Abstract

Interest in third-generation biomass such as macroalgae has increased due to their high biomass yield, absence of lignin in their tissues, lower competition for land and fresh water, no fertiliza- tion requirements, and efficient CO2 capture in coastal ecosystems. However, several challenges still exist in the development of cost-effective technologies for processing large amounts of macroalgae. Recently, genetically modified micro-organisms able to convert brown macroalgae carbohydrates into bioethanol were developed, but still no attempt to scale up production has been proposed. Based on a giant kelp (Macrocystis pyrifera) farming and bioethanol production program carried out in Chile, we were able to test and adapt this technology as a first attempt to scale up this process using a 75 L fermentation of genetically modified Escherichia coli. Laboratory fermentation tests results showed that although biomass growth and yield are not greatly affected by the alginate:mannitol ratio, etha- nol yield showed a clear maximum around a 5:8 alginate:mannitol ratio. In M. pyrifera, a much greater proportion of alginate and lower mannitol abundance is found. In order to make the most of the carbo- hydrates available for fermentation, we developed a four-stage process model for scaling up, includ- ing acid leaching, depolymerization, saccharification, and fermentation steps. Using this process, we obtained 0.213 Kg ethanol Kg−1 dry macroalgae, equivalent to 9.6 m3 of ethanol hectare−1 year−1, reaching 64% of the maximum theoretical ethanol yield. We propose strategies to increase this yield, including synthetic biology pathway engineering approaches and process optimization targets. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd