LAUSR

Abstract A new tool was developed for second generation ethanol production from non-sterilized beet molasses to energy recovery from the agro-industrial byproduct. The rotary biofilm reactor (RBR) used in repeated-batch fermentation for long-term bioethanol production showed high energy recovery efficiency. This study will serve as a base line of initial studies in this field as no reports are available regarding the application of RBR for bioethanol production. Repeated-batch fermentations were carried out by replacement of the fermentation broth (3.5 L) by equal volume of fresh medium or with 15% and 30% recycling volume in RBR and the reactor without the discs. The fermentation was carried out under the following conditions: an inoculum concentration of 5.6 g dry baker’s yeast/L, initial sugar concentration of 15% (w/v), initial pH 5.0, temperature 30 °C, and rotation speed of 40 rpm. The high bioethanol concentration (average value 52.3 g/L) and the average bioethanol productivity (1.45 g/L/h) were stable for 60 days by recycling 30% of the volume of the broth every 36 h in repeated-batch fermentation using the RBR. The energy evaluation data indicated a positive energy balance with an energy ratio of 1.63 MJ/MJ. The other energy indicators such as energy consumption, energy conversion, energy yield, and energy recovery were 16.5 MJ/kg bioethanol produced, 4.7 MJ/kg beet molasses, 1.3 MJ/100 g sugar utilized, and 84.8%, respectively. The results showed that non-sterilized beet molasses is a promising feedstock for bioethanol production in industrial scale by Saccharomyces cerevisiae using the RBR and this process is considered energetically feasible.