Biochar-supported Nanoscale Zero-valent Iron Research Articles

Ecological effects of biochar-supported nanoscale zero-valent iron on Eisenia foetida in cadmium-contaminated soil: Oxidative stress, DNA damage, gene expression and transcriptomics analysis

Biochar-supported nanoscale zero-valent iron (nZVI@BC) has been widely used in heavy metal contaminated soil for remediation. However, studies on the soil ecological effects of nZVI@BC were rare. In this study, nZVI@BC was synthesized by the liquid phase reduction and GnZVI@BC was prepared by a green synthesis method which was reduced by green tea extract instead of NaBH4. Earthworms (Eisenia foetida) as indicator organisms were exposed to Cd-contaminated soil. The immobilization effects and enrichment in earthworms of Cd were measured. Besides, oxidative stress, DNA damage, gene expression and transcriptomics of earthworms were deeply explored. The results indicated that the immobilization efficiency of BC, nZVI@BC and GnZVI@BC for Cd was 76.01%, 85.49%, and 80.76%, respectively. The effects of Cd on superoxide dismutase, glutathione S-transferase, peroxidase, and catalase in earthworms reduced, reactive oxygen species and malondialdehyde contents decreased, and DNA damage was relieved. In addition, the gene toxicity of Cd to earthworms was restrained, and the genes expression of sod, cat and gst tended to be stable. With nZVI@BC, the main pathways affected by the differential genes were cellular oxidative phosphorylation and transforming growth factor-β signaling pathways. With GnZVI@BC, there were mainly structure of the cell phagosome, metabolism of taurine, hypotaurine, and alanine processes. This study will provide references for ecological risk assessment of nZVI@BC in practical applications.

Activation of persulfate by g-C3N4/nZVI@SBC for degradation of total petroleum hydrocarbon in groundwater

In this study, we synthesized a high removal efficiency catalyst using biochar-supported nanoscale zero-valent iron and g-C3N4, denoted as g-C3N4/nZVI@SBC, to activate persulfate (PS) for the degradation of total petroleum hydrocarbon (TPH) in groundwater. We characterized the morphology and physiochemical properties of g-C3N4/nZVI@SBC with scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), BET surface area analysis, and X-ray photoelectron spectroscopy (XPS). To assess the performance of the g-C3N4/nZVI@SBC catalyst, we investigated various reaction parameters, such as the mass ratio of g-C3N4 to nZVI@SBC, PS concentration, initial pH, initial TPH concentration, and the presence of coexisting ions in the system. The results from batch experiments and repeated use trials indicate that g-C3N4/nZVI@SBC exhibited both excellent catalytic activation capability and impressive durability, making it a promising choice for TPH degradation. Specifically, when the PS concentration reached 1 mM, the catalyst dosage was 0.3 g/L, and the g-C3N4 to nZVI@SBC mass ratio was 2, we achieved a remarkable TPH removal efficiency of 93.8%. Through electron paramagnetic resonance (EPR) testing and quenching experiments, we identified sulfate radicals, hydroxyl radicals, and superoxide radicals as the primary active substance involved in the TPH degradation process. Moreover, the g-C3N4/nZVI@SBC composite proved highly effective for in-situ TPH removal from groundwater and displayed an 86% removal rate, making it a valuable candidate for applications in permeable reactive barriers (PRB) aimed at enhancing environmental remediation. In summary, by skillfully utilizing g-C3N4/nZVI@SBC, this study has made notable advancements in synthesis and characterization, presenting a feasible and innovative approach to addressing TPH pollution in groundwater.

Sustainable remediation of Cr(VI)-contaminated soil by soil washing and subsequent recovery of washing agents using biochar supported nanoscale zero-valent iron

Soil contamination by Cr(VI) has attracted widespread attention globally in recent years, but it remains a significant challenge in developing an environmentally friendly and eco-sustainable technique for the disposal of Cr(VI)-contaminated soil. Herein, a sustainable cyclic soil washing system for Cr(VI)-polluted soil remediation and the recovery of washing agents using biochar supported nanoscale zero-valent iron (nZVI-BC) was established. Citric acid (CA) was initially screened to desorb Cr(VI) from contaminated soil, mobilizing Cr from the highly bioaccessible fractions. The nZVI-BC exhibited superior properties for Cr(VI) and Cr(total) removal from spent effluent, allowing effective recovery of the washing agents. The elimination mechanism of Cr(total) by nZVI-BC involved the coordinated actions of electrostatic adsorption, reduction, and co-precipitation. The contributions to Cr(VI) reduction by Fe0, surface-bound Fe(II), and soluble Fe(II) were 0.6 %, 39.8 %, and 59.6 %, respectively. Meanwhile, CA favored the activity of surface-bound Fe(II) and Fe0 in nZVI-BC, enhancing the production of soluble Fe(II) to strengthen Cr(VI) removal. Finally, the recovered washing agent was proven to be reused three times. This study showcases that the combined soil washing using biodegradable chelant CA and effluent treatment by nZVI-BC could be a sustainable and promising strategy for Cr(VI)-contaminated soil remediation.

Removal mechanism of Pb(ii) from soil by biochar-supported nanoscale zero-valent iron composite materials

Removal mechanism of Pb(<scp>ii</scp>) from soil by biochar-supported nanoscale zero-valent iron composite materials

Preparation of biochar-supported nanoscale zero-valent iron (nZVI@BC) and its adsorption and degradation of chlortetracycline in water and soil

Preparation of biochar-supported nanoscale zero-valent iron (nZVI@BC) and its adsorption and degradation of chlortetracycline in water and soil

Enhanced removal of estrogens from simulated wastewater by biochar supported nanoscale zero-valent iron: performance and mechanism

The intensification of estrogen non-point source pollution has drawn global attention due to their contribution to ecological environment problems worldwide, and it is critical to develop effective, economic and eco-friendly methods for reducing estrogens pollution. To address the agglomeration and oxidation of nano zero-valent iron (nZVI), biochar-nanoscale zero-valent iron composite (nZVI-biochar) could be a feasible choice for estrogens removal. This study summarized biochar and nZVI-biochar preparation, characterization, and unusual applications for estrone (E1), 17β-estradiol (E2), and estriol (E3) removal. The properties of biochar and nZVI-biochar in characterization, effects of influencing factors on the removal efficiency, adsorption kinetics, isotherm and thermodynamics were investigated. The experiment results showed that nZVI-biochar exhibited the superior removal performance for estrogens pollutants compared to biochar. Based on the quasi-second-order model, estrogens adsorption kinetics were observed, which supported the mechanism that chemical and physical adsorption existed simultaneously on estrogens removal. The adsorption isotherm of estrogens could be well presented by the Freundlich model and thermodynamics studies explained that nZVI-biochar could spontaneously remove estrogens pollutants and the main mechanisms involved π-π interaction, hydrophobic interaction, hydrogen bonding and degradation through ring rupture. The products analyzed by GC–MS showed that estrogens degradation was primarily attributed to the benzene ring broken, and Fe3+ promoted the production of free radicals, which further proved that nZVI-biochar had the excellent adsorption performances. Generally, nZVI-biochar could be employed as a potential material for removing estrogens from wastewater.Graphical

Natural substance-mediated synthesis for biochar-supported nanoscale zero-valent iron enhanced the performance of the catalytic process

Nanoscale zero-valent iron (nZVI) has gained increasing attention as a heterogeneous catalyst. However, problems such as aggregation, oxidation, or iron leaching limit its application. An appropriate dispersant and carrier may help solve the problems. Natural substances and their waste have been investigated as potential dispersants and carriers. Chinese herbal medicine residue is a promising raw material for this purpose. Here, black bean peel, a natural substance, was used as a dispersant and stabilizer, and biochar from chaga mushroom residue was used as a support for the first time to synthesize a zero-valent iron composite (B-nZVI-BC). X-ray diffraction (XRD) and electron spin resonance (ESR) studies confirm that the natural extracts prevented the agglomeration and oxidation of nZVI and promoted hydroxyl radical (·OH) generation. The experimental results showed that the B-nZVI-BC (2:1) + H2O2 system reduced Fe leaching to 0.66 mg/L. The synergistic effects of natural extracts, biochar (BC), and nZVI activated H2O2 for tetracycline (TC) removal and increased the removal from 67.56% to 90.07%. New insights were provided into the green synthesis and regeneration of nZVI, offering a promising solution for its practical application.

Unveiling the role of biochar in simultaneous removal of hexavalent chromium and trichloroethylene by biochar supported nanoscale zero-valent iron

The simultaneous removal of hexavalent chromium (Cr(VI)) and Trichloroethylene (TCE) is facing great challenges, and the influences of the biochar on their removal by nanoscale zero-valent iron (nZVI) are poorly understood and seldom addressed in the literature. The rice straw pyrolysis at 700 °C (RS700) and their supported nZVI composites were investigated on the removal of Cr(VI) and TCE by batch experiments. The surface area and chromium bonding state of biochar supported nZVI with and without Cr(VI)-TCE loading were analyzed by Brunauer-Emmett-Teller analysis and X-ray photoelectron spectroscopy. In single pollutants system, the highest removal amounts of Cr(VI) and TCE were observed in RS700-HF-nZVI (76.36 mg/g) and RS700-HF (32.32 mg/g), respectively. The Cr(VI) removal was attributed to the reduction by Fe(II) with the adsorption by biochar primarily controlling the TCE removal. The mutual inhibition was revealed in simultaneous removal of Cr(VI) and TCE, in which the reduction of Cr(VI) was decreased due to the adsorption of Fe(II) by biochar, while the TCE adsorption was primarily inhibited owing to the blockage of surface pores of biochar supported nZVI by chromium‑iron oxides. Therefore, biochar supported nZVI could be potentially used for the combined contaminated groundwater remediation, but the mutual inhibition should be evaluated.

Polycaprolactone-Modified Biochar Supported Nanoscale Zero-Valent Iron Coupling with Shewanella putrefaciens CN32 for 1,1,1-Trichloroethane Removal from Simulated Groundwater: Synthesis, Optimization, and Mechanism

1,1,1-Trichloroethane (1,1,1-TCA) is a typical organochloride solvent in groundwater that poses threats to human health and the environment due to its carcinogenesis and bioaccumulation. In this study, a novel composite with nanoscale zero-valent iron (nZVI) supported by polycaprolac-tone (PCL)-modified biochar (nZVI@PBC) was synthesized via solution intercalation and liquid-phase reduction to address the 1,1,1-TCA pollution problem in groundwater. The synergy effect and improvement mechanism of 1,1,1-TCA removal from simulated groundwater in the presence of nZVI@PBC coupling with Shewanella putrefaciens CN32 were investigated. The results were as follows: (1) The composite surface was rough and porous, and PCL and nZVI were loaded uniformly onto the biochar surface as micro-particles and nanoparticles, respectively; (2) the optimal mass ratio of PCL, biochar, and nZVI was 1:7:2, and the optimal composite dosage was 1.0% (w/v); (3) under the optimal conditions, nZVI@PBC + CN32 exhibited excellent removal performance for 1,1,1-TCA, with a removal rate of 82.98% within 360 h, while the maximum removal rate was only 41.44% in the nZVI + CN32 treatment; (4) the abundance of CN32 and the concentration of adsorbed Fe(II) in the nZVI@PBC + CN32 treatment were significantly higher than that in control treatments, while the total organic carbon (TOC) concentration first increased and then decreased during the culture process; (5) the major improvement mechanisms include the nZVI-mediated chemical reductive dechlorination and the CN32-mediated microbial dissimilatory iron reduction. In conclusion, the nZVI@PBC composite coupling with CN32 can be a potential technique to apply for 1,1,1-TCA removal in groundwater.

Removal of Aqueous Cr(VI) by Tea Stalk Biochar Supported Nanoscale Zero-Valent Iron: Performance and Mechanism

Removal of Aqueous Cr(VI) by Tea Stalk Biochar Supported Nanoscale Zero-Valent Iron: Performance and Mechanism

Post-sulfidation of biochar supported nanoscale zero-valent iron with different sulfur precursors: Reactivity and selectivity on tetrabromobisphenol A reduction

Herein, post-sulfidation method is applied for the first time to synthesize biochar supported sulfidated nanoscale zero valent iron (S-nZVI/BC), and the impact of sulfur (S) precursors (Na2S, Na2S2O3, and Na2S2O4) on the physicochemical properties, reactivity, selectivity, pH resistance, and long-term performance of S-nZVI/BC was investigated for tetrabromobisphenol A (TBBPA) degradation. Detailed characterizations indicated that S-nZVI/BC with different S precursors altered distribution/content of S species (i.e., S2−, Sn2−, and SO42−) in shell and core (>10 nm). The BC largely contributed to increase the sulfidation efficiency and dispersion of S-nZVI. The reactivity of S2−-nZVI/BC was ∼ 9.6 and ∼ 3.0–6.7 times higher than that of nZVI/BC and other S-nZVI/BCs, respectively, deriving from the higher Fe0 crystallinity, more hydrophobicity and proportion of reduced S species. Remarkably, the adverse effect of surface oxidized S species (i.e., SO42−) was more significant than the promoting effect induced by the surface reduced S species (i.e., S2− and Sn2−) on reactivity when there were excessive SO42− species. The selectivity of S2O42−-nZVI/BC was ∼ 203 and ∼ 1.5–3.5 times higher than that of nZVI/BC and other S-nZVI/BCs at same dosed S/Fe molar ratio (0.3), respectively, which was well correlated with the [S/Fe]particle molar ratio. Besides, increased electron efficiency with pH rise was because the passivation of surface FexOy layer (hydrogen evolution reaction sites) enabled electrons more selectively transported to FeSx surface (debromination sites). S2−-nZVI/BC remained more reactive after aging in water over 30 d than nZVI/BC and other S-nZVI/BCs. This work suggested that S precursors had crucial effects on the property and performance of S-nZVI/BC, which can be designed for specific application scenarios.

Biochar-supported nano-scale zerovalent iron activated persulfate for remediation of aromatic hydrocarbon-contaminated soil: an in-situ pilot-scale study

Biochar supported nano-scale zerovalent iron (nZVI/BC) for persulfate (PS) activation has been studied extensively for the degradation of pollutants on the lab scale, but it was rarely applied in practical soil remediation in the field. In this research, we developed a facile ball-milling method for the mass production of nZVI/BC, which was successfully applied to activate persulfate for the remediation of organic polluted soil on an in-situ pilot scale. In-situ high-pressure injection device was developed to inject nZVI/BC suspension and PS solution into the soil with a depth of 0–70 cm. The removal efficiency of target pollutants such as 2-ethylnitrobenzene (ENB, 1.47–1.56 mg/kg), biphenyl (BP, 0.19–0.21 mg/kg), 4-(methylsulfonyl) toluene (MST, 0.32–0.43 mg/kg), and 4-phenylphenol (PP, 1.70–2.46 mg/kg) at different soil depths was 99.7%, 99.1%, 99.9% and 99.7%, respectively, after 360 days of remediation. The application of nZVI/BC significantly increased the degradation rates of contaminants by 11–322%, ascribed to its relatively higher efficiency of free radical generation than that of control groups. In addition, it was found that nZVI/BC-PS inhibited soil urease and sucrase enzyme activities by 1–61% within 55 days due to the oxidative stress for microbes induced by free radicals, while these inhibition effects disappeared with remediation time prolonged (> 127 days). Our research provides a useful implementation case of remediation with nZVI/BC-PS activation and verifies its feasibility in practical contaminated soil remediation.Graphical

Carbothermal Synthesis of Sludge Biochar Supported Nanoscale Zero-Valent Iron for the Removal of Cd2+ and Cu2+: Preparation, Performance, and Safety Risks

The practical application of nanoscale zero-valent iron (NZVI) is restricted by its easy oxidation and aggregation. Here, sludge biochar (SB) was used as a carrier to stabilize NZVI for Cd2+ and Cu2+ removal. SB supported NZVI (SB-NZVI) was synthesized using the carbothermic method. The superior preparation conditions, structural characteristics, and performance and mechanisms of the SB-NZVI composites for the removal of Cd2+ and Cu2+ were investigated via batch experiments and characterization analysis. The optimal removal capacities of 55.94 mg/g for Cd2+ and 97.68 mg/g for Cu2+ were achieved at a Fe/sludge mass ratio of 1:4 and pyrolysis temperature of 900 °C. Batch experiments showed that the SB-NZVI (1:4-900) composite had an excellent elimination capacity over a broad pH range, and that weakly acidic to neutral solutions were optimal for removal. The XPS results indicated that the Cd2+ removal was mainly dependent on the adsorption and precipitation/coprecipitation, while reduction and adsorption were the mechanisms that play a decisive role in Cu2+ removal. The presence of Cd2+ had an opposite effect on the Cu2+ removal. Moreover, the SB-NZVI composites made of municipal sludge greatly reduces the leaching toxicity and bio-availability of heavy metals in the municipal sludge, which can be identified as an environmentally-friendly material.

Pyrolytic synthesis and performance efficacy comparison of biochar-supported nanoscale zero-valent iron on soil polluted with toxic metals

ABSTRACT Toxic and hazardous metals such as cadmium (Cd) and Lead (Pb) can cause cancer in humans; hence, reducing their bioavailability in the soil is crucial for human health and environmental safety. In this study, biochar modified with nanoscale zero-valent iron (nZVI-BC) was synthesized from low-cost adsorbent waste materials and iron (iii) oxide (Fe2O3) via carbothermal reduction process for stabilization of Pb and Cd in the soil. Furthermore, an evaluation of treatment efficiency on exposure health hazards for both carcinogenic and non-carcinogenic risks was done. The results revealed that nZVI-modified eggshell biochar was able to reduce the concentration bioavailable of Pb and Cd in soil by (69–75%) and (62–65%), and reduce the toxicity leaching of Pb and Cd by (53–66%) and (68–75%), respectively. The treatments reduced carcinogenic risk (CR) and hazard index (HI) in children and adults by 35–47% for Pb and 25–36% for Cd, respectively. Hence, this study proposes a new way to reduce and modify environmental wastes to make nZVI-supported biochar that can remediate toxic metals from the soil, improve soil nutrients, reduce human exposure health risks, and enhance the environment’s health.

The synthetic composite materials using PHBV, nZVI and biochar enhanced denitrification performance in water treatment

Solid carbon source (SCS)-based denitrification is a promising technique for nitrogen removal from sewage. However, a sustainable and effective supply of carbon sources, crucial to denitrification performance, has always been challenging. This study developed four synthetic SCSs: biochar (BC), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), PHBV loaded on biochar (BCP), and PHBV loaded on biochar-supported nanoscale zero-valent iron (BCPF), to examine their denitrification efficiency enhancement. Insufficient carbon sources caused low nitrate removal (<45%) in the BC reactor during the entire experiment. At the biofilm formation stage (influent nitrate: 40 mg L-1), the relatively higher nitrate removal in biochar-based SCS reactors than in the P reactor in the first 4 h indicated that the biochar's rapid release of carbon sources played a priming role in denitrification. Then, the subsequent sharp decrease in nitrate removal revealed the biochar's unsustainable release of carbon sources for the denitrifiers. Similar to the P reactor, the nitrate removal in BCP and BCPF reactors gradually increased after 12 h until the 48 h mark, where the high nitrate removal efficiency was stabilized (P: 79.93%−93.74%, BCP: 86.90%−100%, and BCPF: 91.68%−100%), except in the BC reactor. Evidently, the decomposed products from PHBV provided sustainable carbon sources for the denitrifiers. Compared with the P reactor in the continuous running stage, BCP and (especially) BCPF reactors exhibited excellent resistance to load impact. Here, PHBV supplied sustainable carbon sources and electron donors for denitrification, while nZVI served as extra electron donors. The biochar dominantly provided habitats for denitrifiers and functioned as an electron mediator.

Synthesis of magnetic nZVI@biochar catalyst from acid precipitated black liquor and Fenton sludge and its application for Fenton-like removal of rhodamine B dye

Black liquor and Fenton sludge are common industrial wastes that come from the conventional kraft pulping process and the Fenton wastewater treatment process, respectively. In this study, the biochar-supported iron-based catalysts were synthesized through a simple one-step pyrolysis method using acid-precipitated black liquor (APBL) as carbon source and Fenton sludge as iron source, and were then applied for Fenton-like removal of rhodamine B (RhB) dyes. The optimized catalyst (Fe@BC FAK ), pyrolyzed at 900 ºC with KOH as the activator, was mesoporous biochar-supported nanoscale zero-valent iron (nZVI). Under the optimal conditions (50 mg L −1 RhB, initial pH 3, 2 mM H 2 O 2 concentration, catalyst dosage of 0.2 g L −1 ), the Fe@BC FAK /H 2 O 2 system achieved almost 100% RhB dye removal within 10 min. Moreover, the Fe@BC FAK /H 2 O 2 system also exhibited excellent removal efficiencies for malachite green , crystal violet, and methylene blue . The Fe@BC FAK had a good magnetic separation ability (146.4 emu g −1 ) and maintained a high removal efficiency of RhB (83.8%) in the presence of H 2 O 2 after five times of recycling/reuse. The degradation of RhB dye was mainly attributed to •OH, including surface-bound •OH and free •OH. Besides the excellent catalytic ability and Fe(III) reduction ability of nZVI itself, the biochar supports with high specific surface area and mesoporous structure also played important roles in the removal of RhB dye, such as adsorbing RhB dyes, alleviating nZVI aggregation, and accelerating the reduction of Fe(III) to Fe(II). • Catalyst was synthesized from two industrial wastes by one-step pyrolysis method. • The degradation reaction was obtained efficiently at pH 3 with low H 2 O 2 consumption. • Fe@BC FAK exhibited excellent catalytic ability and reusability in removing RhB. • Biochar support facilitated Fe(III) reduction, mass transfer and H 2 O 2 activation.

Remediation of Cr(VI)-Contaminated Soil by Biochar-Supported Nanoscale Zero-Valent Iron and the Consequences for Indigenous Microbial Communities.

Biochar/nano-zero-valent iron (BC-nZVI) composites are currently of great interest as an efficient remediation material for contaminated soil, but their potential to remediate Cr-contaminated soils and effect on soil microecology is unclear. The purpose of this study was to investigate the effect of BC-nZVI composites on the removal of Cr(VI) from soil, and indigenous microbial diversity and community composition. The results showed that after 15 days of remediation with 10 g/kg of BC-nZVI, 86.55% of Cr(VI) was removed from the soil. The remediation of the Cr-contaminated soil with BC-nZVI resulted in a significant increase in OTUs and α-diversity index, and even a significant increase in the abundance and diversity of indigenous bacteria and unique bacterial species in the community by reducing the toxic concentration of Cr, changing soil properties, and providing habitat for survival. These results confirm that BC-nZVI is effective in removing Cr(VI) and stabilizing Cr in soil with no significant adverse effects on soil quality or soil microorganisms.

Remediation mechanism of Cu, Zn, As, Cd, and Pb contaminated soil by biochar-supported nanoscale zero-valent iron and its impact on soil enzyme activity

Recently, heavy metal contaminated soil has been widespread concerned. Herein, rice straw-derived biochar-supported nanoscale zero-valent iron (nZVI@BC) composite was prepared and characterized, and its remediation performance in Cu, Zn, As, Cd, and Pb contaminated soil were evaluated. nZVI@BC demonstrated better immobilization effect on multiple heavy metals than biochar, and the residual component of Cu, Zn, As, Cd, and Pb increased by 10.27%, 7.18%, 7.44%, 9.26%, and 12.75%, respectively. After nZVI@BC treatment, the soil pH, the available iron, cation exchange capacity, total organic carbon, and dissolved organic carbon increased. Besides, soil enzyme (catalase, urease, and fluorescein diacetate hydrolase) activities significantly increased, especially, the catalase activity was doubled. Furthermore, the immobilization mechanism was explored, including surface adsorption, electrostatic attraction, ion exchange, coprecipitation, oxidation-reduction, and complexation. Additionally, the adsorption sites of Pb and Cu were more competitive, and As synergistically promoted the adsorption of Pb, forming a ternary surface complex PbFeAsO4OH. Therefore, it well demonstrates that nZVI@BC may be a potential technology for remediation of multiple heavy metals contaminated soil.

Remediation and Optimisation of Petroleum Hydrocarbon Degradation in Contaminated Water by Persulfate Activated with Bagasse Biochar-Supported Nanoscale Zerovalent Iron

In this study, biochar (BC) was prepared from bagasse and then successfully loaded with nanoscale zerovalent iron (nZVI) to produce BC-supported nZVI, termed nZVI@BC. Satisfactory results were obtained using a nZVI@BC-activated persulfate (PS), termed nZVI@BC/PS, to remediate total petroleum hydrocarbons (TPH)-contaminated water. The effects of three influencing factors—the dosage of nZVI@BC, DnZVI@BC, the concentration of PS, CPS, and the initial pH, pHi—on TPH removal were examined through single-factor and batch tests. The results show the following. Each factor considerably influenced the performance of the prepared nZVI@BC/PS reaction system in removing TPH. The TPH degradation process conformed to a first-order kinetic model. The response surface method (RSM) was used in tandem with a Box–Behnken design to optimise the variables involved in TPH degradation. The three influencing variables (i.e., DnZVI@BC, CPS, and pHi) were set in the range of 0.4–1.0 g/L, 20–160 g/L, and 2.21–9.42, respectively, during the experiment. An optimised quadratic model used to fit the experimental data displayed a high level of significance (p &lt; 0.0001) with a very high regression value (R2 = 0.9906; adjusted R2 = 0.9786). Analyses of regression and variance revealed that the quadratic model sufficiently explains the TPH degradation rate. An electron paramagnetic resonance (EPR) spectroscopic analysis of the nZVI@BC/PS system revealed that SO4−·, ·OH, O2−·, and 1O2 participated in the activation and degradation processes. The results of this study show that nZVI@BC-activated PS systems possess great potential for applications in TPH-contaminated wastewater treatment and environmentally sustainable development.

Biochar-supported nanoscale zero-valent iron can simultaneously decrease cadmium and arsenic uptake by rice grains in co-contaminated soil

Cadmium (Cd) and Arsenic (As) in rice grains are a primary exposure source for human beings. However, the simultaneous stabilization of Cd and As in soil becomes difficult due to the opposite properties of those. In this study, we investigated the simultaneous effects of biochar-supported nanoscale zero-valent iron (nZVI-BC) and water management on the decrease of Cd and As bioaccumulation in rice grain. Compared to the control, 0.25–1.00% nZVI-BC coupled with alternate wetting and drying (AWD) management simultaneously decreased the bioaccumulation of Cd and As in rice grains by 15.85–69.16% and 23.06–59.45%, respectively. The cancer risk associated with rice consumption effectively reduced by 15.60–52.41% after the application of nZVI-BC, and the lowest cancer risk was detected in 1.00% nZVI-BC under AWD management. Furthermore, rice cultivated under AWD management had a lower total cancer risk than that cultivated under continuous flooded (CF) management with the same amendment of type and dose. The reduction of soil Cd and As availability and the formation of iron plaque dominated the decrease of Cd and As uptake by rice grains. The elevated soil pH was responsible for Cd adsorption, and the dominant mechanism for As immobilization was the formation of complexes. The iron plaque was double-edged, promoting and inhibiting Cd uptake by rice, wherein the inhibition was predominant under aerobic conditions. In addition, iron plaque was a barrier to preventing the As accumulation by rice, a larger amount of As was immobilized on the iron plaque with nZVI-BC treatment. This study sheds new insights on the simultaneous remediation of Cd and As co-contaminated paddy fields.