Insights into estrogenic activity removal using carbon nanotube electrochemical filter

Estrogenic compounds in drinking water: A systematic review and risk analysis

Estrogenic compounds are the endocrine disruptors that receive major attention because of their ability to imitate the natural female hormone, 17β-estradiol and cause adverse effects on the reproductive system of animals. The presence of estrogenic compounds in drinking water is a warning to assess the risks to which human beings are exposed. The present work has the objectives of carrying out a systematic review of studies that investigated estrogenic compounds in drinking water around the world and estimate the human health and estrogenic activity risks, based on the concentrations of each compound reported. The systematic review returned 505 scientific papers from the Web of Science®, SCOPUS® and PubMED® databases and after careful analysis, 45 papers were accepted. Sixteen estrogenic compounds were identified in drinking water, from the classes of hormones, pharmaceutical drugs and personal care products, plasticizers, corrosion inhibitors, pesticides and surfactants. Di-(2-ethylhexyl) phthalate (DEHP) was the compound found at the highest concentration, reaching a value of 1.43 mg/L. Non-carcinogenic human health risk was classified as high for 17α-ethynilestradiol and DEHP, medium for dibutyl phthalate, and low for bisphenol A. The estrogenic activity risks were negligible for all the compounds, except DEHP, with a low risk. None of the estrogenic compounds presented an unacceptable carcinogenic risk, due to estrogenic activity. However, the risk assessment did not evaluate the interactions between compounds, that occurs in drinking water and can increase the risks and adverse effects to human health. Nonetheless, this study demonstrates the need for improvement of drinking water treatment plants, with more efficient technologies for micropollutant removal.

Electrochemical filtration for drinking water purification: A review on membrane materials, mechanisms and roles

Electrochemical filtration can not only enrich low concentrations of pollutants but also produce reactive oxygen species to interact with toxic pollutants with the assistance of a power supply, making it an effective strategy for drinking water purification. In addition, the application of electrochemical filtration facilitates the reduction of pretreatment procedures and the use of chemicals, which has outstanding potential for maximizing process simplicity and reducing operating costs, enabling the production of safe drinking water in smaller installations. In recent years, the research on electrochemical filtration has gradually increased, but there has been a lack of attention on its application in the removal of low concentrations of pollutants from low conductivity water. In this review, membrane substrates and electrocatalysts used to improve the performance of electrochemical membranes are briefly summarized. Meanwhile, the application prospects of emerging single-atom catalysts in electrochemical filtration are also presented. Thereafter, several electrochemical advanced oxidation processes coupled with membrane filtration are described, and the related working mechanisms and their advantages and shortcomings used in drinking water purification are illustrated. Finally, the roles of electrochemical filtration in drinking water purification are presented, and the main problems and future perspectives of electrochemical filtration in the removal of low concentration pollutants are discussed.

Carbon nanotube-wastewater treatment nexus: Where are we heading to?

Water treatment is crucial in solving the rising people's appetite for water and global water shortages. Carbon nanotubes (CNTs) have considerable promise for water treatment because of their adjustable and distinctive arbitrary, physical, as well as chemical characteristics. This illustrates the benefits and risks of integrating CNT into the traditional water treatment resource. Due to their outstanding adsorbent ability and chemical and mechanical properties, CNTs have gained global consideration in environmental applications. The desalination and extraction capability of CNT were improved due to chemical or physical modifications in pure CNTs by various functional groups. The CNT-based composites have many benefits, such as antifouling performance, high selectivity, and increased water permeability. Nevertheless, their full-scale implementations are still constrained by their high costs. Functionalized CNTs and their promising nanocomposites to eliminate contaminants are advised for marketing and extensive water/wastewater treatment.

Ganzoury M, Zhang N, de Lannoy CF. Nanocomposite Polymeric Membranes for Organic Micropollutant Removal: A Critical Review

The prevalence of organic micropollutants (OMPs) and their persistence in water supplies have raised serious concerns for drinking water safety and public health. Conventional water treatment technologies, including adsorption and biological treatment, are known to be insufficient in treating OMPs and have demonstrated poor selectivity toward a wide range of OMPs. Pressure-driven membrane filtration has the potential to remove many OMPs detected in water with high selectivity as a membrane's molecular weight cutoff (MWCO), surface charge, and hydrophilicity can be easily tailored to a targeted OMP's size, charge and octanol-water partition coefficient (Kow). Over the past 10 years, polymeric (nano)composite microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF) membranes have been extensively synthesized and studied for their ability to remove OMPs. This review discusses the fate and transport of emerging OMPs in water, an assessment of conventional membrane-based technologies (NF, reverse osmosis (RO), forward osmosis (FO), membrane distillation (MD) and UF membrane-based hybrid processes) for their removal, and a comparison to the state-of-the-art nanoenabled membranes with enhanced selectivity toward specific OMPs in water. Nanoenabled membranes for OMP treatment are further discussed with respect to their permeabilities, enhanced properties, limitations, and future improvements.

Electrochemical Methods for Water Purification, Ion Separations, and Energy Conversion

Agricultural development, extensive industrialization, and rapid growth of the global population have inadvertently been accompanied by environmental pollution. Water pollution is exacerbated by the decreasing ability of traditional treatment methods to comply with tightening environmental standards. This review provides a comprehensive description of the principles and applications of electrochemical methods for water purification, ion separations, and energy conversion. Electrochemical methods have attractive features such as compact size, chemical selectivity, broad applicability, and reduced generation of secondary waste. Perhaps the greatest advantage of electrochemical methods, however, is that they remove contaminants directly from the water, while other technologies extract the water from the contaminants, which enables efficient removal of trace pollutants. The review begins with an overview of conventional electrochemical methods, which drive chemical or physical transformations via Faradaic reactions at electrodes, and proceeds to a detailed examination of the two primary mechanisms by which contaminants are separated in nondestructive electrochemical processes, namely electrokinetics and electrosorption. In these sections, special attention is given to emerging methods, such as shock electrodialysis and Faradaic electrosorption. Given the importance of generating clean, renewable energy, which may sometimes be combined with water purification, the review also discusses inverse methods of electrochemical energy conversion based on reverse electrosorption, electrowetting, and electrokinetic phenomena. The review concludes with a discussion of technology comparisons, remaining challenges, and potential innovations for the field such as process intensification and technoeconomic optimization.

Silica-catalyzed ozonation of 17α -ethinyl-estradiol in aqueous media-to better understand the role of silica in soils

A promising route for thorough removal of 17α-ethinyl estradiol (EE2) from aqueous media was achieved through ozonation using mesoporous silicas such SBA-15, SBA-16, MCM-41 and MCM-48 as catalysts. Comparison with aluminosilicates along with Zeta potential and particle size measurements allowed demonstrating that EE2 interaction with silanols and hydrophobic -Si-O-Si- groups are essential requirements for the catalytic activity. Acid-base interactions, if any, should have minor contribution. EE2 hydroxylation appears to be an early step in the ozonation on all catalysts, but MCM-41 showed increased activity in phenolic ring cleavage. Confrontation of HPLC-UV and UV-Vis and HPLC-UV measurements revealed highest catalytic activity for MCM-41 and to a lesser extend of MCM-48 due to their higher specific surface area and weaker acid character. These results provide valuable findings for judiciously tailoring optimum [EE2-Silica:Water] interactions for thorough oxidative degradation of endocrine disrupting compounds (EDC).

Removal of endocrine disrupters from the contaminated environment: public health concerns, treatment strategies and future perspectives - A review

Endocrine-disrupting compounds (EDCs) are emerging contaminants of concern (ECC) that disturb endocrine hormones and system functionality even at very low concentrations (i.e. μg/L or ng/L levels). Hence, EDCs are found in all components of the environment including surface and groundwater, wastewater, soil, outdoor and indoor air and in the contaminated foods from a variety of sources (run off from agricultural activities, sewage treatment plants, leakage from septic tanks etc.), and the effects are more severe as the majority of EDCs do not have standard regulations. The environmental mobility of EDCs is higher as conventional wastewater treatment does not degrade efficiently and the development of effective and sustainable removal technologies specifically designed for the removal of those emerging micropollutants is essential. Accordingly, EDCs cause various public health diseases such as reproductive abnormalities, obesity, various cancer types, cardiovascular risks, metabolic disorders, epigenetic alterations, autism, etc. This paper reviews the existing and emerging treatment technologies for the removal of phenolic based EDCs, such as natural estrogens (estrone (E1), 17β-estradiol (E2), estriol (E3)), synthetic estrogen 17α-ethinylestradiol (EE2) and phenolic xenoestrogens (4-nonyl phenols (4-NP) and bisphenol-A (BPA)) from the contaminated environment. These includes advanced oxidation processes (AOP), adsorption processes, membrane based filtration, bioremediation, phytoremediation and other integrated approaches. The sustainability of EDCs removal can be assured through the use of combined processes (i.e. low-cost - biological and adsorption methods with efficient and costly - AOPs) techniques through system integration to achieve better removal efficiency than using a single treatment technique. Besides, the public health concerns and future research perspectives of EDCs are also highlighted.

A High Flux Electrochemical Filtration System Based on Electrospun Carbon Nanofiber Membrane for Efficient Tetracycline Degradation

In this work, an electrochemical filter using an electrospun carbon nanofiber membrane (ECNFM) anode fabricated by electrospinning, stabilization and carbonization was developed for the removal of antibiotic tetracycline (TC). ECNFM with 2.5 wt% terephthalic acid (PTA) carbonized at 1000 °C (ECNFM-2.5%-1000) exhibited higher tensile stress (0.75 MPa) and porosity (92.8%), more graphitic structures and lower electron transfer resistance (23.52 Ω). Under the optimal condition of applied voltage 2.0 V, pH 6.1, 0.1 mol L−1 Na2SO4, initial TC concentration 10 ppm and membrane flux 425 LMH, the TC removal efficiency of the electrochemical filter of ECNFM-2.5%-1000 reached 99.8%, and no obvious performance loss was observed after 8 h of continuous operation. The pseudo-first-order reaction rate constant in flow-through mode was 2.28 min−1, which was 10.53 times higher than that in batch mode. Meanwhile, the energy demand for 90% TC removal was only 0.017 kWh m−3. TC could be converted to intermediates with lower developmental toxicity and mutagenicity via the loss of functional groups (-CONH2, -CH3, -OH, -N(CH3)2) and ring opening reaction, which was mainly achieved by direct anodic oxidation. This study highlights the potential of ECNFM-based electrochemical filtration for efficient and economical drinking water purification.

Electrochemical degradation of psychotropic pharmaceutical compounds from municipal wastewater and neurotoxicity evaluations

Contaminants of emerging concern (CECs) are released daily into surface water, and their recalcitrant properties often require tertiary treatment. Electrochemical oxidation (EO) is often used as an alternative way to eliminate these compounds from water, although the literature barely addresses the neurotoxic effects of residual by-products. Therefore, this study investigated the performance of EO in the removal of five CECs (alprazolam, clonazepam, diazepam, lorazepam, and carbamazepine) and performed neurotoxicity evaluations of residual EO by-products in Wistar rat brain hippocampal slices. Platinum-coated titanium (Ti/Pt) and boron-doped diamond (BDD) electrodes were studied as anodes. Different current densities (13-75 A m^-2), pH values (3-10), electrolyte dosages (NaCl), and matrix effects were assessed using municipal wastewater (MWW). The drugs were successfully degraded after 5 min of reaction for both the Ti/Pt and BDD electrodes when a current density of 75 A m^-2 was applied. For Ti/Pt and BDD, neutral and acidic pH demonstrated better CEC removal performance, respectively. Compound degradation using MWW achieved 40% removal after 120 min for Ti/Pt and ranged between 33 and 52% for the BDD anode. For Ti/Pt, neurotoxicity studies using MWW indicated a decrease in reactive oxygen species (ROS) signals. However, when an artificial cerebrospinal fluid (ACSF) medium was reapplied, the signal recovered and increased to a value above the baseline, indicating that cells recovered part of their normal activity but remained in a different condition. For the BDD anode, the treated MWW did not cause significant ROS production variations, suggesting that he EO was effective in eliminating the toxicity of the treated solution.

Environmental aspects of hormones estriol, 17β-estradiol and 17α-ethinylestradiol: Electrochemical processes as next-generation technologies for their removal in water matrices

Hormones as a group of emerging contaminants have been increasingly used worldwide, which has increased their concern at the environmental level in various matrices, as they reach the water bodies through effluents due to the ineffectiveness of conventional treatments. Here we review the environmental scenario of hormones estriol (E3), 17β-estradiol (E2), and 17α-ethinylestradiol (EE2), explicitly their origins, their characteristics, interactions, how they reach the environment, and, above all, the severe pathological and toxicological damage to animals and humans they produce. Furthermore, studies for the treatment of these endocrine disruptors (EDCs) are deepened using electrochemical processes as the remediation methods of the respective hormones. In the reported studies, these micropollutants were detected in samples of surface water, underground, soil, and sediment at concentrations that varied from ng L^-1 to μg L^-1 and are capable of causing changes in the endocrine system of various organisms. However, although there are studies on the ecotoxicological effects concerning E3, E2, and EE2 hormones, little is known about their environmental dispersion and damage in quantitative terms. Moreover, biodegradation becomes the primary mechanism of removal of steroid estrogens removal by sewage treatment plants, but it is still inefficient, which shows the importance of studying electrochemically-driven processes such as the Electrochemical Advanced Oxidation Processes (EAOP) and electrocoagulation for the removal of emerging micropollutants. Thus, this review covers information on the occurrence of these hormones in various environmental matrices, their respective treatment, and effects on exposed organisms for ecotoxicology purposes.

Occurrence, statutory guideline values and removal of contaminants of emerging concern by Electrochemical Advanced Oxidation Processes: A review

A wide variety of chemical compounds are used in human activities; however, part of these compounds reach surface water, groundwater and even water considered for potable uses. Due to the limited efficiency of water treatment by the Water and Wastewater Treatment Plants, the presence of these compounds in natural and human consumption waters can be very harmful due to their high persistence and adverse effects; these characteristics define the contaminants of emerging concern (CECs). Water treatment by Electrochemical Advanced Oxidation Processes (EAOPs) has been evaluated as a promising process for the removal of persistent and recalcitrant organic contaminants. With this background, the present review aims to gather studies and information published between 2015 and 2020 regarding the occurrence of CECs in surface, potable and groundwater, its treatment by EAOPs, the main operating conditions and by-product generation of EAOPs, contaminant toxicity assessments and international statutory guideline values concerning CEC standards and allowable concentrations in the environment and treated drinking water. Therefore, in this review it was found that the compounds bisphenol A (BPA), diethyltoluamide (DEET), 17α-ethinyl estradiol (EE2), perfluorobutanoic acid (PFBA), carbamazepine, caffeine and atrazine were the most frequently detected in water sources, with concentrations ranging from 35.54-4800, 1.21-98, 0.005-38.5, 5-742.904, 0.0071-586, 0.89-1040, and 100-323 (ng L-1), respectively. Among the operational conditions of EAOPs, current density, pH and oxidant concentration are the main operational parameters that have an influence on these treatment technologies, besides the by-products generated, which might be removed by the integration of EAOPs with biological digestion treatments. Regarding the values of water quality standards, many CECs do not have established standard allowable concentration values, which represents a concern toward the possible toxic effects of these compounds on non-target organisms.

Prospects of an Electroactive Carbon Nanotube Membrane toward Environmental Applications

Rapid population growth and industrialization have driven the emergence of advanced electrochemical and membrane technologies for environmental and energy applications. Electrochemical processes have potential for chemical transformations, chloralkali disinfection, and energy storage. Membrane separations have potential for gas, fluid, and chemical purification. Electrochemical and membrane technologies are often used additively in the same unit process, e.g., the chloroalkali process where a membrane is used to separate cathodic and anodic products from scavenging each other. However, to access the maximal potential requires intimate hybridization of the two technologies into an electroactive membrane. The combination of the two discrete technologies results in a range of synergisms such as reduced footprint, increased processing kinetics, reduced fouling, and increased energy efficiency.Due to their high specific surface area, excellent electric conductivity, and desirable robustness, 1D carbon nanotubes (CNTs) hold promise for many applications over a range of industry sectors such as a base material for electrodes and membranes. Importantly, CNT morphology and surface chemistry can be rationally modified and fine-tuning of these CNT physicochemical properties can enhance their functionality toward practical applications. The CNT 1D form allows assembly of a stable thin-film fibrous network by a variety of facile techniques. These CNT networks have pore sizes in the range of 10-500 nm (d_pore ∼ 6-8d_CNT) and thicknesses of 10-200 μm, both similar to those of classical polymer membranes, thus allowing for straightforward incorporation into commercial membrane devices modified for electroactivity inclusion.In this Account, CNTs and their composites are used as model electroactive porous materials to exemplify the design strategies and environmental applications of emerging electroactive membrane technology. The Account begins with a brief summary of the electroactive membrane design principles and flow processes developed by our groups. After the methodology section, a detailed discussion is provided on the underlying physical-chemical mechanisms that govern the electroactive membrane technology. Then we summarize our findings on the rational design of several flow-through electrochemical CNT filtration systems focused on either anodic oxidation reactions or cathodic reduction reactions. Subsequently, we discuss a recently discovered electrochemical valence-state-regulation strategy that is capable to detoxify and sequester heavy metal ions. Finally, we conclude the Account with our perspectives toward future development of the electroactive membrane technology.

Feasibility and mechanism of enhanced 17β-estradiol degradation by the nano Zero Valent Iron-citrate system

17β-Estradiol (17β-E2) as a non-conventional pollutant with high damage, the effective removal of 17β-E2 had been studied wildly. In recent years, nano materials application enabled the rapid removal of 17β-E2. Nano zero valent iron (nZVI) as one of the most widely used nano materials could also be used to degrade 17β-E2. But, the degradation performance of nZVI was limited by oxidation and aggregation. Therefore, this study explored the degradation mechanisms of 17β-E2 by nZVI and the enhancement mechanisms of nZVI by citrate. Firstly, 17β-E2 could be effectively degraded under acidic conditions without the addition of citrate. Citrate had protective effect on nZVI, so the degradation efficiency in neutral condition and degradation rate at all pH values of 17β-E2 were enhanced greatly in nZVI-citrate system. 17β-E2 degradation was mainly about group change and cleavage of ring A, as well as dominated by O₂^-▪ and OH∙ in the absence and presence of citrate. The formation of dimers and trimers proved the existence of laccase-like reaction during the 17β-E2 degradation process by nZVI. In nZVI-citrate system, the laccase-like reaction was replaced by specific cross-coupling of 17β-E2, E1, and citrate. Overall, the study proved that citrate could enhance the degradation of 17β-E2 by nZVI.