Browsing by Author "Qureshi, Nasib"

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    Acetone-butanol-ethanol (ABE) fermentation of soluble and hydrolyzed sugars in apple pomace by Clostridium beijerinckii P260
    Jin, Qing; Qureshi, Nasib; Wang, Hengjian; Huang, Haibo (2019-05-15)
    The decreasing supply of fossil fuels and increasing environmental concern of food waste disposal have raised interests in food waste conversation to biofuels such as butanol. Apple pomace, a food processing waste rich in carbohydrates, is a good feedstock for butanol production. The goal of this study is to present and evaluate a process to thoroughly convert apple pomace water soluble sugars (WSS) and hydrolyzed sugars from structural carbohydrates to acetone-butanol-ethanol (ABE) by fermentation. WSS was extracted from apple pomace by hot water. The solid residue was pretreated with acid or alkali followed by enzymatic hydrolysis to obtain acid hydrolyzed sugars (ACHS) or alkali hydrolyzed sugars (ALHS). Finally, WSS, ACHS, ALHS, WSS + ACHS, and WSS + ALHS were used as substrates to produce ABE by Clostridium beijerinckii P260, respectively. Acid and alkali pretreated apple pomace showed significantly (p < 0.05) higher glucose yield after cellulase hydrolysis compared with that of unpretreated apple pomace. Addition of pectinase increased hydrolyzed glucose yield by 27.9%, 26.9%, and 33.0% for acid pretreated sample, alkali pretreated sample, and unpretreated sample, respectively. Fermentation results revealed that inhibitors generated during pretreatment could negatively affect the ABE fermentation rate and titers; however, this negative effect could be alleviated by mixing the hydrolyzed sugars with water soluble sugars. A total of 202.8, 42.1, 41.4, 260.1, and 262.2 g of ABE was produced from each kg of dry apple pomace using WSS, ACHS, ALHS, WSS + ACHS, and WSS + ALHS as the substrates, respectively, based on the mass balance.
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    Can Xylose Be Fermented to Biofuel Butanol in Continuous Long-Term Reactors: If Not, What Options Are There?
    Qureshi, Nasib; Lin, Xiaoqing; Tao, Shunhui; Liu, Siqing; Huang, Haibo; Nichols, Nancy N. (MDPI, 2023-06-26)
    This study applied concentrated xylose (60–250 g/L) medium to produce butanol (acetone butanol ethanol, or ABE). A control batch fermentation of 61 g/L initial glucose using Clostridium beijerinckii P260 resulted in a productivity and yield of 0.33 g/L·h and 0.43 g/g, respectively. Use of 60 g/L xylose in a batch system resulted in productivity and yield of 0.26 g/L·h, and 0.40 g/g, respectively. In these two experiments, the culture fermented 89.3% glucose and 83.6% of xylose, respectively. When ABE recovery was coupled with fermentation for continuous solvent removal, the culture fermented all the added xylose (60 g/L). This system resulted in a productivity and yield of 0.66 g/L·h and 0.44 g/g, respectively. When the sugar concentration was further increased above 100 g/L, only a small fraction of the sugar was fermented in batch cultures without product removal. However, with simultaneous product removal, all the xylose (150 g/L) was fermented provided the culture was fed with nutrients intermittently. In this system, 66.32 g/L ABE was produced from 150 g/L xylose with a productivity of 0.44 g/L·h and yield of 0.44 g/g. Using the integrated culture system allowed sugar consumption to be increased by 300% (150 g/L). The continuous system using xylose as a feed did not sustain and after 36 days (864 h) of fermentation, it produced only 2–3 g/L ABE. Rather, the culture became acidogenic and produced 4–5 g/L acids (acetic and butyric). This study suggested that xylose be fermented in batch reactors coupled with simultaneous product recovery rather than in continuous reactors.