Elevated salinity levels in wastewater usually have negative consequences to soil quality and crop growth if used directly in irrigation without proper treatment. Though many techniques have been ...developed to solve the problem, high capital costs or energy consumption have hindered their application in wider regions. One economical solution of reusing the wastewater of high salinity is applying natural or synthetic zeolites as ion exchanger and adsorbent. Chemically modified natural zeolites or synthetic zeolites have been utilized to reduce Na+ in various kinds of saline/sodic waters. In this paper, we reviewed the recent technical improvements of using natural or modified zeolites in the field of water salinity reduction. The mechanisms governing the salt removal process by zeolites are mainly ion exchange, adsorption, and salt storage. Factors such as zeolite's geochemical properties, pH, co-existing anions, concentration, valency, surface charge, and experimental conditions all influence the ion exchange process. Adsorption isotherm of Na+ ions on zeolites, mostly reported to follow either Langmuir or Freundlich isotherm, has a composition-dependent behaviour. The adsorption kinetics of Na+ on zeolites is mostly a pseudo-second-order type with an exothermic nature. Sodium removal by zeolites appears to be an effective water treatment technology for maximizing the beneficial use of poor-quality saline/sodic wastewater. However, challenges still remain and further work is required in areas of lowering operational cost and improving zeolite's regenerability. To overcome these challenges, researchers could make more efforts in technical improvements, including alterable surface properties and the incorporation of other approaches to achieve better salt removal outcome.
•Few review articles focus on zeolites for salinity/sodicity reduction in waters.•Mechanisms, influencing factors, challenges and opportunities are discussed.•Zeolites present great potential for salinity reduction in wastewater.
The pollutants classified as “persistent organic pollutants (POPs)”, are being subject to high concern among the scientific community due to their persistence in the environment. TiO2-based ...photocatalytic process has shown a great potential as a low-cost, environmentally friendly and sustainable treatment technology to remove POPs in sewage to overcome the shortcomings of the conventional technologies. However, this technology suffers from some main technical barriers that impede its commercialization, i.e., the inefficient exploitation of visible light, low adsorption capacity for hydrophobic contaminants, uniform distribution in aqueous suspension and post-recovery of the TiO2 particles after water treatment. To improve the photocatalytic efficiency of TiO2, many studies have been carried out with the aim of eliminating the limitations mentioned above. This review summarizes the recently developed countermeasures for improving the performance of TiO2-based photocatalytic degradation of organic pollutants with respect to the visible-light photocatalytic activity, adsorption capacity, stability and separability. The performance of various TiO2-based photocatalytic processes for POPs degradation and the underlying mechanisms were summarized and discussed. The future research needs for TiO2-based technology are suggested accordingly. This review will significantly improve our understanding of the process of photocatalytic degradation of POPs by TiO2-based particles and provide useful information to scientists and engineers who work in this field.
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•The limitations of TiO2-based technology for POPs degradation were discussed.•The approaches for improving the performance of photodegradation were summarized.•The mechanisms of various TiO2-based technologies for POPs removal were discussed.•The future research needs for TiO2-based technology are suggested.
Over the past 20 years, zero-valent iron (ZVI) has been extensively applied for the remediation/treatment of groundwater and wastewater contaminated with various organic and inorganic pollutants. ...Based on the intrinsic properties of ZVI and the reactions that occur in the process of contaminants sequestration by ZVI, this review summarizes the limitations of ZVI technology and the countermeasures developed in the past two decades (1994–2014). The major limitations of ZVI include low reactivity due to its intrinsic passive layer, narrow working pH, reactivity loss with time due to the precipitation of metal hydroxides and metal carbonates, low selectivity for the target contaminant especially under oxic conditions, limited efficacy for treatment of some refractory contaminants and passivity of ZVI arising from certain contaminants. The countermeasures can be divided into seven categories: pretreatment of pristine ZVI to remove passive layer, fabrication of nano-sized ZVI to increase the surface area, synthesis of ZVI-based bimetals taking advantage of the catalytic ability of the noble metal, employing physical methods to enhance the performance of ZVI, coupling ZVI with other adsorptive materials and chemically enhanced ZVI technology, as well as methods to recover the reactivity of aged ZVI. The key to improving the rate of contaminants removal by ZVI and broadening the applicable pH range is to enhance ZVI corrosion and to enhance the mass transfer of the reactants including oxygen and H+ to the ZVI surface. The characteristics of the ideal technology are proposed and the future research needs for ZVI technology are suggested accordingly.
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•The development of ZVI-based technologies in the past two decades was reviewed.•The limitations of ZVI technology and the countermeasures were summarized.•The merits and demerits of each countermeasure were discussed in detail.•The future research needs in the field of ZVI technology were suggested.•The characteristics of an ideal ZVI technology were proposed.
Metabolic reprogramming is an emerging hallmark of cancer cells, in which cancer cells exhibit distinct metabolic phenotypes to fuel their proliferation and progression. The significant advancements ...made in the area of metabolic reprogramming make possible new strategies for overcoming malignant cancer, including triple-negative breast cancer. Triple-negative breast cancer (TNBC) is associated with high histologic grade, aggressive phenotype, and poor prognosis. Even though triple-negative breast cancer patients benefit from standard chemotherapy, they still face high recurrence rates and are more likely to develop resistance to chemotherapeutic drugs. Therefore, there is an urgent need to explore vulnerabilities of triple-negative breast cancer and develop novel therapeutic drugs to improve clinical outcomes for triple-negative breast cancer patients. Metabolic reprogramming may provide promising therapeutic targets for the treatment of triple-negative breast cancer. In this paper, we primarily discuss how triple-negative breast cancer cells reprogram their metabolic phenotype and that of stromal cells in the microenvironment to survive under nutrient-poor conditions. Considering that metastasis and chemoresistance are the main contributors to mortality in triple-negative breast cancer patients, we also focus on the role of metabolic adaption in mediating metastasis and chemoresistance of triple-negative breast cancer tumors.
The technology of integrating nanoscale zero-valent iron (nZVI) and functional anaerobic bacteria has broad prospects for groundwater remediation. This review focuses on the interactions between nZVI ...and three kinds of functional anaerobic bacteria: organohalide-respiring bacteria (OHRB), sulfate reducing bacteria (SRB) and iron reducing bacteria (IRB), which are commonly used in the anaerobic bioremediation. The coupling effects of nZVI and the functional bacteria on the contaminant removal in the integrated system are summarized. Generally, nZVI could create a suitable living condition for the growth and activity of anaerobic bacteria. OHRB and SRB could synergistically degrade organic halides and remove heavy metals with nZVI, and IRB could reactive the passivated nZVI by reducing the iron (hydr)oxides on the surface of nZVI. Moreover, the roles of these anaerobic bacteria in contaminant removal coupling with nZVI and the degradation mechanisms are illustrated. In addition, this review also discusses the main factors influencing the removal efficiency of contaminants in the integrated treatment system, including nZVI species and dosage, inorganic ions, organic matters, pH, type of pollutants, temperature, and carbon/energy sources, etc. Among these factors, the nZVI species and dosage play a fundamental role due to the potential cytotoxicity of nZVI, which might exert a negative impact on the performance of this integrated system. Lastly, the future research needs are proposed to better understand this integrated technology and effectively apply it in groundwater remediation.
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•Interactions between nZVI and functional bacteria (OHRB, SRB, IRB) are summarized.•The coupling effects of nZVI and functional bacteria are discussed.•The roles of the bacteria in pollutant removal coupling with nZVI are illustrated.•Factors influencing the efficacy of the integrated treatment system are discussed.•Future research needs and challenges are proposed.
This study investigated the feasibility and mechanism of sulfide-modified nanoscale zero-valent iron supported on biochar (S-nZVI@BC) for the removal of TCE in the scenario of groundwater ...remediation. The effects of some critical factors, including pyrolysis temperature of biochar, mass ratio of S-nZVI to BC, initial pH, typical groundwater compositions, co-contaminants, and particle aging time, on the TCE removal were examined. The results revealed that the different pyrolysis temperatures could change physicochemical properties of BC, which influenced the TCE adsorption and degradation by S-nZVI@BC. The mass ratio of S-nZVI to BC could determine the extent of adsorption and degradation of TCE. The total removal of TCE was not significantly influenced by the initial pH (3.0–9.0), but the degradation of TCE was enhanced at higher pH. Notably, the typical anions (SO
4
2−
, HCO
3
−
, and HPO
4
2−
), humic acid, and co-contaminants (Cr(VI) and NO
3
−
) in groundwater all slightly influenced the total removal of TCE, but markedly inhibited its degradation. Additionally, after exposure to air over different times (5 days, 10 days, 20 days, and 30 days), the reactivity of S-nZVI@BC composites was apparently decreased due to surface passivation. Nevertheless, the aged S-nZVI@BC composites still maintained relative high removal and degradation of TCE when the reaction time prolonged. Overall, the results showed that the S-nZVI@BC, combining the high adsorption capacity of BC and the high reductive capacity of S-nZVI, had a much better performance than the single S-nZVI or BC, suggesting that S-nZVI@BC is one promising material for the remediation of TCE-contaminated groundwater.
Sulfide-modified nanoscale zero-valent iron (S/nZVI) has been widely studied for groundwater remediation, but the potential environmental risks are poorly understood. This study examined the toxicity ...of S/nZVI to Escherichia coli in aqueous solutions. The sulfidation could reduce toxicity of nZVI, and S/nZVI exhibited a weaker toxicity at lower Fe/S molar ratio, resulting from the lower Fe0 content and higher sulfate and iron oxide. The toxicity of S/nZVI was significantly alleviated in the presence of N-Acetyl-L-cysteine (a scavenger for reactive oxygen species (ROS)), revealing that the ROS-induced oxidative stress was the principal mechanism. Moreover, Transmission Electron Microscopy images elucidated that the membranes of S/nZVI-treated cells were disrupted and S/nZVI existed on E. coli surface and in the cytoplasm. S/nZVI might have interacted with the amine, carboxyl, and ester groups on E. coli cell surface, as demonstrated by Fourier Transform Infrared Spectroscopy analysis. However, the presence of individual groundwater component (e.g., Ca2+, SO42−, HCO3− and humic acid) could more or less alleviate the toxicity of S/nZVI. Furthermore, S/nZVI only exhibited slight toxic effect (<0.15-log after 1 h) in the presence of the mixed components. The same faint toxicity was observed for the aged S/nZVI, indicating that S/nZVI could lose its toxicity over time.
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•S/nZVI exhibited a weaker toxicity than nZVI toward E. coli.•The toxicity of S/nZVI was weaker at lower Fe/S molar ratio.•ROS-induced oxidative stress was the primary mechanism for the toxicity of S/nZVI.•The presence of groundwater components could alleviate the toxicity of S/nZVI.•S/nZVI could gradually loss its toxicity with aging time.
Increasing proportions of the global population are exposed to floods, including many living in the Yellow River floodplain. Since records were first kept in 602 BCE, there have been ∼1500 floods on ...the Yellow River, resulting in the death of millions of people. Counteracting increased flood risk requires an understanding of the relationship between climate, forest cover, erosion, and river flow. However, to assess whether the Yellow River basin is currently experiencing a period of high flood risk requires a long-term perspective. Here we use a variety of paleoenvironmental proxies (pollen, magnetic susceptibility, cladoceran assemblages) preserved in high-resolution, well-dated sediment records retrieved from an alpine lake in the middle Yellow River basin (Chinese Loess Plateau) within the agro-pastoral ecozone to examine how climatic and land-use changes affected aquatic ecosystems over the past ∼2000 years. Further, to examine changes in erosion, runoff production and flood frequency, we synthesize previously published proxy reconstructions of vegetation density, soil erosion, and dry-wet changes, as well as flood records from historical documents. We demonstrate that, following the period around the 10th century, excessive cultural deforestation outweighed climate effects and became the dominant factor that led to an unprecedented flood-rich period when drought conditions were common, cultivation expanded to meet food shortages, heavy silting raised the riverbed, and runoff and flood risk increased. These watershed changes, including enhanced soil erosion, affected the biological communities of aquatic ecosystems that led to the disappearance of planktonic cladocerans that hitherto dominated the assemblages. Increasing temperatures and weakening monsoon precipitation during the past ∼50 years, together with decreased erosion indicated by unprecedented reductions in Yellow River runoff and sediment load resulting from reforestation and damming, led to the re-establishment of planktonic cladocerans. Despite these recent changes, vegetation cover has not recovered to pre-deforestation levels, suggesting that the Yellow River is currently experiencing a high flood risk period. Our results emphasize the importance of considering vegetation–flooding relationships to help improve risk assessments and management protocols for the Yellow River.
•Abrupt cultural deforestation around 10th century linked to expanded cultivation.•Vegetation outweighed precipitation changes in regulating erosion and floods.•Strong responses of Cladoceran to changes in Yellow River sediment load.•Despite recent revegetation, the Yellow River remains at a high risk for flooding.
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A highly efficient method for removal of p-nitrophenol and its conversion p-aminophenol from water was proposed using a novel catalyst–adsorbent composite of gold nanoparticles ...supported on functionalized mesoporous carbon (Au@CMK-3-O). The immobilized gold nanoparticles presented excellent catalytic ability to converse p-nitrophenol into p-aminophenol with the help of sodium borohydride, and the oxidized mesoporous carbon (CMK-3-O) serving as both carrier and adsorbent also exhibited high efficiency to remove p-aminophenol. The morphology and structure of the composite were characterized via SEM, TEM, FTIR and XPS analysis. Moreover, the mechanism of reaction process and the parameters of kinetics and thermodynamics were investigated. The activation energy was figured as 86.8kJmol−1 for the adsorption and reduction of p-nitrophenol to p-aminophenol. The thermodynamic analysis based on the rate constants evaluated by pseudo-first-order model reveals that the adsorption–reduction process is an endothermic procedure with the rise of randomness. The anti-oxidation and regeneration study indicates that Au@CMK-3-O can be reused for 6 times with more than 90% conversion efficiency and keep high activity after exposing in air for 1month, which possesses great prospects in application of nitroaromatic pollutant removal.
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•Eight OPEs and 5 diester were frequently detected in blood and urine of the elderly, respectively.•Indoor air and dust are main sources of the elderly’ exposure to TnBP and TEHP, ...respectively.•The contributions of di-OPEs (especially BEHP) directly ingested from dust to their urinary levels should be concerned.•Diet may be the main pathway of human exposure to several OPEs and di-OPEs.•Reduced metabolic/excretory capacity of the elderly may lead to high accumulation of some OPEs.
Human exposure to OPEs is pervasive and should be of great concern due to associations with adverse health effects, especially in susceptible populations. In this study, body burdens and exposure pathways of OPEs were investigated for 76 healthy elderly people in Jinan, China based on the measured OPE and metabolite concentrations in human bio-samples (whole blood and urine) and paired environmental matrices (air and dust), as well as food frequency questionnaire. Eight of 16 OPEs and 5 of 11 metabolites were detected in > 50% of whole blood and urine samples, respectively. Tri(1-chloro-2-propyl) phosphate (TCIPP), tris(2-chloroethyl) phosphate (TCEP), tri-phenyl phosphate (TPHP), and 2-ethylhexyl di-phenyl phosphate (EHDPP) were frequently detected and abundant in whole blood, while their corresponding metabolites were detected at low frequencies or levels in urine. The reduced metabolic and/or excretory capacity of elderly people may be an important reason, implying a higher health risk to them. Fourteen OPEs had over 50% detection frequencies in indoor air and dust, while 6 di-esters in indoor dust. Tris(2-ethylhexyl) phosphate (TEHP) in indoor dust and tri-n-butyl phosphate (TnBP) in indoor air were positively correlated with paired levels in blood but not with their metabolites (BEHP and DnBP) in urine. Combined with the direct intakes of BEHP and DBP from dust, blood is indicated as more suitable biomarker for TEHP and TnBP exposure. High consumption frequencies of several foods were associated with higher blood concentrations of three OPEs and urinary levels of four di-OPEs, indicating the importance of dietary exposure pathway. Estimated daily total intakes of OPEs via inhalation, dust ingestion, and dermal absorption ranged from 2.78 to 42.0 ng/kg bw/day, which were far less than the reference dosage values. Further studies were warranted to explore the potential health effects of OPE exposure in the elderly populations.
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