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Addressing the critical issue of water pollution, this review article emphasizes the need to remove hazardous dyes and phenolic compounds from wastewater. These pollutants pose severe risks due to their toxic, mutagenic, and carcinogenic properties. The study explores various techniques for the remediation of organic contaminants from wastewater, including an enzymatic approach. A significant challenge in enzymatic wastewater treatment is the loss of enzyme activity and difficulty in recovery post-treatment. To mitigate these issues, this review examines the strategy of immobilizing enzymes on newly developed nanostructured materials like graphene, carbon nanotubes (CNTs), and metal–organic frameworks (MOFs). These materials offer high surface areas, excellent porosity, and ample anchoring sites for effective enzyme immobilization. The review evaluates recent research on enzyme immobilization on these supports and their applications in biocatalytic nanoparticles. It also analyzes the impact of operational factors (e.g., time, pH, and temperature) on dye and phenolic compound removal from wastewater using these enzymes. Despite promising outcomes, this review acknowledges the challenges for large-scale implementation and offers recommendations for future research to tackle these obstacles. This review concludes by suggesting that enzyme immobilization on these emerging materials could present a sustainable, environmentally friendly solution to the escalating water pollution crisis. [ABSTRACT FROM AUTHOR]

Separation of clay minerals from industrial wastewaters is of great academic and practical importance. Current treatment techniques are either not economically viable, not environmentally friendly, or both. Thus, researchers are actively trying to develop optimal and more environmentally friendly wastewater treatment processes. Clay minerals like montmorillonite, bentonite, kaolinite and illite have numerous applications in various industries including, mineral processing, cosmetics, pharmaceuticals, paint, dyes, cement, concrete, functional fillers, paper making, clarification of wines and oils, water treatment and improving drilling mud properties. Their wide applications increased the volume and treatment complexity of water contaminated with them since they form highly stable suspensions in water. Flocculating agents such as polyelectrolytes have the potential to separate the above-mentioned minerals from industrial wastewater effluents. Polyelectrolytes are more effective and environment-friendly flocculants, in contrast to inorganic metal salts and some non-biodegradable synthetic polymers that pose serious hazards to human health and the environment. The development of polyelectrolytes is considered to be among the most important breakthroughs in solid–liquid separation processes, which have resulted in an improved treatment of water polluted with minerals. In the characterization of clay mineral separation using polyelectrolytes, it has been common practice in the past to either emphasize on the flocculation behavior of colloidal clay-polyelectrolyte suspensions (i.e., settling behavior or floc sizes) or on the behavior of networked clay-polyelectrolyte suspensions (i.e., filterability or dewaterability of sediment). However, flocculation and rheological parameters, which are very important factors in optimizing the wastewater treatment process, have rarely been reported in the literature. The aim of this paper, therefore, is to offer a comprehensive review of the state-of-the-art contributions for polyelectrolyte systems, focusing on the development of different types of polyelectrolytes and their applications in flocculating and dewatering clay minerals. Electrokinetics and rheological behavior of different clay minerals using different polyelectrolytes are critically evaluated. The effect of several parameters related to the clay mineral (type, composition), the polyelectrolyte (e.g., synthetic/natural, molecular weight, charge type, charge density, linear vs branched) and the flocculation medium properties (e.g., pH, ionic strength, clay mineral and polyelectrolyte concentration and type) are reviewed. This paper provides up-to-date progress in the treatment of water contaminated with clay minerals using various polyelectrolytes. The gaps and potential parameters of investigation in flocculation optimization studies are identified and more economical and environmentally friendly reagents in wastewater treatment are highlighted. [ABSTRACT FROM AUTHOR]

• ILs and NADES are non-flammable, non-toxic, and biodegradable, being greener and safer than traditional solvents. • NADES have higher vapor pressures and weaker heat stability than Ionic liquids. • ILs can remove organic pollutants from aqueous media efficiently. • NADES have advantages over IL, namely low cost, chemical inertness with water, ease of synthesis in high purity. • Scaling up the synthesis is difficult owing to high raw material costs and difficulty maintaining product quality. Wastewater treatment is a vital process to protect people and local ecosystems from toxic elements found in wastewater and keep the environment clean. However, conventional wastewater treatment methods may not consistently exhibit environmentally friendly characteristics or effectively eliminate organic contaminants from water. The need for an environmentally friendly and efficient technological solution becomes essential. A novel approach for removing organic contaminants from wastewater has recently been discovered that makes use of Natural Deep Eutectic Solvents (NADES) and Ionic liquids (ILs). This approach has yielded significant results and has the potential to revolutionize wastewater treatment technology. ILs and NADES are two types of solvents that have recently received much interest due to their unique characteristics, such as sustainability, biodegradability, and low toxicity. This review presents a comprehensive overview of novel extraction techniques for different organic pollutants from wastewater using ILs, such as pesticides, and dyes, and non-organic pollutants like heavy metals from wastewater using ILs and NADES. It highlights the potential of these solvents as a green alternative to conventional solvents for extracting organic pollutants. Besides, it illustrates the categories of ILs and NADES, their benefits and drawbacks, their major challenges, and the possible difficulties that can arise while scaling up their applications. Additionally, the paper delivers a detailed compilation of various applications of ILs in the extraction of organic contaminants. This review aims to provide valuable insights for the continuous development of NADES and ILs, as well as to enhance understanding of these innovative green solvents, and to promote their utilization in the extraction of organic pollutants from wastewater. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO)-based nanomaterials have garnered significant attentions for various industrial applications due to their remarkable structural and physicochemical properties. Consequently, the impact of the increased discharge of GO into the environment also becomes a matter of significant concern due to the toxicity of GO nanoparticles to human health and the ecosystem. Therefore, efficient removal of GO from wastewaters before discharge into water bodies is crucial and remains a critical challenge in wastewater treatment due to the formation of highly stable GO suspensions in aqueous media. Accordingly, this work investigates the flocculation of aqueous GO suspensions using a range of single and hybrid coagulant/flocculant systems comprising a choline chloride-based natural deep eutectic solvent (NADES) coagulant and commercial high-molecular-weight polyacrylamide (PAM) based flocculants with variable surface charge densities. The effect of variations in the coagulant/flocculant charge type, charge density, and dosage on GO deflocculation was examined using residual turbidity, zeta potential, and floc size measurements. Cationic PAMs demonstrated the best performance among single flocculant systems with GO removal efficiency exceeding 97% and compact settleable flocs (D 50 > 20 µm) at optimum doses in the range of 15–20 mg/L. The high charge density of FO 4800 SH further enhanced the GO removal efficiency by 1.1% and reduced the required optimum dose by 5 mg/L compared to FO 4350 SH. Hybrid flocculant systems revealed that anionic PAMs are the best performing flocculants when utilized with a fixed concentration of NADES coagulant. High GO removal efficiencies exceeding 98%, maximum zeta potential reduction, and the formation of large flocs (D 50 > 20 µm) were achieved. The low charge density variant AN 923 SH offered better flocculation conditions by reducing the optimum PAM dose required by 5 mg/L compared to AN 956 SH. The NADES/AN 923 SH hybrid system was determined to be the optimal combination for a highly efficient treatment of GO suspensions at a fixed NADES dose of 0.048 M and a low optimum PAM dose of 5 mg/L that resulted in a GO removal efficiency of 98.1%, turbidity of 2.5 NTU, zeta potential of − 3.7 mV, and a mean D 50 floc size of 26.1 µm. [Display omitted] • Graphene Oxide (GO) removal using natural deep eutectic solvent (NADES) coagulant and polyacrylamide (PAM) flocculants. • Cationic PAMs removed more than 97% GO from suspensions in single coagulant/flocculant systems. • NADES/anionic PAM systems exceeded 98% GO removal in hybrid coagulant/flocculant systems. • Charge type and density of PAMs influenced the flocculation efficiency of GO suspensions. • Hybrid systems considerably reduced the optimum PAM dose by > 66% for maximum GO removal. [ABSTRACT FROM AUTHOR]

The scarcity of water, especially in arid and semi-arid regions of the world is exerting great pressure on resources and establishing more need to provide good quality water for human and other consumptions. Water recovery/recycle/reuse has proven to be effective and successful in creating a new and reliable water supply. Accordingly, attention is being paid to the effective treatment of alternative sources of water (apart from fresh water) such as seawater, storm water, wastewater (e.g. treated sewage water), and industrial wastewater. In this review, the use of carbon nanotubes (CNTs), member of the fullerene structural family, is considered with special focus on the removal of heavy metals from water (lead, chromium, cadmium, arsenic, copper, zinc and nickel). A critical review into the adsorption behavior and use of the CNTs is given with attention being paid to the effects of surface modifications on the adsorption behavior and subsequent heavy metal removal. A review of the effect of a number of key variables including pH, CNTs dosage, time, ionic strength, temperature and surface charge are given. It will be demonstrated that, surface modification enhances positively the adsorption capacity of CNTs towards cadmium, chromium, lead, mercury, copper, zinc, cobalt and nickel as did the solution pH. CNTs have been proven to an excellent adsorbent for the removal of different heavy metals from water. However, most of the applications of CNTs are on lab scale in batch experiments. In spite of high costs, CNTs are expected to be a promising adsorbent in the future due to its high adsorption capacity compared to many traditional adsorbents. Researchers are also in quest of novel environment friendly techniques for the surface modification of CNTs to further improve their properties. Still, the feasibility of CNTs application in large scale treatment needs to be further studied. Effective techniques for regeneration/reuse of CNTs also need to be explored yet. One of the main hurdles that limit the applications of CNTs in large scale operation is the cost of CNTs. Future research works on developing a cost-effective way of CNT production and testing the toxicity of CNTs and CNT-related materials are recommended. [ABSTRACT FROM AUTHOR]

Water treatment is a key aspect for the sustainable management of oil & gas operations. Osmotic concentration (OC) is an advanced water treatment process, adapted from forward osmosis (FO), that does not require water recovery from the draw solution. In this study, two commercial hollow fiber FO membranes [Module 1, cellulose triacetate (CTA) and Module 2, thin film composite (TFC)] were evaluated at pilot scale using actual process water obtained from a gas production facility. The evaluation focused on assessing the membrane productivity, fouling potential and chemical cleaning efficiency while normalizing the performance using a theoretical model that account for the variability of the operating conditions. Performance tests showed that Module 2 has a higher flux compared to Module 1, 9.9 L/m2·h vs 1.7 L/m2·h; and lower specific reverse solute flux (RSF) for most of the ions. Additionally, Module 1 benchmark experiment showed a 13% flux loss attributed to inorganic fouling (calcium phosphate precipitation) while the flux loss in Module 2 was <5% possibly due to enhanced module hydrodynamics and variation in membrane chemistry. Chemical cleaning (citric acid) proved to be successful in restoring the flux for Module 1. From the 8.1 mg/L organic carbon present in the feed, advanced organic characterization revealed that certain group of hydrophilic organics are able to pass through Module 1, but not Module 2, translating to a specific forward organic solute flux of 0.9 mg/L and 0.1 mg/L for Module 1 and 2, respectively. Finally, key sustainable and environmental considerations were presented in support of further development of process implementation. The OC process has strong potential for full-scale installation; however, demonstrating its performance in the field would be the next step necessary for successful implementation of the technology. [Display omitted] • Side-by-side pilot study of 2 commercial FO membranes with industrial wastewater • TFC showed higher water flux (9.9 vs 1.7 L/m2·h) compared to cellulose triacetate. • CTA showed 13% fouling due to calcium phosphate scaling; TFC showed <5% fouling • Certain hydrophilic organics can pass through CTA but not TFC module. • Citric acid cleaning restored the CTA module flux back to their initial performance. [ABSTRACT FROM AUTHOR]