Effects of sheep bone biochar on soil quality, maize growth, and fractionation and phytoavailability of Cd and Zn in a mining-contaminated soil

Efficient cadmium-resistant plant growth-promoting bacteria loaded on pig bone biochar has higher efficiency in reducing cadmium phytoavailability and improving maize performance than on rice husk biochar

Green agriculture faced challenges due to the shortage of efficient cadmium (Cd)-resistant plant growth-promoting bacteria (CdR-PGPB) and their low survival rate and activity during application. In this study, a diverse range of efficient CdR-PGPB were isolated from the rhizosphere soil of Desmodium elegans, especially those with high phosphate-solubilizing capabilities (272.87-450.45 mg L-1). Two highly efficient CdR-PGPB namely, XH1 and XH3 were loaded on to rice husk biochar (RHB) and pig bone biochar (PBB), labelled as RHBM and PBBM respectively. This study aimed to explore their effectiveness and mechanisms in promoting maize growth in a Cd-contaminated planting system. Results showed that PBBM performed best among all treatments. It significantly decreased soil phytoavailable Cd by 53.19 % and Cd content in maize shoot by 85.89 %. It also increased soil available phosphorus by 145.72 %, soil alkaline phosphatase activity by 76.34 %, maize shoot/root biomass by 47.06 %/67.98 %, Chlorophyll (a/b) content by 66.80 %/134.13 % and peroxidase activity by 171.96 %. These results were achieved through the synergistic action of efficient CdR-PGPB and PBB. Therefore, PBBM proved to be a promising and innovative application technique for sustainable agricultural development in Cd-contaminated farmland ecosystems.

A Novel Method for the Enhancement of Sunflower Growth from Animal Bones and Chicken Feathers

The present study aimed at converting meat industry waste, particularly waste bones and chicken feathers, into biochar to recycle valuable nutrients present in it, which ultimately become part of the municipal waste. The bone biochar (BB) and feathers biochar (FB) were prepared at 550 °C, and their potential was evaluated as an organic amendment for the growth of sunflower. The ash content (AC) and fixed carbon (FC) improved significantly in prepared biochars as compared to raw feedstock. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analyses signaled the occurrence of various functional groups viz. amide group and hydroxyapatite, porosity, and multiple nutrients. Application of BB and FB in potted soil alone as well as in composites (1:1, 1:2, 2:1) at 1%, 3%, and 5% (w/w) and synthetic fertilizer significantly increased soil pH, electrical conductivity (ECe), organic matter (OM) and water holding capacity (WHC), while reducing the bulk density (BD). The growth of plants grown in soil treated with a 2:1 composite of feathers and bone biochar at 5% application rate showed significantly greater differences in plant height, total chlorophyll content, and plant dry weight than the control but was comparable to growth with chemical fertilizer, rendering it a potential alternative to chemical-based synthetic fertilizer.

Fabrication of engineered biochar for remediation of toxic contaminants in soil matrices and soil valorization

Biochar has emerged as an efficacious green material for remediation of a wide spectrum of environmental pollutants. Biochar has excellent characteristics and can be used to reduce the bioavailability and leachability of emerging pollutants in soil through adsorption and other physico-chemical reactions. This paper systematically reviewed previous researches on application of biochar/engineered biochar for removal of soil contaminants, and underlying adsorption mechanism. Engineered biochar are derivatives of pristine biochar that are modified by various physico-chemical and biological procedures to improve their adsorption capacities for contaminants. This review will promote the possibility to expand the application of biochar for restoration of degraded lands in the industrial area or saline soil, and further increase the useable area. This review shows that application of biochar is a win-win strategy for recycling and utilization of waste biomass and environmental remediation. Application of biochar for remediation of contaminated soils may provide a new solution to the problem of soil pollution. However, these studies were performed mainly in a laboratory or a small scale, hence, further investigations are required to fill the research gaps and to check real-time applicability of engineered biochar on the industrial contaminated sites for its large-scale application.

Heavy metals immobilization and bioavailability in multi-metal contaminated soil under ryegrass cultivation as affected by ZnO and MnO2 nanoparticle-modified biochar

Pollution by heavy metals (HMs) has become a global problem for agriculture and the environment. In this study, the effects of pristine biochar and biochar modified with manganese dioxide (BC@MnO2) and zinc oxide (BC@ZnO) nanoparticles on the immobilization and bioavailability of Pb, Cd, Zn, and Ni in soil under ryegrass (Lolium perenne L.) cultivation were investigated. The results of SEM-EDX, FTIR, and XRD showed that ZnO and MnO2 nanoparticles were successfully loaded onto biochar. The results showed that BC, BC@MnO2 and BC@ZnO treatments significantly increased shoots and roots dry weight of ryegrass compared to the control. The maximum dry weight of root and shoot (1.365 g pot-1 and 4.163 g pot-1, respectively) was reached at 1% BC@MnO2. The HMs uptake by ryegrass roots and shoots decreased significantly after addition of amendments. The lowest Pb, Cd, Zn and Ni uptake in the plant shoot (13.176, 24.92, 32.407, and 53.88 µg pot-1, respectively) was obtained in the 1% BC@MnO2 treatment. Modified biochar was more successful in reducing HMs uptake by ryegrass and improving plant growth than pristine biochar and can therefore be used as an efficient and cost effective amendment for the remediation of HMs contaminated soils. The lowest HMs translocation (TF) and bioconcentration factors were related to the 1% BC@MnO2 treatment. Therefore, BC@MnO2 was the most successful treatment for HMs immobilization in soil. Also, a comparison of the TF values of plant showed that ryegrass had a good ability to accumulate all studied HMs in its roots, and it is a suitable plant for HMs phytostabilization.

Evaluation Health Risks and Sorption of Hexavalent Chromium (Cr(VI) by Biochar and Iron Doped Zinc Oxide Modified Biochar (Fe-ZnO@BC) Using Trifolium: A Green Synthesis Technique

Contamination of aquatic and terrestrial environment with hexavalent chromium Cr(VI) is one of the major hazards worldwide due its carcinogenicity, persistency and immobility. Different research techniques have been adopted for Cr(VI) remediation present in terrestrial and aquatic media, while adsorption being the most advance, low cost, environmentally friendly and common method. The present study discussed the mechanisms of Parthenium hysterophorus derived biochar, iron-doped zinc oxide nanoparticles (nFe-ZnO) and Fe-ZnO modified biochar (Fe-ZnO@BC) involved in Cr(VI) mobility and bioavailability. Pot experiments were conducted to study the effect of Parthenium hysterophorus derived biochar, nFe-ZnO and Fe-ZnO@BC application rates (2%, 2 mg/kg, 10 mg/kg, respectively). The results indicated that the addition of soil amendments reduced Cr(VI) mobility. The findings revealed that the reduction in chromium mobility was observed by P. hysterophorus BC, and Fe-ZnO@BC but nFe-ZnO application significantly (p = 0.05) reduced Cr(VI) and CrT uptake as compared to the control treatments. The results of SEM coupled with EDS showed a high micropores and channel, smooth surface which helped in adsorption, and may enhance soil conditions. The concentration index (CI) by different amendments in trifolium plant was followed the descending order as: nFe-ZnO > Fe-ZnO@BC > P. hysterophorus BC after 30, 60 and 90 days of harvesting, respectively. In addition, human health risk index was found less than one (H1 < 1.0) in amended soils as compared to control treatments.

Impact of lead and zinc heavy metal pollution on the growth and phytoremediation potential of Sulla carnosa in Sebkha el Kalbia, Tunisia

Heavy metal pollution from human and natural activities poses significant environmental and health concerns for wildlife and humans, with lead and zinc being particularly threatening. This study focuses on Sebkha el Kalbia in Tunisia, highlighting the challenges faced by local communities in addressing heavy metal pollution. The area is prone to contamination through rivers and streams that transport pollutants from industrial zones and rural areas into the salt pan. The recent establishment of an industrial zone has worsened pollution levels, calling for strict regulatory measures and clean technologies to limit heavy metal pollution and protect human health and the environment. The study assesses the impact of lead and zinc pollution on the growth of Sulla carnosa and its potential for phytoremediation. Soil and plant samples from contaminated areas were analyzed, revealing high levels of heavy metal contamination. The growth parameters of Sulla carnosa, such as plant height, weight, and enzymatic activity, were examined, showing a significant reduction in plant growth when exposed to high metal concentrations. Specifically, in the presence of 100 ppm of lead (Pb), net photosynthetic assimilation (An) decreased by 52%, while the amount of Pb increased by 78%. At 800 ppm of Pb, An decreased by 87%, and the amount of Pb increased by over 800%. Furthermore, the relationship between net photosynthetic assimilation and lead (Pb) content remained significant but negative. At high doses (800 ppm), the biomass produced decreases by 64%, while the amount of Zn increases 2.7 times. These results suggest that at low doses, zinc is not toxic. These findings highlight Sulla carnosa as a potential candidate for phytoremediation with preferential metal accumulation in the roots and improved enzymatic activity, underscoring the urgency of addressing heavy metal pollution in Sebkha el Kalbia.

Impact of some amendments on kinetics of leaching dissolved organic carbon and ammonium in calcareous sandy soil under vinasse addition

The access of vinasse leachates to water bodies and groundwater exacerbates environmental problems, especially eutrophication. Therefore, a column experiment was performed to examine the effect of adding zeolite (ZL), bone char (BC), and wood chips biochar (WCB) in the presence of vinasse on carbon dioxide (CO2) emission, leaching dissolved organic carbon (DOC) and ammonium (NH4+) in calcareous sandy soil, as well as studying the kinetics of leaching dissolved organic carbon and ammonium. This column experiment contains four treatments: soil alone (CK), soil + zeolite (SZL), soil + bone char (SBC), and soil + wood chips biochar (SWCB). These amendments were applied to the soil at a level of 4%. Vinasse was added to all treatments at a level of 13 mL per column. The leached total cumulative DOC and total cumulative soluble ammonium amounts decreased significantly with applying ZL, BC, and WCB compared with the soil alone. The effectiveness of these amendments in lowering the total cumulative DOC leaching is in the order of SBC > SWCB > SZL > CK. However, the effectiveness of these amendments in decreasing the total cumulative NH4+ leaching is in the order of SZL > SWCB > SBC > CK. The rate constant (k) of DOC leaching decreased significantly with the application of bone char compared to soil alone treatment. In the presence of vinasse, the apparent half-life of leached DOC from the soil was 8.1, 12.9, 36.7, and 15.5 days for soil CK, SZL, SBC, and SWCB treatments, respectively. Half-life values of leached soluble ammonium from the soil in the presence of vinasse addition were 10.1, 39.5, 28.5, and 37.9 days for CK, SZL, SBC, and SWCB treatments, respectively. Amending soil with BC increased significantly the phosphorus availability, however, applying ZL and BC caused a significant increase in the available potassium in calcareous sandy soil compared to the control treatment. According to these results, it is recommended not to add vinasse alone to sandy soils, but it is preferred to be co-applied with BC amendment at the level of 4% better than ZL and WCB. This would decrease leaching DOC and ammonium to the water table and groundwater as well as enhance nutrient retention in the soil, which in turn, plays a vital role in reducing the harmful effect of vinasse and improving soil fertility.

Effects of BC on metal uptake by crops (availability) and the vertical migration behavior in soil: A 3-year field experiments of crop rotation

Biochar (BC) has been substantiated to effectively reduce the available content of heavy metals (HMs) in soil-plant system; however, the risk of biochar (BC)derived dissolved organic matter (DOM) induced metal vertical migration has not been well documented, especially in the long-term field conditions. Therefore, this study investigated HM vertical migration ecological risks and the long-term effectiveness of the amendment of biochar in the three successive years of field trials during the rotation system. The results revealed that biochar application could increase soil pH and DOM with a decrease in soil CaCl2 extractable pool for Pb, Cu, and Cd. Furthermore, the results indicated a significant decrease in acid phosphatase activities and an increase in urease and catalase activities in the soil. Cucumber was shown to be safe during a three-year rotation system in the field. These results suggest that BC has the potential to enhance soil environment and crop yields. BC derived DOM-specific substances were identified using parallel factor analysis of excitation-emission matrix in deep soil (0-60 cm). The study incorporated HM concentration fluctuations in deep soils, providing an additional interpretation of DOM and co-migration of HMs.The environmental risk associated with the increase in DOM hydrophobicity should not be ignored by employing BC for soil HM remediation applications. The study enhances understanding of biochar-derived DOM's migration and stabilization mechanisms on heavy metals, providing guidelines for its use as a soil amendment.

Preparation, characterisation and applications of bone char, a food waste-derived sustainable material: A review

The production of increasing quantities of by-products is a key challenge for modern society; their valorisation - turning them into valuable compounds with technological applications - is the way forward, in line with circular economy principles. In this review, the conversion of bones (by-products of the agro-food industry) into bone char is described. Bone char is obtained with a process of pyrolysis, which converts the organic carbon into an inorganic graphitic one. Differently from standard biochar of plant origin, however, bone char also contains calcium phosphates, the main component of bone (often hydroxyapatite). The combination of calcium phosphate and graphitic carbon makes bone char a unique material, with different possible uses. Here bone chars' applications in environmental remediation, sustainable agriculture, catalysis and electrochemistry are discussed; several aspects are considered, including the bones used to prepare bone char, the preparation conditions, how these affect the properties of the materials (i.e. porosity, surface area) and its functional properties. The advantages and limitations of bone chars in comparison to traditional biochar are discussed, highlighting the directions the research should take for bone chars' performances to improve. Moreover, an analysis on the sustainability of bone chars' preparation and use is also included.

Micro/nanoscale bone char alleviates cadmium toxicity and boosts rice growth via positively altering the rhizosphere and endophytic microbial community

This present study investigated pork bone-derived biochar as a promising amendment to reduce Cd accumulation and alleviate Cd-induced oxidative stress in rice. Micro/nanoscale bone char (MNBC) pyrolyzed at 400 °C and 600 °C was synthesized and characterized before use. The application rates for MNBCs were set at 5 and 25 g·kg^-1 and the Cd exposure concentration was 15 mg·kg^-1. MNBCs increased rice biomass by 15.3-26.0% as compared to the Cd-alone treatment. Both types of MNBCs decreased the bioavailable Cd content by 27.4-54.8%; additionally, the acid-soluble Cd fraction decreased by 10.0-12.3% relative to the Cd alone treatment. MNBC significantly reduced the cell wall Cd content by 50.4-80.2% relative to the Cd-alone treatment. TEM images confirm the toxicity of Cd to rice cells and that MNBCs alleviated Cd-induced damage to the chloroplast ultrastructure. Importantly, the addition of MNBCs decreased the abundance of heavy metal tolerant bacteria, Acidobacteria and Chloroflexi, by 29.6-41.1% in the rhizosphere but had less impact on the endophytic microbial community. Overall, our findings demonstrate the significant potential of MNBC as both a soil amendment for heavy metal-contaminated soil remediation and for crop nutrition in sustainable agriculture.

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.

Meat and bone meal biochar can effectively reduce chemical fertilizer requirements for crop production and impart competitive advantages to soil

Safe and effective circulation of nutrient-rich meat and bone meal (MBM) could become a carbon-based alternative to limited chemical fertilizers (CFs). Therefore, MBM biochars (MBMCs) were produced at 500, 800, and 1000 °C to evaluate their effects on plant growth, nutrient uptake, and soil characteristics. The results revealed that MBMC produced at 500 °C (MBMC500) contained the maximum amount of C, N, and phytoavailable P. All additional MBMC doses with recommended CF increased sorghum shoot yield (6.7-16%) and significantly improved P uptake. Additional experiments were conducted with decreasing doses of CF (100-0%) with or without MBMC500 (7 t/ha) to quantify its actual fertilizing value. MBMC500 showed the capability to reduce CF requirement by 20% without compromising the optimum yield (by 100% CF) while increasing pH, CEC, total-N, available-P, Mg, and microbial population of post-harvest soil. Although a δ¹⁵N analysis confirmed MBMC500 as a source of plant N, a reduction in N uptake by MBMC500 + 80% CF treatment compared to 100% CF might have limited further sorghum growth. Thus, future studies should concentrate on producing MBMC with better N utilization capability and achieving maximum CF reduction without negative environmental impacts.

Competitive adsorption and immobilization of Cd, Ni, and Cu by biochar in unsaturated soils under single-, binary-, and ternary-metal systems

This study investigated the competitive adsorption and immobilization of cadmium (Cd), nickel (Ni), and copper (Cu) by biochar in unsaturated soils under single-, binary-, and ternary-metal systems. The results showed that the immobilization effects by the soil itself were in the order of Cu > Ni > Cd, and the adsorption capacities of freshly contaminated heavy metals by biochar were in the order of Cd > Ni > Cu in unsaturated soils. The adsorption and immobilization of Cd by biochars in soils was weakened by competition more in the ternary-metal system than that in the binary-metal system; the competition with Cu caused a more significant weakening effect than that with Ni. For Cd and Ni, nonmineral mechanisms preferentially adsorbed and immobilized Cd and Ni compared to mineral mechanisms, but the contributions of the mineral mechanisms to the adsorption gradually increased and became dominant with increasing concentrations (at average percentages of 62.59%-83.30% and 41.38%-74.29%, respectively). However, for Cu, the contributions of the nonmineral mechanisms to Cu adsorption were always dominant (average percentages of 60.92%-74.87%) and gradually increased with increasing concentrations. This study highlighted that the types of heavy metals and coexistence should be focused when remediating heavy metal contamination in soils.

Contaminant containment for sustainable remediation of persistent contaminants in soil and groundwater

Contaminant containment measures are often necessary to prevent or minimize offsite movement of contaminated materials for disposal or other purposes when they can be buried or left in place due to extensive subsurface contamination. These measures can include physical, chemical, and biological technologies such as impermeable and permeable barriers, stabilization and solidification, and phytostabilization. Contaminant containment is advantageous because it can stop contaminant plumes from migrating further and allow for pollutant reduction at sites where the source is inaccessible or cannot be removed. Moreover, unlike other options, contaminant containment measures do not require the excavation of contaminated substrates. However, contaminant containment measures require regular inspections to monitor for contaminant mobilization and migration. This review critically evaluates the sources of persistent contaminants, the different approaches to contaminant remediation, and the various physical-chemical-biological processes of contaminant containment. Additionally, the review provides case studies of contaminant containment operations under real or simulated field conditions. In summary, contaminant containment measures are essential for preventing further contamination and reducing risks to public health and the environment. While periodic monitoring is necessary, the benefits of contaminant containment make it a valuable remediation option when other methods are not feasible.

Mixed pollutants adsorption potential of Eichhornia crassipes biochar on Manihot esculenta processing industry effluents

The starch is one of the most essential food stuff and serves as a raw material for number of food products for the welfare of human. During the production process enormous volume of effluents are being released into the environment. In this regard, this study was performed to evaluate the physicochemical traits of Manihot esculenta processing effluent and possible sustainable approach to treat this issue using Eichhornia crassipes based biochar. The standard physicochemical properties analysis revealed that the most the parameters (EC was recorded as 4143.17 ± 67.12 mhom^-1, TDS: 5825.62 ± 72.14 mg L^-1, TS: 7489.21 ± 165.24 mg L^-1, DO: 2.12 ± 0.21 mg L^-1, BOD 2673.74 ± 153.53 mg L^-1, COD: 6672.66 ± 131.21 mg L^-1, and so on) were beyond the permissible limits and which can facilitate eutrophication. Notably, the DO level was considerably poor and thus can support the eutrophication. The trouble causing E. crassipes biomass was used as raw material for biochar preparation through pyrolysis process. The temperature ranging from 250 to 350 °C with residence time of 20-60 min were found as suitable temperature to provide high yield (56-33%). Furthermore, 10 g L^-1 concentration of biochar showed maximum pollutant adsorption than other concentrations (5 g L^-1 and 15 g L^-1) from 1 L of effluent. The suitable temperature required to remediate the pollutants from the effluent by biochar was found as 45 °C and 35 °C at 10 g L^-1 concentration. These results conclude that at such optimized condition, the E. crassipes effectively adsorbed most of the pollutants from the M. esculenta processing effluent. Furthermore, such pollutants adsorption pattern on biochar was confirmed by SEM analysis.

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.

Cow bone-derived biochar enhances microbial biomass and alters bacterial community composition and diversity in a smelter contaminated soil

Bone waste could be utilized as a potential amendment for remediation of smelter-contaminated soils. Nevertheless, the influences of cow bone-derived biochar (CB) on soil microbial biomass and microbial community composition in multi-metal contaminated mining soils are still not clearly documented. Hence, the cow bone was used as feedstock material for biochar preparation and pyrolyzed at two temperatures such as 500 °C (CB500) and 800 °C (CB800), and added to a smelter soil at the dosage of 0 (unamended control), 2.5, 5, and 10% (w/w); then, the soil treatments were cultivated by maize. The CB effect on soil biochemical attributes and response of soil microbial biomass, bacterial communities, and diversity indices were examined after harvesting maize. Addition of CB enhanced total nutrient contents (i.e., total nitrogen up to 26% and total phosphorus P up to 27%) and the nutrients availability (i.e., NH₄ up to 50%; NO₃ up to 31%; Olsen P up to 48%; extractable K up to 18%; dissolved organic carbon up to 74%) in the treated soil, as compared to the control. The CB500 application revealed higher microbial biomass C (up to 66%), P (up to 41%), and bacterial gene abundance (up to 76%) than the control. However, comparatively a lower microbial biomass nitrogen and diversity indices were observed in the biochar (both with CB500 and CB800) treated soils than in the unamended soils. At the phylum level, the highest dose (10% of CB500 and CB800 resulted in contrasting effects on the Proteobacteria diversity. The CB500₁₀ favored the Pseudomonas abundance (up to 793%), Saccharibacteria (583%), Parcubacteria (138%), Actinobacteria (65%), and Firmicutes (48%) microbial communities, while CB800₁₀ favored the Saccharibacteria (386%), Proteobacteria (12%) and Acidobacteria (11%), as compared to the control. These results imply that CB500 and CB800 have a remarkable impact on microbial biomass and bacterial diversity in smelter contaminated soils. Particularly, CB500 was found to be suitable for enhancing microbial biomass, bacterial growth of specific phylum, and diversity, which can be useful for bioremediation of mining soils.

Biochar for the removal of contaminants from soil and water: a review

Biochar shows significant potential to serve as a globally applicable material to remediate water and soil owing to the extensive availability of feedstocks and conducive physio-chemical surface characteristics. This review aims to highlight biochar production technologies, characteristics of biochar, and the latest advancements in immobilizing and eliminating heavy metal ions and organic pollutants in soil and water. Pyrolysis temperature, heat transfer rate, residence time, and type of feedstock are critical influential parameters. Biochar’s efficacy in managing contaminants relies on the pore size distribution, surface groups, and ion-exchange capacity. The molecular composition and physical architecture of biochar may be crucial when practically applied to water and soil. In general, biochar produced at relatively high pyrolysis temperatures can effectively manage organic pollutants via increasing surface area, hydrophobicity and microporosity. Biochar generated at lower temperatures is deemed to be more suitable for removing polar organic and inorganic pollutants through oxygen-containing functional groups, precipitation and electrostatic attraction. This review also presents the existing obstacles and future research direction related to biochar-based materials in immobilizing organic contaminants and heavy metal ions in effluents and soil.

Graphical Abstract

Aspergillus niger-mediated release of phosphates from fish bone char reduces Pb phytoavailability in Pb-acid batteries polluted soil, and accumulation in fenugreek

Soil receiving discharges from Pb-acid batteries dismantling and restoring units (PBS) can have a high concentration of phytoavailable Pb. Reducing Pb phytoavailability in PBS can decline Pb uptake in food crops and minimize the risks to humans and the environment. This pot study aimed to reduce the concentration of phytoavailable Pb in PBS through Aspergillus niger (A. niger)-mediated release of PO₄^3- from fish bone [Apatite II (APII)] products. The PBS (Pb = 639 mg kg^-1 soil) was amended with APII powder (APII-P), APII char (APII-C), and A. niger inoculum as separate doses, and combining A. niger with APII-P (APII-P + A. niger) and APII-C (APII-C + A. niger). The effects of these treatments on reducing the phytoavailability of Pb in PBS and its uptake in fenugreek were examined. Additionally, enzymatic activities and microbial biomass carbon (MBC) in the PBS and the indices of plant physiology, nutrition, and antioxidant defense machinery were scoped. Results revealed that the APII-C + A. niger treatment was the most efficient one. Compared to the control, it significantly reduced the Pb phytoavailability (DTPA-extractable Pb fraction) in soil and its uptake in plant shoots, roots, and grain, up to 61%, 83%, 74%, and 92%. The grain produced under APII-C + A. niger were safe for human consumption as Pb concentration in grain was 4.01 mg kg^-1 DW, remaining within the permissible limit set by WHO/FAO (2007). The APII-C + A. niger treatment also improved soil pH, EC, CEC, MBC, available P content and enzymatic activities, and the fenugreek quality parameters. A. niger played a significant role in solubilizing PO₄^3- from APII-C, which reacted with Pb and formed insoluble Pb-phosphates, thereby reducing Pb phytoavailability in PBS and its uptake in plants. This study suggests APII-C + A. niger can remediate Pb-polluted soils via reducing Pb phytoavailability in them.

One stone two birds: Bone char as a cost-effective material for stabilizing multiple heavy metals in soil and promoting crop growth

Remediation of farmland soils contaminated with high levels of multiple heavy metals near PbZn smeltery is still a great challenge. It is of great significance to find cost-effective green remediation technologies for stabilization of multiple heavy metals in soil and reduce metal accumulation in crops with ensured yield. In this study, we demonstrated that bone char (BC) is an effective heavy metal stabilizer which can substantially increase residual fractions of heavy metals and reduce metal accumulation in pea (Pisum sativum) with its enhanced growth. We chose the soils contaminated with high levels of Pb, Zn, Cu and Cd near the Baiyin PbZn smeltery as the tested soil. After 2 months of BC application, the relative mobile fractions (non-residual fractions) of Cu, Zn, Pb and Cd in the contaminated soil decreased while the residual fraction increased significantly. The leachability of Cu, Zn, Pb and Cd decreased by 91.2%, 38.6%, 67.6% and 54.3%, respectively compared with the control. BC application remarkably promoted pea growth and reduced accumulation of heavy metals in shoots. The mechanisms for stabilization of multiple heavy metals BC include ion exchange, surface complexation and subsequent mineralization, accompanied with release of Ca and phosphate. The immobilization of heavy metals led to their reduced toxicity to plant, and thus increased pea growth. The results show that BC is a cost-effective and sustainable heavy metal stabilizer with phosphate fertilization function. It can simultaneously immobilize multiple heavy metals in soil and facilitate crop production.

Hydroxyapatite tailored hierarchical porous biochar composite immobilized Cd(II) and Pb(II) and mitigated their hazardous effects in contaminated water and soil

A novel composite of hydroxyapatite tailored hierarchical porous biochar (HA-HPB) was synthesized and used for the adsorptive immobilization of Cd(II) and Pb(II) in water and soil. The hierarchical porous biochar (HPB) was prepared from rice husk through a molten-salt-assisted pyrolysis approach; then, a series of HA-HPB (with 0.5, 1, 2, 3, and 4 g of HPB) was prepared with co-precipitation procedure. All HA-HPBs, particularly HA-3HPB, revealed significantly higher removal efficiency of Cd(II) and Pb(II) (≥99.5%) in water than pristine biochar (5.79 - 24.12%). The immobilization efficiency of HA-3HPB for Cd(II) and Pb(II) was slightly inhibited by the ionic strength and co-existing cations. The Langmuir adsorption capacities of Cd(II) and Pb(II) were 88.1 and 110.2 mg/g, respectively. Ion exchange, complexation, cation-π interaction, and precipitation were the key mechanisms involved in the immobilization of Cd(II) and Pb(II) using HA-3HPB. The HA-3HPB reduced the availability of soil Cd (63.5 - 87.8%) and Pb (64.6 - 92.9%) compared to the unamended soil, and thus reduced their content in the Chinese cabbage shoots by 69.3 -95.4% for Cd and 66.5 -97.2% for Pb. These findings demonstrate the effectiveness of HA-HPB for remediation of Cd(II) and Pb(II) contaminated water and soil and mitigating the potential risks.

Value-added materials recovered from waste bone biomass: technologies and applications

As the world population increases, the generation of waste bones will multiply exponentially, increasing landfill usage and posing health risks. This review aims to shed light on technologies for recovering valuable materials (e.g., alkaline earth material oxide such as CaO, hydroxyapatite, beta tri-calcium phosphate, phosphate and bone char) from waste bones, and discuss their potential applications as an adsorbent, catalyst and catalyst support, hydroxyapatite for tissue engineering, electrodes for energy storage, and phosphate source for soil remediation. Waste bone derived hydroxyapatite and bone char have found applications as a catalyst or catalyst support in organic synthesis, selective oxidation, biodiesel production, hydrocracking of heavy oil, selective hydrogenation and synthesis of bioactive compounds. With the help of this study, researchers can gather comprehensive data on studies regarding the recycling of waste bones, which will help them identify material recovery technologies and their applications in a single document. Furthermore, this work identifies areas for further research and development as well as areas for scaling-up, which will lead to reduced manufacturing costs and environmental impact. The idea behind this is to promote a sustainable environment and a circular economy concept in which waste bones are used as raw materials to produce new materials or for energy recovery.

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.

Biochar in environmental friendly fertilizers - Prospects of development products and technologies

According to the circular economy concept, the production of fertilizers should be closed in a loop, which prevents excessive emissions and harmful effects to the environment. Biological wastes are problematic to collect and transport. They undergo a biological transformation that causes greenhouse gases emission and sanitary hazards. Biomass sources used for organic or organo-mineral fertilizers must be free of pathogens and rich in macro and microelements. Solid residues can be processed thermally. Biochar is a carbon produced by biomass pyrolysis without oxygen presence and has been used for many years to improve soil quality and enhance the efficiency of fertilization. There are many research works on the use of biochar in fertilization. This study is also extended by the latest developments and technologies from the patent database (recent year) and biochar-based fertilizers market. To the best of our knowledge, there is no such review currently available in scientific databases. Based on the collected data, the best method of biochar management was proposed - soil application. Biochar applied to soil has several advantages: it improves soil structure and its sorption capacity, enhances soil-nutrient retention and water-holding capacity, immobilizes contaminants from soil (sorption), reduces greenhouse gas emissions and soil nutrient leaching losses while stimulating the growth of a plant.

Removal of potentially toxic elements from contaminated soil and water using bone char compared to plant- and bone-derived biochars: A review

Conversion of hazardous waste materials to value-added products is of great interest from both agro-environmental and economic points of view. Bone char (BC) has been used for the removal of potentially toxic elements (PTEs) from contaminated water, however, its potential BC for the immobilization of PTEs in contaminated water and soil compared to bone (BBC)- and plant (PBC)-derived biochars has not been reviewed yet. This review presents an elaboration for the potentials of BC for the remediation of PTEs-contaminated water and soil in comparison with PBC and BBC. This work critically reviews the preparation and characterization of BC, BBC, and PBC and their PTEs removal efficiency from water and soils. The mechanisms of PTE removal by BC, BBC, and PBC are also discussed in relation to their physicochemical characteristics. The review demonstrates the key opportunities for using bone waste as feedstock for producing BC and BBC as promising low-cost and effective materials for the remediation of PTEs-contaminated water and soils and also elucidates the possible combinations of BC and BBC aiming to effectively immobilize PTEs in water and soils.

Migration and Transformation of Multiple Heavy Metals in the Soil–Plant System of E-Waste Dismantling Site

E-waste generation has become a major environmental issue worldwide. Heavy metals (HMs) in e-waste can be released during inappropriate recycling processes. While their pollution characteristics have been studied, the migration and transformation of different multi-metal fractions in soil–plant system of e-waste dismantling sites is still unclear. In this study, pot experiments were conducted to investigate the migration and transformation of different multi-metal fractions (Cu, Pb, Zn and Al) in the soil–plant system using two Chinese cabbage cultivars (heavy metals low-accumulated variety of Z1 and non-low-accumulated Z2) treated with or without biochar. The result showed that the acid-soluble fraction of Cu, Pb, Zn and Al in soil decreased by 5.5%, 55.7%, 7.8% and 21.3%, but the residual fraction (ResF) of them increased by 48.5%, 1.8%, 30.9% and 43.1%, respectively, when treated with biochar and plants, compared to that of the blank soil (CK). In addition, Pb mainly existed as a reducible fraction, whereas Cu existed as an oxidisable fraction. Biochar combined with plants significantly increased the ResF of multi-metals, which reduced the migration ability of Pb among all other metals. The relative amount of labelled ¹³C in the soil of Z1 was higher than that of Z2 (25.4 fold); among them, the Gram-negative bacteria (18-1ω9c, 18-1ω7c) and fungi (18-2ω6c) were significantly labelled in the Z1-treated soil, and have high correlation with HM migration and transformation. In addition, Gemmatimonadete were significantly positive in the acid-soluble fraction of HMs, whereas Ascomycota mostly contributed to the immobilisation of HMs. Therefore, the distribution of fractions rather than the heavy metal type plays an important role in the HM migration in the soil–plant system of e-waste dismantling sites.

Speciation, transportation, and pathways of cadmium in soil-rice systems: A review on the environmental implications and remediation approaches for food safety

Cadmium (Cd) contamination in paddy fields is a serious health concern because of its high toxicity and widespread pollution. Recently, much progress has been made in elucidating the mechanisms involved in Cd uptake, transport, and transformation from paddy soils to rice grains, aiming to mitigate the associated health risk; however, these topics have not been critically reviewed to date. Here, we summarized and reviewed the (1) geochemical distribution and speciation of Cd in soil-rice systems, (2) mobilization, uptake, and transport of Cd from soil to rice grains and the associated health risks, (3) pathways and transformation mechanisms of Cd from soil to rice grains, (4) transporters involved in reducing Cd uptake, transport, and accumulation in rice plants, (5) factors governing Cd bioavailability in paddy, and (6) comparison of remediation approaches for mitigating the environmental and health risks of Cd contamination in paddy fields. Briefly, this review presents the state of the art about the fate of Cd in paddy fields and its transport from soil to grains, contributing to a better understanding of the environmental hazards of Cd in rice ecosystems. Challenges and perspectives for controlling Cd risks in rice are thus raised. The summarized findings in this review may help to develop innovative and applicable methods for controlling Cd accumulation in rice grains and sustainably manage Cd-contaminated paddy fields.