Use of marine macroalgae (seaweed) as an energy feedstock for production of biodiesel, bioethanol, biogas, and biohydrogen has been investigated. Seaweed has a faster growth rate, lower land usage, higher CO2 absorption and uptake rate, no need for fertilizers and no competition for food or freshwater resources compared to lignocellulosic biomass. The red seaweed Eucheuma denticulatum has a high content of easily degradable carbohydrates, making it a potential substrate for the production of bioethanol. The carbohydrates in red seaweed comprise a neutral polymer (agarose) and a sulfate polysaccharide (agaropectin). Therefore, galactose and glucose are obtained by agarose and agaropectin hydrolysis.
Various pretreatment techniques have been introduced to enhance the overall hydrolysis yield, and can be categorized into physical, chemical, biological, enzymatic or a combination. Dilute acid hydrolysis is commonly used to prepare seaweed hydrolysates for enzymatic saccharification and fermentation for economic reasons.
In this study, hyper thermal acid hydrolysis pretreatment of Eucheuma denticulatum was carried out with 12% (w/v) seaweed slurry content, 90 mM of H3PO4 at 150°C for 10 min. To improve the efficiency of the ethanol fermentation of mixed monosaccharides, the use of Candida lusitaniae with adaptive evolution was evaluated for the ethanol fermentation. The levels of ethanol production by Separate Hydrolysis and Fermentation (SHF) with non-adapted and adapted C. lusitaniae were 10.1 g/l with ethanol yield (YEtOH) of 0.23 and 18.1 g/l with ethanol yield (YEtOH) of 0.45 at 72 h, respectively. Adaptive evolution was employed in this study to improve the efficiency of ethanol fermentation. Development of the SHF process could enhance the overall ethanol fermentation yields of seaweed, E. denticulatum.