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

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.

Environmental risk associated with accumulation of toxic metalloids in soils of the Odra River floodplain-case study of the assessment based on total concentrations, fractionation and geochemical indices

The floodplain soils are often heavily enriched in metal(loid)s released from the industrial areas. A related environmental risk depends on their total concentrations and the forms and conditions conducive to mobilization. This study was aimed to examine the concentrations of metal(loid)s in the Odra floodplain soils and to assess the risk associated with their possible contamination. In this study, topsoil and deeper soil layer samples were collected from the inter- and out-of-embankment zones. Total concentrations of Pb, Zn, Cu, As, Mn and Fe, and their extractable fractions were determined in 1 M NH4NO3 (actual solubility) and by BCR sequential extraction. The environmental risk was assessed based on total concentrations, according to legal regulations, geochemical enrichment indices and extractability of elements, with considering soil morphological features. Some topsoil samples from the inter-embankment zone turned out considerably enriched in Pb, Zn, Cu, and As, as confirmed by geochemical indices. Zn and As concentrations in some samples exceeded the permissible values defined by Polish law. Zn and Mn showed a high actual solubility, but a simple experiment proved that it can be efficiently reduced by liming. BCR fractionation showed that all the elements occurred mainly in reducible forms. Therefore, the risk of their release from the layers that do not indicate redoximorphic features was assessed as negligible. The study showed that such a complementary approach is needed to assess the real environmental risk in the case of soils considerably enriched in potentially toxic elements.

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.

Changes in the Availability and Distribution of Microelement Copper in Cadmium Contaminated Soil and its Accumulation in Rice (Oryza sativa L.) After Biochar Application

This experiment explored the side effect of biochar application on the availability and distribution of the soil microelement copper (Cu) in cadmium (Cd) contaminated soil and its uptake in rice tissues. Biochar was added at 0, 10, 20, 30, and 40 t ha^-1 on topsoil. Results observed that both the concentration of available Cu in the topsoil and subsoil layer decreased by 16.3%-28.9% and 7.5%-59.3%, respectively, after biochar application. The Cu concentration in the < 0.053 mm and 1-2 mm soil aggregates increased as biochar application rate increased. Increasing application rate of biochar reduced the proportion of exchangeable Cu, carbonate bound Cu, and Fe/Mn oxide Cu fraction in the soil profile. However, the fraction of organic bound and residual Cu increased by 5.0%-178.4% and 7.0%-15.6%, respectively. Biochar could immobilize microelement Cu in the soil profile and limit Cu uptake by rice.

Chemical modification of biochars as a method to improve its surface properties and efficiency in removing xenobiotics from aqueous media

Biochar (BC) is a carbonaceous material produced by pyrolysis of biomass, applied in various areas such as water purification, fuel production, soil amendment, etc. Many types of BC are characterized by insufficient textural parameters or poor surface chemistry, and hence by low adsorption capacity. This makes innovative chemical methods increasing BC ability to remove xenobiotics from aquatic environments highly needed. Many of them have already been described in the literature. This review presents them in detail and evaluates their effectiveness in improving textural parameters, surface chemistry, and adsorption capacity of BC.

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

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.

Combined remediation effects of biochar, zeolite and humus on Cd-contaminated weakly alkaline soils in wheat farmland

Threats posed by Cd-contaminated arable soils to food security have attracted increasing attention. The combination of organic and inorganic amendments has been extensively applied to immobilize Cd in paddy soils. However, the regulatory mechanism of Cd fractionation under these combined amendments and the effect on wheat Cd accumulation remain unclear in upland soils. In this work, different combinations of organic and inorganic amendments were prepared with biochar, zeolite and humus, and the Cd-immobilization mechanism was also investigated in field experiments. The results demonstrated that the mixture of biochar, zeolite and humus had excellent Cd immobilization performance in highly Cd-contaminated (4.26 ± 1.25 mg kg^-1) weakly alkaline soils, resulting in 76.5-84.8% decreases in soil available Cd. The contribution of single components to Cd immobilization in the combined amendment follows the order of humus > biochar > zeolite. The combined amendment converted the acid soluble Cd to the Cd bound to the reducible fraction with higher stability, thereby decreasing Cd bioavailability. The maximum Cd decrease rate in wheat roots, straw and grains could reach 68.2%, 45.0% and 59.3%, respectively, and the Cd content in grains (0.098 mg kg^-1) was lower than the food security standards of China (0.1 mg kg^-1). Wheat planting for two successive years in a large-scale field further verified the superior Cd immobilization performance and stability of the combined amendment in moderately to slightly Cd-contaminated soil. The present study provides references for the remediation of Cd-contaminated weakly alkaline upland soils and certain guidance for safe food production.

Efficient Remediation of Cadmium Contamination in Soil by Functionalized Biochar: Recent Advances, Challenges, and Future Prospects

Heavy metal pollution in soil seriously harms human health and animal and plant growth. Among them, cadmium pollution is one of the most serious issues. As a promising remediation material for cadmium pollution in soil, functionalized biochar has attracted wide attention in the last decade. This paper summarizes the preparation technology of biochar, the existing forms of heavy metals in soil, the remediation mechanism of biochar for remediating cadmium contamination in soil, and the factors affecting the remediation process, and discusses the latest research advances of functionalized biochar for remediating cadmium contamination in soil. Finally, the challenges encountered by the implementation of biochar for remediating Cd contamination in soil are summarized, and the prospects in this field are highlighted for its expected industrial large-scale implementation.

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.

Modified Biochars and Their Effects on Soil Quality: A Review

Biochar (BC) has attracted attention due to its impacts on soil quality by enhancing soil fertility, carbon storage and contaminants immobilization. BC also induces changes in microbial community structure and enhances crop productivity in long term scenarios compared to many other organic amendments. However, information related to the role of modified BCs in altering the soil quality is still scarce. BC can be modified by using physical, chemical and microbial methods. Modified BC can change the functional groups, pore size, pore structure, surface area and chemical properties of soil, which plays a key role in changing the soil quality. The addition of modified BCs as soil amendment increased soil CEC (cation exchange capacity), EC (electron conductivity), pH, organic matter, hydraulic conductivity, soil porosity, infiltration rate, microbial activities (enzymes and community), nutrient profile and gas exchange properties, but it varies according to the soil structure and pervading environmental conditions. This study provides a basis for effective practical approaches to modifying BCs for improving soil quality.

Hydrochar and pyrochar for sorption of pollutants in wastewater and exhaust gas: A critical review

Pollutants in wastewater and exhaust gas bring out serious concerns to public health and the environment. Biochar can be developed as a sustainable adsorbent originating from abundant bio-wastes, such as agricultural waste, forestry residue, food waste and human waste. Here we highlight the state-of-the-art research progress on pyrochar and hydrochar for the sorption of pollutants (heavy metal, organics, gas, etc) in wastewater and exhaust gases. The adsorption performance of pyrochar and hydrochar are compared and discussed in-depth, including preparation procedures (carbonization and activation), sorption possible mechanisms, and physiochemical properties. Challenges and perspective for designing efficient and environmental benign biochar-based adsorbents are finally addressed.