Biochar Carbon Research Articles

Biochar carbon removal from residues in Germany—assessment from environmental and economic perspectives

Abstract The topic of biochar carbon removal (BCR), which refers to the pyrolysis of biomass, is increasingly being discussed as a potential solution for the long-term removal of carbon dioxide from the atmosphere. However, BCR technology assessments in Germany, which are used as the basis for strategic decision-making, are often limited to woody biomass as an input material and are based on old data. Consequently, this study focuses on BCR from forest residues, straw and sewage sludge and assesses its contribution to negative emissions under current techno-economic framework conditions. Using life cycle assessment and annuity method, as well as complementary stakeholder engagement formats, the study provides a comprehensive analysis of BCR pathways in Germany based on an empirical, up-to-date data basis. The results highlight the environmental advantages of BCR, particularly in reducing greenhouse gas emissions compared to the conventional treatment of residues. The economic feasibility of BCR is uncertain, with profitability dependent on plant scale, biomass type and the integration of energy co-products. Stakeholder insights underscore the necessity for supportive policies and investment in BCR technology to enhance scalability. This interdisciplinary approach enriches the discourse on BCR’s role in achieving carbon neutrality and offers a robust data foundation for future evaluations.

A critical re‐analysis of biochar properties prediction from production parameters and elemental analysis

AbstractBiochar is the product of intentional pyrolysis of organic feedstocks. It is made under controlled conditions in order to achieve desired physico‐chemical characteristics. These characteristics ultimately affect biochar properties as a soil amendment. When biochar is used for carbon storage, an important property is its persistence in soil, often described by the proportion of biochar carbon remaining in soil after a 100 years (). We analyzed published data on 1230 biochars to re‐evaluate the effect of pyrolysis parameters on biochar characteristics and the possibility to predict from the maximum temperature reached during pyrolysis (HTT). We showed that biochar ash and nitrogen (N) contents were mostly affected by feedstock type. The oxygen to carbon (O:C) and hydrogen to carbon (H:C) ratios were mostly affected by the extent of pyrolysis (a combination of HTT and pyrolysis duration), except for non (ligno)cellulosic feedstocks (plastic waste, sewage sludge). The volatile matter (VM) content was affected by both feedstock type and the extent of pyrolysis. We demonstrated that HTT is the main driver of H:C ‐‐ an indicator of persistence ‐‐ but that it is not measured accurately enough to precisely predict H:C, let alone persistence. We examined the equations to estimate available in the literature and showed that calculated from HTT presented little agreement with calculated from H:C. The sign and magnitude of the bias depended on the equation used to calculate and the dispersion was usually large. This could lead to improper compensation of carbon emissions and wrong reporting of carbon sinks in national carbon accounting schemes. We recommend not to use HTT as a predictor for persistence and stress the importance to rapidly develop more accurate proxies of biochar C persistence in soil.

Exploring resource recovery from diverted organics: Life cycle assessment comparison of options for managing the organic fraction of municipal solid waste

Diversion of the organic fraction of municipal solid waste (OFMSW) from landfills is increasing. Previous life cycle assessment studies have evaluated subsets of OFMSW management options, but conclusions are inconsistent, and none have evaluated diverse applications of material by-products. The primary objective of this work was to identify sustainability-based improvements to the selection, design, implementation, and operation of organics waste diversion management technologies. Process modeling and life cycle assessment were used to compare OFMSW composting, anaerobic digestion, and pyrolysis, with biochar used as a landfill cover, leachate treatment sorbent, and land applicant. Material and energy flows, calculated by newly developed models for the defined functional unit (1 kg MSW over a 20-year timeframe), were translated to environmental performance using ecoinvent and USLCI databases and TRACI method. Additionally, uncertainty, sensitivity, and scenario analyses were conducted to evaluate the implications of model uncertainties, design decisions, and resource recovery tradeoffs. OFMSW pyrolysis usually (65 % of uncertainty assessment simulations) had the best global warming performance mostly due to energy recovery and biochar's carbon sequestration benefit, which was independent of fate. Pyrolyzing the biosolids from OFMSW anaerobic digestion recovered the most energy and had the best performance in 34 % of uncertainty simulations. Material recovery amounts were large (e.g., more biochar was produced than required for novel uses) and warrant feasibility considerations. Global warming performance was more sensitive to uncertainty in carbon sequestration and primary energy production than in fertilizer offset, energy conversion, or heat offset approach. Practical implications include the potential for biochar supply to outweigh demand, and inconsistent revenue from the sale of recovered energy and carbon credits; future research could focus on evaluating the relative social and economic sustainability of the OFMSW management technologies.

The Impact of Different Extraction Conditions on the Concentration and Properties of Dissolved Organic Carbon in Biochars Derived from Sewage Sludge and Digestates

The Impact of Different Extraction Conditions on the Concentration and Properties of Dissolved Organic Carbon in Biochars Derived from Sewage Sludge and Digestates

The kinetics and mechanism of the combustion of the carbon in biochar from oak, as studied in an electrically heated, fluidised bed of sand

The oxidation of small particles (size 200 μm) of char from oak has been studied, by adding a small batch of them to an electrically heated bed of inert, silica sand, fluidised by mixtures of O2 and N2. The concentrations of CO, CO2, and O2, in the off-gases from the bed were continuously monitored, enabling the rate of combustion and also the fraction, X, of the carbon oxidised in each particle to be measured throughout combustion at different, well-controlled temperatures. The rate of oxidation declined as (1 – X) during burnout,becausethe O2 freely contacted the carbon in these tiny particles, whose oxidation was kinetically controlled at 700 °C and below. In fact, these tiny char particles burned in the fluidised bed at 500–700 °C in Zone 1 according to S0(1 – X)(k5CO2 + k6) per g of char. This matches Hurt and Calo’s three-step mechanism, whereby a porous char burns at a rate controlled by two reactions, one first-order in O2, the other zeroth-order in O2. Reactions (V) and (VI) were found to be, respectively, k5 = 1.7 × 103 exp (−139 ± 18 kJ mole−1/RT) m s−1 and k6 = 1.5 exp (−92 ± 20 kJ mole−1/RT) mole s−1 m−2. Reaction (V), between O2 and a surface complex containing oxygen, became faster as X increased, if the temperature exceeded 600 °C; catalysis by potassium was suspected as providing this extra reactive boost.

Biochar carbon nanodots for catalytic acetalization of biodiesel by-product crude glycerol to solketal: process optimization by RSM and life cycle cost analysis

Carbon-based nanodots have garnered recent interest for their simple synthesis and versatile utility, ranging from biomedical to (opto) electronic applications, evolving into a tunable and biocompatible material. Here, for the first time, a biochar (lotus leaf) derived carbon nanodots was synthesized through hydrothermal carbonization. The synthesized hollow spherical biochar was engineered via functionalization by grafting –SO3H active sites. The attained catalyst was broadly analyzed by XRD, FTIR, TGA, BET, SEM–EDX, TEM, and XPS analysis after which it was applied for the acetalization reaction of crude glycerol (a biodiesel by-product) to form solketal, a potential fuel additive to valorize the large waste stream generated from biodiesel industry. Employing the RSM-CCD methodology, the experimental matrix was executed, and subsequent data were scrutinized through multiple regressions to model a quadratic equation. Under specific reaction parameters—a reaction duration of 14 min, a molar ratio of 7.5:1, and a catalyst loading of 5.7 wt.%, maximum solketal yield (95.7%) was attained through the ultrasonication method. Finally, to conclude, life cycle cost analysis (LCCA) for solketal production was studied here which determined the overall cost of solketal production per kilogram to be 0.719 USD ($), indicating high commercial applicability.

Influence of varying aluminum-based combustion compartment sizes on groundnut shell biochar properties

The process variables during biochar production play a crucial role in determining its properties. Factors like temperature, heating rate, reactor configuration, and residence time can significantly impact biochar quality. The aim of this study is to determine the impact of reactor configuration on the yield and properties of groundnut shell biochar. For this investigation, the volumes of aluminum-based combustion compartments in a biomass-fueled TLUD biomass gasifier were varied, and the resulting biochar was analyzed using SEM, EDX, and FTIR. It was observed that the increase in the combustion chamber of the gasifier led to an increase in the amount of biomass fuel utilized in the system, which led to an increased reactor’s temperature and varied carbonization duration and yield. Elemental composition showed that an increase in reactor volume led to an increase in biochar carbon content and reduced silica content. The SEM analysis confirmed that decreasing the combustion compartment sizes increased porosity and roughness, as well as visible fissures and crevices on the biochar surface. FTIR analysis revealed similarities in functional groups, with many peaks appearing at higher wavenumbers as the combustion compartment sizes decreased. This study innovatively examines how varying aluminum-based combustion compartment sizes and biofuel mass affect groundnut shell biochar properties using a TLUD gasifier, emphasizing its significance for optimizing biochar production and advancing sustainable practices.

Nitrogen-Doped Porous Carbons Derived from Peanut Shells as Efficient Electrodes for High-Performance Supercapacitors.

The doping of porous carbon materials with nitrogen is an effective approach to enhance the electrochemical performance of electrode materials. In this study, nitrogen-doped porous carbon derived from peanut shells was prepared as an electrode for supercapacitors. Melamine, urea, urea phosphate, and ammonium dihydrogen phosphate were employed as different nitrogen dopants. The optimized electrode material PA-1-1 prepared by peanut shells, with ammonium dihydrogen phosphate as a nitrogen dopant, exhibited a N content of 3.11% and a specific surface area of 602.7 m2/g. In 6 M KOH, the PA-1-1 electrode delivered a high specific capacitance of 208.3 F/g at a current density of 1 A/g. Furthermore, the PA-1-1 electrode demonstrated an excellent rate performance with a specific capacitance of 170.0 F/g (retention rate of 81.6%) maintained at 20 A/g. It delivered a capacitance of PA-1-1 with a specific capacitance retention of 98.8% at 20 A/g after 5000 cycles, indicating excellent cycling stability. The PA-1-1//PA-1-1 symmetric supercapacitor exhibited an energy density of 17.7 Wh/kg at a power density of 2467.0 W/kg. This work not only presents attractive N-doped porous carbon materials for supercapacitors but also offers a novel insight into the rational design of biochar carbon derived from waste peelings.

Quantifying the negative effects of dissolved organic carbon of maize straw-derived biochar on its carbon sequestration potential in a paddy soil

Biochar of low-medium temperature may contain abundant dissolved organic carbon (BDOC), affecting its priming effect and carbon sequestration potential in soils. However, the direct and quantitative evidence for such impacts remains lacking. This study conducted incubation experiments on maize straw-derived 300/450 °C biochar, BDOC-extracted biochar residues and BDOC, and applied δ13C analysis to quantify biochar's mineralization and their priming effects on native soil organic carbon in a paddy soil. BDOC contained abundant lipid-, protein-, carbohydrate-like species, serving as nutrients for the metabolism of microorganisms, and thus enhanced native soil organic carbon's mineralization by 15–20%. After BDOC extraction, 300 °C biochar-trigged priming effect shifted from a positive (3.7 mg CO2–C kg−1 soil) to a negative state (−14.4 mg CO2–C kg−1 soil), and 450 °C biochar-induced negative priming effect increased by 31%; biochar's mineralization also decreased by 41–65%. Overall, after BDOC extraction, the net carbon balance in biochar-amended soils reduced by 7–8%. Furthermore, BDOC shifted the dominant priming mechanisms of biochar mainly by enhancing soil macro-aggregates while reducing sorptive protection for native soil organic carbon. Its extraction reduced the amount of soil macro-aggregates by 16–25% but enhanced the sorption affinity of native soil organic carbon by biochar by 68–122%. Additionally, after BDOC extraction, the microbial communities in biochar-amended soils contained more fungi and G+-bacteria. These findings proved that BDOC extraction appears a feasible strategy to enhance the short-period carbon sequestration potential of biochar.

Additive effects of basalt enhanced weathering and biochar co-application on carbon sequestration, soil nutrient status and plant performance in a mesocosm experiment

Co-deployment of a portfolio of carbon removal technologies is anticipated in order to remove several gigatons of carbon dioxide from the atmosphere and meet climate targets. However, co-application effects between carbon removal technologies have rarely been examined, despite multiple recent perspectives suggesting potential synergies between basalt enhanced weathering and biochar application. To study the co-application effects of basalt for enhanced weathering and biochar on carbon sequestration, along with related co-benefits and risks, we conducted a fully replicated factorial mesocosm experiment with wheat. Basalt applied alone (74 t ha−1) resulted in an estimated carbon sequestration potential of 1.13 t of equivalent CO2 ha−1 over the course of approximately 6 months. Co-application with biochar (12 t ha−1) did not significantly increase estimated carbon sequestration potential. Total alkalinity fluxes and isotopic evidence indicated nearly exactly additive effects of basalt and biochar co-applied, with no significant interaction effect. Biochar carbon sequestration, approximately 32 t of equivalent CO2 ha−1 in our experiment, was unaffected by basalt addition during our experiment. Co-benefits of basalt and biochar on plant biomass as well as nutrient uptake and availability similarly mostly showed additive tendencies when co-applied. Nonetheless, a few synergistic tendencies were observed when co-applied for plant potassium and magnesium uptake as well as soil calcium availability. Soil calcium availability increased by 126% compared to expected effects based on separate application. Finally, we did not observe a reduction in the increased uptake of potentially harmful trace elements released from basalt when co-applied with biochar. Overall, our results support the co-application of basalt for enhanced weathering and biochar, with additive effects on carbon sequestration and additive, if not synergistic, effects on associated co-benefits.

Biochar as a green solution to drive the soil carbon pump

Biochar is a nature-based green solution to lift soil carbon storage and mitigate carbon release. Here, we propose a novel concept of biochar carbon pump (BCP) that bridges microbial carbon pump (MCP) and mineral carbon pump (MnCP), facilitating effective carbon sequestration. The BCP functions to promote carbon storage by introducing biochar-derived persistent C into soil, enhancing negative priming effects, altering soil microbial communities, and reinforcing organo-organic and organo-mineral interactions. Recognizing the value of BCP in bridging MCP and MnCP to facilitate diverse natural reactions for soil carbon sequestration is particularly significant in addressing climate change.

Upcycling of Waste Polymer Using Surface Modified Hemp Derived Biochar Carbon for Sustainable Packaging Applications

Upcycling of Waste Polymer Using Surface Modified Hemp Derived Biochar Carbon for Sustainable Packaging Applications

Land-neutral negative emissions through biochar-based fertilization—assessing global potentials under varied management and pyrolysis conditions

Climate stabilization is crucial for restabilizing the Earth system but should not undermine biosphere integrity, a second pillar of Earth system functioning. This is of particular concern if it is to be achieved through biomass-based negative emission (NE) technologies that compete for land with food production and ecosystem protection. We assess the NE contribution of land- and calorie-neutral pyrogenic carbon capture and storage (LCN-PyCCS) facilitated by biochar-based fertilization, which sequesters carbon and reduces land demand by increasing crop yields. Applying the global biosphere model LPJmL with an enhanced representation of fast-growing species for PyCCS feedstock production, we calculated a land-neutral global NE potential of 0.20–1.10 GtCO2 year−1 assuming 74% of the biochar carbon remaining in the soil after 100 years (for + 10% yield increase; no potential for + 5%; 0.61–1.88 GtCO2 year−1 for + 15%). The potential is primarily driven by the achievable yield increase and the management intensity of the biomass producing systems. NE production is estimated to be enhanced by + 200–270% if management intensity increases from a marginal to a moderate level. Furthermore, our results show sensitivity to process-specific biochar yields and carbon contents, producing a difference of + 40–75% between conservative assumptions and an optimized setting. Despite these challenges for making world-wide assumptions on LCN-PyCCS systems in modeling, our findings point to discrepancies between the large NE volumes calculated in demand-driven and economically optimized mitigation scenarios and the potentials from analyses focusing on supply-driven approaches that meet environmental and socioeconomic preconditions as delivered by LCN-PyCCS.

Ce/N @BC prepared based on plant metallurgy strategy: A novel activator of peroxymonosulfate for the degradation of sulfamethoxazole

A novel carbon catalyst was created based on plant metallurgy strategy for organic pollutants removal. Plants rich in CeO2 NPs in water were used as carbon precursors and pyrolyzed with urea to obtain Ce/N co-doped carbon catalysts, which were used in the degradation of sulfamethoxazole (SMX) by active peroxymonosulfate (PMS). The results showed that the Ce/N @BC/PMS system achieved to 94.5% degradation of SMX in 40 min at a rate constant of 0.0602 cm−1. The activation center of PMS is widely dispersed Ce oxide nanocrystals, and CeO2 NPs promote the formation of oxygen centered PFR with enhanced catalytic ability and longer half-life. In addition, N-doping facilitates the transfer of π-electrons within the sp2 carbon of biochar, increasing active sites and thus improving PMS activation efficiency. The degradation process was contributed to by both radical and non-radical activation mechanisms including 1O2 and direct electron transfer, with O2•- serving as 1O2's precursor. Through the DFT calculations, LC-MS and toxicological analyses, the degradation pathway of pollutants and the toxicity changes throughout the entire degradation process were further revealed, indicating that the degradation of SMX could effectively reduce ecological toxicity.

Effect of Incubation of Biochars Amendment on the Chemical Properties of Acidic Soil

Biochar is considered as universal conditioner to improve soil quality, but its effect on different soil types and rates on soil properties,bacterial community and plant growth are still unclear,particularly in the typical acid soil in southeastern Nigeria. This study was done to know the changes in soil chemical composition which could be caused by dissolution and release of nutrients from biochar in an incubation experiment. The study was conducted during rainy season in 2022 in Sobioma Agro Farms LTD using loamy sand with acidic pH (5.7). The soil were collected from the same farm. Soil was filled in separate plastic bucket with lid (2kg capacity) and treatments imposed as per the treatment details; T1: Corn Cob charred for 60 minutes @ 20 t ha-1 T2: Rice husk charred for 60 minutes @ 20 t ha -1 and T3: Poultry manure charred for 60 minutes @ 20 t ha-1. The treatments were replicated thrice, then repeated for different days of incubation (15,30 and 45days respectively). The experiment was laid out in a completely randomized design (CRD). In this study, the biochar carbon content and Total N ranges from 95.9 to 181.4 gkg" 1 and 5.2 to 8.9 gkg' 1 respectively with the highest values on rice husk biochar (Table 3). Poultry manure showed highest significant (P O.05) effect in Cu (1.61 mgkg- 1), Mn (5.26 mgkg- 1 ) and Fe (6.54 mgkg 1 ) compared to rice husk biochar and corn cob biochar (Table 4). The Cations Exchange Capacity (CEC) and base saturation (BS) increased after amendment of the acidic soil with PMB (5.51 cmolkg' 1 and 85.4% respectively).
 The results revealed that, application of different biochar increased the pH and other soil chemical properties evaluated with slight increase only in exchangeable k and Na and a decrease in exchange acidity (A l and H) of soil. During the incubation experiment changes were noticed, some nutrient element showed a continuous increase with incubation time (exchangeable Al and H in Corn cob and poultry manure biochar respectively) while some reached its maximum at the mid incubation time (CEC, BS, TN, Av.P and OM in poultry manure biochar). In some cases a decline was observed up to the mid incubation period after which an increase was observed (Exchangeable Ca and Mg in corn cob biorchar and Exchangeable k and Na in Rice husk buiochar). This work stresses the importance of biochar to soil quality improvement.

Evaluation of net carbon sequestration and ecological benefits from single biochar-incorporated sorghum farmland systems in saline-alkali areas of Inner Mongolia, China

Biochar is widely recognized as a soil amendment to reduce greenhouse gas emissions and enhance soil carbon storage in agroecosystems; however, the systematic focus on carbon balance and ecological benefits in cropping systems remains unclear in saline-alkali areas under water-saving irrigation. Here, a 2-yr field experiment with carbon footprint method was conducted to determine soil carbon budgets, biochar carbon efficiency performance, and the economic and ecological benefits of mulched drip-irrigated sorghum production, in an arid salinized region of Inner Mongolia, China. Corn straw-derived biochar dosages of 0 (CK), 15 (B15), 30 (B30), and 45 (B45) t hm−2 were just applied into the soil in the first crop growing season. A single application of biochar to soil significantly reduced CO2 emissions for the current and subsequent crop-growing seasons, with 13.1%, 16.7%, and 12.5% reductions for B15, B30, and B45, respectively. Compared with the non-biochar control plots, B15, B30, and B45 also increased NPP by 36.7%, 38.4%, and 27.1%, respectively. The actual effects on improving net carbon sequestration for B15, B30, and B45 in the first year were higher than those in the second year, with mean increases of 1.27, 1.47, and 1.36 times, respectively; however, the efficiencies of biochar for fixing carbon per biochar dosage input for B15 were 72.8% and 64.1% higher than those of B30 and B45, respectively. Net profits were significantly improved by 57.2–87.1% by biochar treatments. The environmental benefits of biochar carbon trading revenues for B15, B30, and B45 increased by 105.9%, 162.1%, and 109.6%, respectively. The minimum observation for carbon productivity and the maximum measurements for both the economic and ecological benefits were B15. The B15 also significantly increased sorghum yield and grain number. Results demonstrate that biochar application in the current growing season helps reduce soil carbon emissions, increases net carbon sequestration for current and subsequent sorghum agroecosystems, and enhances net profit and ecological benefits. The optimal positive synergistic effect was observed at a biochar application rate of 15 t hm−2 for reducing soil carbon emissions, increasing crop production, and improving the ecological environment.

Biochar dispersion in a tropical soil and its effects on native soil organic carbon.

Although biochar application to soils has been found to increase soil quality and crop yield, the biochar dispersion extent and its impacts on native soil organic carbon (SOC) has received relatively little attention. Here, the vertical and lateral migration of fine, intermediate and coarse-sized biochar (<0.5, 0.5-1 and 1-5 mm, respectively), applied at low and high doses (1.5-2 and 3-4% w/w, respectively), was tracked using stable isotope methods, along with its impact on native SOC stocks. Biochar was homogeneously mixed into the surface layer (0-7 cm depth) of a loamy sandy Acrisol in Zambia. After 4.5 y, 38-75% of the biochar carbon (BC) was lost from the applied layer and 4-25% was detected in lower soil layers (7-30 cm). Estimating BC mineralization to be no more than 8%, 25-60% was likely transported laterally out of the experimental plots. This conclusion was supported by observations of BC in the control plot and in soils up to 2 m outside of the experimental plots. These processes were likely progressive as recovery of BC in similar plots 1 year after application was greater in both surface and lower soil layers than after 4.5 y. Fine and intermediate-sized BC displayed the greatest downward migration (25.3 and 17.9%, respectively), particularly when applied at lower doses, suggesting its movement through soil inter-particle spaces. At higher dosages, fine and intermediate-sized particles may have clogged pore, so coarse biochar displayed the greatest downward migration when biochar was applied at higher doses. In the BC treatment plot soil profiles, native SOC stocks were reduced by 2.8 to 24.5% (18.4% on average), i.e. positive priming. However, some evidence suggested that the soils may switch to negative priming over time. The dispersion of biochar in soil should be considered when evaluating biochar's agronomic benefits and environmental effects.

Modelling biochar long-term carbon storage in soil with harmonized analysis of decomposition data

The climate change mitigation benefits of biochar systems arise largely from carbon storage in biochar. However, while biochar is increasingly recognized as a carbon dioxide removal technology, there are on-going scientific discussions on how to estimate the persistence of biochar carbon when biochar is used in soils. Estimates vary from decades to millennia, building on different modelling approaches and evidence. Here, we revisited the persistence estimates derived from extrapolation of biochar incubation experiments, with the aims of making incubation data available, modelling choices transparent, and results reproducible. An extensive dataset of biochar incubations, including 129 biochar decomposition time series, was compiled and is made available alongside code for its analysis. Biochar persistence correlations were sensitive to data selection procedures and to the curve fitting modelling step, while soil temperature adjustments methods had less impact. Biochar H/C ratio remained the main predictor of biochar persistence, in line with previous research, regardless of the extrapolation assumptions (multi-pool exponential functions or power function) used in curve fitting. The relation between H/C and percentage of biochar carbon remaining after 100 years (BC100) was better explained by a power model than a linear model, with R2 values between 0.5 and 0.9. Using multi-pool exponential functions, estimated BC100 varied between 90 % and 60 % for H/C from 0 to 0.7. However, using power functions, BC100 was constrained between 90 % and 80 % for the same H/C range. Additional information about the biochar, the pyrolysis conditions or the environmental incubation conditions did not significantly increase explained variance. Notably, the dataset lacks observations at H/C ratios below 0.2, of biochar made from manure and biosolids, biochar from processes other than slow pyrolysis, field studies, and incubation temperatures below 10 °C, which should guide future experimental work. The detailed analysis performed in this study does not cast doubts on the longevity of biochar carbon storage; rather, it confirms previous knowledge by critically examining the modelling, elucidating the assumptions and limitations, and making the analysis fully reproducible. There is a need for further interdisciplinary work on integration of various theories and approaches to biochar persistence, ultimately leading to the formulation of policy-relevant conclusions.

Comparative analysis of biochar carbon stability methods and implications for carbon credits

Biochar is an emerging negative emission technology. Its ability to sequester carbon and subsequent carbon credit valuation hinge on the stability of its carbon structure. The widely used indicators of carbon stability H:Corg and O:Corg provide conservative results as these are based on limited incubation experiments and associated modeling results. The results from these accepted methods and other derived methods have not been compared as indicators of carbon stability in a variety of biochar samples. Furthermore, the influence of contrasting feedstock and production techniques on biochar carbon stability is not well explored. Therefore, to address these challenges, a comprehensive stability analysis of 21 different biochar samples with contrasting feedstocks and pyrolysis techniques was conducted using a combination of instrumental methods and derived indicators of carbon stability. Methods such as biochar carbon half-life, thermo-stable fraction, oxidation resistance (R50), and carbon sequestration potential (CS) were used. Based on the initial carbon content of the biochar, simple pyrolysis techniques have similar potential for carbon credits as biochar produced from advanced pyrolysis techniques. Results indicate that the carbon stability of a biochar product is primarily a factor of feedstock type. We found that biochar carbon stability is not related to volatile matter or fixed carbon content for biochar produced using a simple pyrolysis technique and mixed feedstock. Biochars with H:Corg < 0.4 were deemed to have lower carbon stability when compared using different methods. No correlation was observed between the carbon stability of biochar using H:Corg and other methods, however, correlations were observed between half-life, O:Corg, fixed carbon, number of aromatic peaks in FTIR spectrum, R50, and CS. Therefore, it is recommended that data from additional incubation and modeling studies need to be considered to increase the confidence in carbon stability results having major implications to carbon credits.

Effect of various potassium agents on product distributions and biochar carbon sequestration of biomass pyrolysis

Biomass to biochar through pyrolysis is promising for carbon-negative biomass energy. Potassium could enhance biochar formation whereas the difference among potassium agents has not been understood. Herein, 13 potassium agents were adopted, and the product compositions and carbon distributions of slow and intermediate pyrolysis were investigated. Results show that neutral agents have a weak influence on the products, while high-basicity agents enhance biochar formation, decrease organics yields, and promote H2 generation (9–144 cm3/g) and phenols selectivity (64–79 area%). Especially, due to the anion properties, borate and phosphates deviate from the basicity tendency; acetate contributes to increasing acetic acid selectivity (up to 43 area%) while oxidizing agents promote CO2 and H2O yields. Potassium performs obvious enhancement of biochar carbon sequestration, increasing by 2–49 % for intermediate pyrolysis and -8–51 % for slow pyrolysis with biochar carbon retention reaching 55 % and 77 %, respectively. Meanwhile, the thermally unstable phases of biochar were also generated. General correlation analysis indicates that CO yields and phenols selectivity highly relate to biochar carbon retention. This study sheds light on the key role of acid-base properties and anion properties, and provides insight into AAEM-catalytic biomass pyrolysis.