This review investigates antifouling agents used in the process of membrane separation (MS), in reverse osmosis (RO), ultrafiltration (UF), nanofiltration (NF), microfiltration (MF), membrane distillation (MD), and membrane bioreactors (MBR), and clarifies the fouling mechanism. Membrane fouling is an incomplete substance formed on the membrane surface, which will quickly reduce the permeation flux and damage the membrane. Foulant is colloidal matter: organic matter (humic acid, protein, carbohydrate, nano/microplastics), inorganic matter (clay such as potassium montmorillonite, silica salt, metal oxide, etc.), and biological matter (viruses, bacteria and microorganisms adhering to the surface of the membrane in the case of nutrients) The stability and performance of the tested nanometric membranes, as well as the mitigation of pollution assisted by electricity and the cleaning and repair of membranes, are reported. Physical, chemical, physico-chemical, and biological methods for cleaning membranes. Biologically induced biofilm dispersion effectively controls fouling. Dynamic changes in membrane foulants during long-term operation are critical to the development and implementation of fouling control methods. Membrane fouling control strategies show that improving membrane performance is not only the end goal, but new ideas and new technologies for membrane cleaning and repair need to be explored and developed in order to develop future applications.

Water shortage is a major worldwide issue. Filtration using genuine polymeric membranes demonstrates excellent pollutant separation capabilities; however, polymeric membranes have restricted uses. Nanocomposite membranes, which are produced by integrating nanofillers into polymeric membrane matrices, may increase filtration. Carbon-based nanoparticles and metal/metal oxide nanoparticles have received the greatest attention. We evaluate the antifouling and permeability performance of nanocomposite membranes and their physical and chemical characteristics and compare nanocomposite membranes to bare membranes. Because of the antibacterial characteristics of nanoparticles and the decreased roughness of the membrane, nanocomposite membranes often have greater antifouling properties. They also have better permeability because of the increased porosity and narrower pore size distribution caused by nanofillers. The concentration of nanofillers affects membrane performance, and the appropriate concentration is determined by both the nanoparticles’ characteristics and the membrane’s composition. Higher nanofiller concentrations than the recommended value result in deficient performance owing to nanoparticle aggregation. Despite substantial studies into nanocomposite membrane manufacturing, most past efforts have been restricted to the laboratory scale, and the long-term membrane durability after nanofiller leakage has not been thoroughly examined.

Due to the impacts of water scarcity, the world is looking at all possible solutions for decreasing the over-exploitation of finite freshwater resources. Wastewater is one of the most reliable and accessible water supplies. As the population expands, so do industrial, agricultural, and household operations in order to meet man’s enormous demands. These operations generate huge amounts of wastewater, which may be recovered and used for a variety of reasons. Conventional wastewater treatment techniques have had some success in treating effluents for discharge throughout the years. However, advances in wastewater treatment techniques are required to make treated wastewater suitable for industrial, agricultural, and household use. Diverse techniques for removing heavy metal ions from various water and wastewater sources have been described. These treatments can be categorized as adsorption, membrane, chemical, or electric. Membrane technology has been developed as a popular alternative for recovering and reusing water from various water and wastewater sources. This study integrates useful membrane technology techniques for water and wastewater treatment containing heavy metals, with the objective of establishing a low-cost, high-efficiency method as well as ideal production conditions: low-cost, high-efficiency selective membranes, and maximum flexibility and selectivity. Future studies should concentrate on eco-friendly, cost-effective, and long-term materials and procedures.

The goal of this study is to develop a new effective guar gum-grafted acrylamide hydrogel for wastewater treatment, abbreviated as (guar gum-g-acrylamide). For the non-biodegradable and hazardous synthetic acid red 8, the produced guar gum-g-acrylamide hydrogel is a promising thermally stable adsorbent. Microwave-aided technique, ammonium persulfate initiator, and N,N′-methylene-bis-acrylamide cross-linker are used to make a hydrogel comprising natural polysaccharides guar gum grafted by poly acrylamide. Fourier transformer infrared (FTIR) spectra and scanning electron microscopy (SEM) demonstrate that varied percentages of acrylamide successfully graft the backbone of guar gum. When the grafting percentage of acrylamide is raised, the hydrogel’s maximum adsorption capacity (qe) increases. At pH 1 of dye solution, maximum adsorption capacity (qe) is 18 mg.g⁻¹, at pH 9; qe is decreased up to 8 mg.g⁻¹. At 0.5 g.L⁻¹ hydrogel, the dye has a low removal percentage (34%), but when the hydrogel dosage is increased to 8 g.L⁻¹, the removal percentage increases to 90%. When the initial AR8 dye concentration was increased from 50 to 300 mg.L⁻¹, the removal percentage reduced to 20% and the adsorbed quantity dye increased from 17 to 44 mg.g⁻¹, but both parameters became limited above this dye concentration. Other ideal conditions for AR8 dye removal by the hydrogel include 60 min of contact time, 150 revolutions per minute (rpm), and a temperature of 20 degrees Celsius. The AR8 dye adsorption kinetic is pseudo-second order, assuming electrostatic interaction between the negatively charged AR8 dye molecules and the positively charged hydrogel-functional group. The adsorption values fit the Langmuir isotherm, with q_max. of 54.054 mg.g⁻¹. The adsorbed quantity (qe) decreases as the temperature rises, indicating that dye molecules physisorbed on the hydrogel pores, and the maximum adsorption capacity is at 20 °C. The exothermic and spontaneity of adsorption were confirmed by the negative values of heat of adsorption (∆H°_ads.) and standard Gibbs free energy of adsorption (∆G°_ads.). The reusability of the hydrogel was validated after three cycles of desorption of AR8 dye from the hydrogel surface in alkaline solution.

A novel eco-friendly adsorbent was fabricated by mixing mushroom-derived cadmium sulfide and polyethyleneimine-functionalized biochar that was fabricated from coffee waste with a chitosan biopolymer. The green-synthesized CdS/PEI-BC/CTS composite was analyzed using several characterization methods to identify its morphological, compositional, and structural characteristics. In addition, the adsorption property of the composite was investigated for hexavalent chromium as a model for anionic heavy metals. The best adsorption conditions to efficiently adsorb Cr(VI) onto CdS/PEI-BC/CTS were scrutinized in the batch mode. The experimental results elucidated that the higher adsorption efficacy for Cr(VI) was 97.89% at pH = 3, Cr(VI) concentration = 50 mg L⁻¹, CdS/PEI-BC/CTS dose = 0.01 g, and temperature = 20 °C. The impact of co-interfering anionic species on Cr(VI) adsorption was identified in simulated wastewater. The recycling property of the CdS/PEI-BC/CTS composite was assessed for ten runs to ensure the applicability of the green composite. The adsorption mechanism and interaction types were proposed on the basis of kinetic and isotherm studies, along with analysis tools. The mechanistic study proposed that the Cr(VI) adsorption onto CdS/PEI-BC/CTS occurred via chemical and physical pathways, including protonation, electrostatic interactions, reduction, and coordination bonds.