Continuous production of bioethanol using microalgal sugars extracted from Nannochloropsis gaditana

Abstract

We developed a continuous production process of bioethanol from sugars extracted from Nannochloropsis gaditana. To improve algal sugar production, the reaction conditions of acid-thermal hydrolysis were investigated based on five different types of acid and their concentrations (1-4%), and the loading ratio of solid/liquid (S/L). As a result, the maximum hydrolysis efficiency (92.82%) was achieved under 2% hydrochloric acid with 100 g/L biomass loading at 121 oC for 15 min. The hydrolysates obtained from N. gaditana were applied to the main medium of Bretthanomyces custersii H1-603 for bioethanol production. The maximum bioethanol production and yield by the microalgal hydrolysate were found to be 4.84 g/L and 0.37 g/g, respectively. In addition, the cell immobilization of B. custersii was carried out using sodium alginate, and the effect of the volume ratio of cell/sodium alginate on bioethanol productivity was investigated in a batch system. The optimal ratio was determined as 2 (v/v), and the immobilized cell beads were applied in the continuous stirred tank reactor (CSTR). Continuous ethanol production was performed using both free cells and immobilized cells at 1 L CSTR. In both groups, the maximum bioethanol production and yield were achieved at dilution rate of 0.04 h^-1 (3.93 g/L and 0.3 g/g by free cell, and 3.68 g/L and 0.28 g/g by immobilized cell, respectively).