Suitability of Composting Process for the Disposal and Valorization of Brewer’s Spent Grain

Abstract

The brewing industry is characterized by the large production of by-products. Following the fundamentals of a circular economy, several attempts to recycle brewers’ spent grain (BSG) have been investigated. However, little information is available on its use for composting. Considering the main parameters required for optimal development of composting, the objective of the present review was to analyze the literature to determine whether the microbial and physicochemical characteristics of BSG make it suitable for direct composting. As the main factors in the composting process, we considered the BSG moisture content, total carbon, total nitrogen, C/N ratio, and pH. As described in the literature, the BSG moisture content, C/N ratio, and pH range from 70.6% to 81.3%, 7.1 to 26.5, and 3.8 to 6.9, respectively. This C/N ratio range is lower than the composting target range (20–30). Instead, the mean moisture content in the literature is higher than the 60% to 65% recommended for composting. Optimum pH for aerobic stabilization of compost ranges from 5.5 to 7.5, while the BSG pH in the literature is typically more acidic. Therefore, BSG is not suitable for direct composting. Addition of lignocellulosic bulking agents improves the reduction of moisture content during composting, while also optimizing the substrate properties, such as C/N ratio, air spaces, and pH, to positively affect the composting process. Moreover, livestock manure should be included as a starting material to promote the composting process. In this context, two hypothetical initial mixtures of BSG plus a lignocellulosic bulking agent and livestock manure are presented.

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

“…It was reported that around 3.4 and 4.5 million tons of BSG were produced from the brewing industry in Europe and the United States, respectively [14]. The huge quantities of BSG generated in the breweries, their low market value, their high moisture content associated with a difficulty in their storage, and their bad environmental effect made their disposal challenging [72]. The market price of BSG (40.23 USD/ton) is lower than the price of other cellulosic crops (between 50 and 150 USD/ton), which is mainly because BSG have high moisture content and are sold as is [14].…”

Studying Microbial Communities through Co-Occurrence Network Analyses during Processes of Waste Treatment and in Organically Amended Soils: A Review

“…The third and last phase is a maturing stage, which is characterized by the decrease in the temperature to the mesophilic range, a slower decomposition rate of the remaining recalcitrant substrates and the enrichment of the compost in humic substances (i.e., humification) [1,11]. Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria, among Bacteria, and Ascomycota, among Fungi, have shown to be the predominant groups during composting processes, with their relative abundances changing depending on the starting materials and the type of composting procedure [15][16][17]. The duration of the composting process is highly variable, ranging from two months (for easily degradable wastes) up to several years (for highly recalcitrant materials).…”

The MicroBioDiverSar Project: Exploring the Microbial Biodiversity in Ex Situ Collections of Sardinia

“…Eighty-six yeasts and bacteria species of the MGA-UNISS collection, genetically and phenotypically characterized, are included in the MBDS catalogue, starting from the first isolations dating back to 1965 until today. These are mainly yeasts isolated from food and environmental matrices such as olives and olive oil, milk and cheeses, grapes, wine and must, fish, shellfish, meat, soil, and by-products of beer processing such as brewers' spent grain and wastewater [42][43][44]. As for bacteria, since 2012, 91 strains belonging to 36 species have been isolated, genetically characterized, and divided into 50 different biochemical profiles.…”