Hierarchical porous structured polysulfide supported nZVI/biochar and efficient immobilization of selenium in the soil

Surface Modification of Polyurethane Sponge with Zeolite and Zero-Valent Iron Promotes Short-Cut Nitrification

Partial nitrification-Anammox (PN-A) is a cost-effective, environmentally friendly, and efficient method for removing ammonia (NH4+-N) pollutants from water. However, the limited accumulation of nitrite (NO2--N) represents a bottleneck in the development of PN-A processes. To address this issue, this study developed a composite carrier loaded with nano zero-valent iron (nZVI) and zeolite to enhance NO2--N accumulation during short-cut nitrification. The modified composite carrier revealed electropositive, hydrophilicity, and surface roughness. These surface characteristics correlate positively with the carrier's total biomass adsorption capacity; the initial adsorption of microorganisms by the composite carrier was increased by 8.7 times. Zeolite endows the carrier with an NH4+-N adsorption capacity of 4.50 mg/g carrier. The entropy-driven ammonia adsorption process creates an ammonia-rich microenvironment on the surface of the carrier, providing effective inhibition of nitrite-oxidizing bacteria (NOB). In tests conducted with a moving bed biofilm reactor and a sequencing batch reactor, the composite carrier achieved a 95% NH4+-N removal efficiency, a NO2--N accumulation efficiency of 78%, and a doubling in total nitrogen removal efficiency. This composite carrier enhances NO2--N accumulation by preventing biomass washout, inhibiting NOB, and enriching PN-A functional bacteria, suggesting its potential for large-scale, stable PN-A 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.

Artificial Humic Acid Mediated Carbon-Iron Coupling to Promote Carbon Sequestration

Fe (hydr)oxides have a substantial impact on the structure and stability of soil organic carbon (SOC) pools and also drive organic carbon turnover processes via reduction-oxidation reactions. Currently, many studies have paid much attention to organic matter-Fe mineral-microbial interactions on SOC turnover, while there is few research on how exogenous carbon addition abiotically regulates the intrinsic mechanisms of Fe-mediated organic carbon conversion. The study investigated the coupling process of artificial humic acid (A-HA) and Fe(hydr)oxide, the mechanism of inner-sphere ligands, and the capacity for carbon sequestration using transmission electron microscopy, thermogravimetric, x-ray photoelectron spectroscopy, and wet-chemical disposal. Furthermore, spherical aberration-corrected scanning transmission electron microscopy-electron energy loss spectroscopy and Mössbauer spectra have been carried out to demonstrate the spatial heterogeneity of A-HA/Fe (hydr)oxides and reveal the relationship between the increase in Fe-phase crystallinity and redox sensitivity and the accumulation of organic carbon. Additionally, the dynamics of soil structures on a microscale, distribution of carbon-iron microdomains, and the cementing-gluing effect can be observed in the constructing nonliving anthropogenic soils, confirming that the formation of stable aggregates is an effective approach to achieving organic carbon indirect protection. We propose that exogenous organic carbon inputs, specifically A-HA, could exert a substantial but hitherto unexplored effect on the geochemistry of iron-carbon turnover and sequestration in anoxic water/solid soils and sediments.

Overlooked encounter process that affects physical behaviors of stabilized nanoscale zero-valent iron during in situ groundwater remediation

Dynamic encountering between groundwater matrices and nanoscale zero-valent iron (NZVI) injected for in situ subsurface remediation affects NZVI's mobility and has not been well recognized. Polyacrylic acid (PAA)-stabilized NZVI (NZVI-PAA) and Mg(OH)2-coated NZVI (NZVI@Mg(OH)2) were investigated as representative NZVIs stabilized by enhanced electrostatic repulsion and reduced magnetic attraction, respectively. Encounters with divalent cations and humic acid (HA) induced the drastic aggregation and sedimentation (presedimentation) of NZVI-PAA owing to Lewis acid-base interactions and heteroaggregation. In addition, encountered groundwater electrolytes could not effectively provide electrostatic repulsion for NZVI-PAA, resulting in breakthrough ripening dynamics. The presedimentation and ripening behaviors of NZVI-PAA were eliminated and unheeded after mixing the NZVI slurry with groundwater by sonication. In comparison, the encountering process barely impacted NZVI@Mg(OH)2, for which settling was hindered. Although the particle-collector attraction promoted NZVI@Mg(OH)2 adsorption on pristine and hybrid-coated sands, the Langmuirian blocking dynamics of the NZVI@Mg(OH)2 breakthrough demonstrated its high mobility after adsorption sites of sand surface were exhausted. Extended Derjaguin-Landau-Verwey-Overbeek analysis and transport modeling provided insights into overlooked effects of encountering on physical behaviors of different stabilized NZVIs, which should be considered during practical applications under diverse subsurface conditions.

The influence of cysteine in transformation of Cd fractionation and microbial community structure and functional profile in contaminated paddy soil

Remediating cadmium (Cd) contaminated paddy soil is vital for agroecology, food safety, and human health. Soil washing is more feasible to reduce remediation method due to its high efficiency. However, green, low-cost and more efficient washing agents are still required. In this study, we investigated the ability of cysteine as a washing agent for soil washing to remove Cd from contaminated paddy soil. Through a batch experiment, we evaluated the removal efficiency of cysteine as a washing agent by comparing their removal rate with that of a microbial inoculant and sulphuric acid as other washing agents. The transformation of Cd fractionation and microbial community structure and functional profile in paddy soils after cysteine leaching was studied by using sequential extraction and high-throughput sequencing. Results showed that cysteine had better efficiency in the removal of Cd from paddy soil in comparison to sulphuric acid and the microbial inoculant, and could achieve a maximum removal rate of 97 % Cd in paddy soil. Cysteine decreased the proportion of Cd in the exchangeable fraction, carbonate bound fraction, iron and manganese bound fraction, and organic matter bound fraction and was best for the removal of the residual fraction, which contributed to its higher Cd removal ability. Considering the economic benefits of the reagents used, cysteine was shown to be economically feasible for use as a leaching agent. In addition, cysteine could significantly increase the relative abundance of Thermochromatium, Sideroxydans, Streptacidiphilus, and Frankia which promoted the nitrogen and sulfur metabolism in the paddy soil. In summary, this study revealed that cysteine was readily available, cheap, non-toxic, highly efficient, and even has fertilizing properties, making it eco-friendly and ideal for remediation of Cd-contaminated paddy soils. Besides, the health of paddy soils would also benefit from cysteine's promotion of microbial nitrogen and sulfur metabolism.

The effect of manure-borne doxycycline combined with different types of oversized microplastic contamination layers on carbon and nitrogen metabolism in sandy loam

The different forms and properties of microplastics (MPs) have different effects on the elemental cycles in soil ecosystems, and this is further complicated when the soil contains antibiotics; meanwhile, oversized microplastic (OMP) in soil is always ignored in studies of environmental behavior. In the context of antibiotic action, the effects of OMP on soil carbon (C) and nitrogen (N) cycling have rarely been explored. In this study, we created four types of oversized microplastic (thick fibers, thin fibers, large debris, and small debris) composite doxycycline (DOX) contamination layers (5-10 cm) in sandy loam, hoping to reveal the effects on soil C and N cycling and potential microbial mechanisms when exposed to the combination of manure-borne DOX and different types of OMP from the perspective of metagenomics in the longitudinal soil layer (0-30 cm). The results showed that all different forms of OMP, when combined with DOX, reduced the soil C content in each layer, but only reduced the soil N content in the upper layer of the OMP contamination layer. The microbial structure of the surface soil (0-10 cm) was more noteworthy than that of the deeper soil (10-30 cm). The genera Chryseolinea and Ohtaekwangia were key microbes involved in C and N cycling in the surface layer and regulated carbon fixation in photosynthetic organisms (K00134), carbon fixation pathways in prokaryotes (K00031), methane metabolism (K11212 and K14941), assimilatory nitrate reduction (K00367), and denitrification (K00376 and K04561). The present study is the first to reveal the potential microbial mechanism of C and N cycling under OMP combined with DOX in different layers, mainly the OMP contamination layer and its upper layer, and the OMP shape plays an important role in this process.

Recent developments in modification of biochar and its application in soil pollution control and ecoregulation

Soil pollution has become a real threat to mankind in the 21st century. On the one hand, soil pollution has reduced the world's arable land area, resulting in the contradiction between the world's population expansion and the shortage of arable land. On the other hand, soil pollution has seriously disrupted the soil ecological balance and significantly affected the biodiversity in the soil. Soil pollutants may further affect the survival, reproduction and health of humans and other organisms through the food chain. Several studies have suggested that biochar has the potential to act as a soil conditioner and to promote crop growth, and is widely used to remove environmental pollutants. Biochar modified by physical, chemical, and biological methods will affect the treatment efficiency of soil pollution, soil quality, soil ecology and interaction with organisms, especially with microorganisms. Therefore, in this review, we summarized several main biochar modification methods and the mechanisms of the modification and introduced the effects of the application of modified biochar to soil pollutant control, soil ecological regulation and soil nutrient regulation. We also introduced some case studies for the development of modified biochars suitable for different soil conditions, which plays a guiding role in the future development and application of modified biochar. In general, this review provides a reference for the green treatment of different soil pollutants by modified biochar and provides data support for the sustainable development of agriculture.

Selenium-sulfur functionalized biochar as amendment for mercury-contaminated soil: High effective immobilization and inhibition of mercury re-activation

The contamination of soils by mercury (Hg) seriously threatens the local ecological environment and public health. S-functionalized amendments are common remediation technology, yet, Hg re-activation often occurs in the commonly used immobilization remediation by S-functionalized amendments, resulting in an unsatisfactory remediation effect. In this study, a novel FeS-Se functionalized biochar composite (FeS-Se-BC) amendment was prepared and applied for the efficient remediation of Hg-polluted soil. An immobilization efficiency of 99.62% and 99.22% for H₂O-extractable Hg and TCLP solution-extractable Hg was achieved with the application of FeS-Se-BC_(0.05) after 180 d. The analyses of XPS, Hg-TPD, SEM-EDS demonstrated that excellent remediation performance by FeS-Se-BC resulted from the synergistic effect of FeS and Se to form HgS and HgSe concurrently. In comparison to the treatments of biochar and FeS-functionalized biochar (FeS-BC), FeS-Se-BC promoted the transformation of exchangeable, carbonate-bound, and Fe-Mn oxides-bound Hg fractions into organic material-bound, and residual fractions, effectively reducing the risk of Hg-contaminated soil from a highly dangerous level to a low risk. Furthermore, the introduction of Se clearly inhibited the re-activation of Hg and reduced the release of Hg by 81.12% compared to FeS-BC when the ratio of S^2- to Hg was 5: 1 due to the formation of extremely stable HgSe. These results suggest that FeS-Se-BC has good potential for remediation of Hg-polluted soils which provides a new inhibitory idea for Hg re-activation after immobilization.

Functionalized biochars: Synthesis, characterization, and applications for removing trace elements from water

Biochar (BC) has been recognized as an effective adsorbent to remove trace elements (TEs) from water. However, low surface functionality and small pore size can limit the adsorption ability of pristine biochar. These limitations can be addressed by using functionalized biochars which are developed by physical, chemical, or biological activation of biochar to improve their physico-chemical properties and adsorption efficiency. Despite the large amount of research concerning functionalized biochars in recent decades, to our knowledge, no comprehensive review of this topic has been published. This review focuses solely on the synthesis, characterization, and applications of functionalized/engineered biochars for removing TEs from water. Firstly, we evaluate the synthesis of functionalized biochars by physical, chemical, and biological strategies that yield the desired properties in the final product. The following section describes the characterization of functionalized biochars using various techniques (SEM, TEM, EDS, XRD, XANES/NEXAFS, XPS, FTIR, and Raman spectroscopy). Afterward, the role of functionalized biochars in the adsorption of different TEs from water/wastewater is critically evaluated with an emphasis on the factors affecting sorption efficiency, sorption mechanisms, fate of sorbed TEs from contaminated environments and associated challenges. Finally, we specifically scrutinized the future recommendations and research directions for the application of functionalized biochar. This review serves as a comprehensive resource for the use of functionalized biochar as an emerging environmental material capable of removing TEs from contaminated water/wastewater.

Passivation of lead and cerium in soil facilitated by biochar-supported phosphate-doped ferrihydrite: Mechanisms and microbial community evolution

The massive exploitation and application of heavy metals and rare earth elements (REEs) lead to their exceeding the standard in soil. Herein, a new type of biochar supported phosphorus doped ferrihydrite (P-FH@BC) has been designed and enhance passivation of Pb and Ce in soil. SEM images of P-FH@BC showed P-FH nanoparticles adhered to the natural cavity and large pore diameter on the surface of biochar, which greatly avoided the agglomeration of nanoparticles. The residual state of lead or cerium increased 161.4% or 43.9% by adding 3% P-FH@BC after 90 days of incubation in 500 mg/kg lead or cerium simulated contaminated soil. The passivation of cerium by P-FH@BC is obviously inhibited with the coexistence of lead. The results of P-FH@BC magnetically separated from the soil characterization indicate that complexation, co-precipitation and the formation of secondary minerals mainly contribute to the high efficiency passivation ability of P-FH@BC for lead and cerium. By changing the addition of P-FH@BC, the soil pH can be adjusted and the soil organic matter and P contents can be improved. Moreover, P-FH@BC is an environmentally friendly material without ecotoxicity. And bacterial richness and diversity in soil were improved after passivation of Pb and Ce by adding P-FH@BC.

Fe-N complex biochar as a superior partner of sodium sulfide for methyl orange decolorization by combination of adsorption and reduction

To enhance the decolorization of methyl orange (MO), Fe-N complex biochar (Fe-N-BC) was developed as an accelerator in the sodium sulfide (Na₂S) reduction system. The decolorization effect and mechanism of MO in the Fe-N-BC/Na₂S composite system were studied. Surface pore analysis, Raman spectroscopy, FT-IR, XPS, and electrochemical analysis were used to characterize Fe-N-BC and unmodified biochar (BC). These results demonstrated that Fe-N-BC had better adsorption performance (specific surface area 463.46 m² g^-1) and electron transfer capacity than BC. By adding Fe-N-BC to the Na₂S reduction system for MO, it was found that the decolorization of MO was greatly improved (increased by 93%). Besides, the effects of critical factors such as the initial concentration of Na₂S, the dosage of Fe-N-BC, pH value, and temperature on the decolorization rate of MO were evaluated. Through the analysis of the action mechanism, the cooperation mode of Fe-N-BC and Na₂S was to form an infinite cycle of adsorption-reduction-regeneration, so as to realize the rapid decolorization of MO. On the one hand, Fe-N-BC could adsorb MO and Na₂S on its surface to increase the contact opportunity; on the other hand, it could act as a redox mediator to accelerate the electron transfer of the reduction reaction. In addition, the degradation of MO by Na₂S was also an in-situ regeneration of Fe-N-BC. These findings may provide a feasible method to decolorize azo dyes quickly by cooperating with chemical reducing agents from a new perspective.

Effects of biochar-based materials on the bioavailability of soil organic pollutants and their biological impacts

Motivated by the unique structure and superior properties, biochar-based materials, including pristine biochar and composites of biochar with other functional materials, are considered as new generation materials for diverse multi-functional applications, which may be intentionally or unintentionally released to soil. The influencing mechanism of biochar-based material on soil organisms is a key aspect for quantifying and predicting its benefits and trade-offs. This work focuses on the effects of biochar-based materials on soil organisms within the past ten years. 206 sources are reviewed and available knowledge on biochar-based materials' impacts on soil organisms is summarized from a diverse perspective, including the pollutant bioavailability changes in soil, and potential effects of biochar-based materials on soil organisms. Herein, effects of biochar-based materials on the bioavailability of soil organic pollutants are detailed, from the perspective of plant, microorganism, and soil fauna. Potential biological effects of pristine biochar (PBC), metal/metal compounds-biochar composites (MBC), clay minerals-biochar composites (CMBC), and carbonaceous materials-biochar composites (CBC) on soil organisms are highlighted for the first time. And possible mechanisms are presented based on the different characters of biochar-based materials as well as various environmental interactions. Finally, the bottleneck and challenges of risk assessment of biochar-based materials as well as future prospects are proposed. This work not only promotes the development of risk assessment system of biochar-based materials, but broadens the strategy for the design and optimization of environmental-friendly biochar materials.

Fabrication, application, and mechanism of metal and heteroatom co-doped biochar composites (MHBCs) for the removal of contaminants in water: A review

The potential risk of various contaminants in water has recently attracted public attention. Biochars and modified biochars have been widely developed for environmental remediation. Metal and heteroatom co-doped biochar composites (MHBCs) quickly caught the interest of researchers with more active sites and higher affinity for contaminants compared to single-doped biochar by metal or heteroatoms. This study provides a comprehensive review of MHBCs in wastewater decontamination. Firstly, the main fabrication methods of MHBCs were external doping and internal doping, with external doping being the most common. Secondly, the applications of MHBCs as adsorbents and catalysts in water treatment were introduced emphatically, which mainly included the removal of metals, antibiotics, dyes, pesticides, phenols, and other organic contaminants. Thirdly, the removal mechanisms of contaminants by MHBCs were deeply discussed in adsorption, oxidation and reduction, and degradation. Furthermore, the influencing factors for the removal of contaminants by MHBCs were also summarized, including the physicochemical properties of MHBCs, and environmental variables of pH and co-existing substance. Finally, futural challenges of MHBCs are proposed in the leaching toxicity of metal from MHBCs, the choice of heteroatoms on the fabrication for MHBCs, and the application in the composite system and soil remediation.

Selenium (Se) recovery for technological applications from environmental matrices based on biotic and abiotic mechanisms

Selenium (Se) is an essential element with application in manufacturing from food to medical industries. Water contamination by Se is of concern due to anthropogenic activities. Recently, Se remediation has received increasing attention. Hence, different types of remediation techniques are listed in this work, and their potential for Se recovery is evaluated. Sorption, co-precipitation, coagulation and precipitation are effective for low-cost Se removal. In photocatalytic, zero-valent iron and electrochemical systems, the above mechanisms occur with reduction as an immobilization and detoxification process. In combination with magnetic separation, the above techniques are promising for Se recovery. Biological Se oxyanions reduction has been widely recognized as a cost-effective method for Se remediation, simultaneously generating biosynthetic Se nanoparticles (BioSeNPs). Increasing the extracellular production of BioSeNPs and controlling their morphology will benefit its recovery. However, the mechanism of the microbial production of BioSeNPs is not well understood. Se containing products from both microbial reduction and abiotic methods need to be refined to obtain pure Se. Eco-friendly and cost-effective Se refinery methods need to be developed. Overall, this review offers insight into the necessity of shifting attention from Se remediation to Se recovery.

An economical strategy towards the managing of selenium pollution from contaminated water: A current state-of-the-art review

During the last few decades, contamination of selenium (Se) in groundwater has turned out to be a major environmental concern to provide safe drinking water. The content of selenium in such contaminated water might range from 400 to 700 μg/L, where bringing it down to a safe level of 40 μg/L for municipal water supply employing appropriate methodologies is a major challenge for the global researcher communities. The current review focuses mostly on the governing selenium remediation technologies such as coagulation-flocculation, electrocoagulation, bioremediation, membrane-based approaches, adsorption, electro-kinetics, chemical precipitation, and reduction methods. This study emphasizes on the development of a variety of low-cost adsorbents and metal oxides for the selenium decontamination from groundwater as a cutting-edge technology development along with their applicability, and environmental concerns. Moreover, after the removal, the recovery methodologies using appropriate materials are analyzed which is the need of the hour for the reutilization of selenium in different processing industries for the generation of high valued products. From the literature survey, it has been found that hematite modified magnetic nanoparticles (MNP) efficiently adsorb Se (IV) (25.0 mg/g) from contaminated groundwater. MNP@hematite reduced Se (IV) concentration from 100 g/L to 10 g/L in 10 min at pH 4-9 using a dosage of 1 g/L. In 15 min, the magnetic adsorbent can be recycled and regenerated using a 10 mM NaOH solution. The adsorption and desorption efficiencies were over 97% and 82% for five consecutive cycles, respectively. To encourage the notion towards scale-up, a techno-economic evaluation with possible environmentally sensitive policy analysis has been introduced in this article to introspect the aspects of sustainability. This type of assessment is anticipated to be extremely encouraging to convey crucial recommendations to the scientific communities in order to produce high efficiency selenium elimination and further recovery from contaminated groundwater.

The beneficial and hazardous effects of selenium on the health of the soil-plant-human system: An overview

Selenium (Se), which can be both hazardous and beneficial to plants, animals and humans, plays a pivotal role in regulating soil-plant-human ecosystem functions. The biogeochemical behavior of Se and its environmental impact on the soil-plant-human system has received broad attention in the last decades. This review provides a comprehensive understanding of Se biogeochemistry in the soil-plant-human system. The speciation, transformation, bioavailability as well as the beneficial and hazardous effects of Se in the soil-plant-human system are summarized. Several important aspects in Se in the soil-plant-human system are detailed mentioned, including (1) strategies for biofortification in Se-deficient areas and phytoremediation of soil Se in seleniferous areas; (2) factors affecting Se uptake and transport by plants; (3) metabolic pathways of Se in the human body; (4) the interactions between Se and other trace elements in plant and animals, in particular, the detoxification of heavy metals by Se. Important research hotspots of Se biogeochemistry are outlined, including (1) the coupling of soil microbial activity and the Se biogeochemical cycle; (2) the molecular mechanism of Se metabolic in plants and animals; and (3) the application of Se isotopes as a biogeochemical tracer in research. This review provides up-to-date knowledge and guidelines on Se biogeochemistry research.

Selenium-agarose hybrid hydrogel as a recyclable natural substrate for selenium-enriched cultivation of mung bean sprouts

Selenium (Se) is an essential trace element for human beings and animals. Traditional plant Se enrichment technology suffers from selenium pollution. Herein, environmentally friendly Se-agarose (Se-Agar) hybrid hydrogels are prepared by simply mixing agar with different Se species including selenocarrageenan (SeCA), selenite and Se yeast under heating and stirring for 0.5 h without any other reagent. Such Se-Agar hybrid hydrogels with excellent biocompatibility were used as natural substrates for the cultivation of Se-enriched mung bean sprouts. Compared with Se yeast, SeCA and selenite show a better Se enrichment effect on mung bean sprouts. Furthermore, the growth indices including plant weight and plant height of mung bean sprouts were investigated with different concentrations and sources of Se. Notably, the Se-Agar hybrid hydrogels could be easily regenerated and reused for multiple cycles. The results indicated that Se-Agar hybrid hydrogels as recyclable natural substrates offer a simple, sustainable and affordable strategy for plant Se enrichment.

Vertical distribution of the toxic metal(loid)s chemical fraction and microbial community in waste heap at a nonferrous metal mining site

Over the past few decades, nonferrous mining has produced numerous waste rock and part of the waste that has not been properly treated was generally dumped at roadsides and hill slopes. However, the vertical distributions of toxic metal(loid)s and composition of microbial communities in waste heap and the under-laid pristine soil are rarely studied. In this work, the fraction-related distributions of toxic metal(loid)s were investigated at a waste heap profile and the indigenous microbial assemblages were also analyzed by Illumina sequencing of 16 s rRNA genes. Results showed that compared to the under-laid pristine soil, content of toxic metal(loid)s, especially Cd, As and Pb, in waste rock layer were higher. Most of As in subsoil existed as non-specifically sorbed and specifically-sorbed fractions, which could be ascribed to the migration from the upper layer. The mobility was significantly correlated with Eh, EC, clay content, CEC and the total content of metal(loid)s. Phyla Proteobacteria, Acidobacteria and Firmicutes dominated the microbial communities. The microbial community compositions at the genus level were similar, but their relative abundances were mainly influenced by pH, CEC, Eh, SOM, and bioavailability content of toxic metal(loid)s. Besides, microbial functions of elements (S, Fe, Mn and As) oxidation/reduction and metabolites (siderophore, biosurfactant, organic acid, phosphatase and urease) potentially were used for pollutants bioremediation.

Immobilization of cadmium in contaminated soils using sulfidated nanoscale zero-valent iron: Effectiveness and remediation mechanism

Sulfidated nanoscale zero-valent iron (S-nZVI) has shown excellent removal capacity for the removal of cadmium (Cd) in aqueous phase. Herein, the effectiveness and the mechanism of S-nZVI for the remediation of Cd contaminated soil were investigated for the first time. The results of sequential extraction procedures (SEP) showed that the exchangeable (EX) Cd was decreased by over 97.6% at the optimal dosage of 5 g kg^-1 S-nZVI during 30 d incubation and converted to less available Cd such as iron-manganese oxides-bound (OX) and organic matter-bound (OM) fractions. pH has negligible effect on the immobilization of Cd in soil, since OX fraction was stabilized in the range of 72-92% at initial soil pH range from 5.3 to 7.5. SEM-EDS analysis of the separated magnetic particles implied that Cd was successfully enriched on S-nZVI and the distribution of Cd was closely related to Fe, S, and O. CdO and CdS was confirmed as the key products for Cd immobilization in soil. Meanwhile, the S-nZVI was oxided to α-FeOOH, γ-FeOOH, and γ-Fe₂O₃. The existence of CdO was visibly related to the iron oxides, suggesting the synergetic immobilization effect by iron oxides. Overall, S-nZVI was promising for the remediation of Cd-contaminated soil.

Selenium in wastewater can be adsorbed by modified natural zeolite and reused in vegetable growth

Modified natural zeolites (MNZ) are widely used in pollutant removal, but how to address these MNZ that have adsorbed pollutants must be considered. Selenium is an essential trace element for metabolism and is also a water pollutant. Selenium is adsorbed in the water by MNZ in this study first. Then the Brassica chinensis L. was planted in the soil which contains the MNZ loaded with selenium (MNZ-Se) to explore selenium uptake. MNZ-Se release tests in water and soil were also considered. The results showed the following: (1) The maximum adsorption capacity of MNZ for selenium is 46.90 mg/g. (2) Water release experiments of MNZ-Se showed that regardless of how the pH of the aqueous solution changes, the trend of the release of selenium from MNZ-Se in aqueous solution is not affected and first decreases before stabilizing. (3) Soil release experiments of MNZ-Se showed that the selenium content in the soil increased and reached the concentration in the standard of selenium-rich soil. Addition amount and soil pH value will affect the release ratio. The release ratio of MNZ-Se in the water was higher than that in the soil. (4) With an increase in the soil MNZ-Se content, the selenium content in the soil and B. c increases. Above all, MZN can be a good medium for water pollutant removal and soil improvement.

Impact of manure on soil biochemical properties: A global synthesis

Manure application mitigates land degradation and improves soil fertility. Despite many individual studies on manure effects, a comprehensive overview of its consequences for a broad range of soil properties is lacking. Through a meta-analysis of 521 observations spanning the experiments from days after pulse addition up to 113 years with continues manure input, we quantified and generalized the average responses of soil biochemical properties depending on climate factors, management, soil, and manure characteristics. Large increase of pools with fast turnover (microbial carbon (C) and nitrogen (N): +88% and +84%, respectively) compared to stable organic matter pools (+27% for organic C, and +33% for total N) reflects acceleration of C and N cycles and soil fertility improvement. Activities of enzymes acquiring C-, energy-, N-, phosphorus- and sulfur were 1.3-3.3 times larger than those in soil without manure for all study durations included. Soil C/N ratio remained unaffected, indicating the stability of coupled C and N cycles. Microbial C/N ratio decreased, indicating a shift towards bacterial domination, general increase of C and N availability and acceleration of element cycling. Composted manure or manure without mineral fertilizers induced the greatest increase compared to non-composted manure or manure with mineral fertilizers, respectively, in most biochemical properties. The optimal manure application rate for adjusting proper soil pH was 25 Mg ha^-1 year^-1. Among manure types, swine manure caused the greatest increase of N-cycle-related properties: microbial N (+230%), urease (+258%) and N-acetyl-β-D-glucosaminidase (+138%) activities. Manure application strategies should avoid P and N losses and pollution via runoff, leaching or gaseous emissions due to fast mineralization and priming of soil organic matter. In conclusion, manure application favors C accumulation and accelerates nutrient cycling by providing available organic substances and nutrients and thus increasing enzyme activities.

Green immobilization of toxic metals using alkaline enhanced rice husk biochar: Effects of pyrolysis temperature and KOH concentration

Biochar is a "green" material that has been widely used in environmental applications for its capability to remove or immobilize contaminants in different environmental media (i.e. soil, water and air) and mitigate climate change. In this study, the feasibility of using KOH enhanced biochar for soil Cd and Pb stabilization was investigated, and the effects of pyrolysis temperature and alkaline concentrations for modification were explored. Field-emission scanning electron microscopy (FESEM), N₂ adsorption-desorption, and Fourier Transform Infrared Spectroscopy (FTIR) analyses were conducted to reveal the influence on biochar physiochemical properties. The immobilization performances were examined through Toxicity Characteristics Leaching Procedure (TCLP), and Response Surface Methodology (RSM) was adopted to visualize the results from leaching tests. The stabilization mechanisms of alkaline enhanced biochars were investigated using Time of Flight Secondary Ion Mass Spectroscopy (TOF-SIMS), Tessier sequential extraction method and X-ray diffraction (XRD) analyses. The results indicated that rice husk biochar pyrolyzed at a relatively low temperature (i.e., 300 °C) and activated by moderate alkaline concentrations (i.e., 1 M or 3 M KOH) rendered optimum stabilization performance. KOH activation was a double-edged sword, with high alkaline concentrations destroying biochar's cell structures. Moreover, the integration of TOF-SIMS, XRD and sequential leaching method shed lights on the underlying mechanisms involved in metal stabilization. Surface complexation between toxic metals and oxygen-containing functional groups rather than liming or precipitation was proven to be the fundamental stabilization mechanism.