2-02: Higher dry matter concentrations in pretreatment and fermentation

Worldwide at least 10 different processes are under development for the pretreatment of lignocellulose (breaking the bonds between lignin and polysaccharides) and subsequent hydrolysis. TNO is working on thermal/mild acid, dilute acid, concentrated acid and alkaline pretreatment. Two challenges are: how to prevent accumulation of pretreatment by-products that inhibit fermentation processes (e.g. furfural) and how to carry out the processes at high dry matter concentrations (which is important for the economy of fermentation processes). Recently TNO is able to carry out dilute acid pretreatment of wheat straw at 30-60 % w/w/ dry matter without accumulating furfural, HMF and levulinic acid. After enzymatic hydrolysis 95% of the polysaccharides could be converted into monosaccharides. Fed batch simultaneous saccharification and fermentation (enzymes and micro-organism in one reactor) was successfully carried out to convert pretreated wheat straw of such high dry matter content into ethanol. Similar fed batch SSF were carried out using Pseudomonas putida to demonstrate that submerged aerobic fermentations can be carried out as well using 30% dry matter wheat straw as a substrate in conventional fermenters. A fed batch set up is required to continuously liquefy the 1 cm long straw pieces.