Production of biogas and fermentable sugars from spent brewery grains: Evaluation of one- and two-stage thermal pretreatment in an integrated biorefinery

Abstract

In this study, the production of fermentable sugars and biogas from thermally pretreated brewer’s spent grains (BSGs) was investigated. There were two autohydrolysis conditions (C1-1S: 180 ºC, 30 min, 5 mLH2O gBSG−1 and C2-1S: 180 ºC, 60 min, 5 mLH2O gBSG−1) which were evaluated, with and without a previous low severity pretreatment (80 ºC, 10 min, 10 mLH2O gBSG−1). The highest specific methane production (302.4 NLCH4 kgCOD−1) and enzymatic hydrolysis yield (EHY of 98%, 50 FPU gBSG−1) were obtained from the two-stage pretreatment, with the second stage operated at 180 °C for 60 min, 5 mLH2O gBSG−1. However, in the integrated process, the two-stage pretreatment with the second stage performed at 180 °C for 30 min, and 5 mLH2O gBSG−1 was the best condition to produce fermentable sugars from enzymatic hydrolysis of pretreated BSGs, using a lower enzyme loading (EHY of 93%, 25 FPU gBSG−1). The burning of biogas produced from an anaerobic digestion of liquid fractions (hydrolysates) generated after two-stage thermal pretreatment in a combined heat and power system can produce a net thermal energy of 1.71 MJ kgBSG dry basis−1 and electrical energy of 0.392 kW h kgBSG dry basis−1.