Submitted to: Chemical Engineering Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/23/2024
Publication Date: 3/3/2024
Citation: Banerjee, S., Dien, B.S., Eilts, K.K., Sacks, E.J., Singh, V. 2024. Pilot-scale processing of Miscanthus x giganteus for recovery of anthocyanins integrated with production of microbial lipids and lignin-rich residue. Chemical Engineering Journal. https://doi.org/10.1016/j.cej.2024.150117.
DOI: https://doi.org/10.1016/j.cej.2024.150117

Interpretive Summary: Building a cellulosic based industry in the United States will promote rural economic development, the supply of domestic sustainable biofuels, and meeting climate change goals because over one billion tons of biomass can be made available. Sources of cellulosic biomass include crop residues (i.e., corn stalks and leaves), forestry waste, and perennial grasses cropped as dedicated bioenergy plants on land not suitable for growing row corps. A big barrier to the use of cellulosic biomass is extracting enough value to generate profits because current processes are dedicated to solely producing biofuel. Here we explore a novel way to generate additional profits based on the commercial bioenergy grass miscanthus. We noticed that some non-commercial cultivars have highly colored leaves and stems because they produce anthocyanins. Anthocyanins are the chemicals that make fruit colorful. Their market value is over 300 million dollars where they are prized by food manufacturers as vegetable-based pigments and a wide range of health promoting benefits. Herein miscanthus was used to produce sugars at an industrial facility and the sugars were converted by yeast to oil, which can be used for biodiesel. Most of the anthocyanins present in the plant were recovered by washing them out with water after the first processing step. Therefore, a new value-product was realized by selecting colorful plant cultivars without affecting the sugar yield. Future work will focus on improving the recovery of the dyes and preparing them as a food ready ingredient. This project is of interest to farmers, agriculture companies, and government policy makers interested in expanding the use of biomass in the United States.

Technical Abstract: Chemical-free hydrothermal pretreatment of Miscanthus x giganteus (MxG) at the lab scale using high liquid-to-solid ratios resulted in recovery of anthocyanins and enhanced enzymatic digestibility of residual biomass. In this study, the process is scaled up by using a continuous feed hydrothermal pretreatment reactor operated at a low liquid-to-solid ratio (50% w/w solids) as an important step towards commercialization. Anthocyanin yield was 70%w/w at pilot-scale, which was reduced from the 94% w/w yield achieved at lab scale. The pretreated biomass was subsequently refined mechanically using a disc mill to increase accessibility of cellulose by cellulases. Enzymatic saccharification of the pretreated and disc-milled residue yielded 238 g/L sugar concentration by operating in fed-batch mode enzymatically at 10% to 50% w/v solids content. Two strains of Rhodosporidium toruloides were evaluated for converting the hydrolysate sugars into microbial lipids, and strain Y-6987 had the highest lipid titer (11.0 g/L). Further, the residue left after enzymatic saccharification was determined to be enriched 1.7-fold in the lignin content. This lignin-rich residue has value as a feedstock for production of sustainable aviation fuel precursors and other high-value lignin-based chemicals. Hence the proposed biorefinery based on MxG creates an opportunity for generating revenue from multiple high-value products. As the demand for biofuels and biobased products is rising, the biorefinery products from miscanthus would create a niche in the industrial sector.