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Long-term exposure to fine particulate matter (PM2.5) is associated with kidney dysfunction. However, few studies have investigated acute effects of PM2.5 elemental constituents on renal function. We evaluated associations between personal PM2.5 and its elemental constituents and kidney function, assessed by an estimated glomerular filtration rate (eGFR) in Biomarkers of Air Pollutants Exposure in the Chinese aged 60-69 study. Seventy one older individuals were visited monthly between September 2018 and January 2019. Each participant wore a PM2.5 monitor for 72 h, responded to a questionnaire, and underwent a physical examination with blood sampling. Linear mixed-effect models were used to estimate associations between personal PM2.5 elemental constituents and eGFR. We found that significant changes in eGFR from -1.69% [95% confidence interval (CI): -3.34%, -0.01%] to -3.27% (95% CI: -5.04%, -1.47%) were associated with interquartile range (IQR) increases in individual PM2.5 exposures at various lag periods (7-12, 13-24, 0-24, 25-48, and 49-72 h). An IQR increase in 72 h moving averages of copper, manganese, and titanium in personal PM2.5 corresponded to -2.34% (95% CI: -3.67%, -0.99%) to -4.56% (95% CI: -7.04%, -2.00%) changes in eGFR. Personal PM2.5 and some of its elemental constituents are inversely associated with eGFR in older individuals.

The effects of iron oxide nanoparticles (IONPs, including Fe2O3 NPs and Fe3O4 NPs) on composting were investigated through evaluating their influences on organic matter (OM) degradation, dehydrogenase (DHA) and urease (UA) activities, and quality of the final compost product. Results showed that composting amended with Fe2O3 NPs was more effective to facilitate OM degradation. At the end of composting, the total OM loss in T-C, T-Fe2O3 NPs and T-Fe3O4 NPs was 66.19%, 75.53% and 61.31%, respectively. DHA and UA were also improved on the whole by the amendment of IONPs, especially Fe2O3 NPs. Although relationships between enzyme activities and environmental variables were changed by different treatments, temperature was the most influential to variations of both DHA and UA in all treatments, which independently explained 75.1%, 34.7% and 38.4% of variations in the two enzyme activities in T-C, T-Fe2O3 NPs and T-Fe3O4 NPs, respectively. Compared with DHA, UA was more closely related to the environmental parameters. The germination index in T-C, T-Fe2O3 NPs and T-Fe3O4 NPs was 134.49%, 153.64% and 146.76%, and the average shoot length was 3.16, 3.87 and 3.45 cm, respectively, indicating that amendment of IONPs, especially Fe2O3 NPs, could promote seed germination and seedling growth. Therefore, composting amended with IONPs was a feasible and promising method to improve composting performance, enzyme activities as well as quality of the final compost product.

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. Keywords: Nanoscale zero-valent iron, Organohalide-respiring bacteria, Sulfate reducing bacteria, Iron reducing bacteria, Groundwater remediation

The health impact of airborne contaminants has been challenging to assess due to current limitations in measurement technologies. The emergence of wearable passive samplers coupled with high resolution mass spectrometry (HR-MS) chemical analysis has enabled comprehensive characterization of personal exposures. We conducted a repeated-measure study among 84 older adults in Jinan, China, as part of the Biomarkers for Air Pollutants Exposure (China BAPE) study. Study objectives were: 1) to characterize the occurrence, magnitude, and distribution of personal exposure to airborne contaminants; 2) to evaluate the temporal variation of chemical exposures across the study population; and 3) to identify behavioral and environmental factors that influence the observed variance in chemical exposures. The FreshAir wristband was worn by participants for three consecutive days each month from September 2018 to January 2019 and collected with paired time-activity logs. Passive air samplers were also deployed in parallel at a local outdoor air monitoring station. Spearman’s Rho trend test and trajectory cluster analysis were used to identify exposure trends and variation patterns, respectively. Out of the 70 airborne compounds of potential concern screened, 26 compounds from 10 chemical classes were found to be above detection thresholds across >70% of the study population. Personal exposures were predominantly characterized by nine polycyclic aromatic hydrocarbons (PAHs), four phthalates, three nitroaromatics, and two volatile organic compounds (VOCs). Phthalate personal exposures were positively correlated with outdoor temperatures while the inverse relationship was observed for certain PAHs (p

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 (SO42−, HCO3−, and HPO42−), humic acid, and co-contaminants (Cr(VI) and NO3−) 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.

In this study, the dispersion stability and reactivity of sulfide-modified nanoscale zerovalent iron (SNZVI) coated with different surface stabilizers (i.e., starch, sodium dodecylbenzene sulfonate (SDBS), or carboxymethyl cellulose (CMC)) were investigated. All the three types of surface stabilizers could enhance the dispersion stability of SNZVI but exerted differing influences on the reactivity toward trichloroethylene (TCE) removal. The coating of starch on SNZVI markedly improved TCE removal, which was positively correlated with the enhanced dispersion stability (i.e., more active surface sites). However, although the SDBS and CMC could enhance the dispersion stability of SNZVI, they resulted in an inhibition in TCE removal, especially for CMC. It was presumed that the coated SDBS/CMC on the surface of SNZVI occupied the active surface sites for TCE removal. Besides, the effect of groundwater geochemistry (i.e., pH, Ca2+, and humic acid (HA)) was examined. The increasing pH from 5 to 9 led to a slight decrease for all stabilized SNZVI particles. The presence of Ca2+ or HA exerted distinct influence on the TCE removal by the three stabilized SNZVI. The Ca2+/HA exerted an insignificant effect on the reactivity of CMC-SNZVI but markedly decreased the reactivity of starch-SNZVI and SDBS-SNZVI. The varying effects of Ca2+/HA should be due to their distinct interactions with different types of stabilizers on the surface of SNZVI.

Pollution of Sb(III) in water has caused great concern in recent years. Nanoscale zero-valent iron (nZVI) can detoxify Sb(III) polluted water, but the rapid passivation and low adsorption capacity limit its practical application. Hence, this study provides a new and efficient nanotechnology to remove Sb(III) using the sulfidated nanoscale zero-valent iron (S-nZVI). The S-nZVI exhibits higher Sb(III)-removal efficiency than pristine nZVI under both aerobic and anoxic conditions. The adsorption capacity of Sb(III) by optimized S-nZVI (465.1 mg/g) is 6 times as high as that of the pristine nZVI (83.3 mg/g) under aerobic conditions. The results indicate that Sb(III) and Sb(V) can be immobilized on the surface of S-nZVI by forming Fe-S-Sb precipitates. Moreover, characterization results demonstrate that the existence of S2− can not only activate H2O2 to produce hydroxyl radical, but also accelerate the cycle of Fe3+/Fe2+ to improve the efficiency of Fenton reaction. Therefore, S-nZVI can produce more hydroxyl radicals to oxidize Sb (III) to Sb (V) and results in 2.3-fold higher oxidation rate of Sb(III) compared to pristine nZVI. The formed FeS layer on the S-nZVI surface can also improve the release ability of Fe2+ and accelerate the formation of nZVI corrosion products. S-nZVI thus holds great potential to be applied in antimony removal.

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.

Metal-free catalysis for green degradation of aqueous organic pollutants has caused extensive concern in recent years. In this study, hexagonally-ordered mesoporous carbon (CMK-3) was applied to activate persulfate (PS) for the degradation of 2,4-dichlorophenol (2,4-DCP) with superior removal rate of 90% in 20 min. The high catalytic efficiency was probably ascribed to the accelerated electron transfer resulting from the large adsorption capacity of CMK-3. It was found that specific surface areas (SSA), defective sites and functional groups on the activator were highly related to its catalytic efficiency and passivation. Compared to other nanocarbons, CMK-3 had better reusability due to its ordered mesoporous structure with large SSA and high defective degrees. For the first time, a two-pathway mechanism was proposed for metal-free activation process of PS, indicating that radical and non-radical oxidation worked together in PS activation for complete 2,4-DCP decomposition, and non-radical pathway played a dominant role while radical pathway was critical in accelerating the reaction. OH, SO4 − and O2 − all took part in the radical oxidation process, in which the contribution of OH was dominant. Besides, high decomposition efficiency was also achieved in pharmaceutical wastewater treatment by the CMK-3/PS system. This research proposed a new electron transfer mechanism for metal-free activation process of PS, which can provide a theoretical support for further studies.

In this work, biochar-supported nanoscale zero-valent iron (nZVI/BC) was synthesized and used as an activator for Fenton-like removal of sulfamethazine (SMT). The possible removal mechanisms in the reaction system were proposed. nZVI was mainly responsible for H2O2 decomposing to generate OH for the degradation of SMT, while BC played multiple roles, i.e., preventing nZVI aggregation, adsorbing SMT, activating H2O2, and alleviating nZVI passivation. The effects of various factors (i.e., the mass ratio of nZVI to BC, solution pH, H2O2 concentration and nZVI/BC dosage) on SMT removal were evaluated. The highest removal efficiency (74.04%) of SMT (10 mg/L) was achieved at the optimal conditions (the mass ratio of nZVI and BC = 1:5, pH = 3, H2O2 = 20 mM and nZVI/BC = 1.2 g/L). Additionally, the feasibility of recycling of nZVI/BC composites was examined. It was found that the removal efficiency of SMT decreased significantly from 74.04% to 53.28% and 38.02%, respectively, in the second and third run of experiments. X-ray diffraction analysis of the recycled composites demonstrated the gradual loss of Fe0 content after each run of experiment, which resulted in the decrease of catalytic activity of nZVI/BC composites and thus the drop of SMT removal.

This study evaluated the contributions of environmental variables to the variations in bacterial 16S rDNA, nitrifying and denitrifying genes abundances during composting in the presence of polyvinylpyrrolidone coated silver nanoparticles (PVP-AgNPs). Manual forward selection in redundancy analysis (RDA) indicated that the variation in 16S rDNA was significantly explained by NO3--N, while nitrifying genes were significantly related with pH, and denitrifying genes were driven by NO3--N and TN. Partial RDA further revealed that NO3--N solely explained 28.8% of the variation in 16S rDNA abundance, and pH accounted for 61.8% of the variation in nitrifying genes. NO3--N and TN accounted for 34.2% and 9.2% of denitrifying genes variation, respectively. The RDA triplots showed that different genes shared different relationships with environmental parameters. Based on these findings, a composting with high efficiency and quality may be conducted in the future work by adjusting the significant environmental variables.

Sulfide-modified nanoscale zero-valent iron (S/NZVI) has been considered as an efficient material to degrade trichloroethylene (TCE) in groundwater. However, some critical factors influencing the dechlorination of TCE by S/NZVI have not been investigated clearly. In this study, the effects of Fe/S molar ratio, initial pH, dissolved oxygen and particle aging on TCE dechlorination by S/NZVI (using dithionite as sulfidation reagent) were studied. Besides, the feasibility of reactivation of the aged-NZVI by sulfidation treatment was looked into. The results show that the Fe/S molar ratio and initial pH significantly influenced the TCE dechlorination, and a higher TCE dechlorination was observed at Fe/S molar ratio of ∼60 under alkaline condition. Spectroscopic analyses demonstrate that the enhanced TCE dechlorination was associated with the presence of FeS on the surface of S/NZVI. Dissolved oxygen had little effect on TCE dechlorination by S/NZVI, revealing that the FeS layer could be able to alleviate the surface passivation of NZVI caused by oxidation. Aging of S/NZVI up to 10–20 d only slightly decreased the dechlorination efficiency of TCE. Although an obvious drop in dechorination efficiency was observed for the S/NZVI aged for 30 d, it still exhibited a higher reactivity than the bare NZVI. This indicates that sulfidation of NZVI did prolong its lifetime. Additionally, sulfidation treatment was used to reactivate the aged NZVI, and the results show that the reactivated NZVI even had higher reactivity than the fresh NZVI, suggesting that sulfidation treatment would be a promising method to reactivate the aged NZVI.

Polyvinylpyrrolidone coated silver nanoparticles (PVP-AgNPs) were applied at different concentrations to reduce total nitrogen (TN) losses and the mechanisms of nitrogen bio-transformation were investigated in terms of the nitrogen functional enzymes and genes. Results showed that mineral N in pile 3 which was treated with AgNPs at a concentration of 10 mg/kg compost was the highest (6.58 g/kg dry weight (DW) compost) and the TN loss (47.07%) was the lowest at the end of composting. Correlation analysis indicated that TN loss was significantly correlated with amoA abundance. High throughput sequencing showed that the dominant family of ammonia-oxidizing bacteria (AOB) was Nitrosomonadaceae, and the number of Operational Taxonomic Units (OTUs) reduced after the beginning of composting when compared with day 1. In summary, treatment with AgNPs at a concentration of 10 mg/kg compost was considerable to reduce TN losses and reserve more mineral N during composting.

This study investigated the degradation of tetracycline (TC) by Fe/Ni bimetallic nanoparticles (Fe/Ni BNPs) and nanoscale zero-valent iron (NZVI) in aqueous solution. Results revealed that Fe/Ni BNPs showed much better performance than NZVI. The effects of pH (5, 7 and 9), initial TC concentration and competitive anions (NO3−, H2PO4−, SO42− and HCO3−) on the removal of TC by Fe/Ni BNPs were investigated. The results indicated that the removal of TC was higher under acidic conditions and the reaction reached equilibrium more quickly at lower initial TC concentrations. The presence of NO3− greatly hindered the removal of TC, while the other anions (i.e., H2PO4−, SO42− and HCO3−) exhibited less inhibition. The significant impact of NO3− was due to the fact that Fe/Ni BNPs could be consumed via redox reaction with NO3−. Total organic carbon (TOC) and liquid chromatography-mass spectrometry (LC-MS) analysis shed light on the removal mechanisms of TC by Fe/Ni BNPs. The decrease of TOC in solution and the appearance of intermediate products on the surface of Fe/Ni BNPs indicated that both adsorption and degradation were involved in the reaction process. Based on the results of LC-MS, the detailed pathway of TC degradation by Fe/Ni BNPs was proposed.

To assess the fate and long-term reactivity of bimetallic nanoparticles used in groundwater remediation, it is important to trace the physicochemical transformation of nanoparticles during aging in water. This study investigated the short-term (within 5 d) and long-term (up to 90 d) aging process of Fe/Ni bimetallic nanoparticles (Fe/Ni BNPs) in simulated groundwater and the consequent effect on the particle reactivity. Results indicate that the morphological, compositional and structural transformation of Fe/Ni BNPs happened during the aging. In the 5-d short-term aging, Fe0 corrosion occurred rapidly and was transformed to ferrous ions which were adsorbed onto the surface of Fe/Ni BNPs, accompanied by the elevation of solution pH and the negative redox potential. In the long-term aging, scanning electron microscopy (SEM) images show that the particles transformed from spherical to rod-like and further to sheet-like and needle-like. X-ray diffraction (XRD) analysis reveals that the main aging product was magnetite (Fe3O4) and/or maghemite (γ-Fe2O3) after aging for 60–90 d. Energy dispersive spectrometer (EDS) analysis demonstrates that the mass ratio of Fe/Ni increased with aging, revealing that Ni were possibly gradually entrapped and covered by the iron oxides. Besides, the release of Ni into solution was also detected during the aging. The reactivity of the aged Fe/Ni BNPs was examined by studying its performance in tetracycline (TC) removal. The aged Fe/Ni BNPs within 2 d kept similar removal efficiency of TC as the fresh particles. However, the removal efficiency of TC by Fe/Ni BNPs aged for 5–15 d dropped by 20–50% due to aggregation and oxidation of particles, and the removal efficiency further decreased slowly with the prolongation of aging time up to 90 d. This reveals that Fe/Ni BNPs were vulnerable to passivation in water environments.

Studies on the removal of As(III) by Fe-based materials have been carried out for decades, but the time-consuming process and low removal capacity are obstacles for large-scale practical applications. Here, a rapid and efficient technique was proposed for the removal of As(III) using Cu-doped Fe@Fe2O3 core–shell nanoparticles (CFF) synthesized by a facile two-step reduction method and aging process, which realized a thorough removal of As(III) from smelting wastewater at neutral pH within 30 min. The copper doped in CFF not only provided two extra oxygen reduction pathways to enhance the molecular oxygen activation, but also improved the electron transfer ability and removal efficiency of As(III). The existence of copper contributed to the rapid oxidization and adsorption of As(III), and the removal rate increased nearly 10-times in the aerobic system. Meanwhile, the proposed Cu-doped Fe@Fe2O3 core–shell nanoparticles and shifted oxygen reduction pathway could be easily scaled up for other transition metals, such as Ni. Molecular dynamics (MD) simulations based on the large-scale atomic/molecular massively parallel simulator (LAMMPS) were also employed to investigate the formation process of CFF. Furthermore, the removal efficiency of arsenic in smelting wastewater remained to be 90% after 6 times of cycling. Therefore, the distinctive oxidation activities of CFF hold great promise for applications in arsenic removal.

When temperate phages and their hosts have a consistent interest, they are considered reciprocal. Based on the bacterium-phage collaboration, lysogenic phage treatment is a promising method to resist pollution through lysogenic phage reshaping indigenous microbial communities to maintain their ecological function under environmental stress. However, the potential factors affecting the establishment of bacterium-phage collaboration are still poorly understood. Here, lysogenic phages carrying arsenic biotransformation genes (ABGs) were induced from the enriched arsenic-resistant microorganisms (from arsenic-contaminated sites). The diversity analysis of viral arsC and arsM demonstrated that arsM tended to proliferate rapidly under high arsenic levels, and the transduction of arsM might be the key to lysogenic phages to help the hosts relieve the stress of high arsenic. Microcosm experiments confirmed that with the increase of the As(III) content (0% to 50%, of 200 mg/kg total arsenic) in the soil, inoculation of lysogenic phages with both arsC and arsM resulted in more transduction of arsM (0.06 ± 0.007 to 0.23 ± 0.024 per 16S rRNA) among soil microorganisms. In contrast, inoculation of lysogenic phages carrying the only arsC transduces more arsC (0.12 ± 0.037 to 0.315 ± 0.051 per 16S rRNA) compare with the control. This article confirmed that different arsenic species proportions and different viral gene compositions could change the abundance of ABGs in the soil microbe, which might provide basic knowledge for further understanding of arsenic pollution control mediated by lysogenic phage.

Nanoscale zero-valent iron (NZVI) has been widely used for the degradation of trichloroethylene (TCE) in contaminated water, however, it is suffering from being easy to aggregate and having low adsorption capacity for TCE. In order to overcome the shortcomings of NZVI, modified NZVI particles with biochar (NZVI/BC) were applied in this study for removal and degradation of TCE, given the high stability and adsorption capacity of BC. The effects of pyrolysis temperature of BC, mass ratio of NZVI/BC and solution pH on the removal and degradation efficiency of TCE were studied. The different pyrolysis temperatures of BC resulted in the differences on the surface areas, aromaticity and noncarbonized fractions, which determined the sorption capacity of TCE. Compared with pure NZVI, the NZVI/BC at different mass ratios could increase the removal efficiency of TCE to 99%, which was attributed to the higher adsorption capacity of BC for TCE. Besides, the yield of final products (ethane, ethylene and acetylene) differed at different mass ratios of NZVI/BC. Generally, the main product was ethylene in all reactions and the yield of acetylene and ethane were relatively low. Solution pH had little effect on the total removal of TCE but significantly influenced the yield of final products. The yield of ethylene decreased with the increasing pH. The results indicate that solution pH could not affect the sorption of TCE but influenced the degradation rate of TCE by NZVI/BC.

Three types of modified biochar (BC) were produced respectively with acid (HCl) treatment (HCl-BC), base (KOH) treatment (KOH-BC) and oxidation (H2O2) treatment (H2O2-BC) of raw biochar. Both the raw biochar and modified biochars supported zero valent iron nanopartilces (nZVI) (i.e. nZVI@BC, nZVI@HCl-BC, nZVI@KOH-BC and nZVI@H2O2-BC) were synthesized and their capacities for Cr(VI) removal were compared. The results showed that the nZVI@HCl-BC exhibited the best performance and the underlying mechanisms were discussed. The surface elemental distribution maps of the nZVI@HCl-BC after reaction with Cr(VI) showed that Fe, Cr and O elements were deposited on the surface of HCl-BC evenly, indicating that the formed Cr(III)/Fe(III) could settle on the surface of HCl-BC uniformly rather than coated only on the nZVI surface. This reveals that the supporter HCl-BC could also play a role in alleviating the passivation of nZVI. Besides, the effects of mass ratio (nZVI/HCl-BC), pH, and initial Cr(VI) concentration on Cr(VI) removal were examined. At lower mass of HCl-BC, nZVI aggregation cannot be fully inhibited on the surface of HCl-BC, whereas excessive biochar can block the active sites of nZVI. Additionally, it was found that Cr(VI) removal by nZVI@HCl-BC was dependent on both pH and initial Cr(VI) concentration.

This study investigated the degradation of trichloroethene (TCE) by nanoscale zero-valent iron (nZVI) w/o persulfate (PS) in the absence and presence of ethylenediaminetetraacetic acid (EDTA). In the absence of EDTA, the degradation of TCE obeyed the pseudo-first-order kinetics, and the rate constants increased exponentially with increasing molar ratio of PS and nZVI. Ethene was found to be the main reaction products in either the single nZVI system or nZVI/PS system. The presence of EDTA increased TCE degradation by nZVI in a short reaction period (within 360 min), whereas the TCE degradation was almost ceased after 1 day in a long-term (6 days) experiment, resulting in a lower TCE degradation than that in the absence of EDTA. However, EDTA drastically decreased TCE degradation in nZVI/PS system. The positive effect of EDTA in the nZVI system should be attributed to its possible inhibition of the precipitation of Fe 2+ /Fe 3+ , which could reduce the surface passivation of nZVI. On the other hand, the adverse effect should be due to the rapid corrosion of nZVI by EDTA and the generation of a large amount of Fe 2+ ions in short time, which could possibly lead to a rapid consumption of sulfate radicals originally for the degradation of TCE.

This study evaluated the influence of silver nanoparticles (AgNPs) on evolutions of organic matter and nitrogen during co-composting of sewage sludge and agricultural waste. Two co-composting piles were conducted, one was treated without AgNPs (pile 1) and the other with AgNPs (pile 2). Results showed that the AgNPs affected the quality of final composts. Less organic matter (OM) losses were determined in pile 2 (57.96%) than pile 1 (61.66%). 27.22% and 30.1% of the initial total organic matter (TOC) was decomposed in pile 1 and pile 2, respectively. The final water soluble carbon (WSC) concentration in pile 2 was 23559.27 mg/kg DW compost which was significantly lower than pile 1 (25642.75 mg/kg DW compost). Changes of different forms of nitrogen in the two piles showed that AgNPs could reduce the losses of TN but increase the losses of mineral N.

This study investigated the long-term compositional and structural evolution of bare nZVI (nanoscale zero-valent iron) and carboxymethyl cellulose (CMC) coated nZVI (CMC-nZVI) in simulated groundwater under anaerobic conditions. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman and Fourier transform infrared spectroscopy (FTIR) were used to characterize the corrosion products of nZVI and CMC-nZVI. Results show that both structure and chemical composition of the aging products of nZVI/CMC-nZVI transformed over time. The SEM images show that the original spherical particles transformed into the sheet-like and needle-like materials for the aged nZVI, but formed bulk aggregates with some flaky-shaped structures for the aged CMC-nZVI. Compare with the aging products of nZVI and CMC-nZVI (i.e., magnetite/lepidocrocite) in the deionized water under anaerobic conditions, the formed secondary products in the simulated groundwater were complicated. The composition analysis confirm that magnetite, lepidocrocite, feroxyhyte and iron carbonate hydroxide hydrate/iron oxide hydroxide chloride were the main corrosion products for both bare nZVI and CMC-nZVI, except that the amount of each secondary mineral varied for different particles. Besides, small amount of calcium carbonate was also identified in the aging products of nZVI. This indicates that the groundwater ions could be involved in the formation of secondary minerals during nZVI corrosion.

Nanoscale zero-valent iron (NZVI) particles, applied for in-situ subsurface remediation, are inevitable to interact with various microbes in the remediation sites directly or indirectly. This review summarizes their interactions, including the effects of NZVI on microbial activity and growth, the synergistic effect of NZVI and microbes on the contaminant removal, and the effects of microbes on the aging of NZVI. NZVI could exert either inhibitive or stimulative effects on the growth of microbes. The mechanisms of NZVI cytotoxicity (i.e., the inhibitive effect) include physical damage and biochemical destruction. The stimulative effects of NZVI on certain bacteria are associated with the creation of appropriate living environment, either through providing electron donor (e.g., H2) or carbon sources (e.g., the engineered organic surface modifiers), or through eliminating the noxious substances that can cause bactericidal consequence. As a result of the positive interaction, the combination of NZVI and some microbes shows synergistic effect on contaminant removal. Additionally, the aged NZVI can be utilized by some iron-reducing bacteria, resulting in the transformation of Fe(III) to Fe(II), which can further contribute to the contaminant reduction. However, the Fe(III)-reduction process can probably induce environmental risks, such as environmental methylation and remobilization of the previously entrapped heavy metals.

The effects of humic acid (HA) and its different molecular weight (MW) fractions on the sedimentation of nanoscale zero-valent iron (NZVI) in the absence and presence of cations (i.e., Na+/Mg2+/Ca2+) were investigated. Ultrafiltration (UF) was used as the method of fractionation to obtain four different MW fractions (separated by ultrafiltration membranes of 10 kDa, 50 kDa, and 100 kDa). Differing sedimentation behavior was observed for NZVI with different MW fractions of HA. Generally, the degree of settling of NZVI particles in the presence of high MW fractions of HA was lower than that of low MW fractions of HA and that without HA. The results were mainly attributed to the steric stabilization provided by the high MW fractions of HA. The presence of Na+/Mg2+/Ca2+ alone had insignificant influence on the settling of NZVI, but both Mg2+ and Ca2+ exerted an obvious influence on the settling of NZVI in the co-presence of HA. The settling behavior of NZVI was further examined in the co-presence of different MW fractions of HA and Ca2+. The co-presence of low MW HA fractions and Ca2+ led to a lower settling of NZVI. This might be due to the formation of a layer of HA-Ca2+ complex on the particle surface, providing stronger steric stabilization. Nevertheless, in the co-presence of high MW HA fractions and Ca2+, the settling of NZVI was initially reduced but accelerated with time, which might be due to the gradual aggregation of NZVI with time resulted from the bridging effect of HA-Ca2+ complex.

Three types of raw biochar (i.e. CBC, OBC, PBC produced from cornstalk, orange peel and peanut hull, respectively) and the modified ones (i.e., KMnO4-, KOH- and H3PO4-treatment) were employed to activate H2O2 for the removal of tetracycline (TC). The effects of pyrolysis temperatures, H2O2 concentration and initial pH were examined. TC removal by raw biochars w/o H2O2 was dependent on the feedstock and pyrolysis temperature of biochar, but the removal efficiency was still quite low under optimum conditions. The KMnO4-treatment significantly enhanced the adsorption of TC on all three biochars, but only enhanced the TC removal by CBC + H2O2. The KOH-treatment had insignificant effect on the adsorption of TC on biochar, but improved the performance of CBC/PBC + H2O2. The H3PO4-treatment had a negative impact on TC removal by biochar w/o H2O2. Overall, H2O2 could either enhance or decrease the TC removal by biochar, depending on biochar type, H2O2 concentration and solution pH.

With the ever-growing water pollution issues, advanced oxidation processes (AOPs) have received growing attention due to their high efficiency in the removal of refractory organic pollutants. Transition metal sulfides (TMSs), with excellent optical, electrical, and catalytical performance, are of great interest as heterogeneous catalysts. These TMSs-based heterogeneous catalysts have been demonstrated to becapable and adaptable in water purification through advanced oxidation processes. The aim of this review is to conduct an exhaustive analysis and summary of recent progress in the application of TMSs-based AOPs for water decontamination. Firstly, the commonly used tuning strategies for TMSs-based catalysts are concisely introduced, including artificial size and shape control, composition control, doping, and heterostructure manufacturing. Then, a comprehensive overview of the current state-of-the-art progress on TMSs-based AOPs (i.e., Fenton-like oxidation, photocatalytic oxidation, and electro chemical oxidation processes) for wastewater treatment is discussed in detail, with an emphasis on their catalytic performance and involved mechanism. In addition, influencing factors of water chemistry, namely, pH, temperature, dissolved oxygen, inorganic species, and natural organic matter on the catalytic performance of established AOPs are analyzed. Furthermore, the reusability and stability of TMSs-based catalysts in these AOPs are also outlined. Finally, current challenges and future perspectives related to TMSs-based catalysts and their applications for AOPs wastewater treatment are proposed. It is expected that this review would shed some light on the future development of TMSs-based AOPs towards water purification.

To assess the long-term fate and the associated risks of nanoscale zero-valent iron (nZVI) used in the water remediation, it is essential to understand the chemical transformations during aging of nZVI in water. This study investigated the compositional and structural evolution of bare nZVI and carboxymethyl cellulose (CMC) coated nZVI in static water over a period of 90 days. Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy were used to characterize the corrosion products of nZVI and CMC-nZVI. Results show that both the structures and the compositions of the corrosion products change with the process of aging, but the coating of CMC could slow down the aging rate of nZVI (as indicated by the slower drop in Fe(0) intensity in XRD pattern). For the bare nZVI, magnetite (Fe3O4) and/or maghemite (γ-Fe2O3) are the dominant corrosion products after 90 days of aging. However, for the CMC-nZVI, the core-shell spheres collapses to acicular-shaped structures after aging with crystalline lepidocrocite (γ-FeOOH) as the primary end product. Moreover, more lepidocrocite present in the corrosion products of CMC-nZVI with higher loading of CMC, which reveals that the CMC coating could influence the transformation of iron oxides.

This study investigated the correlation between the colloidal stability and reactivity of surface-modified nano zero-valent iron (SM-nZVI) as affected by the surface coating (i.e., polyacrylic acid [PAA] and starch) under various geochemical conditions. Generally, the colloidal stability of nZVI was enhanced with increasing loading of surface coating, while there is an optimum loading for the most efficient Cr(VI) removal by SM-nZVI. At lower loadings than the optimum loading, the surface coating could enhance the particle stabilization, facilitating the Cr(VI) reduction by providing more available surface sites. However, the over-loaded surface coating on the surface of nZVI particles decreased the Cr(VI) reduction due to the occupation of the reactive sites and the inhibition of the mass transfer of Cr(VI) ions from water to the particle surface by providing the electrostatic or steric repulsion. The effects of Ca(2+) ions or humic acid (HA) on the colloidal stability and reactivity of PAA-modified nZVI (P-nZVI) and starch-modified nZVI (S-nZVI) were examined. Differing stability behavior and reactivity were observed for different SM-nZVI. It was found that the presence of Ca(2+) or HA altered surface chemistry of SM-nZVI, the particle-particle interaction and the particle-contaminant interaction, and hence influencing the stability behavior and reactivity of the particles.

In the reduction of Cr(VI) by nanoscale zero-valent iron (nZVI), the reactivity of nZVI drops overtime due to surface passivation, which severely inhibits its effective utilization. This study investigated the effect of EDDS (ethylene diamine disuccinic acid) on the Cr(VI) reduction by nZVI at different pH (5.6, 7.0 and 9.0) and the underlying mechanisms. The removal of Cr(VI) by nZVI increased from around 60–100% as the concentration of EDDS increased from 0 to 4–5 mM at pH 5.6–7.0. It was proposed that the EDDS chelated with the generated Cr(III)/Fe(III) and inhibited their co-precipitation onto nZVI surface. However, under alkaline condition (pH 9.0), the EDDS slightly decreased the Cr(VI) reduction, which was due to the fact that the EDDS facilitated the reaction between nZVI/Fe(II) with dissolved oxygen (DO) in the solution. In the absence of DO, a similar positive effect of EDDS on Cr(VI) reduction was observed at pH 9.0 as that at pH 5.6–7.0. Additionally, it was found that the EDDS could significantly increase the kinetics of nZVI corrosion in deionized water. These results demonstrate that EDDS could be used effectively as a chelating agent for inhibiting the surface passivation and increasing the effective utilization of nZVI.

This study investigated the effect of fulvic acid (FA) on the colloidal stability and reactivity of nano zero-valent iron (nZVI) at pH 5, 7 and 9. The sedimentation behavior of nZVI differed at different pH. A biphasic model was used to describe the two time-dependent settling processes (i.e., a rapid settling followed by a slower settling) and the settling rates were calculated. Generally, the settling of nZVI was more significant at the point of zero charge (pHpzc), which could be varied in the presence of FA due to the adsorption of FA on the nZVI surface. More FA was adsorbed on the nZVI surface at pH 5–7 than pH 9, resulting in the varying sedimentation behavior of nZVI via influencing the electrostatic repulsion among particles. Moreover, it was found that there was a tradeoff between the stabilization and the reactivity of nZVI as affected by the presence of FA. When FA concentration was at a low level, the adsorption of FA on the nZVI surface could enhance the particle stabilization, and thus facilitating the Cr(VI) reduction by providing more available surface sites. However, when the FA concentrations were too high to occupy the active surface sites of nZVI, the Cr(VI) reduction could be decreased even though the FA enhanced the dispersion of nZVI particles. At pH 9, the FA improved the Cr(VI) reduction by nZVI. Given the adsorption of FA on the nZVI surface was insignificant and its effect on the settling behavior of nZVI particles was minimal, it was proposed that the FA formed soluble complexes with the produced Fe(III)/Cr(III) ions, and thus reducing the degree of passivation on the nZVI surface and facilitating the Cr(VI) reduction.

The current study developed a new perspective whether crystalline structures influence the adsorption of heavy metals on magnetic iron oxides synthesized by applying surfactant sodium dodecyl sulfate (SDS)-templated strategy. The products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive analysis of X-ray (EDAX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transformed infrared spectroscopy (FT-IR), and ζ-potential analyzer. Most SDS were removed after calcination and the phase of iron oxide transformed from amorphous Fe 3 O 4 to (α + γ)-Fe 2 O 3 and finally to highly crystalline α-Fe 2 O 3 , followed by decreasing surface area and pore volume with increasing calcining temperatures. Amorphous Fe 3 O 4 exhibited a better adsorption capacity towards Pb (II) and Cd (II) than that of (α + γ)-Fe 2 O 3 and α-Fe 2 O 3 , suggesting that metals adsorption by amorphous iron oxide was superior to that owns high degree of crystallization. The removal performances containing ion exchange, hydrolysis of heavy metals, electrostatic attraction and chemical binding or specific interaction were consistent with XPS and other measurements. After five adsorption–desorption cycles, all synthesized iron oxides still maintained above 79% removal efficiency for both Pb (II) and Cd (II). This study provides a promising potential for the application of iron oxides as adsorbents for heavy metals treatment in wastewater.

This study investigated the performance of immobilized Phanerochaete chrysosporium loaded with nitrogen-doped TiO2 nanoparticles in the treatment of raw landfill leachate with a very low biodegradability ratio (BOD5/COD) of 0.09. The effects of various operating parameters, such as initial chemical oxygen demand (COD) concentration, pH, temperature, and biosorbent dosage, were evaluated with respect to the removal efficiency of total organic carbon (TOC) and ammonia nitrogen (NH3-N). For the immobilized biosorbents, an optimum pH of 6.0 for TOC and 7.0 for NH3-N were found suitable for TOC and NH3-N removal at temperature of 37°C, respectively. The most superior removal efficiencies of TOC and NH3-N of landfill leachate were over 75% and 74% in 72 h at an initial COD concentration of 200 mg L(-1), respectively. In addition, heavy metals were partly removed by the immobilized biosorbents during the process of landfill leachate treatment. The species and mass percentage of organic compounds in landfill leachate after the treatment were found to have considerably declined according to the gas chromatography coupled with mass spectrometry (GC-MS) system. These results indicate that the immobilized P. chrysosporium loaded with nitrogen-doped TiO2 nanoparticles could be a convenient and efficient method for the treatment of landfill leachate.

Iron nanoparticle-doped magnetic ordered mesoporous carbon (Fe/OMC) was prepared by co-impregnation and carbothermal reduction methods, and used for highly effective adsorption and degradation of bisphenol A (BPA). Several techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption–desorption isotherms were applied to characterize the prepared composites. Batch experiments were conducted to explore the decontamination performance, and the results showed that the removal capacity can reach an equilibrium value of 311 mg g−1 at an initial BPA concentration of 200 mg L−1. Kinetic study showed that it agreed well with the pseudo-second-order model (R2 = 0.999). In addition, the Langmuir and Freundlich models were used to describe the removal process. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis confirmed the existence of Fe0 nanoparticles in the obtained composites. The mechanism of interaction between Fe/OMC and BPA was investigated by Fourier transform infrared spectrometry (FTIR), XRD and XPS analyses. Furthermore, thermodynamics studies were carried out and the exhausted composites could be regenerated with ethanol and easily separated with a magnet.

Personal exposure to air pollution is affected by its concentration in the microenvironment and individual time-activity patterns. To investigate personal black carbon (BC) exposure levels and identify their potential determinants, we conducted a panel study among 67 elderly residents aged 60–69 years in Jinan, China. Personal BC exposure was measured using portable real-time monitors, while corresponding ambient BC concentrations and meteorological conditions were also collected from the local central site. Time-activity and household characteristics were recorded. A linear mixed-effects model was used to identify potential determinants of personal BC exposure. The daily average personal BC exposure concentration was 4.1 ± 2.0 μg/m3 (±standard deviation, SD), which was significantly lower than the ambient concentration (4.6 ± 2.5 μg/m3) (p

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 (

Bimetallic Fe/Cu nanoparticles were successfully stabilized by chitosan used for remediating hexavatlent chromium contaminated wasterwater. However, the over-loaded chitosan on the surface of Fe/Cu particles limited the Cr(VI) reduction due to the occupation of the surface reactive sites. Weighing the colloid stability and the reduction reactivity, the optimal dosage of chitosan is 2.0 wt% and the optimal Cu doping dosage is 3.0 wt%. SEM and TEM images showed that the chitosan-stabilized Fe/Cu bimetallic nanoparticles (CS-Fe/Cu nanoparticles) were uniformly dispersed, which had loose and porous surface. FTIR characterization showed that the binding sites of nZVI and chitosan. XRD demonstrated that the presence of copper and chitosan did not change the existence form of zero-valent iron. Most importantly, the contribution of chitosan and Cu in the removal mechanism was studied by the reduction experiments and the XPS analysis. On the one hand, chitosan could effectively combine with Cr(VI) due to chelation, on the other hand, Cu played an important role in the precipitation and coprecipitation phenomena. These findings indicate that CS-Fe/Cu has the potential to be a promising material for wastewater treatment.

This study examined the feasibility of nanoscale zero-valent iron (nZVI) for the single and combined removal of Cr(VI) and Cd(II) with or without ethylene diamine disuccinic acid (EDDS). The effects of pH and dissolved oxygen (DO) on the removal process were investigated. Results show that the single removal of either Cr(VI) or Cd(II) by nZVI was pH dependent, where the higher Cr(VI) removal was achieved under acidic conditions, whereas the higher Cd(II) removal was achieved under alkaline conditions. The presence of DO enhanced Cd(II) removal but inhibited Cr(VI) removal under alkaline conditions. In the co-existence of Cr(VI) and Cd(II), it was found that Cd(II) exerted insignificant effect on Cr(VI) removal, while the presence of Cr(VI) remarkably enhanced the Cd(II) removal. The addition of EDDS exhibited different influences on Cr(VI) and Cd(II) removal, which were associated with pH and DO. The EDDS enhanced Cr(VI) removal at pH 5.6–9.0 in the absence of DO, but decreased Cr(VI) removal at pH 9.0 in the presence of DO. For the removal of Cd(II) at pH 5.6–7.0, either facilitation or inhibition effect of EDDS was observed, depending on EDDS concentration and the co-existence of Cr(VI). However, Cd(II) removal was always significantly inhibited by EDDS at pH 9.0.

Groundwater vulnerability assessment delineating areas that are susceptible to contamination from future scenarios has aroused worldwide attention. In this study, the authors (1) estimate f...

The sequestration of Se(IV) and Se(VI) by nanoscale zero-valent iron (NZVI) particles were compared under different solution conditions. Firstly, the comparison was conducted at three pH values (4.0, 6.0 and 8.0) in deionized water. Generally, the removal of Se(IV)/Se(VI) by NZVI was more rapid under acidic conditions and the removal efficiency of Se(IV) was much higher than that of Se(VI). Moreover, the pH variation exhibited much larger influence on the sequestration of Se(VI) than that of Se(IV) by NZVI. The spectroscopic analysis showed that both the Se(IV) and Se(VI) were reduced to Se0 and Se2-, while NZVI was transformed into iron (hydr)oxides. When the selenium-NZVI reactions occurred in synthetic groundwater, all the reaction systems were inhibited in varying degrees. The individual effects of humic acid (HA) and typical inorganic ions were also examined. It seems that HA could substantially hinder the sequestration of Se(IV) compared with that in deionized water, while sulfate (SO42-) and bicarbonate (HCO3-) inhibited the Se(VI) removal significantly. Notably, the presence of cations (i.e., Na+ or Ca2+) ions did not cause obvious interference to the Se(IV)/Se(VI) removal by NZVI, while the presence of Ca2+ could alleviate the adverse effect of HA on Se(IV) removal to some degree.

This study investigated the evolutions of different microbial populations and multivariate relationships between their abundances and environmental variables during composting with amendment of Fe (hydr)oxide nanoparticles. Piles treated with nanohematite and nanomagnetite were denoted as T-nanohematite and T-nanomagnetite, and another one was T-control. It was found that nanohematite more effectively increased bacteria and fungi abundances with 1.24∼1.58 times average value of T-control, while nanomagnetite was more useful to actinomycetes. As the most significant variable, the total effect of temperature in T-control and T-nanomagnetite was increased to 0.87 and 0.92, respectively, because both the direct and indirect effects were positive, while it in T-nanohematite was reduced to 0.18 by the negative indirect effect. Partial redundancy analysis suggested that each microbial abundance shared different relationships with composting parameters. Overall, actinomycetes was more sensitive to changes of composting parameters than bacteria and fungi.

Composting amended with iron oxide nanoparticles (FeONPs, α-Fe2O3 and Fe3O4 NPs) were conducted to study the impacts of FeONPs on nitrogen conservation and microbial community. It was found that amendment of FeONPs, especially α-Fe2O3 NPs, reduced total nitrogen (TN) loss, and reserved more NH4+-N and mineral N. Pearson correlation analysis revealed that decrease of ammonia-oxidizing bacteria (AOB) in FeONPs treatments played more important role than ammonia-oxidizing archaea (AOA) in reserving more NH4+-N and mineral N, and reducing TN loss. Bacterial community composition at phylum level did not shift with addition of FeONPs. Firmicutes, Actinobacteria, and Proteobacteria were the three most dominant phyla in all treatments. Overall, this study provides a method to reduce TN loss and improve mineral N reservation during composting, and gives a deep insight into the role of AOB and AOA in nitrogen transformation.

Sulfidated nanoscale zerovalent iron (S-NZVI) is attracting considerable attention due to its easy production and high reactivity to pollutants. We studied the reactivity of optimized S-NZVI (Fe/S molar ratio 6.9), comparing with pristine nanoscale zerovalent iron (NZVI), at various pH solutions (6.77-9.11) towards p-nitrophenol (PNP) under aerobic and anoxic conditions. Studies showed that the optimized extent of sulfidation could utterly enhance PNP degradation compared to NZVI. Batch experiments indicated that in anoxic S-NZVI systems the degradation rate constant increased with increasing pH up to 7.60, and then declined. However, in aerobic S-NZVI, and in anoxic or aerobic NZVI systems, it decreased as pH increased. It was manifested that anoxic S-NZVI systems preferred to weaker alkaline solutions, whereas aerobic S-NZVI systems performed better in acidic solutions. The highest TOC removal efficiency of PNP (17.59%) was achieved in the aerobic S-NZVI system at pH 6.77, revealing that oxygen improved the degradation of PNP by excessive amounts of hydroxyl radicals in slightly acidic conditions, and the TOC removal efficiency was supposed to be further improved in moderate acidic solutions. Acetic acid, a nontoxic ring opening by-product, confirms that the S-NZVI system could be a promising process for industrial wastewater containing sulfide ions.

Nanoscale zero-valent iron (NZVI) particles are usually modified with surface coating to mitigate the particle stability in water during the environmental application. However, the surface coating may not only influence the particle stabilization but also the particle cytotoxicity. In this study, we investigated the dual effects of carboxymethyl cellulose (CMC) on the colloidal stability and cytotoxicity of NZVI towards gram-negative Escherichia coli ( E. coli ) and discussed the interrelation between particle stability and cytotoxicity. The effect of CMC concentration, ionic strength (Ca 2+ ) and aging treatment on the particle cytotoxicity were also examined. Specifically, the aqueous stability of NZVI suspensions with CMC ratio dose-dependently strengthened within 1 h. The inactivation of E. coli by bare NZVI was significant and concentration- and time-dependent. On the contrary, an increasing reduction in cytotoxicity of NZVI with CMC ratio increasing was observed, even though the particles became more dispersed. TEM analysis demonstrates the membrane disruption and the cellular internalization of nanoparticles after exposure of E. coli to NZVI. However, in the case of CMC-modified NZVI (CNZVI), the bacterial cell wall displays an outer shell of a layer of nanoparticles attached around the outer membrane, but the cell membrane was kept intact. The presence of Ca 2+ can either increase or decrease the cytotoxicity of NZVI and CNZVI, depending on the concentration. The aged NZVI and CNZVI particles did not seem to present obvious bactericidal effect due to the transformation of Fe 0 to the less toxic or non-toxic iron oxides, as indicated by the XRD analysis.