Ethanol Production from Brewers’ Spent Grain Pretreated by Dilute Phosphoric Acid

Abstract

This paper deals with the characterization of brewer's spent grain (BSG) and the optimization of the phosphoric acid pretreatment for this feedstock. The influence of temperature and acid concentration on BSG was studied, and the optimal conditions were found to be 155 °C and 2% H 3 PO 4 . The use of both pretreatment and enzymatic hydrolysis together recovered 92% of total sugars in BSG, mainly solubilized in the prehydrolysate (63%). Escherichia coli SL100 fermented this mixed sugar solution containing hemicellulosic sugars and starchy glucose without previous detoxification with an ethanol yield of 0.40 g/g. Considering also the glucose released from the cellulosic structure and converted to ethanol by a simultaneous saccharification and fermentation process, an overall ethanol yield of 17.9 g of ethanol per 100 g of raw BSG was achieved. Thereby, the process configuration proposed in this work allowed 69% of the total sugars in the BSG to be converted to ethanol.

Brewers’ spent grain liquor as a feedstock for lactate production with Lactobacillus delbrueckii subsp. lactis

“…Hot trub and yeast contribute to 15% of the by-products, which are produced during brewing [42]. On top, most biorefinery concepts lack a use for BSG liquor [8,9,16,43]. Therefore, a process was developed, which proposes a potential use for BSG liquor and comprises an application for the Brewers' yeast side stream.…”

“…Recent work on BSG mainly focusses on different pretreatment strategies to break the structural integrity of the lignocellulosic biomass and increase steric accessibility of these structural-bond polymers for enzymatic saccharification. The pretreatment can be performed, among others, by diluted sulfuric acid hydrolysis [7,8], diluted phosphoric acid hydrolysis [9], alkali treatment [10][11][12], and liquid hot water (LHW) pretreatment [13][14][15]. The following enzymatic saccharification is carried out with different cellulase and hemicellulase mixtures, obtaining a sugar-rich fraction, which can serve as a fermentation medium for the production of bulk chemicals.…”

“…The soluble components of BSG, called BSG liquor, can be removed by pressing (present work), washing [8,9] or by autoclave-assisted pretreatment at 100 • C, as high temperatures increase the solubility of the adherent molecules [15,16]. In most studies, dealing with the solid BSG residue, BSG liquor is not used any further.…”

Aufbau eines Bioraffineriekonzeptes für Biertreber mit vorgelagertem Pressschritt

“…Die meisten Konzepte verzichten vor dem hydrothermalen Aufschluss auf die Abtrennung der wasserlöslichen, anhaftenden Komponenten des Trebers , , . Einige Konzepte entfernen die anhaftenden Glucosaccharide durch mehrmaliges Waschen , oder durch Abkochen bei 100 °C im Autoklaven , , da eine Temperaturerhöhung die Löslichkeit dieser Verbindungen erhöht. Die angesprochenen Ansätze nutzen diese zuckerhaltige Fraktion jedoch nicht weiter.…”

“…Das Abpressen hat vier Vorteile: (i) Da lösliche Zucker abgetrennt werden, ist beim folgenden hydrothermalen Aufschluss eine geringere Produktion von hydrothermalen Abbauprodukten zu erwarten. Hydrothermale Abbauprodukte sind u. a. Hydroxymethylfurfural (HMF), Furfural, Essigsäure und Ameisensäure, die vielfach als hemmend für das Wachstum von Mikroorganismen beschrieben werden , , , . Changzhi Li et al beobachteten bei der HMF‐Produktion mittels Mikrowellenaufschluss eine geringere Ausbeute bei der Nutzung von Cellulose anstelle von Glucose als Substrat, was die Annahme bestätigt, dass lösliche Zucker leichter zu Inhibitoren abgebaut werden als strukturell gebundene Cellulose .…”