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Oxidation of Brewers Spent Grain for the Release of Fermentable Sugars by Direct Pretreatment in an Electrolysis Reactor
Broeker, T., Hoffarth, M., Oppermann, L., Wolff, V., Neubauer, P. and Schneider, J.

Brewer?s spent grains (BSG) is a brewery side stream product available in large amounts that can provide so called drop-in compounds, sugars or ethanol. Technically challenging is the degradation of the lignin to release the carbohydrates (cellulose). Wet oxidation with active chlorine as a comparably gentle delignification method promises advantages compared with established harsh acidic or alkaline treatments. In case of brewer?s spent grains (BSG), the consumption of oxidation agents by other organic non-lignin compounds may pose particularly difficulties. Therefore, a new method of oxidation pretreatment was introduced in which the substrate is placed directly into the electrolytic reactor to be permanently fed by oxidation agent. This technique was compared for the treatment of BSG and standard lignocellulosic substrates wheat straw (WS) and maize silage (MS) with an immersion in oxidation agent. The experimental setup consist of the two oxidative pretreaments (direct cell treatment and submerse treatment) followed by a standard enzymatic and fermentation process for the conversion of the released cellulose to sugar and alcohol. Oxidation of BSG and WS worked most efficiently at 4??C and 20 ?C at a pH value 7.0. The ratio of the active chlorine concentration in relation to biomass content in the treated mash was determined regarding the chlorine consumption rate and the efficiency of delignification. This ratio can therefore be optimised to obtain a rapid and efficient process. The active chlorine demand for BSG per dry matter substrate infeed was up to 810 mg/g while WS required only about 300 mg/g. A reduction of lignin up to 9.4 g/100 g d.m. was achieved for BSG, 10.7 g/100 g d.m for MS and even 17.7 g/100 g d.m. for WS. The direct treatment provided in 30 min a remarkable higher glucose yield for BSG and WS than the submerse treatment for 6 h. However, a 5 day submerse treatment reached and exceeded slightly the direct treatment results (0.20 g glucose per g dry matter biomass for BSG, 0.41 g/g d.m. for WS).

Descriptors: electrolysis, lignocellulose, pretreatment, wet oxidation, brewers spent grain, fermentable sugars, wheat straw, bioeconomy

BrewingScience, 70 (March/April 2017), pp. 74-84