Application In Soil Remediation Research Articles

Sustainable Stabilizer Derived from Calcium- and Phosphorus-Rich Biowaste for Remediation of Heavy Metal-Contaminated Soil: A Critical Review

Soil pollution by heavy metals (HMs) is a major environmental problem around the world. The addition of biowaste-based stabilizers for HM remediation has recently gained attention due to its relatively low cost and eco-risk, abundance, ease of operation, and quick remediation results. Among these stabilizers, shell (crustacean shell, bivalve shell, and eggshell), starfish, and bone-based stabilizers are particularly attractive because of their high Ca and P contents, allowing for highly efficient HM immobilization and simultaneous supplement of nutrients to the soil. However, a comprehensive review focusing on these stabilizers is currently missing. Therefore, this review attempts to summarize the HM immobilization efficiency of these stabilizers and the mechanisms associated with HM stabilization, and perform an operation cost estimation and cost comparison. Cost comparisons among different stabilizers are widely ignored in reviews due to the lack of reliable cost estimation tools or methods. However, for practical application in soil remediation, cost is one of the most important factors to consider. Thus, a simple but reasonable cost estimation method is developed and discussed in this review. Bivalve shell-based stabilizers demonstrated the most promising results for the immobilization of soil HMs in terms of higher performance and lower cost. Current research limitations, challenges, and recommendations regarding possible future research directions are also provided.

Biochar from Co-Pyrolyzed Municipal Sewage Sludge (MSS): Part 2: Biochar Characterization and Application in the Remediation of Heavy Metal-Contaminated Soils.

The disposal of municipal sewage sludge (MSS) from wastewater treatment plants poses a major environmental challenge due to the presence of inorganic and organic pollutants. Co-pyrolysis, in which MSS is thermally decomposed in combination with biomass feedstocks, has proven to be a promising method to immobilize inorganic pollutants, reduce the content of organic pollutants, reduce the toxicity of biochar and improve biochar's physical and chemical properties. This part of the review systematically examines the effects of various co-substrates on the physical and chemical properties of MSS biochar. This review also addresses the effects of the pyrolysis conditions (temperature and mixing ratio) on the content and stability of the emerging pollutants in biochar. Finally, this review summarizes the results of recent studies to provide an overview of the current status of the application of MSS biochar from pyrolysis and co-pyrolysis for the remediation of HM-contaminated soils. This includes consideration of the soil and heavy metal types, experimental conditions, and the efficiency of HM immobilization. This review provides a comprehensive analysis of the potential of MSS biochar for environmental sustainability and offers insights into future research directions for optimizing biochar applications in soil remediation.

Mechanistic insight into the effects of interaction between biochar and soil with different properties on phenanthrene sorption

Soil composition varies considerably in nature, so it is vital to investigate the mechanism of the effect of various soil parameters on biochar sorption capacity. In this study, two biochars (W4 and W7) were derived from wheat straw at temperatures of 400 and 700 °C and were incubated with three different soils. Changes in biochar surface features by aging in the soils and the consequent impact on phenanthrene sorption were examined. The results showed that the effect of adding biochar on phenanthrene sorption capacity (Koc) varied by soil. When biochar was freshly mixed with soil, the Koc value in soil with higher clay content was more dramatically altered by biochar, which is due to clay particles adhering to the biochar surface. Moreover, the Koc value was significantly decreased by the addition of W4 but increased by the addition of W7 in general. After aging, most of the Koc value decreased. The greatest decrease in Koc value was observed in biochar and soil composed with the highest clay content for W4 (24–63%), as well as soil composed with the highest organic matter content for W7 (46–64%). This is because the surface polarity and micropores of biochar dropped the most rapidly in these mixes, resulting in a significant decrease in hydrophobic and pore-filling properties. The results revealed that the impact of biochar-soil interactions on phenanthrene sorption is related to not only biochar properties but also soil clay particles, soil organic matter content and pH. The findings of the study can be utilized to assess the efficacy of biochar application in soil remediation for various features.

Effect of physical and chemical co-application of biochar and sulfidated nano scale zero valent iron on the NB degradation in soil: Key roles of biochar

Sulfidated nano zero-valent iron (S-nZVI) can efficiently degrade nitrobenzene (NB) in water. However, its practical application in soil remediation is constrained by limited contact with soil-sorbed NB, leading to sparse research. Herein, Biochar (BC), with its notable adsorption capacity, was coupled with S-nZVI to assess the role of physical (S-nZVI + BC) and chemical (S-nZVI@BC) co-application of BC and S-nZVI, respectively, on enhancing NB degradation in soil. Regardless of the physical or chemical co-application, there was a remarkable advantage after addition of BC relative to S-nZVI alone. In physical co-application, the NB degradation rate of S-nZVI + BC increased as the increasing BC concentration from 0 to 3.5 g·L−1, attributed to enhanced NB desorption via the solubilization effect of BC, facilitating interaction with S-nZVI. Beyond this concentration, no significant improvement was observed, possibly due to BC obstructing reactive sites on S-nZVI surface. In chemical co-application, the S-nZVI@BC (S-nZVI/BC mass ratio of 1:1) exhibited a high NB degradation rate constant (1.097 h−1) during reaction. Apart from solubilization effect, BC in S-nZVI@BC endowed S-nZVI with a higher anti-oxidation property, hydrophobicity, electron transfer capacity, and dispersion effect, accounting for the higher reactivity of S-nZVI@BC over S-nZVI + BC. Besides, the water/soil ratio and initial soil pH significantly affected NB degradation rate, with the optimum water/soil ratio and initial soil pH being 3 and 5, respectively. Our finding broadens the applicability of BC and may offer a highly effective way in soil remediation.

Sodium citrate-sodium hydroxide synergy on remediating asphaltene-contaminated solids

Asphaltenes are the heaviest and surface-active polyaromatic compounds in crude oil. Their precipitation and deposition on sand surfaces switch the wettability of sand from water-wet to oil-wet, which is harmful to the oil recovery process. In this study, we demonstrate the synergistic effect between sodium hydroxide (NaOH) and sodium citrate (Na3Cit) on remediating asphaltene-contaminated silica from both experimental and molecular dynamics (MD) simulation perspectives. Asphaltene desorption efficiency increased from 39 % (Na3Cit only) to 84 % (NaOH + Na3Cit), attributed to better remediation of natural silica wettability and reduced silica-asphaltene adhesion with the co-addition chemicals. Fundamental insights for NaOH-Na3Cit synergy were revealed by MD simulation. The bonding between an asphaltene model compound (C5Pe) and the quartz (101) surface became thermodynamically less favorable when both NaOH and Na3Cit were present in the system, forcing the C5Pe molecules to move away from the surface. In summary, we highlight the NaOH-Na3Cit synergy in promoting the asphaltene detachment from silica surfaces, which has important implications in oil recovery and soil remediation applications.

Preparation and Modification of Biochar and Application of Modified Biochar in Remediation of Contaminated Soil

Biochar, with its unique properties including high specific surface area, has become an increasingly popular material in the field of environmental restoration. The present paper provides a systematic analysis and summary of the preparation, characterization, and modification strategies for traditional biochar, as well as its application in soil remediation. A variety of different methods have been developed and applied to produce biochar, of which the most commonly used method is pyrolysis which consists mainly of slow and fast pyrolysis, followed by hydrothermal carbonization. Biochar can be modified by the injection of acids, alkalis, metal oxides, metal ions, steam and gas. On this basis, the utilization of modified biochar in soil restoration and remediation was further analyzed. Modified biochar breaks through various limitations such as the instability of traditional biochar, and performs an irreplaceable function not only in adsorption of organic pollutants, but also in the removal of heavy metal pollution. Additionally, managers also need to avoid the potential risk of secondary contamination by releasing polycyclic aromatic hydrocarbons (PAHs) into the surrounding environment. The aim of this paper is to explore the basic properties and preparation methods of biochar, to identify its restrictions and different modification methods, to highlight the contribution that modified biochar can make to today's sustainability-focused world, and to lay the groundwork for future research.

Migration of spent grain-modified colloidal ferrihydrite: Implications for the in situ stabilization of arsenic, lead, and cadmium in co-contaminated soil

The increase of metal mining, processing, and smelting activities has precipitated a substantial escalation in the contamination of soil by heavy metals. Ferrihydrite (FH) has been commonly used as an amendment for the immobilization of heavy metals in contaminated soil. However, FH suffers from drawbacks such as agglomeration and nonmigratory characteristics, which limit its practical application in soil remediation. Herein, a novel spent grain-modified ferrihydrite (FH-SG) colloidal system was developed, and the FH-SG transport mechanisms in the soil medium were fully studied, focusing in particular on the simultaneous in situ stabilization of arsenic (As), lead (Pb), and cadmium (Cd) in co-contaminated soil. The results showed that the stabilization rates of the FH-SG material reached 94.66%, 96.12%, and 95.52% for water-soluble As, Pb, and Cd, respectively, and 72.22%, 49.39%, and 25.30% for bioavailable As, Pb, and Cd, respectively. The FH-SG material demonstrates notable migration properties in porous media. Theoretical calculation results of a single collector show that the migration deposition of FH-SG material in media is primarily governed by its inherent diffusion characteristics with minimal influence by gravitational forces and media interception. It is noteworthy that the maximum migration distance in quartz sand and soil media with different particle sizes can reach 2.07–2.92 m and 0.78–1.08 m, respectively. Altogether, our findings clearly demonstrate that FH-SG exhibits better stabilization and migration than those of FH alone and most proposed FH colloidal systems. The FH-SG colloidal system holds significant promise for the remediation of various kinds of complex polluted soil.

EDDS and polystyrene interactions: implications for soil health and management practices

Ethylenediamine-N,N'-disuccinic acid (EDDS) has been studied extensively for its potential use as an amendment in agriculture due to its numerous beneficial properties. The widespread usage of microplastics (MPs) poses a growing threat to plant growth. This study investigated the effects of Polystyrene MPs (PSMPs) and EDDS on soil pH, EC, organic matter (OM), available nutrients, and maize (Zea mays L.) growth in a calcareous soil. Results showed that both PS and EDDS had significant effects on soil pH, with higher concentrations leading to a decrease in pH. PSMPs negatively impacted soil health by increasing EC and decreasing OM, nitrogen (N), phosphorus (P), and potassium (K). EDDS had potential applications in soil remediation and phytoremediation by decreasing EC and increasing N, P, and K. The interaction between EDDS and PSMPs suggests that their effects on soil pH may be modulated by each other. The study highlights the potential negative impacts of high concentrations of PS on soil health and the potential benefits of using EDDS at lower concentrations in soil remediation and phytoremediation. However, further research is needed to understand the mechanisms and environmental impacts of EDDS and the combined effects of EDDS and PSMPs on soil properties and plant growth.

Fingering and strain localization in porous media during imbibition processes

SummaryFingered infiltration of a wetting fluid through a porous network is a widely studied subject in the field of fluid mechanics. However, the effect of this heterogeneous percolation on the response of granular materials, in particular fine‐grained soils, is a poorly investigated and badly understood topic which deserves deep analysis, considering, among others, possible applications in soil remediation and underground energy storage. This paper presents a first application of a new formulation of unsaturated poromechanics based on a phase field approach that allows to characterize on the one hand the occurrence of fingering hydraulic instabilities and on the other one to capture their effects on the irreversible, and possible unstable, deformation of the solid skeleton. The envisaged application concerns the behavior of fine‐grained soils whose dilatant/contractant behavior is more and more attracting the interest of the scientific community both in the fields of experimental research and numerical modeling.

Preparation and water erosion resistance properties of tara gum-g-poly (acrylic acid-co-methyl methacrylate) emulsion

The main purpose of this paper is to synthesize a new kind of green and environmental protection emulsion, which can be used as water erosion resistant materials. Here, a non-toxic polymer was prepared by grafting acrylic acid (AA) and methyl methacrylate (MMA) onto the long chains of tara gum (TG) to synthesize a copolymer emulsion (TG-g-P (AA-co-MMA)). The structure, thermal stability, morphology and wettability of the polymer were characterized by conventional methods, and the effects of key synthesis conditions on the performance of the emulsion (viscosity) were optimized. The erosion resistance and compressive strength of polymer-treated loess and laterite soils were evaluated under laboratory conditions. The results showed that the successful grafting of AA and MMA monomers onto TG improved its thermal stability and viscosity. In soil performance tests with low amounts of polymer additive, a 0.3 wt% application of TG-g-P (AA-co-MMA) to loess could resist continuous precipitation for >30 h with an erosion rate of 2.0 %. The compressive strength of the laterite treated with 0.4 % TG-g-P (AA-co-MMA) was 3.7 MPa, which was about three times that of the untreated soil. The results from this study suggest that TG-g-P (AA-co-MMA) emulsions have good potential for soil remediation applications.

Performance enhancement of white rot fungi extracellular enzymes via new hydrogel microenvironments for remediation of benzo[a]pyrene contaminated soil

Organic pollutants with low solubility and high ecotoxicity, mutagenicity, and carcinogenicity, are rapidly entering and accumulating in soil, resulting in soil pollution. Several methods have been investigated for remediation of organic contaminated soil, including enzymatic remediation approach. However, free enzymes are easily deactivated, which hinders their practical application in soil remediation. Immobilization of enzyme improves its stability and catalytic performance, but the immobilized material itself becomes secondary pollutants in soil. In this study, Trametes versicolor extracellular enzyme was immobilized on the degradable calcium alginate hydrogel microspheres. The laccase maintained a high activity. In addition, the addition of cellulose improved the strength of the carrier. Hydrogel microspheres solved the problems of easy inactivation of free enzyme and secondary contamination of immobilized materials. By a novel combination of extracellular enzymes and hydrogel microenvironments, immobilized enzymes not only demonstrate outstanding performance in thermal stability and pH adaptability, but also achieves a significant improvement in biocatalytic activity for benzo[a]pyrene contaminated soil. The thermal stability of immobilized enzyme was much higher than that of free enzyme. When the temperature increased to 50 °C, the activity of immobilized enzyme remained at 93.15% of the maximum enzyme activity, while the activity of free enzyme decreased to 63.76%. At pH 8, the immobilized enzyme activity maintained 74.84% of the maximum enzyme activity, while the free enzyme activity was only 11.86%. Immobilized enzymes can effectively remove 91.40% of benzo[a]pyrene from soil within 96 h. Furthermore, the catalytic oxidation of benzo[a]pyrene by enzymes that have been immobilized ultimately results in the production of 6,12-benzo[a]pyrene-dione. Molecular dynamics simulation showed that the catalytic degradation of benzo[a]pyrene was mainly through the interaction of amino acid residues PRO-391 with the Pi-alkyl of benzo[a]pyrene. This study presents an innovative strategy for designing and developing immobilized enzymes for use in biocatalytic applications related to eco-remediation of soil.

Simultaneous adsorption of Cd and As by a novel coal gasification slag based composite: Characterization and application in soil remediation

Cadmium (Cd) and arsenic (As) co-contamination has become increasingly serious in China agricultural soil due to rapid industrialization and urbanization. The opposite geochemical behaviors of Cd and As pose huge challenges for developing a material for their simultaneous immobilization in soils. Coal gasification slag (CGS) as a by-product of coal gasification process, is always dumped into a local landfill, which has a negative impact on environment. Few reports have been available on applying CGS as a material to immobilize simultaneously multiple soil heavy metals. A series of iron-modified coal gasification slag (IGS) composites IGS3/5/7/9/11 (with different pH values) were synthesized by alkali fusion and iron impregnation. After modification, carboxyl groups were activated, and Fe was successfully loaded onto the surface of IGS in the form of FeO and Fe2O3. The IGS7 exhibited the best adsorption capacity with the maximum Cd and As adsorption capacity of 42.72 mg/g and 35.29 mg/g, respectively. The Cd was mainly adsorbed through electrostatic attraction and precipitation, while the As through complexation with iron (hydr)oxides. IGS7 significantly reduced the bioavailability of Cd and As in soil with Cd bioavailability reduced from 1.17 mg/kg to 0.69 mg/kg and As bioavailability reduced from 10.59 mg/kg to 6.86 mg/kg at 1 % IGS7 addition. The Cd and As were all transformed to more stable fractions after IGS7 addition. The acid soluble and reducible Cd fractions were transformed into oxidizable and residual Cd fractions, and the non-specifically and specifically adsorbed As fractions were transformed to amorphous iron oxide-bound As fraction. This study provides valuable references for the application of CGS to the remediation of Cd and As co-contaminated soil.

Remediation and immobilization of Cr(VI)-contaminated soil using stabilized nanoscale iron sulfide and ecological impact

Soil contaminated with hexavalent chromium seriously threatens the environment and human health. The use of FeS, which has a high redox activity and excellent reduction capacity, limits its application in soil remediation due to its premature surface oxidation and massive aggregation. To prevent premature surface oxidation and agglomeration, cetyltrimethylammonium bromide-supported nano-ferrous sulfide (CTAB-nFeS) was chemically synthesized and used for immobilizing Cr(VI) in contaminated soil. In order to evaluate the role of CTAB stabilization of nFeS and interaction mechanisms were investigated by XPS, FTIR, XRD, and FESEM. Batch experiments showed a complete reduction of Cr(VI) within 3 h with only 235% excess of CTAB-nFeS at a soil pH of 8 compared to days as reported in the literature with alternative FeS forms. The reduction kinetic data could be satisfactorily fitted into the second-order rate model. The rate constant linearly depends on the soil-to-water ratio, but its logarithmic form is linear in the given pH range. The oxidation-reduction potential increases with decreasing initial pH, thus positively impacting the reduction process. XPS analysis revealed the reduction process as multi-steps (reduction, adsorption, and co-precipitation). Ecological studies showed improved plant growth and earthworm survival rate in the remediated soil. Medium-term stability experiments suggested a significant decrease in TCLP leachate concentration of Cr after CTAB-nFeS treatment and remained stable for 60 d. Overall results of our study suggested a sustainable, feasible, and effective strategy for in-situ remediation of Cr(VI)-contaminated soil using CTAB-nFeS at natural pH.

Langmuir monolayers as models of the lipid matrix of cyanobacterial thylakoid membranes

Cyanobacteria are omnipresent photosynthetic microorganisms that are crucial for the proper functioning of multiple environmental niches. Recently, these organisms have found various applications in soil remediation, waste utilization, and the production of biodegradable polymers. A significant volume of the cyanobacterial cell is occupied by thylakoid membranes, where the photosynthesis process is localized. These membranes are inhomogeneous and highly compartmentalized; however, the stimuli and forces leading to such a high degree of self-organization are not entirely understood. In our study, we apply Langmuir monolayers formed by the main lipids of cyanobacterial membranes: monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulfoquinovosyldiacylglycerol (SQDG), and phosphatidylglycerol (PG), as versatile models of thylakoid membranes. Special attention was paid to the binary system formed by the two neutral glycolipids MGDG and DGDG, as these two substances are most abundant in the membrane. Then the effects implied by the incorporation of anionic lipids were investigated. The morphology of the monolayers was studied by Brewster angle microscopy, while the ordering of the monolayer-forming molecules on the molecular scale was investigated with the Grazing incidence X-ray diffraction technique. It was proved that the inhomogeneous structure of cyanobacterial membrane is an intrinsic property of the applied structural lipids. It was also proved that the increase in anionic lipid content, frequently applied by cyanobacteria as a response to unfavorable environmental conditions, leads to significant changes in the morphology of the model membranes.

Preparation and characterization of sodium polyacrylate grafted montmorillonite nanocomposite for the adsorption of cadmium ions form aqueous solution

High-efficiency adsorbents made from clay minerals have a wide application in remediation of soil and water pollution, especially in the treatment of refractory and highly toxic heavy metals. Montmorillonite itself has a good adsorption capacity and a large modification space for its layered structure. Therefore, carboxylate polymer grafted montmorillonite was developed to improve the adsorption capacity of heavy metals in this paper. Two kinds of modified preparation routes were compared, and a series of batch adsorption tests were conducted to evaluate the influence degree of parameters (contact time, pH, temperature, and cadmium concentration). The structural changes of montmorillonite samples before and after modification were characterized by a series of microscopic analyses and measurement techniques. The results show that the silicon hydroxyl produced by the hydrolysis of silane coupling agent can indeed be grafted by dehydration condensation with Si/Al-OH on clay surface. The grafting chain can be greatly increased by C=C double bond breaking polymerization. The polycarboxylate group can effectively improve the adsorption performance of modified montmorillonite for cadmium ions. The maximum adsorption capacity of modified montmorillonite increased by about 224.75%, reaching 63.49 mg/g. The adsorption model of montmorillonite conforms to Langmuir monolayer adsorption model, while modified montmorillonite samples exhibit Freundlich adsorption model and S-type isothermal adsorption curve characteristics of resin. The preparation method of neutralizing after polymerization of acrylic acid was proposed to be better, which provides technical guidance for scientific and efficient application.

Insights into growth-promoting effect of nanomaterials: Using transcriptomics and metabolomics to reveal the molecular mechanisms of MWCNTs in enhancing hyperaccumulator under heavy metal(loid)s stress

Carbon nanotubes present potential applications in soil remediation, particularly in phytoremediation. Yet, how multi-walled carbon nanotubes (MWCNTs) induced hyperaccumulator growth at molecular level remains unclear. Here, physio-biochemical, transcriptomic, and metabolomic analyses were performed to determine the effect of MWCNTs on Solanum nigrum L. (S. nigrum) growth under cadmium and arsenic stresses. 500 mg/kg MWCNTs application significantly promoted S. nigrum growth, especially for root tissues. Specially, MWCNTs application yields 1.38-fold, 1.56-fold, and 1.37-fold enhancement in the shoot length, root length, and fresh biomass, respectively. Furthermore, MWCNTs significantly strengthened P and Fe absorption in roots, as well as the activities of antioxidative enzymes. Importantly, the transcriptomic analysis indicated that S. nigrum gene expression was sensitive to MWCNTs, and MWCNTs upregulated advantageous biological processes under heavy metal(loid)s stress. Besides, MWCNTs reprogramed metabolism that related to defense system, leading to accumulation of 4-hydroxyphenylpyruvic acid (amino acid), 4-hydroxycinnamic acid (xenobiotic), and (S)-abscisic acid (lipid). In addition, key common pathways of differentially expressed metabolites and genes, including “tyrosine metabolism” and “isoquinoline alkaloid biosynthesis” were selected via integrating transcriptome and metabolome analyses. Combined omics technologies, our findings provide molecular mechanisms of MWCNTs in promoting S. nigrum growth, and highlight potential application of MWCNTs in soil remediation.

Biochar-based fertilizers and their applications in plant growth promotion and protection.

Soil is an integral part of the ecosystem because it serves as a habitat for various microorganisms and lays the foundation for supporting plant growth and development. Therefore, factors such as increased anthropogenic activities hand by hand with other natural processes that harm the ecosystem may eventually lead to a decline in soil quality and fertility, hindering the growth of plants and soil microbial communities. Given the current global scenario of increasing human intervention, it is essential to find effective measures and reliable technologies to restore soil quality. Biochar is an emerging soil ameliorant employed for soil health restoration and is primarily generated through the anoxygenic pyrolysis of biomass. The biochar application in soil remediation may be beneficial due to biochar's unique physicochemical properties, including high carbon and metal fixation abilities. In addition, biochar possesses abilities to reduce the plant's environmental stress injuries. This review briefly overviewed the ingredients and mechanism of biochar productions. We then emphatically reviewed the advances in biochar applications in soil bioremediation, soil microflora growth stimulation, and the alleviation of various biotic and abiotic stresses in plants.

Modeling and monitoring of foam propagation in highly permeable porous media under lateral water flow

Foam injection is a promising option for soil remediation applications. However, predicting how it will propagate in highly permeable aquifers under groundwater flow is challenging. Here, we have studied pressure and saturation variations during foam propagation. A 2D tank packed with 1 mm glass beads was used to study foam injection in highly permeable porous media under lateral flow. Specifically, we evaluated the efficiency of pressure and time-domain reflectometer (TDR) sensors to predict foam propagation using an imaging technique. A numerical model coupling two-phase flow and surfactant transport was developed to simulate the experimental results. This model takes into account the effect of non-Newtonian behavior of foam, surfactant concentration, and critical capillary pressure through the definition of the mobility reduction factor (MRF). The experimental results show that the foam injection pressure first increases with a logarithmic law and then stabilizes. This pressure stabilization can be related to the state of pseudo-equilibrium between foam generation and destruction. We observed an asymmetrical foam propagation due to water lateral flow. Comparisons of the liquid saturation fields calculated by analysis of TDR probes and estimated by imaging show that the TDR sensors monitor foam propagation well in saturated porous media. They can predict the shape of the injected foam. Contrary to pressure sensors, it is possible to capture weak foam behavior using TDR sensors. Finally, the numerical model we have developed correctly captures the shape of foam propagation and its ability to divert water flows. This model produces the propagation of the strong foam well and predicts the saturation and pressure fields with good precision.

Transformation of sulfidized nanoscale zero-valent iron particles and its effects on microbial communities in soil ecosystems

Sulfidized nanoscale zero-valent iron (S-nZVI) is a promising material for in situ soil remediation. However, its transformation (i.e., aging) and effects on the microbial community in soil ecosystems are largely unknown. In this study, S-nZVI having low (S-nZVI (L)) and high sulfur-doping (S-nZVI (H)) were incubated in soil microcosms and bare nZVI was used as a control. Their aged products were characterized using microspectroscopic analyses and the changes in the corresponding soil microbial community were determined using high-throughput sequencing analyses. The results indicate that severe corrosion of both bare and S-nZVI occurred over 56 days of aging with significant morphological and mineral changes. Magnetite, lepidocrocite, and goethite were detected as the main aged products. In addition, sulfate ions, pyrite, and iron polysulfide were formed in the aged products of S-nZVI. Cr(VI) removal test results indicated that S-nZVI(L) achieved the best results after aging, likely because of the optimal FeS arrangement on its nanoparticle surfaces. The presence of nZVI and S-nZVI increased the abundance of some magnetotactic microorganisms and altered bacterial and fungal community structures and compositions. Moreover, the addition of S-nZVI enriched some bacterial and fungal genera related to sulfur cycling because of the presence of sulfide-bearing material. The findings reveal the transformation of S-nZVI during aging and its effects on microbial communities in soil ecosystems, thereby helping to the evaluation of S-nZVI application in soil remediation.

BIOSURFACTANT PRODUCTION BY ENDOPHYTIC ISOLATES FROM RHIZOMES OF ZINGIBER ZERUMBET

Biosurfactants (BS) or green surfactants are amphiphilic compounds that enhance the bioavailability of hydrophobic organic compounds and also exhibit anti-phytopathogenic properties. BSproducing isolates thus find applications in soil remediation and development of biocontrol agents. Endophytes that confer several benefits to host plant constitute a good resource for prospecting BSproducing isolates. The present study screened the Z. zerumbet endophytes identified in earlier studies for BS production by hydrocarbon overlay agar method, CTAB- Methylene blue agar assay and determining Emulsification Index (EI24). EI24 was observed as the most desirable parameter to determine BS production compared to hydrocarbon overlay agar and CTAB- methylene blue agar plate assay. Isolate ZzADK4 (Bacillus spp) showed highest emulsification activity (58%) determined as EI% with kerosene. UV-vis spectral scans identified the endophytes as producing LP class of BS with absorbance maxima spanning 207- 216 nm. LP class of BS producing endophytic isolates identified in the present study constitute potential solutions with applications in soil remediation and the development of biocontrol agents (BCAs).