Biodiesel derived crude glycerol and tuna condensate as an alternative low-cost fermentation medium for ethanol production by Enterobacter aerogenes

Abstract

In this work, waste-based raw materials; crude glycerol from biodiesel plant and tuna condensate from tuna canning factory, were used to substitute the expensive complex medium for ethanol production from Enterobacter aeroegenes TISTR 1468. The optimum crude glycerol concentration was 21.43 g/L (˜20 g/L), giving 6.72 g/L ethanol. Using tuna condensate as a nitrogen source for studying the effect of initial C/N ratio (115–365 g/g) revealed the insignificant difference on ethanol production in every C/N ratio tested with a noticeable increase of byproducts (2,3-butanediols) at the high C/N ratio. The addition of inorganic salts and trace element into crude glycerol-tuna condensate (GT) medium resulted in 2-fold increase of ethanol production (12.73 g/L), complete substrate consumption and reduced the formation of byproducts. Optimization studies based on Plackett-Burman design indicated that the most influential parameter amongst the inorganic salt components was phosphate buffer with 77.6% contribution. However, phosphate buffer could be replaced by keeping the pH constant at 7.0 using 3 N NaOH. Under the optimum condition; 20 g/L crude glycerol, initial C/N ratio of 115 g/g and the pH maintained at 7, the ethanol production was 12.33 g/L with 24% higher than the theoretical yield. The selectivity of ethanol production increased upto 3-fold larger than the expensive complex medium.