Biobased production of volatile fatty acids from brewer's spent grain: Optimization and insights into the impact of protein extraction on process performance

This study investigates the production of volatile fatty acids (VFAs) from anaerobic digestion of raw brewer's spent grains (RBSG) and the solid fraction of brewer's spent grains pretreated by alkaline extraction (PBSG). The variables pH (5-9) and temperature (20-50 degrees C) were optimized using Doehlert experimental design. The maximum concentrations of VFAs obtained were 8126.6 +/- 108.8 mg L-1 for RBSG and 8005.3 +/- 267.9 mg L-1 for PBSG. Protein removal did not affect the fermentative production of VFAs from BSG. However, the type of substrate influenced the VFAs profile and the microbial community. Clostridiaceae and Peptostreptococcaceae were the most abundant members in the reactors fed with raw BSG. On the other hand, Bacteroidaceae and Oscillospiraceae played important roles in the anaerobic digestion of pretreated BSG, accounting for more than 52% of the identified microorganisms. A multiproduct biorefinery with protein removal and subsequent VFAs production had a higher potential revenue (US$ 37,909.00 per ton of RBSG), compared to VFAs production according to a single product model (US$ 258.80 per ton of RBSG) (pH 8 and temperature of 20 degrees C). This study provides insights from physicochemical, biological, and engineering perspectives, paving the way for future research focused on utilizing RBSG and PBSG for VFAs production.