Abstract
Hydrolysis is the heart of the lignocellulose-to-bioethanol conversion process. Using enzymes to catalyze the hydrolysis represents a more environmentally friendly pathway compared to other techniques. However, for the process to be economically feasible, solving the product inhibition problem and enhancing enzyme reusability are essential. Prior research demonstrated that a flat-sheet membrane bioreactor (MBR), using an inverted dead-end filtration system, could achieve 86.7% glucose yield from purified cellulose in 6 h. In this study, the effectiveness of flat-sheet versus radial-flow MBR designs was assessed using real, complex lignocellulose biomass, namely date seeds (DSs). The tubular radial-flow MBR used here had more than a 10-fold higher membrane surface area than the flat-sheet MBR design. With simultaneous product separation using the flat-sheet inverted dead-end filtration MBR, a glucose yield of 10.8% from pretreated DSs was achieved within 8 h of reaction, which was three times higher than the yield without product separation, which was only 3.5% within the same time and under the same conditions. The superiority of the tubular radial-flow MBR to hydrolyze pretreated DSs was confirmed with a glucose yield of 60% within 8 h. The promising results obtained by the novel tubular MBR could pave the way for an economic lignocellulose-to-bioethanol process.
Highlights
Lignocellulose is the most abundant biomass, with an estimated yearly availability of 200 × 109 tons
This shows that immobilization can be considered a good approach to retaining the enzyme inside the reactor, it is not suitable to be used in conventional reactor systems for cellulose hydrolysis, since the enzyme would still be subjected to deactivation by the produced sugars, which results in a drop in stability [12]
Over 30% of total lignin was removed, which confirms the effectiveness of the alkaline pretreatment
Summary
Lignocellulose is the most abundant biomass, with an estimated yearly availability of 200 × 109 tons. A similar drop in conversion was reported, in which the conversion decreased from 72% in the first cycle to 52% in the second This shows that immobilization can be considered a good approach to retaining the enzyme inside the reactor, it is not suitable to be used in conventional reactor systems for cellulose hydrolysis, since the enzyme would still be subjected to deactivation by the produced sugars, which results in a drop in stability [12]. We aim at validating the applicability of the newly designed and constructed inverted dead-end MBR using real waste lignocellulosic biomass, namely DSs, which are more complex In another configuration, a polyethylene hairy membrane, of an unidentified membrane cut-off, was used to absorb both substrate and enzymes. The positive results of this work could pave the way for economic bioethanol production from lignocellulosic waste
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