Sustainable Integrated Process towards a Complete Exploitation of Brewer's Spent Grain

Brewer's Spent Grain (BSG) is the most abundant by-product generated during the first steps of the brewing process and represents about 85% of the total waste. It is usually disposed of due to its complex composition and the high level of moisture, which makes it difficult to store and transport. Up to now, its main exploitation is the use as animal feed. From an economic point of view, the handling or disposal of BSG often represents a cost in the brewery balance, especially when the waste production exceeds the farmers demand and it is necessary to pay specialized disposal companies for transportation and treatment. One of the major challenges in biomass valorization is the efficient biomass fractionation because the complex structure of the plant cell wall and the high crystallinity of cellulose make the feedstock recalcitrant to separation into its components. In the present work, BSG was recovered from a local brewery and processed with a new approach in order to obtain the most complete valorization. In particular, the whole process has been divided in two main parts. A first pretreatment with hot water in autoclave allowed the separation of a solution containing the soluble proteins and sugars which accounted for 25 % of the total starting biomass. This first step permitted the preparation of a valuable growing medium which was successfully employed for different microbial fermentations leading to valuable fungal biomass as well as triglycerides with a high content of linear or branched fatty acids, depending on the microorganism used. The water-insoluble residue was then submitted to a lignocellulose deep-eutectic-solvent-mediated fractionation which allowed the recovery of two main fractions: BSGT Cellulose and BSGT Lignin. The latter was tested as potential precursor for the development of cement water reducers with encouraging results. This combined multistep strategy for the treatment of the waste biomass appears to be a promising sustainable strategy for the development of a full exploitation of BSG from a circular economy perspective.