Biochar characteristics and early applications in anaerobic digestion-a review

In the recent years, special focus has been given to the issues related to the management of biomass conversion systems by-products. In the view of transforming those products, mostly treated today as wastes, in valuable products, different valorization pathways can be considered. As an example, considerable attention has been devoted to the potential use of carbon-rich materials such as soil amendments and for long term carbon storage. These materials, produced by biomass thermochemical conversion are known as biochars. Several processes, from pyrolysis to gasification and hydrothermal carbonization, are today available for biochar production although characterized by relatively high costs. To overcome this restraint, an option is represented by the achievement of further economic benefits by extending its value chain. Coupling thermochemical processes to Anaerobic Digestion is thus an emerging field of research aimed at expanding usable feedstock with biologically recalcitrant substrates, such as paper, woody materials etc. Biochar in fact may promote the biomethane production, by acting both as support for bacteria colonies, conductor for electron transfer among species, sorbent for indirect inhibitors, and reactant in biochars labile carbon methanization. Thus, system integration of biogas and biochar is promising taking advantage of several profitable synergies. The aim of the paper is to review biochar characteristics and study early applications so far demonstrated and carried out, for the use of biochar in the anaerobic digestion processes.