Biochar Properties Research Articles

Biochar and vegetation effects on discharge water quality from organic-substrate green roofs

Green roofs have been increasingly used to improve stormwater management, but poor vegetation performance on roof systems, varying with vegetation type, can degrade discharge quality. Biochar has been suggested as an effective substrate additive for green roofs to improve plant performance and discharge quality. However, research on the effects of biochar and vegetation on discharge quality in the long term is lacking and the underlying mechanisms involved are unclear. We examined the effects of biochar amendment and vegetation on discharge quality on organic-substrate green roofs with pre-grown sedum mats and direct-seeded native plants for three years and investigated the key factors influencing discharge quality. Sedum mats reduced the leaching of nutrients and particulate matter by 6–64% relative to native plants, largely due to the higher initial vegetation cover of the former. Biochar addition to sedum mat green roofs resulted in the best integrated water quality due to enhanced plant cover and sorption effects. Structural equation modeling revealed that nutrient leaching was primarily influenced by rainfall depth, time, vegetation cover, and substrate pH. Although biochar-amended sedum mats showed better discharge quality from organic-substrate green roofs, additional ecosystem services may be provided by native plants, suggesting future research to optimize plant composition and cover and biochar properties for sustainable green roofs.

Feedstock and pyrolysis temperature influence biochar properties and its interactions with soil substances: Insights from a DFT calculation

The use of biochar for soil improvement and emission reduction has been widely recognized for its excellent performance. However, the choice of feedstock and pyrolysis temperature for biochar production significantly affects its surface parameters and interactions with soil substances. In this study, we retrieved 465 peer-reviewed papers on the application of biochar in reducing greenhouse gas emissions and nutrient losses in soil and analyzed the changes in biochar physicochemical parameters from different feedstock and pyrolytic temperatures. Molecular simulation computing technology was also used to explore the impacts of these changes on the interaction between biochar and soil substances. The statistical results from the peer-reviewed papers indicated that biochar derived from wood-based feedstock exhibits superior physical characteristics, such as increased porosity and specific surface area. Conversely, biochar derived from straw-based feedstock was found to contain excellent element content, such as O, N, and H, and biochar derived from straw and produced at low pyrolysis temperatures contains a significant number of functional groups that enhance the charge transfer potential and adsorption stability by increasing surface charge density, charge distribution and bonding orbitals. However, it should be noted that this enhancement may also activate certain recalcitrant C compounds and promote biochar decomposition. Taken together, these results have significant implications for biochar practitioners when selecting suitable feedstock and pyrolysis temperatures based on agricultural needs and increasing their understanding of the interaction mechanism between biochar and soil substances.

New insights into biochar ammoniacal nitrogen adsorption and its correlation to aerobic degradation ammonia emissions

One of the technical barriers to the wider use of biochar in the composting practices is the lack of accurate quantification linking biochar properties to application outcomes. To address this issue, this paper investigates the use of ammonia nitrogen adsorption capacity by biochar as a predictor of ammonia emission during composting in the presence of biochar. With this in mind, this work investigated the use of ammonia nitrogen adsorption capacity of biochar when mixed with solid digestate, and the reduction in ammonia emissions resulting from the addition of biochar during aerobic degradation of solid digestate. A biochar synthesized at 900 °C, another synthesized at 450 °C, and two derivatives of the latter biochar, one chemically modified with nitric acid and the other with potassium hydroxide, were tested. This study concluded that the chemical characteristics of the biochar, including pH and oxygen/carbon atomic ratio, had a greater influence on the adsorption of ammonia nitrogen than physical attributes such as specific surface area. In this regard, nitric acid modification had superior performance compared to hydroxide potassium modification to increase biochar chemical attributes and reduce ammonia emissions when applied to aerobic degradation. Finally, a significant linear correlation (p-value < 0.05, r2 = 0.79) was found between biochar ammonia nitrogen adsorption capacity and ammonia emissions along composting, showing the potential of this variable as a predictive parameter. This study provides insights for future explorations aiming to develop predictive tests for biochar performance.

Examining diverse remediation mechanisms of biochar in soil contaminated with polycyclic aromatic hydrocarbon (PAH) of various ring structures: A global meta-analysis

Biochar is a widely recognized solution for addressing polycyclic aromatic hydrocarbon (PAH) contamination. However, it is unclear how the different physicochemical properties of PAHs affect remediation mechanisms, thereby affecting the remediation efficiency of biochar. In this study, a meta-analysis of 56 studies with 2236 observations was conducted to quantify the contributions of the preparation parameters and physicochemical properties of biochar, soil properties, and application measures to remediation efficiency. The research results revealed that PAH contents in the contaminated soil were significantly reduced by an average of 24.99 % after the application of biochar. Random Forest analysis identified feedstock, biochar SSA, soil pH, and rate of biochar application to be the most critical factors among the four categories. The reduction of PAH contents in the contaminated soil first decreased from 37.61 % to 17.44 % and then increased to 40.29 % with an increase in the number of aromatic rings from 2 to 6. Our study results suggest that biochar prepared from bio-waste at low temperatures could be favorable for reducing the content of NAP in soil. Wood-derived biochar pyrolyzed at a relatively high temperature is recommended for remediation of soil contaminated with PAHs with 5 or 6 aromatic rings. Our study provides a new perspective and an optimized strategy for the remediation of PAH-contaminated soils with biochar.

Biochar from co-pyrolysis of biological sludge and sawdust in comparison with the conventional filling media of vertical-flow constructed wetlands for the treatment of domestic-textile wastewater.

A biochar from co-pyrolysis of a mixture of sawdust and biological sludge (70/30, w/w), providing a high environmental compatibility in terms of water leachable polycyclic aromatic hydrocarbons and inorganic elements, together with a remarkable surface area (389 m2/g), was integrated into laboratory-scale vertical-flow constructed wetlands (VF-CWs), planted with Phragmites australis and unplanted. Biochar-filled VF-CWs have been tested for 8 months for the refining of effluents from the tertiary clariflocculation stage of a wastewater treatment plant operating in a mixed domestic-industrial textile context, in comparison with systems filled with gravel. VF-CW influents and effluents were monitored for chemical oxygen demand (COD), nitrogen and phosphorus cycles, and absorbance values at 254 and 420 nm, the latter as rapid and reliable screening parameters of the removal of organic micropollutants containing aromatic moieties and/or chromophores. Biochar-based systems provided a statistically significant improvement in COD (Δ = 22%) and ammonia (Δ = 35%) removal, as well as in the reduction of UV-Vis absorbance values (Δ = 32-34% and Δ = 28% for 254 and 420 nm, respectively), compared to gravel-filled microcosms. The higher removal of organic was mainly attributed to the well-known adsorption properties of biochars, while for nitrogen the biological mechanisms seem to play a predominant role.

Attempts to obtain clean biochar from hyperaccumulator through pyrolysis: Removal of heavy metals and transformation of phosphorus

The sound disposal of the ensuing heavy metal-rich plants can address the aftermath of phytoremediation. In this study, the first attempt was made to obtain heavy metals-free and phosphorus-rich biochar from phytoremediation residue (PR) by pyrolysis, and the effects of chlorinating agent type, chlorine dosage, and pyrolysis residence time on heavy metal removal, phosphorus (P) transformation, and biochar properties were investigated. The results showed that as chlorine dosage and pyrolysis residence time increased, added polyvinyl chloride (PVC) reduced the concentration of Zn in biochar to one-tenth of that in PR by intensified chlorination, where both Zn concentration (2727.50 mg/kg) and its leaching concentration (29.13 mg/L) met the utilization requirements, in which the acid-base property of biochar plays a key role in heavy metal leaching. Meanwhile, more than 90% of P in PR remained in biochar and the bioavailability of P in biochar enhanced with the decomposition of organic P to inorganic P, where the concentration of plant-availability P (Pnac) expanded from 1878.40 mg/kg in PR to 8454.00 mg/kg in biochar. This study demonstrated that heavy metal hyperaccumulator can be converted into heavy metal-free and phosphorus-rich biochar with promising applications, which provides new perspectives for the treatment of such hazardous wastes.

Biocarbon-Enhanced Flexible Nanofiber Mats for Sustainable Energy Generation and Wearable Device Applications

A broad diversity of nanofillers and polymers have been used to prepare polymer nanocomposites having potential applications in transportation, sports materials, aerospace, electronics, communication, energy, environment, and biomedical. Polyvinylidene fluoride (PVDF) finds a remarkable place in energy applications attributed to its highest known piezo- and pyroelectric properties. Like most carbon materials, Biochar has excellent electrical conductivity, since it comprises graphene layers with a great amount of carbon content. This study explores the behavior of composite nanofibers fabricated from rice straw-derived biochar-PVDF as wearable mats to harvest body energy into electricity. The composite nanofiber mats were fabricated using the electrospinning technique to get the benefit of both the piezoelectric properties of PVDF and the excellent electric properties of Biochar. The research found that incorporating 12 wt % of Biochar greatly enhances the piezoelectric content of the nanofiber mats without noteworthy loss in flexibility. In addition, the effects of membrane thickness (0.5, 0.9, and 1 mm) on their output voltages as a performance factor of the nanogenerator were measured. Results indicated that the effect of thickness was most influential in the thickness of 1 mm of PVDF/biochar nanofibers generator. The results of this work imply promising application development of such flexible composite piezoelectric nanofibrous membranes for environmentally sustainable energy generation and wearable self-powered electrical devices.

Cr and N co-doped biochar driving controllable peroxydisulfate activation pathways to degrade tetracycline: Pyrrolic N inducing singlet oxygen generation

Efficiently inducing nonradical pathway in peroxydisulfate (PDS) activation is promising in environmental decontamination due to the oxidation selectivity and anti-interference ability, but still remains challenges, e.g., low efficiency and high cost. In this study, a series of Cr and N co-doped biochar (Cr-N/BC) was synthesized via pyrolysis by using melamine-retanned chrome shaving (MCS) as precursors, to activate PDS toward the tetracycline (TC) degradation. The introduction of pyrrolic N on Cr-N/BC not only boosted the catalyst reactivity, but also altered the complexation state of PDS, thus triggering a shift in oxidative modes from the radical pathway into a singlet oxygen (1O2) dominated nonradical pathway, in which, the relative contribution of the nonradical oxidation to the TC degradation increased from 0 to 98%. Structure-activity relationship determination unveiled that pyrrolic N on Cr-N/BC surface greatly changed the charge distribution and chemical property of biochar, thereby facilitating the decomposition of PDS and generation of 1O2. In addition, ecotoxicological safety of the intermediates of TC in the 1O2-dominated pathway was evaluated to validate the superiority of the nonradical process. This study advances our understanding of designing reaction-oriented nonradical carbon-catalysis for selective decontamination.

Excess sludge-based biochar loaded with manganese enhances catalytic ozonation efficiency for landfill leachate treatment

This study developed an efficient and stable landfill leachate treatment process, which was based on the combination of biochar catalytic ozonation and activated sludge technology for intensive treatment of landfill leachate, aiming to achieve the standard discharge of leachate. The focus is to investigate the effect of manganese loading on the physicochemical properties of biochar and the mechanism of its catalytic ozonation. It was found that more surface functional groups (CO, Mn–O, etc.) and defects (ID/IG = 1.27) were exposed via the change of original carbon structure by loading Mn, which is conducive to the generation of lattice oxygen. Meanwhile, generating different valence states of Mn metal can improve the redox properties and electron migration rate, and encourage the production of reactive oxygen species (ROS) during the reaction process and enhance the catalytic efficiency. The synergistic action of microorganisms, especially denitrifying bacteria, was found to play a key role in the degradation of nitrogenous pollutants during the activated sludge process. The concentration of NH+4-N was reduced from the initial 1087.03 ± 9.56 mg/L to 9.05 ± 1.91 mg/L, while COD was reduced from 2290 ± 14.14 mg/L to 86.5 ± 2.12 mg/L, with corresponding removal rates of 99.17% and 99.20%, respectively. This method offers high efficiency and stability, achieving discharge standards for leachate (GB16889-2008). The synergy between Mn-loaded biochar and microorganisms in the activated sludge is key to effective treatment. This study offers a new approach to solving the challenge of waste leachate treatment.

Enhancing the thermal storage performance of biochar/paraffin composite phase change materials: Effect of oleophobic modification of biochar

Composite phase change materials (PCMs) possess excellent temperature-regulating capabilities, which can effectively reduce building energy consumption, ultimately contribute to energy saving and carbon reduction. In this study, oleophobic modification was carried out on the Zn modified - white pine biochar. The resultant oleophobic material (Zn-WPC-A) showed excellent supporting capability in the preparation of paraffin wax (PW)/biochar composite PCMs (PW/Zn-WPC-A). The oleophobic properties of biochar could effectively prevent PW leakage, and resulted in a high PW loading rate of 84.26% and an encapsulation efficiency of 82.26%. Zn-WPC-A demonstrated good physical and chemical compatibility with PW. The inclusion of Zn-WPC-A effectively promoted the nucleation in the crystallization process of PW. PW/Zn-WPC-A exhibited a thermal conductivity 3.28 times that of pure PW, displaying excellent thermal responsiveness. The fusion enthalpy of PW/Zn-WPC-A was 107.2 J/g. Furthermore, it displayed excellent stability within the working temperature range with no leakage observed. Simulated housing application experiments illustrated that the use of PW/Zn-WPC-A as building insulation material effectively slowed down the variation rate of indoor temperature. Therefore, the composite PCM using oleophobic modified biochar as supporting material showed excellent thermal performance and strong temperature-regulating capability.

Pb(ΙΙ), Cd(ΙΙ), and Mn(ΙΙ) adsorption onto pruning-derived biochar: physicochemical characterization, modeling and application in real landfill leachate

The aim of this study was to systemically evaluate how different pyrolysis temperatures (400, 550, and 700 °C) and particle sizes (1–2 mm and 63–75 µm) were influenced biochar evolution, made from urban pruning waste, during pyrolysis process and to establish their relationships with biochar potential for removal of lead (Pb), cadmium (Cd), and manganese (Mn) from real municipal solid waste landfill leachate. The effects of pH (2–7), contact time (30–300 min) and adsorbent dosage (0.1–5 g L−1) on heavy metals removal were also examined. The results showed that physicochemical properties of biochar were greatly influenced by pyrolysis temperature. Particle size, however, showed little influence on biochar characteristics (p > 0.05). The yield, volatile matter, hydrogen and oxygen contents, and surface functional groups decreased consistently with increasing pyrolysis temperature. An increase in the pH, electrical conductivity, ash, fixed carbon, and specific surface area values was also found. In biochar samples formed at high temperatures (i.e., 550 and 700 °C), Fourier transform infrared spectroscopy-FTIR studies confirmed the increase in aromaticity. Field emission scanning electron microscopy-FESEM images showed differences in the microporous structure and lower size pores at higher temperatures. Biochar pyrolyzed at 700 °C with a particle size of 63–75 µm (i.e., Lv700-63) showed the highest removal efficiency performance. Pb and Cd ions were completely removed (100%) by 0.2 g L−1 Lv700-63 at 7.0 pH and contact times of 120 and 90 min, respectively. The maximum percentage removal of Mn was 86.20% at optimum conditions of 0.2 g L−1 Lv700-63 dosage, 7.0 pH, and 180 min contact time. The findings suggests that the surface complexation, π-electron coordination, and cation exchange were the dominant mechanisms for the Pb, Cd, and Mn removal onto Lv700-63.

Biochar from phytoremediation plant residues: a review of its characteristics and potential applications.

Phytoremediation is a cost-effective and eco-friendly plant-based approach promising technique to repair heavy metal-contaminated soils. However, a significant quantity of plant residues needs to be properly treated and utilized. Pyrolysis is an effective technology for converting residues to biochar, which can solve the problem and avoid secondary contamination. This paper reviews the generation, and physicochemical properties of biochar from phytoremediation residues, and its application in soil improvement, environmental remediation, and carbon sequestration. In spite of this, it is important to be aware of the potential toxicity of heavy metals in biochar and the environmental risks of biochar before applying it to practical applications. Future challenges in the production and application of residue-derived biochar include the rational selection of pyrolysis parameters and proper handling of potentially hazardous components in the biochar.

CO2 Adsorption by Bamboo Biochars Obtained via a Salt-Assisted Pyrolysis Route

Recently, salt-assisted pyrolyzation has been deemed an emerging and efficient method for the preparation of biochars due to its facile operation as well as its good structural and chemical properties. In this work, biochars (MBCx) are prepared by heating bamboo powders in eutectic salts (Li2CO3 + K2CO3) at 500–600 °C in the air. Multiple technologies are employed to examine the physiochemical properties of bamboo biochars. Correlations between heating temperature and structural features and carbon dioxide uptakes of bamboo biochars have been investigated. The results show that heating temperature has a significant influence on the physicochemical properties of bamboo biochars. With the elevation of the heating temperature, the defect structures of bamboo biochars gradually ascend, especially when the heating temperature reaches 600 °C. MBCx biochars visibly exceed conventional bamboo biochar prepared via pyrolyzation in a nitrogen stream free of salt addition. Pyrolysis of bamboo in eutectic salts endows biochars with higher oxygen content and more carbon defects, which likely accounts for their better CO2 capture activities.

Pyrolysis of exhausted biochar sorbent: Fates of cadmium and generation of products

Biochar is a promising sorbent for Cd removal from water, while the disposal of the exhausted Cd-enriched biochar remains a challenge. In this study, pyrolysis was employed to treat the exhausted biochar under N2 and CO2 atmospheres at 600–900 °C, and the fate of Cd during pyrolysis and characteristics of high-valued products were determined. The results indicated that higher temperature and CO2 atmosphere favored the volatilization of Cd. Based on the toxicity characteristic leaching procedure (TCLP) results, the pyrolysis treatment under both atmospheres enhanced the stability of Cd, and the leached Cd concentration of regenerated biochar obtained at high temperatures (>800 °C) was lower than 1 mg/L. Compared with the pristine biochar, the regenerated biochar demonstrated higher carbon content and pH, whereas the contents of oxygen and hydrogen declined, and exhibited promising sorption properties (35.79 mg/g). The atmosphere played an important role in modifying biochar properties and syngas composition. The N2 atmosphere facilitated CH4 production, whereas the CO2 atmosphere increased the proportion of CO. These results implied that pyrolysis can be a valuable and environmental-friendly strategy for the treatment and reuse of exhausted biochar sorbent.

Machine learning for the management of biochar yield and properties of biomass sources for sustainable energy

AbstractBiochar is emerging as a potential solution for biomass conversion to meet the ever increasing demand for sustainable energy. Efficient management systems are needed in order to exploit fully the potential of biochar. Modern machine learning (ML) techniques, and in particular ensemble approaches and explainable AI methods, are valuable for forecasting the properties and efficiency of biochar properly. Machine‐learning‐based forecasts, optimization, and feature selection are critical for improving biomass management techniques. In this research, we explore the influences of these techniques on the accurate forecasting of biochar yield and properties for a range of biomass sources. We emphasize the importance of the interpretability of a model, as this improves human comprehension and trust in ML predictions. Sensitivity analysis is shown to be an effective technique for finding crucial biomass characteristics that influence the synthesis of biochar. Precision prognostics have far‐reaching ramifications, influencing industries such as biomass logistics, conversion technologies, and the successful use of biomass as renewable energy. These advances can make a substantial contribution to a greener future and can encourage the development of a circular biobased economy. This work emphasizes the importance of using sophisticated data‐driven methodologies such as ML in biochar synthesis, to usher in ecologically friendly energy solutions. These breakthroughs hold the key to a more sustainable and environmentally friendly future.

Application of Agro-industrial Solid Waste as Biochar for Iron (II) Removal from Aqueous Solution

In recent years, various industrial activities have introduced a high concentration of iron in the waterbody which causes serious problem to environment. This paper proposed the application of Exhausted Coffee Husk (ECH) as the biosorbent (BS) for removing iron (Fe) (II) in the aqueous solution. The ECH was carbonized into biochar before performing biosorption of the heavy metal ion. The effect of carbonization temperature, time and rate on the performance of the ECH biochar for removing Fe (II) were evaluated. The percentage of removal efficiency (RE) and the capacity of biosorption (mg/g) were considered as the determining parameters. The pyrolysis temperature was varied in a range of 200-600 °C with 50 °C of interval, while the time was in between 1h – 3h with a n interval of 0.5 h, and the temperature gradient of 5 – 25°C/min. The results showed that the temperature had a significant effect on the properties of the ECH biochar as BS for Fe (II). The temperature of 550 °C, at 1.5 h of time and 25 °C/min was chosen as the suggested carbonization temperature of biochar from ECH for biosorption of Fe (II). Keywords: Agro-industrial solid waste, Biosorption, Carbonization, Exhausted coffee husk (ECH), Heavy metal.

Hydrothermal Coupled Pyrolytic Treatment of Sewage Sludge and Food Waste Digestate for Heavy Metal Immobilization and Biochar Properties Enhancement

Hydrothermal Coupled Pyrolytic Treatment of Sewage Sludge and Food Waste Digestate for Heavy Metal Immobilization and Biochar Properties Enhancement

Machine learning insights in predicting heavy metals interaction with biochar

The use of machine learning (ML) in the field of predicting heavy metals interaction with biochar is a promising field of research, mainly because of the growing understanding of how removal efficiency is affected by characteristic variables, reaction conditions and biochar properties. The practical application in biochar still faces large challenges, such as difficulties in data collection, inadequate algorithm development, and insufficient information. However, the quantity, quality, and representation of data have a large impact on the accuracy, efficiency, and generalizability of machine learning tasks. From this perspective, the present data descriptors, the efficiency of machine learning-aided property and performance prediction, the interpretation of underlying mechanisms and complicated relationships, and some potential ways to augment the data are discussed regarding the interactions of heavy metals with biochar. Finally, future perspectives and challenges are discussed, and an enhanced model performance is proposed to reinforce the feasibility of a particular perspective.Graphical

An effective global biochar application strategy for reducing global cropland nitrogen emissions without compromising crop yield: Findings from a global meta-analysis and density functional theory calculation

Biochar is widely used to mitigate nitrogen (N) emissions in global croplands. However, its effectiveness varies due to spatial disparities in external factors such as soil properties and climate conditions, as well as biochar characteristics such as pH and carbon content. In this study, we used a molecular model to assess the distinct impacts of biochar and soil on soil N emissions. We employed a back-propagation neural network optimized using a genetic algorithm (GA-BPNN) to simulate N emissions in global croplands, utilizing data from 351 peer-reviewed papers. Then, a global biochar application strategy aimed at optimizing the reduction of N emissions across global croplands was devised by aligning biochar and soil parameters. Our findings indicate that the high electrophilic and nucleophilic properties of biochar's reactive surface significantly contribute to the reduction of soil N emissions. The GA-BPNN-based machine learning (ML) technology demonstrated superior predictive performance (with R2 ranging from 0.47 to 0.69) in predicting changes in soil N emissions post-biochar application compared to other machine learning algorithms. Our simulations show that optimized global biochar application increases NH3 volatilization but achieves the most significant reduction in global cropland N emissions, amounting to 16.04 Tg N yr−1 and representing approximately 28.45% of the estimated total N emissions from global croplands, all while preserving crop yields. Therefore, aligning biochar properties with specific soil parameters and environmental conditions could be a promising strategy for mitigating N emissions in global croplands and addressing climate degradation.

The Application of Pyrolysis Biochar Obtained from Waste Rapeseed Cake to Remove Copper from Industrial Wastewater: An Overview

Pyrolysis is a thermochemical technology for converting biomass into energy and chemical products consisting of bio-gas, bio-oil, and biochar. Several parameters influence the process efficiency and properties of pyrolysis products. These include the type of biomass, biomass preliminary preparation, gaseous atmosphere, final temperature, heating rate, and process time. This manuscript provides a general summary of the properties of the pyrolytic products of waste rapeseed cake, with particular emphasis on the sorption properties of biochar. Biochar, produced by the pyrolysis process of biomass, is emerging as a powerful tool for carbon sequestration, reducing greenhouse gas emissions, and purifying water from contaminants such as potentially toxic elements and antibiotics. The review found that the biochar obtained as a result of pyrolysis of chemically modified waste rapeseed cake is characterised by its excellent sorption properties. The obtained sorbents are characterised by sorption capacity relative to the copper(II) ion, ranging from 40 mg·g−1 to 100 mg·g−1, according to the pyrolysis conditions and chemical modification method. The purified pyrolysis gas obtained in the high-temperature process can be used to generate heat and energy. Bio-oil, with its significant combustion heat of 36 MJ·kg−1, can be a source of environmentally friendly green biofuel.