Optimization of enzymatic sugar beet hydrolysis in a horizontal rotating tubular bioreactor

BACKGROUND: Sugar beet pulp (SBP) is a promising feedstock for the production of 2nd generation biofuels, but efficientenzymatic hydrolysis remains a key challenge ; therefore, new process designs and/or bioreactor designs are crucial to overcomethis hurdle. In this regard, horizontal rotating tubular bioreactors (HRTB) offer the advantage of high substrate loadings whileminimizing the space and energy demand compared with conventional stirred tank reactors. Here, a statistical approach is usedto optimize the hydrolysis of sugar beet pulp in laboratory experiments, and it is shown that such a process can be implementedin a HRTB.RESULTS:Usingthedesignofexperiments(DOE)method, thereactionconditionsoffourcommercialenzymemixtures(UltrazymAFP-L, Viscozyme L, Pectinase and Cellulase) was optimized for the degradation of SBP in small-scale experiments. UsingUltrazymAFP-Lasthemostefficientmixture, a10 LscaleconversionwasperformedinaHRTB.Atasubstrateloadingof135 g L−1and optimized conversion parameters (enzyme load, pH and rotating speed of the reactor), 0.525 W dm−3were needed toachieve solubilisation of 30% of the total mass of initial SBP after 24 h.CONCLUSION: DOE was found to be an easy-to-apply method that allowed optimizing the conditions for enzymatic hydrolysisof SBP, resulting in a higher sugar yield. The results could be transferred to an HRTB, which is a suitable system for enzymaticconversion and efficient saccharification of semi-solid or solid substrates with relatively low energy consumption.