ORIGINAL ARTICLE The immobilization of yeast for fermentation of macroalgae Rhizoclonium sp. for efficient conversion into bioethanol Phitchaphorn Khammee 1 & Rameshprabu Ramaraj 1 & Niwooti Whangchai 2 & Prakash Bhuyar 3 & Yuwalee Unpaprom 4 Received: 30 April 2020 /Revised: 16 May 2020 /Accepted: 20 May 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract Macroalgae are considered to be one of the rich lignocellulosic biomass materials. Aquatic biomass has gained more attention to biofuels generation in recent years due to its renewable, abundant, and environmentally friendly aspects. Macroalgae are photosynthetic organisms that are found in both marine and freshwater environments. These are considered as a third- generation feedstock for the production of biofuels since they have the ability to synthesize a high amount of lipids, proteins, and carbohydrates. This research study aimed to evaluate the potential of bioethanol production from macroalgae (Rhizoclonium sp.) biomass. The fermentation process was applied in the research by two-way separate hydrolysis and fermentation (SHF). Algae biomass undergoes a pretreatment process to release necessary sugars for yeast digestion. The fermentation process was carried at 30 to 35 °C in the incubator. Finally, the percentage of ethanol was estimated by the ebulliometer. Fermentation was enhanced by immobilization of yeast, which showed the highest concentration of ethanol (65.43 ± 18.13 g/l) after 96 h of fermentation and can be reused for several times for fermentation. Moreover, these study results confirmed that freshwater macroalgae biomass is a suitable and susceptible raw material for bioethanol production. Keywords Rhizoclonium sp. . Bioethanol . Pretreatment . Immobilized yeast 1 Introduction Renewable resources of energy are a part of the Asian region’s fight against climate changes, at the same time they contribute to economic growth, increasing the number of employed peo- ple and provide energetic safety [1]. The utilization of renew- able energy is significantly increasing, together with energy security concerns, efforts to mitigate the environmental impact of fossil fuels, and upgrading in living standards and renew- able technologies [2]. Bioethanol is a renewable liquid fuel that is expected to be most widely used around the globe as ethanol, which can be produced from abundant supplies of starch and cellulose biomass [ 3]. A large number of bioethanol production countries in the world are Brazil, the USA, and Canada. Ethanol fuel is another alternative that comes to use the power of the world in the areas of transport, vehicles, and various chemical components in the industry [4]. Ethanol can be produced from biological processes. They are arising from the plant by the fermentation process to con- vert polysaccharide starch into monosaccharide sugar. Furthermore, convert from sugar to alcohol, by using the en- zyme, or some chemicals hydrolysis followed by fermentation [5]. Then, convert it to pure alcohol by distillation and sepa- ration of water. Their immobilization in an active state may increase the application of enzymes for industrial purposes. Enzyme immobilization offers technical and economic advan- tages, such as cost-reduction of biocatalysts (as they can be reused many times), easy separation from reaction mixtures, and the possibility of using higher enzyme activity per volume in the reactor, compared with soluble enzyme preparations [6], which can be widely used for the components and applications in various industries. Including the application was that it could be used as a mixed proportion additive for current fuel to reduce the imported oil from abroad. * Yuwalee Unpaprom yuwaleeun@gmail.com; yuwalee@mju.ac.th 1 School of Renewable Energy, Maejo University, Chiang Mai 50290, Thailand 2 Fisheries Technology and Aquatic Resources, Maejo University, Chiang Mai 50290, Thailand 3 Department of Biotechnology, Garden City College, 16 KM, Old Madras Road, Bangalore 560049, India 4 Program in Biotechnology, Faculty of Science, Maejo University, Chiang Mai 50290, Thailand Biomass Conversion and Biorefinery https://doi.org/10.1007/s13399-020-00786-y