A biorefinery concept using forced chicory roots for the production of biogas, hydrochar, and platform chemicals

Abstract

Chicory roots (Cichorium intybus L.) are an agricultural residue from salad production. After forcing, the roots contain ingredients from which further products can be obtained. Thus, forced chicory roots can still be considered as a low-cost feedstock for the production of valuable products. Sugars can be extracted and then be used for the production of platform chemicals like 5-hydroxymethylfurfural. Remaining sugars and other components can be degraded during hydrothermal carbonization, where a carbon-enriched hydrochar and a process water enriched in organic components are produced. The process water can be anaerobically digested to produce biogas. In this paper, a cascaded utilization of chicory roots was investigated. Of the initial sugars in the roots, 67.5 wt.% were extracted in a batch extraction with hot water. During hydrothermal carbonization in batch autoclaves, hydrochar yields of up to 66.2 wt.% were achieved. A methane potential of 255 L CH4/kg COD was determined from process water after carbonization. With this additional anaerobic digestion of the process water, a complete utilization of the forced chicory root is achieved. Therefore, in this work, a biorefinery concept for forced chicory roots combining sugar extraction, hydrothermal carbonization, and anaerobic digestion was investigated to elongate the value chain of chicory and to enable an optimum usage of the biomass. The carbon efficiency of this cascaded utilization was 96% whereas the state of the art process only showed 40%.