Decrease In Redox Potential Research Articles

Experimental Simulation of the Influence of Temperature on the Migration of Substances from Bottom Sediments

The results of experimental investigations of the influence of water temperature on the migration of nutrients, organic matter, and metals from bottom sediments into the aquatic environment are discussed in the paper. It has been found that the increase in water temperature from 5°C to 15&degC resulted in the increase in the concentration of inorganic nitrogen, inorganic and total phosphorus, and dissolved silicon respectively by a factor of 1.6, 1.1, 1.2, and 1.4. The increase in water temperature from 5&degC to 25&degC resulted in the increase in the content of these nutrients by a factor of 1.8, 5.8, 1.9, and 2.5. Water temperature increase influenced the contribution of nitrogen compounds to the total balance of inorganic nitrogen. A relative content of ammonium decreased, whereas the contribution of nitrite- and nitrate ions increased as a result of the process of nitrification. The concentration of readily oxidized organic matter and the total content of organic matter also increased almost by a factor of 1.6 with increasing water temperature from 5&degC to 25&degC. Under such conditions, the concentration of aluminum, manganese, and chromium increased by a factor of 1.9, 3.2, and 2.0. In this case, the content of iron and copper remained almost unchanged due to their occurrence in inaccessible fractions of bottom sediments. Artificial aeration at 25&degC was responsible for an insignificant decrease in the concentration of inorganic nitrogen, inorganic and total phosphorus, dissolved organic matter, and also of dissolved aluminum, manganese, and chromium. It has been found that water temperature increase results in the migration of the studied chemical compounds from bottom sediments. However, this process is not as intensive as, for example, with a deficiency of dissolved oxygen and a decrease in pH and redox potential in the near-bottom layer of water.

Field application of glycerol to enhance reductive dechlorination of chlorinated ethenes and its impact on microbial community

Chlorinated ethenes (CEs) are common and persistent contaminants of soil and groundwater. Their degradation is mostly driven by a process of bacterial reductive dechlorination (also called organohalide respiration) in anaerobic conditions. This study summarizes the outcomes of the long-term in-situ application of glycerol for the enhanced reductive dechlorination of CEs on a highly contaminated site. Glycerol injection resulted in an almost immediate increase in the abundance of fermentative Firmicutes, which produce essential sources of carbon (acetate) and electrons (H2) for organohalide-respiring bacteria (OHRB) and change groundwater conditions to be suitable for OHRB growth. The decreased redox potential of groundwater promoted also the proliferation of sulfate-reducing bacteria, which compete for electron donors with OHRB but at the same time support their growth by producing essential corrinoids and acetate. A considerable increase in the abundance of OHRB Dehalococcoides, concurrently with vinyl chloride (VC) reductase gene levels, was revealed by real time polymerase chain reaction (qPCR) method. Consistent with the shifts in bacterial populations, the concentrations of pollutants tetrachloroethylene and trichloroethylene decreased during the monitoring period, with rising levels of cis-1,2-dichloroethylene, VC, and most importantly, the final CE degradation products: ethene and ethane. Our study implies the importance of syntrophic bacterial interactions for successful and complete CE degradation and evaluates glycerol as convenient substrate to enhance reductive dechlorination and as an effective source of electrons for OHRB.

Understanding the mechanisms of zeolite in inhibiting Pb accumulation in different rice cultivars (Oryza sativa).

Zeolite is one of the potential passivating amendments for the immobilization of lead (Pb) in contaminated farmland soils. In this study, pot experiments were carried out to investigate the effects and the mechanisms of zeolite on Pb accumulation in two rice cultivars grown in a slightly Pb-contaminated soil. Results showed that Pb content in grains of Zheyou 18 (ZY-18) decreased by the addition of 6g zeolite kg-1 soil (E6), which can be attributed to the reduction in soil Pb availability, dissolved organic carbon (DOC), water-soluble iron (Fe) and manganese (Mn), and the transfer factor from soil to grain (TFsoil-grain). These reductions were mainly resulting from the significant increase in soil pH, glutathione (GSH), phytochelatins (PCs), and non-protein (NPT) content in rice root, and the decrease in soil redox potential (Eh), due to zeolite addition. Pb content in brown rice of DL-5 was not significantly affected with E6 treatment, whereas it was raised by applying 12g zeolite kg-1 soil (E12). The increase of Pb content of Donglian 5 (DL-5) grains with E12 treatment can be attributed to more Pb uptake by the root, higher Pb transfer factors (TFs) between various parts of rice, and significant decrease in GSH, PCs, and NPT contents in the root. It is concluded that a suitable rate of zeolite addition can immobilize Pb in slightly Pb-contaminated acidic soil. However, the final immobilization effect also depends on rice cultivars.

Influence of tetracycline on arsenic mobilization and biotransformation in flooded soils

This study examined the effect of tetracycline addition on arsenic (As) mobilization and biotransformation in two contrasting soils (upland soil and paddy soil) under flooded conditions. The soils with added tetracycline (0–50 mg kg−1) were incubated for 30 days, and soil properties and microbial functional genes over time were quantified. Tetracycline significantly promoted As reduction and As release into porewater in both soils. The enhancement had resulted from an increase in the concentration of dissolved organic carbon and a decrease in soil redox potential. Tetracycline also increased the abundances of As-reducing genes (arsC and arrA) and the relative abundances of As-reducing bacteria Streptomyces, Bacillus, Burkholderia, Clostridium and Rhodococcus, all of which have been found resistant to tetracycline. These genera play a key part in stimulating As reduction in the presence of tetracycline. The study indicated the significance of tetracycline in the biochemical behavior of As in flooded soils and provided new insights into the potential effects of tetracycline on the quality and safety of agricultural products in the future.

Enhanced transformation of sulfamethoxazole by birnessite in the presence of gallic acid: Kinetics and pathways

The emergence of antibiotic agents like sulfamethoxazole (SMX) in soils and surface water can cause serious threat to human and animal health. In this work, mechanisms for the promotive effect of gallic acid (GA) on the transformation of SMX by birnessite were studied. In the absence of GA, the observed pseudo-first-order reaction constants (kobs) decreased as the pH increased from 4.0 to 8.0, in agreement with the decrease in redox potential of birnessite with increasing pH. The changes in chemical state of surface Mn atoms suggested that Mn(IV) played a major role in SMX transformation. SMX was transformed mainly by the bond cleavage of SN and SC, NH oxidation, and self- or cross-coupling reactions, with the formation of seven transformation products. The presence of GA could significantly promote the transformation of SMX, which was more pronounced at pH 6.0 comparing to the effect observed at 4.0. This promotive effect was attributed to both the addition reactions between SMX and GA quinones and the condensation reactions between -COOH of quinones and -NH2 of SMX or its transformation products. Moreover, the addition reaction between SMX and OH coming from the GA oxidation by birnessite was also proposed, while its contribution to SMX transformation was small. Furthermore, pyrogallol and methyl gallate that do not contain electron-withdrawing substituent like -COOH group are less effective in promoting SMX transformation than GA, suggesting the electron-density of β‑carbon is key to the occurrence of addition reaction. Our results demonstrate the important role of birnessite and naturally occurring phenolic acids in abiotic transformation SMX, which will profoundly affect its mobility and bioavailability in environments.

Nebulized plasma‐activated water has an effective antimicrobial effect on medically relevant microbial species and maintains its physicochemical properties in tube lengths from 0.1 up to 1.0 m

AbstractThis study applies a proof of concept for future applications in controlling the microbiota in tubes and tracheal appliances used in the respiratory tract. Therefore, the physical–chemical parameters of the plasma‐activated and nebulized water (NPAW) are measured in a nebulizer tube with different lengths between 0.1 and 3.0 m. The pH values and oxidation–reduction potential (ORP) do not change during nebulization of PAW over a 1.0 m tube. However, for longer lengths, there is an increase in pH and a decrease in ORP. At 3.0 m, the pH increases approximately 16% compared with the 1.0 m position with a 20% decrease in the ORP values. Hydrogen peroxide (H2O2) measured quantitatively using test strips presents values between 0.5 and 2.0 mg/L for condensed NPAW in different tube lengths between 0.1 and 3.0 m, and maintains the approximate value of 2.0 mg/L in tubes up to 1.0 m, with a reduction proportional to the increase in the length of the tube. The antimicrobial efficacy of NPAW applied for 15 min shows the inactivation of Staphylococcus aureus and Escherichia coli but without significant inactivation of Candida albicans.

The Mechanism Underlying of Long-Term Stable Indigo Reduction State in Indigo Fermentation Using Sukumo (Composted Polygonum tinctorium Leaves).

Indigo fermentation fluid maintains its indigo-reducing state for more than 6 months under open-air. To elucidate the mechanism underlying the sustainability of this indigo reduction state, three indigo fermentation batches with different durations for the indigo reduction state were compared. The three examined batches exhibited different microbiota and consisted of two phases. In the initial phase, oxygen-metabolizing-bacteria derived from sukumo established an initial network. With decreasing redox potential (ORP), the initial bacterial community was replaced by obligate anaerobes (mainly Proteinivoraceae; phase 1). Approximately 1 month after the beginning of fermentation, the predominating obligate anaerobes were decreased, and Amphibacillus and Polygonibacillus, which can decompose macromolecules derived from wheat bran, were predominantly observed, and the transition of microbiota became slow (phase 2). Considering the substrate utilization ability of the dominated bacterial taxa, the transitional change from phase 1 to phase 2 suggests that this changed from the bacterial flora that utilizes substrates derived from sukumo, including intrinsic substrates in sukumo and weakened or dead bacterial cells derived from early events (heat and alkaline treatment and reduction of ORP) to that of wheat bran-utilizers. This succession was directly related to the change in the major substrate sustaining the corresponding community and the turning point was approximately 1 month after the start of fermentation. As a result, we understand that the role of sukumo includes changes in the microbial flora immediately after the start of fermentation, which has an important function in the start-up phase of fermentation, whereas the ecosystem comprised of the microbiota utilizing wheat bran underpins the subsequent long-term indigo reduction.

Mapping experimental and theoretical reactivity descriptors of fe macrocyclic complexes deposited on graphite or on multi walled carbon nanotubes for the oxidation of thiols: Thioglycolic acid oxidation

We have studied the electro-oxidation of thioglycolic acid (TGA) catalyzed by iron phthalocyanines and iron porphyrins (FeN4 complexes) deposited on ordinary pyrolytic graphite and on multiwalled carbon nanotubes. The purpose of this work is to establish both experimental and theoretical reactivity descriptors of MN4 macrocyclic complexes for electrooxidation of thioglycolic acid (TGA) as an extension of previous studies involving other reactions using these types of catalysts. Essentially, the reactivity descriptors are all related to the ability of the metal center in the MN4 moiety to coordinate an extra planar ligand that corresponds to the reacting molecule. This coordinating ability, represented by the M-TGA binding energy can be modulated by tuning the electron-donation ability of the ligand and it is linearly correlated with the Fe(III)/(II) redox potential of the complex. Experimental plots of activity as (log j)E at constant potential versus the Fe(III)/(II) redox potential of the MN4 catalysts give volcano correlations. A semi-theoretical plot of catalytic activities (log j)E vs DFT calculated Fe-TGA binding energies (EbTGA) is consistent with the experimental volcano-type correlations describing both strong and weak binding linear correlations of those volcanos. On the other hand, the Hirshfeld population analysis shows a positive charge on the Fe center of the FeN4 complexes, indicating that electron transfer occurs from the TGA to the Fe center in the FeN4 complexes that act as electron acceptors. The donor (TGA)-acceptor (Fe) intermolecular hardness ΔηDA was also used as reactivity descriptor and the reactivity of the Fe centers as (log j)E increase linearly as ΔηDA increases. If activity is considered per active site, the trends is exactly the opposite, i.e. a plot of (logTOF)E increases linearly as ΔηDA decreases as expected form the Maximum Hardness-Principle. A plot of (logTOF)E versus E°’Fe(III)/(II) gives a linear correlation indicating that the activity per active site increases as the redox potential decreases.

Experimental method for the assessment and characterization of hazardous waste for long-term storage

Long-term landfilling of hazardous waste should be a careful choice for any producer or generator of waste, as the behavior of the waste is different due to the physical-chemical conditions or following contact with other hazardous waste. In this study, the research undertaken was aimed at developing an experimental method for the assessment and characterization of hazardous waste for long-term storage. The method consists in the assessment of the behavior of heavy metals from waste, under different leaching conditions. To study various hazardous wastes, fly ash from the incineration of medical waste and slag from aluminum casting were chosen. Contact time, pH and redox potential are important parameters in the leaching process. The solubility of metals increases at pH values between 2 - 5 pH units and decreases at pH values between 6-12 pH units. The highest solubility of metals (As, Cr, Cu, Ni, Pb and Zn) in the tested waste was obtained after 48 hours at pH values between 2 - 5 pH units. Also, the values of the redox potential decrease almost linearly as the pH value increases. The developed method is a useful tool to assess the behavior of hazardous waste for long-term storage in landfills for this category of wastes.

Highly enhanced dephosphorylation of phytic acid via pre-complexation of PA-Fe2+ in the Fenton system: High activity, wide pH range and ferryl-based mechanism

Phosphate (P) recovery through organic phosphorus (OP) decomposition is extremely crucial for prevention of water eutrophication and the sustainable development of P resources. In this work, for the first time, efficiently abiotic dephosphorylation of phytic acid (PA) through improved Fenton was proposed. The pre-complexation of PA with Fe2+ are creatively revealed to not only enhance the catalytic performance of Fenton reaction to dephosphorylate PA from 33.4 ± 2.1% to 76.3 ± 3.7%, but also extend the pH (3.5–9.0) of Fenton reaction to neutral and alkaline conditions. The pre-complexation of PA with Fe2+ exhibited much higher Fenton reactivity at neutral (65.5 ± 1.2% at pH = 7.0) or alkalescency (76.3 ± 3.7% and 73.1 ± 2.1% at pH of 8.0 and 9.0, respectively) condition than that at acid condition (49.2 ± 2.4% and 57.1 ± 4.3% at pH of 3.6 and 6.0, respectively). Such significant enhancement (p < 0.05) was mainly dependent on the coordination schemes for the complex PA-Fe3+, and ascribed to the accelerated iron cycle, the decreased redox potential of Fe3+/Fe2+, and the generated ferryl species (PA-FeX = O, X means high valence) as main reactive species. PA degradation by this improved Fenton system occurred in a stepwise dephosphorylation manner via I(1,3,4,5,6)P5, I(1,4,5,6)P4 or I(3,4,5,6)P4, I(4,5,6)P3, I(5,6)P2 or I(4,5)P2, and I(5)P1. Furthermore, this improved Fenton system (PA-Fe2+/H2O2) could be a promising method for the attenuation of refractory organic pollutants through ferryl species in natural environment as a kind of “broad-spectrum catalyst”.

Remediation of Chromium-Contaminated Soil Based on Bacillus cereus WHX-1 Immobilized on Biochar: Cr(VI) Transformation and Functional Microbial Enrichment.

Microorganisms are applied to remediate chromium (Cr)-contaminated soil extensively. Nevertheless, the microbial loss and growth inhibition in the soil environment restrain the application of this technology. In this study, a Cr(VI)-reducing strain named Bacillus cereus WHX-1 was screened, and the microbial aggregates system was established via immobilizing the strain on Enteromorpha prolifera biochar to enhance the Cr(VI)-reducing activity of this strain. The mechanism of the system on Cr(VI) transformation in Cr-contaminated soil was illuminated. Pot experiments indicated that the microbial aggregates system improved the physicochemical characteristics of Cr-contaminated soil obviously by increasing organic carbon content and cation exchange capacity, as well as decreasing redox potential and bulk density of soil. Moreover, 94.22% of Cr(VI) was transformed into Cr(III) in the pot, and the content of residue fraction Cr increased by 63.38% compared with control check (CK). Correspondingly, the physiological property of Ryegrass planted on the Cr-contaminated soil was improved markedly and the main Cr(VI)-reducing microbes, Bacillus spp., were enriched in the soil with a relative abundance of 28.43% in the microbial aggregates system. Considering more active sites of biochar for microbial aggregation, it was inferred that B. cereus WHX-1 could be immobilized by E. prolifera biochar, and more Cr(VI) was transformed into residue fraction. Cr stress was decreased and the growth of plants was enhanced. This study would provide a new perspective for Cr-contaminated soil remediation.

Degradation of Congo red by UV photolysis of nitrate: Kinetics and degradation mechanism

The efficiency of Congo red (CR) removal by low-pressure ultraviolet photolysis of nitrate (UV/NO3−) process was investigated in this study. Results showed that CR degradation through direct UV (254 nm) photolysis could be ignored, but CR was obviously removed in UV/NO3− process. Moreover, the contributions of UV, NO2 and OH to the degradation of CR were explored to be roughly 0.63%, 17.46% and 81.90%, respectively. In addition, the observed pseudo-first-order rate constants for the degradation of CR (kobs) were assessed by the effects of different water matrices and operation conditions, including NO3− dosage, CR concentration, solution pH, chloride ion (Cl−), natural organic matter (NOM) and carbonate/bicarbonate (CO32−/HCO3−). The kobs was increased by nearly 12.9 times with the addition of NO3− dosage from 1 mM to 200 mM due to the generation of more active components (e.g., OH and NO2). Higher doses of CR reduced the kobs, which could be attributed to the filter effects of CR on UV irradiation. Although the photolysis of NO3− could be expedited under acidic conditions, the kobs was decelerated because of the protonation of CR (pKa = 4.1, 25 °C). While in alkaline conditions, the kobs was also reduced as the decrease in redox potential of OH. The presence of Cl− (0–7 mM) exhibited no scavenging effect on the kobs, which suggested the secondary radicals (i.e., chlorine radicals (e.g., Cl, Cl2−)) could oxidize CR effectively. NOM restricted the degradation of CR significantly, resulting from the filter effects of NOM (ε = 0.11 LmgC−1cm−1) on UV and the effects of radical scavenging. The kobs was improved obviously with the participation of CO32−/HCO3− (0–7 mM), ascribing to the oxidation of carbonate radical (CO3−) and the increased steady state concentration of NO2. The degradation of CR in UV/NO3− process has the potential for practical applications in real water. Furthermore, eight intermediates were proposed by Liquid chromatography-tandem mass spectrometry (LC-MS/MS). Hydroxylation, nitrification and other aromatic products in the reaction of CR with OH and/or NO2 were readily produced by H-abstraction, addition reaction and electron transfer.

Sulfidated nano-scale zerovalent iron is able to effectively reduce in situ hexavalent chromium in a contaminated aquifer

In a number of laboratory studies, sulfidated nanoscale zero-valent iron (S-nZVI) particles showed increased reactivity, reducing capacity, and electron selectivity for Cr(VI) removal from contaminated waters. In our study, core-shell S-nZVI particles were successfully injected into an aquifer contaminated with Cr(VI) at a former chrome plating facility. S-nZVI migrated towards monitoring wells, resulting in a rapid decrease in Cr(VI) and Crtot concentrations and a long-term decrease in groundwater redox potential observed even 35 m downstream the nearest injection well. Characterization of materials recovered from the injection and monitoring wells confirmed the presence of nZVI particles, together with iron corrosion products. Chromium was identified on the surface of the recovered iron particles as Cr(III), and its occurrence was linked to the formation of insoluble chromium-iron (oxyhydr)oxides such as CrxFe(1−x)(OH)3(s). Injected S-nZVI particles formed aggregates, which were slowly transformed into iron (oxyhydr)oxides and carbonate green rust. Elevated contents of Fe0 were detected even several months after injection, indicating good S-nZVI longevity. The sulfide shell was gradually disintegrated and/or dissolved. Geochemical modelling confirmed the overall stability of the resulting Cr(III) phase at field conditions. This study demonstrates the applicability of S-nZVI for the remediation of a Cr(VI)-contaminated aquifer.

Simulating uranium sorption onto inorganic particles: The effect of redox potential

An analytical expression is proposed to simulate the effects of pH and redox potential (E) on the sorption of uranium onto model inorganic particles in aquatic environments instead of following an experimental approach providing a list of empirical sorption data. The expression provides a distribution coefficient (Kd) as function of pH, E and ligand concentration (complex formation) applying a surface complexation model on one type of surface sites (>SuOH). The formulation makes use of the complexation and hydrolysis constants for all species in solution and those sorbed at the surface, using correlations between hydrolysis constants and surface complexation constants, for the specific sorption sites. The model was applied for the sorption of uranium onto aluminol, iron hydroxide and silanol sites, mimicking respectively ‘clean’ clay or ‘dirty’ clay and ‘clean’ sand or ‘dirty’ sand (‘dirty’ referring to iron hydroxide contaminated), in absence or presence of carbonates in solution. The calculated distribution coefficients are very sensitive with the presence or absence of carbonates. The Kd values obtained by applying the model are compared with values reported in the literature for the sorption of uranium onto specific adsorbents. It is known that in surface water, U(VI) and its hydroxides are the primary stable species usually observed. However, reduction to U(IV) is possible and may be simulated during sorption or when the redox potential (E) decreases. Similar simulations are also applicable to study the sorption of other redox sensitive elements.

Water management increased rhizosphere redox potential and decreased Cd uptake in a low-Cd rice cultivar but decreased redox potential and increased Cd uptake in a high-Cd rice cultivar under intercropping

Excessive Cd in crop grains is toxic to humans. We conducted a field experiment to investigate the effects of intercropping on rice yield and grain Cd content as well as a pot experiment to compare the rhizosphere redox potentials of low-Cd ‘Zhuliangyou 189’ and the neighboring high-Cd ‘Changxianggu’ that mediated Cd uptake in a flooded or a ridge–furrow system. In the field experiment, Cd removal from contaminated soil in intercropping was 1.44 times higher than that in monoculture of Zhuliangyou 189. In both Zhuliangyou 189 and Changxianggu, intercropping improved the grain yield and decreased grain Cd content. In the pot experiment, Fe plaque amount was strongly and positively correlated with bulk soil Fe(II) content, root H2O2 concentration, and Fe(II)-oxidizing ability of root bacteria but negatively correlated with Fe(II)-oxidizing ability of bulk soil bacteria and root Cd content. In Zhuliangyou 189, intercropping increased root H2O2 concentration, rhizosphere redox potential, iron plaque amount but decreased Cd bioavailability, Fe(II)-oxidizing ability of bulk soil bacteria, and organ Cd content. In the flooded system, Zhuliangyou 189 showed higher bulk soil Fe(II) content than Changxianggu. In the ridge–furrow system, ridges decreased the Fe(II)-oxidizing ability of root and bulk soil bacteria, thereby decreasing Fe plaque amount and increasing organ Cd content of rice. In both monoculture and intercropping systems, rice cultivars planted on ridges showed higher Cd bioavailability and lower bulk boil Fe(II) content than those planted in furrows.

Electronic-structure tuning of honeycomb layered oxide cathodes for superior performance

Recently honeycomb-ordered Na3M2XO6 (M = Ni, Cu, Co; X = Sb, Bi etc.) layered oxide cathode materials have attracted significant interest because of their excellent voltage platform and high energy density. Despite their excellent prospects, they still suffer from insufficient rate capability and poor structure stability. Herein, we find that the specific capacity, electronic conductivity and structural stability of honeycomb-ordered Na3Ni2SbO6 cathode material can be well promoted through partial Ru substitution. By combining the experimental analyses and theoretical calculations, we reveal that the partial substitution of Sb(V) with low valence Ru(IV) generated a strong Ru-O covalency reduces the bandgap, leading to a decreased redox potential and enhanced electrochemical kinetics. Meanwhile, the formed honeycomb RuNi6-ring superstructure with structural distortion can adapt large strain fluctuation during cycling and eventually enhance the electrochemical cyclability. Such a proposed strategy provides valuable insights into further developments of the high-performance honeycomb layered oxides cathodes.

Composted Chicken Manure for Anaerobic Soil Disinfestation Increased the Strawberry Yield and Shifted the Soil Microbial Communities

Anaerobic soil disinfestation (ASD), as a bio-fumigation technology, has been developed to control soil-borne pests. There is increasing evidence showing that carbon sources and cover tarps play an important role in the ASD suppression of soil-borne pests, but little is known about the effect of composted chicken manure (CCM) and totally impermeable films (TIF) against soil-borne pests in the strawberry production system. In experiments, the colonies of Fusarium spp. and Phytophthora spp., which are recognized to cause strawberry soil-borne diseases, decreased significantly after ASD. The soil promoted a significant increase in ammonium nitrogen, nitrate-nitrogen and organic matter, but a decrease in oxidation-reduction potential after ASD. Besides, the strawberry plant height, stem thickness and yield were significantly higher than in the non-amended soil. Compared to the untreated control, ASD, both at 6 and 12 ton/ha of CCM, significantly (p = 0.05) increased strawberry marketable yield and income. The economic benefit could be due to the suppression of soil-borne diseases and the improvement of soil nutrition. The soil bacterial and fungal diversity and richness increased after soil fumigation. The increased presence of biological control agents led to the suppression of soil-borne pathogens. In summary, ASD with CCM amendments could be applied in pre-plant fumigation to control strawberry soil-borne pests, strengthen soil fertility, improve crop yield and increase growers’ income.

Effects of the application of an organic amendment and nanoscale zero-valent iron particles on soil Cr(VI) remediation.

Chromium is considered an environmental pollutant of much concern whose toxicity depends, to a great extent, on its valence state, with Cr(VI) being more soluble, bioavailable, and toxic, compared to Cr(III). Nanoremediation is a promising strategy for the remediation of metal pollutants by changing their valence state. However, among other aspects, its effectiveness for soil remediation is seriously hampered by the interaction of nanoparticles with soil organic matter. In this study, soil was (i) amended with two doses of a municipal solid organic waste and (ii) artificially polluted with 300 mg Cr(VI) kg-1 DW soil. After a period of aging, a nanoremediation treatment with nanoscale zero-valent iron particles (1 g nZVI kg-1 DW soil) was applied. The efficiency of the remediation treatment was assessed in terms of Cr(VI) immobilization and recovery of soil health. The presence of the organic amendment caused (i) a decrease of redox potential, (ii) Cr(VI) immobilization via its reduction to Cr(III), (iii) a stimulation of soil microbial communities, and (iv) an improvement of soil health, compared to unamended soil. By contrast, nZVI did not have any impact on Cr(VI) immobilization nor on soil health. It was concluded that, unlike the presence of the organic amendment, nanoremediation with nZVI was not a valid option for soils polluted with Cr(VI) under our experimental conditions.

Remediation of hexavalent chromium in contaminated soil using amorphous iron pyrite: Effect on leachability, bioaccessibility, phytotoxicity and long-term stability

A large amounts of arable land is facing a high risk of hexavalent chromium (Cr(VI)) pollution, which requires remediation using a low toxic agent. In this study, the remediation effect of amorphous iron pyrite (FeS2(am)) on Cr(VI) in Cr(VI)-contaminated soil was evaluated by systematically analyzing the variation of the leachability, bioaccessibility, phytotoxicity, and long-term stability of the remediated soil. The effectiveness of FeS2(am) on the leachability was assessed by alkaline digestion and the toxicity characteristic leaching procedure (TCLP); the effect on the bioaccessibility was evaluated via the physiologically based extraction test (PBET) and the Tessier sequential extraction; the effect on the phytotoxicity was assessed via phytotoxicity bioassay (seed germination experiments) based on rape (Brassica napus L.) and cucumber (Cucumis Sativus L.), and the long-term stability of the Cr(VI)-remediated soil was appraised using column tests with groundwater and acid rain as the influents. The results show that FeS2(am), with a stoichiometry of 4× exhibited a high efficiency in the remediation of Cr(VI) and decreased its leachability and bioaccessibility during the 30-day remediation period. In addition, seed germination rate, accumulation and translocation of Cr, and root and shoot elongation of rape and cucumber of remediated soil are not significantly different from those of clean soil, illustrating that FeS2(am) is suitable for remediating Cr(VI) contaminated arable soil. The stabilization of Cr(VI) in contaminated soil using FeS2(am) was maintained for 1575 days. The long-term effectiveness was further confirmed by the increasing amount of free Fe and Mn in the effluent and the decreasing redox potential. In summary, FeS2(am) has an excellent efficiency for the remediation of Cr(VI), demonstrating it is a very promising alternative for use in the contaminated arable soil.

Electronic-Structure Tuning of Honeycomb Layered Oxide Cathodes for Superior Performance

Recently honeycomb-ordered Na3M2XO6 (M = Ni, Cu, Co; X = Sb, Bi etc.) layered oxide cathode materials have attracted significant interest because of their excellent voltage platform and high energy density. Despite their excellent prospects, they still suffer from insufficient rate capability and poor structure stability. Herein, we find that the specific capacity, electronic conductivity and structural stability of honeycomb-ordered Na3Ni2SbO6 cathode material can be well promoted through partial Ru substitution. By combining the experimental analyses and theoretical calculations, we reveal that the partial substitution of Sb(V) with low valence Ru(IV) generated a strong Ru-O covalency reduces the bandgap, leading to a decreased redox potential and enhanced electrochemical kinetics. Meanwhile, the formed honeycomb RuNi6-ring superstructure with structural distortion can adapt large strain fluctuation during cycling and eventually enhance the electrochemical cyclability. Such a proposed strategy provides valuable insights into further developments of the high-performance honeycomb layered oxides cathodes.