A Two-Stage Process for Conversion of Brewer’s Spent Grain into Volatile Fatty Acids through Acidogenic Fermentation

Abstract

This work is focused on the valorization of brewer’s spent grains (BSG) into volatile fatty acids (VFA) through acidogenic fermentation. VFAs are building blocks for several applications, such as bioplastics’ production. Using acid hydrolysis as pre-treatment, several batch assays were performed and the impact of organic load (OL) and pH on VFA production from BSG hydrolysate was assessed. Regardless of the condition, the produced acids were mainly butyric and acetic acids followed by propionic acid. The OL had a direct impact on the total organic acid concentration with higher concentrations at the highest OL (40 gCOD L−1). pH affected the concentration of individual organic acid, with the highest fermentation products (FP) diversity attained at pH 5.0 and OL of 40 gCOD L−1. To assess the potential application of organic acids for biopolymers (such as polyhydroxyalkanoates) production, the content in hydroxybutyrate (HB) and hydroxyvalerate (HV) monomers was estimated from the respective precursors produced at each pH and OL. The content in HV precursors increased with pH, with a maximum at pH 6.0 (ca. 16% C-mol basis). The acidogenic fermentation of BSG hydrolysate was also assessed in continuous operation, using an expanded granular sludge bed reactor (EGSB). It was shown that the BSG hydrolysate was successfully converted to VFAs without pH control, achieving higher productivities than in the batch operation mode.

Valorization of Brewery Waste through Polyhydroxyalkanoates Production Supported by a Metabolic Specialized Microbiome

“…Brewers' spent grain (BSG) is a by-product of beer production, obtained from wort filtration. It represents about 85% of the total by-products generated during beer production [12][13][14]. BSG is a lignocellulosic material composed of fibers (ca.…”

“…70% of cellulose, hemicellulose and lignin), proteins (ca. 30%), minerals, and lipids [13][14][15][16]. However, the chemical composition of this residue depends on the variety of barley used, the harvest time and cultivation, and the malting and mashing conditions [15].…”

Acidogenic Fermentation of Brewers’ Spent Grain Monitored through Two-Dimensional Fluorescence Spectroscopy

“…Raw BSG supplied by an industrial Portuguese brewery (Super Bock Bebidas S.A., Matosinhos, Portugal) was dried at 70 °C and ground in a hammermill. Dried BSG powder was hydrolyzed as described by Guarda et al 15 but with some changes. More information related to the pretreatment can be found in the Supporting Information.…”

Valorization of Brewers’ Spent Grains: Pretreatments and Fermentation, a Review

“…Particularly, using biomass from agro-industrial waste materials as a substrate in these biotechnological applications, to produce microbial cell biomass and to grow different fungi without the need for extra nutrients, has been at the center of attention [8]. Due to the high nutritional value of BSG, mainly its high hemicellulose content ranging between 19 and 42% [19], this secondary raw material can produce through fermentation several value-added products, such as organic acids, amino acids, volatile fatty acids, enzymes, vitamins, second-generation biofuels and other products [23,39]. For instance, a study done by Marcus and Fox reported that BSG can be processed into various enzymes, including α-amylase, β-amylase, cellulases, glucanases, hemicellulases, etc., and to other products such as xylitol, bioethanol, and citric acid through fungal fermentation of BSG [40].…”