Biochar Yield Research Articles

Utilization of cotton gin waste biochars for agronomic benefits in soils

AbstractCotton gin waste (CGW) is produced in large quantities (1–1.5 × 106 metric ton/year) in the Texas High Plains (THP), one of the largest cotton-producing regions in the USA. We examined locally supplied CGW for soil amendment as biochar (CGW-BC) with a view toward rainfed cropping systems, which will likely become increasingly necessary due to declines in groundwater availability for irrigation. Sixteen unique biochar samples were produced under varying conditions of time, temperature, and post-processing wash in a muffle furnace. We performed material characterization on the biochar. We then incubated CGW-BC samples that seemed favorable for increasing the water holding capacity increase for 10 days with local, rainfed, clay loam soil. We found that increasing the pyrolysis time and temperature decreased the biochar yield but only up to 40 min. Beyond 40 min, the yield did not decrease further. Additionally, the majority of mass loss occurred during pyrolysis and not during crush-sieving or postproduction washes. CGW-BC produced at higher temperatures and for longer times had greater thermal stability. This interesting aspect of thermal stability, which did not always follow strict time‒temperature trends, may be because cotton gin waste is a heterogeneous material. We found that the addition of acid decreases the mineral content while lowering the thermal stability of lower temperature (450 °C) biochars. Regarding the CGW-BC surface area, we found that higher temperatures generally increase the micropore surface area. Using a GAB isotherm, water vapor surface area did not correlate with the highest WHC when water was added to the soil. In fact, biochar, which was pyrolyzed in less time at a lower temperature and with the use of acid washing, better held the water in soil-biochar mixtures. The measurements suggested that CGW-BC could be a valuable soil amendment that could increase the WHC without adversely increasing the pH. Our initial investigation revealed how scaled-up production of CGW-BC for soils might be economically and sustainably pursued for use in rainfed cropping, deficit irrigation, or ranchlands.

Untapped potential of food waste derived biochar for the removal of heavy metals from wastewater

The presence of heavy metals in water pose a serious threat to both public and environmental health. However, the advances in the application of low cost biochar based adsorbent synthesize from various feedstocks plays an effective role in the of removal heavy metals from water. This study implies the introduction of novel method of converting food waste (FW) to biochar through pyrolysis, examine its physiochemical characteristics, and investigate its adsorption potential for the removal of heavy metals from water. The results revealed that biochar yield decreased from 18.4 % to 14.31 % with increase in pyrolysis temperature from 350 to 550 °C. Likewise, increase in the pyrolysis temperature also resulted in the increase in the ash content from 39.87 % to 42.05 % thus transforming the biochar into alkaline nature (pH 10.17). The structural and chemical compositions of biochar produced at various temperatures (350, 450, and 550 °C) showed a wide range of mineralogical composition, and changes in the concentration of surface functional groups. Similarly, the adsorption potential showed that all the produced biochar effectively removed the selected heavy metals from wastewater. However a slightly high removal capacity was observed for biochar produced at 550 °C that was credited to the alkaline nature, negatively charged biochar active sites due to O-containing functional groups and swelling behavior. The results also showed that the maximum adsorption was recorded at pH 8 at adsorbent dose of 2.5 g L−1 with the contact time of 120 min. To express the adsorption equilibrium, the results were subjected to Langmuir and Freundlich isotherms and correlation coefficient implies that the adsorption process follows the Freundlich adsorption isotherm. The findings of this study suggest the suitability of the novel FW derived biochar as an effective and low cost adsorbent for the removal of heavy metals form wastewater.

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.

Physical Properties of Biochar Produced from Pyrolysis of Arabica Coffee Pulp: The Effect of Pre-Washing Process

Coffee pulp is a potential source of biomass which abundantly available in coffee exporter countries such as Brazil, Colombia, Indonesia etc. It is necessary to develop technologies to convert coffee pulp into value-added products. This study aims to investigate the slow pyrolysis process of arabica coffee pulp in a pilot scale reactor and evaluate the properties of resulting biochar. Prior to pyrolysis experiment, some of coffee pulp were soaked in tap water for 20 h with a ratio of water to coffee pulps of 1:5. As comparison, another set of pyrolysis experiment was carried out without soaking and washing of feedstock. The pyrolysis process was carried out in a batch reactor at temperatures within the range of 400 to 420°C. During the run, the reaction temperature versus time was recorded and products yield were quantified. Characterization of biochar product was performed under proximate, bomb calorimeter and density analyses. The yield of biochar and pyrolytic oil, respectively were 33% and 36%. Biochar characterization results suggested a significant decrease in the ash content when washing pretreatment was applied. Increases in the calorific value and bulk density were also observed from pre-washed coffee pulp sample.

Prospective of biochar material production and process optimization using co-pyrolysis approach-A mini-review

This mini-review explores the perspective of biochar material production using the co-pyrolysis approach, which involves the thermal decomposition of biomass and other carbonaceous materials in the absence of oxygen at low temperatures (300-500°C). The study investigates the co-pyrolysis of biomass with different materials such as plastics, tires, municipal solid waste, and other organic waste to produce a high biochar yield. The review focuses on the benefits of co-pyrolysis, including higher yield and better quality of biochar, as well as reduced environmental impact by using different waste materials as feedstock. The review also highlights co-pyrolysis challenges, such as process optimization, feedstock preparation, and product characterization. The study concludes that co-pyrolysis of biomass with different materials can be a promising approach for producing high-quality biochar with multiple applications. However, more research is needed to optimize the co-pyrolysis process and evaluate the economic feasibility of biochar production using a computation approach.

تطوير وتقييم وحدة الفحم الحيوي ذات التدفق المستمر للكتلة الحيوية لقشور الأرز

This study aims to develop and evaluate a locally manufactured carbonization unit with a screw conveyor. Various carbonization temperatures (350, 400, and 450°C) and feeding rates (50, 75, and 100 kg/h) were examined to determine optimal conditions for producing biochar from rice husk (RH). The results revealed that increasing the pyrolysis temperature from 350 to 450°C decreased RH biochar yield, while increasing the feeding rate from 50 to 100 kg/h increased it. Ash content was 22.4% at 350°C for 100 kg/h, and the maximum value was 31.4% at 450°C and 50 kg/h. The BET surface area of the biochar increased from 105.71 to 312.32 m2/g at 450°C, with slight non-significant changes at a 100 kg/h feed rate. RH biochar showed decreasing H and O values with higher temperatures and lower feed rates. RH biochar at 450°C and 50 kg/h showed increased macro porosity and surface area, rendering it suitable for agricultural application as a soil amendment.

Influence of reaction parameters on biofuels derived from solvothermal liquefaction of Citrus limetta fruit wastes

Citrus limetta or sweet lime is a widely consumed fruit worldwide. The wastes generated from their processing are enormous and are discarded without any value-addition. Biomass liquefaction in hydrogen-donor solvent is an effective thermochemical conversion technique to produce value added products such as biocrude and biochar from wet biomasses directly. Thus, liquefaction studies of Citrus limetta peel and pulp were conducted using solvent methanol at temperatures of 240 °C–280 °C, 30 min residence time as well as 1:2, 1:3 and 1:4 ratios of biomass to solvent. The impact of temperature as well as biomass to solvent ratio on yield of biocrude and biochar were investigated herein. Biocrude produced from Citrus limetta peel at 240 °C and 1:3 ratio of biomass to solvent is maximum (12.5 wt. %). At reaction parameters of 280 °C and 1:4 ratio of biomass to solvent, biocrude from Citrus limetta pulp showed higher heating value of 27.18 MJ kg−1 which was the maximum obtained in this study. The gas-chromatography mass-spectrometry (GC-MS) indicated presence of alcohols, phenols, alkanes, ketones, ethers, esters and fatty acid methyl esters as major compounds. The characteristics and energy content of biochar demonstrated their potentiality for bioenergy applications.

Sequential co-processing of olive mill wastewater and organic residues by anaerobic co-digestion and pyrolysis for the generation of bioadsorbent and low-cost media for microalgae cultivation

This investigation aims to evaluate the co-valorization of olive mill wastewater with other organic residues involving acid pretreatment, co-digestion, pyrolysis, and microalgae cultivation. Phosphoric acid pretreatment (5%, 60°C for 1 h) was used to solubilize the organic matter in a mixture of coffee grounds, orange peel, olive mill wastewater, and cardboard. The acidic treatment led to the production of 328 Nml of biogas/gVS, while the untreated mixture provided 257 Nml of biogas/gVS. The solid digestates were subjected to pyrolysis (500°C for 1 h), providing a biochar yield of approximately 44% for both digestates. Adsorption tests using methylene blue revealed an adsorption capacity of the biochar generated from the digestate of the acid pre-treated mixture of 4 mg/g, which was higher than that of the biochar from the untreated mixture (3.5 mg/g). The liquid digestates were also used as growth media for microalgae. Compared to the reference media (BG11), the use of the digestates-based media resulted in a lower growth rate (0.04 d-1) and biomass (247 mg/L) but significantly higher lipid content (49%). The study shows, therefore, that the use of acid pretreatment had a positive effect on biogas production (solubilization of sugars), on the adsorption efficiency of the biochar (improvement of the porosity of the material), and on the production of lipids from the microalgae which can be destined to biodiesel.

Enhanced phosphorus and potassium recovery through co-pyrolysis of nutrient-rich biomass feedstocks for engineered biochar production

Engineered biochars were produced via slow pyrolysis at 600 °C for 1 h from selected carbon-rich (diyar wood, sawdust, cotton stalk, sunflower straw, and banana stem) and nutrient-rich (eggshell, chicken bone, chicken manure, and sewage sludge) biomass residues with enhanced P and K recovery. Separate pyrolysis of both category feedstocks and co-pyrolysis of selected carbon-rich and nutrient-rich feedstocks mixed at 3:1 ratio was conducted. Higher biochar yield (41 %) was achieved in the co-pyrolysis of sewage sludge and sunflower stalk compared to average (38.5 %) of their separate pyrolysis. Moreover, increased K recovery (5.3 % to 19.5 %) and increased P recovery (1.8 % to 25.5 %) was achieved in biochar through co-pyrolysis of nutrient-rich and selected carbon-rich feed stocks compared with their separate pyrolysis. The chicken bone and sewage sludge can be ideal feedstocks for enhanced P and K recovery through their co-pyrolysis with carbon rich biomass such as banana stem or sunflower stalk.

Insights into microplastics (MPs) removal using aquatic plant-derived biochar from Taihu Lake at varying carbonization temperatures

Microplastics (MPs), recognized as significant emerging contaminants, are prevalent in both terrestrial and aquatic ecosystems. This study investigates the potential of biochar derived from Polygonum amphibium L. (PAL) sourced from Taihu Lake and processed through a low-temperature carbonization method, for in the removal of MPs. This approach addresses the escalating presence of MPs in aqueous environment, especially during the COVID-19 pandemic, simultaneously tackles the issue of waste biomass contributing to eutrophication. The study focused on the impact of carbonization temperatures (450℃-550℃) on physicochemical properties of biochar. Additionally, the effect of contact time, initial concentration of MPs, and environmental factors at various carbonization temperatures were also examined. The results reveal that the biochar yield and adsorption performance of biochar are significantly influenced by carbonization temperature. The adsorption capacity of biochar for MPs removal increases with the carbonization temperature up to 500 ℃, attributed to enhanced diffusion, surface adsorption, interactions, and cation-π electron interactions between the biochar and MPs. However, at a pyrolysis temperature of 550 ℃, the increase in adsorption capacity of biochar-550 is marginal due to increased competitive binging and destabilization of biochar under basic conditions. Overall, the optimum carbonization temperature is identified as 500 ℃, yielding a char rate is 32.23% and an adsorption capacity for MPs of 80.3 mg/g, thereby offering a promising solution for MP removal and water eutrophication management.

Pyrolysis of macroalgae: Insight into product yields and biochar morphology and stability

Pyrolysis of biomass residues into biochar is seen as a feasible way to mitigate climate change by biological carbon storage (carbon dioxide removal, CDR) and to substitute fossil fuel with sustainable biofuel. This study applies a combination of flash and ramp heating pyrolysis, and organic petrography to investigate the hydrocarbon (biofuel) potential and biochar stability and morphotypes of eight brown, red, and green macroalgal species of different tissue complexity. The carbon stability of biochar derived from macroalgae has not previously been assessed using organic petrography (reflectance measurements) and evaluated in the context of the geological carbon cycle. The biochar, hydrocarbon, and CO + CO2 yields vary due to different chemical composition of the macroalgal species, but the product yield variations are not related to the brown, red, or green macroalgal groups. The total biofuel yield shows an inverse trend with biochar yield. A slower heating rate produces more biochar and higher CO + CO2 and lower biofuel yields than the combined flash pyrolysis and faster heating rate. The morphotype composition of the biochar was qualitatively examined by reflected light microscopy while carbon stability was assessed by random reflectance (Ro) measurements. The diverse morphotype compositions observed in biochar formed under similar pyrolysis conditions likely stem from variations in the original algal composition. While some biochar samples show morphologies resembling the original macroalgal structure, porous morphotypes predominantly characterize the biochar samples overall. Despite a maximum pyrolysis production temperature (PT) of 650 °C, the highest mean Ro value among all biochar samples is 2.91%, corresponding to a carbonization temperature (CT) of 526 °C. This observation is tentatively related to the less lignocellulosic structure of the macroalgae compared to terrigenous biomass. Four biochar samples have their entire Ro distribution range above the inertinite benchmark (IBRo2%) of Ro = 2% indicating high carbon stability. Conversely, the remaining four biochar samples exhibit Ro distributions extending below IBRo2%, indicating the presence of a carbon fraction with lower long-term stability in soil. The statistically significant inverse relationship observed between the mean Ro values and the peak hydrocarbon generation temperature (Tmax) can be attributed to the behavior of residual macromolecules within the biochar. When these macromolecules reach peak biofuel generation at a lower temperature, they undergo carbonization over a more extended time interval during pyrolysis. Consequently, this prolonged exposure to the pyrolysis process leads to higher degrees of carbonization, as reflected by higher Ro values. In conclusion, the findings from pyrolysis and organic petrography reveal: (1) Macroalgae demonstrate potential for biofuel production, although biofuel yields contingent upon both the species of macroalgal and the heating rate employed, and (2) This study documents for the first time that flash+ramp pyrolysis of macroalgae yields biochar suitable for long-term carbon storage. However, both the carbon stability inferred from Ro frequency distributions and biochar yields show variations across different macroalgal species and heating rate.

The synergistic pyrolysis effects of polyethylene terephthalate with the additive of sewage sludge

Pyrolysis could be one of the promising ways for polyethylene terephthalate (PET) waste-based char production, while the adherence environmental persistent free radicals (EPFRs) brought the risks for the wide application. Co-pyrolysis was employed as the potential way to reduce the EPFRs and improve the char quality simultaneously with the introduction of sewage sludge (SS), and the optimization reaction conditions and the relative mechanisms were proposed in this work. EPFRs in PET-based char were found to decrease from 1.07 × 1018–4.84 × 1018 spins·g−1 to 2.17 × 1017–4.90 × 1017 spins·g−1, with 38.86–48.55% reduction at the mass ratio of 1:1 (PET:SS). The corresponding activation energy decreased by 78.83% with 30.93% higher biochar yield rate due to the synergistic effects. Co-pyrolysis facilitated the decomposition of benzoic acid and its derivatives by enhancing the cleavage of oxygen-containing functional groups and led to the binding of nitrogen with more pyrolysis intermediates, resulting in a reduction of precursors for oxygen/oxygenated-carbon centered radicals. More phenyl radicals were polymerized into carbon-centered radicals through hydride transfer and crosslinking in the mixed system. The additive of SS promoted the aromatization degree, enhanced the defect and pore structure of the biochar, and led to a 43.62-fold increase in the surface area of PET-based char at 400 °C. This work provides a potential approach to reduce EPFRs from the pyrolysis of plastic waste and to deal with multiple waste streams in venous industry park under the implementation of zero waste cities construction.

Sustainable bio-oil from banana peel waste biomass: Optimization study and effect of thermal drying

<p>Banana waste has a high level of volatile matter, making it a promising feedstock for pyrolysis in bio-oil generation. Thus, an oven drying method optimization study was conducted to find the drying process of Saba banana peel on flap opening and fan speed. Based on the ANOVA results, it was found that the drying process using 60% fan speed and 40% flap opening for 6 hours of drying time could remove 84.07% of the moisture content from the banana peel. Differential thermal analysis (DTA) was employed to characterize dried banana peels. The TGA study showed that the volatile matter concentration of the dried banana peels was 76.47% when using the ASTM drying method and 70.95% when using the improvement parameter optimization for the drying process. The bio-oil's high heating value (HHV) at 300 °C was 38.88 MJ/kg. The yields of bio-oil, biochar, and syngas obtained from the pyrolysis process were 16.6%, 36.45%, and 46.96%, respectively. The carbon hydrogen nitrogen sulfur (CHNS) ultimate analysis study showed a bio-oil elemental composition of 65.59% carbon, 8.27% hydrogen, 2.94% nitrogen, 0.93% sulfur, and 22.27% oxygen. Fourier transform infrared (FTIR) spectroscopy showed that functional groups including alcohol, alkane, phenol, and primary alcohol are present.</p>

Hydrothermal co-liquefaction of microalgae, sugarcane bagasse, brewer's spent grain, and sludge from a paper recycling mill: Modeling and evaluation of biocrude and biochar yield

Biomass can be used as an energy source to thermochemical conversion processes to biocrude production. However, the supply and dependence on only one biomass for biocrude production can be an obstacle due to its seasonality, availability, and logistics costs. In this way, biomass waste and agroindustrial residues can be mixture and used as feedstock to the hydrothermal co-liquefaction (co-HTL) process as an alternative to obtaining biocrude. In this sense, the present paper analyzed the biocrude yield influence of the co-HTL from a quaternary unprecedented blend of different biomasses, such as sugarcane bagasse, brewer's spent grain (BSG), sludge from a paper recycling mill (PRM), and microalgae (Chlorella vulgaris). In this way, a simplex lattice design was employed and co-HTL experiments were carried out in a 2000 mL high-pressure stirred autoclave reactor under 275 °C for 60 min, considering 15% of feedstock/water ratio. Significant effects in each feedstock and their blends were analyzed aiming to increase biocrude and biochar yield. It was found that the addition of microalgae is only significant when considered more than 50% into the blend with BSG and PRM sludge to increase biocrude yield.

Oriented pyrolysis of biomass for hydrogen-rich gas and biochar production: An energy, environment, and economic assessment based on life cycle assessment method

This study aimed to analyze a technology of hydrogen-rich gas from full-component oriented pyrolysis (FCOP) of biomass using energy, economic, and environmental life cycle assessment. Firstly, the study taked corn straw (CS) as the research object, the yield of hydrogen-rich gas and char produced by the oriented pyrolysis method are 78.26% and 20.35%, and the yield of biochar produced by activating char with phosphoric acid is 40%. Secondly, the system boundary of FCOP of biomass to produce hydrogen-rich gas and biochar was creatively designed, establishing the energy, environmental, and economic analysis comprehensive model. Various energy, economic, and environmental indicators were computed to facilitate process optimization for hydrogen-rich gas co-production biochar and explored the feasibility of the process. The results show that the stage of hydrogen-rich gas prepared by FCOP of biomass is an important factor affecting energy output and input, and has the highest standard pollutant emissions (92.11%). This process has low carbon emissions and GHG emissions, showing good sustainability and application prospects, which has important guiding significance for realizing cleaner production and solving the energy crisis. Thirdly, taking the large-scale system of producing hydrogen-rich gas co-production biochar, which processes 40,000 t of CS per year, as an example, the economic benefit analysis results were obtained, that is, IRR, NPV, and Pm are 22%, 6.33 million yuan, and 7.3 years, respectively. Meanwhile, the key factors, including the initial investment, expenses of biomass and catalyst, and the sale income of hydrogen and biochar, which are the main factors affecting the economic efficiency of technology, and uncertainties were identified through sensitivity analysis. Finally, we put forward in the background of ecological civilization, the research focus and thinking for the development of hydrogen production technology from pyrolysis/gasification of biomass were proposed. The results obtained can be valuable in practical applications to enhance the sustainability and viability of hydrogen production in biomass conversion and utilization activities. The applied energy, economic, and environmental methodologies appear to be reliable and comprehensive tools for assessing the whole-life sustainability and viability of biofuel.

Impact of high-temperature biomass pyrolysis on biochar formation and composition

The development and utilization of biomass play a vital role in reducing fossil fuel dependency and mitigating greenhouse gas emissions. High-temperature pyrolysis provides a promising route for converting biomass into valuable products without tar formation. Kinetic models are essential for understanding biomass pyrolysis processes, aiding reactor design and optimization. In this study, rice husk (RH) and corn straw (CS) are selected, which exhibit significant differences in ash content but are widely present. Pyrolysis is performed using a thermogravimetric analyzer coupled with a mass spectrometer (TGA-MS). The results show a rapid decrease in solid residue oxygen content at elevated temperatures, which stabilized after reaching 900°C, accounting for about 8–10%. MS quantification indicates increased release of H2O and CO during this stage. Fourier transform infrared spectroscopy (FTIR) analysis on the biochar unveils that this phenomenon is attributed to the stretching vibration of C-O bonds and the conversion of -OH groups. The remaining oxygen primarily exists as carbonyl and carboxyl groups. Subsequently, the CRECK-S-B biomass pyrolysis kinetic model is updated, specifically targeting the transformation mechanism of oxygen-containing solids at high temperatures to improve the prediction of biochar yield and elemental composition. The relative error of oxygen content prediction is less than 10%. The accuracy of the model is validated through experimental data and an extensive literature database, leading to the establishment of a comprehensive database. The updated model demonstrates significantly enhanced prediction accuracy for pyrolysis temperatures above 800°C, expanding its applicability range. Moreover, it achieves an accuracy rate exceeding 80% for char yield and elemental content in the temperature range of 200–1000°C, including torrefaction conditions. It provides a theoretical foundation for the effective utilization of high-temperature biochar, offers a novel insight into biomass thermochemical conversion, and contributes to the sustainable development of biomass energy.

Co-pyrolysis of sewage sludge and sawdust: Synergistic effects of product yield and synthetic gas calorific value

Co-pyrolysis of sludge and sawdust, which are two renewable and abundant biomass resources, offers a promising environmental-friendly way to produce valuable energy products. In this study, the synergistic effect between sludge and sawdust was quantified by fixed bed reactor and thermogravimetric experiments. The product yield and product quality were also studied. The results showed that both temperature and sawdust addition significantly affected the distribution of co-pyrolysis products. Biochar yield decreased with increasing temperature, with the highest yield at 700 °C. With the addition of sawdust, the yield of biochar first increased and then decreased. The highest biochar yield was 58.1 wt% after adding 10 wt% sawdust. The yield of bio-oil initially decreases and then increases with temperature. With the addition of sawdust, the yield of bio-oil first decreased and then increased. The process condition of a temperature of 700 °C–800 °C and a sawdust addition ratio of less than 30 wt% is more favorable for the production of bio-oil. Increasing temperature and the addition of sawdust boosteded syngas production and calorific value. When the sawdust ratio was 10 wt%, it exhibited the most pronounced influence on gas yield and demonstrated less susceptibility to temperature variations. The most obvious increase in the calorific value of syngas was observed at 700 °C and 10 wt% sawdust ratio. Taking into account the product yield and product quality, the optimum conditions for co-pyrolysis were determined to be 750 °C and a sawdust ratio of 10 wt%.

Predicting biochar properties and pyrolysis life-cycle inventories with compositional modeling

Biochar, formed through slow pyrolysis of biomass, has garnered attention as a pathway to bind atmospheric carbon in products. However, life cycle assessment data for biomass pyrolysis have limitations in data quality, particularly for novel processes. Here, a compositional, predictive model of slow pyrolysis is developed, with a focus on CO2 fluxes and energy products, reflecting mass-weighted cellulose, hemicellulose, and lignin pyrolysis products for a given pyrolysis temperature. This model accurately predicts biochar yields and composition within 5 % of experimental values but shows broader distributions for bio-oil and syngas (typically within 20 %). This model is demonstrated on common feedstocks to quantify biochar yield, energy, and CO2 emissions as a function of temperature and produce key life cycle inventory flows (e.g., 0.73 kg CO2/kg poplar biochar bound carbon at 500 °C). This model can be adapted to any lignocellulosic biomass to inform development of pyrolysis processes that maximize carbon sequestration.

A new approach to explore and assess the sustainable remediation of chromium-contaminated wastewater by biochar based on 3E model

As a cost-effective material, biochar, known as ‘black gold’, has been widely used for environmental applications (EA), including chromium-contaminated wastewater remediation. However, limited reports focused on the multiple impacts of biochar, including energy consumption (EC) and environmental risk (ER). Hence, to recommend biochar as a green material for sustainable development, the three critical units were explored and quantitatively assessed based on an adapted 3E model (EA-EC-ER). The tested biochar was produced by limited-oxygen pyrolysis at 400–700 °C by using three typical biomasses (Ulva prolifera, phoenix tree, and municipal sludge), and the optimal operational modulus of the 3E model was identified using six key indicators. The findings revealed a significant positive correlation between EC and biochar yield (p < 0.05). The biochar produced by phoenix tree consumed more energy due to having higher content of unstable carbon fractions. Further, high-temperature and low-temperature biochar demonstrated different chromium removal mechanisms. Notably, the biochar produced at low temperature (400 °C) achieved better EA due to having high removal capacity and stability. Regarding ER, pyrolysis temperature of 500 °C could effectively stabilize the ecological risk in all biochar and the biochar produced by Ulva prolifera depicted the greatest reduction (37-fold). However, the increase in pyrolysis temperature would lead to an increase in global warming potential by nearly 22 times. Finally, the 3E model disclosed that the biochar produced by Ulva prolifera at 500 °C with low EC, high EA, and low ER had the most positive recommendation index (+78%). Importantly, a rapid assessment methodology was established by extracting parameters from the correlation. Based on this methodology, about eight percent of biochar can be the highest recommended from more than 100 collected peer-related data. Overall, the obtained findings highlighted that the multiple impacts of biochar should be considered to efficiently advance global sustainable development goals.

Machine learning models for predicting biochar properties from lignocellulosic biomass torrefaction

This study developed six machine learning models to predict the biochar properties from the dry torrefaction of lignocellulosic biomass by using biomass characteristics and torrefaction conditions as input variables. After optimization, gradient boosting machines were the optimal model, with the highest coefficient of determination ranging from 0.89 to 0.94. Torrefaction conditions exhibited a higher relative contribution to the yield and higher heating value (HHV) of biochar than biomass characteristics. Temperature was the dominant contributor to the elemental and proximate composition and the yield and HHV of biochar. Feature importance and SHapley Additive exPlanations revealed the effect of each influential factor on the target variables and the interactions between these factors in torrefaction. Software that can accurately predict the element, yield, and HHV of biochar was developed. These findings provide a comprehensive understanding of the key factors and their interactions influencing the torrefaction process and biochar properties.