Valorization of brewer’s spent grain (BSG) into biochar for agricultural applications

Biochars (BC) have gained increasing interest for their potential contribution to climate change mitigation. As they are produced from organic waste, their use promotes the valorization of agro-industrial residues and the sequestration of carbon in stable forms, reducing greenhouse gasses emissions and improving the sustainability of different production processes through green economy. In this context, the comprehensive characterization of their physicochemical properties is essential for optimizing their design and suitability for each specific application.

In this work, brewer's spent grain (BSG) was used to produce a biochar through the pyrolysis process. The BSG was first conditioned by washing and drying. Subsequently, and according to previous essays, it was submitted to a mild condition of pyrolysis in a stainless-steel tubular reactor under controlled conditions. Obtained BC exhibited the typical amorphous carbon signal (24°) by X-ray diffraction (XRD) and a porous structure by Scanning Electron Microscopy (SEM). Textural properties showed a specific surface area (S_BET) around 90 m² g^-1 and an average pore size of 4 nm. Furthermore, surface chemical composition analyzed by X-ray Photoelectron Spectroscopy (XPS) was related to the green condition of synthesis and the intrinsic chemical composition of BSG, showing the presence silicon and oxygenated compounds. Moreover, the potential phytotoxic effects of BC filtrates were assessed using two regional native species by evaluating germination percentage (GP) and root-to-shoot length ratio (R/S). BC filtrates increased GP by 22% in Atriplex crenatifolia and by 11.4% in Parkinsonia praecox at a BC concentration of 25%, compared with the control. Regarding seedling development, A. crenatifolia seedlings treated with BC showed an increase of more than 25% in the R/S ratio, while P. praecox seedlings treated with 100% BC showed a 30% increase. These results suggest that BC filtrates did not exert phytotoxic effects under the conditions evaluated. Thus, the biochar reported herein derived from agro-industrial waste, exhibited suitable properties for its potential use as a soil amendment.