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Cu (II) is a toxic heavy metal commonly identified in groundwater contaminants. Bentonite-based cutoff wall is the most used method in isolating and adsorbing contaminants, while the bentonite in it easily to fail due to Cu(II) exchange. This study synthesized a novel material through the modification of calcium bentonite (CaB) utilizing sodium hexametaphosphate (SHMP) and nano zero-valent iron (NZVI). The characteristics, adsorption performance, and mechanism of the NZVI/SHMP-CaB were investigated comprehensively. The results showed that SHMP can disperse CaB and reduce flocculation, while NZVI can be further stabilized without agglomeration. The best adsorption performance of NZVI/SHMP-CaB could be obtained at the dosage of 2% SHMP and 4% NZVI. The NZVI/SHMP-CaB exhibited an outstanding removal efficiency of over 60% and 90% at a high Cu(II) concentration (pH = 6, Cu(II) = 300 mg/L) and acidic conditions (pH = 3–6, Cu(II) = 50 mg/L), respectively. The adsorption of Cu(II) by NZVI/SHMP-CaB followed a pseudo-second-order kinetic model, and fitting results from the Freundlich isothermal model suggested that the adsorption process occurred spontaneously. Besides the rapid surface adsorption on the NZVI/SHMP-CaB and ion exchange with interlayer ions in bentonite, the removal mechanism of Cu(II) also involved the chemical reduction to insoluble forms such as Cu0 and Cu 2 O. The generated FePO 4 covered the surface of the homogenized NZVI particles, enhancing the resistance of NZVI/SHMP-CaB to acidic and oxidative environments. This study indicates that NZVI/SHMP-CaB is a promising alternative material which can be used for heavy metal removal from contaminated soil and water. [Display omitted] • NZVI/SHMP-CaB, a novel material, was synthesized for the removal of heavy metals. • Adsorption performance and mechanism of NZVI/SHMP-CaB were investigated. • Optimal ratio of 2% SHMP and 4% NZVI to CaB provided best adsorption performance. • Cu(II) was removed by rapid adsorption, ion exchange, and chemical reduction. [ABSTRACT FROM AUTHOR]

Nanoscale zero-valent iron (nZVI) is attracting increasing attention as the most commonly used environmental remediation material. However, given the high surface area and strong reducing capabilities of nZVI, there is a lack of understanding regarding its effects on the complex anaerobic methane production process in flooded soils. To elucidate the mechanism of CH 4 production in soil exposed to nZVI, paddy soil was collected and subjected to anaerobic culture under continuous flooding conditions, with various dosages of nZVI applied. The results showed that the introduction of nZVI into anaerobic flooded rice paddy systems promoted microbial utilization of acetate and carbon dioxide as carbon sources for methane production, ultimately leading to increased methane production. Following the introduction of nZVI into the soil, there was a rapid increase in hydrogen levels in the headspace, surpassing that of the control group. The hydrogen levels in both the experimental and control groups were depleted by the 29th day of culture. These findings suggest that nZVI exposure facilitates the enrichment of hydrogenotrophic methanogens, providing them with a favorable environment for growth. Additionally, it affected soil physicochemical properties by increasing pH and electrical conductivity. The metagenomic analysis further indicates that under exposure to nZVI, hydrogenotrophic methanogens, particularly Methanobacteriaceae and Methanocellaceae , were enriched. The relative abundance of genes such as mcrA and mcrB associated with methane production was increased. This study provides important theoretical insights into the response of key microbes, functional genes, and methane production pathways to nZVI during anaerobic methane production in rice paddy soils, offering fundamental insights into the long-term fate and risks associated with the introduction of nZVI into soils. • NZVI increased methane production and CO 2 consumption in paddy fields. • NZVI accelerated iron reduction rate and increased DOC content in soil. • NZVI enhanced hydrogenotrophic methanogenesis pathway in paddy soils. • NZVI promoted the enrichment of hydrogenotrophic methanogens. [ABSTRACT FROM AUTHOR]

In this work, nano zero-valent iron (nZVI) was added to a lab-scale continuous stirring tank reactor (CSTR) for food waste slurry treatment, and the effect of dosing rate and dosage of nZVI were attempted to be changed. The results showed that anaerobic digestion (AD) efficiency and biomethanation stability were optimum under the daily dosing and dosage of 0.48 g/gTCOD. The average daily methane (CH 4) yield reached 495.38 mL/gTCOD, which was 43.65% higher than that at control stage, and the maximum CH 4 content reached 95%. However, under single dosing rate conditions, high nZVI concentrations caused microbial cell rupture and loosely bound extracellular polymeric substances (LB-EPS) precipitation degradation. The daily dosing rate promoted the hydrogenotrophic methanogenesis pathway, and the activity of coenzyme F 420 increased by 400.29%. The microbial analysis indicated that daily addition of nZVI could promote the growth of acid-producing bacteria (Firmicutes and Bacteroidetes) and methanogens (Methanothrix). • The effect of nZVI dosing rates and dosages on methanogenesis was investigated. • The CH 4 content can reach 95% under the daily dosing and dosage of 0.48 g/gTCOD in CSTR. • Different nZVI dosing rate could affect the microbial cells and EPS. • Methanothrix was enriched by DIET enhancement under nZVI daily dosing. [ABSTRACT FROM AUTHOR]

Effective in-situ technology to treat carcinogenic compounds in contaminated areas poses a major challenge. Our objective was to load nano-zero-valent iron (nZVI) onto leonardite char (LNDC), an alternative carbon source from industrial waste, for use as a persulfate (PS) activator for styrene treatment in soil and water. By adding a surfactant during synthesis, cetyltrimethylammonium bromide (CTAB) promotes a flower-like morphology and the nZVI formation in smaller sizes. Results showed that nZVI plays a crucial role in PS activation in both homogeneous and heterogeneous reactions to generate reactive oxygen species (ROS), which can remove 98% of styrene within 20 min. Quenching experiments indicated that singlet oxygen (1O 2), superoxide radicals (O 2 •–), and sulfate radicals (SO 4 •–) were the main species working together to degrade styrene. XPS analysis also revealed a role of surface oxygen-containing groups (i.e., C O, C–OH) in activating PS for SO 4 •– and 1O 2 generation. The possible reaction mechanism of PS activation by LNDC-CTAB-nZVI composite and factors affecting treatment efficiency (i.e., PS concentration, catalyst dosage, pH, and humic acid) were illustrated. The molarity/molality ratio of PS to nZVI should be set greater than 1 for effective styrene removal. GC-MS analysis showed that styrene was degraded to a less toxic benzaldehyde intermediate. However, the excessive use of PS and catalysts can harm plant growth, requiring a combining approach to achieve safer use for real applications. Overall results supported the use of the LNDC-CTAB-nZVI/PS system as an efficient in-situ treatment technology for soil and water remediation. • CTAB promotes a flower-like morphology and reduces the size of nZVI. • LNDC-CTAB-nZVI/PS system can remove 98% of styrene within 20 min. • 1O 2 , O 2.•–, and SO 4 •– were the active species for styrene degradation. • Styrene was degraded to a less toxic benzaldehyde intermediate. • The effect of the LNDC-CTAB-nZVI/PS system on plant growth was revealed. [ABSTRACT FROM AUTHOR]

Hexavalent chromium (Cr), one of the most common heavy metals, is widely found in contaminated soil and groundwater. Nano zero-valent iron (nZVI) is used to treat Cr(VI) in polluted groundwater. However, due to agglomeration, rapid sedimentation, and limited mobility of nanoparticles in the aquatic environment, nZVI is not widely used in groundwater treatment. In this study, we used sodium alginate (SA) to modify nZVI to generate dispersed SA-nZVI. SA-nZVI particles were found to embed in the polymer material and exist as an amorphous state with a diameter less than 100 nm. Compared with traditional nZVI and carboxymethyl cellulose (CMC)-nZVI, SA-nZVI had better stability and higher absolute zeta potential. The presence of SA enhanced mobility of nZVI and effectively prevented sedimentation and aggregation. Furthermore, SA-nZVI had a higher Cr(VI) removal rate than (CMC)-nZVI under both acidic and alkaline conditions. XPS analysis showed that Cr(VI) was reduced to Cr(III) and formed Cr(OH) 3 as precipitates after treatment with SA-nZVI. In addition, NO 3 − had no effect on the final removal rate of Cr(VI) by SA-nZVI. These results suggest that SA-nZVI has high penetration and a high removal rate in Cr(VI) removal and can be used to stabilize nZVI to remediate Cr(VI)-contaminated groundwater in the future. • Sodium alginate was used to disperse nZVI to develop a new type nZVI material (SA-nZVI). • SA-nZVI has higher penetration and higher removal rate than traditional nZVI in chromium removal. • SA-nZVI is a promising material for Cr(VI) contaminated groundwater remediation [ABSTRACT FROM AUTHOR]

Abstract Stable surfactant foam might play a vital role in the effective remediation of diesel oil contaminated soil-a major environmental hazard. This paper, first of its kind, is reporting the remediation of diesel-contaminated desert soil, coastal soil and clay soil by aqueous alkylpolyglucoside phosphate (APG-Ph) surfactant foams stabilized by Fe0 and Fe 3 O 4 nanoparticles. Zero-valent iron (Fe0, ∼28 nm) and iron oxide (Fe 3 O 4 , ∼20 nm) nanoparticles are synthesized by liquid-phase reduction and precipitation methods, respectively. The effect of these nanoparticles on foamability, foam stability, surface tension and remediation of diesel-contaminated soils are examined at various concentrations (volume %) of alkylpolyglucoside phosphate (APG-Ph) surfactant and nanoparticles (mg/l). The maximum values of foamability and foam stability recorded for 0.1 vol % APG-Ph foam stabilized by 3.5 mg/l Fe0 are 108.3 and 110.4 mL, respectively. At the same conditions, the Fe 3 O 4 results in 99.4 and 87.5 mL, respectively, depicting the better performance of Fe0. Reduction in surface tension of 0.1 vol % APG-Ph solution (50.75 mN/m) with the addition of 3.5 mg/l Fe0 (9.51 mN/m) and Fe 3 O 4 (19.45 mN/m) nanoparticle is observed. Both the nanoparticles enhance remediation. The foam formed with 0.1 vol % APG-Ph and stabilized by 3.5 mg/l Fe0 shows the maximum diesel removal efficiency of 95.3, 94.6, and 57.5% for coastal soil, desert soil and clay soil, respectively. On the other hand, Fe 3 O 4 (3.5 mg/l) stabilized APG-Ph foam of the same concentration shows merely 76.0, 79.6 and 51.6% diesel removal efficiency for coastal soil, desert soil, and clay soil, respectively. The rate of diesel removal by zero-valent iron and iron oxide nanoparticle stabilized foams are found to be well described by the first order kinetic model. Higher foamability, foam stability, and reducing capacity accompanying lower surface tension, compared to those of the Fe 3 O 4 nanoparticle stabilized foam, could explain higher diesel removal efficiency of the Fe0 nanoparticle stabilized foam. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Activated carbon-supported nano-zero-valent iron (nZVI@AC) is considered to be one of the most promising materials for in-situ remediation of pollutants in aqueous environment, while liquid phase reduction (LPR) is one of the most commonly used preparation methods for nZVI@AC. However, the complex operation and the requirement of various agents limit the practical application of the traditional liquid-phase reduction (TLPR). In this study, an improved liquid phase reduction method (ILPR) was proposed, which was characterized by solid-state dosing of reducing agents. Compared with TLPR, ILPR simplified the preparation process, while there was no requirement of polyethylene glycol and ethanol. When the Cd(II) removal efficiency was used as the evaluation index, the preferred parameters of ILPR were as follows: AC/FeSO 4 ·7H 2 O mass ratio was 15:1; NaBH 4 dosage was 8 g; ultrasonic time was 1 h; stirring time was 20 min. Moreover, the Cd(II) removal efficiency of nZVI@AC prepared by ILPR (nZVI@AC-I) was greater than 92.00%, which was superior to that of nZVI@AC prepared by TLPR (nZVI@AC-T). The characterization results showed that the pore parameters, surface functional groups and iron contents of nZVI@AC-I and nZVI@AC-T were basically the same. However, the distribution of iron-containing particles on the surface of nZVI@AC-I was more uniform. Furthermore, the Fe0 in nZVI@AC-I had a smaller particle size and a higher content. Overall, this study provided a promising approach for nZVI@AC preparation. [Display omitted] • A liquid-phase reduction method using the solid reducing agent is proposed. • This method successfully synthesized nano zero-valent iron/activated carbon. • This method produced Fe0 with smaller particle size and higher content. • This method does not require the use of dispersants and ethanol. • The material synthesized by this method exhibited a better removal rate of Cd(II). [ABSTRACT FROM AUTHOR]

This study evaluates the NO 3 − removal from groundwater through Heterotrophic Denitrification (HDN) (promoted by the addition of acetate and/or an inoculum rich in denitrifiers) and Abiotic Chemical Nitrate Reduction (ACNR) (promoted by pulse injection of zerovalent iron nanoparticles (nZVI)). HDN and ACNR were applied, separately or combined, in packed soil column experiments to complement the scarce research on pulse-injected nZVI in continuous-flow systems mimicking a Well-based Denitrification Barrier. Together with NO 3 −, the removal of two common pesticides (dieldrin and lindane) was evaluated. Results showed that total NO 3 − removal (>97%) could be achieved by either bioestimulation with acetate (converting NO 3 − to N 2 (g) via HDN) or by injecting nZVI (removing NO 3 − via ACNR). In the presence of nZVI, NO 3 − was partially converted to N 2 (g) and to a lower extent NO 2 −, with unreacted NO 3 − being likely adsorbed onto Fe-(oxy)hydroxides. Combination of both HDN and ACNR resulted in even a higher NO 3 − removal (>99%). Interestingly, nZVI did not seem to pose any toxic effect on denitrifiers. These results showed that both processes can be alterned or combined to take advantage of the benefits of each individual process while overcoming their disadvantages if applied alone. With regard to the target pesticides, the removal was high for dieldrin (>93%) and moderate for lindane (38%), and it was not due to biodegradation but to adsorption onto soil. When nZVI was applied, the removal increased (generally >91%) due to chemical degradation by nZVI and/or adsorption onto formed Fe-(oxy)hydroxides. [Display omitted] • Denitrification (HDN) and chemical reduction by nZVI (ACNR) were assessed for NO 3 − removal. • Both HDN and ACNR removed NO 3 − at high percentages (>97%), but might present limitations. • Combination of HDN and ACNR can ensure the overcoming of these limitations. • Pulse injection of nZVI did not seem to pose any toxic effect to denitrifying bacteria. • Pesticides were also removed, but likely via abiotic processes (e.g. adsorption). [ABSTRACT FROM AUTHOR]

The in-situ hydrogen supply by nano zero-valent iron (nZVI, nFe0) corrosion provided a feasible way to improve the efficiency of biogas biological upgrading. This work studied the effects of nZVI at different dosages (0, 2, 4, 6, 8 and 10 g/L) on anaerobic digestion of kitchen wastewater by two buffer systems 2-[4-(2-hydroxyethyl) piperazin-1-yl] ethanesulfonic acid (HEPES) and sodium hydrogen carbonate (NaHCO 3). The addition of nZVI improved the content of methane (CH 4) and stability of anaerobic digestion process. In HEPES buffer system, the CH 4 was all increased and the maximum reached 90.51% with 10 g/L nZVI, higher than 32.25% compared to the control. The maximum hydrogen enrichment (HE) was 113 ppb after nZVI addition, indicating the mass transfer efficiency of hydrogen (H 2) was improved. Microbial community analysis showed that the total relative abundance of Methanobacterium and Methanolinea at 10 g/L nZVI was 53.72%, which was 1.62 times of the control group. However, in the NaHCO 3 buffer system with 10 g/L nZVI addition, the content of CH 4 and the loosely bound extracellular polymeric substances (LB-EPS) was lower than the control. The results indicated that the addition of nZVI was feasible for biogas upgrading, and the bidirectional effect of nZVI on the promotion or inhibition of bio-methanation might be related to the buffer system of the anaerobic process. [Display omitted] • In-situ hydrogen evolution by nano zero-valent iron could enhance methane content. • Different buffer systems could affect the performance of biogas upgrading. • 10 g/L nano zero-valent iron led to the highest methane content of 90.51% (v/v). • Changes of microbial community after adding nano zero-valent iron was explored. [ABSTRACT FROM AUTHOR]

The extracellular polymeric substances coating magnetic powders-supported nano zero-valent iron (nZVI@EPS@Fe 3 O 4) was synthesized, using reduction and adsorption to treat Sb(V) wastewater. The adsorption performance and mechanism were investigated under aerobic and anaerobic conditions. The adsorption capacity of nZVI@EPS@Fe 3 O 4 (79.56 mg/g at pH = 5) was improved compared to that of the original materials (60.74 mg/g). The spectral analysis shows that both nZVI and EPS@Fe 3 O 4 in nZVI@EPS@Fe 3 O 4 played an important role in reducing Sb(V) to Sb(III) and adsorbing Sb. The reducibility and adsorption capacity of nZVI@EPS@Fe 3 O 4 towards Sb(V) remained strong under aerobic condition (62% Sb(III), 79.56 mg/g), although they were slightly weaker than those under anaerobic condition (74% Sb(III), 91.78 mg/g). nZVI@EPS@Fe 3 O 4 showed good performance in regeneration experiments. nZVI@EPS@Fe 3 O 4 is promising as a cost-effective and highly efficient material for Sb(V)-contaminated water. This study is meaningful in understanding the redox behaviour of nZVI composites in aerobic and anaerobic conditions. • nZVI@EPS@Fe 3 O 4 improved Sb adsorption capacity compared to original materials. • Reducibility/adsorbability were compared under aerobic/anaerobic conditions. • Sb(V) reducibility/adsorbability remained strong under aerobic condition. • Functional groups on magnetic EPS were also responsible for Sb(V) reduction. • nZVI@EPS@Fe 3 O 4 showed great recycling performance. [ABSTRACT FROM AUTHOR]

Bisphenol A (BPA) is a toxic environmental pollutant commonly found in wastewater. Using non-toxic materials and eco-friendly technology to remove this pollutant from wastewater presents multiple advantages. Treatment of wastewater with clay minerals has received growing interest because of the environment friendliness of these materials. Bentonite is a 2:1 layered phyllosilicate clay mineral that can support nano-metal catalysts. It can prevent the agglomeration of nano-metal catalysts and improve their activity. In this article, a green catalytic nano zero-valent iron/bentonite composite material (NZVI@bentonite) was synthesized via liquid-phase reduction. The average size of NZVI was approximately 40–50 nm. Good dispersion and low aggregation were observed when NZVI was loaded on the surface or embedded into the nanosheets of bentonite. Degradation of BPA, a harmful contaminant widely found in wastewater at relatively high levels, by NZVI@bentonite was then investigated and compared with that by pristine NZVI through batch Fenton-like reaction experiments. Compared with pristine NZVI and bentonite alone, the NZVI@bentonite showed a higher BPA degradation ratio and offered highly effective BPA degradation up to 450 mg/g in wastewater under optimum operating conditions. Adsorption coupled with the Fenton-like reaction was responsible for BPA degradation by NZVI@bentonite. This work extends the application of NZVI@bentonite as an effective green catalyst for BPA degradation in aqueous environments. Image 1 • Bentonite-supported nano-zero-valent iron (NZVI@bentonite) were synthesized. • The synthesized composite NZVI@bentonite was characterized in detail. • The degradation ratio for bishphenol A (BPA) in wastewater were studied. • The degradation mechanisms of BPA by NZVI@bentonite were discussed. • NZVI@bentonite affords highly effective degradation of BPA 450 mg/g. [ABSTRACT FROM AUTHOR]