The widespread occurrence and ubiquitous distribution of estrogens, i.e., estrone (E1), estradiol (E2), and estriol (E3) in our water matrices, is an issue of global concern. Public and regulatory authorities are concerned and placing joint efforts to eliminate estrogens and related environmentally hazardous compounds, due to their toxic influences on the environmental matrices, ecology, and human health, even at low concentrations. However, most of the available literature is focused on the occurrence of estrogens in different water environments with limited treatment options. Thus, a detailed review to fully cover the several treatment processes is needed. This review comprehensively and comparatively discusses many physical, chemical, and biological-based treatments to eliminate natural estrogens, i.e., estrone (E1), estradiol (E2), and estriol (E3) and related synthetic estrogens, e.g., 17α-ethinylestradiol (EE2) and other related hazardous compounds. The covered techniques include adsorption, nanofiltration, ultrafiltration, ultrasonication, photocatalysis of estrogenic compounds, Fenton, Fenton-like and photo-Fenton degradation of estrogenic compounds, electro-Fenton degradation of estrogenic compounds, ozonation, and biological methods for the removal of estrogenic compounds are thoroughly discussed with suitable examples. The studies revealed that treatment plants based on chemical and biological approaches are cost-friendly for removing estrogenic pollutants. Further, there is a need to properly monitor and disposal of the usage of estrogenic drugs in humans and animals. Additional studies are required to explore a robust and more advanced oxidation treatment strategy that can contribute effectively to industrial-scale applications. This review may assist future investigations, monitoring, and removing estrogenic compounds from various environmental matrices. In concluding remarks, a way forward and future perspectives focusing on bridging knowledge gaps in estrogenic compounds removal are also proposed.

This study developed a process of genetically engineered bacteria Rhodococcus erythropolis expressing Nirs and AMO combined with membrane bioreactor (MBR), nanofiltration (NF) and reverse osmosis (RO) membrane (pRho-NA-MNR) for advanced treatment of landfill leachate. Results demonstrated that pRho-NA-MNR presented higher removal rate of chemical oxygen demand (COD), biological oxygen demand (BOD), ammonia nitrogen (N–NH₄), total nitrogen (TN) and total organic carbon (TOC) than activated sludge (AS-MNR) system. Administration of pRho-NA increased nitrification by converting N–NH₄ to nitrite (N–NO₂) and Nitrate (N–NO₃), and promoting denitrification by converting N–NO₂ to nitrogen (N₂) in the landfill leachate treatment, promoted the pH control, increased sludge activity and effluent yield, shortened phase length adaptation under alternating aerobic-anoxic conditions. pRho-NA increased the nitration and denitrifying rate in the aerobic and anaerobic stage in the system by increasing Cyt cd1 and Cyt c expression in the activated sludge. Nitrogen removal by nitrification and denitrification was positively correlated to the concentration of Nirs and AMO expression. Treatment with pRho-NA promoted pollutant removal efficiency of membrane bioreactor, nanofiltration and reverse osmosis membrane processes in landfill leachate. In conclusion, data suggest that pRho-NA-MNR facilitates the formation of granular sludge and enhances comparable removal of nitrogen and organic compounds, indicating the practice of this process should be considered in landfill leachate treatment system.

Water is the material basis for living organisms and one of the primary resources to maintain the sustainable development of the earth’s ecological environment. As a water purification method, nanofiltration (NF) separation technology has been widely considered by researchers in recent years. However, most of the studies on NF in the literature focus on membrane modification, and there are only a few reviews available. In this paper, the latest research progress of NF is reviewed, and the processes of NF membrane preparation using phase inversion, layer by layer, and interfacial polymerization are described. Polymer materials used for NF membrane preparation are reviewed and the main types of nanofillers to generate thin film nanocomposite membranes, including metal organic frameworks, boron nitride, Ti₃C₂TX, graphene oxide, SiO₂, and iron oxide are discussed. Membrane fouling is inevitable during NF operation and this paper analyzes the mechanisms of fouling and summarizes key pretreatment and cleaning methods required to remediate the long-term effects of cake layer formation. The steric hindrance effect, Donnan effect, and dielectric exclusion are analyzed, and some common characterization methods are summarized. The practical applications of NF are briefly introduced including groundwater, pharmaceutical wastewater, and textile wastewater treatment. Finally, the shortcomings and prospects of the existing research progress are put forward.

During zinc hydrometallurgy process, the chloride ions in the materials go into the leaching solution, which have abominable effects on equipment, electrowinning, and environment. So, it is necessary to remove chloride ions from zinc sulfate solution. The present review outlines the current research of removal methods of chlorine by holistically highlighting the advantages and mechanisms. The main techniques used to remove chloride ions from zinc sulfate solution are also discussed in detail. Among the methods, the precipitation method using copper slag to remove chlorine is widely used and the chlorine removal rate is up to 98%. In addition, the combination of electrochemistry and nanofiltration technology can form a closed-loop production process with less waste output and near-zero emissions. In addition, the challenges and possible future directions of chlorine removal from zinc sulfate solutions are also delineated.

Researchers in recent years have utilized a broad spectrum of treatment technologies in treating bakers’ yeast production wastewater. This paper aims to review the treatment technologies for the wastewater, compare the process technologies, discuss recent innovations, and propose future perspectives in the research area. The review observed that nanofiltration was the most effective membrane process for the treatment of the effluent (at >95% pollutant rejection). Other separation processes like adsorption and distillation had technical challenges of desorption, a poor fit for high pollutant load and cost limitations. Chemical treatment processes have varying levels of success but they are expensive and produce toxic sludge. Sludge production would be a hurdle when product recovery and reuse are targeted. It is difficult to make an outright choice of the best process for treating the effluent because each has its merits and demerits and an appropriate choice can be made when all factors are duly considered. The process intensification of the industrial-scale production of the bakers’ yeast process will be a very direct approach, where the process optimisation, zero effluent discharge, and enhanced recovery of value-added product from the waste streams are important approaches that need to be taken into account.

The following work provides a perspective on the degradation of cytostatic pollutants through TiO₂ heterogeneous photocatalysis. Cytostatic drugs are emerging pollutants used for cancer treatment found in hospital and domestic wastewater. Small amounts of cytostatic pollutants may pose severe health problems in human beings, animals, and plants after prolonged contact. This research presents a general review of some water treatment methods, such as aerobic activated sludge, enzymatic degradation, nanofiltration and chlorination, that have been used for the degradation or elimination of cytostatic drugs in wastewater. In recent years, photocatalysis has become important to solve this problem; these advanced oxidation process uses pure and modified TiO₂ to degrade cytostatic contaminants and convert them into non-harmful substances or to eliminate them completely. This work contains a comprehensive review of the heterogeneous photocatalysis process and mechanism, and its application on the removal of cytostatic pollutants. Even if research on the topic is still scarce, this literature review provides interesting highlights on the scope of the research field, and the path such research could follow.

It is reported that residual aluminum from coagulation pretreatment can increase membrane fouling in nanofiltration (NF) or reverse osmosis (RO) desalination systems. However, the membrane fouling mechanism of residual aluminum and the effective control measures are not very clear. In this study, the nanofiltration membrane fouling caused by poly-aluminum chloride (PACl), the inhibitory effect of amino trimethylene phosphonic acid (ATMP) on aluminum foulants, and calcium carbonate scale in the presence of residual aluminum were investigated by permeate experiments and scanning electron microscopy (SEM) observation of the fouled membranes. Besides, the effect of adding ultrafiltration before nanofiltration on reducing membrane fouling caused by residual aluminum was also investigated. The results showed that most of the residual aluminum in feed eventually formed insoluble particles and fine flocs, and accumulated gradually on the membrane surface, which was a typical colloid particle fouling. ATMP can reduce the membrane fouling caused by residual aluminum to some extent, and the permeate flux ratio (J/Jc) increased from 0.83 to 0.89 when ATMP increased to the optimal dose of 6 mg⋅L⁻¹. However, this means can still effectively eliminate carbonate scale, even in the presence of residual aluminum. Moreover, ultrafiltration pretreatment prior to nanofiltration was very effective to control membrane fouling, and the comprehensive cost was calculated to be only 0.006 $⋅m⁻³. Therefore, the combined process of coagulation-ultrafiltration as a pretreatment of nanofiltration or reverse osmosis should be an ideal way to prevent membrane fouling caused by residual aluminum.

Arsenic contamination in drinking water is recognized as major health hazard worldwide. As reported in literature, more than 19% Indians are consuming lethal levels of arsenic for drinking purposes. In this work, arsenic (III) removal was studied using HFN300 polyethersulfone nanofiltration membrane in spiral wound configuration. Various membrane parameters such as hydraulic permeability (4.87 L m⁻² h⁻¹ bar⁻¹), mass transfer coefficient (0.957*10⁻⁶ m s⁻¹), reflection coefficient (0.9), and solute permeability (2*10⁻⁹ m s⁻¹) were estimated using film theory combined Spiegler-Kedem (FTCSK) model. The higher value of reflection coefficient suggested the impervious nature of nanofiltration (NF) membrane used for arsenic (III) solute rejection. The influence of various operating parameters such as transmembrane pressure, initial feed concentration, and feed flowrate on membrane performance was also examined. It was found that arsenic (III) rejection was dependent on pressure and feed concentration. Result showed that more than 96.4% arsenic (III) rejection was achieved for 50 mg L⁻¹ of feed at optimized conditions. As HFN300 membrane was negatively charged at pH 8 and arsenic (III) was available in neutral solute form, electro-migration was not considered for solute rejection mechanism. Solution diffusion with significant coupling between solute and solvent, steric hindrance effect, convection, and solute-membrane affinity interactions were considered dominant factors for the possible solute rejection mechanism. Rejection efficiency (% R) and permeate flowrate (Q₂) were simulated and compared with experimental results. It was found that simulated results were in excellent agreement with the experimental results. The maximum error obtained was within 10% for both % R and Q₂. This confirms the efficacy of FTCSK model in predicting arsenic (III) removal using NF membrane. The annualized cost per cubic metre of treated water was estimated as 3.32 $/m³. This further confirms the feasibility of using NF process in removing arsenic from contaminated water.

Although water occupies 75% of the earth’s surface, only 0.0067% of the total water is available for human activities. These statistics further decline with the population growth and consequent multiplication in the amount of annual waste produced. The demand for clean and safe drinking water has always been a prime concern in the global scenario. Among various types of waste materials, endocrine-disrupting chemicals (EDCs) and pharmaceutical effluents have become a constant threat to the aquatic ecosystem and possess challenges worldwide. Endocrine-disrupting chemicals (EDCs) are a mixed group of emerging concern chemicals with the ability to mimic the mechanisms of biosynthesis, transport, and metabolism of hormones. These chemicals pose various health threats such as early puberty, infertility, obesity, diabetes, reproductive disorders, cancerous tumors, and related disorders (immune cells, hormones’ activity, and various organs). On the other hand, pharmaceutical compounds such as antibiotics also harm the natural environment, human health, and soil microbiology. Their low concentration, ranging from a few ng/L to μg/L, gives rise to a micro-pollution phenomenon, which makes it difficult to detect, analyze, and degrade in wastewater treatment plants. Activated carbons (ACs) and other adsorbents, including naturally occurring materials (wood, keratin) are considered as nanomaterials (NMs) reference for the separation of organic pollutants. It is generally acknowledged that mass-transfer phenomena control sorption kinetics at the liquid/solid interface, with retention controlled by the sorbent/sorbate properties. Therefore, the type of interaction (strong or weak van der Waals forces) and the hydrophilic/hydrophobic properties of the adsorbent are two crucial factors. Besides, EDCs and pharmaceutical compound sorption on such kinds of nanoporous solids depend on both the molecule size and charge density. The applications of nanomaterials on non-conservative methods, like advanced oxidation processes or AOPs (e.g., photocatalysis and Fenton reaction), are contemplated as more apt in comparison to conservative technology like reverse osmosis nanofiltration, and adsorption, etc. One of the reasons is that AOPs generate free radicals (hydroxyls), which are strong oxidants for the demineralization of organic compounds and the extreme case that hydroxyl radicals can attack any kinds of pollutants with the generation of only water and carbon dioxide as final products. AOPs may imply the use of NMs as either catalysts or photocatalysts, which improve the selective removal of the target pollutant. Therefore, various literature reviews have revealed that there is a timely need to upgrade the efficiency of the remediation approaches to protect the environment against EDCs and pharmaceuticals adequately. There is currently a lack of definitive risk assessment tools due to their complicated detection and associated insufficiency in the health risk database. Hence, our present review focuses on applying carbon-based nanomaterials to remove EDCs and pharmaceuticals from aqueous systems. The paper covers the effect of these pollutants and photocatalytic methods for treating these compounds in wastewater, along with their limitations and challenges, plausible solutions, and prospects of such techniques.

In this work, the novel direct synthesis method of dimethylacetamide-based graphene oxide (GO) was performed through electrochemical exfoliation assisted by commercially available single-tail sodium dodecyl sulphate (SDS) surfactant. Then, the synthesised GO (SDS–GO) was incorporated into polyvinylidene fluoride (PVDF) solution to produce a nanofiltration (NF) membrane through the phase immersion method. The addition of GO into the preparation of membrane solution alters the membrane morphology and improves the hydrophilicity. TiO₂ was also used as an additive for the NF membrane fabrication to further increase the membrane hydrophilicity. The fabricated PVDF/SDS–GO/TiO₂ and PVDF/SDS–GO NF membranes were compared with pure PVDF membrane. Then, the fabricated NF membranes were tested for methylene blue (MB) rejection with 10 ppm MB concentration. On the basis of the dead-end cell measurement operated at the pressure of 2 bar, the PVDF/SDS–GO/TiO₂ presents high MB rejection (92.76%) and the highest dye flux (7.770 L/m² h). This dye flux value was sevenfold higher than that of pure PVDF membrane (1.146 L/m² h) which was due to the utilisation of both GO and TiO₂ that improved the membrane hydrophilicity as indicated by the lowest contact angle (64.0 ± 0.11°). High porosity (57.46%) also resulted in the highest water permeability (4.187 L/m² h bar) of the PVDF/SDS–GO/TiO₂ NF membrane.