Development of a scalable design for biofuel production from green macroalgae hydrolysates

International audience ; This study investigated the valorization of green macroalgae in ethanol by the yeast Saccharomyces cerevisiae. The proof of concept was conducted with two green macroalgae hydrolysates, namely Ulva rigida and Chaetomorpha linum and the fermentation process was scaled-up from 250 mL and 500 mL shake flasks to a 3 L stirred-tank bioreactor. Firstly, the experiments used a synthetic medium based on algal hydrolysate, examining factors like nitrogen source, inoculum size, and salt content. After 72 h, ethanol yields were similar across the systems: 0.43 g.g -1 in the bioreactor, compared to 0.46 and 0.45 g.g -1 in 250 mL and 500 mL flasks, respectively. Secondly, fermenting green algae hydrolysate was tested, under similar conditions (without aeration and pH adjustment, with nitrogen enrichment, and 1 % v/v inoculum) resulted in an ethanol concentration of 9.05 g.L -1 , a yield of 0.44 g.g -1 , and 85.86 % efficiency. Thirdly, operating the process at larger scale was carried out on pilot scale of 77 L with Chaetomorpha linum hydrolysate. Glucose was fully consumed in 9 h, and maximum ethanol production (5.61 g.L -1 ) occurred after 11 h, with a yield of 0.52 g.g -1 which corresponds to the theoretical yield.