A critical review of biochar-based materials for the remediation of heavy metal contaminated environment: Applications and practical evaluations

Advancing horizons in vegetable cultivation: a journey from ageold practices to high-tech greenhouse cultivation-a review

Vegetable cultivation stands as a pivotal element in the agricultural transformation illustrating a complex interplay between technological advancements, evolving environmental perspectives, and the growing global demand for food. This comprehensive review delves into the broad spectrum of developments in modern vegetable cultivation practices. Rooted in historical traditions, our exploration commences with conventional cultivation methods and traces the progression toward contemporary practices emphasizing the critical shifts that have refined techniques and outcomes. A significant focus is placed on the evolution of seed selection and quality assessment methods underlining the growing importance of seed treatments in enhancing both germination and plant growth. Transitioning from seeds to the soil, we investigate the transformative journey from traditional soil-based cultivation to the adoption of soilless cultures and the utilization of sustainable substrates like biochar and coir. The review also examines modern environmental controls highlighting the use of advanced greenhouse technologies and artificial intelligence in optimizing plant growth conditions. We underscore the increasing sophistication in water management strategies from advanced irrigation systems to intelligent moisture sensing. Additionally, this paper discusses the intricate aspects of precision fertilization, integrated pest management, and the expanding influence of plant growth regulators in vegetable cultivation. A special segment is dedicated to technological innovations, such as the integration of drones, robots, and state-of-the-art digital monitoring systems, in the cultivation process. While acknowledging these advancements, the review also realistically addresses the challenges and economic considerations involved in adopting cutting-edge technologies. In summary, this review not only provides a comprehensive guide to the current state of vegetable cultivation but also serves as a forward-looking reference emphasizing the critical role of continuous research and the anticipation of future developments in this field.

Definitive Review of Nanobiochar

Nanobiochar is an advanced nanosized biochar with enhanced properties and wide applicability for a variety of modern-day applications. Nanobiochar can be developed easily from bulk biochar through top-down approaches including ball-milling, centrifugation, sonication, and hydrothermal synthesis. Nanobiochar can also be modified or engineered to obtain "engineered nanobiochar" or biochar nanocomposites with enhanced properties and applications. Nanobiochar provides many fold enhancements in surface area (0.4-97-times), pore size (0.1-5.3-times), total pore volume (0.5-48.5-times), and surface functionalities over bulk biochars. These enhancements have given increased contaminant sorption in both aqueous and soil media. Further, nanobiochar has also shown catalytic properties and applications in sensors, additive/fillers, targeted drug delivery, enzyme immobilization, polymer production, etc. The advantages and disadvantages of nanobiochar over bulk biochar are summarized herein, in detail. The processes and mechanisms involved in nanobiochar synthesis and contaminants sorption over nanobiochar are summarized. Finally, future directions and recommendations are suggested.

Combining biochar and grass-legume mixture to improve the phytoremediation of soils contaminated with potentially toxic elements (PTEs)

The combination of soil amendments with plants can be a viable option for restoring the functionality of PTEs-contaminated soils. Soil recovery could be further optimized through the mixed cropping of plant species (e.g. legumes and grasses) with different physiological characteristics. The aim of this study was to assess the phytoremediation ability of Vicia villosa Roth. And Lolium rigidum Gaud. Grown alone or in mixture in a soil contaminated with PTEs (C), i.e. Cd (23 mg kg-1), Pb (4473 mg kg-1) and Zn (3147 mg kg-1), and amended with 3% biochar (C + B). Biochar improved soil fertility and changed PTEs distribution, reducing soluble fractions and increasing the more stable ones. The addition of biochar increased the plant biomass of hairy vetch and annual ryegrass, both in monoculture and when in mixture. For example, shoot and root biomass of the C + B intercropped hairy vetch and annual ryegrass increased 9- and 7-fold, and ∼3-fold respectively, compared to the respective C plants. The biochar addition decreased PTE-uptake by both plants, while mixed cropping increased the uptake of PTEs by shoots of hairy vetch grown in C and C + B. The bioaccumulation, translocation factors, and mineralomass showed that hairy vetch and annual ryegrass behaved as phytostabilising plants. PTE mineralomasses proved that mixed cropping in C + B increased the overall capacity of PTE accumulation by plant tissues, particularly the root system. Therefore, the combination of biochar and legumes/grasses mixed cropping could be an effective solution for the recovery of PTEs-contaminated soils and the mitigation of their environmental hazard.

Life Cycle Assessment of Raw and Fe-Modified Biochars: Contributing to Circular Economy

Biochar is a carbonaceous material, which can be decorated with metals, that has been garnering attention to be used in the treatment of water due to its contribution to waste management and circular economy. This study presents the life cycle assessment (LCA) regarding the generation of Pinus patula raw biochar and its modification with iron (Fe-modified biochar). SimaPro 9.3.0.3 software was used to simulate the environmental impacts of both carbonaceous materials. The potential environmental effects obtained from the production of Pinus patula raw biochar were mainly ascribed to the source of energy utilized during this process. The potential impacts demonstrated that the generation of gases and polycyclic aromatic hydrocarbons are the main concern. In the case of Fe-modified biochar, the potential environmental effects differed only in the stage of the biomass modification with the metal. These effects are associated with the extraction of Fe and the generation of wastewater. These findings provide an insight into the environmental effects linked to the production of raw and Fe-modified biochar. However, further LCA research should be performed concerning other materials and compounds than can be generated during the biomass thermochemical conversion.

Biochar as a negative emission technology: A synthesis of field research on greenhouse gas emissions

Biochar is one of the few nature-based technologies with potential to help achieve net-zero emissions agriculture. Such an outcome would involve the mitigation of greenhouse gas (GHG) emission from agroecosystems and optimization of soil organic carbon sequestration. Interest in biochar application is heightened by its several co-benefits. Several reviews summarized past investigations on biochar, but these reviews mostly included laboratory, greenhouse, and mesocosm experiments. A synthesis of field studies is lacking, especially from a climate change mitigation standpoint. Our objectives are to (1) synthesize advances in field-based studies that have examined the GHG mitigation capacity of soil application of biochar and (2) identify limitations of the technology and research priorities. Field studies, published before 2022, were reviewed. Biochar has variable effects on GHG emissions, ranging from decrease, increase, to no change. Across studies, biochar reduced emissions of nitrous oxide (N2 O) by 18% and methane (CH4 ) by 3% but increased carbon dioxide (CO2 ) by 1.9%. When biochar was combined with N-fertilizer, it reduced CO2 , CH4 , and N2 O emissions in 61%, 64%, and 84% of the observations, and biochar plus other amendments reduced emissions in 78%, 92%, and 85% of the observations, respectively. Biochar has shown potential to reduce GHG emissions from soils, but long-term studies are needed to address discrepancies in emissions and identify best practices (rate, depth, and frequency) of biochar application to agricultural soils.

Biochar as a Green Sorbent for Remediation of Polluted Soils and Associated Toxicity Risks: A Critical Review

Soil contamination with organic contaminants and various heavy metals has become a global environmental concern. Biochar application for the remediation of polluted soils may render a novel solution to soil contamination issues. However, the complexity of the decontaminating mechanisms and the real environment significantly influences the preparation and large-scale application of biochar for soil ramification. This review paper highlights the utilization of biochar in immobilizing and eliminating the heavy metals and organic pollutants from contaminated soils and factors affecting the remediation efficacy of biochar. Furthermore, the risks related to biochar application in unpolluted agricultural soils are also debated. Biochar production conditions (pyrolysis temperature, feedstock type, and residence time) and the application rate greatly influence the biochar performance in remediating the contaminated soils. Biochars prepared at high temperatures (800 °C) contained more porosity and specific surface area, thus offering more adsorption potential. The redox and electrostatic adsorption contributed more to the adsorption of oxyanions, whereas ion exchange, complexation, and precipitation were mainly involved in the adsorption of cations. Volatile organic compounds (VOCs), dioxins, and polycyclic aromatic hydrocarbons (PAHs) produced during biochar pyrolysis induce negative impacts on soil alga, microbes, and plants. A careful selection of unpolluted feedstock and its compatibility with carbonization technology having suitable operating conditions is essential to avoid these impurities. It would help to prepare a specific biochar with desired features to target a particular pollutant at a specific site. This review provided explicit knowledge for developing a cost-effective, environment-friendly specific biochar, which could be used to decontaminate targeted polluted soils at a large scale. Furthermore, future study directions are also described to ensure a sustainable and safe application of biochar as a soil improver for the reclamation of polluted soils.

Artificial aging induced changes in biochar,s properties and Cd2+ adsorption behaviors

Fresh biochar has been widely applied to the remediation of heavy metals in soil by its property of adsorption, but the changes in its physicochemical properties and in situ adsorption performance over time cannot be ignored. In this study, the sorption of Cd²⁺ by corn straw biochars (CB) and municipal sludge biochars (SB) produced at 350 °C and 650 °C before and after H₂O₂ oxidation, and dry-wet and freeze-thaw aging were investigated using batch sorption experiments. The changes of physicochemical properties of biochar before and after aging were analyzed by various characterization methods. Based on these results, the impact of aging on the Cd²⁺ adsorption behavior could be clarified, which showed that CB650 was able to display the highest adsorption capacity in fresh biochars. Aging treatments reduced the ash content and pH value of CB, and significantly diminished the adsorption performance of Cd²⁺. These changes indicated that precipitation was a critical factor in the adsorption of Cd²⁺ on CB. The adsorption capacity of SB was enhanced after H₂O₂ oxidation, but weakened after dry-wet and freeze-thaw aging. This was closely related to the increase or decrease in the content of oxygen-containing functional groups, which in turn enhanced or inhibited its ability to compound with heavy metals. These results are of great significance for evaluating its long-term application prospects in the natural environment.

Nano Modifications of Biochar to Enhance Heavy Metal Adsorption from Wastewaters: A Review

Biochar (BC) is a carbon-rich material that can be obtained by thermal decomposition of agricultural solid waste under oxygen-limited conditions. It has received increasing attention as a cost-effective sorbent to treat metal-contaminated water due to attributes such as high porosity and the presence of various functional groups. The heavy metal (HM) sorption and removal capacity of BC can be enhanced by developing novel biochar nanohybrids (BNHs) that can be produced via surface modification of BC with nanomaterials. Loading of nanomaterials on the biochar surface can improve its physicochemical properties through alterations in the functional group profile, porosity, and availability of active sites on the BC surface which can enhance the HM adsorption ability. This manuscript provides information on preparation of nano-based biochar hybrids emanating from the type of modifying agent for the removal of different HM ions from wastewaters, and the underlying mechanisms have been discussed. Further, this compilation discusses published literature depicting the influence of different processes of preparation on the physicochemical properties and adsorption capacity of nanobiochar hybrids. The potential risks of BNHs have been reviewed to effectively avoid the possible harmful impacts on the environment, and future research directions have been proposed.

Novel Fuller Earth, Rock Phosphate, and Biochar for Phytomanagement of Toxic Metals in Polluted Soils

The present study was aimed to assess the efficacy of individual and combined effects of novel fuller earth, rock phosphate, and biochar (grapefruit peel) at 1% dosage on maize plant growth, soil chemical properties anduptake of toxic metals (TMs), such as Cu, Zn, Fe, and Cd, by maize plant sown in Korangi (district of Karachi, Pakistan) heavily polluted and Korangi less polluted (K-HP and K-LP) soils. The obtained results indicate that the dry biomass of maize crop increased by 14.13% with combined (FE1% + GBC1%) on K-HP soil and 18.24% with combined (FE 1% + GBC 1%) effects on K-LP soil. The maximum immobilization of Cu, Zn, Fe, and Cd was observed by 36% with GBC1%, 11.90% with FE1%, 98.97% with combined RP1% + GBC1%, 51.9% with FE1% + GBC1% for K-HP, 11.90% with FE1%, 28.6% with FE1%, 22.22% with RP1% + GBC1%, and 57.05% with FE 1% + GBC 1% for K-LP soil. After the addition of proposed substances, modification of soil OM, SOC, TOC, and pH level appeared this lead to the changes in the phyto-availability of Cu, Zn, Fe, and Cd in maize plant. It was concluded that the application of individual and combined effects of novel fuller earth, rock phosphate, and biochar (grapefruit peel) have potential to stabilize pollutants from multi-metal polluted soils for safe crop production.

Biochar as a potential strategy for remediation of contaminated mining soils: Mechanisms, applications, and future perspectives

Soil heavy metal contamination caused by mining activities is a global issue. These heavy metals can be enriched in plants and animals through the food chain, and eventually transferred to the human system and threatening public health. Biochar, as an environmentally friendly soil remediation agent, can effectively immobilize heavy metals in soil. However, most researchers concern more about the remediation effect and mechanism of biochar for industrial and agricultural contaminated soil, while related reviews focusing on mining soil remediation are limited. Furthermore, the remediation effect of soil in mining areas is affected by many factors, such as physicochemical properties of biochar, pyrolysis conditions, soil conditions, mining environment and application method, which can lead to great differences in the remediation effect of biochar in diverse mining areas. Therefore, it is necessary to systematically unravel the relevant knowledge of biochar remediation, which can also provide a guide for future studies on biochar remediation of contaminated soils in mining areas. The present paper first reviews the negative effects of mining activities on soil and the advantages of biochar relative to other remediation methods, followed by the mechanism and influencing factors of biochar on reducing heavy metal migration and bioavailability in mining soil were systematically summarized. Finally, the main research directions and development trends in the future are pointed out, and suggestions for future development are proposed.

Investigation of clay brick waste for the removal of copper, nickel and iron from aqueous solution: batch and fixed - bed column studies

The adsorption of copper, iron and nickel ions from an aqueous solution using Makoro granite clay brick waste through batch and fixed – bed column modes was investigated. The adsorbent was characterised using X-Ray Fluorescence, X-Ray Diffraction (XRD), Thermogravimetric Analysis, and Scanning Electron Microscopy (SEM). XRD results revealed crystalline peaks of Quartz (51.28 %) and mullite (23.40%) in fresh and loaded adsorbent with unnotable changes before and after adsorption. SEM images indicate the presence of micro pores and irregularly distributed surfaces. Batch kinetic maximum adsorption capacities for iron, copper, and nickel are 7.60, 6.70 and 6.20 mg g⁻¹ media respectively with 60 min as the optimum time. The maximum adsorption capacities at adsorbent dosage of 5 g L⁻¹ were 10.0, 7.60 and 7.20 mg L⁻¹ for iron, copper and nickel ions. The corresponding adsorption capabilities from the fixed-bed column reactor were 2.23, 2.22 and 0.74 mg g⁻¹ media respectively. The thermodynamics parameters of enthalpy change (ΔH) were 5.21, 9.32 and 5.22 kJ mol⁻¹ respectively for Copper, iron and nickel ions and the corresponding entropy change (ΔS) were -0.04, -0.05 and -0.03 kJmol⁻¹K⁻¹respectively and the process being non-spontaneous and exothermic. Thomas and Yoon-Nelson models yielded similar low coefficient of determination (R²) values (0.06 and 0.07) for copper and iron ions. Further investigations such as the use of real wastewater, competition of anions and further media characterisation and modifications are recommended.

Use of Biochar in Asphalts: Review

The growth of the world population has increased the production of wastes. These are generally incinerated or deposited in outdoor landfills, which impacts the environment and affects human health. A technique that allows to reuse of wastes and diminishes adverse effects on the environment is pyrolysis. Through this technique, a material known as Biochar (BC) is produced, which has proven to have interesting physical-chemical properties for it to be used as an asphalt modifier, and simultaneously, helps to mitigate negative impacts on the environment. The foregoing article presents a bibliographical review on the use of BC as a modifier for asphalt binders and asphalt mixes. This has the purpose of becoming a starting point for future research efforts. In the reviewed literature, there was no review found on this topic. In general terms, BC increases the performance of asphalt binders in high-temperature climates, and tends to reduce its performance in low-temperature ones. Few studies have evaluated the performance of BC on asphalt mixes and the long-term properties associated with durability. Based on the reviewed literature, at the end of the article, recommendations are provided for future study topics.

Biochar promotes arsenic (As) immobilization in contaminated soils and alleviates the As-toxicity in soybean (Glycine max (L.) Merr.)

Pot experiments were carried out to examine the biochar application and its alleviating effect on arsenic (As) toxicity in soybean plants. The data showed that As inhibits the growth indices and it increased with enhanced As-concentration in the substrate. The growth indices declined by more than 40% and the osmolyte concentration, photosynthetic pigments and antioxidant enzymes were decreased significantly among As-stressed plants. However, biochar application effectively mitigated the inhibitory effects of As on the soybean growth and the mitigation effect of treatment is more prevalent to the plants subjected to higher As-treatment. Biochar significantly reduced the As-uptake as revealed by the translocation factor (<1), indicating more As is restrained in the roots. The reduction in the total chlorophyll and carotenoid content was found less in the As-treated soybean plants upon biochar application. Similarly, the osmolytes comprising proline, sugar and protein increased upon application of biochar. The biomarkers viz., membrane stability index (MSI), hydrogen peroxide and malondialdehyde (MDA) content significantly decreased at higher As-levels upon biochar application as was also supported by the heatmap analysis. Moreover, the antioxidative enzymes also showed a significant increase upon addition of biochar. Our data showed that biochar amendment effectively alleviates the As-stress by enhancing the sorption of As in the substrate thus, significantly declining the As concentration in plant leaves, and thus the results of the current study depicting the role of biochar as a promising, cost-effective and eco-friendly amendment to decontaminate the As-polluted soils.

Improvement of Hydrogen Production during Anaerobic Fermentation of Food Waste Leachate by Enriched Bacterial Culture Using Biochar as an Additive

It has become urgent to develop cost-effective and clean technologies for the rapid and efficient treatment of food waste leachate, caused by the rapid accumulation of food waste volume. Moreover, to face the energy crisis, and to avoid dependence on non-renewable energy sources, the investigation of new sustainable and renewable energy sources from organic waste to energy conversion is an attractive option. Green energy biohydrogen production from food waste leachate, using a microbial pathway, is one of the most efficient technologies, due to its eco-friendly nature and high energy yield. Therefore, the present study aimed to evaluate the ability of an enriched bacterial mixture, isolated from forest soil, to enhance hydrogen production from food waste leachate using biochar. A lab-scale analysis was conducted at 35 °C and at different pH values (4, no adjustment, 6, 6.5, 7, and 7.5) over a period of 15 days. The sample with the enriched bacterial mixture supplemented with an optimum of 10 g/L of biochar showed the highest performance, with a maximum hydrogen yield of 1620 mL/day on day three. The total solid and volatile solid removal rates were 78.5% and 75% after 15 days, respectively. Acetic and butyrate acids were the dominant volatile fatty acids produced during the process, as favorable metabolic pathways for accelerating hydrogen production.

Effect of nZVI/biochar nanocomposites on Cd transport in clay mineral-coated quartz sand: Facilitation and rerelease

The development and application of nano-biochar synthesized by ball milling technology is still challenging in the field of environmental remediation because of its higher activity with pollutants. The purpose of this study was to investigate the transport behavior of two kinds of biochar nanoparticles (nanobiochar (NBC) and nZVI-modified nanobiochar (nZVI-NBC)) and Cd2+ in clay mineral (kaolinite, illite, and montmorillonite)-coated quartz sand columns. The interaction between biochar nanoparticles and Cd2+ in saturated porous media was studied in cotransport experiments. Then, the effect of biochar nanoparticles on the release of Cd2+ in contaminated media was explored by elution experiments. The cotransport experiments showed that the mobility of Cd2+ was enhanced by two kinds of biochar nanoparticles, while the transport of biochar was limited due to the presence of Cd2+. The elution experiments showed that the transport of biochar nanoparticles can be inhibited by Cd2+ previously immobilized in the sand column, and Cd2+ can be rereleased by biochar nanoparticles. The rerelease ability of nZVI-NBC to Cd2+ is weaker than that of NBC because nZVI is more easily retained in the sand column after oxidation, thus strengthening the immobilization of Cd2+. In general, the recoveries of NBC, nZVI-NBC and Cd2+ in saturated porous media were reduced by the presence of clay minerals. The experimental results describing the stability of biochar nanoparticles in sand columns are consistent with those predicted by the Derjaguin-Landau-Verwey-Overbeek theory. The transport behavior of Cd2+ and biochar nanoparticles in sand columns can be well simulated by advection-dispersion-reaction. These findings reveal the interaction between biochar nanoparticles and heavy metals in the soil environment and provide new insights into the transport and fate of environmental remediation materials and pollutants in the underground environment.