whereas others have much poorer performances of under 3%. For desalination, reverse osmosis yielded the highest energy optimality of 67.43%. Furthermore, the ideal energy optimality needed by atmospheric water harvesting to become comparable to desalination is at least 89.9%, which is almost impossible to practically achieve.

A review of reverse osmosis membrane materials for desalination—Development to date and future potential

Optimal Design of a Hybrid Membrane System Combining Reverse and Forward Osmosis for Seawater Desalination

Chapter 22 - Metal-organic framework-based processes for water desalination: Current development and future prospects

The transition from fossil fuels to renewable energy sources is imperative to mitigate climate change and achieve sustainable development goals (SGDs). Hydrogen, as a clean energy carrier, holds great potential for decarbonizing various sectors, yet its production remains predominantly reliant on fossil fuels. This study explores a novel approach to sustainable hydrogen production by integrating offshore wind energy with reverse osmosis (RO) desalination technology. The proposed configuration harnesses offshore wind power to energize both a RO desalination system and water electrolysis unit. Initially, the wind energy powers the RO desalination process, purifying seawater, and then desalinated water is directed to water electrolysis system for generating green hydrogen directly from seawater. The resulting renewable hydrogen holds potential for diverse applications, including marine industries, and can be transported onshore as needed. The RO system is configured to treat 20 kg s−1 of seawater with a salinity of 35 000 ppm, aiming for a high recovery ratio and reduced freshwater salinity. A pressure exchanger (PX) is integrated to recover energy from high‐pressure brine stream and transfer it to the low‐pressure feed water, thus reducing the overall energy consumption of the RO process. The concentrated brine extracted from RO desalination is proposed to be utilized for the production of sodium hydroxide that can further pretreat incoming seawater and enhance the effectiveness of the filtration process by mitigating membrane fouling. This pressure exchanger increases the energy efficiency of the RO system from 63.1% to 64.0% and exergetic efficiency from 13.9% to 18.2% increasing the overall first and second law efficiencies to 37.9% and 33.5%. By leveraging offshore wind power to drive RO desalination systems, this research not only addresses freshwater scarcity but also facilitates green hydrogen generation, contributing to the advancement of renewable energy solutions and fostering environmental sustainability.

The integration of desalination plants and mineral production

V-7-100 - Petroclival meningloma. Presigmoid approach

Chapter 15 - Environmental Life Cycle Analysis of Water Desalination Processes