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Biochar Carbon Stability Test Method: An assessment of methods to determine biochar carbon stability
Abstract and Figures
Twenty seven methods currently used to characterize biochar were assessed in terms of their usefulness
to determine the stability of biochar carbon in the environment. The International Biochar Initiative (IBI),
which led the effort, gathered fourteen world-class experts in different fields of biochar relevant to
stability, who guided the process for obtaining a simple, yet reliable, measure for biochar stability.
Important requisites were defined for the test, including cost, repeatability and availability.
Identification of a cost-effective, scientifically valid test to measure the stable carbon component of
biochar is imperative to distinguish biochar from non-biochar (non-stable) materials, and to develop a
biochar offset protocol for carbon markets. The stability of biochar carbon in soils makes it a highly
promising product for consideration as a strategy for climate change mitigation. The definition of the
variable BC+100, which stands for the amount of biochar carbon that is expected to remain stable after
100 years, along with predictions of stability based on simple (Alpha) and more sophisticated (Beta) methods, allowed to correlate a molar ratio (H/Corg) to the relative stability of biochar. The process for
identifying the Biochar Carbon Stability Test Method is summarized here, and the method itself is
available as a separate, technical document.
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... However, biochar is considered to be able to sequester C in soil for the long term, reduce GHG emissions and also reduce the C footprint by replacing fertilizers. The metal-data analysis demonstrated (Budai et al. 2013) that biochar with H/C > 4 sequestered 50% of its carbon, and biochar having H/C < 4 sequestered 70% of its carbon for 100 years. Hence, the carbon sequestration potential (CSP) of biochar will range from 50 to 70% of its carbon content. ...
The cultivation of aromatic grasses on marginal/degraded land attracts attention due to their remediation potential, low input cost, and economic gain. During the distillation of these aromatic grasses, a huge amount of solid and liquid waste (hydrosol) is generated, which is not only rich in carbon content but also has a good amount of nutrient. This review summarized the potential of aromatic plants for the restoration and vaporization of distilled waste into different value-added products. In this review, estimates of the economic cost and carbon dynamics for cultivation, distillation, and waste valorisation of aromatic grasses were made using available data. Based on the literature, the available degraded land reported for India (38,600 ha) was used for the calculation. The review discussed Scientometrics analysis, the remediation potential of aromatic plants, and various routes of valorization of distilled waste generated to achieve sustainable development goals. Scientometrics analysis demonstrated the studies that include the phytoremediation potential of aromatic grasses in recent years. Among the aromatic grasses, Chrysopogon zizaniodes (L.) Nash., Cymbopogon flexuosus and Cymbopogon martini were majorly used for reclamation purposes for dry land, mine-affected areas, and metal and pesticide-contaminated soils. The estimated profitability of the cultivation and carbon sequestration potential of these grasses in marginal/degraded land could be 22–629 million USD. Our estimations showed that the cost of carbon sequestration by the cultivation of the aromatic plant in degraded land could be 16–45 million USD. The conversion of distilled waste generated into compost, vermicompost, and biochar could sequester about 0.02 X10 ⁵ -335 X10 ⁵ t of carbon (cost: 0.2–1913 million USD). The use of hydrosol and smoke water released during the process could sequester about 0.014 to 7403 t of carbon ( cost 0.001 to 0.42 million USD). Overall the review demonstrated the sustainability and carbon footprinting of the remediation process by aromatic grasses. The review allowed the exploration of knowledge-based strategies to unlock the potential of aromatic plants for restoration and carbon sequestration, along with the value addition of distilled waste in a sustainable manner. However, more databases are needed to support the information, which includes the productivity and selectivity of individual aromatic plant for different soil and agro-climatic regions.
Graphical Abstract
... Moreover, biochars with increased surface areas have greater numbers of binding sites for organic C molecules, thereby enhancing their C sequestration capacity [106]. This augmented surface area enables a higher degree of organic matter adsorption, effectively transforming the biochar into a C reservoir within the soil [107]. ...
Biochar, a sustainable solid material derived from biomass pyrolysis enriched in carbon, has emerged as a promising solution for soil carbon sequestration. This comprehensive review analyzes the current knowledge on biochar’s application in this context. It begins by examining biochar properties and production methods, highlighting its recalcitrant nature as a potential stable carbon sink. The influence of various feedstocks and pyrolysis conditions on various physicochemical properties of biochar and its soil carbon sequestration potential is explored. Mechanisms through which biochar enhances soil carbon sequestration are discussed, including its role as a physical barrier against carbon loss and its ability to promote stable soil aggregates and influence soil microorganisms. Challenges and limitations, such as variations in biochar properties and optimal application rates, are addressed, along with strategies for maximizing biochar effectiveness through amendments. The review concludes by emphasizing the importance of long-term field studies, standardized protocols, and economic assessments to support the widespread adoption of biochar for soil carbon sequestration and its potential in climate change mitigation.
... Moisture content was 1.8% w/w w.b., and volatile matter and ash content resulted, respectively, in 13.0 and 8.7% w/w d.b. Fixed carbon content and H/C molar ratio indicate a good degree of carbonisation and stability for the biochar obtained [40,41]. H/C molar ratio values fluctuate depending on the feedstock and the process used; generally, materials with low H/C molar ratio represent products with higher stability and resistance to degradation, similar to in this case, where the molar H/C ratio resulted in 0. 35. ...
... Moisture content was 1.8% w/w w.b., and volatile matter and ash content resulted, respectively, in 13.0 and 8.7% w/w d.b. Fixed carbon content and H/C molar ratio indicate a good degree of carbonisation and stability for the biochar obtained [40,41]. H/C molar ratio values fluctuate depending on the feedstock and the process used; generally, materials with low H/C molar ratio represent products with higher stability and resistance to degradation, similar to in this case, where the molar H/C ratio resulted in 0. 35. ...
Juniperus communis L. is a species commonly grown in regions of the Northern Hemisphere, and is a good candidate to be cultivated in marginal lands. Plants coming from a pruning performed in a natural population located in Spain were used to assess the yield and quality of different products obtained following the cascade principle. A total of 1050 kg of foliage biomass were crushed, steam-distilled, and separated into fractions to produce biochar and absorbents for the pet industry using pilot plants. The obtained products were analysed. The essential oil, with a yield of 0.45% dry basis and a qualitative chemical composition similar to that described for the berries in international standards or monographs, showed antioxidant activity with promising CAA results (inhibition of 89% of the cell’s oxidation). However, regarding antibacterial and antifungal activities, it only inhibited the growth of microorganisms at the maximum concentration tested, 2.5%. Concerning the hydrolate, it did not show bioactivity. Regarding the biochar, whose yield was 28.79% dry basis, interesting results were obtained for its characterisation as a possible soil improver for agronomic purposes (PFC 3(A)). Finally, promising results were obtained regarding the use of common juniper as absorbent, taking into account the physical characterisation and odour control capacity.
... Thus, VM is not completely representative of the labile fraction in MAB. As per International Biochar Initiative (IBI) standards [34], based on H/C org , the most carbonized biochar types here are B550 and B514, and they belong to class 2 (10% ⩽ C org ⩽ 30%). At least 50% of their carbon will be stable in soil for 100 years (BC +100 ). ...
The increase in mineral and ash-rich waste biomass (MWB) generation in emerging economies poses critical environmental problems and bottlenecks the solid waste and wastewater treatment systems. Transforming these MWB such as sewage sludge from wastewater treatment (SSW) to biochar can be a sustainable method for their disposal and resource recovery. However, such biochar has limited applicability due to the relatively low organic content and possibly contaminated nature of SSW. This may be offset through combined pyrolysis with other MWB, which can also support municipal solid waste management. Studies on this MWB co-pyrolysis are lacking and have not yet seen successful long-term implementation. This work is the second part of authors’ research encompassing an analytical and lab-scale investigation of biochar production from MWB through pyrolysis for the case of Chennai city, India. Here, the physicochemical properties of biochar derived from lab-scale co-pyrolysis of SSW with other MWB such as anaerobic digestate from waste to energy plants of food, kitchen or market waste fermentation, and banana peduncles (BP) collected from vegetable markets and their thermolysis mechanism are comprehensively investigated for purpose of carbon sequestration. Also, a novel preliminary investigation of the effect of sample weight (scaling effect) on the analytical pyrolysis of biomass (BP as model substrate) is undertaken to elucidate its impact on the heat of pyrolysis and carbon distribution in resultant biochar. The maximum carbon sequestration potential of the derived biochar types is 0.22 kg CO 2 kg ⁻¹ biomass. The co-pyrolysis of MWB is exothermic and governed by the synergetic effects of the components in blends with emission profiles following the order CO 2 > CH 4 > CO > NH 3 . Co-pyrolysis reduced the heavy metal enrichment in SSW biochar. The derived biochars can be an immediate source of N, P and S in nutrient-deficient acidic soils. The biochar has only up to 4-ring polyaromatic compounds and a residence time longer than 1 h at 500 °C is necessary to improve carbonization. The heat released during analytical pyrolysis of the model biomass and distribution of carbon in the resultant biochar are significantly influenced by scaling effects, drawing attention to the need for a more detailed scaling investigation of biomass pyrolysis.
... The results of the elemental analysis of the biochar are shown in Fig. 3 (a). The relatively low O/C and H/C ratios indicate that the biochar used in this study had high aromaticity and maturity [26,27]. The SEM image are shown in Fig. 3 (b). ...
Carbonation is generally considered beneficial for the calcium leaching resistance of cement-based materials. However, many studies have demonstrated that early accelerated carbonation has detrimental effects on the calcium leaching resistance. In this study, the calcium leaching behavior of an early-carbonated cement paste was investigated in detail. The results showed that 8–16 h of carbonation mitigated the reduction in compressive strength caused by calcium leaching; however, further prolongation of carbonation caused an increased decline in strength at the later leaching stage. In contrast to the calcium leaching results for the powdered samples, the decalcification level of calcium silicate hydrate during the leaching test for the cubic specimens was similar to or even higher than that of the early-carbonated specimens. CaCO3 and silica gel played key roles in these phenomena; the former provided ideal hardness and calcium sequestration, with the potential to generate protective films, while the latter acted as an ideal filler and binder. Nonetheless, considering the risk of rapid degradation during long-term calcium leaching, excessive carbonation curing of cement-based materials should still be avoided in aqueous environments.
... The degree of aromatization in the biochar generated is indicated by the lowest hydrogen-to-carbon molar ratio (H/C), which was found in biochar made from cotton stalk and mustard husk to be 0.02 and 0.01. At least 70% of the organic carbon in biochar is anticipated to persist in soil for at least 100 years with 95% confidence when the H/C molar ratio is less than or equal to 0.4 [42]. In this investigation, it was discovered that the biochar generated used less or the same amounts of H/C and O/C molar ratios as biochar produced in a batch-type reactor utilising a variety of agricultural wastes, animal dung, grasses, and wood [43][44][45]. ...
... The C-rich biochar, a co-product of biomass pyrolysis, is typically used as a soil amendment to improve soil quality and sequester carbon (Laird, 2008;Laird et al., 2010). Biochar C is intrinsically recalcitrant to microbial degradation and will remain in soils for 100s-1000s of years (Budai et al., 2013). ...
Biochar has been used to address several environmental problems and may be efficacious as a carrier of N fertilizer in slow-release N-fertilizer (SRF) formulations. Our objective was to compare the efficacy of SRF pellets formulated with different mass ratios of biochar and urea with traditional N fertilizers for improving N use efficiency by maize (Zea mays L.) grown under greenhouse conditions. Two different soil types, four SRF formulations with different biochar to urea (BCN) ratios (1:2 BCN, 1:3 BCN, 1:4 BCN, and 1:6 BCN), three traditional N fertilizers (urea, urea ammonium nitrate, and S-coated urea), and unfertilized controls for each soil were tested. The accelerated urea release test showed significantly less loss of urea for the SRF over time than the traditional N fertilizers. The biochar based SRF formulations significantly (p <0.05) decreased nitrate leaching loss for both soils relative to the traditional fertilizers. All the SRF formulations increased maize shoot (1-34%) and root (0-23%) biomass, N-recovery efficiency (17-50%), and soil potential mineralizable-N relative to urea and S-coated urea. The results also indicate that the biochar-to-urea ratio in the SRF formulation can be used to influence the timing of N release and plant N uptake. The results of the greenhouse study suggest that biochar-based SRFs have potential agronomic and environmental benefits; however, more research is needed to assess their agronomic value under field conditions. This article is protected by copyright. All rights reserved.
Amount, stability, and distribution of black carbon (BC) were studied at
four sites of a large peatland ("Witzwil") formerly used as a disposal for
combustion residues from households to derive BC displacement rates in the
profile. Possible artefacts from thermal oxidation with Differential
Scanning Calorimetry (DSC) on BC quantification of C-rich deposits were
inferred by choosing three sites from a second peatland with no historical
record of waste disposal as a reference ("Seebodenalp"). All sites were
under grassland at time of sampling, but were partially cropped in the past
at Witzwil. Mean BC contents in topsoils of Witzwil ranged from 10.7 to 91.5
(0–30 cm) and from 0.44 to 51.3 (30–140 cm) mg BC g−1 soil,
corresponding to BC/OC ratios of 0.04 to 0.3 (topsoil) and 0.02 to 0.18
(deeper soil). At three sites of Seebodenalp, BC was below the detection
limit of 0.4 mg g−1 organic soil, indicating negligible formation of BC
during thermal oxidation of peat. 13C NMR spectra corroborated the high
BC contents at Witzwil. The data support a considerable vertical transport
of BC given that soils were ploughed not deeper than 30 cm since abandonment
of waste application about 50 years ago. The total amount of BC in the
Witzwil profiles ranged from 3.2 to 7.5 kg BC m−2, with 21 to 69
percent of it stemming from below the former ploughing depth. Under the
premise of negligible rates of BC consumption since abandonment of waste
application, minimum BC transport rates in these peats are 0.6 to 1.2 cm a−1. The high mobility of BC might be explained by high macro-pore
volumes in combination with occasional water saturation. By means of DSC
peak temperatures, different types of BC could be distinguished, with deeper
horizons containing BC of higher thermal stability. Application of
combustion residues likely involved a mixture of various BC types, of which
thermally more stable ones, most likely soots, were preferentially
transported downwards.
The recalcitrant properties of black carbon (BC) grant it to be a
significant pool of stable organic C (OC) in soils. Up to now, however,
the longevity of BC under different climates is still unclear. In this
study, we used BC samples from historical charcoal blast furnace sites
to examine the stability of BC across a climatic gradient of mean annual
temperatures (MAT) from 3.9 to 17.2°C. The results showed that OC
concentration and OC storage in the BC-containing soils at a soil depth
of 0-0.2 m were 9.0 and 4.7 times higher than those in adjacent soils,
respectively. Organic C in the BC-containing soils was more stable, with
a significantly lower amount of the labile OC fraction (4.4 mg
g-1 OC versus 27.5 mg g-1 OC) and longer half-life
of the recalcitrant OC fraction (59 years versus 9 years) than the
adjacent soils determined by incubation experiments. The stability of BC
was primarily due to its inherently recalcitrant chemical composition as
suggested by short-term incubation and solid state 13C
nuclear magnetic resonance spectra of isolated BC particles. A
significant negative relationship between OC storage and MAT further
indicated that OC storage was decreased with warmer climate. However,
the lack of a relationship between MAT and BC mineralization suggested
that the stability of the remaining BC was similar between sites with
very different MAT. Despite the fact that warming or cooling result in
immediate consequences for BC stocks, it may have little impact on the
stability of remaining BC over the period studied.
Observed increases in the mineralization rate of labile organic carbon (LOC) in the presence of black carbon (BC) have led to speculation that corresponding decreases in non-pyrogenic (i.e. non-BC) soil organic carbon (npSOC) could significantly reduce or negate the C sequestration benefit of BC in soils. Here we show that the potential effect of an increased LOC decomposition rate on long-term npSOC stocks is negligible, even when using assumptions that would favour large losses, potentially causing no more than 3–4 % loss of npSOC over 100 years if 50 % of above-ground crop residues were converted to BC annually. Conversely, if the BC-stimulated enhanced stabilization of npSOC that has been observed in laboratory trials is extrapolated to the long-term, it would greatly increase soil carbon stocks by 30–60 %. Annual additions of BC derived from crop residues would increase total SOC (including both BC and npSOC) by an amount five times greater than the potential increase from enhanced stabilization and an order of magnitude greater than losses of npSOC caused by annual removals of biomass to provide BC feedstock.
Increased crop yield is a commonly reported benefit of adding biochar to soils. However, experimental results are variable and dependent on the experimental set-up, soil properties and conditions, while causative mechanisms are yet to be fully elucidated. A statistical meta-analysis was undertaken with the aim of evaluating the relationship between biochar and crop productivity (either yield or above-ground biomass). Results showed an overall small, but statistically significant, benefit of biochar application to soils on crop productivity, with a grand mean increase of 10%. However, the mean results for each analysis performed within the meta-analysis covered a wide range (from −28% to 39%). The greatest (positive) effects with regard to soil analyses were seen in acidic (14%) and neutral pH soils (13%), and in soils with a coarse (10%) or medium texture (13%). This suggests that two of the main mechanisms for yield increase may be a liming effect and an improved water holding capacity of the soil, along with improved crop nutrient availability. The greatest positive result was seen in biochar applications at a rate of 100tha−1 (39%). Of the biochar feedstocks considered and in relation to crop productivity, poultry litter showed the strongest (significant) positive effect (28%), in contrast to biosolids, which were the only feedstock showing a statistically significant negative effect (−28%). However, many auxiliary data sets (i.e. information concerning co-variables) are incomplete and the full range of relevant soil types, as well as environmental and management conditions are yet to be investigated. Furthermore, only short-term studies limited to periods of 1 to 2 years are currently available. This paper highlights the need for a strategic research effort, to allow elucidation of mechanisms, differentiated by environmental and management factors and to include studies over longer time frames.