Insights into membrane crystallization: A sustainable tool for value added product recovery from effluent streams

Environmentally Friendly Photothermal Membranes for Halite Recovery from Reverse Osmosis Brine via Solar-Driven Membrane Crystallization

Modern society and industrial development rely heavily on the availability of freshwater and minerals. Seawater reverse osmosis (SWRO) has been widely adopted for freshwater supply, although many questions have arisen about its environmental sustainability owing to the disposal of hypersaline rejected solutions (brine). This scenario has accelerated significant developments towards the hybridization of SWRO with membrane distillation-crystallization (MD-MCr), which can extract water and minerals from spent brine. Nevertheless, the substantial specific energy consumption associated with MD-MCr remains a significant limitation. In this work, energy harvesting was secured from renewables by hotspots embodied in the membranes, implementing the revolutionary approach of brine mining via photothermal membrane crystallization (PhMCr). This method employs self-heating nanostructured interfaces under solar radiation to enhance water evaporation, creating a carefully controlled supersaturated environment responsible for the extraction of minerals. Photothermal mixed matrix photothermal membranes (MMMs) were developed by incorporating graphene oxide (GO) or carbon black (CB) into polyvinylidene fluoride (PVDF) solubilized in an eco-friendly solvent (i.e., triethyl phosphate (TEP)). MMMs were prepared using non-solvent-induced phase separation (NIPS). The effect of GO or GB on the morphology of MMMs and the photothermal behavior was examined. Light-to-heat conversion was used in PhMCr experiments to facilitate the evaporation of water from the SWRO brine to supersaturation, leading to sodium chloride (NaCl) nucleation and crystallization. Overall, the results indicate exciting perspectives of PhMCr in brine valorization for a sustainable desalination industry.

Multiscale Process Intensification of Waste Valorization Reactions

ConspectusThe central theme of this Account is the development of intensified and sustainable chemical processes for the sequestration of CO2 in synergism with the utilization of wastes of industrial, urban, and agricultural origins. A challenge when working with solid waste-fluid reactions is that mass transfer limitations across solid-liquid, solid-gas, and gas-liquid interfaces and unfavorable thermodynamics lead to slow reaction rates, incomplete reaction conversions, high energy expenditure and processing costs, and inadequate product properties. The traditional macroscale approaches to overcoming slurry reaction limitations can be effective; however, they come at a cost to the environment. In the treatment or valorization of low-grade and waste resources, such conventional approaches are often unfeasible on an industrial scale. Sustainable solutions are thus needed.In the last six years, we have been exploring and developing approaches to overcoming reaction rate limitations of slurry reactions of environmental relevance by concurrently applying process intensification strategies and multiscale engineering approaches. The scientific approach has relied on laboratory-scale experiments to test and refine the devised multiscale process intensification strategies, with thermodynamic and computational modeling work supporting the experimental work and with advanced characterization techniques being used to elucidate reaction and transport mechanisms and aid the development of nanoscale reaction models and micro- and macroscale process models. The research streams, associated with the four key references, discussed next are (a) brine carbonation; (b) mineral carbonation and enhanced weathering; (c) process intensification and integration; and (d) characterization techniques.Within the four research streams, a number of mineral carbonation processes have been investigated and can be classified as (i) ambient weathering and carbonation; (ii) gas-(wet) solid accelerated carbonation; (iii) aqueous accelerated carbonation; (iv) supercritical accelerated carbonation; and (v) CO2 mineralization from brine. In some cases, the research was aimed at producing valuable products with reduced environmental risk or a reduced carbon footprint, such as an organomineral fertilizer and zeolites. In other cases, the aim was to assess the reactivity of minerals to match the right feedstock with the right carbonation process, in view of maximizing net carbon sequestration. There were also cases where the carbonation process was reimagined by the use of innovative reaction conditions, reactors, and reagents. The experience with accelerated weathering and carbonation in engineered processes has been translated into the field of enhanced rock weathering (ERW) in agriculture, where the multidisciplinary approach used has served to advance ERW science and technology in ways that have had a resounding effect on recent commercial deployment.The completed research serves to encourage the adoption of process intensification technologies in place of conventional processes, in industry and among the research community, and to catalyze the development of the types of sustainable processes required by the chemical, metallurgical, and minerals industries (which are critical to the green transition) to reduce their environmental impact and carbon emissions. Moreover, the multiscale process intensification approaches developed may also be extended to other industrial, urban, and agricultural processes where the reduction of energy intensity, carbon intensity, and environmental footprint could be achieved.

Membrane distillation crystallization for water and mineral recovery: The occurrence of fouling and its control during wastewater treatment

Membrane distillation crystallization (MDC) is an emerging technology envisaged to manage challenges affecting the desalination industry. This technology can sustainably treat concentrated solutions of produced water and industrially discharged saline wastewater. Simultaneous recovery of clean water and minerals is achieved through the integration of crystallization to membrane distillation (MD). MDC has received vast research interest because of its potential to treat hypersaline solutions. However, MDC still faces challenges in harnessing its industrial applications. Technically, MDC is affected by fouling/scaling and wetting thereby hindering practical application at the industrial level. This study reviews the occurrence of membrane fouling and wetting experienced with MDC. Additionally, existing developments carried out to address these challenges are critically reviewed. Finally, prospects suggesting the sustainability of this technology are highlighted.

Reverse Osmosis Concentrate: Physicochemical Characteristics, Environmental Impact, and Technologies

This study's aim is to generate a complete profile of reverse osmosis concentrate (ROC), including physicochemical characteristics, environmental impact, and technologies for ROC treatment, alongside element recovery with potential valorization. A systematic literature review was used to compile and analyze scientific information about ROC, and systematic identification and evaluation of the data/evidence in the articles were conducted using the methodological principles of grounded data theory. The literature analysis revealed that two actions are imperative: (1) countries should impose strict regulations to avoid the contamination of receiving water bodies and (2) desalination plants should apply circular economies. Currently, synergizing conventional and emerging technologies is the most efficient method to mitigate the environmental impact of desalination processes. However, constructed wetlands are an emerging technology that promise to be a viable multi-benefit solution, as they can provide simultaneous treatment of nutrients, metals, and trace organic contaminants at a relatively low cost, and are socially accepted; therefore, they are a sustainable solution.