Effect of biochar from peanut shell on speciation and availability of lead and zinc in an acidic paddy soil

Heterogeneous precipitation behavior and mechanism during the adsorption of cationic heavy metals by biochar: Roles of inorganic components

Heavy metals are commonly adsorbed by biochar in contaminated water and soil. However, the behaviour and underlying mechanisms of heterogeneous precipitation between the inorganic components of biochar and cationic heavy metals remain poorly understood. In this study, we comprehensively investigated the nucleation, growth, and aggregation of precipitates, ion exchange-coupled precipitation behaviour, adsorption-precipitation correlation, and the influence of environmental factors (e.g., anion content, pH, initial concentration, type of heavy metals, and biochar size). The kinetic results indicated that the generation of precipitates was accompanied by an adsorption reaction with a gradual increase in crystal size and aggregation behaviour. Moreover, precipitation includes both surface and solution precipitation. The increasing local concentration of Pb(II) around the biochar at high initial concentrations increased the supersaturation of the nucleating substance, which decreased the potential for heterogeneous nucleation and facilitated heterogeneous precipitation. Correlation analysis revealed the presence of a coupling mechanism between precipitation and cation exchange. The enhanced electrostatic attraction at high pH could lower the heterogeneous nucleation potential barrier, thus promoting heterogeneous precipitation. The small biochar size extended the induction time, which was unfavourable for heterogeneous nucleation. This study provides a deeper understanding of the heterogeneous precipitation behaviour of the inorganic components of biochar and cationic heavy metals.

Predicting bioavailable barium transfer in soil-bok choy systems: A study induced by shale gas extraction in Chongqing, China

Barium (Ba) is a significant contaminant from shale gas extraction and is also used in various other industries. However, there has been very limited attention paid to Ba. Elucidating the Ba in soil-crop system are of great significance for both human health risk assessment and pollution control. In this study, the bioavailability of Ba in soils was studied by using various characterization methods. Then the major factors dominating the transfer of Ba in soil-bok choy system and a suitable predicted model was derived. The results showed that Ba was mainly accumulated in the roots (transfer factor < 0.3). The relationships between Ba in shoots and the bioavailability of Ba characterizing with different methods increased in the order of CH3COOH (R2 = 0.81) < ethylenediamine tetraacetic acid (R2 = 0.87) < pore water (R2 = 0.89) < diffusive gradients in thin film (R2 = 0.90) < CaCl2 (R2 = 0.91). The major soil properties affecting Ba in shoots were pH (r = -0.32, P > 0.05), cation exchange capacity (r = -0.43, P < 0.01) and labile Al (r = 0.38, P < 0.05). Bioavailability of Ba can preferably model the Ba transfer in soil-bok choy system. The best reliable model was LogBa[shoot] = 0.591LogBa[soil-Pore water] + 1.749 (R2 = 0.963, P < 0.001). This model without measuring soil physicochemical properties, making it easier and more convenient to use in practice. Overall, these results highlight the role of metal bioavailability in predicting their transfer in soil-plant systems.

Sulfur-functionalized biochar: Synthesis, characterization, and utilization for contaminated soil and water remediation-a review

The development of innovative, eco-friendly, and cost-effective adsorbents is crucial for addressing the widespread issue of organic and inorganic pollutants in soil and water. Recent advancements in sulfur reagents-based materials, such as FeS, MoS2, MnS, S0, CS2, Na2S, Na2S2O32-, H2S, S-nZVI, and sulfidated Fe0, have shown potential in enhancing the functional properties and elemental composition of biochar for pollutant removal. This review explores the synthesis and characterization of sulfur reagents/species functionalized biochar (S-biochar), focusing on factors like waste biomass attributes, pyrolysis conditions, reagent adjustments, and experimental parameters. S-biochar is enriched with unique sulfur functional groups (e.g., C-S, -C-S-C, C=S, thiophene, sulfone, sulfate, sulfide, sulfite, elemental S) and various active sites (Fe, Mn, Mo, C, OH, H), which significantly enhance its adsorption efficiency for both organic pollutants (e.g., dyes, antibiotics) and inorganic pollutants (e.g., metal and metalloid ions). The literature analysis reveals that the choice of feedstock, influenced by its lignocellulosic content and xylem structure, critically impacts the effectiveness of pollutant removal in soil and water. Pyrolysis parameters, including temperature (200-600 °C), duration (2-10 h), carbon-to-hydrogen (C:H) and oxygen-to-hydrogen (O:H) ratios in biochar, as well as the biochar-to-sulfur reagent modification ratio, play key roles in determining adsorption performance. Additionally, solution pH (2-8) and temperature (288, 298, and 308 K) affect the efficiency of pollutant removal, though optimal dosages for adsorbents remain inconsistent. The primary removal mechanisms involve physisorption and chemisorption, encompassing adsorption, reduction, degradation, surface complexation, ion exchange, electrostatic interactions, π-π interactions, and hydrogen bonding. This review highlights the need for further research to optimize synthesis protocols and to better understand the long-term stability and optimal dosage of S-biochar for practical environmental applications.

Preparation of a biochar-lignosulfonate composite material and its adsorption performance for Cu2

Biochar was prepared using peanut shells as raw materials, and then composite amino-functionalized lignosulfonate was used to prepare a biochar/lignosulfonate adsorbent (BC-CLS). The morphology and structure of BC-CLS were characterized using FT-IR, SEM, zeta potential, and XPS. The adsorption performance of BC-CLS was evaluated by batch adsorption experiments and dynamic adsorption experiments (adsorption column flow adsorption). The results showed that BC-CLS adsorbent exhibited significant adsorption performance for Cu2+, including a short equilibrium time (50 min), fast adsorption rate (11 mg g-1 min-1), and high static saturation adsorption capacity (354 mg g-1). Dynamic adsorption experiments indicated that the maximum adsorption capacity of BC-CLS adsorbent was approximately 280 mg g-1, with a removal rate of over 99% after five cycles, meeting the wastewater discharge standard (less than 1 mg L-1). The results demonstrated that the adsorption capacity of BC-CLS adsorbent for Cu2+ was controlled by multiple adsorption mechanisms, including electrostatic attraction, precipitation, and metal ion complexation. Additionally, under pH = 5 conditions, using a 40 mg per L Cu2+ solution, the adsorption performance of BC-CLS adsorbent remained above 60% after five adsorption-desorption experiments, indicating good cycling stability of BC-CLS adsorbent.

Biochar as a partner of plants and beneficial microorganisms to assist in-situ bioremediation of heavy metal contaminated soil

Synergistic remediation of heavy metal (HM) contaminated soil using beneficial microorganisms (BM) and plants is a common and effective in situ bioremediation method. However, the shortcomings of this approach are the low colonisation of BM under high levels of heavy metal stress (HMS) and the poor state of plant growth. Previous studies have overlooked the potential of biochar to mitigate the above problems and aid in-situ remediation. Therefore, this paper describes the characteristics and physicochemical properties of biochar. It is proposed that biochar enhances plant resistance to HMS and aids in situ bioremediation by increasing colonisation of BM and HM stability. On this basis, the paper focuses on the following possible mechanisms: specific biochar-derived organic matter regulates the transport of HMs in plants and promotes mycorrhizal colonisation via the abscisic acid signalling pathway and the karrikin signalling pathway; promotes the growth-promoting pathway of indole-3-acetic acid and increases expression of the nodule-initiating gene NIN; improvement of soil HM stability by ion exchange, electrostatic adsorption, redox and complex precipitation mechanisms. And this paper summarizes guidelines on how to use biochar-assisted remediation based on current research for reference. Finally, the paper identifies research gaps in biochar in the direction of promoting beneficial microbial symbiotic mechanisms, recognition and function of organic molecules, and factors affecting practical applications.

Quantification of the effect of biochar application on heavy metals in paddy systems: Impact, mechanisms and future prospects

Biochar (BC) has shown great potential in remediating heavy metal(loid)s (HMs) contamination in paddy fields. Variation in feedstock sources, pyrolysis temperatures, modification methods, and application rates of BC can result in great changes in its effects on HM bioavailability and bioaccumulation in soil-rice systems and remediation mechanisms. Meanwhile, there is a lack of application guidelines for BC with specific properties and application rates when targeting rice fields contaminated with certain HMs. To elucidate this topic, this review focuses on i) the effects of feedstock type, pyrolysis temperature, and modification method on the properties of BC; ii) the changes in bioavailability and bioaccumulation of HMs in soil-rice systems applying BC with different feedstocks, pyrolysis temperatures, modification methods, and application rates; and iii) exploration of potential remediation mechanisms for applying BC to reduce the mobility and bioaccumulation of HMs in rice field systems. In general, the application of Fe/Mn modified organic waste (OW) derived BC for mid-temperature pyrolysis is still a well-optimized choice for the remediation of HM contamination in rice fields. From the viewpoint of remediation efficiency, the application rate of BC should be appropriately increased to immobilize Cd, Pb, and Cu in rice paddies, while the application rate of BC for immobilizing As should be <2.0 % (w/w). The mechanism of remediation of HM-contaminated rice fields by applying BC is mainly the direct adsorption of HMs by BC in soil pore water and the mediation of soil microenvironmental changes. In addition, the application of Fe/Mn modified BC induced the formation of iron plaque (IP) on the root surface of rice, which reduced the uptake of HM by the plant. Finally, this paper describes the prospects and challenges for the extension of various BCs for the remediation of HM contamination in paddy fields and makes some suggestions for future development.

Reviewing the role of biochar in paddy soils: An agricultural and environmental perspective

The main challenge of the twenty-first century is to find a balance between environmental sustainability and crop productivity in a world with a rapidly growing population. Soil health is the backbone of a resilient environment and stable food production systems. In recent years, the use of biochar to bind nutrients, sorption of pollutants, and increase crop productivity has gained popularity. This article reviews key recent studies on the environmental impacts of biochar and the benefits of its unique physicochemical features in paddy soils. This review provides critical information on the role of biochar properties on environmental pollutants, carbon and nitrogen cycling, plant growth regulation, and microbial activities. Biochar improves the soil properties of paddy soils through increasing microbial activities and nutrient availability, accelerating carbon and nitrogen cycle, and reducing the availability of heavy metals and micropollutants. For example, a study showed that the application of a maximum of 40 t ha-1 of biochar from rice husks prior to cultivation (at high temperature and slow pyrolysis) increases nutrient utilization and rice grain yield by 40%. Biochar can be used to minimize the use of chemical fertilizers to ensure sustainable food production.

Soil acidification and salinity: the importance of biochar application to agricultural soils

Soil acidity is a serious problem in agricultural lands as it directly affects the soil, crop production, and human health. Soil acidification in agricultural lands occurs due to the release of protons (H+) from the transforming reactions of various carbon, nitrogen, and sulfur-containing compounds. The use of biochar (BC) has emerged as an excellent tool to manage soil acidity owing to its alkaline nature and its appreciable ability to improve the soil's physical, chemical, and biological properties. The application of BC to acidic soils improves soil pH, soil organic matter (SOM), cation exchange capacity (CEC), nutrient uptake, microbial activity and diversity, and enzyme activities which mitigate the adverse impacts of acidity on plants. Further, BC application also reduce the concentration of H+ and Al3+ ions and other toxic metals which mitigate the soil acidity and supports plant growth. Similarly, soil salinity (SS) is also a serious concern across the globe and it has a direct impact on global production and food security. Due to its appreciable liming potential BC is also an important amendment to mitigate the adverse impacts of SS. The addition of BC to saline soils improves nutrient homeostasis, nutrient uptake, SOM, CEC, soil microbial activity, enzymatic activity, and water uptake and reduces the accumulation of toxic ions sodium (Na+ and chloride (Cl-). All these BC-mediated changes support plant growth by improving antioxidant activity, photosynthesis efficiency, stomata working, and decrease oxidative damage in plants. Thus, in the present review, we discussed the various mechanisms through which BC improves the soil properties and microbial and enzymatic activities to counter acidity and salinity problems. The present review will increase the existing knowledge about the role of BC to mitigate soil acidity and salinity problems. This will also provide new suggestions to readers on how this knowledge can be used to ameliorate acidic and saline soils.

Sulfoaluminate cement-modified straw biochar as a soil amendment to inhibit Pb-Cd mobility in the soil-romaine lettuce system

Biochar is widely used to remediate soil polluted by potentially toxic elements (PTEs), while the effect of a new type of biochar, obtained from modified cement material, on the mobility of Pb and Cd in the soil-plant system is still unknown. In this study, soils doped with sulfoaluminate cement modified biochar (SBC) were characterized using a series of approaches including FTIR, XRD, and XPS, and combined with pot experiments to explore its synergistic effects on the speciation transformation, accumulation, and mobility of both Pb and Cd in a soil-romaine lettuce system in heavily contaminated soils containing 500 mg·kg-1-Pb and 3 mg·kg-1-Cd. The results showed that SBC effectively immobilized Pb and Cd in the soil and that this was achieved through cation exchange, complexation, and gel encapsulation. Moreover, SBC also changed the soil physicochemical properties and indirectly affected the speciation transformation of Pb and Cd. FTIR and XRD analyses revealed that the groups such as -OH, -COOH, SO42-, and SiO32-introduced by SBC stimulated the conversion from the soluble to the residual state of Pb. XPS analysis indicated that, the deviation of the C-O-C, C-OOH, and O-CO peak and the increased in area suggested that organic groups in the SBC were engaged in the immobilization mechanism of Pb and Cd. The transformation of residual Cd in other extractable fractions might be due to either enhanced soil reducibility or competitive adsorption with Pb. In 5% SBC soil, Pb was reduced by 27.69% and 64.84%, and Cd was reduced by 20.45% and 35.87% for shoots and roots of romaine lettuce, respectively. SBC showed a significantly positive correlation with SOM, while SOM showed a highly significantly negative correlation with both Pb and Cd in the roots. In summary, SBC can be strongly recommended as a green amendment to remediate Pb-Cd contaminated soil and to inhibit the mobility to plant.

Recent advances in biochar amendments for immobilization of heavy metals in an agricultural ecosystem: A systematic review

Over the last several decades, extensive and inefficient use of contemporary technologies has resulted in substantial environmental pollution, predominantly caused by potentially hazardous elements (PTEs), like heavy metals that severely harm living species. To combat the presence of heavy metals (HMs) in the agrarian system, biochar becomes an attractive approach for stabilizing and limiting availability of HMs in soils due to its high surface area, porosity, pH, aromatic structure as well as several functional groups, which mostly rely on the feedstock and pyrolysis temperature. Additionally, agricultural waste-derived biochar is an effective management option to ensure carbon neutrality and circular economy while also addressing social and environmental concerns. Given these diverse parameters, the present systematic evaluation seeks to (i) ascertain the effectiveness of heavy metal immobilization by agro waste-derived biochar; (ii) examine the presence of biochar on soil physico-chemical, and thermal properties, along with microbial diversity; (iii) explore the underlying mechanisms responsible for the reduction in heavy metal concentration; and (iv) possibility of biochar implications to advance circular economy approach. The collection of more than 200 papers catalogues the immobilization efficiency of biochar in agricultural soil and its impacts on soil from multi-angle perspectives. The data gathered suggests that pristine biochar effectively reduced cationic heavy metals (Pb, Cd, Cu, Ni) and Cr mobilization and uptake by plants, whereas modified biochar effectively reduced As in soil and plant systems. However, the exact mechanism underlying is a complex biochar-soil interaction. In addition to successfully immobilizing heavy metals in the soil, the application of biochar improved soil fertility and increased agricultural productivity. However, the lack of knowledge on unfavorable impacts on the agricultural systems, along with discrepancies between the use of biochar and experimental conditions, impeded a thorough understanding on a deeper level.

Co-pyrolysis of biomass and phosphate tailing to produce potential phosphorus-rich biochar: efficient removal of heavy metals and the underlying mechanisms

Application of biochar to treat heavy metal polluted wastewater has received increasing attention; however, the immobilization ability of pristine biochar for metal ions is still limited. In this study, phosphate tailing was co-pyrolyzed with sawdust and peanut shell to acquire phosphorus-rich biochars with high removal rates for Cd, Zn, Pb, and Cu. Meanwhile, the improvement mechanisms by phosphate tailing were clarified by XRD, FTIR, SEM-EDS, BET-N₂, and model fitting. Results showed that after phosphate tailing impregnation, surface area of sawdust, and peanut shell biochars increased from to 11.6 m² g^-1, and from 43.5 to 53.4 m² g^-1, respectively. Functional groups of -COOH and CO₃^2- on biochar increased and the P₂O₇^4- newly generated. Besides, large amounts of Ca(PO₃)₂ and Ca₂P₂O₇ crystals were detected in biochar ash. As for sawdust biochar, loading of phosphate tailing raised the sorption rates of Cd, Zn, Pb, and Cu by 0.35, 0.61, 1.10, and 2.64 times, respectively, as for peanut shell biochar, it was raised by 0.12, 0.47, 0.11, and 1.98 times, respectively. The sorption isotherms by phosphate tailing-loaded biochars were better fitted to Langmuir (R² = 0.85-1.00) than Freundlich model (R² = 0.58-0.91). Heavy metals could bind with -OH and -COOH on phosphate tailing-loaded biochars, meanwhile generated phosphorus-rich precipitation with PO₃^- and P₂O₇⁴⁺, including Cd₂P₂O₇, Cd(PO₃)₂, Zn (PO₃)₂, Pb (PO₃)₂, Pb₂P₂O₇, Cu(PO₃)₂, and Cu₂P₂O₇. This study proposed an innovative method to produce phosphorus-rich biochars by loading phosphate tailing for highly efficient removal of heavy metals from water bodies, and also realized the resource utilization of phosphate tailing, which was of great significance to reduce environmental pollution.

Insights into the effects of tea pruning litter biochar on major micronutrients (Cu, Mn, and Zn) pathway from soil to tea plant: An environmental armour

A field study was conducted from 0 to 360 days to investigate the effect of tea pruning litter biochar (TPLBC) on the accumulation of major micronutrients (copper: Cu, manganese: Mn, and zinc: Zn) in soil, their uptake by tea plant (clone: S.3 A/3) and level of contamination in soil due to TPLBC. To evaluate the level of contamination due to TPLBC, a soil pollution assessment was carried out using the geo-accumulation index (I_geo), enrichment factor (EF), contamination factor (CF), potential ecological risk factor (PERF), individual contamination factor (ICF), and risk assessment code (RAC). The total content of Cu, Mn, and Zn gradually increased with increasing doses of TPLBC at 0D, and then decreased with time. The fractionation of the three micronutrients in soil changed after the application of TPLBC. The contamination risk assessment of soil for Cu, Mn, and Zn based on the I_geo, EF, CF, PERF,ICF, and RAC suggested that the application of TPLBC does not have any adverse effect on soil. Except for Mn, the bioconcentration and translocation factors were less than one for Cu and Zn. Results from this study revealed that the application of 400 kg TPLBC ha^-1 is significantly better than the other treatments for Cu, Mn, and Zn at a 5% level of significance.

Pros and Cons of Biochar to Soil Potentially Toxic Element Mobilization and Phytoavailability: Environmental Implications

While the potential of biochar (BC) to immobilize potentially toxic elements (PTEs) in contaminated soils has been studied and reviewed, no review has focused on the potential use of BC for enhancing the phytoremediation efficacy of PTE-contaminated soils. Consequently, the overarching purpose in this study is to critically review the effects of BC on the mobilization, phytoextraction, phytostabilization, and bioremediation of PTEs in contaminated soils. Potential mechanisms of the interactions between BC and PTEs in soils are also reviewed in detail. We discuss the promises and challenges of various approaches, including potential environmental implications, of BC application to PTE-contaminated soils. The properties of BC (e.g., surface functional groups, mineral content, ionic content, and π-electrons) govern its impact on the (im)mobilization of PTEs, which is complex and highly element-specific. This review demonstrates the contrary effects of BC on PTE mobilization and highlights possible opportunities for using BC as a mobilizing agent for enhancing phytoremediation of PTEs-contaminated soils.

Lead absorption capacity in different parts of plants and its influencing factors: a systematic review and meta-analysis

People pose a serious risk by plants contaminated with lead in soil. However, the strength of lead enrichment capacity in root, stem, and leaf of the plant is still controversial. Therefore, a meta-analysis was conducted to investigate the ability of lead enrichment of root, stem, and leaf and the main influencing factors for lead absorption. The results of this study indicated that all parts of plant can significantly accumulate lead. Concentrations of lead followed an order of root > stem > leaf. Alkaline soil was conducive to the absorption of lead. When the lead concentration in the soil was higher than 20 mg/kg, the lead absorption in root was more. Lead is absorbed most in trees and least in Gramineae. It is argued that this study is beneficial to select plants suitable for absorption of lead from polluted soil. This study also can help to clarify the influencing factors for lead enrichment in different parts of the plant.

Chemical Fractionations of Lead and Zinc in the Contaminated Soil Amended with the Blended Biochar/Apatite

Heavy metal contamination in agricultural land is an alarming issue in Vietnam. It is necessary to develop suitable remediation methods for environmental and farming purposes. The present study investigated the effectiveness of using peanut shell-derived biochar to remediate the two heavy metals Zn and Pb in laboratory soil assays following Tessier’s sequential extraction procedure. The concentration of heavy metals was analyzed using Inductively coupled plasma mass spectrometry (ICP-MS). This study also compared the effectiveness of the blend of biochar and apatite applied and the mere biochar amendment on the chemical fractions of Pb and Zn in the contaminated agricultural soil. Results have shown that the investigated soil was extremely polluted by Pb (3047.8 mg kg−1) and Zn (2034.3 mg kg−1). In addition, the pH, organic carbon, and electrical conductivity values of amended soil samples increased with the increase in the amendment’s ratios. The distribution of heavy metals in soil samples was in the descending order of carbonate fraction (F2) > residue fraction (F5) > exchangeable fraction (F1) > Fe/Mn oxide fraction (F3) > organic fraction (F4) for Pb and F5 ≈ F2 > F1 > F3 > F4 for Zn. The peanut shell-derived biochar produced at 400 °C and 600 °C amended at a 10% ratio (PB4:10 and PB6:10) could significantly reduce the exchangeable fraction Zn from 424.82 mg kg−1 to 277.69 mg kg−1 and 302.89 mg kg−1, respectively, and Pb from 495.77 mg kg−1 to 234.55 mg kg−1 and 275.15 mg kg−1, respectively, and immobilize them in soil. Amending the biochar and apatite combination increased the soil pH, then produced a highly negative charge on the soil surface and facilitated Pb and Zn adsorption. This study shows that the amendment of biochar and biochar blended with apatite could stabilize Pb and Zn fractions, indicating the potential of these amendments to remediate Pb and Zn in contaminated soil.

In-situ stabilization of potentially toxic elements in two industrial polluted soils ameliorated with rock phosphate-modified biochars

The present study was aimed at determining the efficacy of rock phosphate (RP) 3% loaded in a green coconut shell, chicken manure, and vegetable waste to make green coconut-modified biochar (GMB), chicken manure modified-biochar (CMB), and vegetable waste-modified biochar (VMB) in the fixation of Cr, Pb, Cu, Zn, Ni, and Cd in Sharafi goth and Malir polluted soils. The impact of RP impregnated with organic waste material to produce modified biochars (MBs) on stabilizing PTEs from polluted soils and reducing their uptake by mustard plant has not yet been thoroughly investigated. All modified BCs in 0.5, 1, and 2% doses were used to stabilize Cr, Pb, Cu, Zn, Ni, and Cd in two polluted soils and to reduce their uptake by the mustard plant. The obtained results revealed that the maximum mustard fresh biomass was 17.8% higher with GMB 1% in Sharafi goth polluted soil and 25% higher with VMB 0.5% in Malir polluted soil than in the control treatment. After applying modified BCs, immobilization of Cr, Pb, Cu, Ni, and Cd was observed in both soils and it reduced the uptake of these elements by mustard plants. On the other hand, although Zn mobilization increased by 0.38% for CMB 0.5% and by 5.9% for VMB 0.5% in Sharafi goth polluted soil, as well as by 3.15% for GMB 1%, 6.34% for GMB 2%, and 4.78% for VMB 0.5% in Malir polluted soil, this was due to changes in soil pH and OM. It was found that GMB 1%, CMB 0.5%, and VMB 0.5% have the potential to increase Zn uptake by mustard, while VMB 2% can reduce the element uptake by the plant. Redundancy analysis showed that soil chemical parameters were negatively correlated with PTEs in both soils and reduced their uptake by mustard. The present study revealed that MBs can stabilize PTEs in industrial and wastewater soils polluted with multiple metals and reduce their uptake by plants.

A review of pristine and modified biochar immobilizing typical heavy metals in soil: Applications and challenges

In recent years, the application of biochar in the remediation of heavy metals (HMs) contaminated soil has received tremendous attention globally. We reviewed the latest research on the immobilization of soil HMs by biochar almost in the last 5 years (until 2021). The methods, effects and mechanisms of biochar and modified biochar on the immobilization of typical HMs in soil have been systematically summarized. In general, the HMs contaminating the soil can be categorized into two groups, the oxy-anionic HMs (As and Cr) and the cationic HMs (Pb, Cd, etc.). Reduction and precipitation of oxy-anionic HMs by biochar/modified biochar are the dominant mechanism for reducing HMs toxicity. Pristine biochar can effectively immobilize cationic HMs. The commonly applied modification method is to add substances that can precipitate HMs to the biochar. In addition, we assessed the risks of biochar applications. For instance, biochar may cause the leaching of certain HMs; biochar aging; co-transportation of biochar nanoparticles with HMs. Future work should focus on the artificial/intelligent design of biochar to make it suitable for remediation of multiple HMs contaminated soil.

The efficiency of potato peel biochar for the adsorption and immobilization of heavy metals in contaminated soil

We investigated the potential application of potato peel biochar (PPB) for the adsorption and immobilization of heavy metals (Cd, Pb, and Ni) in contaminated acidic soil. The addition of PPB to the soil, especially at the application rate of 8%, increased soil pH, cation exchange capacity (CEC), and organic carbon (OC). The maximum adsorption capacity of Cd, Pb, and Ni in the soil amended with PPB at the application rate of 8% was 3215.9, 4418.67, and 3508.51 mg kg^-1, respectively. Compared to the control, the addition of 8% PPB to the soil decreased the soluble and exchangeable fraction of Cd, Pb, and Ni to 84.3, 90.6, and 79.1 mg kg^-1, respectively. In contrast, the addition of 8% PPB to the soil increased the organically-bound and residual fractions of metals in the following order: Pb > Cd > Ni, and Cd > Pb > Ni, respectively. The results of this study showed that potato peel biochar has the potential to stabilize and reduce the bioavailability of heavy metals in contaminated acidic soil. Therefore, potato peel biochar can serve as an eco-friendly, low-cost, and efficient adsorbent to immobilization of heavy metals in contaminated acidic soils.NOVELTY STATEMENTEffect of biochar produced from potato peel on the adsorption of the heavy metals in contaminated acidic soil.Immobilization of heavy metals in contaminated acidic soil amended with potato peel biochar.Improving the chemical properties of soil amended with potato peel biochar.

Preparation of ball-milled phosphorus-loaded biochar and its highly effective remediation for Cd- and Pb-contaminated alkaline soil

Pyrolytic biochar is a good material for remediating soils contaminated with heavy metals; however, it exhibits strong alkalinity, which easily causes soil alkalization and fertility reduction. Herein, a series of novel biochar materials (BPBCs) were prepared by combined ball milling and phosphorus (P)-loading. The optimized BPBC were fabricated in the basis of Cd and Pb adsorption capacities of the biochar, with pyrolysis at 700 °C, ball milling for 12 h and the addition of 5% red P (BPBC700). Ball milling could effectively grind pristine biochar into submicron particles and nanoscale P particles could be uniformly loaded on BPBC700. Moreover, the oxidative conversion of red P into phosphorus oxides, phosphoric acid and (hydro)phosphates was promoted due to reactions with the carbonates, alkaline minerals and O-containing functional groups of biochar. These reactions also decreased the biochar and soil pH to nearly neutral by acid-base neutralization. Pot experiments showed that BPBC700 had better effects than the pristine or ball-milled biochar in improving soil properties (e.g., cation exchange capacity and organic carbon), increasing the concentrations of soil nutrients (e.g., N and P), promoting alkaline phosphatase, catalase and urease activities, decreasing soil mobility and plant accumulation of Cd and Pb, and alleviating Cd and Pb stress on maize plants. Thus, BPBC is a promising and ecofriendly amendment to enhance its adsorption ability on Cd and Pb, soil quality and plant productivity in contaminated soil.

Amendments and bioaugmentation enhanced phytoremediation and micro-ecology for PAHs and heavy metals co-contaminated soils

Co-existence of polycyclic aromatic hydrocarbons (PAHs) and multi-metals challenges the decontamination of large-scale contaminated sites. This study aims to comprehensively evaluate the remediation potential of intensified phytoremediation in coping with complex co-contaminated soils. Results showed that the removal of PAHs and heavy metals is time-dependent, pollution-relevant, and plant-specific. Removal of sixteen PAHs by Medicago sativa L. (37.3%) was significantly higher than that of Solanum nigrum L. (20.7%) after 30 days. S. nigrum L. removed higher amounts of Cd than Zn and Pb, while M. sativa L. uptake more Zn. Nevertheless, amendments and microbial agents significantly increased the phytoremediation efficiency of pollutants and shortened the gap between plants. Cd removal and PAHs dissipation reached up to 80% and 90% after 90 days for both plants. Heavy metal stability in soil was promoted after the intensified phytoremediation. Plant lipid peroxidation was alleviated, regulated by changed antioxidant defense systems (superoxide dismutase, peroxidase, catalase). Soil enzyme activities including dehydrogenase, urease, and catalase increased up to 5-fold. Soil bacterial diversity and structure were changed, being largely composed of Proteobacteria, Actinobacteria, Patescibacteria, Bacteroidetes, and Firmicutes. These findings provide a green and sustainable approach to decontaminating complex-polluted environments with comprehensive improvement of soil health.

Characteristics of fungal communities and the sources of mold contamination in mildewed tobacco leaves stored under different climatic conditions

Tobacco mildew is a common postharvest problem caused by fungal growth. It can directly decrease product quality and cause serious economic loss in the tobacco industry. However, the fungal community characteristics of mildewed tobacco leaves and the related influencing factors remain unknown. Here, next-generation sequencing was used to characterize the fungal communities present in mildewed and healthy tobacco leaves stored under three different climatic conditions. Mildewed leaves showed a higher pH and total nitrogen content as well as a lower carbon nitrogen ratio than healthy leaves. Fungal diversity and richness were significantly lower in the mildewed tobacco leaves than in healthy tobacco leaves, with saprophytic fungi such as Xeromyces, Aspergillus, and Wallemia being the dominant molds. Network analysis showed that the complexity, connectivity, and stability of the fungal network were significantly poorer in heavy mildew tobacco leaves than in healthy leaves. NMDS and PERMANOVA analysis showed that the distribution of fungal communities in warehoused tobacco leaves differed significantly across different regions, and temperature and humidity were the key factors affecting these differences. Mildew-causing fungi were significantly enriched in tobacco leaf samples collected in the period between the completion of flue-curing and the start of pre-re-curing. This study demonstrated that mildew is an irreversible process that destroys the balance of the tobacco ecosystem, and that environmental factors play important roles in shaping fungal communities in tobacco leaves.Key points• The diversity and composition of the fungal communities in mildewed tobacco leaves were significantly different from those in healthy tobacco leaves.• Climatic factors may play an important role in shaping fungal communities in tobacco leaves.• Tobacco leaves were most vulnerable to mold contamination between the post-flue-curing and pre-re-curing period.

Chemical fractionation of copper and zinc after addition of carrot pulp biochar and thiourea-modified biochar to a contaminated soil

In this study, there is presented a thorough investigation of the effect of biochar produced via pyrolysis of carrot pulp with pre and post-modification by thiourea (CH₄N₂S) at three rates (0, 4%, and 8%) on fractionation of Cu and Zn in acidic soil. The sequential extraction procedure of BCR was utilized for the determination of heavy metals fractionation. According to the FTIR analysis, the thiourea-modified biochar (TMB) had more surface functional groups in comparison with the carrot pulp biochar (CB). The 8% TMB application, was more effective in increasing the CEC, pH, EC, and SOC of the soil than the 8% CB treatment. The BCR test revealed that after the addition of CB and TMB, the acid extractable Cu and Zn decreased considerably. Thiourea-modified biochar was more effective than pristine biochar in decreasing the acid extractable metals fraction. The addition of TMB induced the conversion of the acid extractable fraction of Cu to residual and organic matter bound fractions, and the acid extractable fraction of Zn to residual, organic matter bound and oxides bound fractions. This work suggests that thiourea-modified biochar can be a low-cost and effective amendment for immobilizing Cu and Zn in contaminated acidic soils.

Effects of biochar on the migration and transformation of metal species in a highly acid soil contaminated with multiple metals and leached with solutions of different pH

A number of recent studies have been conducted on soil metal immobilization by biochars but there is little information on the migration and transformation of metal species in soils contaminated with multiple metals as affected by biochar and acid rain. Here, a column study investigated the effects of biochar derived from maize straw pyrolyzed at 600 °C on metal (Cu, Pb, Zn and Cd) mobility in a highly acid soil during leaching with simulated acid rain. All four metals examined were released at early stages of the leaching process and the percentages of the metals leached followed the sequence Zn > Cd > Cu > Pb. Acid rain with high acidity resulted in larger amounts of metals leached, particularly at the later stages of leaching. This enhancement of leaching by highly acidic leaching solutions was eliminated by amendment with biochar. However, the effects of biochar on metal mobility depended on metal species, with significant immobilization of soil Cu, Zn and Pb (>90%, 26% and 72%, respectively) but with no effect on soil Cd. Overall, simulated acid rain enhanced soil metal mobility and biochar reduced soil metal mobility and also alleviated the effects of acid rain. More emphasis is needed on metal speciation in the use of biochars for soil metal immobilization in areas with acid rain. The use of biochars in phytoremediation may decrease the toxicity of soil metals to the hyperaccumulator plant.

Towards a Soil Remediation Strategy Using Biochar: Effects on Soil Chemical Properties and Bioavailability of Potentially Toxic Elements

Soil contamination with potentially toxic elements (PTEs) is considered one of the most severe environmental threats, while among remediation strategies, research on the application of soil amendments has received important consideration. This review highlights the effects of biochar application on soil properties and the bioavailability of potentially toxic elements describing research areas of intense current and emerging activity. Using a visual scientometric analysis, our study shows that between 2019 and 2020, research sub-fields like earthworm activities and responses, greenhouse gass emissions, and low molecular weight organic acids have gained most of the attention when biochar was investigated for soil remediation purposes. Moreover, biomasses like rice straw, sewage sludge, and sawdust were found to be the most commonly used feedstocks for biochar production. The effect of biochar on soil chemistry and different mechanisms responsible for PTEs' immobilization with biochar, are also briefly reported. Special attention is also given to specific PTEs most commonly found at contaminated soils, including Cu, Zn, Ni, Cr, Pb, Cd, and As, and therefore are more extensively revised in this paper. This review also addresses some of the issues in developing innovative methodologies for engineered biochars, introduced alongside some suggestions which intend to form a more focused soil remediation strategy.

Interactive assessment of lignite and bamboo-biochar for geochemical speciation, modulation and uptake of Cu and other heavy metals in the copper mine tailing

This study was designed to examine the combined effect of bamboo-biochar (BC) and water-washed lignite (LGT) at copper mine tailings (CuMT) sites on the concentration of Cu and other metals in pore water (PW), their bioavailability, and change in geochemical speciation. Rapeseed (first cropping-season) and wheat (second cropping-season) were grown for 40-days each and the influence of applied-amendments on both cropping seasons was observed and compared. A significant increase in pH, water holding capacity (WHC), and soil organic carbon (SOC) was observed after the applied amendments in second cropping-seasons. The BC-LGT significantly reduced the concentration of Cu in PW after second cropping seasons; however, the concentration of Pb and Zn were increased with the individual application of biochar and LGT, respectively. BC-LGT and BC-2% significantly reduced the bioavailability of Cu and other HMs in both cropping seasons. The treated-CuMT was subjected to spectroscopic investigation through X-ray photoelectron spectroscopy (XPS), Fourier transform Infrared spectroscopy (FTIR), and X-ray powder diffraction (XRD). The results showed that Cu sorption mainly involved the coordination with hydroxyl and carboxyl functional groups, as well as the co-precipitation or complexation on mineral surfaces, which vary with the applied amendment and bulk amount of Mg, Mn, and Fe released during sorption-process. The co-application of BC-LGT exerted significant effectiveness in immobilizing Cu and other HMs in CuMT. The outcomes of the study indicated that co-application of BC-LGT is an efficacious combination of organic and inorganic materials for Cu adsorption which may provide some new information for the sustainable remediation of copper mine tailing.

Controlling Factors and Prediction of Lead Uptake and Accumulation in Various Soil-Pepper Systems

Lead (Pb) is a typical toxic heavy metal element in soils and plants, which has a potential threat to human health through the food chain. Uptake of Pb in the soil-vegetable system has attracted broad attention, whereas reports on the main controlling factors of Pb uptake and accumulation in different soil-vegetable systems are limited. The effect of soil properties on Pb uptake and accumulation in pepper (Capsicum annuum L.) was studied by a pot experiment with 16 typical soils in China. The results showed that the Pb bioavailability was lower in alkaline soils, and that soil cation exchange capacity (CEC), CaCO₃ , and total phosphorus contents might influence the uptake and transfer of Pb by peppers. Soil pH and CEC were the most significant factors affecting Pb accumulation in pepper fruits. Soil pH was negatively correlated with Pb uptake and accumulation due to its influence on Pb mobility and bioavailability. The accumulation of Pb decreased as soil CEC increased, which might inhibit the absorption and transfer of Pb in peppers. The multiple linear regression function based on soil Pb content, pH, and CEC could provide enough information for a good prediction of the accumulation of Pb in soil-pepper systems (R²  = 0.733). The results are in favor of developing a Pb threshold for vegetables in agricultural soils in China, thus improving the food safety of crops. Environ Toxicol Chem 2021;40:1443-1451. © 2021 SETAC.

Facile preparation of sulfonated biochar for highly efficient removal of toxic Pb(II) and Cd(II) from wastewater

Biochar is deemed as the ideal material for the effective removal of heavy metals in wastewater treatment. Herein, we developed a facile one-step solvothermal method for the preparation of sulfonated biochar (SBC) from Axonopus compressus under a low-temperature condition. FTIR and XPS analysis demonstrate that plenty of -OH, -COOH and -SO₃H moieties are generated on the surface of SBC during the sulfonation process. Due to high electronegativity and strong complexation of these moieties, SBC can rapidly adsorb Pb(II) and Cd(II) with capacities of 191.07 and 85.76 mg/g respectively within 5 min. SBC can be reused for 5 cycles with a negligible loss of adsorption capacity. In addition, different biomass-based biochars are prepared under the identical experimental conditions, and they are successfully applied in the treatments of Pb(II) and Cd(II). The satisfying results indicate that one-step low-temperature sulfonation could be a universal method, and various types of biomass waste could be the abundant, effective, economical material source for the treatment of environmental heavy metal pollution in future.

Biochar Aging: Mechanisms, Physicochemical Changes, Assessment, And Implications for Field Applications

Biochar has triggered a black gold rush in environmental studies as a carbon-rich material with well-developed porous structure and tunable functionality. While much attention has been placed on its apparent ability to store carbon in the ground, immobilize soil pollutants, and improve soil fertility, its temporally evolving in situ performance in these roles must not be overlooked. After field application, various environmental factors, such as temperature variations, precipitation events and microbial activities, can lead to its fragmentation, dissolution, and oxidation, thus causing drastic changes to the physicochemical properties. Direct monitoring of biochar-amended soils can provide good evidence of its temporal evolution, but this requires long-term field trials. Various artificial aging methods, such as chemical oxidation, wet-dry cycling and mineral modification, have therefore been designed to mimic natural aging mechanisms. Here we evaluate the science of biochar aging, critically summarize aging-induced changes to biochar properties, and offer a state-of-the-art for artificial aging simulation approaches. In addition, the implications of biochar aging are also considered regarding its potential development and deployment as a soil amendment. We suggest that for improved simulation and prediction, artificial aging methods must shift from qualitative to quantitative approaches. Furthermore, artificial preaging may serve to synthesize engineered biochars for green and sustainable environmental applications.

Bamboo-biochar and hydrothermally treated-coal mediated geochemical speciation, transformation and uptake of Cd, Cr, and Pb in a polymetal(iod)s-contaminated mine soil

In this study, polymetal(iod)s-contaminated mining soil from the Huainan coalfield, Anhui, China, was used to investigate the synergistic effects of biochar (BC), raw coal (RC), and hydrothermally treated coal (HTC) on the immobilization, speciation, transformation, and accumulation of Cd, Cr, and Pb in a soil-plant system via geochemical speciation and advanced spectroscopic approaches. The results revealed that the BC-2% and BC-HTC amendments were more effective than the individual RC, and/or HTC amendments to reduce ethylene-diamine-tetraacetic acid (EDTA)-extractable Cd, Cr, and Pb concentrations by elevating soil pH and soil organic carbon content. Soil pH increased by 1.5 and 2.5 units after BC-2% and BC-HTC amendments, respectively, which reduced EDTA-extractable Cd, Cr, and Pb to more stabilized forms. Metal speciation and X-ray photoelectron spectroscopy analyses suggested that the BC-HTC amendment stimulated the transformation of reactive Cd, Cr, and Pb (exchangeable and carbonate-bound) states to less reachable (oxide and residual) states to decrease the toxicity of these heavy metals. Fourier transform infrared spectroscopy and X-ray diffraction analyses suggested that reduction and adsorption by soil colloids may be involved in the mechanism of Cd(II), Cr(VI), and Pb(II) immobilization via hydroxyl, carbonyl, carboxyl, and amide groups in the BC and HTC. Additionally, the BC-2% and BC-HTC amendments reduced Cd and Pb accumulation in maize shoots, which could mainly be ascribed to the reduction of EDTA-extractable heavy metals in the soil and more functional groups in the roots, thus inhibiting metal ion translocation by providing the electrons necessary for immobilization, compared to those in roots grown in the unamended soil. Therefore, the combined application of BC and HTC was more effective than the individual application of these amendments to minimize the leaching, availability, and exchangeable states of Cd, Cr, and Pb in polymetal(iod)s-contaminated mining soil and accumulation in maize.

Evaluation of Different Types and Amounts of Amendments on Soil Cd Immobilization and its Uptake to Wheat

Using amendments is a cost-effective method to soil cadmium (Cd) remediation, whereas knowledge about how different amendments and rates affect remediation efficiency remains limited. This study aimed to evaluate the impacts of different types and amounts of amendments on soil Cd immobilization and its uptake by plants. Biochar (BC), zeolite (ZE), humic acid (HA), superphosphate (SP), lime (L), and sodium sulfide (SS) were applied at three rates (low, medium, and high) ranging from 0.5 to 5%. The concentration of CaCl₂-extractable Cd was considerably affected by the amendments, except HA, and the high doses achieved better immobilization effects than the low doses did. The addition of amendments decreased weak acid soluble Cd by 4.1-44.0% but slightly increased the fractions of oxidizable and residual Cd. These amendments (except BC and HA dose of 1%) decreased Cd accumulation in grains by 1.3-68.8% and (except SP) in roots by 16.3-65.5% compared with the control. The SP efficiently immobilized Cd but posed a potential soil acidification risk. Moreover, SS treatment increased the soil electrical conductivity (EC) value and restricted the growth of wheat, possibly due to high-salt stress. BC, ZE, and L exerted significant effects on the reduction in available Cd as the application rate increased. These amendments enhanced Cd immobilization mainly by changing Cd availability in soil and influencing its redistribution in different fractions in soil and root uptake by plants. This study concluded that BC-5%, ZE-1%, and L-0.5% can be used for Cd immobilization in acidic or neutral soils.

Residual effects of tobacco biochar along with different fixing agents on stabilization of trace elements in multi-metal contaminated soils

The residual effect of tobacco biochar (TB ≥ 500°C) mono and co-application with Ca-hydroxide (CH), Ca-bentonite (CB) and natural zeolite (NZ) on the bio-availability of trace elements TE(s) in alkaline soils has not been deeply studied yet. A pot study that had earlier been investigated TB mono and blended with CH, CB and NZ on the immobilization of Pb, Cu Cd, and Zn by Chinese cabbage. Maize crop in the rotation was selected as test plant to assess the residual impact of amendments on stabilization of Pb, Cu Cd, and Zn in mine polluted (M-P), smelter heavily and low polluted (S-HP and S-LP, respectively) soils. The obtained results showed that stabilization of Pb, Cd, Cu and Zn reached 63.84% with TB + CB, 61.19% with TB + CH, 83.31% with TB + CH and 35.27% with TB + CH for M-P soil, 36.46% with TB + NZ, 38.46% with TB + NZ, 19.40% with TB + CH and 62.43% with TB + CH for S-LP soil, 52.94% TB + NZ, 57.65% with TB + NZ, 52.94% with TB + NZ, and 28.44% with TB + CH for S-LP soil. Conversely, TB + CH and TB alone had mobilized Pb and Zn up to 19.29% and 34.96% in M-P soil. The mobility of Zn reached 8.38% with TB + CB and 66.03% with TB for S-HP and S-LP soils. The uptake and accumulation of Pb, Cd, Cu and Zn in shoot and root were reduced in three polluted soils. Overall, the combination of TB along with CH, CB and NZ has been proven to be effective in Pb, Cd, Cu and Zn polluted mine/smelter soils restoration.

Effect of thiourea-modified biochar on adsorption and fractionation of cadmium and lead in contaminated acidic soil

Biochar was obtained through pyrolysis of carrot pulp (CP) and then further modified with thiourea (CH₄N₂S). We investigated the effect of carrot pulp biochar (CPB) and modified CPB (MCPB) for adsorption and chemical fractionation of cadmium (Cd) and lead (Pb) in contaminated acidic soil. Application of modified biochar significantly (p < 0.05) increased the pH, soil organic carbon (SOC), and cation exchange capacity (CEC) of the soil, especially at the 8% application rate. The adsorption equilibrium data showed that the adsorption behavior of Cd and Pb could be described more reasonably by the pseudo-second-order kinetic model and the Langmuir isotherm model more accurately fitted the experimental data than Freundlich and Temkin isotherm models. The maximum adsorption capacity of soil treated with MCPB at the 8% application rate for Cd and Pb were 4122.7 and 5219.6 mg kg^-1, respectively. Sequential chemical extractions revealed that incorporation soil with MCPB induced the transformation of the acid-soluble fraction of Cd to oxidizable and residual fractions, and the acid-soluble fraction of Pb to reducible, oxidizable, and residual fractions. The results demonstrated that the application of MCPB could effectively immobilize Cd and Pb, thereby reducing their mobility in contaminated acidic soil.

The adsorption, regeneration and engineering applications of biochar for removal organic pollutants: A review

In recent years, with the continuous development of industry and agriculture, the content of organic pollutants in the environment has been increasing, which has caused serious pollution to the environment. Adsorption has proven to be an effective and economically viable method of removing organic contaminants. Since biochar has many advantages such as various types of raw materials, low cost, and recyclability, it can achieve the effect of turning waste into treasure when used for environmental treatment. This paper summarizes the source and production of biochar, points out its research status in the removal of organic pollutants, expounds its adsorption mechanism on organic pollutants, introduces the relevant adsorption parameters, summarizes its regeneration methods, studies its application of engineering, and finally analyses of benefits and describes the development prospects.

Comparison of the lead and copper adsorption capacities of plant source materials and their biochars

Lead (Pb) and Cu are the most common pollutants found in industrial effluents which affect ecosystem and human health. To remove Pb and Cu from aquatic system, cost-effective and environmentally friendly adsorbents are required. Therefore, the study evaluated the adsorption of Pb and Cu by waste plant materials and their biochars. The adsorption kinetics and isotherms were applied to compare the Pb and Cu adsorption capacities using the gingko (Spiraea blumei) leaf (GL), peanut shell (PS), and Metasequoia leaf (ML), and their derived biochars (GB, PB, and MB, respectively). The GB showed a significantly higher Pb adsorption capacity than the other adsorbents. Maximum Pb adsorption by GB was 138.9 mg/g followed by GL (117.6 mg/g). The highest Cu adsorption (59.9 mg/g) was also achieved by GB followed by GL (57.8 mg/g). The carbonates and the phosphate functional groups in the GB and higher affinity of Pb to the functional groups contributed to higher Pb adsorption. The Pb adsorption kinetics on the plant source materials and their biochars followed a pseudo-second order model. The Pb and Cu adsorption capacities, with the exception of the GL, ML, and GB, are better explained by Langmuir-isotherm models. The carbonization did not always lead to better heavy metal adsorption. The Pb and Cu adsorption significantly reduced with carbonization of ML because of disappearance of oxygen containing functional groups. Therefore, appropriate method to prepare metal adsorbent should be selected depending on feedstocks and metal removal mechanisms. The GL is the most-abundant fallen leaf in the streets of the Republic of Korea; therefore, the use of the GL biochar for heavy-metal adsorption will also reduce the cost for waste disposal.