Exploring the synergistic effect of chromium (Cr) tolerant Pseudomonas aeruginosa and nano zero valent iron (nZVI) for suppressing Cr uptake in Aloe Vera.

Chromium (Cr) contamination of soil has substantially deteriorated soil health and has interfered with sustainable agricultural production worldwide and therefore, its remediation is inevitable. Inoculation of plant growth promoting rhizobacteria (PGPR) in association with nanotechnology has exerted broad based impacts in agriculture, and there is an urgent need to exploit their synergism in contaminated soils. Here, we investigated the effect of co-application of Cr-tolerant "Pseudomonas aeruginosa CKQ9" strain and nano zerovalent iron (nZVI) in improving the phytoremediation potential of aloe vera (Aloe barbadensis L.) under Cr contamination. Soil was contaminated by using potassium dichromate (K2Cr2O7) salt and 15 mg kg-1 contamination level in soil was maintained via spiking and exposure to Cr lasted throughout the duration of the experiment (120 days). We observed that the co-application alleviated the adverse impacts of Cr on aloe vera, and improved various plant attributes such as plant height, root area, number of leaves and gel contents by 51, 137, 67 and 49% respectively as compared to control treatment under Cr contamination. Similarly, significant boost in the activities of various antioxidants including catalase (124%), superoxide dismutase (87%), ascorbate peroxidase (36%), peroxidase (89%) and proline (34%) was pragmatic under contaminated soil conditions. In terms of soil Cr concentration and its plant uptake, co-application of P. aeruginosa and nZVI also reduced available Cr concentration in soil (50%), roots (77%) and leaves (84%), while simultaneously increasing the relative production index by 225% than un-inoculated control. Hence, integrating PGPR with nZVI can be an effective strategy for enhancing the phytoremediation potential of aloe vera.

Combined effect of PGPR and nanotechnology in the bioremediation of toxic contaminants is well reported in literature. Most of these reports comprise the use of hyperaccumulator plants for phytoextraction of heavy metals. However, phytostabilization potential of hyperaccumulators is still un-explored. Current study investigated the role of PGPR and Fe-NPs in suppressing the uptake of Cr in aloe vera, a hyperaccumulator plant.

Green cleanup of styrene-contaminated soil by carbon-based nanoscale zero-valent iron and phytoremediation: Sunn hemp (Crotalaria juncea), zinnia (Zinnia violacea Cav.), and marigold (Tagetes erecta L.).

Accidental chemical spills can result in styrene-contaminated soil. Styrene negatively affects human health and the environment. The objective of this study was to remediate styrene-contaminated soil using a combination of activated carbon-based nanoscale zero-valent iron (nZVI-AC) and phytoremediation by sunn hemp (Crotalaria juncea), zinnia (Zinnia violacea Cav.) and marigolds (Tagetes erecta L.). The results showed that all three plant types could potentially increase the removal efficiency of styrene-contaminated soil. At 28 days, all three plants showed complete removal of styrene from the soil with 1 g/kg of nZVI-AC, activated carbon-based nZVI synthesized by tea leaves (Camellia sinensis) (T-nZVI-AC), or activated carbon-based nZVI synthesized by red Thai holy basil (Ocimum tenuiflorum L.) (B-nZVI-AC). However, styrene removal efficiencies of sunn hemp, zinnia, and marigold without carbon-based nZVI were 30%, 67%, and 56%, respectively. Statistical analysis (ANOVA) revealed that the removal efficiencies differed significantly from those of phytoremediation alone. With the same removal efficiency (100%), the biomass of sunn hemp in nano-phytoremediation treatments differed by approximately 55%, whereas the biomass of zinnia differed by >67%, compared with that of the control experiment. For marigold, the difference in biomass was only 30%. Styrene was adsorbed on surface of soil and AC and then further oxidized under air-water-nZVI environment, while phytovolatilization played an important role in transporting the remaining styrene from the contaminated soil to the air. Marigold was used as an alternative plant for the nano-phytoremediation of styrene-contaminated soil because of its sturdy nature, high biomass, tolerance to toxic effects, and ease of cultivation. Remediation of one cubic meter of styrene-contaminated soil by a combination of carbon-based nanoscale zero-valent iron and phytoremediation by marigolds emitted 0.0027 kgCO2/m3.

Performance evaluation of sulfidated nanoscale iron for hexavalent chromium removal from groundwater in sequential batch study.

Chromium [Cr] contamination in groundwater is one of the serious environmental concerns due to the carcinogenicity of its water-soluble and mobile hexavalent [Cr(VI)] form. In spite of the existence of multiple precipitation and adsorption-based Cr(VI) remediation technologies, the usage of sulfidated nano zerovalent iron (S-nZVI) has recently attracted researchers due to its high selectivity. Although S-nZVI effectively immobilized Cr(VI), its long-term performance in multiple shifted equilibrium has not been explored. In this contribution, influences of S-nZVI dosage, initial concentration of Cr(VI), pH, ionic strength, total hardness, sulfate, carbonate, and silicate were probed in ultrapure water. Further experiments were performed in synthetic groundwater to investigate the effects of initial concentration of Cr(VI) in the pH range of 4-8 for 1 g L-1 S-nZVI dosage. Cr(VI) removal rate was quantified in groundwater without pH fixation. Finally, a comparative study between conventional nano zerovalent iron (nZVI) and S-nZVI was conducted in sequential batch reactors to investigate their respective efficiencies during repeated usage. Mechanistic interpretation of the processes governing the immobilization of Cr(VI) was done by integrating the results of these experiments with the metadata. While aggregation due to magnetic properties and rapid oxidation of Fe decreased the efficiency of nZVI with repeated usage, sulfidation minimized the passivation and favored an extended reducing environment because of continuous electron transfer from iron and sulfur components.

Clean water production from plastic and heavy metal contaminated waters using redox-sensitive iron nanoparticle-loaded biochar.

The unceasing release of tiny plastics (microplastics and nanoplastics) and their additives, like metal ions, into the aquatic systems from industries and other sources is a globally escalating problem. Their combined toxic effects and human health hazard are already proven; hence, their remediation is requisite. This study utilised the nano-zerovalent iron-loaded sugarcane bagasse-derived biochar (nZVI-SBC) for simultaneous removal of Nanoplastics (NPs) of different functionality and size along with metal ions (Ni2+, Cd2+, AsO43-, and CrO42-). Batch and column experiments were conducted, and the results showed an efficient removal of contaminants with maximum sorption of carboxylate-modified NPs of size 500 nm (qmax = 90.3 mg/g) among all three NPs types. Significant removal was observed in Cd2+ in case of cations and CrO42- in case of anions with qmax = 44.0 and 87.8 mg/g, respectively. Kinetics and the isotherm modelling better fitted the pseudo-second-order kinetic model and Sips isotherm model, respectively for both NPs and metal ions. The designed material worked well in pH range of 4-8, ionic strength 1-20 mM and in complex aqueous matrices, with >90% removal. FTIR, zeta potential and the imaging analysis of the reaction precipitates confirmed the electrostatic attraction, pore retention and complexation as the potential mechanisms for removing NPs, whereas, XPS studies confirmed the reduction co-precipitation and surface complexation as the possible mechanism for removing metal ions. High values of attachment efficiency factor calculated from colloidal filtration theory (CFT) validated the experimental results and justified the high sorption of carboxylate modified 500 nm NPs particles. The synthesized material successfully removed both NPs of varying size and functionality and metal ions simultaneously with significant efficacy in complex environmental samples proving the broad applicability of material in realistic environmental conditions and different types of water treatment processes.

Fabrication of Chitin microspheres supported sulfidated nano zerovalent iron and their performance in Cr (VI) removal.

Sulfidated nanoscale zerovalent iron (S-nZVI) has been extensively studied for the reductive removal of Cr(VI), but its applicability is limited by agglomeration and unexpected efficiency reduction. In this study, chitin microsphere supported sulfidated nanoscale zero-valent iron (S-nZVI@Chi-M) was prepared by in-situ one-step reduction method and used to remove Cr(VI) from water. Compared to chitin and chitosan powder, Chi-M with nanofibrous structure and large surface area performed best in stabilizing S-nZVI with a Fe0 loading content of 3.01 wt%. The S-nZVI particles were homogeneously distributed on the surface of Chi-M, effectively avoiding agglomeration. Compared with bare nanoparticles and supported nZVI, S-nZVI@Chi-M showed significantly enhanced Cr(VI) removal capacity (924.5 mg Cr(VI) for per gram of effective Fe0). The influences of sulfidation degree, dosages, initial Cr(VI) concentration, pH, DO, humic acid and typical ions on Cr(VI) removal kinetics were further studied. S-nZVI@Chi-M could be recycled for at least 4 times with acceptable reactivity. The mechanism investigation results indicated that the Cr(VI) removal was a complex process of reduction, adsorption and co-precipitation under the synergistic effect of Chi-M and S-nZVI. This work provides new ideas for the continuous fabrication of highly reactive nanoparticles, hopefully expanding the application scope of biomass resources in pollution remediation.

Synergistic effect of sulfidated nano zerovalent iron and proton-buffering montmorillonite in reductive immobilization of alkaline Cr(VI)-contaminated soil.

Effective remediation of Cr(VI)-contaminated soil with strong alkalinity and high Cr(VI) concentration is a severe challenge. Herein, a proton-buffering montmorillonite-supported sulfidated nano zerovalent iron (nFeS/Fe0@H-Mt) was developed for remediation of alkaline Cr(VI)-contaminated soil. The reductive efficiencies of water-soluble Cr(VI) reached 99.7%, 99.3% and 99.8% in three tested soils with initial concentrations of 439.6, 3307.5 and 4626.7 mg kg-1, respectively, after 15 d of nFeS/Fe0@H-Mt treatment. Further speciation analyses demonstrated most available Cr species (exchangeable and carbonate-bound Cr) were transformed into more stable Cr species. The leachable Cr(VI) and total Cr obtained by toxicity leaching procedures decreased to extremely low levels and maintained long-term stability for 120 d. Such superior reductive immobilization performance of FeS/Fe0@H-Mt was attributed to the synergistic effect of sulfidated nano zerovalent iron and proton-buffering montmorillonite, which induced the coordination of proton donation and electron transfer. The proton-buffering montmorillonite (H-Mt) could prevent the aggregation of nanoparticles and provide protons to accelerate the corrosion of Fe0. In addition, the FeS component improved electron selectivity and facilitated electron transfer of Fe0 to Cr(VI). Our study demonstrated that the coordination of proton donation and electron transfer significantly enhanced the Cr(VI) reduction under the alkaline condition thus leading to effective remediation of alkaline Cr(VI)-contaminated soil.

Presence of polystyrene microplastics in Cd contaminated water promotes Cd removal by nano zero-valent iron and ryegrass (Lolium Perenne L.).

Microplastics, as emerging contaminants, have attracted widespread attention for their increasing detection frequency in aquatic environment. It has been reported that microplastics may co-presence with heavy metals in water, which might have impact on heavy metals removal in water. Furthermore, the effects of microplastics on the co-remediation efficiency of plants with engineered nanomaterials are ambiguous. To this end, this study was dedicated to unveil the intrinsic effects of polystyrene microplastics (PSMPs) on the cadmium (Cd) removal efficiency by co-remediation of ryegrass (Lolium perenne L.) and three engineered nanomaterials, respectively were nano-zerovalent iron (nZVI), carboxymethylcellulose-modified-nZVI (C-nZVI) and sulfidated nZVI (S-nZVI). Significant changes were observed in Cd content, plant biomass, chlorophyll b and antioxidant enzymes. It was surprising to find that with the treatment of nZVI or C-nZVI, polystyrene microplastics would enter plants roots, and these plants were found to contain more Cd among all series. Accordingly, four possible mechanisms were proposed to explain why plants that observed the internalization of PSMPs contained more Cd. This work reveals the impact of coexisting microplastics in water on Cd remediation efficiency and provides new insights into the entry of polystyrene microplastics into plant roots.

Enhanced nitrobenzene removal in soil by biochar supported sulfidated nano zerovalent iron: Solubilization effect and mechanism.

Sulfidated nano zerovalent iron (S-nZVI) is reported to be effective in removal of aqueous organic contaminants. However, little is known about its potential use in reductive degradation of soil-sorbed contaminants. In this study, biochar (BC) supported S-nZVI (S-nZVI@BC) was successfully synthesized through sulfidation and carbon loading modification, which effectively combined the solubilization characteristics of BC and high reduction characteristics of S-nZVI. Transmission electron microscopy (TEM) with an energy-dispersive X-ray spectroscopy (EDS) analysis suggested that sulfur and iron were evenly distributed throughout BC matrix. The degradation of nitrobenzene (NB) in soil was achieved more efficiently with the as-synthesized S-nZVI@BC composites. Results indicated that S-nZVI@BC with S-nZVI/BC mass ratio of 3:1, dosage of 10 mg/g exhibited superior NB removal (98%) and aniline (AN) formation (90%) efficiency within 24 h without formation of other intermediates, higher than those of S-nZVI. Meanwhile, the surface FeSX layer enhanced the antioxidant capacity of S-nZVI@BC and participated in the reduction of NB. The soil-sorbed NB decreased from 14% to 1.4%, indicating that the addition of BC played an important role in solubilization of NB from soil. Solubilization-reduction was the dominant mechanism for NB removal. This research indicated that S-nZVI@BC held the potential to enhance in-situ remediation of NB-contaminated soil.

Nitrates Removal from Simulated Groundwater Using Nano Zerovalent Iron Supported by Polystyrenic Gel.

The main objectives of this present paper were to indicate the immobilization of nano zerovalent iron (nZVI) onto a polymeric material (Purolite A400) and the synthesis of the polymeric material (A400-nZVI) through sodium borohydride (NaBH4) reduction. The obtained polymeric material (A400-nZVI) was used for the nitrate ions removal from a simulated groundwater at different conditions. The polymeric materials, without and with nano zerovalent iron (A400 and A400-nZVI), were characterized trough the FTIR, SEM-EDAX, XRD, and TGA analysis. The analysis confirmed the presence of nano zerovalent iron (nZVI) onto the polymeric material (A400). The adsorption capacity of A400-nZVI, used as polymeric adsorbent, was evaluated by kinetic and thermodynamic studies. The obtained experimental results indicated that the nitrate ions reduction was fitted well by models: pseudo-second-order kinetic and Freundlich isotherm. According to the kinetic model results, a reaction mechanism could exist in the stage of reactions. The higher value of removal nitrate (>80%) was obtained under acidic condition. The results indicated that the obtained polymeric material (A400-nZVI) can be considered as a potential polymeric adsorbent for different pollutants from groundwater and wastewater.

Synergistic effect of sulfidated nano zerovalent iron and persulfate on inactivating antibiotic resistant bacteria and antibiotic resistance genes.

Antimicrobial resistance continues to be a rising global threat to public health. It is well recognized that wastewater treatment plants are reservoirs of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). However, traditional disinfection techniques are not effective to simultaneously remove ARB and ARGs, and the dynamic analysis of ARB inactivation have also been deficient. In this study, sulfidated nano zerovalent iron (S-nZVI) coupled with persulfate (PS) was applied to simultaneously remove both ARB (E. coli K-12 with RP4 plasmid) and ARGs (extra- and intracellular ARGs). S-nZVI/PS completely inactivated ARB (~7.8-log reduction) within 10 min and degraded all extracellular ARGs (~8.0-log reduction) within 5 min. These efficiencies were significantly higher (decay rate constant, k = 0.138 min-1) than those achieved individually (S-nZVI: k = 0.076 min-1; PS: k = 0.008 min-1), implying a synergistic effect between S-nZVI and PS against ARB and ARGs. The efficient removal rate of ARB was also supported by confocal microscopy and microfluidics at a single-cell level. The complete inactivation of ARB by S-nZVI/PS was also demonstrated in real drinking water and real wastewater effluent that contained natural organic matter and suspended solids. Regrowth assays showed that the treated ARB was not observed after 72 h or longer incubation, suggesting that ARB was permanently inactivated by radicals such as SO4•- and •OH. The destruction of bacterial cells compromised the removal efficiency of the intracellular ARGs, with only ~4.0-log reduction after 60 min treatment by S-nZVI/PS. Collectively, our results suggest the feasibility of S-nZVI coupled with PS for simultaneous ARB and ARGs removal in real water matrices.

Enhanced bisphenol S anaerobic degradation using an NZVI-HA-modified anode in bioelectrochemical systems.

As a substitute for bisphenol A (BPA), bisphenol S (BPS) has a longer half-life, higher chemical inertness and better skin permeability than BPA, and it also has a strong endocrine disruption effect. Relatively few studies have focused on the main processing technology for BPS biodegradation, and the findings indicate that the biodegradation efficiency of BPS was relatively low. Therefore, this paper used an NZVI-HA composite-modified bio-anode to enhance the anaerobic degradation of BPS in a Bioelectrochemical Systems (BES). The results showed that the degradation efficiency of BPS was improved from 31.1% to 92.2% with the NZVI-HA modification compared with the control group (CC-BES). FTIR and XPS analyzes demonstrated that HA can accelerate the reduction rate of Fe3+ and increase the ratio of Fe2+/Fe3+. In addition, HA can form Fe-O-HA complexes with NZVI to promote electron transfer. An analysis of the NZVI-HA-BES intermediate metabolites revealed that complex modification properties altered the BPS degradation pathway. An analysis of microbial diversity indicated that the bacteria related to the degradation of BPS may be Terrimonas, Lysobacter, and Acidovorax.

Nanoscale Zero-Valent Iron Has Minimum Toxicological Risk on the Germination and Early Growth of Two Grass Species with Potential for Phytostabilization.

Two Poaceae species, Agrostis capillaris and Festuca rubra, were selected for their potential as phytostabilizing plants in multicontaminated soils. These species are resistant to contamination and maintain high concentrations of contaminants at the root level. Nanoscale zero-valent iron (nZVI) is an engineered nanomaterial with the ability to stabilize metal(loid)s in soils; its potential toxicological effects in the selected species were studied in a germination test using: (i) control variant without soil; (ii) soil contaminated with Pb and Zn; and (iii) contaminated soil amended with 1% nZVI, as well as in an hydroponic experiment with the addition of nZVI 0, 25, 50 and 100 mg L-1. nZVI had no negative effects on seed germination or seedling growth, but was associated with an increase in shoot growth and reduction of the elongation inhibition rate (root-dependent) of F. rubra seedlings. However, applications of nZVI in the hydroponic solution had no effects on F. rubra but A. capillaris developed longer roots and more biomass. Increasing nZVI concentrations in the growing solution increased Mg and Fe uptake and reduced the Fe translocation factor. Our results indicate that nZVI has few toxic effects on the studied species.

Heterogeneous Fenton Degradation of Patulin in Apple Juice Using Carbon-Encapsulated Nano Zero-Valent Iron (CE-nZVI).

Patulin (PAT), a mycotoxin found mainly in matured apples, is produced by different species of fungi, mainly Penicillium expansum, and is found in various fruits and vegetables used to produce juice. Little focus has been placed on nano-technological methods for the mitigation of this problem. In this work, carbon-encapsulated nano-zero valent iron (CE-nZVI) particles were synthesized and used as heterogeneous Fenton agents for the degradation of PAT in apple juice. The particles were found to have a spherical shape with a diameter of 130 ± 50 nm. In a heterogeneous Fenton degradation (involving CE-nZVI) process, a concentration of 0.05 g/L CE-nZVI with 0.5 mM H2O2 was used. Since the Fenton oxidation process is pH-dependent, placebo degradation was observed at varying pH conditions with an average percentage of PAT degradation of 27.8%, 87.0%, 98.0%, and 99.75% at pH 6, 5, 4.5, and 3.5 respectively, between 1 min to 4 h in a water matrix. In a juice matrix, at the regular pH of juice (3.6), percentage PAT degradation of 72% and 89% was obtained after a 2-h treatment using heterogeneous Fenton oxidation (CE-nZVI/H2O2) systems, using 0.5 mM H2O2 and 1 mM H2O2, respectively.

Degradation of azo dye Acid Red 14 (AR14) from aqueous solution using H2 O2 /nZVI and S2 O8 2- /nZVI processes in the presence of UV irradiation.

Azo dyes are mostly toxic and carcinogenic and cause harm to humans and the environment. This study was conducted to investigate the degradation of azo dye acid red 14 (AR14) from aqueous solution using hydrogen peroxide (H2 O2) /nano zerovalent iron (nZVI) and persulfate (S2 O8 2- )/nZVI processes in the presence of ultraviolet (UV) irradiation. This experimental study was carried out in a laboratory-scale batch photoreactor with a useful volume of 1 L. The nZVI was synthesized by the sodium borohydride (NaBH4 ) reduction method. In these processes, the effects of parameters including initial pH, H2 O2 concentration, S2 O8 2- concentration, nZVI dose, concentration of AR14 dye, and reaction time were studied. The results showed that decolorization increased by increasing the nZVI dosage, H2 O2 and S2 O4 2- concentrations, and reaction time, or decreasing dye concentration and pH. However, a too high oxidant concentration (H2 O2 and S2 O4 2- ) could inhibit the degradation. The experimental conditions for degradation of AR14 by UV/S2 O8 2- /nZVI and UV/H2 O2 /nZVI processes were as follows: [H2 O2 ] = 10 mM, [S2 O8 2- ] = 8 mM, AB14 dye = 100 mg/L, pH = 3, and nZVI dose = 0.05 g. Under these conditions, the highest removal efficiencies of AR14, chemical oxygen demand (COD), and total organic carbon (TOC) for the UV/S2 O8 2- /nZVI process were 93.94%, 86.5%, and 81.6%, respectively, while these values were 89.3%, 79.57%, and 72.9% for the UV/H2 O2 /nZVI, respectively. Also, the average oxidation state (AOS) was decreased from 2.93 to 2.14 in the effluent of the UV/S2 O8 2- /nZVI process and from 2.93 to 2.2 for the UV/H2 O2 /nZVI process. The results showed that the ratio of biochemical oxygen demand (BOD5 ) to COD in the effluents of the UV/S2 O8 2 /nZVI and UV/H2 O2 /nZVI processes after 90 min was 0.63 and 0.74, respectively. These findings suggest biodegradability improvement. PRACTITIONER POINTS: Photocatalytic degradation of azo dye Acid Red 14 (AR14) was achieved using H2 O2 /nZVI and S2 O8 2- /nZVI processes in the presence of UV irradiation. Effects of operating parameters on photocatalytic degradation AR14 dye were evaluated in the UV/H2 O2 /nZVI and UV/S2 O8 2- /nZVI processes. Biodegradability and mineralization studies of AR14 dye photocatalytic degradation were performed for the UV/H2 O2 /nZVI and UV/S2 O8 2- /nZVI processes.

Sulfidated nano zerovalent iron (S-nZVI) for in situ treatment of chlorinated solvents: A field study.

Sulfidated nano zerovalent iron (S-nZVI), stabilized with carboxymethyl cellulose (CMC), was successfully synthesized on site and injected into the subsurface at a site contaminated with a broad range of chlorinated volatile organic compounds (cVOCs). Transport of CMC-S-nZVI to the monitoring wells, both downgradient and upgradient, resulted in a significant decrease in concentrations of aqueous-phase cVOCs. Short-term (0-17 days) total boron and chloride measurements indicated dilution and displacement in these wells. Importantly however, compound specific isotope analysis (CSIA), changes in concentrations of intermediates, and increase in ethene concentrations confirmed dechlorination of cVOCs. Dissolution from the DNAPL pool into the aqueous phase at the deepest levels (4.0-4.5 m bgs) was identifiable from the increased cVOCs concentrations during long-term monitoring. However, at the uppermost levels (∼1.5 m above the source zone) a contrasting trend was observed indicating successful dechlorination. Changes in cVOCs concentrations and CSIA data suggest both sequential hydrogenolysis as well as reductive ß-elimination as the possible transformation mechanisms during the short-term abiotic and long-term biotic dechlorination. One of the most positive outcomes of this CMC-S-nZVI field treatment is the non-accumulation of lower chlorinated VOCs, particularly vinyl chloride. Post-treatment soil cores also revealed significant decreases in cVOCs concentrations throughout the targeted treatment zones. Results from this field study show that sulfidation is a suitable amendment for developing more efficient nZVI-based in situ remediation technologies.

Effects of nano-zerovalent iron on antibiotic resistance genes and mobile genetic elements during swine manure composting.

Livestock manure is a reservoir for antibiotic resistance genes (ARGs), and aerobic composting is used widely for recycling animal manure. This study investigated the effects of adding nano-zerovalent iron (nZVI) at 0, 100, and 1000 mg/kg on the fates of ARGs and mobile genetic elements (MGEs) during swine manure composting. Under nZVI at 100 mg/kg, the relative abundances of sul1, sul2, dfrA7, ermF, and ermX decreased by 33.26-99.31% after composting, and the relative abundances of intI2 and Tn916/1545 decreased by 95.59% and 97.65%, respectively. Most of the ARGs and MGEs co-occurred and they had strong correlations with each other. The bacterial community structure was significantly separated by the composting periods, and they clustered together under different treatments in the same phase. Network analysis showed that Solibacillus, Clostridium_sensu_stricto_1, Terrisporobacter, Romboutsia, Turicibacter, Lactobacillus, Planococcus, Dietzia, and Corynebacterium_1 were common potential hosts of ARGs and MGEs. Redundancy analysis suggested that MGEs had key effects on the variations in the relative abundances of ARGs. Adding 100 mg/kg nZVI could reduce the environmental risk of ARGs by decreasing the abundances of MGEs.

Fate and transport of sulfidated nano zerovalent iron (S-nZVI): A field study.

Treatment of nano zerovalent iron (nZVI) with lower valent forms of sulfur compounds (sulfidation) has the potential to increase the selectivity and reactivity of nZVI with target contaminants and to decrease inter-particle aggregation for improving its mobility. These developments help in addressing some of the long-standing challenges associated with nZVI-based remediation treatments and are of great interest for in situ applications. Herein we report results from a field-scale project conducted at a contaminated site. Sulfidated nZVI (S-nZVI) was prepared on site by first synthesizing carboxymethyl cellulose (CMC) stabilized nZVI with sodium borohydride as a reductant and then sulfidating the nZVI suspension by adding sodium dithionite. Transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDS) of CMC-S-nZVI, from synthesis barrels, confirms the presence of both discrete spherical nZVI-like particles (∼90 nm) as well as larger irregular structures (∼500 nm) comprising of iron sulfides. This CMC-S-nZVI suspension was gravity fed into a sandy material and monitored through multiple multi-level monitoring wells. Samples collected from upstream and downstream wells suggest very good radial and vertical iron distribution. TEM-EDS analysis from the recovered well samples also indicates the presence of both nZVI-like particles as well as the larger flake-like structures, similar to those found in the injected CMC-S-nZVI suspension. This study shows that S-nZVI stabilized with CMC can be safely synthesized on site and is highly mobile and stable in the subsurface, demonstrating for the first time the field applicability of S-nZVI.

Enhanced nitrobenzene reduction by modified biochar supported sulfidated nano zerovalent iron: Comparison of surface modification methods.

In our previous study, biochar (BC) supported sulfidated nano zerovalent iron (S-nZVI@BC) was prepared for nitrobenzene (NB) reduction. In this study, in order to further improve the reduction performance of S-nZVI@BC, BC was modified before the loading of S-nZVI through three methods: oxidant (H2O2) pretreatment, alkali (NaOH) pretreatment and acid (HCl) pretreatment. The results indicated that S-nZVI could be evenly distributed onto HCl-BC due to increased surface area, negative surface charge and increased acidic functional groups on HCl-BC. At an initial concentration of 200 mg L-1, NB could be completely removed by S-nZVI@HCl-BC within a reaction time as short as 60 min, indicating rather excellent performance of S-nZVI@HCl-BC. NB reduction performance followed the order: S-nZVI@HCl-BC > S-nZVI@NaOH-BC > S-nZVI@BC > S-nZVI@H2O2-BC. The mass ratio of S-nZVI and HCl-BC was optimized in terms of NB removal efficiency, with 3:1 being identified as the best mass ratio. Furthermore, the mechanism involved in the enhanced NB reduction by S-nZVI@HCl-BC was proposed. This study demonstrated that S-nZVI@HCl-BC is a promising alternative for efficient NB removal from wastewater.

Effects of nano-zerovalent iron on antibiotic resistance genes during the anaerobic digestion of cattle manure.

This study investigated the effects of adding nano-zerovalent iron (nZVI) at three concentrations (0, 80, and 160 mg/L) on the methane yield and the fate of antibiotic resistance genes (ARGs) during the anaerobic digestion (AD) of cattle manure. The addition of nZVI effectively enhanced the methane yield, where it significantly increased by 6.56% with 80 mg/L nZVI and by 6.43% with 160 mg/L nZVI. The reductions in the abundances of ARGs and Tn916/1545 were accelerated by adding 160 mg/L nZVI after AD. Microbial community analysis showed that nZVI mainly increased the abundances of bacteria with roles in hydrolysis and acidogenesis, whereas it reduced the abundance of Acinetobacter. Redundancy analysis indicated that the changes in mobile genetic elements made the greatest contribution to the fate of ARGs. The results suggest that 160 mg/L nZVI is a suitable additive for reducing the risks due to ARGs in AD.

A comparison of the effects of natural organic matter on sulfidated and nonsulfidated nanoscale zerovalent iron colloidal stability, toxicity, and reactivity to trichloroethylene.

Sulfidated nanoscale zerovalent iron (S-NZVI) is a new remediation material with higher reactivity and greater selectivity for chlorinated organic contaminants such as trichloroethene (TCE) than NZVI. The properties of S-NZVI and the effects of groundwater constituents like natural organic matter (NOM) on its reactivity are less well-characterized than for NZVI. In this study, S-NZVI (Fe/S mole ratio = 15) was synthesized by sonicating NZVI in a Na2S solution, yielding particles with greater surface charge, less aggregation, and higher reactivity with TCE compared to NZVI. The cytotoxicity of S-NZVI was not mitigated effectively due to the smaller size. The addition of Suwannee River humic acid (SRHA) increased the negative surface charge magnitude and dispersion stability and reduced the toxicity of both NZVI and S-NZVI significantly, but also enhanced the corrosion of particles and the formation of non-conductive film. The degradation rate constant (ksa) of both NZVI and S-NZVI was thus reduced with the increasing concentration of SRHA, which decreased by 78% and 60% to be 0.0004 and 0.0053 L m-2 h-1, respectively, with 200 mg C/L SRHA. Additionally, the performance of S-NZVI in field was evaluated to be depressed in simulated groundwater and the negative effect was exacerbated with increased concentration of SRHA. Hydro-chemical conditions like dissolved oxygen (DO), pH, and temperature also influenced the reactivity of S-NZVI. Hence, S-NZVI was a preferred candidate for in-situ remediation of TCE than NZVI. Nevertheless, the integrity of the FeS shell on S-NZVI influenced by NOM need to be considered during the long-term use of S-NZVI in groundwater remediation.