In this study, a low-cost granular activated carbon doped with Fe2O3 nanoparticles (Fe–GAC) was prepared via a modified sol-gel technique and utilized for the elimination of lead (Pb(II)) and chromium (Cr(T)) ions from synthetic and actual brackish water. The effect of adsorption parameters on the removal of Pb(II) and Cr(T) ions from the water was evaluated in batch adsorption tests. The characterization results validated the distribution of well-defined Fe2O3 nanoparticles onto the GAC surface. GAC loaded with 5 wt.% of Fe2O3 (Fe–GAC 5) exhibited a maximum surface area of 848.2 m2 g−1. The equilibrium data of Cr(T) adsorption were in close agreement with the Langmuir and Sips models with R2 values of 0.95 and 0.96, respectively. However, the R2 values of the equilibrium data for Pb(II) adsorption were greater than 0.91 for all four models, i.e., Langmuir, and Sips, Freundlich and Redlich-Peterson. The maximum Langmuir adsorption capacities of Pb(II) and Cr(T) by Fe–GAC 5 at pH 5.6 and room temperature were 11.9 and 22.1 mg g−1, respectively. Pseudo-second order (R2Pb(II) = 0.99, R2Cr(T) = 0.99) and Elovich kinetic models (R2Pb(II) = 1, R2Cr(T) = 1) were found the most suitable for describing the adsorption kinetics data of Pb(II) and Cr(T) using Fe–GAC 5. The adsorption/desorption studies illustrated that the Fe–GAC is reusable and can be regenerated using 1.0 M HCl. Moreover, the Fe–GAC 5 was found effective to reduce heavy metals loading in actual brackish water to the allowed international standards of drinking water. Accordingly, the Fe–GAC could be a promising material for large-scale applications for the elimination of heavy metals from water.

Pretreatment of raw feed water is an essential step for proper functioning of a reverse osmosis (RO) desalination plant as it minimizes the risk of membrane fouling. Conventional pretreatment methods have drawbacks, such as the potential of biofouling, chemical consumption, and carryover. Non-conventional membrane-based pretreatment technologies have emerged as promising alternatives. The present review focuses on recent advances in MF, UF, and NF membrane pretreatment techniques that have been shown to be effective in preventing fouling as well as having low energy consumption. This review also highlights the advantages and disadvantages of polymeric and ceramic membranes. Hybrid technologies, which combine the benefits of conventional and non-conventional methods or different membranes, are also discussed as a potential solution for effective pretreatment. The literature that has been analyzed reveals the challenges associated with RO pretreatment, including the high cost of conventional pretreatment systems, the difficulty of controlling biofouling, and the production of large volumes of wastewater. To address these challenges, sustainable hybrid strategies for ceramic membrane-based systems in RO pretreatment are proposed. These strategies include a thorough assessment of the source water, removal of a wide range of impurities, and a combination of methods such as adsorption and carbon dioxide with a low amount of antiscalants. Furthermore, the suggestion of incorporating renewable energy sources such as solar or wind power can help reduce the environmental impact of the system. A pilot study is also recommended to overcome the difficulties in scaling ceramic systems from laboratory to industrial scale. The review also emphasizes the importance of conducting an effective assessment to suggest a treatment for the brine if needed before being discharged to the environment. By following this framework, sustainable, energy-efficient, and effective solutions can be recommended for pretreatment in desalination systems, which can have significant implications for water scarcity and environmental sustainability.

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