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Removal of Bisphenol A and 17??-Ethinyl Estradiol from Landfill Leachate Using Single-Walled Carbon Nanotubes
Abstract
In this study, the adsorption of bisphenol A (BPA) and 17α-ethinyl estradiol (EE2) from landfill leachate onto single-walled carbon nanotubes (SWCNTs) was investigated. Different leachate solutions were prepared by altering the pH, ionic strength, and dissolved organic carbon (DOC) in the solutions to mimic the varying water conditions that occur in leachate during the various stages of waste decomposition. The youngest and oldest leachate solutions contained varying DOC and background chemistry and were represented by leachate Type A (pH = 5.0; DOC = 2500 mg/L; conductivity = 12,500 μS/cm; [Ca(2+)] = 1200 mg/L; [Mg(2+)] = 470 mg/L) and Type E (pH = 7.5; DOC = 250 mg/L; conductivity = 3250 μS/cm; [Ca(2+)] = 60 mg/L; [Mg(2+)] = 180 mg/L). These solutions were subsequently combined in different ratios to produce intermediate solutions, labeled B-D, to replicate time-dependent changes in leachate composition. Overall, a larger fraction of EE2 was removed as compared to BPA, consistent with its higher log K(OW) value. The total removal of BPA and EE2 decreased in older leachate solutions, with the adsorptive capacity of SWCNTs decreasing in the order of leachate Type A > Type B > Type C > Type D > Type E. An increase in the pH from 3.5 to 11 decreased the adsorption of BPA by 22% in young leachate and by 10% in old leachate. The changes in pH did not affect the adsorption of EE2 in the young leachate, but did reduce adsorption by 32% in the old leachate. Adjusting the ionic strength using Na(+) did not significantly impact adsorption, while increasing the concentration of Ca(2+) resulted in a 12% increase in the adsorption of BPA and a 19% increase in the adsorption of EE2. DOC was revealed to be the most influential parameter in this study. In the presence of hydrophilic DOC, represented by glucose in this study, adsorption of the endocrine disrupting compounds (EDCs) onto the SWCNTs was not affected. In the absence of SWCNTs, hydrophobic DOC (i.e., humic acid) adsorbed 15-20% of BPA and EE2. However, when the humic acid and SWCNTs were both present, the overall adsorptive capacity of the SWCNTs was reduced. Hydrophobic (π-π electron donor-acceptor) interactions between the EDCs and the constituents in the leachate, as well as interactions between the SWCNTs and the EDCs, are proposed as potential adsorption mechanisms for BPA and EE2 onto SWCNTs.
... Nanoscale materials are an emerging class of materials that are highly desired for a broad range of applications, including but not limited to catalysis, optical, biological, microelectronic, and environmental applications, due to their unique superior properties [11]. Carbon nanotubes, in particular, have been successfully used to remove organic pollutants from water and wastewater [12][13][14][15]. This chapter focuses on the use of multi-walled carbon nanotubes alone and in combination with TiO₂ (a photocatalyst) (i.e. ...
... Carbon based nanomaterials are among the most widely used nanomaterials for environmental applications [10,11,14,22,23]. Amongst others, some of the desired properties of carbon based nanomaterials for water treatment include their large surface area, high intraparticle diffusion, chemical recalcitrance and high electrical conductivity [10,11,13,24]. ...
... During multilayer adsorption process, the adsorbate molecules initially interact with adsorbent surface before attaching to those of their own kind. Whereas, during mono-layer adsorption, the adsorbate molecules only interacts with the surface of adsorbent [13]. It is clear from the adsorption constants' values listed in Table 2 that the BTEX adsorption on MWNTs could not be explained by Langmuir isotherm model (negative values of Q 0 and K L ). ...
The presence of common industrial organic compounds and emerging micropollutants (e.g., pharmaceuticals and personal care products) in industrial and municipal wastewaters, respectively, has been recognized as a serious environmental problem owing to the recalcitrance and persistence of these compounds in the aquatic environment. In the past two decades, carbon nanotubes and their composites have been gradually applied for the removal of undesirable organic contaminants from water via adsorption. This chapter describes the removal of established toxic chemicals from oil and gas produced water and emerging micropollutants from treated municipal wastewater through the application of multiwalled carbon nanotubes (MWNTs) and their composites with titanium dioxide.
... The SWCNT paper electrode neither needs to transfer onto the conducting electrode surfaces nor needs to do any modification. It has been proposed that π-electron interactions can facilitate the adsorption of lipophilic molecules on SWCNT surfaces [25]. BPA has high lipophilicity due to presence of two benzene rings. ...
... The theoretical limit-of-detection (LOD), defined as LOD = 3 s/m (where s is the standard deviation of the blank solution (0.014 μA), and m is the slope of the calibration curve), was estimated to be 0.082 μM using the first linear segment. The experimental LOD was estimated as 1.0 μM based on S/N ratio of 3. The enhanced sensing performance of the SWCNT paper electrode can be attributed to the high effective surface area and increased adsorption of BPA on graphitic surfaces due to the π-π interaction [25,26]. Table 1 compares the various electrochemical assays that have utilized carbon nanotubes in different forms. ...
The electrochemical detection of BPA often requires modification of electrodes to overcome BPA's slower kinetics and higher oxidation potential. This work reports a modification-free, paper electrode based on vacuum-filtered SWCNT thin film. The prepared electrode does not need to be polished or transferred into the conducting substrates. The linear sweep voltammetric detection showed a linear response from 0.5-10 μM and 25-100 μM with a detection limit of 0.08 μM. The interference study and good recovery percentage (93−105%) in real water samples demonstrated the method's selectivity. The sensor can be promising for developing a simple, low-cost, portable, and paper-based BPA monitoring system.
... Adsorption on the other hand does not require high operating pressures and can be very effective in removing target molecular pollutants through physical and/or chemical interactions with the adsorbent (Ding et al. 2016). The latter may include synthetic or natural materials such as activated carbon (AC) which possesses a high surface area and porous structure that makes it an efficient micropollutant adsorbent (Saha et al. 2010;Tagliavini et al. 2017;Joseph et al. 2011;Ellerie et al. 2013). This was further demonstrated where sustainable cost-effective bioderived AC showed excellent adsorption characteristics for oil-water separation (Imran et al. 2021;. ...
Increased harmful pollutants emission into the environment poses a serious threat to the ecosystem and human health and mitigation of such problem has become a worldwide focus. In this research, the treatment of contaminated oily wastewater is investigated using a composite adsorptive membrane made of double-layer activated carbon-polymeric membranes shielded by a superhydrophilic (SHPI) porous material. The latter was prepared by immobilizing ZnO nanoparticles on stainless steel mesh using the spraying method. Using methylene blue dye and hexadecane as model contaminants, the composite membrane showed efficient pollutant adsorption as well as an almost total oil repellence by the SHPI material. Both experimental and theoretical studies of the adsorption characteristics were also conducted in a pilot-scale hybrid adsorptive membrane reactor using the prepared material. Estimation of the energy consumption in terms of electrical energy per order (EEO) was investigated and found much lower than that of nanofiltration (NF) for the treatment of dye-contaminated effluents. An order of magnitude estimation of treatment unit cost using the proposed approach was found to compare favorably with reported conventional wastewater treatment costs.
... Carbon nanotubes (CNTs) are mechanically robust and have exhibited extraordinary electrical, optical, and physicochemical characteristics [38]. They have good potential for water treatment applications through adsorptive removal of organic and inorganic contaminants from aquatic systems [7,[39][40][41]. CNTs are another type of material functionalized using DESs and may be single-walled or multi-walled or composites with other substances [10,42]. ...
Recently, new knowledge about the functionalization and synthesis of adsorbent materials for water treatment applications has been achieved using deep eutectic solvents (DESs). The improvements in functionalizing adsorbents employing DESs for water treatment, such as the removal of micropollutants, dyes, heavy metals, and other organic and inorganic contaminants from aqueous systems, are highlighted in this review. We describe the base materials employed for DES-based synthesis and functionalization of adsorbents as well as their physicochemical characteristics and water treatment applications (target chemicals and removal efficiency). The majority of the DESs significantly improved the removal of pollutants by increasing effective surface area and introducing desired functionalities. DESs were applied either during or after the production of adsorbent materials.
... These studies show that this compound can increase the risk of cancer in specific ovarian, breast, and prostate cancers (Rochester J.R., 2013 et al.,), as well as a variety of metabolic issues such as obesity, endometrial hyperplasia, recurrent miscarriages, and polycystic ovary syndrome (Di Donato et al., 2017). Other extraordinary issues related to bisphenol A publicity are cardiovascular disease, altered immune machine activity, diabetes in adults, infertility and precocious puberty (Rees-Clayton et al., 2011), Several technologies, such as coagulation, floculation, sedimentation, filtration (Joseph et al., 2012), carbon nanomaterials (CNMs) (e.g., carbon nanotubes (CNTs) (Joseph et al., 2011), and graphene oxides (GOs) For bisphenol A removal, membrane filtration, ultraviolet (UV) irradiation (Duan et al., 2017), organic methods (Wang G et al., 2006), and superior oxidation strategies (Rivas et al., 2008), (Rivero, et al., 2014), have been studied for bisphenol A removal. Therefore, effective, extra-sustainable techniques are sought to dispose of such contaminants from water and wastewater (Ioannou-Ttofa et al., 2016). ...
The goal of this study is to determine the ability of activated carbon derived from waste leather from theleather industry to adsorbed bisphenol-A, an endocrine disruptor, from aqueous solution. The functionalizedactivated carbon was found to have the best adsorption capacity at acidic pH. The weak vander Waals forceof attraction between the activated carbonâs surface and bisphenol-A The kinetics of adsorption were foundto fit well with a pseudo second-order reaction. Langmuir, freundlich, DKR, and the Elovich models wereused to correlate equilibrium isothermal data. Adsorption was observed, and there were no remarkablechanges after three hours. The effect of particle size revealed that the smallest one adsorbsmore due to theavailability of a large number of surface areas. The minimum initial concentration of theadsorbate favouredhigh adsorption. The process was endothermic, feasible, and spontaneous. Nearly 90% of adsorptions in anacidic medium were found. Overall, it was found that the activated carbon derived from waste leathercould be a new sustainable chemical technology for water purification.
... Possible reason for the reduced sorption capacity can be due to the filling of the pores of HBCB with the NaCl. Moreover, there are many previous studies in favor of the fact that the increased concentrations of salt reduced the sorption capacity of many organic compounds by occupying the pores (Joseph et al. 2011). ...
This study elaborates the simultaneous removal of three different fluoroquinolones (FQs), i.e., Norfloxacin (NOR), Lomefloxacin (LOM), and Enrofloxacin (ENR) from water using hydrogel beads of humic acid coated biochar (HA-BC) and chitosan. In our previous study, this adsorbent has already achieved tremendous results for the removal of a single FQ, i.e., ciprofloxacin. Now, initial concentrations of all FQs were set 100 mg/L each, and the maximum adsorbed amounts were 38.08 mg/g (NOR), 25.03 mg/g (LOM), and 29.72 mg/g (ENR). Adsorption attained equilibrium after 24 h, which obeyed the pseudo-second-order kinetic model. The mutation of humic acid-biochar/chitosan hydrogel beads (HBCB) with alcoholic solvents, i.e., methanol and ethanol to replace water decreased its sorption capacities from 38.08 mg/g (NOR) to 34.91 mg/g and 32.19 mg/g, respectively. Similarly, from 25.03 mg/g (LOM) to 22.81 mg/g and 19.91 mg/g, and 29.72 mg/g (ENR) to 26.52 mg/g and 24.64 mg/g. Adsorption isotherm data for all FQs were up to both Langmuir and Freundlich, but it suited more to that of Langmuir adsorption isotherm model. Sorption capacities, for all FQs, had a minor decline due to addition of NaCl, NaNO3, and Na2SO4. However, there was a huge decline when Na3PO4 was added into the adsorption system. Adsorbent was desorbed and regenerated for consecutive removal, and it showed good adsorption in the 4th cycle, i.e., 47 mg/g net adsorption. These results prove that HBCB is not only effective for adsorption removal of ciprofloxacin but also for other FQs too.
Graphical Abstract
... The keywords "bisphenol a", "carbon nanotube" and "modified electrode" appeared from 2004 to 2011, with a highlighted intensity of 1.9081, 3.4487, and 1.9755, respectively (Table 8). According to the timeline mapping hotspots of research from 2004-2011, the removal of bisphenol using MCNTs [52,53] and the application of MCNTs in electrodes [54] started to be focused on in this period. The long duration of the emergent words indicates that these keywords were widely followed by researchers and active research activities during this period. ...
The application of modified carbon nanotubes (MCNTs) in the field of wastewater treatment has received much attention in recent years. To better understand the research progress and trends of MCNTs in wastewater treatment, this paper presents a bibliometric analysis of the scientific literature on the application of MCNTs in wastewater, highlight how it has evolved over the years, and identify the sectors for which the study could be beneficial. The CiteSpace software was used to perform the analysis of the data in which specific maps were used to represent the network of the relationships among countries, journals, organizations, authors, and keywords related to the investigated topic and subtopics. The results show that in the time frame of the study, most attention has been focused on the functional modification of carbon nanotubes, the study of their application in water treatment, and the study of the patterns and mechanisms of pollutant removal. The recycling of MCNTs and their environmental risks have not been sufficiently studied. In conclusion, the recycling and regeneration methods of MCNTs, as well as the potential ecological, environmental and health risks will be the focus of future research and more research should be invested.
... The concentration of Fe reduces to below the detection limit during BPA and MB degradation, under both silent and ultrasonic-assisted treatment. Hence, the significant removal of BPA and MB from the medium may be due to better hydrophobic interaction with leachate constituents, and nanomaterials in a free radical system (Joseph et al. 2011). ...
This work investigates the efficacy of α-MnO2 nanorods for persulfate-mediated degradation of bisphenol A (BPA) and methylene blue (MB), in silent and ultrasonic-assisted systems. The conversion of α-MnO2 nanoparticle flakes to nanorods occurs upon calcination at a temperature of 400 °C for 3 h under the ramping conditions. The comparative characterization of nanomaterials pre- and post-calcination reveals better physical, chemical, and thermal properties of α-MnO2 nanorods. The impact of various operational parameters such as pH, dosage of nanorods, persulfate dose, selected contaminant concentration, ultrasound frequency and power, scavengers, and landfill leachate medium on the degradation of pollutants is also assessed. The ultrasonic assistance yields higher removal for both BPA and MB than the silent system. This may be attributed to the generation of more radicals as ultrasound activates persulfate. This can be due to acoustic cavitation, which leads to better solute dissociation and excited state. The results obtained through scavenger tests reveal that both OH• and SO4•− can contribute to degradation, but the role of SO4•− is found dominant. Significant removal of BPA and MB ((BPA)silent, 87.12%; (MB)silent, 96.54%; (BPA)ultrasonic, 88.75%; (MB)ultrasonic, 93.86%)) is observed in landfill leachate medium. The degradation pathway for pollutants is also proposed. The toxicity of pollutants and their degradation intermediates are evaluated using Ecological Structure Activity Relationships (ECOSAR) program. The results indicate reduced toxicity of BPA intermediates, while most MB degradation intermediates show higher toxicity. Therefore, it can be affirmed that removing pollutants does not ensure a completely non-toxic process. However, the study proposes a comprehensive toxicity evaluation and eliminating toxic intermediates for completely harmless wastewater treatment.
... Depends on the concentration of steroid and hormone's. (56-90%) [155,166] Activated sludge systems with UV disinfection Not effective (49%) [155,[167][168][169][170] Photocatalysis (µg/liter levels) Effective (>95%) [167,[171][172][173][174][175] ...
Micro-pollutants especially estrogens, progesterone, androgens, glucocorticoids, and growth hormones, are biological and chemical impurities that find their way into natural aquatic environments in trace quantities (ng/L), and possess a significant disturbance by impacting human and aquatic life. Due to the significant progress in in the analysis and detection techniques, these trace elements have been observed and quantified in several studies. However, as a result of limited methods and management technology, the adverse effects by these micro-pollutants in surface and coastal water is largely unknown. For this study, the compounds of estrogens, progesterone, androgens, glucocorticoids, and growth hormones have been selected according to their high frequent detection value in environmental waters. The concentration of the selected steroid and hormones ranges from 0.1–196 ng/L (estrogens), less than 0.1 to 439 ng/L (progesterone), 0.06–86 ± 2 (androgens), less than 0.1 to 433 ng/L (glucocorticoids), and 26.6 ng/g to 100 ng/L (growth hormones), and their percentage of removal efficiency varies from less than 10% to 99%, as the measurement of compounds concentration was found to be very low. Here, we report that future studies are necessary to detect the entry routes of these compounds into the environmental water, as well as to explore the technological approaches which are able to resolve this issue permanently.
... It was found of different electrolytes and ionic strength on the adsorption of AF and MB was shown in Fig. 4c, d. The results indicated that the adsorption capacities of both AF and MB decreased with the increase of electrolyte concentrations or ionic strength, which was by the findings of previous studies on the adsorptive removal of organic materials [48]. ...
The removal of dye pollutants from dyeing and printing industrial wastewater is a very important issue, and different methods have developed for this purpose. Here, a hydrogel adsorbent gelatin/chitosan/β-cyclodextrin/sodium humate (GEL/CS/β-CD/SH) was developed by a simple method for removal of the reactive dyes in aqueous solutions. The hydrogel used as an adsorbent had a good adsorption to different kinds of organic dyes. In this work, we focused on the adsorption process of GEL/CS/β-CD/SH hydrogels to the cationic dyes methylene blue (MB) and anionic dyes acid fuchsin (AF), which are commonly used in the printing and dyeing industry. The effects of dye solution pH, ionic strength, temperature, and contact time were investigated in a batch system. The adsorption thermodynamic and dynamic behaviors towards AF and MB were investigated in detail. The adsorption process could occur spontaneously at environmental temperature. The results indicated that the maximum adsorption capacity of AF and MB reached 1666.7 mg/g and 714.3 mg/g, respectively. Moreover, the GEL/CS/β-CD/SH hydrogel could be degraded completely by microorganisms in the soil. Therefore, GEL/CS/β-CD/SH hydrogel has a potential application as an effective adsorbent for the treatment of dyeing wastewater.
... Table 1 presents both measured and estimated degrees of removal for selected EDCs/PPCPs in WW treatment plants under dry-weather circumstances, using representative samples of the current literature concerning biodegradability, along with tendencies regarding sorption to sludge and oxidation by chlorination/ozonation. Numerous prior researches have reported that EDCs/PPCPs are eliminated to various levels by both conventional and advanced treatment techniques such as coagulation/flocculation (Westerhoff et al., 2005;Joseph et al., 2012;Jung et al., 2015), chlorination (Westerhoff et al., 2009), activated carbon Snyder et al., 2007;Jung et al., 2013), carbon nanoparticles (e.g., carbon nanotubes (Joseph et al., 2011a;Joseph et al., 2011b;Zaib et al., 2012) and graphene oxides (Nam et al., 2015)), metal-organic frameworks (Jun et al., 2019a;Jun et al., 2020b), MXenes (Jun et al., 2019b;Jun et al., 2020a), membrane (Yoon et al., 2006Heo et al., 2013), O 3 (Westerhoff et al., 2005;Moreira et al., 2015), ultraviolet (UV) radiation Farzadkia et al., 2014;Duan et al., 2017), sonodegradation (Rahimi et al., 2016;Rao et al., 2016;Serna-Galvis et al., 2016), non-thermal plasma (NTP) (Ansari et al., 2020), and biodegradation (Yoon et al., 2010;Ryu et al., 2011Ryu et al., , 2014. Unlike commonly recognized advanced oxidation methods such as O 3 /H 2 O 2 , UV/TiO 2 , UV/H 2 O 2 , and UV/Fe 3+ /H 2 O 2 processes, the NTP process has lately been employed as an advanced treatment method for the elimination of complicated organic chemicals in water and WW (Gerrity et al., 2010;Ceriani et al., 2018;Feng et al., 2018;Fan et al., 2021). ...
Contaminants of emerging concerns such as endocrine-disrupting compounds (EDCs) and pharmaceuticals/personal-care products (PPCPs) constitute a problem since they are not completely eliminated by traditional water and wastewater treatment methods. Non-thermal plasma (NTP) is considered as one of the most favorable treatment methods for the removal of organic contaminants in water and wastewater. The degradation of selected EDCs and PPCPs of various classes was reviewed, based on the recent literature, to (i) address the effect of the main NTP treatment parameters (water quality and NTP conditions: pH, initial concentration, temperature, background common ion, NOM, scavenger, gas type/flow rate, discharge/reactor type, input power, and energy efficiency/yield) on the degradation of contaminants and their intermediates, (ii) assess the influences of different catalysts and hybrid systems on degradation, (iii) describe EDC and PPCP degradation along with their properties, and (iv) evaluate mineralization, pathway, and degradation mechanism of selected EDCs and PPCPs for different cases studied. Furthermore, areas of potential research in NTP treatment for the degradation of EDCs and PPCPs in aqueous solutions are recommended. It could be reasonably predicted that this review is valid for developing our understanding of the fundamental scientific principles concerning the catalytic NTP of EDCs and PPCPs, providing helpful and practical references for researchers and designers on the effective removal of EDCs/PPCPs and the optimized operation of catalytic NTP systems.
... At a dosage range of 10-15 g/L, the adsorption rate of both the PS and the CPC-PS slowed down with a final BPA removal efficiency of 65.8% and 90.2%, and a final DCP removal efficiency of 52.8% and 80%. The BPA adsorption showed a superior performance compared to the DCP adsorption, which might be ascribed to a higher hydrophobicity of BPA (Log o/w of 3.30) than DCP (Log o/w of 3.09) (Ding et al. 2016;Joseph et al. 2011). The above results clearly corroborated the enhanced BPA and DCP adsorption onto the CPC-PS. ...
Using biomass wastes as adsorbents is a promising option for organic waste reclamation, but unfortunately, their adsorption capacity is usually limited, especially for hydrophobic organic pollutants. To address this issue, this work prepared cetylpyridinium chloride (a cationic surfactant)-modified pine sawdust (CPC-PS) and further demonstrated their performance for hydrophobic bisphenol A (BPA) and 2,4-dichlorophenol (DCP) adsorption. Compared to the PS, the CPC-PS improved the maximum adsorption capacity for BPA and DCP by approximately 98% and 122%, respectively. The kinetic and thermodynamic analyses showed that the BPA and DCP adsorption onto the CPC-PS fitted the pseudo-second-order kinetics and the Freundlich model. After regeneration using NaOH, the adsorption capacity of the CPC-PS for BPA still maintained 80.2% of the initial value after five cycles. Based on the experimental results, the CPC-PS was proposed to enhance the BPA and DCP adsorption through the solubilization of hemimicelles for hydrophobic organic pollutants, the π-π stacking between benzene-ring structures, and the hydrogen binding between the adsorbents and the pollutants. This work provides a viable method to use surfactant-modified pine sawdust as effective adsorbents to remove hydrophobic pollutants.
... Other materials (e.g., zeolite, clays) are effective adsorbents for landfill leachate treatment comparable with AC (Augusto et al., 2019;Halim et al., 2010;Joseph et al., 2011;Modin et al., 2011;Singh et al., 2012), but cost-efficiency and/or lack of information on scaling-up applications have impeded their wider application. This highlights a current knowledge gap and an opportunity for future research. ...
Sanitary landfill is the most popular way to dispose solid wastes with one major drawback: the generation of landfill leachate resulting from percolation of rainfall through exposed landfill areas or infiltration of groundwater into the landfill. The landfill leachate impacts on the environment has forced authorities to stipulate more stringent requirements for pollution control, generating the need for innovative technologies to eliminate waste degradation by-products incorporated in the leachate. Natural attenuation has no effect while conventional treatment processes are not capable of removing some the pollutants contained in the leachate which are reported to reach the natural environment, the aquatic food web, and the anthroposphere. This review critically evaluates the state-of-the-art engineered materials and technologies for the treatment of landfill leachate with the potential for real-scale application. The study outcomes confirmed that only a limited number of studies are available for providing new information about novel materials or technologies suitable for application in the removal of pollutants from landfill leachate. This paper focuses on the type of pollutants being removed, the process conditions and the outcomes reported in the literature. The emerging trends are also highlighted as well as the identification of current knowledge gaps and future research directions along with recommendations related to the application of available technologies for landfill leachate treatment.
... This is followed by hydrogen bonding and hydrophobic interaction. Our result is consistent with other studies which attribute π-π interaction and hydrogen bonding as main interactions in adsorption-based removal of hormonal contaminants (Bope et al. 2018;Joseph et al. 2011;Han et al. 2013b). Therefore, future functionalisation of the polymeric membrane adsorbents can take advantage of these observed intermolecular interactions to include aromatic and hydrogen bond moieties for better retention of EE2 and other hormonal contaminants. ...
The increasing occurrence of steroidal hormone micropollutant in the aquatic environment and their associated consequences have caused serious environmental concerns globally. Adsorptive removal of hormonal pollutants using polymeric membranes has been suggested but information on their performance in various environmental conditions is lacking. In this study, we examined the effect of salinity on the performance of polyethersulfone (PES) membrane to remove synthetic hormone 17α-ethinyl estradiol (EE2) from water. Our results show that an increase of salinity from 0 to 3% results in higher retention of EE2 onto PES membrane from 79.3 to 98.7%. The experimental results fit the Freundlich isotherm model better as compared to the Langmuir model. The Freundlich parameters n and K f yielded the highest values at 3% salinity. The molecular simulation results suggest that a high salinity increases the binding energy between EE2 and PES membranes, promoting the PES-EE2 interaction through π – π interaction, hydrogen bonding and hydrophobic interaction. This study provides valuable information for improving design of specialised treatment facilities (in farming, pharmaceutical industries, etc.) to allow better removal of EE2 and other low-polar organic contaminants from water via a membrane-based sorption-elution method, and we recommend the inclusion of salinity as a factor in modelling the adsorption capacity of membranes to prevent the oversaturation of membrane and minimise the release of contaminants into the environment.
... Rights reserved. of vertebrates by disrupting the function of hormone and endocrine systems [1]. Currently, many EDCs can be found in wastewater and landfill leachates [2,3]; bisphenol A (BPA), a typical EDCs, is found in many products, such as food, beverage packaging, paper coatings and flame retardants because it is the main additive in polycarbonates, acrylic esters and epoxy resins, which are widely used in the industrial production of plastic food containers and metal can linings. With the extensive usage of BPA and its constant release into the environment, it has become a general toxic pollutant in various environmental media. ...
To prepare a robust biocatalyst and enhance the removal of bisphenol A in wastewater, succinic anhydride was reacted with laccase to obtain succinic anhydride-modified laccase (SA-laccase) and then co-crystallized with Cu3(PO4)2 to form SA-laccase@Cu3(PO4)2 hybrid nanoflowers (hNFs). The activity of SA-laccase@Cu3(PO4)2 reached 5.27 U/mg, 1.86-, 2.88- and 2.15-fold those of bare laccase@Cu3(PO4)2, laccase@Ca3(PO4)2 and laccase@epoxy resin, respectively. Compared with free laccase, the obtained hNFs present enhanced activity and tolerance to pH and high temperature in the removal of BPA. Under the optimum conditions of pH 6.0 and 35 °C, BPA removal reached 93.2% using SA-laccase@Cu3(PO4)2 hNFs, which was 1.21-fold of that using free laccase. In addition, the obtained SA-laccase@Cu3(PO4)2 hNFs retained nearly 90% of their initial catalytic activity for BPA removal after 8 consecutive batch cycles. This efficient method for preparing immobilized laccase can also be further developed and improved to acquire green biocatalysts for removing persistent organic pollutants in wastewater.
Graphic abstract
... EDCs are other kinds of water pollutants that arouse the world concern owing to their immense presence in the aquatic ecosystem as well as harmful effect to human beings (Jung et al. 2015;Katsigiannis et al. 2015). EDCs are very dangerous to animals and humans due to their ability to mimic the biological activity of natural hormones in living things (Batra et al. 2019;Joseph et al. 2011). A common representative organic contaminant among EDCs, bisphenol A, has persistence features in the aquatic environment and in human beings (Calafat et al. 2005;Calafat et al. 2008). ...
For a potential and efficient solution in the mitigation of aquatic pollution, this study reported a well-designed and developed protected granulated activated carbon (GAC) material which ensures high strength property and adsorption performance to meet the industrial application. The prepared GAC material was shaped into a spherical core using natural binders basically assumed to constitute waste solids materials. Then after, the granulated carbon core (GAC core) was protected by a porous ceramic shell which confined the material with strong protection and high mechanical strength to resist against degeneration and pressure drop as a limiting factor for most sorbents employed in solution. The CSGAC characterization results proved that the ceramic shell has a smaller thickness (0.1 cm), good mechanical strength (2.0 MPa), and additionally, it presents larger porous channels which promote the fast and higher adsorption performance making it the desired material for the application in the real liquid environment. The test results showed that the prepared material had higher removal of triclosan (TCS) (30–40 mg/L) than BPA counterpart from the aqueous solutions. Moreover, it showed higher adsorption performance compared to the unprotected carbon materials. Furthermore, the mechanisms of BPA and TCS adsorption by core-shell granulated activated carbon (CSGAC) were discussed.
Water treatment plays a crucial role in meeting the growing demand for water and preventing future shortages. The unique and adaptable arbitrary, physical, and chemical properties of carbon nanotubes (CNTs) make them an attractive candidate for use in water treatment. CNTs are employed in environmental applications because of their exceptional adsorbent, mechanical, and chemical characteristics. Functional groups chemically or physically modify pure CNTs, improving their desalination and extraction capabilities. The advantages of CNT-based composites, such as antifouling performance, excellent selectivity, and higher water permeability, reassure us of their effectiveness in water treatment. This review comprehensively discusses the structural features and synthetic methods of CNTs. The functionalization and the pros and cons of functionalized CNT materials are also discussed. Pharmaceutical compounds are often manufactured using batch processes, resulting in the production of various products in waste-water. The occurrence of pharmaceutical compounds in drinking water arises from two distinct origins: the pharmaceutical industry's manufacturing procedures and the widespread use of pharmaceutical compounds, which leads to their presence in urban and agricultural waste-water. This review discusses role of CNT-based nano-materials in effectively removing pharmaceutical waste from wastewater through adsorption and photocatalytic processes. Lastly, the future approach is discussed to develop CNT-based nanomaterials better.
Pharmaceutical drugs, including antibiotics and hormonal agents, pose a significant threat to environmental and public health due to their persistent presence in aquatic environments. Colistin (KOL), fluoxetine (FLUO), amoxicillin (AMO), and 17-alpha-ethinylestradiol (EST) are pharmaceuticals (PhCs) that frequently exceed regulatory limits in water and wastewater. Current removal methods are mainly ineffective, necessitating the development of more efficient techniques. This study investigates the use of synthetic zeolite (NaP1_FA) and zeolite-carbon composites (NaP1_C), both derived from fly ash (FA), for the removal of KOL, FLUO, AMO, and EST from aquatic environments. Batch adsorption experiments assessed the effects of contact time, adsorbent dosage, initial concentration, and pH on the removal efficiency of the pharmaceuticals. The results demonstrated that NaP1_FA and NaP1_C exhibited high removal efficiencies for all tested pharmaceuticals, achieving over 90% removal within 2 min of contact time. The Behnajady-Modirshahla-Ghanbary (BMG) kinetic model best described the adsorption processes. The most effective sorption was observed with a sorbent dose of 1–2 g L⁻¹. Regarding removal efficiency, the substances ranked in this order: EST was the highest, followed by AMO, KOL, and FLUO. Sorption efficiency was influenced by the initial pH of the solutions, with optimal performance observed at pH 2–2.5 for KOL and FLUO. The zeolite-carbon composite NaP1_C, due to its hydrophobic nature, showed superior sorption efficiency for hydrophobic pharmaceuticals like FLUO and EST. The spectral analysis reveals that the primary mechanism for immobilizing the tested PhCs on zeolite sorbents is mainly due to physical sorption. This study underscores the potential of utilizing inexpensive, fly ash-derived zeolites and zeolite-carbon composites to remove pharmaceuticals from water effectively. These findings contribute to developing advanced materials for decentralized wastewater treatment systems, directly addressing pollution sources in various facilities.
Recently, emerging nanoadsorbents, such as graphene/(reduced) graphene oxide (GO)-based nanomaterials, have been prepared and used in different environmental applications, particularly water purification. This study is a review of the research progress on adsorption mechanisms for bisphenol A removal, which is significantly influenced by the physicochemical properties of various graphene/(reduced) GO-based nanomaterials and water quality conditions. In addition, this study presents the beneficial knowledge for the application of these nanomaterials for water purification. Results on the removal of bisphenol A and several other comparable contaminants using various graphene/(reduced) GO-based nanoadsorbents suggest that their removal can vary significantly depending on the properties of compounds or adsorbents and water chemistry conditions. Therefore, the bisphenol A adsorption performance of these nanomaterials is discussed: (i) to evaluate the overall adsorption capacities of various graphene/(reduced) GO-based nanomaterials based on the properties of nanomaterials and comparable contaminants; (ii) to summarize the influences of main water quality factors, such as pH, temperature, background ions/alkalinity, and natural organic matter or other organics, on adsorption; (iii) to discuss the key mechanisms that affect adsorption on these nanomaterials; and (iv) to describe the possible desorption and reusability of these carbon-based nanomaterials.
Bisphenol A (BPA), an endocrine-disrupting compound with estrogenic behavior, is of great concern within the scientific community due to its high production levels and increasing concentration in various surface aquifers. While several materials exhibit excellent capacity for the photocatalytic degradation of BPA, their powdered nature and poor chemical stability render them unsuitable for practical application in large-scale water decontamination. In this study, a new class of nanocomposite membranes based on sulfonated polyethersulfone (sPES) and multiwalled carbon nanotubes decorated with TiO2 nanoparticles (MWCNTs-TiO2) were investigated as efficient and scalable photocatalysts for the photodegradation of BPA in aqueous solutions. The MWCNTs-TiO2 hybrid material was prepared through a facile and inexpensive hydrothermal method and extensively characterized by XRD, Raman, FTIR, BET, and TGA. Meanwhile, nanocomposite membranes at different filler loadings were prepared by a simple casting procedure. Swelling tests and PFG NMR analyses provided insights into the impact of filler introduction on membrane hydrophilicity and water molecular dynamics, whereas the effectiveness of the various photocatalysts in BPA removal was monitored using HPLC. Among the different MWCNTs-TiO2 content nanocomposites, the one at 10 wt% loading (sP-MT10) showed the best photoactivity. Under UV irradiation at 254 nm and 365 nm for 240 min, photocatalytic oxidation of 5 mg/L bisphenol A by sP-MT10 resulted in 91% and 82% degradation, respectively. Both the effect of BPA concentration and the membrane regenerability were evaluated, revealing that the sP-MT10 maintained its maximum BPA removal capability over more than 10 cycles. Our findings indicate that sP-MT nanocomposite membranes are versatile, scalable, efficient, and highly reusable photocatalysts for the degradation of BPA, as well as potentially for other endocrine disruptors.
The present study investigated the use of a nanocomposite, produced by reinforcing nanosize zinc ferrite (ZnFe2O4) in a porous β-CD based polymeric matrix (β-CD-E-T/ZnFe2O4), for the removal of Bisphenol A (BPA) from aqueous solutions via adsorption. The thermal stability of the β-CD-based polymer and β-CD-E-T/ZnFe2O4 nanocomposite were investigated using simultaneous thermal analysis at four heating rates. Non-isothermal isoconversion methods were employed to study the thermal degradation kinetics of the β-CD based polymer before and after ZnFe2O4 nano-filling. The results showed that ZnFe2O4 nano-reinforcement increased the activation energy barrier for the thermal degradation of the β-CD-based polymeric matrix. Adsorption experiments showed that the β-CD-E-T/ZnFe2O4 nanocomposite exhibited very high BPA adsorption within 5 minutes. Isotherm, kinetics, and thermodynamic investigations revealed that the adsorption of BPA was via multilayer adsorption on a heterogeneous β-CD-E-T/ZnFe2O4 surface. The thermodynamic studies indicated that BPA adsorption on β-CD-E-T/ZnFe2O4 was spontaneous and exothermic. Overall, the β-CD-E-T/ZnFe2O4 nanocomposite showed less thermal degradation and high efficiency for removing BPA from contaminated water, indicating its potential as a promising material for wastewater treatment applications.
Emerging contaminants are characterized by toxicity, environmental durability, and bioaccumulation. How to effectively remove them has attracted tremendous attention in the field of environmental science and engineering. Nanomaterial-microbe coupling systems driven by photo-electrochemistry have high degradation efficiency and low cost by combining the advantages of nanomaterials and microorganisms in pollutant treatment. This review summarizes the recent development of the nanomaterial-microbe system for the removal of emerging contaminants, which is divided into exogenous nanomaterial-microbe and endogenous nanomaterial-microbe. The interaction mechanism of materials and microorganisms is addressed from the particular perspective of extracellular electron transfer and redox reactions, and the advantages and challenges of the pollutants treatment are analyzed. Furthermore, future applications in the degradation of emerging contaminants in environmental fields have been prospected.
Multi-walled carbon nanotube (MWCNT) were synthesized using ethyl acetate and waste cooking oil as more green and sustainable carbon sources, and further successfully applied for the adsorption of norfloxacin and 17α-ethinylestradiol.
Endocrine disrupting chemicals (EDCs) are emerging water contaminants and efficient elimination is a greater challenge for environmental engineers. The present communication is intended to synthesize the novel dense nanocomposite materials precursors to the bentonite and 3-mercaptopropyletrimethoxy silane/or 3-aminopropyletriethoxy silane. The materials are highly dense, hence the surface area is significantly reduced compared to the pristine bentonite. Further, the materials are intended to be utilized in the elimination of one of the important EDC 17α-ethinylestradiol (EE2). The sorption mechanism is greatly demonstrated based on various parametric studies. It is shown that grafted silane with bentonite network provides enhanced hydrophobicity with organophilic nature and greatly favors the uptake of EE2 at a wide range of pH (5.0–10.0). Relatively rapid uptake of EE2 by the nanocomposite solids followed by a pseudo-second-order kinetic model indicated that the materials are highly efficient for elimination of EE2. Increasing the concentration of EE2 (1.0 to 10.0 mgL−1) favored the extent of removal of EE2 and followed the Langmuir adsorption isotherm. Further, the increase in background electrolytes by 1,000 times did not affect the removal of EE2 by these nanocomposites, indicating the sorbing species are attracted with relatively stronger forces. Moreover, the simultaneous presence of several co-ions did not affect the percentage elimination of EE2; this, perhaps, shows an enhanced selectivity of materials towards the 17α-ethinylestradiol. A high loading capacity of EE2 is achieved under column reactor operation using these nanocomposites. Additionally, the materials are promising in the real matrix treatment.
Herein, we report an integrated coagulation/ photo-Fenton (CPF) process for advanced treatment of mature landfill leachate using nascent aluminum ions as coagulant and hydrogen peroxide (H2O2) as oxidant for Fenton reaction, which were in-situ produced by a novel chlorine and nitrogen co-doped aluminum-graphite (Cl, N-Al-Gr) composite. The coagulation of the MBR-treated landfill leachate was performed by nascent aluminum ions generated in Cl, N-Al-Gr/O2 system; and the resulting coagulation effluent was treated by photo-Fenton oxidation in the presence of ultraviolet (UVA). The Cl, N-Al-Gr composite exhibited excellent performance for in-situ H2O2 production (813.9 mg/L). The humic substances in landfill leachate could promote the cycle of Fe³⁺/Fe²⁺, and the removal efficiency of total organic carbon (TOC) and color was 88.1% and 97.6%, respectively under the optimized condition. The current study suggested that “coagulation + Fenton” process using nascent Al³⁺ as coagulant and in-situ generated H2O2 for Fenton oxidation could be a new way for wastewater treatment.
In this paper, five recombinant strains: GS115-LacA, GS115-LacB, GS115-LacC, KM71H-Lcc1 and GS115-Lcc2 were selected to produce laccase isozymes with high activities, which reached 13,001 U/L, 10,254 U/L, 11,495 U/L, 9924 U/L and 10,031 U/L on 15th, respectively. Then, we investigated the specificity of several recombinant laccase isozymes for the degradation of endocrine disrupting chemicals (phenolic compounds). The results showed that LacB had the most efficient in degradation of bisphenol A and octyl phenol, while Lcc1 degraded 4-n-octylphenol, gossypol and hydroquinone better. Finally, the effects of degradation conditions were optimized, which shown that the degradation rates of phenolic compounds increased with the optimum temperature and pH by different laccases were different, which were closely related to their enzymatic properties. Under the optimum reaction conditions, the degradation rate of bisphenol A, gossypol, 4-n-octylphenol, octyl phenol and hydroquinone were 95.4%, 93.2%, 89.6%, 71.0% and 91.9% at 8 h, 8 h, 12 h, 24 h and 1 h, respectively. Furthermore, the recombinant laccases were used to degrade phenolic compounds in several laccase/mediator systems, which ABTS and vanillin showed most enhancement on degradation rates and reduction of degradation times. In LacB-ABTS and Lcc1-guaiacol/vanillin systems, the degradation rates of five phenolic compounds reached the maximum with totally 100% within 4 h. All of the results open up promising perspectives for the degradation and oxidative biotransformation of typical phenolic pollutants in the environment.
Graphical Abstract
Landfill leachate poses significant risks to the environment and human health if not managed properly due to its potential to contaminate soil, ground, and surface waters. Consequently, effluent standards for landfill leachate have been continuously reviewed to manage these risks. A combination of treatment techniques (e.g., physico-chemical and biological) are usually required to treat landfill leachate due to its complexity, variability, and potentially high concentrations of pollutants. This review considers the various types of techniques used to treat landfill leachate/leachate concentrate, including advanced oxidation process (AOP), membrane bioreactor, denitrification, biofilm reactors, and electrocoagulation. The occurrence and treatment of emerging contaminants in landfill leachate, and opportunities for development are also considered. The review covers the basic principles through to the latest developments in research, including the effectiveness of engineering applications, their economic and technical challenges, together with current gaps in the knowledge and the prospects for leachate treatment. A systematic review of the technical characteristics of the engineering applications, used in leachate membrane concentrate treatment, showed that low-energy direct heat transfer evaporation technology had good prospects for future development. Refractory organic compounds, high concentrations of ammonia, high salinity, and concentrated leachate were of high concern. Hence, extensive research has been conducted on the degradation of refractory organic compounds using various AOPs, and the denitrification of ammonia species by novel biological pathways (e.g., anaerobic ammonium oxidation, short-cut denitrification processes). Despite the significant number of promising laboratory scale applications, further research is needed to demonstrate their effectiveness on a commercial/large scale.
Pharmaceuticals, steroids, personal care products, and disruptive endocrine substances are increasingly being used for healthcare objectives and to improve living conditions, resulting in the widespread presence of micropollutants in various water sources. Traditional water/ sewage and wastewater treatment plants are limited in their ability to cope with faced with these pollutants, making it challenging to supply safe and clean water for drinking and other domestic purposes. In this review, carbon nanotubes (CNTs) and CNTs related composites/ membranes have been considered suitable for settling this emerging issue. The existence of emerging micropollutants and their deleterious effects on human and animal health are discussed in this review. The efficient removal of micropollutants from different water sources using different types of CNTs (pristine/ functionalized) and CNTs-based composites/ membranes have been reviewed and evaluated. Moreover, fabrication approaches CNTs- based composites/membranes are also presented with their merits and demerits. Lastly, the current barriers and future perspectives are discussed in detail. The present review provides an in-depth understanding of the removal of micropollutants from CNTs and CNTs related composites/ membrane and allows future researchers to resolve the barriers related to their applications at an industrial scale.
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.
The phytoremediation of phenolic endocrine disrupting compounds (EDCs) in coastal waters by intertidal macroalgae was firstly investigated. The results showed that intertidal macroalgae could remove bisphenol A (BPA) and nonylphenol (NP) at environmental relevant concentration, and Ulva pertusa was the most efficient one. In most cases, the order of EDCs removal efficiency could be expressed as: green algae > brown algae > red algae. The in-situ monitoring using a charge‐coupled device imaging system confirmed the accumulation of EDCs in the intertidal macroalgae. The removal mechanisms included the initial rapid biosorption process, followed by the slow accumulation and biodegradation. The removal efficiency of BPA and NP was slightly dependent on temperature and nutrient concentration. A linear relationship was observed between the initial concentration and the average removal rate (R² > 0.99). The BPA and NP at the environmental relevant concentration (100 μg L⁻¹) could be removed efficiently using Ulva pertusa even after three cycles in pilot-scale experiments. The high removal efficiency of NP and BPA was also confirmed by the field investigation from the intertidal zone with abundant Ulva pertusa. These findings demonstrated that intertidal macroalgae could play essential role for the phytoremediation of phenolic EDCs in coastal waters.
This work reports the synthesis of mesoporous carbon using the solvent-free soft template method and their application for the adsorption of the emerging contaminant 17α-ethinylestradiol. For the first time, for the flexible solvent-free method, we evaluated how the precursor carbon/surfactant ratio (p/s), heating rate, stabilization time and self-assembly temperature, can influence textural properties of the materials. According to the results, the carbon source/surfactant ratio was the one which influenced textural characteristics most. The materials synthesized in p/s-1 had a smaller medium pore diameter (3.4 nm) while materials synthesized in p/s-0.5 showed an average diameter of larger pores (4.9 nm). Transmission micrographs indicated the formation of two types of pore ordering: wormholes and honeycombs. However, despite some differences in pore ordering, all materials showed textural quality. We found that the adsorption of 17α-ethinylestradiol is more affected by the diameter, volume and mesoporous content than by the type of pore ordering. Thus, materials with a high diameter and mesoporous content showed 99% removal with a maximum adsorption capacity of 157 mg/g. Also, the adsorption capacity of the material remained almost 100% until the fourth cycle and above 85% until the tenth cycle.
Wastewater features-directed design of an adsorbent is promising but challenging strategy for sustainable remediation of actual bisphenol A (BPA)-polluted water. Herein, we report that the discarded cigarette butt-derived porous carbon (AC-800) exhibit high capacity (865 mg/g), rapid reaction rate (186.9 mg/g/min) and outstanding durability for adsorption of BPA. Different from the most reported carbon-based adsorbents, quantitative structure-activity relationship studies unveil that graphitic defect plays a crucial role in the improvement of adsorptivity. Further studies illuminate that π-π interactions, electrostatic attraction and hydrogen-bond interaction play a negligible role whereas long-range hydrophobic interaction synergized with short-range dispersion force make a substantial contribution to BPA adsorption on AC-800. Benefited from this unique adsorption mechanism, AC-800 features a remarkable anti-interference capability and realizes the efficient clean-up of BPA from actual wastewater with complex backgrounds. This work sheds new light on mechanistic insight into the BPA adsorption on carbon-based materials and develops a fit-for-purpose designed adsorbent toward green remediation of practical wastewater.
The wide application of endocrine disruptors (EDs) has recently created great public concerns because of their toxicities. Previous studies have stated that the effect of oxygen-containing functional groups of carbon nanotubes (CNTs) for Bisphenol A (BPA) sorption, but no study has been quantified the exact contribution of the oxygen-containing functional groups. Moreover, the role of solvents on the adsorption of BPA should be considered. Considering the well properties of CNTs, graphitized (MG), carboxylated (MC) and hydroxylated (MH) multi-walled CNTs were selected as model adsorbents, BPA was used as model adsorbate. Solubility and single point adsorption coefficient (logKd) of BPA were n-hexadecane > water > methanol, suggesting that hydrophobic interaction was the main mechanism for BPA sorption on CNTs. For different functional groups of CNTs, π-π interaction between MH and BPA may be stronger than that of MC, and thus the sorption of BPA on MH was higher than that of MC. Moreover, hydrogen bond resulted in the higher adsorption of BPA on MH when compared with MC. The oxygen-containing functional groups of CNTs played a key role for BPA sorption in methanol because the values of contribution were 20%-45% for -OH and were 5% -25% for -COOH. In n-hexadecane, other factors such as hydrophobic interactions should be considered because the contribution percentages of -OH were ca.15% and the values for -COOH were ca.10%. The results are expected to provide important information on the interaction of EDs and CNTs.
In the current scenario, the conservation of environment is an urge. Among various environmental hazards, the knocking area is waste water treatment. Scientists are constantly engaged in finding the advanced technology with high proficiency and low investment. One such technique called as nanotechnology has interesting application in the field of waste water treatment. However, information accessible is restricted. The present text reviews the application of various nano-materials for wastewater treatment techniques. The five main classes includes: First, Nano adsorbents like metal oxides, applied usually for removal of heavy metals. Second, nanomaterials of carbon used for effective adsorption and conduction process. Third, graphene-based nanoparticles for environmental remediation. Fourth, nanotubes have been used for effective removal of pollutants by means of, hybrid Nano membranes, Nano fibers and carbon nanotube membranes. Fifth is recyclable nano composites, mats, beads in water decontamination. Finally, some zero valent Nano sized metals showing strong adsorption capability and operational simplicity.
This paper discusses the application of nanomaterials in wastewater treatment. Such nanomaterial’s which affordable, eco-friendly are, and efficiently work at large scale is the need of hour.
With the industrial development, population increasing and climate change, water pollution becomes a critical issue around the world. As a result, the remediation of water pollution urgently calls for new advanced technologies. This review specifically deals with nanocatalysts and other nanomaterials for water remediation of organic pollutants. It systematically summarizes the types and structures of organic pollutants, and the classes of nanomaterials and their application for the remediation of organic pollutants in water. Unlike inorganic heavy metals that are of limited types of pollutants, organic molecules are more than millions with various functional groups, properties and applications. The organic contaminants generally contain pharmaceuticals, personal care products, endocrine disruptors, pesticides, detergents, organic dyes, and common industrial organic wastes. Nanomaterials used for organic pollutants remediation can be generally classified as inorganic nanomaterials (e.g. transition metal/metal oxide/metal sulfide nanoparticles, carbon-based nanomaterials) and organic molecule-based nanomaterials (e.g. metal-organic frameworks, nanomembranes, and organic polymer-based nanomaterials). Oxidation, adsorption, and degradation are the most common strategies employed for nanomaterials remediation of organic pollutants in water. The types of substrate activation modes involve coordination, electron transfer, photo-redox, radical reactions, adsorption, ligand activation, electrostatic, π-π, hydrophobic, acid-base, H-bonding interactions, and van der Waals interactions.
This work reports the use of an iron ore tailings from waste dam as a catalyst and support for carbon nanotubes synthesis and their application in the adsorption of the 17α-ethinylestradiol hormone. The synthesis was carried out by Chemical Vapor Deposition (CVD) in a Fluidized Bed system using: ethylene at temperatures of 500, 600 and 700 °C, and acetonitrile at 500, 600, 700, 800 and 900 °C. The transmission electron microscopy (TEM) results showed that the two higher temperatures in each case favored the formation of nanostructures like carbon nanotubes (CNTs), with good yields. The ethylene source generated classic tubular structures of multiple walls. On the other hand, acetonitrile provided the formation of tubes with less organization, known as bamboo like. This morphology was caused by the insertion of nitrogen into the graphite structure (doping), which originates from the carbon source. The adsorptive capacity of the materials for 17α-Ethinylestradiol removal ranging from 9.2 mg g-1 to 22.3 mg g-1. The kinetic and adsorption isotherm studies were also performed for the systems. As for kinetics, all of them presented pseudo-second order behavior. In relation to the type of isotherm, the systems showed Freundlich behavior, that is, the adsorption occurs in multiple layers. Finally, it was concluded that the use of an iron ore tail as a catalyst in the production of CNTs by CVD is feasible. The materials synthesized still had good adsorptive capacity for an emerging contaminant, thus this study allowed the investigation of two environmental problems.
The present study investigated the decontamination of bisphenol A (BPA) from water through the coupled adsorption-photodegradation process. A biogenic synthetic route for the fabrication of novel SnO2 quantum dot encapsulated carbon nanoflake (SnO2–CNF) as an integrated photocatalytic adsorbent (IPCA) has been proposed and characterized with sophisticated analytical techniques. The synergistic effect of SnO2–CNF nanocomposite for the removal of BPA has been established through detailed study of integrated adsorption-photodegradation process. The Langmuir adsorption capacity was found to be 250 mg/g which is ∼1.7 and ∼5.3 times higher than that of bare CNF and bare SnO2 respectively. The overall removal efficiency through the coupled adsorption-photodegradation process has also been found to be synergistically superior (∼98%) to CNF (∼72%) and SnO2 (∼46%). The removal process of BPA has been extensively studied using adsorption kinetics model, adsorption isotherm models, and photodegradation kinetics studies. The effect of pH and multiple cycles of utilization on the overall removal efficiency have also been investigated. Both hydrogen bonding and π- π interaction might be responsible for the efficient adsorption of bisphenol A over SnO2–CNF adsorbent. The electron-hole generation of SnO2 under UV illumination coupled with electron sinking ability of CNF might as well facilitate superior photocatalytic efficiency.
Short activated carbon fibers (ACF) with high surface area were fabricated via carbonization in N2 and activation in CO2 at high temperatures, with cellulose fibers as the raw materials. The obtained ACF were subsequently deposited into the support layer of a polyethersulfone (PES) ultrafiltration membrane by a facile filtration process to obtain the sandwich structured ACF-PES composite membrane. The hormone (17β-estradiol, E2) adsorption kinetics and isotherm of ACF in static conditions, as well as E2 removal by filtration with the ACF-PES composite membrane were investigated. In static conditions, ACF rapidly and efficiently adsorbs E2 evidenced by a high removal of >97 %. The fitting of second order kinetics and linear (Henry) adsorption isotherm models indicated the availability of easily accessible adsorption sites. Besides, such efficient E2 adsorption was contributed by many interactions between E2 and ACF, namely hydrophobic interactions, hydrogen bonding and π-π stacking. The incorporation of ACF in a PES membrane resulted in a minor loss of filtration flux compared with the control membrane, but significantly improved E2 removal through adsorption pathway. With only 1.0 mg ACF incorporated (loading 2.0 g/m2), the composite membrane could reject 76 % of E2 from a 100 ng/L solution at a flux of 450 L/m2∙h, demonstrating that ACF-PES can overcome the permeability-selectivity trade-off of traditional UF membranes.
Nowadays, sanitary landfilling is the most common approach to eliminate municipal solid waste, but a major drawback is the generation of heavily polluted leachates. These leachates must be appropriately treated before being discharged into the environment. Generally, the leachate characteristics such as COD, BOD/COD ratio, and landfill age are necessary determinants for selection of suitable treatment technologies. Rapid, sensitive and cost-effective bioassays are required to evaluate the toxicity of leachate before and after the treatment. This review summarizes extensive studies on leachate treatment methods and leachate toxicity assessment. It is found that individual biological or physical-chemical treatment is unable to meet strict effluent guidelines, whereas a combination of biological and physical-chemical treatments can achieve satisfactory removal efficiencies of both COD and ammonia nitrogen. In order to assess the toxic effects of leachate on different trophic organisms, we need to develop an appropriate matrix of bioassays based on their sensitivity to various toxicants and a multispecies approach using organisms representing different trophic levels. In this regard, a reduction in toxicity of the treated leachate will contribute to assessing the effectiveness of a specific remediation strategy.
In this study, the original Bohart-Adams model was employed to analyze the experimental data of 17α-ethinylestradiol (EE2) separation in lab-scale anthracite columns with low initial concentration. Besides, the assumptions for the simplified Bohart-Adams model were calculated and discussed. The results revealed that the breakthrough curves of EE2 separation in anthracite columns under different conditions were asymmetrical N-shaped and could be divided into three parts. The third part of the breakthrough curves was successfully fitted by the original Bohart-Adams model with high R2 values (higher than 0.918) and low ARS values (less than 0.141). As expected, the assumptions for the simplified Bohart-Adams model were not tenable during the whole experiment process. As a result, the EE2 separation capacities (N0° and N0s) obtained from the original and simplified Bohart-Adams model were quite different, and most N0° values were greater than N0s values. The N0° value used to evaluate the pollutant separation capacity in lab-scale column would be more accurate. In addition, physical interception and chemical adsorption simultaneously worked in the EE2 separation in anthracite columns. Physical interception and bed depth in anthracite columns at low flow rate were related in quadratic function (R2 > 0.988).
Magnetic vermiculite-modified (MV) by poly(trimesoyl chloride- melamine) (MP) was synthesized and used as a novel proficient adsorbent for the treatment of water/wastewater including bisphenol A (BPA) as a toxic pollutant. The MV-MP adsorbent was synthesized by loading of Fe2O3 nanoparticles and then modified with trimesoyl chloride and melamine by interfacial polymerization method. The developed adsorbent was analyzed morphologically and chemically by FTIR, SEM, as well as EDX techniques. The impacts of studied experimental parameters on the adsorption yield were examined by factorial design analysis. The isotherm model investigations showed that the Langmuir isotherms were the best fits for BPA compared to the Freundlich isotherm. The kinetic findings demonstrated that the pseudo-second-order (PSO) kinetic model showed a better correlation with the adsorptions of BPA than the pseudo-first-order (PFO) model. The thermodynamic results verified that the BPA adsorption on MV-MP was preceded via a spontaneous and exothermic process under the considered temperature conditions. The MV and MV-MP composites had excellent removal ability with a maximum adsorption capacity of 174.81 and 273.67 mg g⁻¹, respectively. The adsorbent had a considerable adsorption/desorption capacity after seven reuse cycles. By taking into account of all results, it can be concluded that the synthesized MV-MP composite is a promising adsorbent for the remediation of BPA from polluted water/wastewater.
The extensive application of antibiotics in livestock industry inescapably leads to their release to the aquatic environment. The occurrence of multiple engineered nanomaterials (ENMs) in various water systems also has been widely observed. The interaction between the coexisting antibiotics and ENMs will affect their transport and fate in water. In this study, the adsorption of two representative veterinary antibiotics—tylosin (TYL) and sulfamethazine (SMT) by binary nano-adsorbents—carbon nanotubes (CNTs) and titanium dioxide nanoparticles (nTiO2) was investigated. Results exhibited that the adsorption behavior and mechanisms of TYL/SMT by the binary nano-adsorbents were highly pH-dependent. Under near-neutral condition (pH unadjusted), nTiO2 inhibited the adsorption of TYL/SMT by CNTs, mainly because of adsorption sites competition, weaker EDA interaction and less negatively charged CNT-nTiO2 clusters formation. Under acidic condition (pH 5.0), nTiO2 heteroaggregated with the oppositely charged CNTs via electrostatic attraction and generated large agglomerates, thus significantly decreased the possible adsorption sites of the adsorbents. Under alkaline condition (pH 8.0), nTiO2 inhibited the adsorption of TYL, but slightly promoted the adsorption of SMT, which resulted from the weaker electrostatic repulsion between the anionic SMT⁻ and the less negatively charged nTiO2. The adsorption behavior and mechanisms were also confirmed by the dynamic light scattering (DLS) and electrophoretic mobility (EPM) measurement, the transmission electron microscopy (TEM) images and the Derjaguin–Landau–Verwey–Overbeek (DLVO) calculation. The observations of this study highlighted the mechanisms controlling the adsorption affinity between antibiotics and binary nano-adsorbents, and also opened up new horizons for the interaction and fate of nanomaterials and organic contaminants in the aquatic environment.
Numerous perfluoroalkyl and polyfluoroalkyl substances (PFASs) have been widely found in both wastewater effluent and drinking water worldwide; thus, these chemicals have become a global issue as emerging organic contaminants. Aliphatic PFASs with saturated carbon-fluorine bonds appear to be incompletely removed during conventional chemical/physical (coagulation, flocculation, sedimentation, and filtration) and biological (activated sludge) treatment processes. However, they can be effectively removed by advanced treatment technologies such as sorption, membranes, and oxidation. Thus, it is essential to understand the removal mechanisms of various PFASs during these advanced treatment processes, in particular because the physicochemical characteristics of various PFASs impose difficult challenges regarding determining the transport and fate of these compounds in aqueous solution. Several review studies have been conducted to evaluate the removal of PFASs in various drinking water treatment and environmental remediation processes. However, to the best of our knowledge, very little information is still available on the effects of water quality conditions on the removal of PFASs. Therefore, in this study, we comprehensively summarize the recent state of knowledge of selected advanced water treatment technologies (sorption, membrane, and oxidation) for the removal of PFASs under different water quality conditions (e.g., pH, temperature, background ions, natural organic matter, and solute concentration).
Porous carbon derived from amine-functionalized MIL-125 metal-organic framework (C-MIL-125-NH2) was prepared by carbonization at high temperature under inert atmosphere, and used for adsorption of bisphenol A (BPA) and 4-tert-butylphenol (4-tBP). The obtained carbon showed bimodal porosity and fast extraction of both pollutants in batch conditions following a pseudo-second-order model. The adsorption mechanism was studied by the measurement of zeta potential, and the results suggested that π-π stacking interactions between the carbon material and the phenol molecules probably are the main sorption mechanism. The prepared C-MIL-125-NH2 was incorporated into mechanically stable membranes for flow-through solid-phase extraction of studied phenols prior to HPLC analysis. The hybrid material showed excellent permeance to flow, easy regeneration and good performance for the simultaneous enrichment of mixtures of BPA and 4-tBP, facilitating their determination when present at low concentration levels.
Novel nanomaterials for bioassay applications represent a rapidly progressing field of nanotechnology and nanobiotechnology. Here, we present an exploration of single-walled carbon nanotubes as a platform for investigating surface-protein and protein-protein binding and developing highly specific electronic biomolecule detectors. Nonspecific binding on nanotubes, a phenomenon found with a wide range of proteins, is overcome by immobilization of polyethylene oxide chains. A general approach is then advanced to enable the selective recognition and binding of target proteins by conjugation of their specific receptors to polyethylene oxide-functionalized nanotubes. This scheme, combined with the sensitivity of nanotube electronic devices, enables highly specific electronic sensors for detecting clinically important biomolecules such as antibodies associated with human autoimmune diseases.
Numerous mathematical models have been developed to simulate processes governing leachate occurrence and behaviour in landfills. The emphasis of these models have generally been on estimating leachate quantity and quality in order to control its associated environmental impacts, particularly on ground and surface water pollution, enhance methanogenesis and landfill stabilization, and provide guidance in the design of leachate control, recirculation and collection systems. These models have been successful to a limited extent, more in estimating leachate quantity than its composition, because of inherent uncertainties associated with estimating model parameters that can adequately describe the complex biological, chemical, and physical processes in landfills. They become increasingly useful as more field data are obtained and used for calibration and validation purposes. This paper presents a review of mathematical models designed to simulate leachate generation and transport in municipal solid waste landfills. The paper also describes future needs and potential improvements to current modelling techniques.
The major potential environmental impacts related to landfill leachate are pollution of groundwater and surface waters. Landfill leachate contains pollutants that can be categorized into four groups (dissolved organic matter, inorganic macrocomponents, heavy metals, and xenobiotic organic compounds). Existing data show high leachate concentrations of all components in the early acid phase due to strong decomposition and leaching. In the long methanogenic phase a more stable leachate, with lower concentrations and a low BOD/COD-ratio, is observed. Generally, very low concentrations of heavy metals are observed. In contrast, the concentration of ammonia does not decrease, and often constitutes a major long-term pollutant in leachate. A broad range of xenobiotic organic compounds is observed in landfill leachate. The long-term behavior of landfills with respect to changes in oxidation-reduction status is discussed based on theory and model simulations. It seems that the somewhere postulated enhanced release of accumulated heavy metals would not take place within the time frames of thousands of years. This is supported by a few laboratory investigations. The existing data and model evaluations indicate that the xenobiotic organic compounds in most cases do not constitute a major long-term problem. This may suggest that ammonia will be of most concern in the long run.
For over 70 years, scientists have reported that certain synthetic and natural compounds could mimic nat-ural hormones in the endocrine systems of animals. These substances are now collectively known as en-docrine-disrupting compounds (EDCs), and have been linked to a variety of adverse effects in both humans and wildlife. More recently, pharmaceuticals and personal care products (PPCPs) have been discovered in various surface and ground waters, some of which have been linked to ecological impacts at trace con-centrations. The majority of EDCs and PPCPs are more polar than traditional contaminants and several have acidic or basic functional groups. These properties, coupled with occurrence at trace levels (i.e., ,1 mg/L), create unique challenges for both removal processes and analytical detection. Reports of EDCs and PPCPs in water have raised substantial concern among the public and regulatory agencies; however, very little is known about the fate of these compounds during drinking and wastewater treatment. Numerous studies have shown that conventional drinking and wastewater treatment plants can not completely remove many EDCs and PPCPs. Oxidation with chlorine and ozone can result in transformation of some com-pounds with reactive functional groups under the conditions employed in water and wastewater treatment plants. Advanced treatment technologies, such as activated carbon and reverse osmosis, appear viable for the removal of many trace contaminants including EDCs and PPCPs. Future research needs include more detailed fate and transport data, standardized analytical methodology, predictive models, removal kinetics, and determination of the toxicological relevance of trace levels of EDCs and PPCPs in water.
A recent study by the Toxic Substances Hydrology Program of the U.S. Geological Survey (USGS) shows that a broad range of chemicals found in residential, industrial, and agricultural wastewaters commonly occurs in mixtures at low concentrations downstream from areas of intense urbanization and animal production. The chemicals include human and veterinary drugs (including antibiotics), natural and synthetic hormones, detergent metabolites, plasticizers, insecticides, and fire retardants. One or more of these chemicals were found in 80 percent of the streams sampled. Half of the streams contained 7 or more of these chemicals, and about one-third of the streams contained 10 or more of these chemicals. This study is the first national-scale examination of these organic wastewater contaminants in streams and supports the USGS mission to assess the quantity and quality of the Nation's water resources. A more complete analysis of these and other emerging water-quality issues is ongoing.
Keywords:
pharmaceuticals;
hormones;
other wastewater contaminants;
steroids;
nonprescription drugs;
veterinary pharmaceuticals
Large numbers and large quantities of endocrine-disrupting chemicals have been released into the environment since World War II. Many of these chemicals can disturb development of the endocrine system and of the organs that respond to endocrine signals in organisms indirectly exposed during prenatal and/or early postnatal life; effects of exposure during development are permanent and irreversible. The risk to the developing organism can also stem from direct exposure of the offspring after birth or hatching. In addition, transgenerational exposure can result from the exposure of the mother to a chemical at any time throughout her life before producing offspring due to persistence of endocrine-disrupting chemicals in body fat, which is mobilized during egg laying or pregnancy and lactation. Mechanisms underlying the disruption of the development of vital systems, such as the endocrine, reproductive, and immune systems, are discussed with reference to wildlife, laboratory animals, and humans.
Endogenous and exogenous chemical signals have evolved as a means for organisms to respond to physical or biological stimuli in the environment. Sensitivity to these signals can make organisms vulnerable to inadvertent signals from xenobiotics. In this review we discuss how various chemicals can interact with steroid-like signaling pathways, especially estrogen. Numerous compounds have estrogenic activity, including steroids, phytoestrogens, and synthetic chemicals. We compare bioavailability, metabolism, interaction with receptors, and interaction with cell-signaling pathways among these three structurally diverse groups in order to understand how these chemicals influence physiological responses. Based on their mechanisms of action, chemical steroid mimics could plausibly be associated with recent adverse health trends in humans and animals.
Water scarcity and pollution rank equal to climate change as the most urgent environmental issue for the 21st century. To date, the percolation landfill leachate into the groundwater tables and aquifer systems which poses a potential risk and potential hazards towards the public health and ecosystems, remains an aesthetic concern and consideration abroad the nations. Arising from the steep enrichment of globalization and metropolitan growth, numerous mitigating approaches and imperative technologies have currently drastically been addressed and confronted. Confirming the assertion, this paper presents a state of art review of leachate treatment technologies, its fundamental background studies, and environmental implications. Moreover, the key advance of activated carbons adsorption, its major challenges together with the future expectation are summarized and discussed. Conclusively, the expanding of activated carbons adsorption represents a potentially viable and powerful tool, leading to the superior improvement of environmental conservation.
Various heavy metals in the landfill leachates were measured up to very low concentration levels of micrograms per litre. Though no violation to Japanese effluent standards was found in respect of individual metal, leachate or treated leachate it still contains higher concentrations of total heavy metals than surrounding water environment. The effluent concentration after treatment was of the same order as raw leachate. Maximum metal solubilities in leachate were calculated taking the presence of inorganic metal complexes into account. Solubilities of metals were high enough and they were not the limiting factor determining concentrations after coagulation. The coagulation with higher pH was not successful in reducing concentration of leachate - origin - metals contrary to the case of pure chemical metals. The heavy metals especially nickel and copper in the leachate were associated with organic matter and consequently they remained in solution unless organic matter was removed. Application of nanofiltration to leachate treatment was studied. It was possible to separate metals from less toxic salts by low retention nanofiltration membranes.
Landfill bioreactor technology offers important advantages in the management and treatment of municipal solid waste, including accelerated waste stabilization rates, enhanced gas production, facilitated leachate management, volume reduction and minimized long-term liability. These advantages have been documented in laboratory- , pilot- and full-scale investigations. Although challenges remain in implementing the technology, bioreactor landfills are designed and operated with increasing frequency. (C) 1994 ISWA
The generation of leachate and gas from landfills is a well documented phenomenon which impacts landfill design and operation. Leachate and gas production are both influenced by the contents of the landfill, the local climate, and the manner in which the facility is operated. Gas composition and volume will be discussed in this chapter as will leachate composition. The quantity of leachate produced from a landfill is a function of site surface hydrology, which in turn is a function of climate, the presence of groundwater and the numerous factors affecting infiltration of surface water into the landfill. Leachate quantity is discussed in a later chapter.
The huge number of landfills and the resulting seepage water leads to a negative influence on the ground water quality. Organic acids were isolated over a period of three years from anaerobic and aerobic leachate water and from model aquifers which were fed by the leachates. The amount of isolated DOC increased from the anaerobic samples to the aerobic ones. The characterization of the isolated acids clearly reflects an increase of the molecular weight and of the functional group content with increasing age of the landfill, and in the process of aerobic digestion. The results are not only of interest for a detailed understanding of the fate of organic material from landfill leachates and of the transport of pollutants in the groundwater, but represent a man-made influence on the genesis of humic substances.
廃棄物埋立処分場からの浸出水中に存在する化学物質を特徴づけるため, 400化合物以上を対象にガスクロマトグラフ―質量分析法を中心に用いて測定を行なった。外因性内分泌攪乱物質とされる化合物のうち, PCB, ダイオキシン, DDTなどの有機塩素系農薬のように疎水性の強い化合物の濃度は非常に低く, 周辺の環境水レベルであった。一方, プラスチックに関連すると思われるフタル酸エステル, ビスフェノールAやフェノール類などの外因性内分泌攪乱物質とされる化学物質は, 高い濃度で測定された。
Adsorption of 17 alpha-ethinyl estradiol (EE2) and bisphenol A (BPA) on carbon nanomaterials (CNMs) was investigated. Single point adsorption coefficients (K) showed significant relationship with specific surface areas of CNMs for both chemicals, indicating surface area is a major factor for EDC adsorption on CNMs. BPA adsorption capacity is higher than EE2 on fullerene and single-walled carbon nanotubes (SWCNT). Our molecular conformation simulation indicated that BPA has a unique ability to adsorb on the curvature surface of CNMs because of its "butterfly" structure of two benzene rings. The higher adsorption capacity of BPA over EE2 is well explained by considering helical (diagonal) coverage of BPA on the CNMs surface and wedging of BPA into the groove and interstitial region of CNM bundles or aggregates. The comparison of K(HW) (hexadecane-water partition coefficient) normalized adsorption coefficients between ENS and several polyaromatic hydrocarbons indicates that pi-pi electron donor-acceptor system is an important mechanism for the adsorption of benzene-containing chemicals on CNMs. The high adsorption capacity and strong desorption hysteresis of both chemicals on SWCNT indicate that SWCNT is a potential adsorbent for water treatment.
Naturally occurring, macromolecular dissolved organic matter (NOM) is known to foul activated carbon adsorbents, reducing the ability of fixed-bed adsorbers to efficiently remove targeted synthetic organic contaminants (SOCs). An accurate description of the effects of NOM competition on SOC adsorption equilibria is required to develop dynamic models, which have application to process design and analysis. A model was developed, using an approach based on the Ideal Adsorbed Solution Theory (IAST), to predict trichloroethylene (TCE) adsorption by activated carbon preloaded with humic acid. The IAST model was formulated for a bisolute system in which TCE and humic acid single-solute uptakes were described by the Langmuir-Freundlich and Freundlich isotherms, respectively. The humic mixture was modeled as a single component based on previous studies that identified the low-molecular-weight hydrophobic fraction as the most reactive with regard to preloading effects. Isotherms for this fraction, isolated from whole humic acid using ultrafiltration, were measured, and molar concentrations were computed based on an average molecular weight determined using size-exclusion chromatography. The IAST model was modified to reflect the hypothesis that TCE molecules can access adsorption sites which humic molecules cannot and that no competition can occur on these sites. The model was calibrated with data for TCE uptake by carbon preloaded with the low-molecular-weight humic acid fraction and was verified by predicting TCE uptake by carbon preloaded with whole humic acid. Further improvement to the model was possible by accounting for pore blockage as a mechanism which can reduce the effective surface area available in TCE.
A useful extraction for humic acid from anaerobic municipal solid-waste landfill leachate is presented. Extraction was accomplished by adding NaOH pellets to give a 0.57N NaOH solution under an N2 atmosphere. The separation of the humid and fulvic acid fractions was carried out using Matricel type filters (0.45-µm pore size diam). The infrared characterization of leachate humic acids was markedly improved in time and sample-size-requirement reductions by using a Matricel filter made out of a PVC copolymer as a support for these acids. The results obtained compared very favorably with the infrared KBr pellets. The infrared spectra of leachate humic acids proved to be similar to the lake-ooze humic acid spectra reported by Stevenson and Goh (1971).
Humid substances represent > 60% of the total organic C found in anaerobic landfill leachates. Fulvic acid predominates in young unstable leachates, and decreases in concentration with age. Humic acids increase with the age of the leachates, eventually decreasing as the leachate becomes more stable and diluted.
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Landfill leachate contains a variety of pollutants that may potentially contaminate the ground water and affect the quality of surface waters and well waters. The literature has been critically reviewed in order to assess the attenuation processes governing the contaminants in leachate‐affected aquifers. After an introductory section on leachate composition, the physical and chemical frameworks for the attenuation processes are discussed in terms of dilution/dispersion and redox zones in the plume, respectively. A separate section focuses on the microbiology in terms of the occurrence of bacteria in plumes, the fate of pathogens, and microbial mediation of redox processes. In individual sections, the attenuation of dissolved organic matter, anthropogenic‐specific organic compounds, inorganic macrocomponents as anions and cations, and heavy metals are discussed. The focus is on laboratory experiences and field investigations.
Two different types of leachate from a municipal waste tip have been analyzed. The first type of leachate was collected from a waste tip in the acidification stage. The organic load of this leachate was high and consisted mainly of free volatile acids (over 95% of the TOC). Volatile amines and ethanol were also present (0.8 and 0.7% of the TOC respectively). The leachate was extracted with hexane and the extract was analyzed with infrared and nuclear magnetic resonance spectroscopy and a gas chromatograph-mass spectrometer combination. In the extract alcohols, hydrocarbons, esters, terpenes and phthalates have been identified. High molecular weight compounds were present only in a low concentration.The second type of leachate was collected from a waste tip in the methane fermentation stage. The organic load was relatively low. An important part of the organics was identified as high molecular weight compounds. About 32% of the organic carbon consisted of compounds with a molecular weight over 1000. Acids, amines and alcohols could not be detected. This means that the organic compounds present were end products of degradation processes.Furthermore there was a remarkable difference in heavy metal content between the two types of leachate.
Landfill bioreactor technology offers important advantages in the management and treatment of municipal solid waste, including accelerated waste stabilization rates, enhanced gas production, facilitated leachate management, volume reduction andminimized long-term liability. These advantages have been documented in laboratory- , pilot- and full-scale investigations. Although challenges remain in implementing the technology, bioreactor landfills are designed and operated with increasing frequency.
Carbon nanotubes are novel and interesting nanomaterials in the field of nanometer research because of their many unique electronic, mechanical, and chemical properties. Therefore, the application of carbon nanotubes in analytical chemistry is of great interest. In our work, a trace enrichment method based on the application of multiwalled carbon nanotubes (MWNTs) as a solid‐phase extraction (SPE) sorbent for chlorobenzenes was developed. The SPE conditions affecting extraction recoveries, including the sample volume, the type of eluents, the volume, and the flow rate of eluent, were optimized. The adsorption characteristic was compared between MWNTs and current SPE sorbents, including C18 silica and activated carbon. The results showed that the adsorption capacities of MWNTs, C18 bonded silica, and activated carbon for 1,2‐dichlorobenzene at an equilibrium concentration of 90 µg/mL were 237, 189, and 150 mg/g, respectively. The results also showed that MWNTs had higher extraction recoveries for chlorobenzenes. This method would be applied to the determination of chlorobenzenes as well as persistent organic pollutants (POPs) in natural and polluted waters.
The flow inside an adsorption column for the treatment of landfill leachate is a poorly understood parameter due to lack of studies on its fluid dynamics. In order to address this matter, axial dispersion modelling was conducted to determine the flow pattern of landfill leachate in a column with palm shell-activated carbon (PSAC) as media. In addition, the treatment profile of leachate via adsorption onto PSAC in terms of chemical oxygen demand (COD) and turbidity removal as well as leachate pH was studied. Lithium chloride (LiCl) was used as a non-reactive tracer. The vessel dispersion number (D/uL) was determined to be between 0.01 and 1, implying small and slow dispersion occurring in a plug flow-like dynamics. The model was applicable for modeling of leachate flow inside a pack bed column. Empty bed contact time (EBCT) was utilized to determine the treatment profile with regards to COD and turbidity removal from leachate. The highest 50% breakthrough of COD removal at 1460mg/g was obtained at EBCT of 14.7min. The EBCT has no significant effect on turbidity removal and effluent pH.
Landfill Bioreactor Design and Operation covers the history and background of landfill technology, research studies of actual bioreactor landfills, expected leachate and gas yields, specific design criteria, operation guidelines, and reuse of landfill sites to avoid having to establish new sites. For anyone looking for an alternative to large, wasteful landfill sites, this book provides a practical alternative to the problem.
This study utilized carbon nanotubes (CNTs) to remove bisphenol A (BPA) from aqueous solution. The surfaces of CNTs were modified by SOCl2/NH4OH under microwave irradiation. The surface characteristics of as-grown and modified CNTs were analyzed by measuring zeta potential, and using a scanning electron microscope, a surface area analyzer and a Fourier transform infrared spectroscope. The specific surface area of modified CNTs exceeded that of as-grown CNTs. The pHiep values of as-grown CNTs and modified CNTs were determined to be 4.3 and 6.5, respectively. Some amine functionalities were formed on the surface of modified CNTs; therefore, the surface of the modified CNTs contained more positive charges than that of the as-grown CNTs. The adsorption kinetics were examined using pseudo first- and second-order models, intraparticle diffusion and Bangham's models. The equilibrium data were simulated using Langmuir, Freundlich, Dubinin and Radushkevich (D–R) and Temkin isotherms. The results reveal that the pseudo second-order model and Langmuir isotherm fit the kinetics and equilibrium data, respectively. The adsorption capacity of BPA on the surface of CNTs fluctuates very little with pH in the range of 3–9, suggesting the high stability of CNTs as an adsorbent for BPA over a rather wide pH range. The values of ΔH0 and ΔS0 were calculated to be −11.7kJ/mol and 46.1J/mol, respectively. The isotherm and thermodynamic simulations indicate that the adsorption of BPA onto as-grown CNTs proceeds by physisorption process.
Nanofiltration (NF) has attracted increasing attention during recent years due to the development of new applications. The advantage of NF compared with reverse osmosis (RO) and ultrafiltration (UF) is that it is possible to separate organic substances from some types of salts. It is, furthermore, also possible to separate different kinds of salts due to the negatively charged groups on the membrane. The retention of sulphate salts by the membranes used in this investigation was 88–96%, while the retention of chloride salts was only 12–47% at low salt concentrations. This difference in retention is due to the charge density of the anion. The retention of NaCl was found to be strongly related to the concentration. The retention decreased from 45% to 7% when the concentration was increased from 0.05 M to 1 M. Although the repulsion of the anion mainly determines the retention of salt solutions, it was observed that the cation can affect the retention, especially in salt solutions with a high concentration of monovalent anions. It was found that the retention of divalent cations was three times higher than that of monovalent cations in this type of salt solution. In chloride solutions with mixed cations, it was shown that a monovalent cation passed through the membrane preferentially to the divalent cations, to such an extent that the retention became negative. NF was utilized to treat a landfill leachate with an extremely high salt content from a waste cell containing mainly ash because of the good separation of cations. Most of the heavy metals, which are multivalent cations, are rejected while the monovalent cations, which are rather harmless substances, pass through the membrane. The retention of, for example, cadmium, zinc, lead and chromium was found to be higher than 70%, while the retention of potassium and sodium was less than 10%. Since the transmembrane osmotic pressure was low, due to the low retention of the monovalent ions, the flux was several times higher than for RO membranes. The flux of the leachate, with a conductivity of 6800 mS/m, was above 50 l/m2h at 3 MPa and 25°C.
Disposal of waste to landfill remains the most common means of waste management worldwide. The most serious environmental impact of waste disposal to landfill is contamination of local groundwater by the generated leachate. One measure designed to prevent this occuring is the classification of the nature of the waste (hazardous or nonhazardous) in order to determine the most appropriate means, of disposal. Of the numerous tests developed to classify solid waste, the toxicity characteristic leaching procedure (TCLP) is the most commonly used in Australia. This test was developed in the United States. Since its dissemination, the TCLP has been subject to extensive scrutiny. regarding its effectiveness as a compliance tool for waste classification, particularly in view of the advances in waste management practices over the past decade. Within Australia, concerns also exist regarding its applicability for Australian conditions. This review on landfill practices and waste classification found the TCLP to be. limited in its usefulness as a regulatory tool within Australia. Moreover, this review identified various gaps in the knowledge pertaining to landfills, leachate generation, and waste classification that necessitate action to improve waste management practices in the future.
Various heavy metals in the landfill leachates were measured up to very low concentration levels of micrograms per litre. Though no violation to Japanese effluent standards was found in respect of individual metal, leachate or treated leachate it still contains higher concentrations of total heavy metals than surrounding water environment. The effluent concentration after treatment was of the same order as raw leachate. Maximum metal solubilities in leachate were calculated taking the presence of inorganic metal complexes into account. Solubilities of metals were high enough and they were not the limiting factor determining concentrations after coagulation. The coagulation with higher pH was not successful in reducing concentration of leachate - origin - metals contrary to the case of pure chemical metals. The heavy metals especially nickel and copper in the leachate were associated with organic matter and consequently they remained in solution unless organic matter was removed. Application of nanofiltration to leachate treatment was studied. It was possible to separate metals from less toxic salts by low retention nanofiltration membranes.
Purpose
Carbon nanomaterials (CNMs) have attracted a great deal of research interest for their potential environmental applications because of their unique properties. Adsorption of organic chemicals on CNMs was reported to be important in controlling their environmental risks. However, the kinetics of the adsorption is hardly investigated in literature. The objective of this work was, therefore, to quantitatively describe the sorption kinetics of 17 α-ethinyl estradiol (EE2) and bisphenol A (BPA) on CNMs as compared to activated carbon (AC).
Materials and methods
Batch adsorption/desorption (kinetic) experiments were conducted, and different kinetic models were used to process experimental data and obtain kinetic parameters.
Results and discussion
CNM adsorption kinetics could be described well using the improved pseudo second order kinetics model, and negative relationships were observed between the equilibrium solid-phase concentration and the modified rate constant (k
2a*). The rearrangement of CNM aggregates after adsorbing high concentrations of adsorbates could be the reason of decreased adsorption rate with increasing EE2 or BPA loading on CNMs. The diffusion-controlled kinetic process seems not important for the adsorption of EE2 and BPA on CNMs; whereas, their adsorption on AC appears to be diffusion controlled, as indicated by a linear relationship between solid-phase concentration and t
0.5.
Conclusions
Single-walled carbon nanotubes adsorb large amounts of EE2 and BPA fast and retain them strongly. These results suggest that single-walled carbon nanotubes have potential for applications in the treatment and purification of water contaminated by the chemicals.
Municipal solid waste landfills represent an accumulation of material with less or more pollution potential. A part of this material is transfered to the environment by gas and leachate. To judge the environmental risk of landfills it is necessary to make statements about future emission streams. Today such statements are impossible but some less or more realistic estimations could be made. Results from different investigations are combined to extrapolate measured element transfer from an observed period into the future.
Conclusions:
-A decrease of leachate quantity could not be estimated. This is only possible with additional top sealing systems.
-The most important emission stream over a long time is leachte. For many elements the period until concentrations below todays limiting values is some hundred years and more. The combination of decreasing concentration slopes with time and decreasing pollution limits could multiply the period of environmental risks.
-The knowledge of processes in landfills in detail is too small. Therefore the presented results are only hypothesis without possibility of verification in an imaginable time.
-A final storage quality defined as near zero pollution potential of solids and pollution stream of liquids cannot reached during the next centuries. The possibility of such defination should be verified under the view of whole mass transport in the environment.
PurposePseudo-first order (PFOM) and pseudo-second order kinetic (PSOM) models are widely used in describing the adsorption kinetics
in soils/sediments. This study intends to apply these models to describe the adsorption kinetics of organic contaminants on
carbon nanomaterials. However, we noticed several improper applications of these two models.
Materials and methodsIn the first part of this two-part series work, we summarized and commented on the application of PFOM and PSOM. More importantly,
we conducted simple mathematical simulations to illustrate the improper applications of these two models.
Results and discussionOur results indicated that linearized PSOM has higher adaptability to adsorption kinetic data because of its mathematical
advantage in comparison to linearized PFOM. Mechanistic discussion on sorption should consider this point. In addition, the
rate constant (k
2a, h–1mg–1kg) in the general expression of PSOM is solid phase concentration (q
a)-dependent and could not be applied to compare the adsorption rate directly. Our simulation indicated that the modified rate
constant (k
2a* = k
2a⋅q
a) is an appropriate parameter to describe adsorption rate. The corrected data analysis method was applied to reanalyze some
literature results and new observations were discussed and provided.
ConclusionsIt is vital to apply the correct models in data analysis and properly discuss the results derived from these models. This
study summarized several important points for the correct application of PFOM and PSOM which are presently widely used. The
modified models and the correct model parameters will be applied in the second part of this two-part series.
KeywordsAdjusted coefficient of determination-Mathematical modeling-Model derivation-Rate constant-Water treatment
The adsorption of four ultrafiltration fractions of natural organic material (NOM) had a significant effect on the surface area and pore volume distributions of a coal-based activated carbon. This effect was dependent on the size of the compounds; the smaller fraction had the greatest effect on the micropore volume, and the larger fractions had a greater effect on the mesopore volume. Only the mesopore volume of a wood-based activated carbon was reduced by adsorption of the NOM fractions. The competitive adsorption between five NOM ultrafiltration fractions and 2-methylisoborneol (MIB) was greatest for the smallest fraction (ultrafiltration molecular weight <500), as this fraction was the most similar in size to MIB and therefore provided direct competition for the same adsorption sites. The NOM in a natural water sample displayed the greatest competition with MIB, due to the presence of small compounds that were lost during the concentration and desalting procedures used to obtain the NOM fractions. The competition between MIB and the largest ultrafiltration fraction was very small and could probably be attributed to smaller compounds present in this fraction.
Mesoporous carbon, CMK-3, was prepared by large pore hexagonal mesoporous silica SBA-15. The structural order and textural properties of all the materials were studied by XRD, HRTEM, and nitrogen adsorption. Adsorption of l-histidine (His) over various porous adsorbents such as CMK-3, SBA-15, and activated carbon was studied from solutions with different pH. His adsorption was observed to be pH dependent with maximum adsorption near the isoelectric point of the amino acid. CMK-3 showed a larger amount of His adsorption as compared to SBA-15 and the conventional adsorbent, namely activated carbon. CMK-3 registers the total adsorption capacity of ca. 1350 μmol g−1 which is ca. 12 times higher than the adsorption capacity of SBA-15. This large difference could be mainly due to the stronger hydrophobic interaction between the non-polar side chains of amino acids and the hydrophobic surface of the mesoporous carbon as compared to mesoporous silica. The influence of ionic strengths on the adsorption of His was also studied and the results are discussed. Nitrogen adsorption of CMK-3 after His adsorption confirmed that His molecules are tightly packed inside the mesopores.
On many landfill sites the most environmentally friendly and economical way to treat landfill leachate is to reduce its volume by 75 to 80% using reverse osmosis and then return the concentrate to the landfill by controlled reinjection. If this procedure is not yet authorized by local authorities then the treatment process must achieve very high rates of recovery by using a combination of reverse osmosis and nanofiltration technology with controlled crystallization to reduce the volume of concentrate for further processing.
The as-grown CNTs and graphitized CNTs were used as adsorbents to remove 1,2-dichlorobenzene from water. The experiments demonstrate that it takes only 40 min for CNTs to attain equilibrium and the adsorption capacity of as-grown and graphitized CNTs is 30.8 and 28.7 mg/g, respectively, from a 20 mg/l solution. CNTs can be used as adsorbents in a wide pH range of 3–10. Thermodynamic calculations indicate that the adsorption reaction is spontaneous with a high affinity and the adsorption is an endothermic reaction.
Commercial single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) were purified by sodium hypochlorite solutions and were employed as adsorbents to study the adsorption characteristics of zinc from water. The properties of CNTs such as purity, structure and nature of the surface were greatly improved after purification which made CNTs become more hydrophilic and suitable for adsorption of Zn2+. In general, the adsorption capacity of Zn2+ onto CNTs increased with the increase of pH in the pH range of 1–8, fluctuated very little and reached maximum in the pH range of 8–11 and decreased at a pH of 12. A comparative study on the adsorption of Zn2+ between CNTs and commercial powdered activated carbon (PAC) was also conducted. The maximum adsorption capacities of Zn2+ calculated by the Langmuir model are 43.66, 32.68, and with SWCNTs, MWCNTs and PAC, respectively, at an initial Zn2+ concentration range of 10–. The short contact time needed to reach equilibrium as well as the high adsorption capacity suggests that SWCNTs and MWCNTs possess highly potential applications for the removal of Zn2+ from water.
A review is presented on the resonance Raman spectra from one isolated single wall carbon nanotube. The reasons why it is possible to observe the spectrum from only one nanotube are given and the important structural information that is provided by single nanotube spectroscopy is discussed. Emphasis is given to the new physics revealed by the various phonon features found in the single nanotube spectra and their connection to spectra observed for single wall nanotube bundles. The implications of this work on single wall carbon nanotube research generally are also indicated.
Gravimetric techniques were employed to determine the adsorption capacities of commercially available purified electric arc and HiPco single-walled carbon nanotubes (SWNTs) for organic compounds (toluene, methyl ethyl ketone (MEK), hexane and cyclohexane) at relative pressures, p/p0, ranging from 1 × 10−4 to 0.95 and at isothermal conditions of 25, 37 and 50 °C. The isotherms displayed both type I and type II characteristics. Adsorption isotherm modeling showed that SWNTs are heterogeneous adsorbents, and the Freundlich equation best describes the interaction between organic molecules and SWNTs. The heats of adsorption were 1–4 times the heats of vaporization, which is typical for physical adsorption of organic vapors on porous carbons.
Samples of dissolved organic carbon (DOC) were obtained from landfill leachate-polluted groundwater at Vejen Landfill, Denmark. The humic acids, fulvic acids and the hydrophilic fraction were isolated and purified. Based on DOC measurements, the fulvic acid fraction predominated, accounting for about 60% of the total amount of DOC with an apparent molecular weight of about 1800 Da. The hydrophilic fraction constituted about 30% of the total amount of DOC with an apparent molecular weight of about 2100 Da, and the humic acid fraction made up about 10% of the total amount of DOC with an apparent molecular weight of about 2600 Da. The elemental compositions of the humic acids, fulvic acids and the hydrophilic fraction were in the ranges typical for humic substances from other origins. The O/C ratios for humic acids, fulvic acids and the hydrophilic fraction were similar in the leachate-polluted groundwater. For humic acids the O/C ratios were slightly higher than reported in the literature, indicating a high content of carboxylic groups, phenolic groups or carbohydrates. Acid-base titration indicated that, in the fulvic acids and the hydrophilic fraction, carboxylic acids were the dominating functional group, representing about 6 meq g−1. The weakly acidic groups in fulvic acids and the hydrophilic fraction represented about 1 and 3 meq g−1, respectively. The total acidity in fulvic acids and the hydrophilic fraction accounted for 48–57% of the O/C ratio. In the humic acids, carboxylic groups made up about 3 meq g−1 and the weakly acidic groups made up about 1.5 meq g−1. The total acidity accounted for 29–32% of the O/C ratio. The characterization of DOC in leachate-polluted groundwater in terms of humic acids, fulvic acids and hydrophilic fraction showed that the hydrophilic fraction resembles, in many ways, humic and fulvic acids; thus, a distinction between the fractions may be related to the methods only and be of little practical value. The three fractions constituting the DOC content in a sample should all be considered when evaluating processes such as metal complexation and transport of metals and hydrophobic, organic contaminants. © 1998 Elsevier Science Ltd. All rights reserved
Reports of endocrine disrupting compounds (EDCs) and pharmaceuticals and personal care products (PPCPs) have raised substantial concern among important potable drinking water and reclaimed wastewater quality issues. Our study investigates the removal of EDC/PPCPs of 52 compounds having different physico-chemical properties (e.g., size, hydrophobicity, and polarity) by nanofiltration (NF) and ultrafiltration (UF) membranes using a dead-end stirred-cell filtration system. EDC/PPCPs were applied to the membrane in one model water and three natural waters. Experiments were performed at environmentally relevant initial EDC/PPCP concentrations ranging typically from 2 to <250 ng/L. EDC/PPCP retention was quantified by liquid and gas chromatography with mass spectroscopy–mass spectroscopy. A general separation trend due to hydrophobic adsorption as a function of octanol–water partition coefficient was observed between the hydrophobic compounds and porous hydrophobic membrane during the membrane filtration in unequilibrium conditions. The results showed that the NF membrane retained many EDC/PPCPs due to both hydrophobic adsorption and size exclusion, while the UF membrane retained typically hydrophobic EDC/PPCPs due mainly to hydrophobic adsorption. However, the transport phenomenon associated with adsorption may depend on water chemistry conditions and membrane material.
Surface modification of a coal-based activated carbon (F400) was performed using thermal and chemical methods. Nitric acid oxidation of the conventional sample produced samples with weakly acidic functional groups and the presence of such groups was confirmed by Fourier transform infra red (FTIR) spectroscopy, pH titration, zeta potential measurements and sodium uptake capacity results. There was a significant loss in microporosity of the oxidised samples which was caused by humic substances that were formed as a by-product during the oxidation process. Thermal treatment produced a carbon with some basic character while amination of the thermally treated carbon gave a sample containing some amino (–NH2) groups and these groups were detected by X-ray photoelectron spectroscopy (XPS) analysis.
The presence of electrolytes (salts) in aqueous solution modifies the solubility and related properties of organic compounds in water. Reported data for salting-out constants (Setschenow constants) which relate solubility to the salt concentration of aromatic and alkane hydrocarbons, and their chlorinated derivatives, and some organic acids have been compiled for 25 aqueous salt solutions at 20–25 °C. The salting-out sequences for various electrolytes are discussed and it is shown that the salting-out effect is greater for organic solutes with large molar volumes. A compilation of salting-out constants for NaCl solutions and seawater (natural or synthetic) with a variety of solutes, shows that the Setschenow constants are similar for natural or artificial seawater (at salinity of 30–35%.) and NaCl solutions (at 3.0–3.5% or 0.5 M). A simple correlation is suggested for estimating the Setschenow constants for a variety of organic solutes in seawater which typically yields a reduction in solubility by a factor of 1.36. The hydrophobicity of organic solutes is therefore increased by this factor, as is the air-water partition coefficient, implying an increased partitioning from aqueous solution into air, organic carbon and lipid phases. The effect must be quantified when comparing the behavior of organic contaminants in freshwater and marine conditions.
We investigated the adsorption-desorption by multiwalled carbon nanotubes (MWCNTs) of two pharmaceuticals, oxytetracycline (OTC) and carbamazepine (CBZ). The pharmaceuticals demonstrated relatively fast sorption kinetics on MWCNTs. All adsorption isotherms were nonlinear and fit the Polanyi-Manes model (PMM). The single point adsorption coefficient (K) values for OTC were more than 1 order of magnitude higher than those for CBZ on corresponding MWCNTs. The adsorbed volume capacity (Q(0)) and K values of PMM showed a significant relationship with surface areas and the meso- and micropore volume of MWCNTs for both chemicals. Depending on the MWCNT outer diameter, 13.8-25.2% and 62.7-90.6% of initially adsorbed OTC and CBZ, respectively, were desorbed after 200 h. The rate of desorption of both OTC and CBZ depended upon pH and the quantity of initially adsorbed pharmaceuticals, as well as aggregation in the case of OTC.
The initial aggregation kinetics of single-walled carbon nanotubes (SWNTs) were studied using time-resolved dynamic light scattering. Aggregation of SWNTs was evaluated in the presence of natural organic matter [Suwannee River humic acid (SRHA)], polysaccharide (alginate), protein [bovine serum albumin (BSA)], and cell culture medium [Luria-Bertani (LB) broth] with varying solution concentrations of monovalent (NaCl) and divalent (CaCl(2)) salts. Increasing salt concentration and adding divalent calcium ions induced SWNT aggregation by screening electrostatic charge and thereby suppressing electrostatic repulsion, similar to observations with aquatic colloidal particles. The presence of biomacromolecules significantly retarded the SWNT aggregation rate. BSA protein molecules were most effective in reducing the rate of aggregation followed by SRHA, LB, and alginate. The slowing of the SWNT aggregation rate in the presence of the biomacromolecules and SRHA can be attributed to steric repulsion originating from the adsorbed macromolecular layer. The remarkably enhanced SWNT stability in the presence of BSA, compared to that with the other biomacromolecules and SRHA, is ascribed to the BSA globular molecular structure that enhances steric repulsion. The results have direct implications for the fate and behavior of SWNTs in aquatic environments and biological media.
With the significant increase in the production and use of carbon nanotubes (CNTs), they will be inevitably released into aquatic environments. Therefore, the fate and transport of CNTs in aqueous solutions have attracted extensive attention. In the present work, the effects of natural organic matter (NOM), solution pH and ionic strength on adsorption of three synthetic organic chemicals (SOCs) by both pristine and surface functionalized single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) were investigated. The three SOCs (phenanthrene, biphenyl, and 2-phenylphenol) with different planarity, polarity, and hydrogen/electron-donor/acceptor ability, representing typical scenarios for the SOC-CNT interactions, were employed as probe molecules. Among the three background solution characteristics examined, NOM showed the most significant effect on SOC adsorption, while solution pH and ionic strength exhibited minimal or negligible impacts. The presence of NOM greatly suppressed the SOC adsorption by CNTs, and the impact on the SWNTs was higher than that on the MWNTs. The planarity and hydrophobicity of SOCs were two important factors determining the effects of NOM, solution pH and ionic strength on their adsorption by CNTs.
Carbon nanotubes (CNTs) have drawn special research attention because of their unique properties and potential applications. This review summarizes the research progress of organic chemical adsorption on CNTs, and will provide useful information for CNT application and risk assessment. Adsorption heterogeneity and hysteresis are two widely recognized features of organic chemical-CNT interactions. However, because different mechanisms may act simultaneously, mainly hydrophobic interactions, pi-pi bonds, electrostatic interactions, and hydrogen bonds, the prediction of organic chemical adsorption on CNTs is not straightforward. The dominant adsorption mechanism is different for different types of organic chemicals (such as polar and nonpolar), thus different models may be needed to predict organic chemical-CNT interaction. Adsorption mechanisms will be better understood by investigating the effects of properties of both CNTs and organic chemicals along with environmental conditions. Another majorfactor affecting adsorption by CNTs is their suspendability, which also strongly affects their mobility, exposure, and risk in the environment. Therefore, organic chemical-CNT interactions as affected by CNT dispersion and suspending merit further experimental research. In addition, CNTs have potential applications in water treatment due to their adsorption characteristics. Thus column and pilot studies are needed to evaluate their performance and operational cost.