This study explored waste-based Pichia stipitis inoculum development and bioethanol fermentation from detoxified hydrolysate using Saccharomyces cerevisiae, optimised P. stipitis inoculum, and their co-culture. P. stipitis inoculum development (PSID) optimisation was carried out using waste lubricant oil (WLO) concentration (g/L), temperature (℃), and incubation time (h) with inoculum size as the response factor. Thereafter, the simultaneous saccharification and co-fermentation (SSCF) processes were modelled to establish the positive effects of solid loading, co-inoculation time and inoculation ratio. Upon validation of the PSID model, the addition of waste lubricant oil as a carbon source enhanced P. stipitis growth and reduced cultivation time 5-fold. The most desirable co-fermentation conditions were achieved at zero-hour co-inoculation time, inoculation ratio 1:4 (S. cerevisiae to P. stipitis) and 10% solid loading, resulting in 48.7 g/L and 0.51 g/g bioethanol concentration and yield, respectively. This study provides significant insights onto P. stipitis inoculum development and the importance of inoculum development, inoculum size proportion, and time of inoculation for improved bioethanol production using detoxified hydrolysate.
Adebule et al. (2026) studied this question.