Mitigation of arsenic accumulation in arugula (Eruca sativa Mill.) using Fe/Al/Zn impregnated biochar composites

Predicting the efficiency of arsenic immobilization in soils by biochar using machine learning

Arsenic (As) pollution in soils is a pervasive environmental issue. Biochar immobilization offers a promising solution for addressing soil As contamination. The efficiency of biochar in immobilizing As in soils primarily hinges on the characteristics of both the soil and the biochar. However, the influence of a specific property on As immobilization varies among different studies, and the development and application of arsenic passivation materials based on biochar often rely on empirical knowledge. To enhance immobilization efficiency and reduce labor and time costs, a machine learning (ML) model was employed to predict As immobilization efficiency before biochar application. In this study, we collected a dataset comprising 182 data points on As immobilization efficiency from 17 publications to construct three ML models. The results demonstrated that the random forest (RF) model outperformed gradient boost regression tree and support vector regression models in predictive performance. Relative importance analysis and partial dependence plots based on the RF model were conducted to identify the most crucial factors influencing As immobilization. These findings highlighted the significant roles of biochar application time and biochar pH in As immobilization efficiency in soils. Furthermore, the study revealed that Fe-modified biochar exhibited a substantial improvement in As immobilization. These insights can facilitate targeted biochar property design and optimization of biochar application conditions to enhance As immobilization efficiency.

Rapid immobilization of arsenic in contaminated soils by microwave irradiation combined with magnetic biochar: Microwave-induced electron transfer for oxidation and immobilization of arsenic (III)

Biochar with adjustable redox activity is an effective strategy for immobilization of excess arsenic (As(III)) contaminated soil. However, biochar exhibits limitations in terms of electron transfer efficiency and immobilization efficiency due to insufficient activation energy. In this study, As(III) in the soil was rapidly immobilized by adding magnetic biochar (Fe-BC) and introducing microwave irradiation energy to enhance electron transport efficiency. The results showed that the pore structure and iron species (ZVI, Fe3O4) loaded onto the biochar could be modulated by controlling the temperature and time of microwave pyrolysis, which enhanced the microwave absorption capacity and the immobilization performance of As. After adding Fe-BC (10 wt%) and treating with microwave irradiation for 3 h, the content of As(III) in the soil was reduced to 54.56 %. Compared with the conventional heating treatment, the percentage of stabilized As (residual form) increased by 11.21 %. The localized hot spots formed through the absorption of microwave energy by biochar promote the formation of arsenic-containing mineral crystals (FeAsO4 and Fe3AsO7), thus enhancing the immobilization efficiency. In addition, microwave-induced electron transfer facilitated the oxidation of As(III) to As(V) by surface quinone and carbonyl groups on the Fe-BC. Density functional theory calculation further proved that the surface groups of the Fe-BC had a stronger electron-withdrawing ability under microwave irradiation, thereby promoting the adsorption and immobilization of As(III). This work provided a new perspective on the technology of rapid remediation of heavy metals contaminated soil using biochar.

Insight into the mechanism of nano-TiO2-doped biochar in mitigating cadmium mobility in soil-pak choi system

Soil cadmium (Cd) pollution poses severe threats to food security and human health. Previous studies have reported that both nanoparticles (NPs) and biochar have potential for soil Cd remediation. In this study, a composite material (BN) was synthesized using low-dose TiO2 NPs and silkworm excrement-based biochar, and the mechanism of its effect on the Cd-contaminated soil-pak choi system was investigated. The application of 0.5 % BN to the soil effectively reduced 24.8 % of diethylenetriaminepentaacetic acid (DTPA) Cd in the soil and promoted the conversion of Cd from leaching and HOAc-extractive to reducible forms. BN could improve the adsorption capacity of soil for Cd by promoting the formation of humic acid (HA) and increasing the cation exchange capacity (CEC), as well as activating the oxygen-containing functional groups such as CO and CO. BN also increased soil urease and catalase activities and improved the synergistic network among soil bacterial communities to promote soil microbial carbon (C) and nitrogen (N) cycling, thus enhancing Cd passivation. Moreover, BN increased soil biological activity-associated metabolites like T-2 Triol and altered lipid metabolism-related fatty acids, especially hexadecanoic acid and dodecanoic acid, crucial for bacterial Cd tolerance. In addition, BN inhibited Cd uptake and root-to-shoot translocation in pak choi, which ultimately decreased Cd accumulation in shoots by 51.0 %. BN significantly increased the phosphorus (P) uptake in shoots by 59.4 % by improving the soil microbial P cycling. This may serve as a beneficial strategy for pak choi to counteract Cd toxicity. These findings provide new insights into nanomaterial-doped biochar for remediation of heavy metal contamination in soil-plant systems.

Metal oxide modified biochars for fertile soil management: Effects on soil phosphorus transformation, enzyme activity, microbe community, and plant growth

Metal oxide modified biochars are increasingly being used for intensive agricultural soil remediation, but there has been limited research on their effects on soil phosphorus transformation, soil enzyme activity, microbe community and plant growth. Two highly-performance metal oxides biochars (FeAl-biochar and MgAl-biochar) were investigated for their effects on soil phosphorus availability, fractions, enzyme activity, microbe community and plant growth in two typical intensive fertile agricultural soils. Adding raw biochar to acidic soil increased NH4Cl-P content, while metal oxide biochar reduced NH4Cl-P content by binding to phosphorus. Original biochar slightly reduced Al-P content in lateritic red soil, while metal oxide biochar increased it. LBC and FBC significantly reduced Ca2-P and Ca8-P properties while improving Al-P and Fe-P, respectively. Inorganic phosphorus-solubilizing bacteria increased in abundance with biochar amendment in both soil types, and biochar addition affected soil pH and phosphorus fractions, leading to changes in bacterial growth and community structure. Biochar's microporous structure allowed it to adsorb phosphorus and aluminum ions, making them more available for plants and reducing leaching. In calcareous soils, biochar additions may dominantly increase the Ca (hydro)oxides bounded P or soluble P instead of Fe-P or Al-P through biotic pathways, favoring plant growth. The recommendations for using metal oxides biochar for fertile soil management include using LBC biochar for optimal performance in both P leaching reduction and plant growth promotion, with the mechanisms differing depending on soil type. This research highlights the potential of metal oxide modified biochars for improving soil fertility and reducing phosphorus leaching, with specific recommendations for their use in different soil types.

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.

Remediation of cadmium or arsenic contaminated water and soil by modified biochar: A review

Biochar has a high specific surface area with abundant pore structure and functional groups, which has been widely used in remediation of cadmium or arsenic contaminated water and soil. However, the bottleneck problem of low-efficiency of pristine biochar in remediation of contaminated environments always occurs. Nowadays, the modification of biochar is a feasible way to enhance the performance of biochar. Based on the Web of science™, the research progress of modified biochar and its application in remediation of cadmium or arsenic contaminated water and soil have been systematically summarized in this paper. The main modification strategies of biochar were summarized, and the variation of physicochemical properties of biochar before and after modification were illustrated. The efficiency and key mechanisms of modified biochar for remediation of cadmium or arsenic contaminated water and soil were expounded in detail. Finally, some constructive suggestions were given for the future direction and challenges of modified biochar research.

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

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

Effects of Combined Applications of Biogas Slurry and Biochar on Phosphorus Leaching and Fractionations in Lateritic Soil

Diverse soil phosphorus (P)-leaching phenomena induced by environmental disturbance have gained increasing attention. Two kinds of typical organic materials, biochar and biogas slurry, (BS) are widely utilized to amend agricultural soil, but there is little research that gives insight into their co-effects on soil P-leaching and corresponding mechanisms. Herein, a total of six treatments (viz., control, 2% (w/w) biochar, low ratio BS with or without 2% (w/w) biochar, high ratio BS with or without 2% (w/w) biochar) were conducted to investigate the P-leaching and fraction transformation mechanisms. The column experiment results showed that compared to control, sole BS application or biochar both can slightly enhance the soil-P loss by 134.8% and 39.8%. High ratios of BS induced higher P loss than the low ratios of BS by 125.1%. In comparison with the sole BS treatment, combined BS and biochar application increase P loss but result in less soil leaching of basic cations. The incubation experiment results showed that the enhanced P-leaching in combined BS and biochar treatment is probably attributable to the enhanced soil pH, decreased DPS, soil P adsorption capacity, and transformation of moderately labile Fe–P into labile P. This research helps in understanding the abiotic process of biochar and BS in promoting soil P-leaching and soil-P management using biochar and biogas slurry.

Pre-magnetic bamboo biochar cross-linked CaMgAl layered double-hydroxide composite: High-efficiency removal of As(III) and Cd(II) from aqueous solutions and insight into the mechanism of simultaneous purification

Trivalent arsenic (As(III)) and divalent cadmium (Cd(II)) contamination in water environment is an urgent issue because of their most toxic physicochemical properties. Herein, the simultaneous purification of As(III) and Cd(II) from aqueous solution was achieved by use of a pre-magnetic Fe modified bamboo biochar that cross-linked CaMgAl layered double-hydroxide composite (Fe-BC@LDH). In a binary system, adsorption equilibrium of As(III) and Cd(II) onto specific sorbent Fe-BC@LDH was reached within 100 and 10 min of contact time under anaerobic conditions, respectively, and the maximum adsorption capacities of As(III) and Cd(II) by Fe-BC@LDH were respectively calculated to be ⁓265.3 and ⁓320.7 mg/g at pH 4.5 and 5- and 14-times than that of unmodified biochar. Moreover, adsorption in a competitive or single system, the sorbent displayed a greater preference for Cd(II). Importantly, the removal of As(III) and Cd(II) onto the composite was more favorable in a binary system due to formation of ternary FeOCdAs bonding configuration as well as the redox transformation of As(III) to As(V), inner-sphere complexation of MOAs/Cd (MFe, Ca, Mg, Al), electrostatic attraction, and co-precipitation of scorodite and hydroxy‑iron‑cadmium. Furthermore, the nanocomposite was still highly efficient after 5 adsorption cycles. This study demonstrated that the synthesized cost-effective Fe-BC@LDH is a promising candidate for the simultaneous separation of As(III) and Cd(II) from wastewater.

Immobilization of hexavalent chromium in contaminated soil by nano-sized layered double hydroxide intercalated with diethyldithiocarbamate: Fraction distribution, plant growth, and microbial evolution

Soil contamination by hexavalent chromium (Cr(VI)) poses great risks to human health and ecosystem safety. We introduced a new cheap and efficient layered double hydroxide intercalated with diethyldithiocarbamate (DDTC-LDH) for in-situ remediation of Cr(VI)-contaminated soil. The content of Cr(VI) in contaminated soil (134.26 mg kg^-1) was rapidly reduced to 1.39 mg kg^-1 within 10 days by 0.5% of DDTC-LDH. This result attains to or even exceeds the effectiveness of most of reported soil amendments for Cr(VI) removal in soils. The production cost of DDTC-LDH ($4.02 kg^-1) was relatively low than some common materials, such as nano zero-valent iron ($22.80-140.84 kg^-1). The growth of water spinach became better with the increase of DDTC-LDH dose from 0% to 0.5%, suggesting the recovery of soil function. DDTC-LDH significantly altered the structure and function of soil microbial communities. The species that have Cr(VI)-resistant or Cr(VI)-reductive ability were enriched in DDTC-LDH remediated soils. Network analysis revealed a significant functional niche differentiation of soil microbial communities. In addition to the enhancement of Cr(VI) reduction, the stimulation of plant growth promoting traits, including siderophore biosynthesis, oxidation resistance to reactive oxygen species, and phosphorus availability by DDTC-LDH was another essential mechanism for the immediate remediation of Cr(VI)-contaminated soil.

Environmental Life Cycle Assessments of Chicken Manure Compost Using Tobacco Residue, Mushroom Bran, and Biochar as Additives

As an environmental management method, the (life cycle assessment) LCA method can be used to compare the differences between various waste treatment processes in order to provide an environmentally friendly and economically feasible method for waste management. This study focused on the reutilization of typical organic waste to produce organic fertilizer in southwest China and used the life cycle assessment method to evaluate three aerobic chicken manure composting scenarios modified with three additives (biochar, mushroom bran, and tobacco residue) from an environmental and economic perspective. The results show that the total environmental loads of the optimized treatments using mushroom bran and biochar mixed with mushroom bran as additives were reduced by 30.0% and 35.1%, respectively, compared to the control treatment (viz. chicken manure composted with tobacco residue). Compared to the control treatment, the optimized composting treatment modified by mushroom bran with and without biochar improved the profit by 23.9% and 35.4%, respectively. This work reflected that the combined composting mode of chicken manure, tobacco residue, mushroom bran, and biochar is an environmentally friendly and economically feasible composting process, which is more suitable for the resource utilization of the typical organic waste in southwest China.

Synergistic effects of ball-milled biochar-supported exfoliated LDHs on phosphate adsorption: Insights into role of fine biochar support

Although biochar supports were widely adopted to fabricate the biochar (BC) supported layered double hydroxides (LDHs) composites (LDH-BC) for efficient environmental remediation, few studies focus on the important role of biochar support in alleviating the stacking of LDHs and enhancing LDH-BC's performance. Through the analysis of the material structure-performance relationship, the "support effect" of fine biochar prepared by ball milling was carefully explored. Compared with the original LDHs on LDH-BC, the LDHs on ball milled biochar (LDH-BMBC) had smaller particle size (from 1123 nm to 586 nm), crystallite size (from 20.5 nm to 6.56 nm), more abundant O-containing functional groups, and larger surface area (370 m² g^-1) and porous structure. The Langmuir model revealed that the maximum theoretical phosphate adsorption capacity of LDH-BMBC (56.2 mg P g^-1) was significantly higher than that of LDH-BC (27.6 mg P g^-1). The leaching experiment proved that the addition of LDH-BMBC in calcareous soil could significantly reduce the release of soil total phosphate (46.1%) and molybdate reactive phosphate (40.4%), even though pristine BC and BMBC significantly enhanced the soil phosphate leaching. This work fabricated high-performance and eco-friendly LDH-BMBC for phosphate adsorption in solution and phosphate retention in soil and also provide valuable insights into fine biochar support effect on LDHs exfoliation, extending the practical use of the engineered ball milled biochars in environment remediation.

Activated low-grade phosphate rocks for simultaneously reducing the phosphorus loss and cadmium uptake by rice in paddy soil

Cadmium (Cd) pollution and phosphorus (P) leaching in paddy soils has raised the global concern. In this study, two kinds of the low grade phosphate rocks activated by the sodium lignosulfonate (SL) and humic acid (HA) were fabricated for soil Cd passivation and reduction of the soil P leaching simultaneously. The mechanisms of the Cd adsorption and passivation by the activated phosphate rocks (APRs) were investigated through the batch experiment and the indoor culture test (i.e., incubation and pot experiments) in the Cd-polluted paddy soil. The effects of the APRs on the potted rice growth, uptake of Cd by rice and P loss were also studied. In comparison with the superphosphate treatment, the cumulative P loss from SL- and HA-APRs were reduced by the 65.2% and 65.3%. In terms of the Cd passivation, the Cd adsorbed on the APRs was through the chemical ways (i.e., ligand exchange and the formation of internal complexes). The application of the APRs significantly decreased the soil exchangeable Cd by 48.9%-55.0%, while the Fe/Mn oxides-bound Cd and residual Cd increased significantly by 19.6%-20.3% and 50.7%-69.4%, respectively. Pot experiment also suggested that both the APRs treatments (SL- and HA-APRs) significantly diminished soil Cd accumulation in rice (by 72.7% and 62.8%) coupling with the significantly decreased P leaching. These results provide a sustainable way to explore a novel cost-effective, high-efficient and bi-functional mineral-based soil amendments for environmental remediation.