Conversion of C6 and C5 sugars in undetoxified wet exploded bagasse hydrolysates using Scheffersomyces (Pichia) stipitis CBS6054

Abstract

Sugarcane bagasse is a potential feedstock for cellulosic ethanol production, rich in both glucan and xylan. This stresses the importance of utilizing both C6 and C5 sugars for conversion into ethanol in order to improve the process economics. During processing of the hydrolysate degradation products such as acetate, 5-hydroxymethylfurfural (HMF) and furfural are formed, which are known to inhibit microbial growth at higher concentrations. In the current study, conversion of both glucose and xylose sugars into ethanol in wet exploded bagasse hydrolysates was investigated without detoxification using Scheffersomyces (Pichia) stipitis CBS6054, a native xylose utilizing yeast strain. The sugar utilization ratio and ethanol yield (Yp/s) ranged from 88-100% and 0.33-0.41 ± 0.02 g/g, respectively, in all the hydrolysates tested. Hydrolysate after wet explosion at 185°C and 6 bar O2, composed of mixed sugars (glucose and xylose) and inhibitors such as acetate, HMF and furfural at concentrations of 3.2 ± 0.1, 0.4 and 0.5 g/l, respectively, exhibited highest cell growth rate of 0.079 g/l/h and an ethanol yield of 0.39 ± 0.02 g/g sugar converted. Scheffersomyces stipitis exhibited prolonged fermentation time on bagasse hydrolysate after wet explosion at 200°C and 6 bar O2 where the inhibitors concentration was further increased. Nonetheless, ethanol was produced up to 18.7 ± 1.1 g/l resulting in a yield of 0.38 ± 0.02 g/g after 82 h of fermentation.

Bioethanol production from carbohydrate-enriched residual biomass obtained after lipid extraction of Chlorella sp. KR-1

“…Dilute acid saccharification, however, may lead to the formation of fermentation-inhibitory byproducts due to the high acid concentration to biomass ratio (Girio et al, 2010;Moxley and Zhang, 2007). Dilute acid saccharification products from lignocellulosic biomass contain several fermentation inhibitors like formic acid or hydroxymethylfurfural, and fermentative yeast did not completely consume sugars from the saccharification broth (Wikandari et al, 2010;Biswas et al, 2013). In contrast to lignocellulosic biomass, simple SHF process achieved an ethanol yield of 79.3% from the diluted acid saccharification broth of the lipid-extracted residual biomass of Chlorella sp.…”

Performance of small‐scale straw‐to‐heat supply chains in Norway

“…New pretreatment methods, enzymes, and yeasts also open the option of ethanol fermentation of lignocellulosic biomass. 28,29 Besides the more diverse energy carriers produced, these technologies also provide increased recovery of nutrients 30 and may alleviate the need for compensatory fertilizing on cereal fields. In some of these technologies (e.g., anaerobic digestion), the straw in fact can be used twice; first as animal bedding in deep straw beds, and then as an energy resource in the digestion chamber.…”

Pretreatment of forest residues of Douglas fir by wet explosion for enhanced enzymatic saccharification

“…It was demonstrated that the use of oxygen during pretreatment enhances the performances and allow for lower temperatures during the pretreatment process, reduces the heat requirement due to the production of heat in the process and minimize the formation of degradation products . Further, unlike other pretreatment methods that use hazardous chemicals, the pretreated biomass materials using WEx can be directly used as substrate for subsequent enzymatic hydrolysis and fermentation without any detoxification (Biswas et al, 2013). The process without such chemical requirement allows for large-scale implementation without having additional chemical recovery step(s) and/or need for chemical waste disposal leading to extra cost.…”