Ethanol production from the wood and fruit juice of paper mulberry via simultaneous saccharification and juice co-fermentation under normal and very high gravity conditions

A novel batch simultaneous saccharification and juice co-fermentation (SSJcF) process was investigated using mixtures of PHP (phosphoric acid plus hydrogen peroxide) pretreated wood and fruit juice of paper mulberry tree. All the different substrate mixture configurations evaluated under normal gravity SSJcF (total sugar titer of 180 g/L) significantly improved both ethanol concentration and yield compared to sole simultaneous saccharification and fermentation (SSF) of paper mulberry wood. Among the different mixing ratios, the feedstock mixture with equal sugar content from each substrate resulted in maximum ethanol concentration, yield and productivity of 77.1 g/L, 83.9 % and 1.1 g/L/h, respectively. The external additions of mineral nutrients also had no impact on fermentation performance of the mixture. Furthermore, SSJcF was evaluated under different levels of high gravity (HG) and very high gravity (VHG) conditions. The total sugar titer of 350 g/L at equal contributions from each substrate reached very high ethanol concentration of 147.0 g/L, with yield and productivity of 82.3 % and 1.5 g/L/h, respectively. By implication, the PM wood and fruit juice mixture could serve as suitable low-cost and non-food feedstock alternative to the typical use of sugary and/or starchy feedstocks for VHG fermentation.