Microbial oil production from dilute acid hydrolysis and enzymatic saccharification of spent coffee ground at high solids condition

Spent coffee ground (SCG) has been indicated as a potential feedstock for bioenergy production by many research reports. However, as a kind of lignocellulosic biomass, SCG also requires pretreatment and enzymatic hydrolysis to liberate the fermentable sugars from it. In this study, a bio-refinery concept was applied to fully utilize the SCG. The locally collected SCG was first extracted by hexane to obtain the coffee oil, and then the de-oiled biomass was subjected to dilute acid hydrolysis and enzymatic saccharification to generate fermentable sugars for microbial oil production. In order to have the optimal pretreatment condition, a response surface methodology was applied to investigate the effects of concentration of dilute sulfuric acid (2-6 %, w/w) and reaction time (1- 2 h) on the yield of fermentable sugar from enzymatic saccharification. The result indicated that the reducing sugar yield was around 0.55 g/g biomass at the optimal condition which was corresponding to ~90% conversion rate of biomass carbohydrate. Moreover, utilization of the reducing sugars for microbial oil production was also investigated and reported.