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

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. • Green macroalgae as a feedstock for bioethanol production. • Lab-scale trials show bioethanol production potential. • Fermentation is possible without nitrogen supplementation and pH control. • Fermentation is possible without sterilization of the algal hydrolysate.