Green Macroalgae Hydrolysate for Biofuel Production: Potential of Ulva rigida

In this study, the green macroalgae Ulva rigida, which contains 34.9% carbohydrates, underwent treatment with commercial hydrolytic enzymes. This treatment yielded a hydrolysate that contained 23 ± 0.6 g·L−1 of glucose, which was subsequently fermented with Saccharomyces cerevisiae. The fermentation process resulted in an ethanol concentration of 9.55 ± 0.20 g·L−1. The optimal conditions for ethanol production by S. cerevisiae were identified as follows: non-sterilized conditions, an absence of enrichment, and using an inoculum size of 118 mg·L−1. Under these conditions, the fermentation of the green macroalgal hydrolysate achieved a remarkable conversion efficiency of 80.78%. The ethanol o/t ratio, namely the ratios of the experimental to theoretical ethanol produced, for Scheffersomyces stipitis, Candida guilliermondii, Kluyveromyces marxianus, and S. cerevisiae after 48 h of fermentation were 52.25, 63.20, 70.49, and 82.87%, respectively. Furthermore, S. cerevisiae exhibited the best outcomes in terms of ethanol production (9.35 g·L−1) and conversion efficiency (80.78%) after 24 h (optimal time) of fermentation.