Volatile fatty acid production from different spent mushroom substrates via anaerobic fermentation: Hydrolysis and acidogenesis efficiency and bacterial community structure

Abstract

Converting renewable biomass resources into biofuels or chemical raw materials is expected to help alleviate energy shortage. Selecting suitable anaerobic fermentation substrates is a key factor in determining high yields of volatile fatty acids (VFAs). Spent mushroom substrates (SMSs) rich in polysaccharides, proteins, lignocellulose and micronutrients may be a high-quality feedstock for producing VFAs. However, the hydrolysis and acidogenesis efficacies of different types of SMSs remain unclear. In this study, we investigated the hydrolysis and acidogenesis performances of four SMSs, namely, Hericium erinaceus (HES), Pleurotus ostreatus (POS), Flammulina velutipes (FVS) and Pleurotus eryngii (PES), and analysed the microbial community composition in the anaerobic fermentation system via 16S rRNA sequencing. Results revealed that the PES reactor afforded the maximum VFA yield of 248.48mg/g, followed by HES, FVS and POS. This might be related to the higher content of polysaccharides and proteins in PES compared to the other three types of SMSs. The higher abundance of Bacillus, Sporolactobacillus, Clostridium_Sensu_Stricto_1 and Clostridium_Sensu_Stricto_19 associated with hydrolysis and acidogenesis in the PES anaerobic fermentation system was responsible for its higher VFA production than the other three SMSs. The carbohydrate metabolism and amino acid metabolism driven by microbes were involved in the hydrolysis and acidogenesis process of SMSs. Notably, the expression levels of key functional genes involved in the VFA production pathway with PES as the fermentation substrate were the highest. These findings provide theoretical support for the large-scale industrial application of SMSs in anaerobic digestion.