Potential applications of Ulva Rigida for biofuel and biochemical production

Problems of environmental deterioration and energy demand could be alleviated by the paradigm shift from fossil to biofuels. Innovative strategies, such as the use of microwave irradiation, sonochemical treatment and solar irradiation were recently developed for the exploitation of biomass for biofuel production. The concept of biomass itself can be understood in an unconventional sense. Apart from terrestrial plant resources, nowadays, seaweed, industrial emissions such as CO₂, and organic remains such as glycogen are being explored as new feedstock for biofuels/chemicals production. Our research group in Israel is working on converting biomass (terrestrial and marine) to biofuels (bioethanol) and biochemicals (levulinic acid, furfural, formic acid) using microwave, sonochemical, and hydrothermal methods. Among several types of biomass, marine algae are a promising choice due to several advantages. Marine algae form an abundant and rich source of biomass. Bioethanol production process based on marine algae could be sustainable. A mild sonication-assisted simultaneous saccharification and fermentation (SSF) process for the conversion of Ulva rigida to bioethanol in a single step is developed in the current study. Bioethanol is a potential biofuel owing to the similarity of its energy density value (23 MJ/L) to that of gasoline (35 MJ/L). Bioethanol could also be a feedstock for the production of C2 hydrocarbons. Any progress in the direction of development of a marine-algae-based bioethanol process would open up a new avenue towards sustainable biorefinery. Ulva rigida, comprising 37 wt% carbohydrate was used as a feedstock for the SSF process. Initially, saccharification process of Ulva rigida (with amylases and cellulases) was carried out under mild sonication conditions (40 kHz, 37°C); 3.1 times higher glucose yield was obtained using sonication of Ulva rigida relative to conventional incubation. The hydrolysate was found to contain glucose exclusively. Subsequently, the SSF process for converting the algae (Ulva rigida) to bioethanol in a single step was also accelerated using sonication. The improvement was observed in the total carbohydrate content of the algae using multi-tropic aqua culture. 27-41 times higher specific growth rates were achieved using this approach. Under specific optimal conditions of growth, a starch amount as high as 32 wt% was accumulated. The high-carbohydrate algae were subjected to the sonication- based SSF process. Under optimal process conditions, an ethanol yield as high as 16 wt% was achieved. A unique solar-energybased continuous flow process for the direct conversion of Ulva rigida to bioethanol is outlined. The conversion of macroalgae to the strategically significant chemical, levulinic acid is discussed. In an acid-catalysed hydrothermal process, 12.8 wt% levulinic acid was produced from Ulva rigida. We therefore elaborate in this chapter on the unconventional strategies developed for the farming as well as conversion of Ulva rigida to biofuels and biochemicals.