Assessment of the effect of pyrolysis operating conditions on phytotoxicity and potential as carrier for AM fungi of vine shoots-derived biochar

Conference Dates

September 15-20, 2019


Biochar production from vine shoots appears as an interesting option to manage this agricultural waste for both environmental and agronomic benefits. In order to produce biochar from biomass at appropriate yields, slow pyrolysis is a particularly suitable option. However, the properties of the resulting biochar strongly depend on the process operating conditions. In this sense, establishing the most appropriate operating conditions is still required with the aim at producing engineered biochars. Furthermore, it should be kept in mind that a certain compromise between the pyrolysis operating conditions and the expected properties of biochar has to be achieved. In other words, the most appropriate conditions to produce a biochar with the desired properties for a given purpose might not be suitable for another one (e.g., pyrolysis conditions leading to a maximization of the carbon sequestration potential can result in biochars with high phytotoxicity and thus not suitable for soil amendment purposes).

The highest temperature reached in the pyrolysis process (i.e., peak temperature) has proven to be a fundamental parameter in determining the physicochemical properties as well as the potential stability of biochar [1]. Nevertheless, few earlier studies have focused on assessing the combined effect of both the absolute pressure and residence time of the vapor phase within the reactor [2].

In light of the above-mentioned considerations, the specific aim of this study is to analyze the effect of the peak temperature (350–500 °C), absolute pressure (0.1–0.5 MPa), and residence time of the vapor phase (50–150 s) on the distribution of pyrolysis products and key properties of produced biochar. In addition to the assessment of the potential stability of biochar (which can be related to its fixed-carbon content and atomic H:C and O:C ratios), its potential toxicity on seed germination as well as its interaction with arbuscular mycorrhizal (AM) fungi were also evaluated. A 2-level factorial design (with the addition of three replicates at the center point) was adopted to objectively analyze the effect of the selected factors on the response variables.

Pyrolysis experiments were conducted in a batch fixed-bed reactor, the details of which are available elsewhere [2]. The content of water in the total condensable fraction was measured using a Karl-Fischer volumetric titrator from Metrohm (Switzerland). The composition of the gas fraction (N2, CO2, CO, CH4, C2Hx and H2) was determined using a micro-GC 490 from Agilent (USA). The initial sample mass of biomass was approximately 500 g. The raw biomass was previously sieved to obtain a particle size of 0.1–1.0 cm in diameter and 1.0–4.0 cm in length. To assess the potential stability of biochar, the fixed-carbon content (determined from the proximate analysis) and the atomic H:C and O:C ratios (calculated from the elemental analysis) have been taken as response variables. On the other hand, the potential phytotoxicity of produced biochars has been evaluated by three different tests, which have been based on previous studies [3,4], and using three different seed families (barley, lettuce and watercress). The germination index and radicle length have been selected as response variables. Furthermore, the potential of biochar as carrier for mycorrhizal communities has been measured as follows: a mixture of biochar and mycorrhizal inoculum was used as substrate on which barley seeds were planted in triplicate; the generated biomass after two months of growing as well as the mycorrhizal percentage of the roots have been taken as response variables. Experimental trials are almost finished and the results from the statistical analyses will be summarized and presented during the course of the conference.


[1] Brassard, P.; Godbout, S.; Raghavan, V. Biosyst. Eng. 2017, 161, 80–92.

[2] Manyà, J. J.; Azuara, M.; Manso, J. A. Biomass Bioenergy 2018, 117, 115–123.

[3] Liang, C.; Gascó, G.; Fu, S.; Méndez, A.; Paz-Ferreiro, J. Soil Tillage Res. 2016, 164, 3–10.

[4] Buss, W.; Masek, O.; Graham, M.; Wüst, D. J. Environ. Manage. 2015, 156, 150–157

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