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The increasing emergence of multidrug-resistant (MDR) pathogens causes difficult-to-treat infections with long-term hospitalizations and a high incidence of death, thus representing a global public health problem. To manage MDR bacteria bugs, new antimicrobial strategies are necessary, and their introduction in practice is a daily challenge for scientists in the field. An extensively studied approach to treating MDR infections consists of inducing high levels of reactive oxygen species (ROS) by several methods. Although further clinical investigations are mandatory on the possible toxic effects of ROS on mammalian cells, clinical evaluations are extremely promising, and their topical use to treat infected wounds and ulcers, also in presence of biofilm, is already clinically approved. Biochar (BC) is a carbonaceous material obtained by pyrolysis of different vegetable and animal biomass feedstocks at 200-1000 °C in the limited presence of O2. Recently, it has been demonstrated that BC's capability of removing organic and inorganic xenobiotics is mainly due to the presence of persistent free radicals (PFRs), which can activate oxygen, H2O2, or persulfate in the presence or absence of transition metals by electron transfer, thus generating ROS, which in turn degrade pollutants by advanced oxidation processes (AOPs). In this context, the antibacterial effects of BC-containing PFRs have been demonstrated by some authors against Escherichia coli and Staphylococcus aureus, thus giving birth to our idea of the possible use of BC-derived PFRs as a novel method capable of inducing ROS generation for antimicrobial oxidative therapy. Here, the general aspects concerning ROS physiological and pathological production and regulation and the mechanism by which they could exert antimicrobial effects have been reviewed. The methods currently adopted to induce ROS production for antimicrobial oxidative therapy have been discussed. Finally, for the first time, BC-related PFRs have been proposed as a new source of ROS for antimicrobial therapy via AOPs.

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Biochar (BC) is a carbonaceous material obtained by pyrolysis at 200-1000 °C in the limited presence of O2 from different vegetable and animal biomass feedstocks. BC has demonstrated great potential, mainly in environmental applications, due to its high sorption ability and persistent free radicals (PFRs) content. These characteristics enable BC to carry out the direct and PFRs-mediated removal/degradation of environmental organic and inorganic contaminants. The types of PFRs that are possibly present in BC depend mainly on the pyrolysis temperature and the kind of pristine biomass. Since they can also cause ecological and human damage, a systematic evaluation of the environmental behavior, risks, or management techniques of BC-derived PFRs is urgent. PFRs generally consist of a mixture of carbon- and oxygen-centered radicals and of oxygenated carbon-centered radicals, depending on the pyrolytic conditions. Here, to promote the more productive and beneficial use of BC and the related PFRs and to stimulate further studies to make them environmentally safer and less hazardous to humans, we have first reviewed the most common methods used to produce BC, its main environmental applications, and the primary mechanisms by which BC remove xenobiotics, as well as the reported mechanisms for PFR formation in BC. Secondly, we have discussed the environmental migration and transformation of PFRs; we have reported the main PFR-mediated application of BC to degrade inorganic and organic pollutants, the potential correlated environmental risks, and the possible strategies to limit them.

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Cadmium (Cd) is classified as a heavy metal (HM) and is found into the environment through both natural processes and intensified anthropogenic activities such as industrial operations, mining, disposal of metal-laden waste like batteries, as well as sludge disposal, excessive fertilizer application, and Cd-related product usage. This rising Cd disposal into the environment carries substantial risks to the food chain and human well-being. Inadequate regulatory measures have led to Cd bio-accumulation in plants, which is increasing in an alarming rate and further jeopardizing higher trophic organisms, including humans. In response, an effective Cd decontamination strategy such as phytoremediation emerges as a potent solution, with innovations in nanotechnology like biochar (BC) and nanoparticles (NPs) further augmenting its effectiveness for Cd phytoremediation. BC, derived from biomass pyrolysis, and a variety of NPs, both natural and less toxic, actively engage in Cd removal during phytoremediation, mitigating plant toxicity and associated hazards. This review scrutinizes the application of BC and NPs in Cd phytoremediation, assessing their synergistic mechanism in influencing plant growth, genetic regulations, structural transformations, and phytohormone dynamics. Additionally, the review also underscores the adoption of this sustainable and environmentally friendly strategies for future research in employing BC-NP microaggregates to ameliorate Cd phytoremediation from soil, thereby curbing ecological damage due to Cd toxicity.

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Biochar (BC), also referred to as "black gold", is a carbon heterogeneous material rich in aromatic systems and minerals, preparable by the thermal decomposition of vegetable and animal biomasses in controlled conditions and with clean technology. Due to its adsorption ability and presence of persistent free radicals (PFRs), BC has demonstrated, among other uses, great potential in the removal of environmental organic and inorganic xenobiotics. Bamboo is an evergreen perennial flowering plant characterized by a short five-year growth period, fast harvesting, and large production in many tropical and subtropical countries worldwide, thus representing an attractive, low-cost, eco-friendly, and renewable bioresource for producing BC. Due to their large surface area and increased porosity, the pyrolyzed derivatives of bamboo, including bamboo biochar (BBC) or activated BBC (ABBC), are considered great bio-adsorbent materials for removing heavy metals, as well as organic and inorganic contaminants from wastewater and soil, thus improving plant growth and production yield. Nowadays, the increasing technological applications of BBC and ABBC also include their employment as energy sources, to catalyze chemical reactions, to develop thermoelectrical devices, as 3D solar vapor-generation devices for water desalination, and as efficient photothermal-conversion devices. Anyway, although it has great potential as an alternative biomass to wood to produce BC, thus paving the way for new bio- and circular economy solutions, the study of bamboo-derived biomasses is still in its infancy. In this context, the main scope of this review was to support an increasing production of BBC and ABBC and to stimulate further studies about their possible applications, thus enlarging the current knowledge about these materials and allowing their more rational, safer, and optimized application. To this end, after having provided background concerning BC, its production methods, and its main applications, we have reviewed and discussed the main studies on BBC and ABBC and their applications reported in recent years.

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For environmental sustainability and to achieve sustainable development goals (SDGs), drinking water treatment must be done at a reasonable cost with minimal environmental impact. Therefore, treating contaminated drinking water requires materials and approaches that are inexpensive, produced locally, and effortlessly. Hence, locally available materials and their derivatives, such as biochar (BC) and activated carbon (AC) were investigated thoroughly. Several researchers and their findings show that the application of locally accessible materials and their derivatives are capable of the adsorptive removal of organic and inorganic contaminants from drinking water. The application of locally available materials such as lignocellulosic materials/waste and its thermo-chemically derived products, including BC and AC were found effective in the treatment of contaminated drinking water. Thus, this review aims to thoroughly examine the latest developments in the use of locally accessible feedstocks for tailoring BC and AC, as well as their features and applications in the treatment of drinking water. We attempted to explain facts related to the potential mechanisms of BC and AC, such as complexation, co-precipitation, electrostatic interaction, and ion exchange to treat water, thereby achieving a risk-free remediation approach to polluted water. Additionally, this research offers guidance on creating efficient household treatment units based on the health risks associated with customized adsorbents and cost-benefit analyses. Lastly, this review work discusses the current obstacles for using locally accessible materials and their thermo-chemically produced by-products to purify drinking water, as well as the necessity for technological interventions.

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Due to the dual issues of antibiotic resistance and bioaccumulation toxicity, antibiotics are ubiquitously present in aquatic environments, and this is causing serious concern. Herein, novel nickel ferrite (NiFe2O4) nanoparticles were successfully loaded onto activated biochar (BC) derived from banana peel (BP) to obtain magnetic nanocomposite (BC-NiFe2O4) as an effective biosorbent for the ciprofloxacin antibiotic (CIP) elimination from pharmaceutical effluent. A facile co-precipitation approach was utilized to construct the heterogeneous BC-NiFe2O4. The synthesized materials were systematically characterized using techniques such as XRD, FE-SEM, EDX, HR-TEM, BET, FTIR, and XPS. In addition, the magnetic measurements indicated the ferromagnetic behavior of the BC-NiFe2O4 sample. The influencing factors (i.e., pH, contact time, initial concentration, dose of adsorbent, ions interference, and solution temperature) of the adsorption process were also well studied. The adsorption capacity of the BC-NiFe2O4 heterostructure was 68.79 mg g-1 compared to the BC sample (35.71 mg g-1), confirming that the loading of magnetically NiFe2O4 nanoparticles onto the surface of porous biochar enhanced its stability and adsorption performance for CIP removal, wherein the metal-antibiotic complex has a significant effect for the removal of CIP. Moreover, the Langmuir adsorption isotherm and the pseudo-second-order model displayed a good fit for the experimental data. The values of △H° and △G° revealed that the adsorption process was endothermic and spontaneous. The coordination affinities, π-π stacking, and H-bonding interactions play a more critical role in the adsorption mechanism that confirmed by FTIR and XPS analysis. To study the stability of BC-NiFe2O4 nanocomposites, desorption and recycling studies were investigated. The results revealed that after three cycles, no significant loss in removal efficiency was detected, reflecting the stability and reusability of the prepared BC-NiFe2O4 nanocomposite.

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Sludge biochar (BC600) and B-doped sludge biochar (BBC600) were prepared with the boric acid doping modified co-pyrolysis method using municipal sludge as precursors, and the materials were structurally characterized by SEM, BET, FTIR, and Zeta potential and static contact angle to investigate the adsorption behavior, mechanism of BC600 and BBC600 on 1,2-DCA in water, and the influencing factors. The results of structural characterization showed that the B element content, specific surface area, and pore volume of biochar increased by 76%, 48%, and 30%, respectively, after the B doping modification; the effect of B doping modification on the surface charge and hydrophobicity of biochar was not significant. The results of adsorption experiments showed that the adsorption of 1,2-DCA by BBC600 was better than that by BC600 due to the larger specific surface area and higher strength of oxygen-containing functional groups of BBC600; the pseudo-first-order kinetic equation could better describe the adsorption of 1,2-DCA by BC600, and the pseudo-second-order kinetic equation could better fit the adsorption of 1,2-DCA by BBC600. The intraparticle diffusion was not the only rate-limiting step affecting the adsorption rate; the biochar material was more dispersed and stable under alkaline conditions, and its oxygen-containing functional groups were deprotonated and had enhanced electron-donating ability, which was beneficial to the adsorption of 1,2-DCA. Humic acid (HA) showed a low concentration-promoting and high concentration-inhibiting effect on the adsorption of 1,2-DCA by BC600, whereas both low and high concentrations of HA showed an inhibitory effect on the adsorption of 1,2-DCA by BBC600. The adsorption of 1,2-DCA by BC600 was inhibited by both low and high concentrations of HA, and HA competed with 1,2-DCA for adsorption; Cl-, SO42-, and NO3- all inhibited the adsorption of 1,2-DCA by biochar, and the degree of inhibition ordered from small to large was Cl-

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The combined pollution of heavy metal Cu and Cd in soil induced by the e-waste dismantling process has become a severe problem. To deal with this issue, crab shell biochar (BC) and Mn/Al-layered double oxide-loaded crab shell biochar (LDO/BC) were prepared using coprecipitation and co-pyrolysis of discarded crab shells and manganese aluminum salt. The experimental results showed that not only were the soil pH, available phosphorus, available potassium, and soil enzymatic activity enhanced, but the contents of DTPA-Cu and DTPA-Cd in the soil were also reduced after remediation by BC and LDO/BC. Microbial community analysis indicated that BC-1% could promote the relative abundance of Gemmatimonadota and Acidobacteriota; meanwhile, LDO/BC-1% could promote the relative abundance of Proteobacteria, which could reduce the accumulation of Cd in plants. Ryegrass was planted for further investigating the toxic effect of heavy metals in soil after remediation. The results demonstrated that after remediating with BC-5% and LDO/BC-1%, ryegrass grew more vigorously and with a lower content of the heavy metals Cu and Cd in the plants than that of CK, and the germination rate increased by 29% and 60%, respectively. Further, LDO/BC-1% had a more excellent remediation performance than that of the other groups, and the Mn in LDO/BC could reduce the content of heavy metal Cd adsorbed by ryegrass in soil.

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As both electron donors and acceptors, biochars (BCs) may interact with multivalent metal ions in the environment, causing changes in ionic valence states and resulting in unknown combined toxicity. Therefore, we systematically investigated the interaction between BCs and Cr (Cr(III) & Cr(VI)) or As (As(III) & As(V)) and their combined cytotoxicity in human colorectal mucosal (FHC) cells. Our results suggest that the redox-induced valence state change is a critical factor in the combined cytotoxicity of BCs with Cr/As. Specifically, when Cr(VI) was adsorbed on BCs, 86.4 % of Cr(VI) was reduced to Cr(III). In contrast, As(III) was partially oxidized to As(V) with a ratio of 37.2 %, thus reaching a reaction equilibrium. Meanwhile, only As(V) was released in the cell, which could cause more As(III) to be oxidized. As both Cr(III) and As(V) are less toxic than their corresponding counterparts Cr(VI) and As(III), different redox interactions between BCs and Cr/As and release profiles between BCs and Cr/As together lead to reduced combined cytotoxicity of BP-BC-Cr(VI) and BP-BC-As(III). It suggests that the valence state changes of metal ions due to redox effects is one of the parameters to be focused on when studying the combined toxicity of complexes of BCs with different heavy metal ions.

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Applying Biochar (BC) or biofertilizers (BF) are potential approaches to reduce the nitrogen input and mitigate soil degradation in the maize soybean relay strip intercropping system (IS). In 2019 and 2020, a two-factor experiment was carried out to examine the effects of BC and BF on soil productivity and yield production in IS. 4 N input levels (8.4, 22.5, 45 kg, and 67.5 kg ha - 1) referred to as N0, N1, N2, and N3 were paired with various organic treatments, including BC (150 kg ha - 1), BF (300 kg ha - 1), and without organic amendments (CK). The results demonstrated that, despite BF decreasing the biomass and N distribution into grains, BF performed better on improved soybean yield (5.2-8.5%) by increasing the accumulation of soybean biomass (7.2 ~ 11.6%) and N (7.7%). Even though BC and BF have a detrimental effect on soybean nitrogen fixation by reducing nodule number and weight, the values of soybean nitrogenase activity and nitrogen fixation potential in BF were higher than those in BC. Additionally, BF performs better at boosting the soil's nitrogen content and nitrate reductase and urease activity. BF increased the concentration of total N, soil organic matter, Olsen-phosphorus, and alkaline hydrolyzable N in the soil by 13.0, 17.1, 22.0, and 7.4%, respectively, compared to CK. Above all, applying BF combination with N2 (45 kg ha - 1 N) is a feasible strategy to raise crop grain output and keep soil productivity over the long term in IS.

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Concerns regarding inevitable soil translocation and bioaccumulation of cadmium (Cd) in plants have been escalating in concomitance with the posed phytotoxicity and threat to human health. Exhibiting a Cd tolerance, Bacillus sp. M6 strain has been reported as a soil amendment owing to its capability of reducing metal bioavailability in soils. The present study investigated the rhizospheric bacterial community of the Cd hyperaccumulator Sedum alfredii using 16S rRNA gene sequencing. Additionally, the Cd removal efficiency of strain Bacillus sp. M6 was enhanced by supplementing with biochar (C), glutamic acid (G), and rhamnolipid (R) to promote the phytoremediation effect of hyperaccumulator S. alfredii. To the best of our knowledge, this is the first time the amendments such as C, G, and R together with the plant-microbe system S. alfredii-Bacillus sp. M6 has been used for Cd bioremediation. The results showed that soil CaCl2 and DTPA (Diethylenetriamine penta-acetic acid) extractable Cd increased by 52.77 and 95.08%, respectively, in all M6 treatments compared to unamended control (CK). Sedum alfredii with Bacillus sp. M6 supplemented with biochar and rhamnolipid displayed a higher phytoremediation effect, and the removal capability of soil Cd (II) reached up to 16.47%. Moreover, remediation of Cd polluted soil by Bacillus sp. M6 also had an impact on the soil microbiome, including ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), and cadmium transporting ATPase (cadA) genes. Quantitative PCR analysis confirmed the Bacillus sp. M6 strain increased the abundance of AOB and cadA in both low Cd (LC) and high Cd (HC) soils compared to AOA gene abundance. Besides, the abundance of Proteobacteria and Actinobacteria was found to be highest in both soils representing high tolerance capacity against Cd. While Firmicutes ranked third, indicating that the additionof strain could not make it the most dominant species. The results suggested the presence of the hyperaccumulator S. alfredii and Cd tolerant strain Bacillus sp. M6 supplemented with biochar, and rhamnolipid, play a unique and essential role in the remediation process and reducing the bioavailability of Cd.

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Focusing on agricultural soil enriched in phosphorus and cadmium (total Cd=0.94 mg·kg-1 and total P=0.86g·kg-1), indoor cultivation experiments were conducted according to the length of the middle rice growth period and the following crop planting period in Hubei. The bioavailability of soil phosphorus and cadmium were examined along with their morphological changes and coupling effect under the influence of material biochar (BC), calcium magnesium phosphate fertilizer (CMP), and fly ash (FA). The results showed that:① When cultured for 140 days, the content of available phosphorus in the soil treated with the conditioning agents was significantly increased compared with the control soil, available phosphorus reached 22.47-37.81mg·kg-1, and the optimal growth requirements of rice were met without additional application of phosphate fertilizer, and adding BC had the best effect. ② The phosphorus in the test soil is mainly inorganic orthophosphate, and the content of different forms of inorganic phosphorus increased under the action of the conditioning agents. The fixed O-P and Ca10-P in the soil gradually changed to more active forms (Ca2-P, Ca8-P, Al-P and Fe-P) over time. ③ The effective Cd content of the soil treated with the conditioning agents was significantly reduced by 8.74%-17.48% relative to the control treatment, which was mainly related to the effect of the three conditioning agents on soil pH. At the same time, compared with the control, the addition of a conditioning agent significantly reduced the exchangeable Cd, and the carbonate-bound Cd and the residual Cd were increased. The abundance of active groups at the surface is related to the adsorption and chelation of Cd2+. The results showed that the three conditioners have the dual functions of phosphorus activation and cadmium passivation in phosphorus-and cadmium-enriched soil, and the effect of biomass carbon and calcium magnesium phosphate fertilizer was greatest, which persisted across the entire rice growth period to the sowing date of the next crop.

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Antimony (Sb) is a highly toxic heavy metal, and the amount of Sb in the soil is increasing due to anthropogenic activities. Recently, biochar (BC) has been used for remediation of Sb-contaminated soil, therefore, understanding the effect of BC-induced changes in soil microbial on the change of Sb speciation will help to elucidate the mechanism of BC in immobilization/mobilization of Sb in contaminated soils. Sb-contaminated soil with 10 wt % of Wheat straw-derived BC (SBC) and fruit (apple) tree-derived BC (FBC) and control was incubated for 130 days. Changes of soil bacterial community composition and Sb oxidation gene induced by BC were explored during the incubation. Dynamic change of Sb speciation was assessed by the citric acid extraction. The redundancy analysis (RDA) and spearman analysis (PCA) was used to analyze the relationship between Sb immobilization/mobilization and change of soil bacterial community induced by BC. The soil properties change induced by BC affected soil bacterial community composition, and Sb mobilization was strongly related to the change of soil bacterial community composition. The relative abundance of Sb oxidation gene increased in the soil amended by BC, which proved that oxidation of Sb(III) after 20 d incubation with SBC and 50 d incubation with FBC incubation. It is noteworthy that the application of BC has a potential mobilizing risk for Sb and both the change of soil bacteria and soil chemical properties play an important role in Sb mobilization. The possible risks induced by BC should be considered before applying the BC to Sb contaminated soil.

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To explore the effects of biochar on the temperature sensitivity of soil respiration and microbial community structure, the soil was subjected to an indoor culture test under two major treatments which were control (CK) and the addition of 3% (mass ratio) biochar (BC). Each major treatment contained four temperature conditions. We analyzed the changes in soil CO2 emission, the content of different soil organic carbon, and the characteristics of the soil bacterial community. The results showed that:①The input of biochar to soil respiration under various temperature conditions was promoted in the early stage and inhibited in the later stage, and after 14 days of cultivation, the input of biochar significantly reduced the temperature sensitivity Q10 values of soil respiration. ② For soil organic carbon fractions, the decline rate of the content of soil inert organic carbon under the CK treatment increased with increasing temperature, and was sensitive to the changes in temperature. However, the input of biochar significantly reduced the temperature sensitivity of the soil inert organic carbon, and narrowed its decline rate under each temperature condition. The decline rate did not increase with increasing temperature. ③The 16S rDNA high-throughput sequencing results showed that at the end of the cultivation, the relative abundance of Massilia in the soil of the CK treatment decreased with increasing temperature, and the input of biochar significantly increased its temperature sensitivity, making the decline rate increase. In contrast to Massilia, the relative abundance of Haliangium in soil of the CK treatment increased significantly with increasing temperature, and the input of biochar significantly reduced its temperature sensitivity, rendering the difference of relative abundance between each temperature condition not significant. This study shows that the input of biochar can significantly reduce the temperature sensitivity of soil respiration, which is related to decreased temperature sensitivity of soil inert organic carbon, and the change in the relative abundance of Massilia and Haliangium after the input of biochar.

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Using phosphorus and cadmium enriched soil (total Cd is 0.94 mg·kg-1, total phosphorus is 0.86 g·kg-1) and low cadmium accumulation genotype Jinqiuhong 3 as experimental materials, we set up four treatments: absolute control (only NK inorganic fertilizer), relative control (CKp, NPK inorganic fertilizer), biochar (only NK inorganic fertilizer), and biochar+phosphate fertilizer (BC-CKp). The availability of phosphorus and heavy metal Cd in soil, the biomass, Cd accumulation characteristics of edible parts of plants, and the basic characteristics of soil were investigated. The results showed that the content of available Cd in soil decreased by 8.23% and 5.68% by BC and BC-CKp treatment with biochar compared with CK0 and CKp treatment without biochar, respectively. At the same time, the content of available phosphorus in soil significantly increased 11.60-16.26 mg·kg-1 of biochar. The content of available Cd in CKp and BC-CKp treated with exogenous phosphate fertilizer was significantly lower than that in CK0 and BC treatments without phosphate fertilizer by 31.43% and 33.29%, respectively. In addition to CK0 treatment, the Cd content of edible parts of Brassica campestris bolting crops in the other three treatment groups (CKp, BC, and BC-CKp) did not exceed the limit value of Cd of the China Food Safety National Standard (GB 2762-2017) of 0.1 mg·kg-1. The results showed that the dual functions of heavy metal Cd passivation and phosphorus activation could be realized by injecting biochar into moderate and mild Cd contaminated soil with phosphorus enrichment at the same time. Under the condition of no additional use of phosphorus fertilizer, planting vegetable crop genotypes with weak absorption and low accumulation of Cd can not only ensure an increase in biomass of edible parts but can also ensure that the heavy metal Cd content in edible parts meets the national standard of food safety.

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A batch of biochar was produced from pyrolysis of Typha angustifolia (TBCs) at 200-500℃ for 2 h and 6 h to investigate the effects of pyrolytic temperature and heating retention time on the physico-chemical properties. Moreover, Escherichia coli (E. coli) HB101 and the seeds of Helianthus annuus were used to preliminarily test the ecological risk of the TBCs. Results showed that the heating retention time (i.e., 2 and 6 h) had no significant effect on the properties of TBCs, while pyrolytic temperature significantly affected TBCs' characteristics. As the pyrolysis temperature increased from 200 to 500℃, the mass yield and contents of hydrogen (H) and oxygen (O) decreased, while the contents of carbon (C) and ash increased. The pH and surface pores also increased with increasing pyrolytic temperature, whereas the O-containing functional group (e.g., -COOH and -OH) decreased. These results indicated the increased carbonization and aromatization of the TBCs. For the inherent nutrients of TBCs, the total phosphorus (TP) and available potassium (K) contents significantly increased as temperature increased. The main components of dissolved organic matter (DOM) of TBCs were humic acid-like and fulvic acid-like organic compounds. As the pyrolysis temperature increased, the content of humic acid-like organic compounds decreased, while the content of fulvic acid-like organic compounds increased. All the TBCs had no significant effect on the growth of E. coli HB101 and the seed germination of Helianthus annuus, indicating the little ecological risk of TBCs under the experimental conditions. These findings provide an alternative way for resource utilization of waste wetland biomass and provide important theoretical data for screening biochar in soil reclamation.

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Soil microbial metabolism is vital for nutrient cycling and stability of an ecosystem. To elucidate the long-term effects of biochar application on nutrient limitations and carbon use efficiency (CUE) of soil microbial metabolisms, biochars pyrolyzed at 450℃ from trunks and branches of fruit trees under an oxygen-limited condition were mixed with the top Lou soils (0-20 cm) with application amounts of 0, 20, 40, 60, and 80 t·hm-2 in 2012. Corn-wheat rotation was carried out afterwards for seven years. The nutrient limitations of soil microbial metabolisms were analyzed quantitatively through ecoenzymatic stoichiometry in 2019. The results indicated that:① With an increase in the biochar application amount, soil moisture, organic carbon, total nitrogen, C:N, C:P, and N:P significantly increased, whereas there were no clear patterns for the active components of carbon, nitrogen, and phosphorus, microbial biomass carbon, nitrogen, phosphorus and total phosphorus. In contrast, the activities of five extracellular enzymes (ß-1,4-glucosidase, cellobiohydrolase, leucine aminopeptidase, ß-1,4-N-acetylglucosaminidase, and phosphatase) were significantly reduced. ② The soil microorganisms suffered from the phosphorus limitation under all treatments in this study. In the treatments of biochar application, the carbon and phosphorus limitations of microbial metabolisms increased significantly with increasing application amount, whereas the microbial CUE decreased significantly. When the application amount was 20 t·hm-2, the carbon limitation (0.625±0.022) and phosphorus limitation (62.153°±0.892°) were lowest, and the microorganism CUE (0.511±0.007) was highest. ③ Partial least-squares path modeling (PLS-PM) showed that soil carbon, nitrogen, phosphorus, and their stoichiometry had a very direct positive effect on phosphorus limitation (P<0.01), and there was a positive correlation between carbon limitation and phosphorus limitation (R2=0.242, P<0.001); in contrast, the carbon and phosphorus limitations had a very significant negative effect on CUE (P<0.001). It was revealed that the excessive application of biochar had caused a soil element stoichiometry imbalance, which deteriorated the phosphorus limitation of the soil microbial metabolism and further led to carbon limitation and reduction of CUE. When the biochar application amount was 20 t·hm-2, C and P limitations were lowest, and microbial CUE was highest. Therefore, 20 t·hm-2 was optimal for regulating soil microbial metabolism, maintaining ecological functions, and reducing carbon dioxide emission produced by microbial metabolism.

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Wheat straw biochar (BC) was modified by KOH and magnetics to generate composited modified biochar (FKC). Based on characterization by scanning electron microscopy-energy dispersive spectrometry (SEM-EDS), Brunauer-Emmett-Teller (BET), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and magnetic (VSM) techniques, the adsorption characteristics and mechanisms of Cd2+ in water and the effects of temperature, pH value, and dosage on the adsorption characteristics of FKC were studied. The results showed that the modified biochar was loose and porous. The specific surface area of FKC increased by 19.11 times, the number of aromatic and oxygen-containing functional groups such as O-H, C=O, and C=C increased, and a new functional group Fe-O formed compared to the BC. FKC is magnetic, and its magnetization is 8.43 emu·g-1, which can be recycled and reused. The adsorption of Cd2+ by FKC fitted well with the pseudo-second-order kinetic model and the Langmuir model, indicating that chemical adsorption is the main adsorption mechanism. The theoretical maximum equilibrium adsorption capacity of FKC is 23.44 mg·g-1, which is 1.47 times that of BC. The thermodynamic parameters suggested the adsorption of Cd2+ by FKC was a spontaneous and endothermic process. The adsorption capacity increased with an increase of pH in the region 2-8, and a biochar dosage of 10 g·L-1 was used. After three cycles of adsorption-desorption-adsorption, the adsorption capacity of Cd2+ by FKC still reached 17.71 mg·g-1, indicating that FKC has good reusability. These results can provide a theoretical basis for the application of KOH and magnet-modified biochar from wheat straw to remove heavy metals from contaminated wastewater.

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To explore the safe utilization of technology in mildly and moderately cadmium (Cd)-contaminated farmland and realize the safe production of agricultural products, two different cadmium-accumulating genotypes of Tsai-tai were used as test crops, using the pot experiment method. The same six treatments were set on the soil where the two test crops were planted:control (CK), addition of 3% (mass fraction) biochar (BC), addition of 0.17% calcium magnesium phosphate fertilizers (CMP), foliar application of 3 mg·L-1 Na2SeO3 aqueous solution (Se), BC+Se, and CMP+Se, to study the changes in available cadmium in soil under different treatments and the characteristics of cadmium accumulation in different parts of the plant. The results showed that:① Under the same treatment, the content of available cadmium in soil near the root of the low-cadmium-accumulating genotype of Tsai-tai of Jinqiuhong Ⅲ was significantly lower than that of the high-cadmium-accumulating genotype of Shiyuehong. BC and CMP had a significant passivating effect on cadmium in the soil near the root of Jinqiuhong Ⅲ, and the passivating effect of BC was better than that of CMP; the effect of passivating treatment was significantly better than that of foliar application of selenium. ② The root system of Tsai-tai of Jinqiuhong Ⅲ had a stronger ability to accumulate cadmium than that of Shiyuehong, and the accumulated cadmium tended to be stored in the root. There were no synergistic effects between the foliar application of selenium and the two kinds of passivants on inhibiting the transfer and enrichment of cadmium to the edible parts of Tsai-tai. ③ Under the treatments of BC and CMP, the content of cadmium in the edible part of Tsai-tai of Jinqiuhong Ⅲ was lower than the limit value of cadmium in GB 2762-2017 (0.10 mg·kg-1). This study shows that for mildly and moderately cadmium-contaminated farmland, applying green passivants such as biochar, calcium magnesium phosphate fertilizers, and planting crops with weak absorption and low accumulation can achieve the safe use of the cadmium-contaminated farmland and safe production of agricultural products.

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Our study underpins the mechanism of organo-mineral interaction between black carbon (BC, biochar) and associated minerals in the historical BC-rich Amazonian Dark Earth (ADE) by using synchrotron-based microscopic (TXM), microspectroscopic (µFTIR) and spectroscopic (XAS and µ-diffraction) approaches. The BC-rich ADE contained over 100% more poorly crystalline minerals than the adjacent tropical soil. Linear combination fitting of k-spacing in the X-ray Absorption Spectra (XAS) revealed that ferrihydrite contributed to 81.1% of the Fe-minerals in BC. A small but distinct peak was observed at 5.7 Å-1 in the extended X-ray absorption fine structure k oscillation of BC, revealing the presence of FeC (including Fe-O-C) covalent bonds. No FeC path was yielded by the XAS fitting when an obvious peak downshift of the first (FeFe1) shell was observed, suggesting that the availability of inner-sphere FeC complexation was limited to the BC surface and interphase region. The main minerals for organo-mineral complexation were short-range-order (SRO) ferrihydrite on BC instead of corner-sharing FeO6 octahedra. Compared to ADE, the coordination number of the first (FeFe1) and second (FeFe2) shell was higher in BC, revealing a higher degree of order in coordination between the neighboring Fe mineral crystals. Black C limited the progressive aging of amorphous Fe phases and greatly enriched SRO ferrihydrite in the redox-fluctuating and high-leaching environment. The transformation of SRO ferrihydrite into the more crystalline Fe oxides was controlled by the local pH environment. A strong signal from the complexed phenolic group (aryl-OH, 1241 cm-1) and a distinct band of inner-sphere complexation (Fe-aryl C, 1380-1384 cm-1) were identified in the FTIR spectra. The enrichment of poorly crystalline minerals can have positive feedback on the long-term stabilization of BC. The scale-up application of biochar to agricultural and ecological systems may have a long-lasting impact on the enrichment and transformation of the SRO minerals in the soil.