Enhanced Repeated-Batch Bioethanol Fermentation of Red Seaweeds Hydrolysates Using Microtube Array Membrane-Encapsulated Yeast

Immobilization of microbial cells has receiving increasing attention in the field of fermentation. In this study, renewable poly-L-lactic acid (PLLA) microtube array membrane (MTAM) yeast immobilization technique was used in repeated-batch bioethanol fermentation of acid hydrolysates of red seaweeds Pterocladiella capillacea and Gracilaria sp. The proximate composition analyses indicated that both of the red seaweeds were rich in carbohydrates, suggesting their great potentials as carbon source for bioethanol fermentation. MTAM-immobilized cells in repeated-batch bioethanol fermentation of the red seaweeds hydrolysates exhibited elevated performance on ethanol concentration (C EtOH), maximum ethanol yields (Y P/S), and initial ethanol production rate (rP EtOH) compared with that using free cells. In addition, pretreatment and acid hydrolysis of biomass could result in inhibitors generation, such as furans and organic acids, which could impede subsequent microbial bioethanol fermentation. The inhibitors tolerance tests indicated that MTAM-immobilized cells showed better sugar utilization and ethanol production in the presences of inhibitor furfurals, 5-hydroxymethylfurfural, acetic acid and formic acid, indicating that MTAM immobilization increase the tolerance of the yeast cells against inhibitors furans and organic acids. This study indicated that the yeasts immobilized in PLLA-MTAM exhibited significantly better bioethanol productivity in the fermentation of red seaweeds hydrolysates and was a feasible, eco-friendly technology for bioethanol fermentation.