Dane Dickinson

Production and characterization of slow pyrolysis biochar: influence of feedstock type and pyrolysis conditions

Biochar was produced by fixed‐bed slow pyrolysis from various feedstock biomasses under a range of process conditions. Feedstocks used were pine wood, wheat straw, green waste and dried algae. Process conditions varied were the highest treatment temperature (HTT) and residence time. The produced chars were characterized by proximate analysis, CHN‐elemental analysis, pH in solution, bomb calorimetry for higher heating value, N2 adsorption for BET surface area and two biological degradation assays (oxygen demand, carbon mineralization in soil). In proximate analysis, it was found that the fixed carbon content (expressed in wt% of dry and ash‐free biochar) in the biochar samples strongly depended on the intensity of the thermal treatment (i.e. higher temperatures and longer residence times in the pyrolysis process). The actual yield in fixed carbon (i.e. the biochar fixed carbon content expressed as wt% of the dry and ash‐free original feedstock biomass weight) was practically insensitive to the highest treatment temperature or residence time. The pH in solution, higher heating value and BET surface positively correlated with pyrolysis temperature. Finally, soil incubation tests showed that the addition of biochar to the soil initially marginally reduced the C‐mineralization rate compared against the control soil samples, for which a possible explanation could be that the soil microbial community needs to adapt to the new conditions. This effect was more pronounced when adding chars with high fixed carbon content (resulting from more severe thermal treatment), as chars with low fixed carbon content (produced through mild thermal treatment) had a larger amount of volatile, more easily biodegradable, carbon compounds.

Toward the Standardization of Biochar Analysis: The COST Action TD1107 Interlaboratory Comparison

Biochar produced by pyrolysis of organic residues is increasingly used for soil amendment and many other applications. However, analytical methods for its physical and chemical characterization are yet far from being specifically adapted, optimized, and standardized. Therefore, COST Action TD1107 conducted an interlaboratory comparison in which 22 laboratories from 12 countries analyzed three different types of biochar for 38 physical-chemical parameters (macro- and microelements, heavy metals, polycyclic aromatic hydrocarbons, pH, electrical conductivity, and specific surface area) with their preferential methods. The data were evaluated in detail using professional interlaboratory testing software. Whereas intralaboratory repeatability was generally good or at least acceptable, interlaboratory reproducibility was mostly not (20% < mean reproducibility standard deviation < 460%). This paper contributes to better comparability of biochar data published already and provides recommendations to improve and harmonize specific methods for biochar analysis in the future.

Cost‐benefit analysis of using biochar to improve cereals agriculture

Biochar has received considerable scientific attention in the past decade as a possible method for carbon storage and increasing agricultural yields. Despite this promise, however, economic assessments of biochar are yet to definitively establish the value of the technology, primarily due to discrepancy between observed short‐term agronomic benefits and expectations of biochar as a lasting soil improver. This study investigated the economic value of biochar as an agricultural technology for long‐term improvement of arable farming. From presently available field trial data, the costs and benefits of using biochar technology to enhance cereals agriculture were evaluated in two generalized geo‐economic agricultural scenarios: North‐Western Europe (NWE) and Sub‐Saharan Africa (SSA). Cost models were developed to estimate the total cost of biochar from initial biomass feedstock acquisition to final soil application for each agricultural setting. Benefits of biochar application were estimated by statistical meta‐analysis of crop yield data from published biochar field trials to find the increase in cereal grain yield attributable to biochar application for both NWE (+0.07 to +0.28 t ha−1 yr−1) and SSA (+0.18 to +1.00 t ha−1 yr−1). The grain yield improvement from a one‐time biochar application was assumed to persist without decay for an independently varying time period, and the increase in grain production then monetised using projected future commodity prices. The Net Present Value (NPV) of applying biochar was then calculated by setting present total costs against present total benefits as a function of biochar performance longevity. Biochar application was found to carry a positive NPV for cereal cropping in SSA in several scenarios where the duration of the biochar yield effect was assumed to extend 30 years into the future. Conversely, NWE biochar scenarios were all found to have negative NPVs even when the benefits time span was indefinitely stretched.

Biochar in European Soils and Agriculture: Science and Practice

As demonstrated by several scientific studies there is no doubt that biochar in general is very recalcitrant compared to other organic matter additions and soil organic matter fractions and also that it is possible to sequester carbon at a climate change relevant time scale (~100 years or more) by soil application of biochar. However, the carbon stability of biochar in soil is strongly correlated with the degree of thermal alteration of the original feedstock (the lower the temperature, the larger the labile fraction) and in depth understanding of the technology used and its effect on the biochar quality is necessary in order to produce the most beneficial biochars for soil application. Beside carbon sequestration in soil biochar may improve the GHG balance by reducing N2O and CH4 soil emissions, although contrasting results are found in the literature. The mechanisms behind these reductions remain unclear and more research is required in order to investigate the various hypotheses in more detail, and to unravel the complex interaction between biochar, crop and soil, especially under field conditions. In conclusion, our current knowledge is largely based on short-term lab studies and pot experiments, which have provided detailed insight in certain processes and aspects of biochar application to soils, but suffer from large uncertainties when scaled-up to the farmers field level. In order to produce more realistic scenarios of the potential impact of biochar on C sequestration and soil GHG emissions there is a need to bring biochar research up to the field-scale, and to perform longer-term studies.