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, N 2 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.

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The bio-based economy relies on sustainable, plant-derived resources for fuels, chemicals, materials, food and feed rather than on the evanescent usage of fossil resources. The cornerstone of this economy is the biorefinery, in which renewable resources are intelligently converted to a plethora of products, maximizing the valorization of the feedstocks. Innovation is a prerequisite to move a fossil-based economy toward sustainable alternatives, and the viability of the bio-based economy depends on the integration between plant (green) and industrial (white) biotechnology. Green biotechnology deals with primary production through the improvement of biomass crops, while white biotechnology deals with the conversion of biomass into products and energy. Waste streams are minimized during these processes or partly converted to biogas, which can be used to power the processing pipeline. The sustainability of this economy is guaranteed by a third technology pillar that uses thermochemical conversion to valorize waste streams and fix residual carbon as biochar in the soil, hence creating a carbon-negative cycle. These three different multidisciplinary pillars interact through the value chain of the bio-based economy.

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