Multiple Controls on the Chemical and Physical Structure of Biochars

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.

Role of modeling and artificial intelligence in process parameter optimization of biochar: A review

Enhancement of crop yield, conservation and quality upgradation of soil, and efficient water management are the main objectives of sustainable agriculture and mitigating climate change's impact on agriculture. In recent days, biochar, obtained via thermochemical alteration of biomass is becoming a powerful agent for soil and water quality improvement, carbon sequestration, greenhouse gas emission reduction, and heavy metal adsorption. The present study predominantly focuses on various process parameters related to biochar preparation through pyrolysis, their impact on biochar production as well as physicochemical characteristics, and the optimization of such process parameters. Different designs of the experiment (DOE) and optimization techniques including traditional and non-traditional optimizations are discussed in the current review, along with their applicability and shortcomings. Since the biochar preparation process is tedious and energy-consuming, the present review will help to understand the importance of optimization in preparing biochar, thereby leading to a better way to prepare biochar.

Enhancing sorption of layered double hydroxide-based magnetic biochar for arsenic and cadmium through optimized preparation protocols

The impact of multiple preparation protocols on properties and performance of modified biochar remains unclear. This study prepared layered double hydroxide (LDH)-based magnetic biochars (LMBCs) with different LDH loading rates (LLR), pyrolysis temperatures, and biomass sources to explore their performance-characterization relationships toward As(III) and Cd(II). Higher LLR and pyrolysis temperature enhanced LMBCs᾿ adsorption capacities by increasing specific surface area (SSA) and metal/O-containing groups. Hence, LMBC produced at 2:1 LLR (LDH: magnetic biochar) and 800 ℃ pyrolysis exhibited maximum adsorption over 2 times that of LMBC with 0.5:1 LLR and 400 ℃ pyrolysis. Bamboo-sourced LMBC demonstrated superior adsorption than sewage sludge and garlic-sourced LMBCs due to its increased SSA, enabling a higher loading of nano-LDH. Adsorption of As(III) and Cd(II) onto LMBCs was governed by metal-mineral and metal-containing group through co-precipitation and complexation. This study provides a reference for adjusting the preparation protocols to improve sorption performance of modified biochar toward multiple heavy metals.

Permanganate activation by glucose-derived carbonaceous materials for highly efficient degradation of phenol and p-nitrophenol: Formation of hydroxyl radicals and multiple roles of carbonaceous materials

Owing to its inertness toward refractory organic pollutants and the release of Mn²⁺, the use of permanganate was limited in soil and groundwater remediation. The present study proposed an improvement strategy based on glucose-derived carbonaceous materials, which enhanced the potential of permanganate degrading organic pollutants. The glucose-derived carbonaceous material with 1000 °C charring temperature was named C1000, which was exploited in activating KMnO₄ for the elimination of refractory organic contaminants. The addition of C1000 in the KMnO₄ system triggered the degradation of refractory p-nitrophenol and quicken phenol degradation. Unlike the detection of Mn(III) species in a solo KMnO₄ system, the presence of C1000 facilitated the formation of ^•OH in the KMnO₄ system, which was confirmed by the use of quenchers such as methanol, benzoic acid, tertiary butanol, and carbonate. Additionally, the glucose-derived carbonaceous material played multiple roles in improving the performance of permanganate, including the enrichment of organic pollutants, donation of electrons to permanganate, and acting as an electron shuttle to facilitate the oxidation of organic pollutants by permanganate. The study's novel findings have the potential to expand the use of permanganate in the remediation of organic pollutants.

Nano-biochar: A novel solution for sustainable agriculture and environmental remediation

Currently, the applications of biochar (BC) in agricultural practices and for environmental remediation purposes have demonstrated multifaceted advantages despite a few limitations. Nano-BC offers considerable opportunities especially for the remediation of hazardous contaminants as well as the improvement of crop productivity. Positive outcomes of nano-BC on soil physico-chemical and biological characteristics have indicated its suitability for agricultural applications. Nano-BC may effectively regulate the mobilization and sorption of important micro- and macro-nutrients, along with the hazardous contaminants including potentially toxic metals, pesticides, etc. Additionally, the sorption characteristics of nano-BC depends substantially on feedstock materials and pyrolysis temperatures. Nevertheless, the conducted investigations regarding nano-BC are in infant stages, requiring extensive field investigations. The nano-enhanced properties of BC on one hand dramatically improve its effectiveness and sustainability, on the other hand, there may be associated with toxicity development in diverse aquatic and/or terrestrial environments. Therefore, risk assessment on soil organisms and its indirect impact on human health is another area of concern linked with the field application of nano-BC. The present review delineates the potentiality of nano-BC as an emerging sorbent for sustainable agriculture and environmental applications.

Element partitioning, emissions, and relative risk during disposal processes of diverse litters, fruit tree branches, and crop straws: dry distillation, incomplete combustion, and sufficient combustion

This study reports the release behaviors, enrichment characteristics, contamination level, and health risk of twenty-one elements in biomass, when dry distillation, incomplete combustion, and sufficient combustion. Results indicate that the element concentration in different kinds of biomass varies greatly. Even for the same kind of biomass, concentration in three products of dry distillation, incomplete combustion, and sufficient combustion is also different: fifteen elements (K, Ca, Mg, Al, Fe, Mn, B, Cu, Zn, Mo, Cd, Cr, Pb, Sb, Sn) have no significant difference in concentration but other six elements (As, Co, Ni, V, Na, P) are the opposite. Multivariate statistical approaches were used to assess five significant factors which affect element concentration, suggesting the contributes from biomass type, moisture content, soil, biomass age or organ, and disposal methods. Disposal methods and biomass type result in significant differences in element enrichment factor. More elements will release during sufficient combustion rather than dry distillation. The increasing of supplied oxygen during disposal process may increase the overall toxicity from elements release. The data of excess lifetime cancer risk (ELCR) suggests that Cr, Ni, Co, Cd, and Pb are the largest contributors to cancer risks during biomass application.

Tailoring biochar for persulfate-based environmental catalysis: Impact of biomass feedstocks

Biochar, a carbonaceous material with engineering potential, has gained attention as an efficient catalyst in persulfate-based advanced oxidation processes (PS-AOPs). Although biomass feedstocks are known as a critical factor for the performance of biochar, the relationship between the catalytic efficiency/mechanism and the types of biomass feedstocks is still unclear. Thus, according to recent advances in experimental and theoretical researches, this paper provides a systematic review of the properties of biochar, and the relationship between catalytic performance in PS-AOPs and biomass feedstocks, where the differences in physicochemical properties (surface properties, pore structure, etc.) and activation path of different sourced biochars, are introduced. In addition, how the tailoring of biochar (such as heteroatomic doping and co-pyrolysis of biomass) affects its activation efficiency and mechanism in PS-AOPs is summarized. Finally, the suitable application scenarios or systems of different sourced biochars, appropriate methods to improve the catalytic performance of different types of biochar and the prospects and challenges for the development of biochar in PS-AOPs are proposed.

Accessing biochar's porosity using a new low field NMR approach and its impacts on the retention of highly mobile herbicides

Agrowaste biochars [sugarcane straw (SS), rice husk (RH), poultry manure (PM), and sawdust (SW)] were synthesized at different pyrolysis temperatures (350, 450, 550, and 650 °C) to evaluate their potential to retain highly mobile herbicides, such as hexazinone and tebuthiuron that often contaminate water resources around sugarcane plantations. A new low field nuclear magnetic resonance approach based on decay due to diffusion in internal magnetic field (NMR-DDIF) was successfully used to determine biochar's porosity and specific surface area (SSA) to clear the findings of this work. SSA of pores with diameters >5.0 μm increased with pyrolysis temperatures and seemed to dictate biochar's retention, which was >70% of the applied amounts at 650 °C. These macropores appear to act as main arteries for herbicide intra-particle diffusion into smaller pores, thus enhancing herbicides retention. Biochar granulometry had little, but herbicide aging had a significant effect on sorption, mainly of tebuthiuron. However, soils amended with 10,000 kg ha^-1 of the biochars showed low sorption potential. Therefore, higher than usual biochar rates or proper incorporation strategies, i.e., surface incorporation, will be needed to remediate areas contaminated with these highly mobile herbicides, thus precluding their leaching to groundwaters.

Synchrotron X-ray microtomography and multifractal analysis for the characterization of pore structure and distribution in softwood pellet biochar

Biochar pores in the micrometer range (1-100 µm) derive from cellular structures of the plant biomass subjected to pyrolysis or can be the result of mechanical processing, such as pelleting. In this study, synchrotron X-ray microtomography was used to investigate the internal pore structure of softwood pellet biochar produced by slow pyrolysis at 550 and 700 °C. The microtomographic data sets consisted of 2025 images of 2560 × 2560 voxels with a voxel side length of 0.87 µm. The three-dimensional reconstructions revealed that pelleting and pyrolysis significantly altered the pore structures of the wood feedstock, creating a network of connected pores between fragments that resembled the wood morphology. While higher pyrolysis temperature increased the specific surface area (as determined by BET nitrogen adsorption), it did not affect the total observed porosity. Multifractal analysis was applied to assess the characteristics of the frequency distribution of pores along each of the three dimensions of reconstructed images of five softwood pellet biochar samples. The resulting singularity and Rényi spectra (generalized dimensions) indicated that the distribution of porosity had monofractal scaling behavior, was homogeneous within the analyzed volumes and consistent between replicate samples. Moreover, the pore distributions were isotropic (direction-independent), which is in strong contrast with the anisotropic pore structure of wood. As pores at the scale analyzed in this study are relevant, for example, for the supply of plant accessible water and habitable space for microorganisms, our findings combined with the ability to reproduce biochar with such pore distribution offer substantial advantages in various biochar applications.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s42773-021-00104-3.

Recent Developments in Understanding Biochar’s Physical–Chemistry

Biochar is a porous material obtained by biomass thermal degradation in oxygen-starved conditions. It is nowadays applied in many fields. For instance, it is used to synthesize new materials for environmental remediation, catalysis, animal feeding, adsorbent for smells, etc. In the last decades, biochar has been applied also to soils due to its beneficial effects on soil structure, pH, soil organic carbon content, and stability, and, therefore, soil fertility. In addition, this carbonaceous material shows high chemical stability. Once applied to soil it maintains its nature for centuries. Consequently, it can be considered a sink to store atmospheric carbon dioxide in soils, thereby mitigating the effects of global climatic changes. The literature contains plenty of papers dealing with biochar’s environmental effects. However, a discrepancy exists between studies dealing with biochar applications and those dealing with the physical-chemistry behind biochar behavior. On the one hand, the impression is that most of the papers where biochar is tested in soils are based on trial-and-error procedures. Sometimes these give positive results, sometimes not. Consequently, it appears that the scientific world is divided into two factions: either supporters or detractors. On the other hand, studies dealing with biochar’s physical-chemistry do not appear helpful in settling the factions’ problem. This review paper aims at collecting all the information on physical-chemistry of biochar and to use it to explain biochar’s role in different fields of application.

Feedstock particle size and pyrolysis temperature regulate effects of biochar on soil nitrous oxide and carbon dioxide emissions

Atmospheric greenhouse gas (GHG) concentration increases are a serious problem impacting global climate. Mitigation of agricultural GHG production is crucial as fertilized soils contribute substantially to changes in GHG atmospheric composition. Biochar derived from agricultural or forestry biowaste has been widely used in agriculture and may help mitigate GHG emissions. While different kinds of biochar and their effects on GHG emissions have been studied, feedstock particle size may interact with pyrolysis temperature to impact biochar effects on GHG emissions, but this has not been investigated. Here, feedstock particle size effects on biochar characteristics and soil nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions were studied using Camellia oleifera fruit shell feedstock with three particle size fractions (0.5-2, 2-5, and 5-10 mm) each pyrolyzed at 300, 450, and 600 °C. Results showed that dissolved organic carbon in biochar increased with particle size when pyrolyzed at 300 °C, but decreased with pyrolysis temperature. The 0.5-2 mm shell-derived biochar was associated with the lowest N₂O and CO₂ emission rates but the highest net nitrogen mineralization rates compared to 2-5 mm and 5-10 mm shell-derived biochar when pyrolyzed at 300 °C. Overall, shell particle size was more important for soil processes at lower pyrolysis temperatures with less variation among particle sizes at higher pyrolysis temperatures. The results indicated that feedstock particle size may interact with pyrolysis temperature and impact mitigation of soil N₂O and CO₂ emissions.

Post-processing of biochars to enhance plant growth responses: a review and meta-analysis

A number of processes for post-production treatment of "raw" biochars, including leaching, aeration, grinding or sieving to reduce particle size, and chemical or steam activation, have been suggested as means to enhance biochar effectiveness in agriculture, forestry, and environmental restoration. Here, I review studies on post-production processing methods and their effects on biochar physio-chemical properties and present a meta-analysis of plant growth and yield responses to post-processed vs. "raw" biochars. Data from 23 studies provide a total of 112 comparisons of responses to processed vs. unprocessed biochars, and 103 comparisons allowing assessment of effects relative to biochar particle size; additional 8 published studies involving 32 comparisons provide data on effects of biochar leachates. Overall, post-processed biochars resulted in significantly increased average plant growth responses 14% above those observed with unprocessed biochar. This overall effect was driven by plant growth responses to reduced biochar particle size, and heating/aeration treatments. The assessment of biochar effects by particle size indicates a peak at a particle size of 0.5-1.0 mm. Biochar leachate treatments showed very high heterogeneity among studies and no average growth benefit. I conclude that physiochemical post-processing of biochar offers substantial additional agronomic benefits compared to the use of unprocessed biochar. Further research on post-production treatments effects will be important for biochar utilization to maximize benefits to carbon sequestration and system productivity in agriculture, forestry, and environmental restoration.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s42773-021-00115-0.

Review of Biochar Properties and Remediation of Metal Pollution of Water and Soil

BACKGROUND

Mining, waste disposal, and agrochemical residues have contributed to pollution of water and soil with toxic metals in most low- and middle-income countries, raising concerns of ecological safety and public health. This has prompted many studies into the production and utilization of biochars to adsorb toxic metal contaminants from soil and water.

OBJECTIVE

The present study presents a review of biochar properties, the mechanisms of toxic metal adsorption onto biochar, and sorption of toxic metal contaminants in water and soil in small scale applications and laboratory experiments.

METHODS

A total of 305 articles were collected, and after screening for relevance, a final of 164 articles from both high- and low- and middle-income countries were used in this review paper.

DISCUSSION

Biochar for sorption has proven effective and its raw materials are readily available, cost effective, environmentally stable and a good form of waste management.

CONCLUSIONS

Different techniques of biochar production influence the properties of biochar and adsorption of toxic metals from water and soil.

COMPETING INTERESTS

The authors declare no competing financial interests.

Residual acidified biochar modulates growth, physiological responses, and water relations of maize (Zea mays) under heavy metal-contaminated irrigation water

A field trial was carried out to examine the influence of residual acidified biochar (a 3:100 (w/w) mixture of citric acid and citrus wood biochar) on soil properties, growth, water status, photosynthetic efficiency, metal accumulation, nutrition status, yield, and irrigation use efficiency (IUE) of maize grown under salty soil and metal-contaminated irrigation water. The acidified biochar (ABC) was applied to faba bean in 2016/2017 in saline soil (electrical conductivity (ECe) 7.6 dS m^-1) with three levels 0, 5, and 10 t ha^-1 with 4 replications. The results summarized that after a year of utilization, acidified biochar still significantly affected the growth and yield by improved soil properties and decreased maize uptake of sodium by transient sodium (Na⁺) binding because of its high adsorption capacity. Growth, physiology, and maize yields were influenced positively by ABC application, under metal-contaminated irrigation water. It was summarized that the utilization of ABC had a significant residual (P ≤ 0.05) effect on reducing nickle (Ni), lead (Pb), cadmium (Cd), and chromium (Cr) accumulation in maize under heavy metal-contaminated irrigation water. However, more detailed open-field experiments should be carried out to assess the long-term residual impacts of ABC for sustaining maize production under biotic stress.

Physicochemical characteristics of biochars can be beneficially manipulated using post-pyrolyzed particle size modification

This work aimed to study the changes in the physicochemical properties of biochars induced by post-pyrolyzed particle size processing. Twelve distinct physicochemical attributes of four different particle sized biochars, derived from three different feedstocks, including rice husk, tea wastes and woodchips; were investigated. Amongst all of the investigated characteristics water repellency (η2 = 0.99) and mean pore diameter (η2 = 0.95) were the characteristics most affected by feedstock type and particle size, respectively. The interaction effect between biochar type and particle size was extremely significant (P < 0.001) for surface area and mean pore diameter. While feedstock mainly controlled biochar characteristics, most characteristics were also particle size dependent, where size dependency was more influential on physical than chemical properties. For most properties a significant interaction effect between biochar type and particle size was also detected.

Removal mechanisms of aqueous Cr(VI) using apple wood biochar: a spectroscopic study

Highly toxic Cr(VI) poses huge threats to human health and ecosystem. This study utilized biochar obtained from apple wood which is favorable for the formation of high C content biochar for removing Cr(VI) from aqueous media. Cr(VI) removal was highly pH-dependent with the highest Cr(VI) removal efficiency (99.9%) at pH 2.0. Fourier-transform infrared spectroscopy (FTIR) results showed that the functionalities CO and CO on biochar were likely involved in Cr(VI) treatment. Results of X-ray photoelectron spectroscopy (XPS) analysis and X-ray absorption near-edge structure (XANES) spectra indicated that the majority of Cr exhibited as the reduced Cr(III) on the biochar. Confocal micro X-ray fluorescence (μ-XRF) maps confirmed the heterogeneous distribution of Cr on biochar. The electrostatic attraction, Cr(VI) reduction, Cr(III) complexation, and ion exchange likely accounted for the principal processes of Cr(VI) removal from water. These results showed that biochar can be an effective reactive medium for remediation of Cr(VI) in an aqueous solution. This study firstly integrated the Cr(VI) removal data with XANES and confocal μ-XRF mapping to obtain a deeper understanding of Cr speciation and distribution on biochar, which was critical for identifying the key role of functional groups and Cr(VI) removal mechanisms using apple wood biochar.

The Preliminary Study of Water-Retention Related Properties of Biochar Produced from Various Feedstock at Different Pyrolysis Temperatures

Physicochemical properties of biochar, which are used as a soil amendment material in agricultural fields, are different depending on biomass feedstock and pyrolysis processes. In this study, we evaluated the influence of feedstock type and pyrolysis temperature on the water-retention related properties of biochar. Wood-chips [cedar (CE) and cypress (CY)]; moso bamboo (MB); rice husk (RH); sugarcane bagasse (SB); poultry manure (PM) and agricultural wastewater sludge (WS) were each pyrolysed at 400, 600 and 800 °C with a retention time of two hours. Scanning electron microscopy micrographs (SEM), hydrophobicity indices, pore-size distribution measured by mercury-intrusion porosimetry, water-retention curves (WRCs) and plant-available water capacities (AWCs) of the biochars were measured to evaluate their potentials as soil-amendment materials for improving soils’ water-retention. As the pyrolysis temperature was increased, the hydrophobicity index decreased. On the other hand, pyrolysis temperature did not affect the distribution of micrometre-range pores, which are useful for plant-available water, of biochars. The AWCs of the biochars formed from CE, CY and SB were greater than those produced from other feedstocks, at 600 and 800 °C. Therefore, we can suggest that the biochars derived from wood-chips (CE and CY) and SB have greater potential for enhancing soils’ water-retention.

Quick electrochemical immunoassay for hantavirus detection based on biochar platform

This work describes the first method using biochar (BC) as carbonaceous platform for immunoassay application. BC is a highly functionalized material obtained through biomass pyrolysis under controlled conditions. Due to the highly functionalized surface, covalent binding between BC and biomolecules can be performed by EDC/NHS conjugation. The application of the modified electrode was done with Hantavirus, that are etiologic agents mainly transmitted by wild rodents. Among its pathologies Hantavirus Cardiopulmonary Syndrome (HCPS) arises at Americas, caused by Hantavirus Araucária and reaches 40% lethality. The diagnostic is based on the presence of specific hantavirus nucleoprotein (Np), under viremic condition or IgG2b antibodies (Ab), during first symptoms. The results presented a device sensitivity of 5.28 μA dec^-1 and a LOD of 0.14 ng mL^-1 to the Np detection, ranging from 5.0 ng mL^-1 to 1.0 μg mL^-1, the Ab detection works as qualitative type sensor above 200 ng mL^-1. Both sensors were evaluated its selectivity and serum samples; selectivity against Gumboro disease, VP2 protein, and antibody IgG2a against Yellow fever disease (YF), respectively. So, the devices here proposed are promising tool suitable for both rodent and human hantavirus clinical surveys.

Biochar Particle Size and Post-Pyrolysis Mechanical Processing Affect Soil pH, Water Retention Capacity, and Plant Performance

It has become common practice in soil applications of biochar to use ground and/or sieved material to reduce particle size and so enhance mixing and surface contact between soils and char particles. Smaller particle sizes of biochars have been suggested to enhance liming effects and nutrient exchange, and potentially to increase water storage capacity; however, data remains scarce and effects on plant growth responses have not been examined. We manipulated biochar particle size by sieving or grinding to generate particles in two size ranges (0.06–0.5 mm and 2–4 mm), and examined effects on soil pH, soil water retention, and plant physiological and growth performance of two test species (ryegrass: Lolium multiflorum, and velvetleaf: Abutilon theophrasti) grown in a granitic sand culture. The small particle sieved biochar had the largest liming effect, increasing substrate pH values by an additional ~0.3 pH units compared to other biochars. Small particle size biochar showed enhanced water retention capacity, and sieved biochars showed 91%–258% larger water retention capacity than ground biochars of similar particle size, likely because sieved particles were more elongated than ground particles, and thus increased soil interpore volume. The two plant species tested showed distinct patterns of response to biochar treatments: ryegrass showed a better growth response to large biochar particles, while velvetleaf showed the highest response to the small, sieved biochar treatment. We show for the first time that post-processing of biochars by sieving and grinding has distinct effects on biochar chemical and physical properties, and that resulting differences in properties have large but strongly species-specific effects on plant performance in biochar-amended substrates.

An overview of the effect of pyrolysis process parameters on biochar stability

Biochar produced from biomass pyrolysis is becoming a powerful tool for carbon sequestration and greenhouse gas (GHG) emission reduction. Biochar C recalcitrance or biochar stability is the decisive property determining its carbon sequestration potential. The effect of pyrolysis process parameters on biochar stability is becoming a frontier of biochar study. This review discussed comprehensively how and why biomass compositions and physicochemical properties and biomass processing conditions such as pyrolysis temperature and reaction residence time affect the stability of biochar. The review found that relative high temperature (400-700 °C), long reaction residence time, slow heating rate, high pressure, the presence of some minerals and biomass feedstock of high-lignin content with large particle size are preferable to biochar stability. However, challenges exist to mediate the trade-offs between biochar stability and other potential wins. Strategies were then proposed to promote the utilization of biochar as a climate change mitigation tool.

Natural climate solutions for the United States

Limiting climate warming to <2°C requires increased mitigation efforts, including land stewardship, whose potential in the United States is poorly understood. We quantified the potential of natural climate solutions (NCS)-21 conservation, restoration, and improved land management interventions on natural and agricultural lands-to increase carbon storage and avoid greenhouse gas emissions in the United States. We found a maximum potential of 1.2 (0.9 to 1.6) Pg CO₂e year^-1, the equivalent of 21% of current net annual emissions of the United States. At current carbon market prices (USD 10 per Mg CO₂e), 299 Tg CO₂e year^-1 could be achieved. NCS would also provide air and water filtration, flood control, soil health, wildlife habitat, and climate resilience benefits.

Production, characterization and adsorption studies of bamboo-based biochar/montmorillonite composite for nitrate removal

Biochar is a promising immobilization tool for various contaminants in liquid wastes, aqueous solutions and soils. To further improve the sorption characteristics, a biochar/montmorillonite composite was produced and synthesized in an experimental pyrolysis reactor, using bamboo as biomass feedstock. The composite was characterized by physico-chemical and structural methods (FTIR, SEM, SEM/EDX, SSA, Low temperature nitrogen adsorption method). Based on these methods, the successful preparation of a bamboo based biochar/montmorillonite composite preparation has been demonstrated. The particles of montmorillonite were distributed across the biochar surface. The adsorption studies for removal nitrates from aqueous solutions were investigated by a batch method at laboratory temperatures. The experimental data were fitted by three adsorption models (Langmuir, Freundlich and DR; R² > 0.93). The maximum adsorption capacity achieved by biochar at pH 4, was about 5 mg g^-1 and by biochar/montmorillonite composite 9 mg g^-1. The results suggest that the bamboo-based biochar/montmorillonite composite can be used effectively in the treatment of industrial effluents or waste water containing anionic pollutants such as nitrates.

An Attempt to Find a Suitable Biomass for Biochar-Based Polypropylene Biocomposites

Four biomass wastes (rice husk, coffee husk, coarse wool, and landfill wood) were added with biochar and polypropylene (PP) to manufacture biocomposites. Individual biomasses were tested for their combustion behavior using cone calorimeter. Biocomposites were analyzed for their fire/thermal, mechanical, and morphological properties. Wood had the most desirable comprehensive effect on both the mechanical and fire properties of composites. In particular, wood and biochar composite exhibited the highest values of tensile/flexural properties with a relatively low peak heat release rate. In general, application of waste derived biochar and biomasses drastically reduced the susceptibility of neat PP towards fire.

Effect of freeze-thaw cycling on grain size of biochar

Biochar may improve soil hydrology by altering soil porosity, density, hydraulic conductivity, and water-holding capacity. These properties are associated with the grain size distributions of both soil and biochar, and therefore may change as biochar weathers. Here we report how freeze-thaw (F-T) cycling impacts the grain size of pine, mesquite, miscanthus, and sewage waste biochars under two drainage conditions: undrained (all biochars) and a gravity-drained experiment (mesquite biochar only). In the undrained experiment plant biochars showed a decrease in median grain size and a change in grain-size distribution consistent with the flaking off of thin layers from the biochar surface. Biochar grain size distribution changed from unimodal to bimodal, with lower peaks and wider distributions. For plant biochars the median grain size decreased by up to 45.8% and the grain aspect ratio increased by up to 22.4% after 20 F-T cycles. F-T cycling did not change the grain size or aspect ratio of sewage waste biochar. We also observed changes in the skeletal density of biochars (maximum increase of 1.3%), envelope density (maximum decrease of 12.2%), and intraporosity (porosity inside particles, maximum increase of 3.2%). In the drained experiment, mesquite biochar exhibited a decrease of median grain size (up to 4.2%) and no change of aspect ratio after 10 F-T cycles. We also document a positive relationship between grain size decrease and initial water content, suggesting that, biochar properties that increase water content, like high intraporosity and pore connectivity large intrapores, and hydrophilicity, combined with undrained conditions and frequent F-T cycles may increase biochar breakdown. The observed changes in biochar particle size and shape can be expected to alter hydrologic properties, and thus may impact both plant growth and the hydrologic cycle.

A critical review on sustainable biochar system through gasification: Energy and environmental applications

This review lays great emphasis on production and characteristics of biochar through gasification. Specifically, the physicochemical properties and yield of biochar through the diverse gasification conditions associated with various types of biomass were extensively evaluated. In addition, potential application scenarios of biochar through gasification were explored and their environmental implications were discussed. To qualitatively evaluate biochar sustainability through the gasification process, all gasification products (i.e., syngas and biochar) were evaluated via life cycle assessment (LCA). A concept of balancing syngas and biochar production for an economically and environmentally feasible gasification system was proposed and relevant challenges and solutions were suggested in this review.

Effect of environmental exposure on charcoal density and porosity in a boreal forest

Although charcoal's density and porosity shape its environmental roles (e.g. controlling its landscape movement and determining the internal pore space available as microbial habitat), the rate of change of these properties in the environment remains largely unknown. With time, charcoal pores may fill or charcoal particles may shatter, altering the ecosystem services delivered. In this study we examined the effects of environmental exposure on the density and porosity of charcoals pyrolyzed at two different temperatures (350 and 520°C). Fresh charcoal made from the dominant local tree (Pinus sylvestris) was returned in litter incubations to Norwegian boreal forest soils for 20months in three different placements: (i) aboveground, (ii) in the humus layer, and (iii) under the humus layer in contact with the mineral subsoil. By varying soil horizon placement we were able to separate the effects of infill from the effects of environmental disturbance on charcoal density and porosity. Environmental exposure changed charcoal density and porosity, and the response varied with environmental placement. Charcoal placed in soil layers increased in porosity by ~1-2% after 20months' incubation. This is likely because open indentations on the charcoal surface became partially occluded, creating more detectable pore space. In contrast, the porosity of charcoal incubated aboveground decreased slightly (~1-2% over 20months). Because there were no minerals or humic substances to infill the aboveground charcoal samples, this porosity reduction was likely caused by breakage of particles induced by weathering. When charcoal particles cleave through pores, internal pore space is destroyed. The small changes observed here indicate that environmental exposure did not trigger rapid shifts in charcoal density and porosity. In addition, these physical properties appear not to have reached equilibrium after 20months incubation, suggesting that the effect of environmental exposure on charcoal's physical properties occurs on the timescale of years to decades.

Biochar particle size, shape, and porosity act together to influence soil water properties

Many studies report that, under some circumstances, amending soil with biochar can improve field capacity and plant-available water. However, little is known about the mechanisms that control these improvements, making it challenging to predict when biochar will improve soil water properties. To develop a conceptual model explaining biochar’s effects on soil hydrologic processes, we conducted a series of well constrained laboratory experiments using a sand matrix to test the effects of biochar particle size and porosity on soil water retention curves. We showed that biochar particle size affects soil water storage through changing pore space between particles (interpores) and by adding pores that are part of the biochar (intrapores). We used these experimental results to better understand how biochar intrapores and biochar particle shape control the observed changes in water retention when capillary pressure is the main component of soil water potential. We propose that biochar’s intrapores increase water content of biochar-sand mixtures when soils are drier. When biochar-sand mixtures are wetter, biochar particles’ elongated shape disrupts the packing of grains in the sandy matrix, increasing the volume between grains (interpores) available for water storage. These results imply that biochars with a high intraporosity and irregular shapes will most effectively increase water storage in coarse soils.

Characterization and quantification of biochar alkalinity

Lack of knowledge regarding the nature of biochar alkalis has hindered understanding of pH-sensitive biochar-soil interactions. Here we investigate the nature of biochar alkalinity and present a cohesive suite of methods for its quantification. Biochars produced from cellulose, corn stover and wood feedstocks had significant low-pK_a organic structural (0.03-0.34 meq g^-1), other organic (0-0.92 meq g^-1), carbonate (0.02-1.5 meq g^-1), and other inorganic (0-0.26 meq g^-1) alkalinities. All four categories of biochar alkalinity contributed to total biochar alkalinity and are therefore relevant to pH-sensitive soil processes. Total biochar alkalinity was strongly correlated with base cation concentration, but biochar alkalinity was not a simple function of elemental composition, soluble ash, fixed carbon, or volatile matter content. More research is needed to characterize soluble biochar alkalis other than carbonates and to establish predictive relationships among biochar production parameters and the composition of biochar alkalis.

Biochar physico-chemical properties as affected by environmental exposure

To best use biochar as a sustainable soil management and carbon (C) sequestration technique, we must understand the effect of environmental exposure on its physical and chemical properties because they likely vary with time. These properties play an important role in biochar's environmental behavior and delivery of ecosystem services. We measured biochar before amendment and four years after amendment to a commercial nectarine orchard at rates of 5, 15 and 30tha(-1). We combined two pycnometry techniques to measure skeletal (ρs) and envelope (ρe) density and to estimate the total pore volume of biochar particles. We also examined imbibition, which can provide information about soil hydraulic conductivity. Finally, we investigated the chemical properties, surface, inner layers atomic composition and C1s bonding state of biochar fragments through X-ray photoelectron spectroscopy (XPS). Ageing increased biochar skeletal density and reduced the water imbibition rate within fragments as a consequence of partial pore clogging. However, porosity and the volume of water stored in particles remained unchanged. Exposure reduced biochar pH, EC, and total C, but enhanced total N, nitrate-N, and ammonium-N. X-ray photoelectron spectroscopy analyses showed an increase of O, Si, N, Na, Al, Ca, Mn, and Fe surface (0-5nm) atomic composition (at%) and a reduction of C and K in aged particles, confirming the interactions of biochar with soil inorganic and organic phases. Oxidation of aged biochar fragments occurred mainly in the particle surface, and progressively decreased down to 75nm. Biochar surface chemistry changes included the development of carbonyl and carboxylate functional groups, again mainly on the particle surface. However, changes were noticeable down to 75nm, while no significant changes were measured in the deepest layer, up to 110nm. Results show unequivocal shifts in biochar physical and chemical properties/characteristics over short (~years) timescales.

Effects of biochar amendment on relieving cadmium stress and reducing cadmium accumulation in pepper

Biochar is widely used in agricultural soils or heavy metal-polluted soils to improve the quality of the soils, which would affect the growth of the plant. However, the information of biochars' effect on the plant growth was still lacking, especially for the physiological response of the plant. Pot experiments were used to examine the effect of willow-derived biochars at two temperatures (450 and 600 °C) on cadmium (Cd) accumulation in pepper and to reveal the response of physiological parameters to exogenous Cd stress (1 and 5 mg/kg). The results showed that the accumulation of Cd in pepper roots was higher than that in pepper shoots. For low level of Cd treatments, high additional rates of the biochars could obviously reduce the accumulation of Cd in the pepper roots. Moreover, there was a negative correlation between the C content of the biochar-amended soils and the Cd content of the pepper root, suggesting that the application of biochar to the soil decreased the Cd accumulation in the root. A positive relationship between the H/C ratios of biochar-amended soils and their corresponding Cd concentrations in pepper root indicated that low thermal temperature-derived biochar could play an important role in immobilizing Cd in the soil. Furthermore, on the condition of low Cd level of treatments, the malondialdehyde content decreased in biochar-amended soils, especially at high biochar application rate. The chlorophyll content increased with increasing the rates of the biochar application. The physiological parameters indirectly proved that the application of biochar did not always alleviate the toxic effects of Cd on pepper leaves at high Cd concentration.

Fast enhancement on bondability of wheat straw surface for bio-composites manufacture via dielectric barrier discharge plasma

The increased roughness, improved wettability, and enhanced polarity after plasma treatment have responsibility for the enhancement on bondability of bio-composite.

Chemical and Isotopic Thresholds in Charring: Implications for the Interpretation of Charcoal Mass and Isotopic Data

Charcoal plays a significant role in the long-term carbon cycle, and its use as a soil amendment is promoted as a C sequestration strategy (biochar). One challenge in this research area is understanding the heterogeneity of charcoal properties. Although the maximum reaction temperature is often used as a gauge of pyrolysis conditions, pyrolysis duration also changes charcoal physicochemical qualities. Here, we introduce a formal definition of charring intensity (CI) to more accurately characterize pyrolysis, and we document variation in charcoal chemical properties with variation in CI. We find two types of responses to CI: either linear or threshold relationships. Mass yield decreases linearly with CI, while a threshold exists across which % C, % N, and δ(15)N exhibit large changes. This CI threshold co-occurs with an increase in charcoal aromaticity. C isotopes do not change from original biomass values, supporting the use of charcoal δ(13)C signatures to infer paleoecological conditions. Fractionation of N isotopes indicates that fire may be enriching soils in (15)N through pyrolytic N isotope fractionation. This influx of "black N" could have a significant impact on soil N isotopes, which we show theoretically using a simple mass-balance model.

Digestion of high rate activated sludge coupled to biochar formation for soil improvement in the tropics

High rate activated sludge (HRAS) is well-biodegradable sludge enabling energy neutrality of wastewater treatment plants via anaerobic digestion. However, even through successful digestion a notable residue still remains. Here we investigated whether this residue can be converted to biochar, for its use as a fertilizer or as a solid fuel, and assessed its characteristics and overall process efficiency. In a first phase, HRAS was anaerobicaly digested under mesophilic conditions at a sludge retention time of 20 days. HRAS digested well (57.9 ± 6.2% VS degradation) producing on average 0.23 ± 0.04 L CH4 per gram VS fed. The digestate particulates were partially air-dried to mimic conditions used in developing countries, and subsequently converted to biochar by fixed-bed slow pyrolysis at a residence time of 15 min and at highest heating temperatures (HHT) of 300 °C, 400 °C and 600 °C. Subsequently, the produced chars were characterized by proximate analysis, CHN-elemental analysis, pH in solution and bomb calorimetry for higher heating value. The yield and volatile matter decreased with increasing HHT while ash content and fixed carbon increased with increasing HHT. The produced biochar showed properties optimal towards soil amendment when produced at a temperature of 600 °C with values of 5.91 wt%, 23.75 wt%, 70.35% on dry basis (db) and 0.44 for volatile matter, fixed carbon, ash content and H/C ratio, respectively. With regard to its use for energy purposes, the biochar represented a lower calorific value than the dried HRAS digestate likely due to high ash content. Based on these findings, it can be concluded that anaerobic digestion of HRAS and its subsequent biochar formation at HHT of 600 °C represents an attractive route for sludge management in tropic settings like in Uganda, coupling carbon capture to energy generation, carbon sequestration and nutrient recovery.

Characterization and selection of biochar for an efficient retention of tricyclazole in a flooded alluvial paddy soil

Biochars, from different organic residues, are increasingly proposed as soil amendments for their agronomic and environmental benefits. A systematic detection method that correlates biochar properties to their abilities to adsorb organic compounds is still lacking. Seven biochars obtained after pyrolysis at different temperatures and from different feedstock (alperujo compost, rice hull, and woody debris), were characterized and tested to reveal potential remedial forms for pesticide capture in flooded soils. Biochar properties were determined by nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared spectroscopy, specific surface area (SSA) assessment and scanning electron microscopy. In addition, dissolved organic matter (DOM) from these biochars was extracted and quantified in order to evaluate the effect on pesticide sorption. The biochars from alperujo compost presented very high affinity to the fungicide tricyclazole (55.9, 83.5, and 90.3% for B1, B4, and B5, respectively). This affinity was positively correlated with the pyrolysis temperature, the pH, the increased SSA of the biochars, and the enhanced aromaticity. Sorptive capacities were negatively related to DOM contents. The amendment with a mixture of compost and biochar endows the alluvial soil with high sorptive properties (from K(fads(soil)) = 9.26 to K(fads(mixture)) = 17.89) without impeding the slow release of tricyclazole.

Nutrient transformation during aerobic composting of pig manure with biochar prepared at different temperatures

The effects of the corn stalk charred biomass (CB) prepared at different pyrolysis temperatures as additives on nutrient transformation during aerobic composting of pig manure were investigated. The results showed that the addition of CB carbonized at different temperatures to pig manure compost significantly influenced the compost temperature, moisture, pH, electrical conductivity, organic matter degradation, total nitrogen, [Formula: see text] and NH3 variations during composting. Compared with control and adding CB charred at lower temperature treatments, the addition of CB prepared over 700°C resulted in higher pH (over 9.2) and NH3 emission and lower potherb mustard seed germination index value during the thermophilic phase. Peak temperatures of composts appeared at 7 days for control and 11 days for CB added treatments. During 90 days composting, the organic matter degradation could be increased over 14.8-29.6% after adding of CB in the compost mixture. The introduction of CB in pig manure could prolong the thermophilic phase, inhibit moisture reduce, facilitate the organic matter decomposition, reduce diethylene triamine pentaacetic acid (DTPA) extractable Zn and Cu contents in pig manure composts and increase ryegrass growth. The study indicated that the corn stalk CB prepared around 500°C was a suitable additive in pig manure composting.

Biochar-induced changes in soil hydraulic conductivity and dissolved nutrient fluxes constrained by laboratory experiments

The addition of charcoal (or biochar) to soil has significant carbon sequestration and agronomic potential, making it important to determine how this potentially large anthropogenic carbon influx will alter ecosystem functions. We used column experiments to quantify how hydrologic and nutrient-retention characteristics of three soil materials differed with biochar amendment. We compared three homogeneous soil materials (sand, organic-rich topsoil, and clay-rich Hapludert) to provide a basic understanding of biochar-soil-water interactions. On average, biochar amendment decreased saturated hydraulic conductivity (K) by 92% in sand and 67% in organic soil, but increased K by 328% in clay-rich soil. The change in K for sand was not predicted by the accompanying physical changes to the soil mixture; the sand-biochar mixture was less dense and more porous than sand without biochar. We propose two hydrologic pathways that are potential drivers for this behavior: one through the interstitial biochar-sand space and a second through pores within the biochar grains themselves. This second pathway adds to the porosity of the soil mixture; however, it likely does not add to the effective soil K due to its tortuosity and smaller pore size. Therefore, the addition of biochar can increase or decrease soil drainage, and suggests that any potential improvement of water delivery to plants is dependent on soil type, biochar amendment rate, and biochar properties. Changes in dissolved carbon (C) and nitrogen (N) fluxes also differed; with biochar increasing the C flux from organic-poor sand, decreasing it from organic-rich soils, and retaining small amounts of soil-derived N. The aromaticity of C lost from sand and clay increased, suggesting lost C was biochar-derived; though the loss accounts for only 0.05% of added biochar-C. Thus, the direction and magnitude of hydraulic, C, and N changes associated with biochar amendments are soil type (composition and particle size) dependent.

Organic and inorganic contaminants removal from water with biochar, a renewable, low cost and sustainable adsorbent--a critical review

Biochar is used for soil conditioning, remediation, carbon sequestration and water remediation. Biochar application to water and wastewater has never been reviewed previously. This review focuses on recent applications of biochars, produced from biomass pyrolysis (slow and fast), in water and wastewater treatment. Slow and fast pyrolysis biochar production is briefly discussed. The literature on sorption of organic and inorganic contaminants by biochars is surveyed and reviewed. Adsorption capacities for organic and inorganic contaminants by different biochars under different operating conditions are summarized and, where possible, compared. Mechanisms responsible for contaminant remediation are briefly discussed. Finally, a few recommendations for further research have been made in the area of biochar development for application to water filtration.

Impact of deashing treatment on biochar structural properties and potential sorption mechanisms of phenanthrene

Knowledge of the mineral effects of biochars on their sorption of hydrophobic organic contaminants (HOCs) is limited. Sorption of phenanthrene (PHE) by plant-residue derived biochars (PLABs) and animal waste-derived biochars (ANIBs) obtained at two heating treatment temperatures (HTTs) (450 and 600 °C) and their corresponding deashed biochars was investigated. The decreased surface polarity and increased bulk polarity of biochars after deashing treatment indicated that abundant minerals of biochars benefit external exposure of polar groups associated organic matter (OM). Organic carbon (OC)-normalized distribution coefficients (K(oc)) of PHE by biochars generally increased after deashing, likely due to enhancement of favorable and hydrophobic sorption sites caused by mineral removal. Positive correlation between PHE log K(oc) by PLABs and bulk polarity combined with negative correlation between PHE log K(oc) values by ANIBs and surface polarity suggested PLABs and ANIBs have different sorption mechanisms, probably attributed to their large variation of ash content because minerals influenced OM spatial arrangement within biochars. Results of this work could help us better understand the impact of minerals, bulk/surface polarity, and sorption domain arrangement of biochars on their HOCs sorption and predict the fate of HOCs in soils after biochar application.