A mucor circinelloides-based integrated biorefinery

Abstract

ABSTRACT The utilization of agro-based waste residue is a prominent example for establishing a circular bioeconomy. When agro-based waste is used to replace commercial growth media in microbial fermentation processes, it becomes expedient that the implementation of the biorefinery concept becomes integrated as the microbial biomass and their metabolites will add to the product spectrum. This study demonstrates an integrated approach towards valorization of sugarcane bagasse and microbial biomass comprising of Mucor circinelloides ZSKP. A maximum reducing sugar recovery of 80.67 g/l was achieved after combining lignocellulosic pretreatment with saccharification. A low temperature, glycerol and ammonium phosphate pretreatment method was established, where glycerol pretreatment conditions were reduced to 150°C and almost a third of the initial duration. This strategy will potentially result in lower energy consumption costs, decreased release of inhibitors and lower water consumption. The ammonium phosphate-containing hydrolysate yielded 12.89 g/l of fungal biomass after fermentation to add to 20.8 g lignin from the delignification step. Sequential fermentations were performed by addition of Saccharomyces cerevisiae as a co-culture to produce biomass and ethanol. The initial aerobic M. circinelloides fermentation was followed by mixed culture anaerobic fermentation. Fermentation of M. circinelloides (3 days aerobic growth) and S. cerevisiae (5 days of anaerobic growth) generated a balanced biomass yield of 17.9 g/l and ethanol yield of 18.69 g/l. Ethanol production demonstrated effective utilization of bagasse hydrolysate and offered the possibility of concurrent production with biodiesel in this biorefinery. The mixed biomass gave a lipid yield of (3.72 g/l) and a chitosan yield of (1.84 g/l), The lignin infused glycerol plasticized chitosan biocomposite plastic had a 100% improvement in thermogravimetric properties with almost 50% more energy needed to increase the temperature of the material when compared to glycerol-only-plasticized biocomposite. The deproteination step in chitosan extraction was modified and replaced with a protein recovery step, with protein yield being improved to a maximum of 187.89 mg/g. The amino acid composition of the protein showed that it has a relatively high content of lysine making it suitable as an animal feed supplement. This study presents strategies to address feasibility concerns for production of fungal chitosan, biodiesel and bioethanol from lignocellulosic waste and realizing the goal of a circular bioeconomy.