Re-utilization of waste glycerol for continuous production of bioethanol by immobilized Enterobacter aerogenes

Waste glycerol, a by-product of biodiesel production, has been continuously increasing in abundance throughout the world since biodiesel was first commercially produced. Therefore, re-utilization of this waste substance is an important area of research at the present time. This study aims to utilize waste glycerol as a media source for bioethanol production. In addition, Enterobacter aerogenes ATCC 29007, one of the greatest ethanol producers, was immobilized using alginate and a continuous stirred tank reactor (CSTR) newly designed for continuous production with immobilized cells. For efficient bioethanol production, four major media components were statistically optimized by response surface methodology (RSM). The optimal concentrations of each factor were determined: about 6.5 g/L peptone, 3.8 g/L ammonium sulfate, 2.1 g/L citrate dehydrate and 12 g/L waste glycerol. Under the optimal conditions, the ethanol production and yield were about 5.38 g/L and 0.96 mol-ethanol/mol-glycerol with pure glycerol, whereas the ethanol production and yield were approximately 5.29 g/L and 0.91 mol-ethanol/mol-glycerol with the waste glycerol during continuous fermentation. Therefore, the suggested model for media optimization was determined to be reliable. Moreover, continuous ethanol production was successfully performed with waste glycerol using the CSTR system.