Effect Of Nano Zero-valent Iron Research Articles

Effect of nano zero-valent iron, potassium persulphate, and biochar on maturity and gaseous emissions during multi-material co-composting

Aerobic composting technology is expected to achieve higher quality composts. This study investigated the effects of exogenous additives on compost maturity and gaseous emissions during co-composting of pig manure and kitchen waste using nano zero-valent iron (NI), potassium persulphate (PS), cornstalk biochar (CB) and pig manure biochar (PB) additives. The results showed that CB and PB reduced electrical conductivity (EC) and increased compost maturity. All additives reduced total greenhouse gas emissions, including methane (CH4), by 28.6–71.5%, while only PB addition reduced nitrous oxide (N2O) emissions by 13.3%. PS addition resulted in the lowest pH value, and ammonia (NH3) emissions decreased by 53.1%. NI reduced hydrogen sulfide emissions by 20.4%. Additionally, all additive reduced dimethyl sulfide (Me2S) emissions by 18.6–44.2%,while they increased dimethyl disulfide (Me2SS) emissions by 7.6–150.6%. Therefore, these additives, especially PS, which exhibited superior performance, can cooperate to reduce greenhouse gas and odors emissions during composting.

The Dual Roles of Nano Zero-Valent Iron and Zinc Oxide in Antibiotics Resistance Genes (ARGs) Spread in Sediment.

Nanoparticles (NPs) are widely used and ubiquitous in the environment, but the consequences of their release into the environment on antibiotics resistance genes (ARGs), microbial abundance, and community, are largely unknown. Therefore, this study examined the effect of nano zero-valent iron (nZVI) and zinc oxide (nZnO) on tetracycline resistance genes (tet-ARGs) and class 1 integron (intI1) in sediment under laboratory incubation. The coexistence of NPs and tetracycline (TC) on tet-ARGs/intI1 was also investigated. It was found that nZVI and nZnO promoted tet-ARGs/intI1 abundance in sediment without TC but reduced the inducing effect of TC on tet-ARGs/intI1 in sediment overlaid with TC solution. Without TC, nZVI, intI1, and the bacterial community could directly promote tet-ARGs spread in nZVI sediment, while intI1 and bacterial abundance were the most directly important reasons for tet-ARGs spread in nZnO sediment. With TC, nZVI and bacterial community could reduce tet-ARGs abundance in nZVI sediment, while nZnO and bacterial community could directly promote tet-ARGs in nZnO sediment. Finally, these findings provided valuable information for understanding the role of NPs in promoting and reducing ARGs in the environment.

Enhancing anaerobic digestion of sulphate wastewater by adding nano-zero valent iron

ABSTRACT In this paper, the effects of nano-zero valent iron (nZVI) on anaerobic digestion of sulphate wastewater with different /COD ratios, including the COD removal rate, methane yield, intermediate products and the change of microbial community structure, were investigated. The results showed that nZVI could effectively enhance the treatment efficiency and methane yield. Compared with the control group without nZVI, the methane yield increased from 348.6833 to 1007.05 mL CH4/gCODremoval with 4 g nZVI loading at /COD = 0.1. nZVI could make electron flow from sulphate reduction to methane production, which increased methane yield even at high sulphate concentration. The microbial community analysis showed that adding nZVI could increase the abundance of acetoclastic methanogens, which accelerated hydrolysis acidification.

Combined toxic effects of dioxin-like PCB77 with Fe-based nanoparticles in earthworm Eisenia fetida

Iron-based nanomaterials hold promise for in situ remediation of persistent halogenated contaminants such as dioxin-like polychlorinated biphenyls, however, their complex interactions and joint toxicity toward beneficial soil biological functions remain unknown. This study examined the effects of nano-zero valent iron (nZVI) on the physiological and morphological changes, on the bioaccumulation of co-existed dioxin-like 3,3′,4,4′-tetrachloro-biphenyls (PCB77), and the joint toxicity of nZVI and PCB77 in earthworms Eisenia fetida. An orthogonally designed experiment was conducted through the exposure of E. fetida to the combined and separate nZVI and PCB77 at various concentrations in soil for 28 days (nZVI at the levels of g-Fe/kg-soil and PCB77 at the levels of mg-PCB/kg-soil). Results indicated that both nZVI and PCB77 inhibited the growth and reproduction of earthworms, and the combined exposure resulted in a synergistic effect. The addition of 10 g/kg nZVI decreased the contents of PCB77 and significantly increased the accumulation of PCB77 to a level ranging 14–97 mg/kg in earthworms in a nZVI dose dependent manner. The observed synergism might relate to the aggravated damage of earthworm epidermis in the presence of nZVI. PCB77 and nZVI at their corresponding high levels (10 mg/kg and 10 g/kg) induced oxidative stress and lipid peroxidation in the earthworms through the increased levels of reactive oxygen species and the subsequent inhibition of antioxidant enzymes including superoxide dismutase and catalase. Further metabolomics analyses revealed that the normal glutamic acid metabolism and tricarboxylic acid cycle were disturbed in earthworms exposed to the combined treatment of 10 mg/kg PCB77 and 10 g/kg nZVI. Our findings suggested that earthworms as a sentinel species could be readily employed in toxicity and tolerance studies to succeed the safe applications of nZVI and interestingly earthworms themselves also hold promise for vermiremediation owing to the high bioaccumulation potential of PCBs from contaminated soils.

Synergetic effect of nano zero-valent iron and activated carbon on high-level ciprofloxacin removal in hydrolysis-acidogenesis of anaerobic digestion

Ciprofloxacin is the most commonly prescribed antibiotic, and its widespread use poses threat to environmental safety. The removal of ciprofloxacin from contaminated water has remained a major challenge. The present study investigated adding nanoscale zero-valent iron (NZVI) and activated carbon (AC) on high-level ciprofloxacin removal in hydrolysis-acidogenesis stage of anaerobic digestion. The results showed that the degradation rate of ciprofloxacin increased from 22.61% (Blank group) to 72.41% after adding NZVI/AC with concentration of ciprofloxacin in effluent decreasing from 8.25 mg L−1 to 3.48 mg L−1. The volatile fatty acids (VFAs) yield increased by 173.7% compared with the Blank group. In addition, the NZVI/AC group achieved the highest chemical oxygen demand (COD) removal rate and acidogenesis rate. The microbial community analysis presented that hydrolytic and acidogenic bacteria and microorganisms related to degrading ciprofloxacin were obviously improved in the NZVI/AC group. Moreover, eleven transformation products and the main degradation pathways were proposed based on mass spectrometry information. In summary, the NZVI/AC addition supplied promising approach for ciprofloxacin wastewater treatment.

Effect of nano zero-valent iron addition on caproate fermentation in carboxylate chain elongation system

Carboxylate chain elongation is a burgeoning research area for producing added value bio-products from organic fraction of municipal solid waste. Effect of nano zero-valent iron (NZVI) on chain elongation and its possible mechanism was investigated. Highest caproate concentration, 28.0 mmol·L−1 was achieved with 2 g·L−1 NZVI amendment, which is about 16.7% higher than the control. Promoted ethanol utilization was considered as the main reason for the increment of caproate production and hydrogen generation. Electron balance analysis shows that NZVI did not improve the total electron recovery efficiency but favoured the electron flow toward longer carboxylate chain product, i.e. caproate. Finally, full-length 16s rRNA sequencing of bacterial community showed NZVI reshaped the bacterial community by exerting reduction selectivity. And Oscillibacter and Clostridium could be the potential functional species for carboxylate chain elongation.

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 1000mg/kg on the fates of ARGs and mobile genetic elements (MGEs) during swine manure composting. Under nZVI at 100mg/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 100mg/kg nZVI could reduce the environmental risk of ARGs by decreasing the abundances of MGEs.

Enhancement of methanogenic activity in anaerobic digestion of high solids sludge by nano zero-valent iron

This study evaluated the effects of nano zero-valent iron (NZVI, 50 nm) on anaerobic digestion of high solids sludge (10 ± 0.5%). Compared to the blank group without NZVI, the group with NZVI at all levels (10, 20 and 30 mM) played a driving role in methane production. The maximal methane production was increased by 37.5% in the group of 30 mM NZVI. The dynamic changes of hydrogen content and VFAs showed that rapid hydrogen evolutional corrosion of NZVI made lower hydrogen partial pressure in the later stage, which was more conducive to conversion of propionic acid. The microscopic analysis indicated that NZVI could flocculate and adsorb on the extracellular polymeric substances (EPS) around the anaerobic microorganisms, protecting most active microbial cell membrane from contact damage. On the other hand, some decaying microbial cells membrane could be destroyed by NZVI and intracellular substances would be released due to the reduction of EPS.

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.

Estimation of LC50 and its Confidence Interval for the Effect of Nano-Zero Valent Iron on the Freshwater Zooplankton Species Daphnia magna

Determination of lethal concentration (LC50) of toxicants leading to 50% mortality of test samples in a toxicity test is very important and could be achieved by running Probit analysis. The response is binomial (death or no death) and relationship between response and various doses or concentrations is typically sigmoid. The Probit value can either be manually calculated by hand, or automatically calculated by computer software using a higher accuracy estimation method, namely the maximum likelihood principle. When a published toxicity study failed to report the 95% confidence interval values, the results can be recalculated via software. In this study, the LC50 and 95% confidence interval values of the effect of nano-zero valent iron towards the freshwater zooplankton Daphnia magna is recalculated by employing the Probit analysis in the SPSS software. The results of the Probit modelling exercise gave an LC50 value of 0.405 mg/L (95% confidence interval, CI was from 0.047 to 0.953) for Nanofer 25S, 0.706 mg/L (95% CI was from 0.151 to 3.203) for Nanofer STAR, 1.020 mg/L (95% CI was from 0.683 to 1.445) for Fe2+ and 5.834 mg/L (95% CI was from 4.190 to 9.189) for Fe3+. The wide 95% confidence interval curves for Nanofer 25S and Nanofer STAR indicate a large uncertainty meaning more data in the future should be obtained to increase the CI. The sub lethal concentration (SLC), which is one fourth of the LC50 value for Nanofer 25S, Nanofer STAR, Fe2+ and Fe3+ were 0.101, 0.176, 0.255 and 1.458 mg/L, respectively.

Effect of nano zero-valent iron application on As, Cd, Pb, and Zn availability in the rhizosphere of metal(loid) contaminated soils

Characterisation of geochemical transformations and processes in soils with special focus on the rhizosphere is crucial for assessing metal(loid) bioavailability to plants during in situ immobilisation and phytostabilisation. In this study, the effects of nano zero-valent iron (nZVI) were investigated in terms of the immobilisation of As, Zn, Pb and Cd in two soil types and their potential uptake by plants using rhizobox experiments. Such system allowed monitoring the behaviour of trace elements in rooted and bulk soil compartments separately. Sunflower (Helianthus annuus L.) and ryegrass (Lolium perenne L.) were tested for As-rich (15.9 g As kg−1) and Zn-rich (4.1 g Zn kg−1) soil samples, respectively. The application of nZVI effectively lowered the uptake of all target risk elements into plant tissues. Efficient immobilisation of As was determined in the As-soil without a significant difference between plant and bulk soil compartments. Similarly, a significant decrease was determined for CaCl2-available fractions of Zn, Pb and Cd in nZVI-treated Zn-soil. The behaviour of As corresponded to changes in Eh, while Zn and Cd showed to be mainly pH-dependent. However, despite the observed stabilisation effect of nZVI, high amounts of As and Zn still remained available for plants. Furthermore, the accumulation of the target risk elements in roots and the overall effect of nZVI transformations in the rhizosphere were verified and visualised by SEM/EDS. The following immobilising mechanisms were suggested: (i) sorption onto both existing and newly formed Fe (hydr)oxides, (ii) formation of secondary Fe-As phases, and (iii) sorption onto Mn (hydr)oxides.

Effects of Nano Zero-Valent Iron on Klebsiella oxytoca and Stress Response

Nano zero-valent iron (NZVI) is a new option for contaminated soil and groundwater treatment, despite little is known on their impact on environmental microorganisms. Klebsiella oxytoca K5 strain, isolated from the NZVI-treated soil, was used to investigate the bacterial, phenotypical and molecular response to commercial NZVI exposure. Cytotoxicity assays at three NZVI concentrations (1, 5 and 10mgmL(-1)) suggested a negligible bacteriostatic effect and the lack of bactericidal effect. Structural changes were analysed by electronic microscopy. Scanning electron microscopy revealed the presence of NZVI around some bacterial cells, but no apparent morphological changes were seen. NZVI attachment to the cell surface was confirmed by transmission electron microscopy, although most of them were not affected. A proteomic approach (two-dimensional electrophoresis, matrix-assisted laser desorption ionization time-of-flight mass spectrometry) was used to investigate NZVI impact. For the first time to our knowledge, results revealed that exposure of a soil bacterium to NZVI resulted in the overproduction of tryptophanase, associated with oxidative stress response. K5 may set up an adaptative stress response involving indole as a signal molecule to inform the bacterial population about environmental changes. These findings would improve knowledge on the molecular mechanisms underlying bacterial response to NZVI exposure.

A novel hybrid nano zerovalent iron initiated oxidation – Biological degradation approach for remediation of recalcitrant waste metalworking fluids

Disposal of operationally exhausted metal working fluids (MWF) through a biological route is an attractive option, since it is effective with relatively low energy demands. However, it is enormously challenging since these fluids are chemically complex, including the addition of toxic biocides which are added specifically to retard bio-deterioration whilst the fluids are operational. Nano-sized elemental iron represents a new generation of environmental remediation technologies. Laboratory scale batch studies were performed to test the degradation ability of a semi-synthetic metalworking fluid (MWF) wastewater (which was found to be resistant to initial bacterial treatment in specifically established bioreactors) by employing a novel hybrid approach. The approach was to combine the synergistic effects of nano zerovalent iron (nZVI) induced oxidation, followed by biodegradation, specifically for the remediation of recalcitrant components of MWF effluent. Addition of nZVI particles to oxygenated wastewater resulted in oxidation of organic contaminants present. Our studies confirmed 78% reduction in chemical oxygen demand (COD) by nZVI oxidation at pH 3.0 and 67% reduction in neutral pH (7.5), and 85% concurrent reduction in toxicity. Importantly, this low toxicity made the nZVI treated effluent more amenable for a second stage biological oxidation step. An overall COD reduction of 95.5% was achieved by the novel combined treatment described, demonstrating that nZVI oxidation can be exploited for enhancing the biodegradability of a recalcitrant wastewater in treatment processes.

Effects of Nano Zero-Valent Iron on Oxidation−Reduction Potential

Oxidation-reduction potential (ORP) measurements have been widely used to assess the results of injection of nano zerovalent iron (nZVI) for groundwater remediation, but the significance of these measurements has never been established. Using rotating disk electrodes (RDE) in suspensions of nZVI, we found the electrode response to be highly complex but also a very sensitive probe for a range of fundamentally significant processes. The time dependence of the electrode response reflects both a primary effect (attachment of nZVI onto the electrode surface) and several secondary effects (esp., oxidation of iron and variations in dissolved H2 concentration). At nZVI concentrations above ∼200 mg/L, attachment of nZVI to the electrode is sufficient to give it the electrochemical characteristics of an Fe(0) electrode, making the electrode relatively insensitive to changes in solution chemistry. Lower nZVI concentrations give a proportional response in ORP, but much of this effect is mediated by the secondary effects noted above. Coating the nZVI with natural organic matter (NOM), or the organic polymers used to make stabile suspensions of nZVI, moderates its effect on ORP measurments. Our results provide the basis for interpretating ORP measurements used to characterize the results of injecting nZVI into groundwater.