Metabolomic and gut-microbial responses of earthworms exposed to microcystins and nano zero-valent iron in soil.

The earthworm-based vermiremediation facilitated with benign chemicals such as nano zero-valent iron (nZVI) is a promising approach for the remediation of a variety of soil contaminants including cyanotoxins. As the most toxic cyanotoxin, microcystin-LR (MC-LR) enter soil via runoff, irrigated surface water and sewage, and the application of cyanobacterial biofertilizers as part of the sustainable agricultural practice. Earthworms in such remediation systems must sustain the potential risk from both nZVI and MC-LR. In the present study, earthworms (Eisenia fetida) were exposed up to 14 days to MC-LR and nZVI (individually and in mixture), and the toxicity was investigated at both the organismal and metabolic levels, including growth, tissue damage, oxidative stress, metabolic response and gut microbiota. Results showed that co-exposure of MC-LR and nZVI is less potent to earthworms than that of separate exposure. Histological observations in the co-exposure group revealed only minor epidermal brokenness, and KEGG enrichment analysis showed that co-exposure induced earthworms to regulate glutathione biosynthesis for detoxification and reduced adverse effects from MC-LR. The combined use of nZVI promoted the growth and reproduction of soil and earthworm gut bacteria (e.g., Sphingobacterium and Acinetobacter) responsible for the degradation of MC-LR, which might explain the observed antagonism between nZVI and MC-LR in earthworm microcosm. Our study suggests the beneficial use of nZVI to detoxify pollutants in earthworm-based vermiremediation systems where freshwater containing cyanobacterial blooms is frequently used to irrigate soil and supply water for the growth and metabolism of earthworms.

Efficient remediation of different concentrations of Cr-contaminated soils by nano zero-valent iron modified with carboxymethyl cellulose and biochar.

Nano zero-valent iron (nZVI) is widely used in soil remediation due to its high reactivity. However, the easy agglomeration, poor antioxidant ability and passivation layer of Fe-Cr coprecipitates of nZVI have limited its application scale in Cr-contaminated soil remediation, especially in high concentration of Cr-contaminated soil. Herein, we found that the carboxymethyl cellulose on nZVI particles could increase the zeta potential value of soil and change the phase of nZVI. Along with the presence of biochar, 97.0% and 96.6% Cr immobilization efficiency through CMC-nZVI/BC were respectively achieved in high and low concentrations of Cr-contaminated soils after 90-days remediation. In addition, the immobilization efficiency of Cr(VI) only decreased by 5.1% through CMC-nZVI/BC treatment after 10 weeks aging in air, attributing to the strong antioxidation ability. As for the surrounding Cr-contaminated groundwater, the Cr(VI) removal capacity of CMC-nZVI/BC was evaluated under different reaction conditions through column experiments and COMSOL Multiphysics. CMC-nZVI/BC could efficiently remove 85% of Cr(VI) in about 400 hr when the initial Cr(VI) concentration was 40 mg/L and the flow rate was 0.5 mL/min. This study demonstrates that uniformly dispersed CMC-nZVI/BC has an excellent remediation effect on different concentrations of Cr-contaminated soils.

Pristine/magnesium-loaded biochar and ZVI affect rice grain arsenic speciation and cadmium accumulation through different pathways in an alkaline paddy soil.

Cadmium (Cd) and arsenic (As) co-contamination has threatened rice production and food safety. It is challenging to mitigate Cd and As contamination in rice simultaneously due to their opposite geochemical behaviors. Mg-loaded biochar with outstanding adsorption capacity for As and Cd was used for the first time to remediate Cd/As contaminated paddy soils. In addition, the effect of zero-valent iron (ZVI) on grain As speciation accumulation in alkaline paddy soils was first investigated. The effect of rice straw biochar (SC), magnesium-loaded rice straw biochar (Mg/SC), and ZVI on concentrations of Cd and As speciation in soil porewater and their accumulation in rice tissues was investigated in a pot experiment. Addition of SC, Mg/SC and ZVI to soil reduced Cd concentrations in rice grain by 46.1%, 90.3% and 100%, and inorganic As (iAs) by 35.4%, 33.1% and 29.1%, respectively, and reduced Cd concentrations in porewater by 74.3%, 96.5% and 96.2%, respectively. Reductions of 51.6% and 87.7% in porewater iAs concentrations were observed with Mg/SC and ZVI amendments, but not with SC. Dimethylarsinic acid (DMA) concentrations in porewater and grain increased by a factor of 4.9 and 3.3, respectively, with ZVI amendment. The three amendments affected grain concentrations of iAs, DMA and Cd mainly by modulating their translocation within plant and the levels of As(III), silicon, dissolved organic carbon, iron or Cd in porewater. All three amendments (SC, Mg/SC and ZVI) have the potential to simultaneously mitigate Cd and iAs accumulation in rice grain, although the pathways are different.

New insights on zero-valent iron permeable reactive barrier for Cr(VI) removal: The function of FeS reaction zone downstream in-situ generated by sulfate-reducing bacteria.

The biogeochemical behavior downstream of the zero-valent iron permeable reactive barrier (ZVI-PRB) plays an enormous positive role in the remediation of contaminated-groundwater, but has been completely neglected for a long time. Therefore, this study conducted a 240-day SRB-enhanced ZVI-PRB column experiment, focusing on what exactly happens downstream of ZVI-PRB. Results show that biosulfidation of SRB inside ZVI-PRB prolonged the complete Cr(VI) removal longevity of ZVI-PRB from 38 days to at least 240 days. More importantly, unlike previous studies that focused on improving the performance of ZVI-PRB itself, this study found an in-situ generated FeS reduction reaction zone downstream of the ZVI-PRB. When the ZVI-PRB fails, the downstream reaction zone can continue to play a role in Cr(VI) removal. The maximum Cr(VI) removal capacity of the aquifer media from the reaction zone reached 155.1 mg/kg, which was 39.7 % of commercial ZVI capacity. The reduction zone was further confirmed to be predominantly FeS rather than FeS2. Biogeochemistry occurring within and downstream of ZVI-PRB leads to the formation of FeS. Gene sequencing revealed significantly higher SRB abundance downstream of ZVI-PRB than within the ZVI-PRB. The understanding of the downstream FeS reaction zone provides new insights for more effective remediation using ZVI-PRB.

Enhanced in-situ sediment remediation by calcium peroxide coupled with zero-valent iron: Simultaneous nitrogen removal and phosphorus stabilization.

As the potential causes of eutrophication, nitrogen (N) and phosphorus (P) in sediments have received wide attention. However, few of the in-situ sediment remediation methods can achieve simultaneous N removal and P stabilization in sediments. In this study, different impacts on N, P and organic matter (OM) properties of sediments and overlying water with different proportions of calcium peroxide (CaO2) coupling with zero-valent iron (ZVI) were explored through incubation experiments. Compared with CaO2 or ZVI alone, the total nitrogen (TN) removal ratios in the whole system at 0.6 g/kg CaO2 coupled with 40 g/kg ZVI increased by 167.91 % and 152.04 %, respectively. Due to the enhancement of oxidation, the removal efficiency of OM from sediments increased by 118.51 %. Meanwhile, the genera related to denitrification (e.g., Anaerobacillus, Haloplasma, and Clostridium_sensu_stricto_8) were also enriched in this coupling group, which was due to the enhanced decomposition of OM and the electron donation of ZVI. In addition, CaO2 coupled with ZVI stabilized P through chemical precipitation, which converted organic phosphorus (OrgP) into more stable calcium bounded P (CaP) in sediments. Hence the coupling effectively increased total P (TP) content in sediments and reduced P concentration in water.

The Application of Nano Zero-Valent Iron in Synergy with White Rot Fungi in Environmental Pollution Control.

Developing efficient and sustainable pollution control technologies has become a research priority in the context of escalating global environmental pollution. Nano zero-valent iron (nZVI), with its high specific surface area and strong reducing power, demonstrates remarkable performance in pollutant removal. Still, its application is limited by issues such as oxidation, passivation, and particle aggregation. White rot fungi (WRF) possess a unique enzyme system that enables them to degrade a wide range of pollutants effectively, yet they face challenges such as long degradation cycles and low degradation efficiency. Despite the significant role of nZVI in pollutant remediation, most contaminated sites still rely on microbial remediation as a concurrent or ultimate treatment method to achieve remediation goals. The synergistic combination of nZVI and WRF can leverage their respective advantages, thereby enhancing pollution control efficiency. This paper reviews the mechanisms, advantages, and disadvantages of nZVI and WRF in pollution control, lists application examples, and discusses their synergistic application in pollution control, highlighting their potential in pollutant remediation and providing new insights for combined pollutant treatment. However, research on the combined use of nZVI and WRF for pollutant remediation is still relatively scarce, necessitating a deeper understanding of their synergistic potential and further exploration of their cooperative interactions.

Long-term performance and mechanism of in-situ biogenetic sulfidated zero-valent iron for enhanced nitrate reduction.

The biogenetic sulfidation of zero-valent iron (BS-ZVI) by sulfate-reducing bacteria (SRB) has been demonstrated to enhance the reactivity of ZVI. However, long-term performance of BS-ZVI and related mechanism were still unknown. Therefore, columns containing sponge iron and SRB are built to prepare BS-ZVI in-situ and study its long-term performance. Over 80 % of NO3‾ was reduced to NH4+ by in-situ BS-ZVI within 140 days, which was higher than the sole ZVI treatment (40 %-60 %). The bonding of ZVI and FeSx was in-situ firstly and finally loaded on ZVI. The reduction of Fe(III) by S(-II) and SRB contributed to the formation of FeSx, which improved the electrons transfer. Moreover, BS-ZVI enhanced the enzymes activity of SRB, thus accelerating the metabolic transformation of lactic acid to acetic acid. The accumulation of acetic acid enhanced the removal efficiency of NO3‾ through the dissolution of passivation layer. Overall, this study demonstrated a reactivity enhancement of ZVI through biogenetic sulfidation, which provided a new alternative method for the remediation of groundwater.

Time-dependent redistribution of soil arsenic induced by transformation of iron species during zero-valent iron biochar composites amendment: Effects on the bioaccessibility of As in soils.

Zero-valent iron biochar composites (ZVI/BC) are considered as effective amendments for arsenic (As)-contaminated soils. However, the mechanisms of transformation of various soil As species during ZVI/BC amendments remain unclear. This study investigated As transformation in four soils (namely, GX, ZJ, HB, and HN) treated with ZVI/BC for 65 days under two soil moisture conditions, unsaturated and oversaturated. Results showed that the 65-day treatment was divided into two stages based on the variation of labile As content. Within 2 days (stage 1), ZVI/BC addition quickly reduced labile As content by 5.91-90.3 % in soils under unsaturated conditions. During days 2-65 (stage 2), labile As ultimately decreased by 0.06-0.31 mg/kg in GX, ZJ, and HB while increasing by 22.1 mg/kg in HN soil, due to its lower pH value and Fe content. The variations of labile As were attributed to changes in multiple Fe minerals and associated As species. In stage 1, the corrosion of ZVI/BC generated amorphous Fe oxides to immobilize labile As, resulting in the accumulation of meta-stable As. In stage 2, amorphous Fe oxides were transformed into crystalline Fe oxides, resulting in the release and re-precipitation of As along with transformation, thus redistributing immobilized As into labile and stable As, which was evidenced by multiple methods, including chemical extraction, XRD, and TEM-EDX. The elevated soil moisture condition would enhance the corrosion of ZVI/BC in stage 1, further forming a reductive environment to facilitate the transformation of Fe minerals in stage 2. Besides, As bioaccessibility in soils was reduced by 10.8-38.7 % after ZVI/BC treatment in in-vitro gastrointestinal simulations. Overall, our study revealed the time-dependent transformation mechanism of soil As species and associated Fe minerals under different soil moisture with ZVI/BC treatments, and highlighted the effectiveness of ZVI/BC as a long-term amendment for As-contaminated soils.

Sustainable Abiotic-Biotic Dechlorination of Perchloroethene with Sulfidated Nanoscale Zero-Valent Iron as Electron Donor Source.

Combining organohalide-respiring bacteria with nanoscale zero-valent iron (nZVI) represents a promising approach for remediating chloroethene-contaminated aquifers. However, limited information is available regarding their synergistic dechlorinating ability for chloroethenes when nZVI is sulfidated (S-nZVI) under the organic electron donor-limited conditions typically found in deep aquifers. Herein, we developed a combined system utilizing a mixed culture containing Dehalococcoides (Dhc) and S-nZVI particles, which achieved sustainable dechlorination with repeated rounds of spiking with 110 µM perchloroethene (PCE). The relative abundance of Dhc considerably increased from 5.2 to 91.5% after five rounds of spiking with PCE, as evidenced by 16S rRNA gene amplicon sequencing. S-nZVI corrosion generated hydrogen as an electron donor for Dhc and other volatile fatty acid (VFA)-producing bacteria. Electron balance analysis indicated that 68.1% of electrons from Fe0 consumed in S-nZVI were involved in dechlorination, and 6.2, 1.1, and 3.2% were stored in formate, acetate, and other VFAs, respectively. The produced acetate possibly served as a carbon source for Dhc. Metagenomic analysis revealed that Desulfovibrio, Syntrophomonas, Clostridium, and Mesotoga were likely involved in VFA production. These findings provide valuable insights into the synergistic mechanisms of biotic and abiotic dechlorination, with important implications for sustainable remediation of electron donor-limited aquifers contaminated by chloroethenes.

Unveiling trends in migration of iron-based nanoparticles in saturated porous media.

Nanoscale zero-valent iron (nZVI) particles are routinely used for environmental remediation, but their transport dynamics in different settings remain unclear, hindering optimization. This study introduces a novel approach to predicting nZVI transport in saturated porous model environment. The method employs advanced long column devices for real-time monitoring via controlled magnetic susceptibility measurements. Numerical modeling with a modified version of the MNMs 2023 software was then used to predict nZVI and its derivatives mobility in field-like conditions, offering insights into the radius of influence (ROI) and shape factor (SF) of their distribution. A standard nZVI precursor was compared with its four major commercial derivatives: nitrided, polyacrylic acid-coated, oxide-passivated, and sulfidated nZVI. All these iron-based nanoparticles exhibited identical particle sizes, morphologies, surface areas, and phase compositions, isolating surface properties, dominated by charge, as the sole variable affecting their mobility. The study revealed optimal transport when the surface charge of nZVI and its derivatives was strongly negative, while rapid aggregation of nZVI derivatives due magnetic attraction reduced their mobility. Modeling predictions based on column scale-up, indicated that detectable concentrations of 20 g L⁻1 were found at distances ranging from 0.4 to 1.1 m from the injection well. Slightly sulfidated nZVI traveled farther than the nZVI precursor and ensured more homogenous particle distribution around the well. Organically modified nZVI migrated the longest distances but showed particle accumulation close to the injection point. The findings suggest that minimal sulfidation combined with organic modification of nZVI surfaces may effectively enhance radial and vertical nZVI distribution in aquifers. Such improvements increase the commercial viability of modified nZVI, reduce their adverse impacts, and boosts their practical applications in real-world scenarios.

Effective co-immobilization of arsenic and cadmium in contaminated soil by sepiolite-modified nano-zero-valent iron and its impact on the soil bacterial community.

Sepiolite-modified nano-zero-valent iron (S-nZVI) is used as an amendment and incubated to remediate As-Cd-contaminated soil under three different soil‒water management conditions [moderately wet (MW), continuously flooded (CF) and alternately wet and dry (AWD)]. The results showed that soil pH is in the order of CF > AWD > MW. The soil pH increased approximately 0.5 to 1 unit by 3% and 5% doses after 36 d of incubation. Soil pH was negatively correlated with available As-Cd content under the three water regimes (p < 0.01). All doses of S-nZVI significantly reduced soil available As-Cd under the three soil moistures by 45-80% for As and 5-45% for Cd. Moreover, S-nZVI addition also promoted the transformation of As-Cd in the acid-extracted fraction, oxidation fraction, and reduced fraction to a more stable residue fraction. High-throughput sequencing results showed that high doses of S-nZVI had a significant adverse effect on soil bacterial diversity and richness. After 36 d of incubation, the Chao1 index and the Shannon index were significantly decreased in MW, CF, and AWD, respectively. Decreasing the S-nZVI dose and increasing the incubation time simultaneously reduced As-Cd availability and S-nZVI ecotoxicity in the soil, thereby effectively maintaining the survivability of the original dominant bacteria, increasing the soil pH, and promoting the interaction between dominant bacteria and soil factors in As-Cd cocontaminated soil.

In situ treatment of contaminated soil using persulfate activated by sulfidated zero-valent iron.

Soil contamination with hazardous substances like phenol poses significant environmental and health risks. In situ soil mixing can be a promising technological solution to this challenge. A persulfate and sulfidated zero-valent iron (S-ZVIbm) system for remediating contaminated soil was developed and tested to be suited to in situ soil mixing. S-ZVIbm was synthesized using a ball mill process, and the optimal sulfur to iron molar ratio for effectively removing phenol from soil removal without pyrophoric risks was 0.12. Soil slurry experiments were performed, and the best phenol oxidation results (high stoichiometric efficiency and sustained oxidation after mixing) were achieved at a persulfate to S-ZVIbm molar ratio of 2:1 and a persulfate to phenol molar ratio of 8:1. A high organic matter content of the silty clay fraction of the soil strongly suppressed persulfate activation, so suppressed phenol removal and increased persulfate consumption. Electron spin resonance and radical scavenging tests confirmed that hydroxyl and sulfate radicals were present during the degradation of phenol. While sulfate radicals predominantly facilitated degradation in the soil, both sulfate and hydroxyl radicals were crucial in the aqueous phase in the absence of soil organic matter. In situ soil mixing simulation tests indicated that the persulfate and S-ZVIbm doses and the mixing rate and duration strongly affected the efficacy of the system, and the optimal conditions for phenol removal were determined. The results indicated that the persulfate/S-ZVIbm system could be tuned to achieve sustained persulfate activation and to remediate contaminated soil employing in situ soil mixing technique.

[Research progress of nanoscale zero-valent iron in synergistic combinations of denitrifying bacteria for nitrate removal].

Nitrate (NO3--N) is a common inorganic nitrogen pollutant in water. Excessive NO3--N can lead to water eutrophication and threaten human health. Nanoscale zero-valent iron (nZVI) has attracted much attention in NO3--N removal due to its high specific surface and excellent electron donor properties. The combination of nZVI and denitrifying bacteria (DNB) demonstrates high efficiency in converting NO3--N into N2. This approach not only substantially enhances the removal rate of NO3--N but also exhibits superior environmental sustainability compared with conventional chemical denitrification methods. Accordingly, it holds substantial promise for mitigating NO3--N pollution and warrants further exploration in the pollution control. Therefore, it is necessary to understand the interaction mechanism between nZVI and DNB for NO3--N removal. This paper details the factors affecting the removal of NO3--N by nZVI combined with DNB, reviews the latest research progress in this field, elaborates on the interaction mechanism between nZVI and DNB for NO3--N removal, and discusses the challenges and future research directions of NO3--N removal by nZVI combined with DNB. This review aims to provide a theoretical basis for the development of efficient approaches for the remediation of NO3--N pollution.

Enhanced the removal of norfloxacin by oxalated zero-valent iron with rich surface Fe(II) sites activating the chlorite.

Oxalic acid-modified ball-milled zero-valent iron (OA-ZVIbm) was employed to activate sodium chlorite (ClO2-) for the removal of norfloxacin (NOR). The complete removal of 20 mg/L NOR was achieved within 60 min by the OA-ZVIbm/ClO2- process. Compared with the ZVIbm/ClO2- process which was the ball-milled zero-valent iron (ZVIbm) activate sodium chlorite, the reaction activity of the OA-ZVIbm/ClO2- process was increased by 102.6 times. Through scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemical testing, and density functional theory (DFT) calculations, which has been confirmed that the introduction of oxalic acid can significantly increase the surface Fe(II) content of OA-ZVIbm, and accelerate the electron transfer rate of iron nuclei, thereby improve the efficiency of ClO2- activation for the removal of NOR. The role of various active species in NOR removal, which were •O2-, 1O2, Fe(IV), ClO2, and •OH, was elucidated through free radical quenching experiments, electron paramagnetic resonance (EPR) spectroscopy, and quantitative detection of active species. These active species all participated in the reaction, while •O2- played a dominant role in the reaction because it could transform into other active species, such as (•OH, 1O2). Inorganic anions and natural organic matter have no significant effect on the removal of NOR in the OA-ZVIbm/ClO2- process. The protonation of oxalic acid ensured its good pH applicability range (pH = 2-11), thus exhibiting excellent performance in NOR removal in real water bodies. This further demonstrates that OA-ZVIbm prepared by oxalic acid ball milling modification is an efficient ClO2- activator, offering promising prospects for antibiotic removal technology.

Roles of silica coating on nanosized zero-valent iron in sequential reduction-oxidation process in a system containing persulfate.

A sequential reduction-oxidation process using silica-coated nanosized zero-valent iron (nZVI) particles (nZVI@SiO2) and persulfate for mineralizing recalcitrant compounds was developed, and the effects of the process on nitrobenzene were evaluated. This sequential process significantly enhanced contaminant mineralization, which could not be effectively achieved by reduction or oxidation alone. The nZVI@SiO2 rapidly reduced nitrobenzene to aniline, then the aniline concentration gradually decreased after persulfate had been added and initiated sequential oxidative degradation. The SiO2 coating on the nZVI@SiO2 limited outward mass transfer of reaction products and increased the efficiency with which nitrobenzene was converted into aniline. Slow release of Fe(II) caused by the coating caused persulfate activation and subsequent aniline oxidation to be more sustained and efficient than without the coating. The final nitrobenzene-aniline mineralization efficiency was higher for the nZVI@SiO2/persulfate system than the nZVI/persulfate system. The SiO2 coating of the nZVI@SiO2 particles was an excellent protective layer, protecting the particles from undesirable consumption through reactions with groundwater components. nZVI@SiO2 particle transformations during the sequential process were investigated, and the operating conditions were optimized to maximize the recalcitrant compound removal efficiency. The results indicated that nZVI@SiO2 and persulfate could be used to mineralize organic contaminants in groundwater through sequential reduction-oxidation.

Sulfidation of Nanoscale Zero-Valent Iron by Sulfide: The Dynamic Process, Mechanism, and Role of Ferrous Iron.

Sulfidation of nanoscale zerovalent iron (nZVI) can enhance particle performance. However, the underlying mechanisms of nZVI sulfidation are poorly known. We studied the effects of Fe2+ on 24-h dynamics of nZVI sulfidation by HS- using a dosed S to Fe molar ratio of 0.2. This shows that in the absence of Fe2+, HS- rapidly adsorbed onto nZVI particles and reacted with surface iron oxide to form mackinawite and greigite (<0.5 h). As nZVI corrosion progressed, amorphous FeSx in solution deposited on nZVI, forming S-nZVI (0.5-24 h). However, in the initial presence of Fe2+, the rapid reaction between HS- and Fe2+ produced amorphous FeSx, which deposited on the nZVI and corroded the surface iron oxide layer (<0.25 h). This was followed by redeposition of colloidal iron (hydr)oxide on the particle surface (0.25-8 h) and deposition of residual FeSx (8-24 h) on S-nZVI. S loading on S-nZVI was 1 order of magnitude higher when Fe2+ was present. Surface characterization of the sulfidated particles by TEM-SAED, XPS, and XAFS verified the solution dynamics and demonstrated that S2- and S22-/Sn2- were the principal reduced S species on S-nZVI. This study provides a methodology to tune sulfur loading and S speciation on S-nZVI to suit remediation needs.

Enhancing pakchoi cabbage yield and quality but reducing human-disease risk of bacterial community from wastewater irrigation by combined nanoscale zerovalent iron and nitrification inhibitor.

It was indispensable to seek effective and feasible measures to alleviate the adverse effects of wastewater irrigation. Nanoscale zerovalent iron (nZVI) and soil nitrogen management might enhance the vegetable yield and quality but mitigate the potential human-disease risks from wastewater irrigation. This study selected the nZVI and nitrification inhibitor as experimental objects. The planted pakchoi cabbage was irrigated with the tap water and wastewater and treated with nZVI and 3, 4-dimethylpyrazole phosphate (DMPP), respectively, the pakchoi cabbage yield and quality, soil enzyme activity and abiotic property, and human-disease risk of bacterial community were quantified. Compared with the control, the nZVI significantly enhanced the pakchoi cabbage yield by 51.5% but reduced the pakchoi cabbage nitrate content by 52.6% under wastewater irrigation condition. The nZVI alone had double-edged sword effects of increasing the pakchoi cabbage yield, reducing the pakchoi cabbage nitrate content and soil human-disease risk but inhibiting the system multifunctionality and soil bacterial community diversity and stability, under wastewater irrigation condition. The nZVI diminished human-disease risk via increasing the soil Firmicutes and Verrucomicrobiota ratios, and the extra DMPP could mitigate the negative effects of nZVI by increasing soil enzyme activity and stimulating soil Acidobacteria ratio. The combinations of nZVI and DMPP could not only enhance the pakchoi cabbage yield and quality but also reduce the human-disease risk of soil bacterial community from wastewater irrigation.

A novel strategy for enhancing high solid anaerobic digestion of fecal slag and food waste using percolate recirculation and dosage of nano zero-valent iron.

To speed up reaching UN Sustainable Development Goal 6 for safe sanitation by 2030, integrating high-solid anaerobic digestion (HSAD) into decentralized systems could recycle fecal slag (FS) and food waste (FW), aiding a circular economy and toilet revolution. In this study, a percolate recirculation system and conductive material were used to improve mass transfer, stability, and enhance methane production in HSAD of FS and FW. This setup consists of a percolate tank and a digester tank, where nano-zero valent iron (nZVI) was dosed in the percolate tank (PnZVI in P) and the digester tank (PnZVI in D) and compared with a control with no additive (PControl). The highest cumulative methane yield of 519.43 mL/gVS was achieved in PnZVI in D, which was 4.52 and 3.59 times higher than that of PControl (144.59 mL/gVS) and PnZVI in P (114.96 mL/gVS). This finding demonstrates that the dosing strategy of PnZVI in D facilitated effective interaction among organic matter, microbial communities, and nZVI, resulting in organics removal efficiencies of 67.42 % (total solid) and 77.22 % (volatile solid). Moreover, microbial community analysis supported the efficacy of the PnZVI in D strategy, revealing the enrichment of Clostridium sensu stricto 1 (46.91 %), which potentially engaged in interspecies electron transport (Interspecies hydrogen transfer (IHT) and direct interspecies electron transfer (DIET)) with Methanobacterium (81.19 %) and Methanosarcina (17.11 %). These interactions contribute to enhanced methane yield and stability maintenance in the HSAD system with percolate recirculation. The findings of this study demonstrate that the implementation of HSAD of FS and FW, coupled with percolate recirculation and the addition of nZVI, holds promise for enabling sustainable sanitation practices in developing regions. Moreover, this approach not only facilitates resource recovery but also eliminates the requirement for water.

Nanoscale zero-valent iron alleviated horizontal transfer of antibiotic resistance genes in soil: The important role of extracellular polymeric substances.

Extracellular polymeric substances (EPS) are tightly related to the horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs), but often neglected in soil. In this study, nanoscale zero-valent iron (nZVI) was utilized for attenuation of ARGs in contaminated soil, with an emphasis on its effects on EPS secretion and HGT. Results showed during soil microbe cultivation exposed to tetracycline, more EPS was secreted and significant increase of tet was observed due to facilitated HGT. Notably, copies of EPS-tet accounted for 71.39 % of the total tet, implying vital effects of EPS on ARGs proliferation. When co-exposed to nZVI, EPS secretion was decreased by 38.36-71.46 %, for that nZVI could alleviate the microbial oxidative stress exerted by tetracycline resulting in downregulation of genes expression related to the c-di-GMP signaling system. Meanwhile, the abundance of EPS-tet was obviously reduced from 7.04 to 5.12-6.47 log unit, directly causing decrease of total tet from 7.19 to 5.68-6.69 log unit. For the reduced tet, it was mainly due to decreased EPS secretion induced by nZVI resulting in inhibition of HGT especially transformation of the EPS-tet. This work gives an inspiration for attenuation of ARGs dissemination in soil through an EPS regulation strategy.

Experimental study on harmful effects of zero-valent Iron on Paraprionospio patiens.

Iron is an essential trace element for living organisms, and it plays an important role in redox reactions in aquatic environments. Although many studies have investigated the application of iron materials to improve water and sediment quality, their negative effects remain unknown. Therefore, this study investigated the effects of three iron materials, i.e., zero-valent iron, iron oxide, and iron oxyhydroxide, on common benthic organisms in a coastal area via exposure experiments. In the exposure experiments, Paraprionospio patiens, a marine polychaete, exhibited abnormal behavior immediately after the addition of zero-valent iron, and the average survival rate after 14 d decreased significantly (Scheffé's test: p < 0.05). This is the first study to show that zero-valent iron on the sediment surface negatively affects the survival of P. patiens. Although Iron materials are often used to improve aquatic environments, their potential adverse effects should be addressed through continuous monitoring after use.