Industrial-scale bioethanol production from brown algae: Effects of pretreatment processes on plant economics

Brown algae, considered as the third generation biomass, offer several advantages over lignocellulosic biomass. However, the current high cost of seaweed cultivation hampers the industrialization of macroalgae-based biofuel production. The aim of this study is to determine the maximum dry seaweed price (MDSP) as an upper limit for purchasing price of brown algae at bioethanol plant gates. In addition, a minimum ethanol-selling price (MESP) was calculated by considering the state-of-the-art bioethanol production technology and current brown algae-cultivation costs. A new simple pretreatment process was economically validated and compared with the traditional acid thermal hydrolysis known as combined pretreatment. The processes were simulated at the scales of 80,000 and 400,000 ton/year of dry brown algae using the Aspen Plus v.8.4 software, and techno-economic models were developed based on mass and energy balance. MDSP for the simple and combined processes was calculated as 64.6 and 26 $/ton (80,000 ton/year) and 91.3 and 71.5 $/ton (400,000 ton/year), respectively. In addition, MESP for the simple and combined processes was determined as 2.39 and 2.85 $/gal (80,000 ton/year) and 2.08 and 2.33 $/gal (400,000 ton/year), respectively. These results indicate that the simple pretreatment is economically superior to the combined pretreatment. A comprehensive sensitivity analysis showed that seaweed price had the highest impact on MESP, thereby confirming that the cost-effective large-scale seaweed cultivation is the key to the success of macroalgae-based biofuel production.