From grass to lactic acid and energy: evaluating pretreatment techniques for enhanced biorefinery outputs

In alignment with the EU’s Circular Economy Framework, there has been a notable shift toward biorefineries as key facilities for converting biomass into commercially viable products. The abundant availability of grass represents a substantial yet underutilized resource for promoting a shift toward bioeconomy. This study aimed to improve the value chain of meadow grass by producing biogas, bio-based fertilizers, and lactic acid, and to determine the revenue potential from these products, addressing the critical challenge of optimizing biomass processing to maximize its value. Consequently, the grass samples were processed with three pretreatment techniques—milling, ensiling, and milling followed by ensiling—and then tested for their methane potential. Furthermore, the milled and ensiled grass was also subjected to an acid treatment followed by enzymatic hydrolysis, and the hydrolysate was assessed for lactic acid production using Lactobacillus delbrueckii and Pediococcus acidilactici. Our findings revealed that milled and ensiled fraction showcased an increase of 17% yielding 75 m³ CH₄/tFM compared to untreated grass. Additionally, the hydrolysate derived from the milled and ensiled fraction stream achieves notable lactic acid production, reaching 240 kg LA/t FM using L. delbrueckii. Anaerobic digestion of ensiled grass can yield considerable benefits, with cost savings of 87 €/tFM for electricity and heat, and 19 €/tDM if used as a phosphorus-rich fertilizer. Alternatively, using this grass fraction for lactic acid production could generate 434 €/tFM in revenue. Further studies are required to assess the broader feasibility and implications of scaling up this approach.

Graphical Abstract