Third generation biobutanol production by <i>Clostridium beijerinckii</i> in a medium containing mixotrophically cultivated <i>Dunaliella salina</i> biomass

This study aims the third generation biobutanol production in P2 medium supplemented D. salina biomass mixotrophically cultivated with marble waste (MW). The wastes derived from the marble industry contain approximately 90% of carbon-rich compounds. Microalgal growth in mixotrophic conditions was optimized in the 0.4-2 g/L of MW concentration range. The highest microalgal concentration was obtained as 0.481 g/L in the presence of 1 g/L MW. Furthermore, some important parameters for the production of biobutanol, such as microalgal cultivation conditions, initial mixotrophic microalgal biomass loading (50-300 g/L), and fermentation time (24-96 h) were optimized. The highest biobutanol, total ABE, biobutanol yield and productivity were determined as 11.88 g/L, 13.89 g/L, 0.331 g/g and 0.165 g/L/h at the end of 72 h in P2 medium including 60 g/L glucose and 200 g/L microalgal biomass cultivated in 1 g/L MW, respectively. The results show that D. salina is a suitable raw material for supporting Clostridium beijerinckii DSMZ 6422 cells on biobutanol production. To the best of our knowledge, this is the first study on the use of MW which is a promising feedstock on the mixotrophic cultivation of D. salina for biobutanol production.