The effect of two different biochars on remediation of Cd-contaminated soil and Cd uptake by Lolium perenne

Remediation of cadmium contaminated soil using K2FeO4 modified vinasse biochar

The remediation of cadmium (Cd) contaminated soil is challenging for agricultural practices. In this study, a novel vinasse biochar modified by potassium ferrate (K₂FeO₄) was synthesized to immobilize Cd in agricultural soil. Three biochars [i.e., vinasse biochar (BC), KMnO₄ modified vinasse biochar (MnBC), and K₂FeO₄ modified vinasse biochar (FeBC)] were applied to compare their efficiencies of Cd immobilization. The results showed that the orders of pH, ash content, and functional groups in different biochar were the same following BC < MnBC < FeBC. Scanning electron microscope images showed that the FeBC has more micropores than MnBC and BC. X-ray diffraction identified manganese oxides and iron oxides within MnBC and FeBC, indicating that Mn and Fe were well loaded on the biochar. In the soil-based pot experiment, both MnBC and FeBC significantly reduced soil available Cd by 23-38% and 36-45% compared with the control, respectively (p < 0.05). In addition, the application of BC, MnBC, and FeBC significantly increased the yield, chlorophyll, and vitamin C of Chinese cabbage (p < 0.05), and decreased its Cd uptake compared with the control. Notably, shoot Cd significantly reduced when 2% FeBC was applied (p < 0.05). Overall, using K₂FeO₄ to modify vinasse biochar enriched the surface functional groups and minerals as well as reduced Cd availability in soil and its uptake by the plant. Our study showed that K₂FeO₄ modified vinasse biochar could be used as an ideal amendment for the remediation of Cd-contaminated soil.

Comparative efficacy of Parthenium hysterophorus (L.) derived biochar and iron doped zinc oxide nanoparticle on heavy metals (HMs) mobility and its uptake by Triticum aestivum (L.) in chromite mining contaminated soils

In this study we investigated the efficacy of a novel material parthenium weed (Parthenium hysterophorus L.) biochar (PBC), iron doped zinc oxide nanoparticles (nFe-ZnO), and biochar modified with nFe-ZnO (Fe-ZnO@BC) to adsorb heavy metals (HMs) and reduce their uptake by wheat (Triticum aestivum L.) in a highly chromite mining contaminated soil. The co-application of the applied soil conditioners exhibited a positive effect on the immobilization and restricted the HMs uptake below their threshold levels in shoot content of wheat. The maximum adsorption capacity was because of large surface area, cation exchange capacity, surface precipitation, and complexation of the soil conditioners. The scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) showed porous smooth structure of parthenium weed derived biochar that helped in HMs adsorption, increase the efficiency of soil fertilizers and nutrients retention which help in the enhancement soil condition. Under different application rates the highest translocation factor (TFHMs) was obtained at 2 g nFe-ZnO rate followed the descending order: Mn > Cr > Cu > Ni > Pb. The overall TFHMs was found <1.0 indicating that low content of HMs accumulation in roots from soil slight transferred to shoot, thus satisfying the remediation requirements.

Using organo-mineral complex material to prevent the migration of soil Cd and As into crops: An agricultural practice and chemical mechanism study

The migration and transformations of Cd and As in soil are different, so it is difficult to simultaneously control them. In this study, an organo-mineral complex (OMC) material was prepared using modified palygorskite and chicken manure, the Cd and As adsorption capacities and mechanism of the OMC were explored, and the response of the crop to the OMC was clarified. The results show that the maximum Cd and As adsorption capacities of the OMC under pH values of 6-8 are 12.19 mg·g^-1 and 5.07 mg·g^-1, respectively. In the OMC system, the modified palygorskite contributed more to the adsorption of the heavy metals than the organic matter. Cd²⁺ may form CdCO₃ and CdFe₂O₄, and AsO₂^- may form FeAsO₄, As₂O₃, and As₂O₅ on the surfaces of the modified palygorskite. Organic functional groups such as hydroxyl, imino, and benzaldehyde groups can participate in the adsorption of Cd and As. The Fe species and carbon vacancy in the OMC system promote the conversion of As³⁺ into As⁵⁺. A laboratory experiment was conducted to compare five commercial remediation agents with OMC. Planting Brassica campestris in the OMC remediated soil with excessive contamination increased the crop biomass and decreased the Cd and As accumulation sufficiently to meet the current national food safety standards. This study emphasizes the effectiveness of OMC in preventing the migration of Cd and As into crops while promoting crop growth, which can provide a feasible soil management strategy for CdAs co-contaminated farmland soil.

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.

Immobilization of Cd and Pb in soil facilitated by magnetic biochar: metal speciation and microbial community evolution

The preparation of magnetic biochar from sewage sludge and rice straw for heavy metal contaminated soil remediation has greater application prospects, but its remediation mechanism was rarely considered by combining soil physicochemical properties with microbial community. In this study, the effects of magnetic sewage sludge biochar (SSB) and rice straw biochar (RSB) on Cd and Pb immobilization in paddy soil were compared and analyzed by 60-day soil incubation experiments. The results illustrated that DTPA-Cd and DTPA-Pb were reduced by 51.53% (43.07%) and 53.57% (50.47%), while the percentage of residual fraction of the BCR procedure was enhanced by 31.27% (30.78%) of Cd and 27.25% (23.22%) of Pb in the SSB (RSB) treatment, respectively. Fe was detected on both SSB and RSB surfaces, but SSB had rougher and a larger specific surface area compared to RSB. The addition of SSB and RSB in paddy soil increased soil pH and TOC content, and affected the diversity and species of soil microbial community. Compared with the CK group, the relative abundance of Proteobacteria, Bacteroidota, and Lysobacter decreased, and the relative abundance of Actinobacteriota, Pontibacter, and Alkaliphilus increased with SSB and RSB treatments, all of which reflected the bioavailability of Cd and Pb reduction.

The Mechanism of Cu2+ Sorption by Rice Straw Biochar and Its Sorption-Desorption Capacity to Cu2+ in Soil

Copper (Cu) pollution in soils has received considerable research attention globally, and biochar has been widely used as an adsorbent for soil pollution of Cu. However, most of the studies focused on the adsorption capacity of biochar, the bioavailability of Cu absorbed by biochar remains unclear. In this work, rice straw biomass was pyrolyzed under oxygen-limited conditions at 400°C (BC400) and 600°C (BC600), their apparent structure, group characteristics, and basic physical and chemical properties were determined. The isothermal and kinetics adsorption of Cu by BC400 and BC600 were analyzed. A pot experiment was used to evaluate the passivation of Cu in the soil by biochar and the bioavailability of Cu adsorbed by biochar in the soil. The smooth surfaces of BC400 evolved into more rough surfaces for BC600, and both types of surfaces may give active sorption sites for Cu, according to SEM pictures. FTIR analysis suggested that BC600 is endowed with more condensed aromatic carbon structures and more available polar functional groups. The adsorption processes of Cu²⁺ by biochar were better fitted Langmuir equation and pseudo-second-order kinetic model. The adsorption isotherms showed monolayer adsorption of Cu²⁺ on biochar. The maximum adsorption capacities of BC600 and BC400 on Cu²⁺ were 43.75 and 30.70 mg g^-1, respectively. Moreover, the pot experiment showed that BC400 and BC600 not only have a strong "passivation" effect on Cu in soil but also prevent the release of adsorbed Cu. Overall, more aromatic carbon structure, more polar functional groups, and higher pH are associated with BC600's increased Cu immobilization ability in soil.

Effects of the increases in soil pH and pH buffering capacity induced by crop residue biochars on available Cd contents in acidic paddy soils

To explore the effects of the increases in pH and pH buffering capacity (pHBC) induced by crop residue biochars on the changes in soil available Cd content, six acidic paddy soils developed from different parents were amended with seeded sunflower plate biochar (SSPBC), peanut straw biochar (PSBC) and corn straw biochar (CSBC). The pH, pHBC, and available Cd of the soils were measured after laboratory incubation. The results showed that the incorporation of crop residue biochars led to the increases in soil pH and pHBC, but a decrease in soil available Cd content. The decreasing order of available Cd content was SSPBC > PSBC > CSBC and was consistent with the changes in soil pH induced by the biochars. During submerging and draining, soil pH increased first and then declined, however the content of available Cd decreased first and then increased significantly. Soil pH in the treatments with biochars showed little change during draining, which was different from the control without the biochars added. This was attributed to the enhancing effect of the biochars on soil pHBC. Also, there was a significant negative correlation between the change in available Cd content and soil pHBC during submerging/draining alternation and suggested that higher pHBC corresponded to smaller soil available Cd content. Consequently, the amount of Cd absorbed by rice was reduced, thereby reducing the potential risk of soil Cd to humans. These results can provide useful references for the remediation of Cd-contaminated paddy soils.

Effect of crop straw biochars on the remediation of Cd-contaminated farmland soil by hyperaccumulator Bidens pilosa L

Cadmium (Cd) due to its strong toxicity and high mobility, which poses a considerable threat to soil environment and human health, has aroused widespread concern. Biochar has been used for remediating Cd-contaminated soil recently, however this method has the risk of fixed-Cd re-release. Phytoremediation can make up for its shortcoming. In this study, a pot experiment was carried out, where Bidens pilosa L. (B.pilosa) was as the tested plant and biochars (maize straw biochar and wheat straw biochar with two particle sizes) were as amendments. The mechanism of how biochars promoted B.pilosa Cd accumulation in Cd-contaminated farmland soil was explored. Results showed that the application of 5% wheat straw fine biochar (WF), wheat straw coarse biochar (WC), maize straw fine biochar (MF) and maize straw coarse biochar (MC) increased the total Cd accumulation of B.pilosa to 251.57%, 217.41%, 321.64% and 349.66%, respectively. Biochars amendment significantly promoted B.pilosa growth and increased Cd accumulation by improving soil physical properties, nutrient levels (available nitrogen, available phosphorus (AP), available potassium (AK) and organic matter (OM)) and microbial activity, and changing the nutrients distribution in B.pilosa organs although tissues although DTPA-Cd reduced to some extent. The effect of MF on AP increase was better than MC, while the effect of WF on AK increase was better than WC. Fine-particle was superior to coarse-particle in increasing B.pilosa biomass of aboveground, OM and microbial activity in soil. The changes of N, P and K concentrations in B.pilsosa roots, stems and leaves were closely related to the changes of AN, AP and AK in soil after biochars application. The results indicated that the combination of straw biochars and hyperaccumulators had the synergistic effect. This study can provide data support and meaningful reference values for remediating actual Cd-contaminated soil.

The influence of application of biochar and metal-tolerant bacteria in polluted soil on morpho-physiological and anatomical parameters of spring barley

The paper presents the results of the model experiment on spring barley (Hordeum vulgare L.) grown in polluted soil. The influence of separate and combined application of wood biochar and heavy metal-tolerant bacteria on morpho-physiological, anatomical and ultrastructural parameters of H. vulgare L. has been studied. The joint application of biochar and bacteria increased the shoot length by 2.1-fold, root length by 1.7-fold, leaf length by 2.3-fold and dry weight by threefold compared to polluted variant, bringing the plant parameters to the control level. The maximal quantum yield of photosystem II decreased by 8.3% in H. vulgare L. grown in contaminated soil, whereas this decrease was less in biochar (7%), bacteria (6%) and in combined application of bacteria and biochar (5%). As for the transpiration rate, the H. vulgare L. grown in polluted soil has shown a decrease in transpiration rate by 26%. At the same time, the simultaneous application of biochar and bacteria has led to a significant improvement in the transpiration rate (14%). The H. vulgare L. also showed anatomical (integrity of epidermal, vascular bundles, parenchymal and chlorenchymal cells) and ultrastructural (chloroplasts, thylakoid system, plastoglobules, starch grains, mitochondria, peroxisomes, ribosomes, endoplasmic reticulum, vacuoles) changes, revealed by light-optical and transmission electron microscopy of leaf sections. The effects were most prominent in H. vulgare L., grown in polluted soil but gradually improved with application of biochar, bacteria and their combination. The use of biochar in combination with metal-tolerant bacteria is an efficient tool for remediation of soils, contaminated with heavy metals. The positive changes caused by the treatment can be consistently traced at all levels of plant organization.