To improve the lignocellulose conversion for ABE in high solids fermentation, this study explored the feasibility of cycling the process through the cellulolytic or/and solventogenic phases via intermittent flushing of the fermentation media.
In addition, several of the conditions were selected to be relevant for so-called high gravity or high solids fermentation as this would offer high product concentration and an improved economy of the ethanol production process [ 8].
The resulting strain exhibiting the phenotype of increased ethanol production and decreased lag time in high solids fermentations was designated AJP50, and used for subsequent studies.
Many factors are affecting ethanol yields when operating at high solids fermentations, such as the nutrients deficiency, the presence of other inhibitors, the viscosity, and the inhomogeneity [ 6].
Hogsett reported a set of sequential high solids fermentations with initial cellulose loadings of 26, 47, and 72 g/L and a maximum cellulose utilization of 65 g/L [ 34].
Moreover, problems with viscosity and partial insolubility of lignocellulosic biomass can cause poor mixing and limited mass and heat transfer especially at high solid operation of fermentation process.
In this context, the high solid loading on saccharification and fermentation and the use of whole-slurry from pretreatment could be promising alternatives to obtain high ethanol concentrations and to decrease operational costs and wastewater.
Hemp and ensiled hemp can be converted into ethanol with steam pretreatment (2% SO2 catalyst, 210°C for 5 min) followed by simultaneous saccharification and fermentation at high solid loading (7.5% water insoluble solids[WIS]) with a result of 171 163 g ethanol/kg raw material (Sipos et al.2010).2010
A severe pretreatment for removing this recalcitrance can result in increased sugar degradation to inhibitors and hence cause difficulties in fermentation at high solid loadings.
Recent studies on high solids hydrolysis and fermentation of lignocellulosic material to ethanol often focus on solids concentrations above 10%.
